2024-03-29T00:57:15Zhttps://laur.lau.edu.lb:8443/oai/requestoai:laur.lau.edu.lb:10725/1072020-11-20T08:00:27Zcom_10725_2055col_10725_2076
A novel approach to reduce spurious switching activity in high-level synthesis. (c2009)
Aaraj (El), Elie
Switching theory
Electric circuit analysis
Power electronics
Includes bibliographical references (l. 103-105).
Optimizing area and timing have long been considered to be the main design challenges in high-level synthesis. A lot of research has been conducted in this area and many techniques to improve performance have been suggested. However, as design applications become more power sensitive, and with the emergence of portable devices that operate under stringent power constraints, power consumption surfaced as a major issue to consider in the design and optimization processes.
This work studies the effects of binding and scheduling on power consumption in high-level synthesis by analyzing unnecessary switching. The major contribution of this work is to reduce the spurious switching activities in a circuit. For this purpose, all spurious and non-spurious switching inputs in a circuit were identified and many techniques were studied to find the optimal register bindings without inducing any increase in the number of storage elements. Power reduction was attained through altering register bindings using a cool-down simulated annealing approach. In order to test these techniques, a high-level synthesis environment, "Eridanus", was developed and several benchmarks consisting of various complexities have been tested. Using the approach suggested in this work, spurious switching activity was reduced by 40% on average.
2010-09-24
2010-09-24
2009
2010-09-24
2009-01-05
Thesis
http://hdl.handle.net/10725/107
https://doi.org/10.26756/th.2009.3
en
oai:laur.lau.edu.lb:10725/1602020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Stochastic-based production costing model. (c2010)
Hamdan, Hassan A.
Electric power systems -- Lebanon
Electric power production -- Lebanon
Energy policy -- Lebanon
Includes bibliographical references (leaves 154-156).
The Lebanese Electric Power System (LEPS) suffers from technical and financial deficiencies that required the development of a policy paper to rescue the power sector from the current drastic situation to a new sustainable, reliable, and efficient delivery of electricity. The plan includes ten strategic initiatives and 42 action steps that are integrated and correlated to cover the sector’s infrastructure, supply/demand, and the legal aspects. This ambitious but realistic policy was prepared after a review of all previous studies, and in collaboration of all concerned parties, whether internal or external, constitutional and political, and was approved consensually by the Council Of Ministers on June 21, 2010.
It is proposed that the implementation of the energy policy will result in a solid power sector with sufficient generation capacity, reliable transmission and distribution networks, and efficient delivery of electricity to cope with the overall socio-economic development of Lebanon. The policy targets a gradual implementation of the initiatives in the short and medium terms totaling 4870 M$ (Government in Lebanon up to 1550 M$, the private sector contribution of 2320 M$, and the international donor community up to 1000 M$), and an additional amount of 1650 M$ in the long term. The full implementation of all the strategic initiatives in this policy will reduce the total losses from 4.4 Billion $ in 2010 to zero in 2014 where 24/24 hours of service is provided, and the possibility of profit making as of 2015; while it will reach 9.5 Billion $ in 2015 if no action is taken.
This thesis uses the Load Modification Technique (LMT) as a stochastic tool to assess the impact of implementing the initiatives of the proposed energy policy on energy production, overall cost, technical and commercial losses, reliability and customer service. New modeling capabilities of the traditional LMT method are proposed in this thesis for off-peak energy dispatch. The proposed LMT technique is used to establish a technical and financial baseline of the LEPS against which the full implementation of the energy policy is compared and the resulting tariff is calculated. Selected scenarios are also presented to show the technical and financial impact of individual projects on the system.
2010-12-20
2010-12-20
2010
2010-12-20
2010-10
Thesis
http://hdl.handle.net/10725/160
https://doi.org/10.26756/th.2010.18
en
oai:laur.lau.edu.lb:10725/1622020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Free-space-optical communications over turbulent channels. (c2009)
Bkassiny, Mario
Optical communications
Includes bibliographical references (leave 91).
Local Area Networks (LAN’s) are being expanded over large geographic areas and
they are used in many business fields. Thus, communication links between buildings
are to be optimized in order to achieve high transmission rates, high performance
levels, low cost and ease of deployment. Free-Space Optics (FSO) is a communication
system that achieves all of the above objectives and, thus, constitutes a strong
candidate solution for such networks.
FSO systems are based on transmitting information through light beams in free atmosphere
and they suffer from fading due to atmospheric scintillations. Fading effects can
be reduced by deploying laser arrays and photo-detector arrays at the transmitter and
receiver sides respectively. Such systems are referred to as Multiple-Input-Multiple-
Output (MIMO) FSO systems. In addition to their robustness against fading, MIMO
FSO systems can also enhance the data rate since the array of lasers can be driven
by independent information sources.
Fading over FSO channels is often modeled by either Log-Normal or Rayleigh distributions.
In this context, the first contribution of this work consists of an analytical
characterization of the diversity order that can be achieved by MIMO FSO systems
over such channels. Based on the Erlang approximation, closed-form expressions of
the error-rate and channel-capacity were derived. These simple expressions offer useful
insights on the performance gains that can be achieved at a given Signal-to-Noise
Ratio (SNR).
On the other hand, for estimating the values of the transmitted signals, exiting MIMO
FSO systems are often associated with Maximum-Likelihood (ML) decoders. Although
these decoders achieve the smallest error rate, they suffer from an increased
complexity since the required decoding time increases exponentially with the size
of the transmitted constellation. The second contribution of this work consists of
proposing two novel simplified ML decoders that reduce the processing time without
increasing the error rate. We also propose suboptimal versions of these decoders
that present the advantage of very fast convergence times at the expense of a slight increase in the error rate. All the presented analysis and designs are supported by
simulations and analytical proofs.
2010-12-20
2010-12-20
2009
2010-12-20
2009-06-26
Thesis
http://hdl.handle.net/10725/162
https://doi.org/10.26756/th.2009.5
en
oai:laur.lau.edu.lb:10725/1632020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Proposal and analysis of novel availability aware protection schemes in WDM optical networks. (c2009)
Sawwah, Timothy I.
Optical communications
Computer networks
Includes bibliographical references (l. 60-61).
With the frequent occurrence of fiber cuts in optical core networks and the tremendous loss that a failure may cause, the design of survivable optical networks is becoming of extreme importance to optical network operators. One of the major concerns in this regard is related to improving the availability of the services that the optical operators offer to their clients. This work addresses this issue by presenting three novel availability-aware protection schemes that achieve high level of availability for optical connections. As a distinguishing feature from existing protection schemes, the proposed schemes introduce relative priorities among the different primary connections contending for the use of the backup resources. In an attempt to gauge the benefit of the proposed protection schemes relative to the ones studied in the open literature, mathematical models are provided for evaluating the average connection availability resulting from the deployment of such schemes. The numerical results obtained from the mathematical models prove that higher availability levels can be realized through the use of the availability-aware protection schemes defined in this work.
2010-12-20
2010-12-20
2009
2010-12-20
2009-06-29
Thesis
http://hdl.handle.net/10725/163
https://doi.org/10.26756/th.2009.6
en
oai:laur.lau.edu.lb:10725/1922020-11-20T08:00:25Zcom_10725_2055col_10725_2076
Cooperative diversity for free space optical communications. (c2010)
Slim, Ahmad
Optical communications
Includes bibliographical references (leaves 38-39).
In this work, we investigate the cooperative diversity technique as a candidate
solution for combating turbulence-induced fading over Free-Space Optical (FSO) links.
In particular, a one-relay cooperative diversity scheme is proposed and analyzed for noncoherent
FSO communications with intensity modulation and direct detection (IM/DD).
The error performance of this diversity scheme is derived in semi-analytical and closedform
expressions in the presence and absence of background radiation, respectively.
Results show the enhanced diversity orders that can be achieved over both Rayleigh and
lognormal fading models.
2011-01-07
2011-01-07
2010
2011-01-07
2010-10-05
Thesis
http://hdl.handle.net/10725/192
https://doi.org/10.26756/th.2010.20
en
oai:laur.lau.edu.lb:10725/3932020-11-20T08:00:25Zcom_10725_2055col_10725_2076
The elderly care center. (c1996)
Sakr, Elie
Includes bibliographical references.
2011-04-18
2011-04-18
1996
2011-04-18
1996-01-01
Thesis
http://hdl.handle.net/10725/393
https://doi.org/10.26756/th.1996.19
en
oai:laur.lau.edu.lb:10725/3942020-11-20T08:00:25Zcom_10725_2055col_10725_2076
Fire station, Beirut. (c1997)
Mattouk, Patrick Elias
Fire stations
Includes bibliographical references.
2011-04-18
2011-04-18
1997
2011-04-18
1997
Thesis
http://hdl.handle.net/10725/394
https://doi.org/10.26756/th.1997.19
en
oai:laur.lau.edu.lb:10725/6822020-11-20T08:00:25Zcom_10725_2055col_10725_2076
Towards an event-driven scheduling of the setup of optical connections. (c2011)
Sinno, Abdelghani
Optical communications -- Technological innovations
Computer networks
Includes bibliographical references (l. 64-66).
Supporting the diverse Quality of Service (QoS) requirements of the everemerging
Internet applications is one challenging task for optical networks'
operators. To come to grips with this challenge, we propose a QoS-Aware Optical
Connection Setup Management scheme that uses the Earliest Deadline First (EDF)
queuing discipline to schedule the setup of the optical connections. The benefits of
this EDF-based scheme are twofold: a) it reduces the blocking probability since
blocked connection requests due to resource unavailability are queued for possible
future setup opportunities and b) it realizes QoS differentiation by ranking the
blocked requests in the EDF queue according to their connection setup time
requirements, which are viewed as deadlines during connection provisioning. As
such, pending less delay-tolerant requests are guaranteed to experience better QoS
than the ones having longer setup time requirements. This work then takes one step
further by proposing various alternatives to the EDF-based management scheme.
More specifically, multiple scheduling strategies aiming at improving the fraction of
successfully established high priority connections are proposed, such as: Greedy
Scheduling (GS), Retrial Based Scheduling (RBS), Soft Scheduling (SS), Round Robin
Scheduling (RRS), and QoS Neutral Scheduling (QNS). Finally, extensive simulations
are performed to gauge the merits of the proposed strategies and to study their
performance in the context of two network topologies, namely, the National Science
Foundation Network (NSFNET) and the European Optical Network (EON).
2011-10-04
2011-10-04
2011
2011-10-04
2011-03-09
Thesis
http://hdl.handle.net/10725/682
https://doi.org/10.26756/th.2011.15
en
oai:laur.lau.edu.lb:10725/6992020-11-20T08:00:26Zcom_10725_2055col_10725_2076
IEEE 802.11 wireless mesh network. (c2008)
Khabbaz, Maurice
IEEE 802.11 (Standard)
Wireless communication systems
Computer networks
Routers (Computer networks)
Includes bibliographical references (l. 90-95).
The IEEE 802.11 Medium Access Control (MAC) gained widespread
popularity as a layer-2 protocol for Wireless Local Area Networks (WLANs). While
the continuous lack of accurate analytical 802.11 MAC models as well as the nonexisting
state of the art IEEE 802.11-based Wireless Mesh Networks (WMNs)
simulation and analysis tools attract our attention, the adaptation of the existing
Mobile Ad-Hoc Networks (MANETs) routing metrics and protocols to 802.1 Is-based
WMNs remains a major source of performance degradation of those latter. This work
addresses these three voids by first providing two distinct mathematical models for
evaluating the queuing delays in an IEEE 802.1 I-based WMN. In the first model each
node is modeled as a discrete time G/GIl queue characterized by general arrival
patterns and service time distribution, whereas in the second model the service time is
represented by a combination of Erlang-k and Coxian-2 distributions, thus nodes are
modeled as either G/E-kll or G/C2/1 queues. Both models account for arbitrary
packet size distributions, number of nodes in the network, channel access time
resulting from the random access mechanism, collision avoidance and exponential
back-off mechanism of 802.11, delays in channel access due to other nodes
transmitting and delays caused by collisions. Second, this manuscript presents two
novel MAC-AWARE and BUFFER-AWARE routing protocols based on a new IEEE
802.1 I-specific routing metrics used to provide Quality of Service (QoS) routing for
both delay-sensitive and packet-loss sensitive traffic generated simultaneously in an
802.lI-based network in DCF mode. A new IEEE 802.II-MAC based networkspecific
simulator that we developed allowed us to verify our models and assert the
correctness and accuracy through extensive simulations.
2011-10-06
2011-10-06
2008
2011-10-06
2008-06-18
Thesis
http://hdl.handle.net/10725/699
https://doi.org/10.26756/th.2008.21
en
oai:laur.lau.edu.lb:10725/7322020-11-20T08:00:25Zcom_10725_2055col_10725_2076
Achieving full transmit diversity for PPM constellations with any number of Antennas via double position and symbol permutations. (c2008)
Baba, Zeina
Wireless communication systems
Optical communications
Pulse modulation (Electronics)
Modulation (Electronics)
Spread spectrum communications
Adaptive antennas
Includes bibliographical references (l. 125-128).
Encoding and decoding techniques present in the literature, mainly designed for
radio frequency (RF) applications, face many problems when applied in optical
wireless (OW) communications. These schemes seem to have lacks in some places
like diversity, rate, or delay criteria. Therefore, we present a general technique for
constructing minimal-delay, fully-diverse and rate-l Space-Time (ST) block codes
for Pulse Position Modulations (PPM) applied with an arbitrary number of transmit
antennas and modulation positions. Introducing the novel idea of time-domain
constellation extension as well as joint position and symbol permutations permitted
to maintain unipolar transmissions the fact that renders the proposed code suitable
for Free Space Optical (FSO) communications with direct detection at the receiver.
To construct this code, it has been shown that for conveying a M -ary PPM symbol,
each symbol duration must contain M + 1 time slots (or positions) rather than M.
This increases the system dimensionality by I but guarantees a code with full
diversity for an arbitrary number of transmit antennas and modulation positions in
the PPM constellation. In parallel, an M -PPM decoder was developed to be applied
with the same systems without any obstacles.
2011-10-11
2011-10-11
2008
2011-10-11
2008-06-18
Thesis
http://hdl.handle.net/10725/732
https://doi.org/10.26756/th.2008.27
en
oai:laur.lau.edu.lb:10725/8542020-11-20T08:00:26Zcom_10725_2055col_10725_2076
EDF-based connection setup management in WDM optical networks. (c2009)
Bardan, Raghed A. El
Wavelength division multiplexing
Optical communications
Includes bibliographical references (leaves 51-54).
The worldwide network domain tendency to evolve towards dynamic Quality of
Service (QoS) enabled wavelength division multiplexing (WDM) optical networks is imminent.
WDM has drastically increased the transmission capacity of today’s optical networks. An
increase in the available bandwidth is promoting the introduction of new services, each having
different quality of service (QoS) requirements. Improving connection setup conditions is
considered to be one of the major requirements in this regard. This work addresses the interesting
topic of quality of service (QoS) aware connection setup provisioning in WDM optical networks.
The impact that the connection setup time of an optical connection may have on the setup of a
connection has not been adequately addressed in the open literature. As such, this work presents
a novel connection setup mechanism that uses the optical connection setup time as a service
differentiator during connection provisioning. The proposed connection setup mechanism utilizes
the well-known Earliest Deadline First (EDF) queuing discipline to achieve deadline-based connection setup management with the deadline being the setup time requirement of an optical
connection. The proposed EDF-based setup scheme has been proved to be optimal and it is
expected to allow the network operator to improve the QoS perceived by their end customers.
Performance of this novel scheme is analyzed by precisely calculating various measures, such as
the fraction of connections provisioned prior to deadline expiration, and the average time it takes
to successfully setup a connection. Our numerical results whose correctness was asserted through
extensive simulations highlighted the service differentiation feature achieved by the EDF-based
connection setup management approach.
2011-10-24
2011-10-24
2009
2011-10-24
2009-06-26
Thesis
http://hdl.handle.net/10725/854
https://doi.org/10.26756/th.2009.35
en
oai:laur.lau.edu.lb:10725/8572020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Novel pseudo random bit generator for improved security. (c2008)
Hobeika, Jad G.
Random number generators
Computer security
Cryptography -- Mathematics
Statistical hypothesis testing
Includes bibliographical references (l. 123-126).
Due to the emergence of new sensitive communication applications like eCommerce and
online banking; secure communication, electronic identification and authentication are
becoming a must. Cryptography is the technique used to secure communication through
encryption of data messages. Pseudo Random Bit Generators (PRBG) are used by
different cryptographic techniques as a tool to encrypt messages. While the well known
Linear Feedback Shift Register (LFSR) PRBG offers good statistical propel1ies it offers
poor security since the knowledge of 2n outputs bits make the whole generated sequence
predictable. This work proposes a new digital PRBG based on AD (Analog to Digital)
conversion of a composed sinusoidal signal. The aim behind the new proposal is to improve the inviolability and the security offered by the classical LFSR. The autocorrelation properties of the proposed generator are studied and compared to the propel1ies of the famous LFSR. Moreover, the effect of six different variables which are namely the bandwidth of the analog signal, the sampling frequency, the period of the analog signal, the coding, the quantizing intervals and the numbers of bits per sample are
studied. The proposed PRBG will be tested using the famous "Five Basic Test" set of statistical testing.
2011-10-24
2011-10-24
2008
2011-10-24
2008-08-08
Thesis
http://hdl.handle.net/10725/857
https://doi.org/10.26756/th.2008.30
en
oai:laur.lau.edu.lb:10725/8702020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Efficient area optimization in high level synthesis using priority-driven simulated annealing. (c2009)
Abi Saad, Maria
Simulated annealing (Mathematics)
Computer-aided design
Includes bibliographical references (l. 84-85).
One of the major enhancements that can be made to the synthesis process is reducing the
overall area of a design in order to either decrease the manufacturing costs or introduce
more functionality to the design. Optimizing the area of the data path is considered a
primary field of research in High-Level Synthesis (HLS). This work proposes an
approach to reduce the area by simultaneously tackling the three central tasks of HLS.
Scheduling, allocation and binding are performed and the optimal solution based on area
reduction is obtained by using simulated annealing with a priority function. The aim of
the priority function is to guide the simulated annealing process into finding the best
solution while at the same time incurring the least possible execution time. In order to
achieve better results than the initial solution, rescheduling, swapping operations
between functional units, swapping variables between registers and swapping inputs to
functional units are considered in the annealing process. A cost function was devised to
evaluate a potential move's success or failure. The simulation environment ttEridanustt
was developed in order to support implementation and testing. Several benchmarks were
tested and the numerical results consisting of the execution time along with the best
solution were recorded to illustrate the performance of the proposed technique. Area
reduction was obtained compared to the conventional HLS flow; furthermore, n average
substantial reduction in design space exploration time was obtained compared to nonpriority
based area optimization techniques.
2011-10-24
2011-10-24
2009
2011-10-24
2009-01-05
Thesis
http://hdl.handle.net/10725/870
https://doi.org/10.26756/th.2009.42
en
oai:laur.lau.edu.lb:10725/9632020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Enhanced technology mapping for FPGAs with exploration of cell configurations. (c2011)
Zgheib, Grace Joseph
Field programmable gate arrays
Programmable logic devices -- Design and construction
Logic circuits -- Design and construction
Data mining
Includes bibliographical references (leaves 53-55).
In the state of the art Field-Programmable Gate Arrays (FPGAs), logic circuits are
synthesized and mapped on clusters of look-up tables. However, when additions need to be
performed, an adder along with a carry-chain is used to ensure a fast execution of such an
arithmetic operation. This carry-chain is a dedicated wire available in the architecture of the
FPGA and is as such independent of the external programmable routing resources.
The proposed idea introduces variable-structure Boolean matching as well as
decomposition of mapped functions in order to take advantage of the carry-chains when
they are not used for addition operations. Previously synthesized and mapped logic
functions are adapted so that their outputs are routed using the dedicated carry-chains
instead of the external programmable interconnects. Mapping onto these chains yields a
reduction in the overall external routing resources as well as the general routing congestion.
Moreover, a generic software platform was developed allowing users to identify and test
various basic-unit structures and compare their performances on particular logic circuits
depending on criteria specified by the user. Such structures may vary from currently
available FPGA architectures to customized theoretical structures well-suited for a specific
design(s). This tool can also propose particular cell structures to map logic circuits while
respecting the user's constraints and insuring the optimization of specific parameters.
2011-11-04
2011-11-04
2011
2011-11-04
2011-08-02
Thesis
http://hdl.handle.net/10725/963
https://doi.org/10.26756/th.2011.16
en
oai:laur.lau.edu.lb:10725/10332023-05-10T09:10:38Zcom_10725_2055col_10725_2076
Power and temperature aware functional unit binding in high level synthesis. (c2011)
Bassil, Layale
Integrated circuits -- Very large scale integration
Electric power consumption
Switching power supplies
Includes bibliographical references (leaves 101-105).
This project elaborates on the possibility of optimizing the power consumed by the
functional units by optimizing the functional unit binding technique. Functional unit
binding maps the operations in each control step to specific functional units. However,
the mapping between the operations and the available functional units has a profound
effect on the power consumed. Hence, by optimizing the functional unit binding
algorithm, it is possible to reduce the power consumption of the functional units which
comprises a large fraction of the overall power of the design. The optimized poweraware
functional unit binding methodology focus on reducing the switching activity of
the functional units by minimizing the transitions of their input operands; this is done by
trying to bind operations having one of its inputs remaining the same between two
consecutive control steps, to the same functional unit.
The second part of this project tackled temperature reduction. The same methodology
used for power reduction was used for temperature reduction by optimizing the
functional unit binding technique. The optimized temperature-aware functional unit
binding focus on reducing the temperature of the functional units by following a
parabola-like cost function; the cost is the temperature dissipated by the functional unit
for every two consecutive switching at its inputs. This will lead to a change in the
binding of operations to functional units giving each functional unit the time to cool
down between any two successive operations.
2011-11-29
2011-11-29
2011-11-29
2011-06-08
Project
http://hdl.handle.net/10725/1033
https://doi.org/10.26756/th.2023.572
en
oai:laur.lau.edu.lb:10725/10352020-11-20T08:00:27Zcom_10725_2055col_10725_2076
A parallel ant colony optimization to globally optimize area in high-level synthesis. (c2011)
Kozhaya, David Elias
Ant algorithms
Mathematical optimization -- Computer programs
Swarm intelligence
Parallel programming (Computer science)
Includes bibliographical references (leaves 98-101).
Data path synthesis is still regarded by researchers as one of the hardest problems in high level
synthesis, the process of transforming a hardware descriptive language model, which
describes the behavior of a given design to an actual register-transfer level or structural
design. Despite the progress that has been achieved in this field of research, there is still an
inevitable necessity for new techniques that achieve better area, timing, and power results
for this NP-hard problem. In contrast with previous approaches which divide the high-level
synthesis problem into sub-tasks and optimize each task independently in an attempt to
reduce its complexity, this work proposes a novel technique using the ant colony
optimization, which respects this division but establishes efficient communication between
these different interdependent tasks.
Substantial modifications are added to the ant colony optimization, most importantly a
perturbation factor allowing the ants to visit previously unexplored solutions due to the
nature of the binding problem. To test the efficiency of the proposed technique, specific
resource bags were designed for a large set of benchmarks of different complexities. The
proposed approach yielded an overall average of 6.8% improvement in area for all tested
benchmarks and allows an easy transition to a parallel programming paradigm which
benefits from the concept of parallel agents present in the ant colony optimization. The
parallel execution makes the proposed technique an appealing solution, easily mappable to
and well-suited for the omnipresent multi-core and multi-processing computing platforms.
A parallel implementation using message passing in java was developed to prove the
effectiveness of the proposed parallel model. Rigorous testing of this model on an 8-core
machine, showed more than eighty four percent utilization of the parallel environment
allowing the proposed technique to run 6.7 times faster than the single-threaded approach.
2011-11-29
2011-11-29
2011
2011-11-29
2011-08-02
Thesis
http://hdl.handle.net/10725/1035
https://doi.org/10.26756/th.2011.36
en
oai:laur.lau.edu.lb:10725/10692020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Environmental impact assessment (EIA) manual for Lebanon. (c1996)
Nemer, Randa
Environmental impact analysis
2012-01-31
2012-01-31
1996
2012-01-31
1996-12-30
Thesis
http://hdl.handle.net/10725/1069
https://doi.org/10.26756/th.1996.36
en
oai:laur.lau.edu.lb:10725/10862020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Delay-tolerant codes for the decode-and-forward cooperation in wireless networks. (c2009)
Marmar, Ali Rida H.
Wireless communication systems
Includes bibliographical references (l. 69-70).
With the great growth of wireless devices and communication, there is a huge demand for higher data rates. To respond to this growing demand, fourth generation (4G) wireless Local Area Networks (LANs) might adopt cooperation techniques where several collocated mobile terminals can cooperate with each other in order to enhance the quality of their corresponding communication links. One popular cooperation strategy is the Decode-and-Forward (DF) strategy. After a first phase where the source node broadcasts its message to the neighboring nodes (relays), these nodes will transmit their decoded versions of this message simultaneously to the destination. To conveniently encode the interfering data streams that are transmitted simultaneously from the different relays, Space-Time (ST) coding techniques must be applied. In this work, we propose a novel ST code that is adapted to the DF strategy with two relays. This code is tolerant to the delays that might occur between the different relays and it presents the main advantage of a reduced decoding complexity. In fact, only three data streams need to be decoded jointly rather than four streams as in the case of the existing solutions. An additional advantage is that the proposed code is totally real and, consequently, it is adapted to low cost carrier-less ultra-wideband transceivers that do not necessitate tracking the phase of the incoming signal.
2012-03-08
2012-03-08
2009
2012-03-08
2009-06-25
Thesis
http://hdl.handle.net/10725/1086
https://doi.org/10.26756/th.2009.60
en
oai:laur.lau.edu.lb:10725/11762020-11-20T08:00:26Zcom_10725_2055col_10725_2076
Enhancement of blocking performance in all-optical WDM networks. (c2012)
Joun, Carla J.
Wavelength division multiplexing
Optical communications
Neural networks (Computer science)
Includes bibliographical references (leaves 58-60).
Optical networking is a promising solution to the growing bandwidth
requirements of today’s communication networks. The continuous challenge
is to look for technological advances to improve network capacity,
reliability, scalability and cost. This work addresses some of these factors by
presenting a rerouting strategy for reducing the effect of the wavelength
continuity constraint and improving the performance of all-optical
wavelength division multiplexing (WDM) networks in terms of blocking
probability. The problem of routing and wavelength assignment (RWA), of
main interest in this study, is critically important for increasing the efficiency
of WDM networks under wavelength continuity constraint.
The proposed scheme introduces a rerouting strategy based on wavelength
reassignment, with the First-Fit (FF) wavelength assignment algorithm, and
route deviation, utilizing the Least Congested Path (LCP) routing algorithm.
In addition, this approach is applied in the context of quality of service (QoS)
differentiation to help network service providers to satisfy and guarantee
service transmission priorities and tolerable delay requirements.
Finally, a neural network model is developed to investigate the prediction of
upcoming blocking times in the network in an attempt to reduce the network disruption caused by unnecessary rerouting, therefore improving the
performance of the proposed strategy. Extensive simulations allowed us to
verify our proposed rerouting strategy and enhancement models and assert
their effectiveness in enhancing the network performance in terms of
blocking probability especially for networks utilizing a small number of
wavelengths per fiber.
2012-06-01
2012-06-01
2012
2012-06-01
2012-02-20
Thesis
http://hdl.handle.net/10725/1176
https://doi.org/10.26756/th.2012.10
en
oai:laur.lau.edu.lb:10725/14802020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Numerical simulation of damage to massive stone columns due to earthquakes. (c2012)
Merchak, Ursula Aref
Earthquake magnitude -- Measurement
Earthquake intensity -- Lebanon -- Baalbeck
Monuments -- Earthquake effects -- Lebanon -- Baalbeck
Earthquake intensity -- Computer simulation
Lebanese American University -- Dissertations
Dissertations, Academic
Includes bibliographical references (leaves 19-20).
Large seismic events have historically occurred in the Middle East and particularly in Lebanon causing severe deterioration and destruction of historical monuments. In 1202 and 1759, Lebanon experienced two of the strongest earthquakes in the history of the region which led to the collapse of 34 monumental columns at the Jupiter temple of Baalbek. This study simulates the effects of earthquakes of varying magnitudes on massive stone columns in order to predict the potential of damage to such columns. The damage in the modeled columns is compared to the actual damage and chipping of the columns in Baalbek. This comparison enables the estimation of the different magnitudes of past earthquakes felt at that site. Numerical simulations were performed using the ADINA software in order to predict and analyze the damage and the collapse of the modeled columns. Two different models were used: a linear elastic model which allows the prediction of the magnitude at which toppling occurs and a second model that admits cracking and crushing of the stone with the aim of reflecting actual damage. The two models were used in predicting the response of the Baalbek colonnades to earthquakes having different magnitudes, thus serving as an indicator of either the occurrence or non-occurrence of past earthquakes with specific magnitudes.
2013-02-28
2013-02-28
2012
2013-02-28
2012-06-15
Thesis
http://hdl.handle.net/10725/1480
https://doi.org/10.26756/th.2012.33
en
oai:laur.lau.edu.lb:10725/15472020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Bidirectional electronic textile token grid network topology. (c2013)
Khalil, Antonio F.
Textile industry -- Data processing
Textile fabrics -- Data processing
Industrial engineering
Computational grids (Computer systems)
Lebanese American University -- Dissertations
Dissertations, Academic
Includes bibligoraphical references (leaf 62).
Electronic Textile (e-textile) applications seem to obtain more and more importance in our daily lives; the huge amount of fabrics around us help electronic textile to mingle and integrate seamlessly with our daily life without interfering or changing our habits and lifestyles. Reliability is a very important factor for an electronic textile application especially in the fields of medicine, security and other fields where system failure is not tolerable and promptness of response is very delicate. The contributions of this study focus on defining a token grid networking scheme that enhances fault tolerance for electronic textile systems and increases the communication speed between the communicating components vis-à-vis other e-textile token grid topologies, it also presents a simulation environment used to examine and validate the defined topology.
2013-09-03
2013-09-03
2013
2013-09-03
2013-06-12
Thesis
http://hdl.handle.net/10725/1547
https://doi.org/10.26756/th.2013.12
en
oai:laur.lau.edu.lb:10725/15502020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Learn while tracking. (c2013)
Toukhtarian, Raffi
Electric motors, Direct current -- Automatic control
Electric motors, Direct current -- Mathematical models
Adaptive control systems
Nonlinear control theory
Error analysis (Mathematics)
Dissertations, Academic
Lebanese American University -- Dissertations
Includes bibliographical references (leaves 40-42).
Controlling a plant and automatically driving its output to track a user-defined reference trajectory with sufficiently small error has been an important problem in control theory and application. This problem is referred to as output tracking problem and has been addressed extensively throughout the last five decades. This topic has been and remains a challenging problem encountered in various engineering applications. Tracking systems are basically characterized in terms of their transient response and steady-state tracking error. Most of the proposed control techniques aim at achieving stable asymptotic tracking, where output error converges to zero as time goes to infinity. One of the most often mentioned open problems in control theory is the output feedback stabilization problem. Few algorithms tackle the uniform output tracking problem, where error converges to zero at all time, without necessitating the use of full state feedback. In particular, iterative learning control (ILC) algorithms are shown to achieve uniform output tracking as the number of iterative cycles goes to infinity. However, the main drawback of ILC algorithms is that the system is required to operate repetitively over a fixed time interval. Learn While Tracking (LWT) algorithm aims at achieving uniform output tracking in the sense of attaining arbitrary small tracking errors as well as arbitrary small transient period. LWT is a multiple-input multiple-output (MIMO) non-repetitive static output feedback digital control law that is founded on high sampling rate. It incorporates information of output errors and control input from previous time samples into the construction of the present control action. The latter awards “learn while tracking” terminology. LWT makes use of high sampling rates in order to provide the controller with an ability to tune the input in a faster manner. This approach was proposed in 2007 but was never further studied. Convergence and robustness characteristics were presented. However, the selection of the controller gain was not well elaborated. In this thesis the basic theory of LWT is revisited. The controller gains of LWT controller are designed for a class of DC motors satisfying the sufficient conditions for convergence and robustness. These gains are experimentally applied to a DC motor. In order to illustrate the performance of LWT in comparison with ILC, numerical and experimental results are presented. Finally, with the intention to explore the potential of LWT to MIMO nonlinear systems, the algorithm is experimentally applied to an induction motor.
2013-09-03
2013-09-03
2013
2013-09-03
2013-06-12
Thesis
http://hdl.handle.net/10725/1550
https://doi.org/10.26756/th.2013.15
en
oai:laur.lau.edu.lb:10725/19192020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Parallel multi-voltage power minimization in VLSI circuits. (c2013)
Younes, Rabih Halim
Low voltage integrated circuits
Integrated circuits -- Very large scale integration
Integrated circuits -- Very large scale integration -- Data processing
Electric power -- Conservation
Lebanese American University -- Dissertations
Dissertations, Academic
Bibliography: leaves 91-93.
Power consumption minimization is nowadays considered a main challenge to VLSI designers, especially with the growth of the mobile computing industry. Previous studies have tried minimizing power consumption at the expense of the overall circuit delay, and have mostly focused at optimizing power at the lower levels of abstraction – during placement and routing. This work presents novel techniques to minimize power consumption during behavioral synthesis and to reduce execution runtime through parallel processing. Design space exploration at higher levels of abstraction yields greater optimization in power, area, and delay; thus, the first contribution intelligently reduces voltages of non-critical paths in order to decrease total power consumption at the behavioral level. Voltage reductions are performed while minimizing the number of voltage conversions introduced in the circuit and maintaining the critical path delay. The second contribution concentrates on exploiting parallelism by distributing independent synthesis tasks to different processing units in the goal of reducing solution exploration time.
A synthesis software suite was implemented to test the proposed approaches. Power consumption was reduced considerably with a negligible overhead of voltage conversion modules. Furthermore, design space exploration time declined significantly due to the use of parallel programming.
2015-02-10
2015-02-10
2015-02-10
2013-08-06
Thesis
http://hdl.handle.net/10725/1919
https://doi.org/10.26756/th.2013.39
en
oai:laur.lau.edu.lb:10725/19202020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Designing policies using a MIMO PID controller for correlated multiple-policy multiple-objective strategic planning. (c2014)
Khalifeh, Joe
Strategic planning
Organizational effectiveness -- Measurement
Input-output analysis
Education, Higher -- Evaluation
Lebanese American University -- Dissertations
Dissertations, Academic
Bibliography: leaves 84-86.
Strategic planning (SP) is the process of aligning an organization’s activities with its own vision and mission. Several strategic planning frameworks and tools were developed such as SWOC, Porter’s five forces and PEST analysis. So far the balanced scorecard (BSC), proposed by Norton and Kaplan, is the most consistent since it accounts for strategic measures in four major perspectives. Shaping relevant decision rules to meet the target measures associated with the BSC four perspectives becomes a multiple-policy multi-objective (MPMO) process. During the past four decades, there has been some development of analytical methods that can guide SP analysts in policy makings of large systems. Different policy design techniques are proposed that help in steering organizations towards meeting a target level. Designing policies is usually constructed as a set of single-policy single-objective subsystem where proportional and, at most, derivative feedback control is presented without taking into consideration the four BSC perspectives.
In this thesis we consider a Master’s University, such as the Lebanese American University, as the organization. We associate the number of enrolled students, the academic reputation, student-to-faculty ratio and research productivity, and faculty recruitment and faculty development funds with the four BSC perspectives. The policies under consideration are number of faculty to be recruited, development funds to be dedicated to faculty at the associate professorial rank, and development funds to be dedicated to faculty at the professional rank. A 28th-order nonlinear state-space model is constructed in order to reflect the relevant system dynamics. A multiple-input multiple-output (MIMO) Proportional-Integral-Derivative (PID) controller is implemented for shaping the correlated three policies involved in this MPMO system. The associated ten-year target levels are set such that the university reputation is significantly improved, and the overall financial balance is considerably large in order to accommodate for capital expansion. Numerical simulations are included to illustrate the effectiveness of the proposed MPMO systematic approach.
2015-02-10
2015-02-10
2015-02-10
2014-06-11
Thesis
http://hdl.handle.net/10725/1920
https://doi.org/10.26756/th.2014.5
en
oai:laur.lau.edu.lb:10725/19732020-11-20T08:00:27Zcom_10725_2055col_10725_2076
The graphic novel's West Asian new wave. (c2014)
Sabbagh, Mona Majzoub
Satrapi, Marjane -- 1969- -- Persepolis
Sacco, Joe -- Palestine
Graphic novels -- Political aspects -- Middle East
Graphic novels -- Middle East -- History and criticism
Dissertations, Academic
Lebanese American University -- Dissertations
Includes bibliographical references (leaves 85-87).
While the graphic novel is becoming a well-established genre in the West with its own definitions, bi-cultural authors develop a new West Asian trajectory, both in form and subject, from their own displacements as well as the region’s historical legacies and conflicts. This thesis, a comparative study of the two graphic novels, Persepolis by Marjane Satrapi and Palestine by Joe Sacco, is an analysis of what distinguishes this regional new wave of the graphic novel. By examining the media and aesthetic strategies that they develop to narrate social and political strife and emergence, this study shows how the graphic novel in West Asia derives as much from regional popular traditions of political cartoons and televised skits (from Iran to Egypt and the Levant) as it does from the western comics tradition. But what are the implications of such a development of the graphic novel in this region?
2015-02-26
2015-02-26
2015-02-26
2014-12-23
Thesis
http://hdl.handle.net/10725/1973
https://doi.org/10.26756/th.2014.41
en
oai:laur.lau.edu.lb:10725/20132021-03-19T09:59:47Zcom_10725_2055col_10725_2076
A scalable family of unitary and differential space-time codes for ultra wideband communications. (c2014)
Fayad, Karl
Space time codes
Coding theory
Wireless communication systems
Lebanese American University -- Dissertations
Dissertations, Academic
Bibliography: leaves 64-66.
Higher data rates have always been the main demand ever since the emergence of telecommunications. This quest for faster and more reliable communications has led to the evolution of numerous generations of wired and wireless communication. One of the most recent and most promising wireless technologies is the Ultra Wideband (UWB) communication. This technology, associated with the usage of Multiple Input Multiple Output (MIMO) techniques and Space Time (ST) codes, can be considered
as the future for short-range wireless communications. Following from the excessive delay spreads of the UWB channels, channel estimation is rather challenging and, consequently, coherent solutions are being slowly disregarded shifting the focus to differential techniques. While the literature related to coherent ST codes for UWB is quite rich, limited contributions targeted the more challenging problem of differential ST codes.
In this work, we propose a novel unipolar ST code for UWB. The proposed technique can be completely implemented in an analog manner while still ensuring full spatial diversity. Being differential and unitary, the presented system further guarantees the optimal detectability of the received signals without any need for channel estimation.
The above features keep the system complexity at a minimum while ensuring full reliability. In addition, the proposed codebook can be partitioned into a number of sub-codebooks with predefined structure resulting in additional scalability capabilities that provide a compromise between data rate and decoding complexity.
2015-06-10
2015-06-10
2016-05-06
2014-12-17
Thesis
http://hdl.handle.net/10725/2013
https://doi.org/10.26756/th.2014.45
en
oai:laur.lau.edu.lb:10725/21522020-11-20T08:00:27Zcom_10725_2055col_10725_2076
Effects of deck transverse cracks on the temperature distribution in composite bridges. (c2014)
Masri, Omar Youssef El
Concrete bridges -- Floors -- Cracking
Concrete bridges -- Effect of temperature on -- Mathematical models
Finite element method
Thermal stresses -- Mathematical models
Dissertations, Academic
Lebanese American University -- Dissertations
Thermally induced stresses in composite steel-concrete bridges are higher than those experienced by their concrete and steel cousins due to dissimilarity in material properties. These thermal stresses are relatively high when compared to service load stresses, leading to significant damage that manifest itself in terms of crack development in the concrete deck. This in turns leads to the corrosion of the steel reinforcement, steel superstructure, along with the deterioration of the concrete through water seepage. The various bridge design codes emphasize the importance of thermal stresses by providing designers with suggested thermal gradients that account for the temperature differential in bridges. However, previous studies have failed to account for the pre-existing construction transverse cracks in the concrete deck and their effect on the temperature distribution in composite bridges.
In this study, a three-dimensional finite element model was developed to investigate the temperature distribution in a selected case study bridge. The model is a realistic depiction of an existing bridge with pre-existing transverse deck cracks and actual environmental boundary conditions for a selected geographical region. The results of a thermo-elastic analysis show that the AASHTO LRFD Bridge Design Specification is overly conservative and overestimates the vertical temperature gradient for the studied bridge. The AASHTO and other models found in existing literature seem to ignore the nonlinear thermal gradient for composite bridges, which produces a nonlinear strain component that can be critical for the bridge design and cannot be treated in a trivial manner. In addition, the pre-service deck transverse cracks appear to have a considerable effect on both, the vertical and the longitudinal temperature distributions in composite steel-concrete bridges, and hence require further assessment.
2015-09-18
2015-09-18
2014
2015-09-18
2014-06-05
Thesis
http://hdl.handle.net/10725/2152
https://doi.org/10.26756/th.2014.50
en
oai:laur.lau.edu.lb:10725/21732019-09-19T08:42:37Zcom_10725_2055col_10725_2075
A numerical model for the solution of thermal elastohydrodynamic lubrication in coated circular contacts
Habchi, Wassim
This paper presents a finite element model for the solution of thermal elastohydrodynamic lubrication in coated circular contacts. The model is based on a full-system finite element resolution of the elastohydrodynamic and heat transfer equations. The effects of the coating's thermal and mechanical properties on lubrication performance are investigated. Two categories of surface coatings are considered based on thermal properties: high and low thermal inertia. It is found that low thermal inertia surface coatings act as insulators leading to a localized increase in the lubricant's temperature at the center of the contact. Therefore, friction can be significantly reduced while film thickness is barely affected. The opposite effect is observed for high thermal inertia coatings. These effects increase with coating's thickness.
2015-09-21
2015-09-21
2015-09-21
Article
0301-679X
http://hdl.handle.net/10725/2173
https://dx.doi.org/10.1016/j.triboint.2014.01.002
Habchi, W. (2014). A numerical model for the solution of thermal elastohydrodynamic lubrication in coated circular contacts. Tribology International, 73, 57-68.
http://www.sciencedirect.com/science/article/pii/S0301679X14000073
en
Tribology International
oai:laur.lau.edu.lb:10725/21772016-08-25T07:15:35Zcom_10725_2055col_10725_2075
Towards the True Prediction of EHL Friction
Habchi, Wassim
Bjorling, M,
Bair, S.
Larsson, R.
Marklund, P.
The capability to predict elastohydrodynamic film-thickness and friction from primary measurements of transport properties of liquid has been an elusive goal for tribologists for 50 years. Most comparisons between predictions and experiments involve some amount of tuning of the model in order to match the experimental results. In true prediction, this cannot be done since there are normally no experimental results to compare to. Primary measurements of lubricant transport properties of Squalane were performed, and used in a numerical friction prediction model. Afterwards, friction was measured in a ball-on-disc tribotester. No tuning of the lubricant properties, model or test setup were applied. The current work on EHL-friction is therefore a true representation of the current level of EHL-friction prediction.
2015-09-21
2015-09-21
2015-09-21
Article
0301-679X
http://hdl.handle.net/10725/2177
http://dx.doi.org/10.1016/j.triboint.2013.04.008
Björling, M., Habchi, W., Bair, S., Larsson, R., & Marklund, P. (2013). Towards the true prediction of ehl friction. Tribology International, 66, 19-26.
http://www.sciencedirect.com/science/article/pii/S0301679X13001849
en
Tribology International
oai:laur.lau.edu.lb:10725/21782019-09-19T06:54:56Zcom_10725_2055col_10725_2075
A Film Thickness Correction Formula for Double- Newtonian Shear-Thinning in Rolling EHL Circular Contacts
Habchi, Wassim
Bair, S.
Qureshi, F.
Covitch, M.
Lubricants which contain a polymeric thickener will often display a second Newtonian plateau in measured flow curves. Like other manifestations of shear-dependent viscosity, this shear response will lead to an inaccurate prediction when the classical film-thickness formulas are employed. A correction formula has been developed from numerical experiments for a range of parameters of the double-Newtonian modified Carreau equation. The parameters of this shear-thinning model were selected from measurements for real lubricants obtained in Couette viscometers and a capillary viscometer. In addition, a full EHL film thickness formula has been derived from the same numerical experiments. The correction formula and the full formula were successfully validated using published film thickness data and published viscosity data for an EHL reference liquid, a polymer solution. Clearly, viscometer measurements of shear-dependent viscosity which contain the inflection leading to the second Newtonian are essential for a film-thickness calculation when a high-molecular-weight component of the lubricant is present.
2015-09-21
2015-09-21
2013
2015-09-21
Article
1023-8883
http://hdl.handle.net/10725/2178
http://dx.doi.org/10.1007/s11249-012-0078-6
Habchi, W., Bair, S., Qureshi, F., & Covitch, M. (2013). A film thickness correction formula for double-Newtonian shear-thinning in rolling EHL circular contacts. Tribology Letters, 50(1), 59-66.
http://link.springer.com/article/10.1007/s11249-012-0078-6
en
Tribology Letters
oai:laur.lau.edu.lb:10725/21792019-12-18T09:36:34Zcom_10725_2055col_10725_2075
Fast and reduced full-system finite element solution of elastohydrodynamic lubrication problems
Habchi, W.
Issa, J.
This paper presents a reduced full-system finite element solution of elastohydrodynamic lubrication (EHL) problems. It aims to demonstrate the feasibility of this approach by applying it to the simple isothermal Newtonian line contact case. However the proposed model can be extended to more complex situations. This model is based on a full-system finite element resolution of the EHL equations: Reynolds, linear elasticity and load balance. A reduced model is proposed for the linear elasticity problem. For this, three different techniques are tested: the classical “modal reduction” and “Ritz-vector” methods and a novel “EHL-basis” method. The reduction order in the first two appears to be insufficient and a large number of degrees of freedom is required in order to attain an acceptable solution. On the other hand, the “EHL-basis” method shows up to be much more efficient, requiring only a few degrees of freedom to compose the elastic deformation of the solid components. In addition, a comparison with the full model shows an order of magnitude execution time gain with errors of the order of only 1‰ for the central and minimum film thicknesses.
2015-09-21
2015-09-21
2013
2015-09-21
Article
0965-9978
http://hdl.handle.net/10725/2179
http://dx.doi.org/10.1016/j.advengsoft.2012.11.009
Habchi, W., & Issa, J. (2013). Fast and reduced full-system finite element solution of elastohydrodynamic lubrication problems: Line contacts. Advances in Engineering Software, 56, 51-62.
http://www.sciencedirect.com/science/article/pii/S0965997812001561
en
Advances in Engineering Software
oai:laur.lau.edu.lb:10725/21802019-12-13T14:25:51Zcom_10725_2055col_10725_2075
Quantitative Compressibility Effects in Thermal Elastohydrodynamic Circular Contacts
Habchi, W.
Bair, S.
This paper investigates the effects of lubricant compressibility on the film-forming performance of thermal elastohydrodynamic lubricated (EHL) circular contacts. Numerical film thickness predictions using the classical Dowson and Higginson relationship are compared to those that would be obtained using a more realistic compressibility model, all other parameters kept unchanged. This allows an isolation of the realistic compressibility effects on the film-forming performance. For realistic predictions, the authors consider two model liquids from the 1953 report of the ASME Research Committee on Lubrication, the most and the least compressible. The compressibility of these liquids is modeled using the Tait equation of state (EoS) while all other transport properties are kept unchanged for the sake of isolating compressibility effects. In addition, the same typical generalized-Newtonian behavior is assumed for both model liquids. The results reconfirm the well-known observations that minimum film thickness is very little affected by lubricant compressibility while central film thickness decreases linearly with the increase in volume compression of the lubricant. It is also observed that the relative errors on central film thicknesses induced by the use of the Dowson and Higginson relationship for compressibility increase with load and temperature and are very little affected by mean entrainment speed. Compressibility is shown to be a significant source of error in film-derived measurements of pressure-viscosity coefficients especially at high temperature. The thermodynamic scaling that provides an accurate and consistent framework for the correlation of the thermophysical properties of liquids with temperature and pressure requires an accurate equation of state. In brief, this paper highlights the importance of using realistic transport properties modeling based on thermodynamic scaling for an accurate numerical prediction of the performance of EHL contacts
2015-09-21
2015-09-21
2015-09-21
Article
0022-2305
http://hdl.handle.net/10725/2180
http://dx.doi.org/10.1115/1.4023082
Habchi, W., & Bair, S. (2013). Quantitative compressibility effects in thermal elastohydrodynamic circular contacts. Journal of Tribology, 135(1), 011502.
http://www.sciencedirect.com/science/article/pii/S0301679X12003258
en
ASME Journal of Tribology
oai:laur.lau.edu.lb:10725/21812019-09-23T08:58:44Zcom_10725_2055col_10725_2075
On friction regimes in quantitative elastohydrodynamics
Habchi, W.
Bair, S.
Vergne, P.
This paper identifies the different friction regimes encountered in elastohydrodynamic lubricated point contacts using a quantitative, physics-based approach. The idea is to link different traction regimes to dimensionless numbers and identify ranges of those numbers where a given regime is encountered or dominates the friction response of the contact. A numerical investigation of traction in point contacts lubricated with a typical mineral oil is employed. The measured thermo-physical properties of the oil are used without any modification to force agreement with experiments. The authors propose four friction regimes delimited by the combined values of three dimensionless parameters.
2015-09-21
2015-09-21
2015-09-21
Article
0301-679X
http://hdl.handle.net/10725/2181
http://dx.doi.org/10.1016/j.triboint.2012.10.005
Habchi, W., Bair, S., & Vergne, P. (2013). On friction regimes in quantitative elastohydrodynamics. Tribology International, 58, 107-117.
http://www.sciencedirect.com/science/article/pii/S0301679X12003258
en
Tribology International
oai:laur.lau.edu.lb:10725/21822019-09-23T09:16:38Zcom_10725_2055col_10725_2075
Stabilized Fully-Coupled Finite Elements for Elastohydrodynamic Lubrication Problems
Habchi, Wassim
Eyheramendy, D.
Vergne, P.
Morales-Espejel, G.
This work presents a model for elastohydrodynamic (EHD) lubrication problems. A finite element full-system approach is employed. The hydrodynamic and elastic problems are solved simultaneously which leads to fast convergence rates. The free boundary problem at the contact’s exit is handled by a penalty method. For highly loaded contacts, the standard Galerkin solution of Reynolds equation exhibits an oscillatory behaviour. The use of artificial diffusion techniques is proposed to stabilize the solution. This approach is then extended to account for non-Newtonian lubricant behaviour and thermal effects. Artificial diffusion procedures are also introduced to stabilize the solution at high loads.
2015-09-21
2015-09-21
2012
2015-09-21
Article
0965-9978
http://hdl.handle.net/10725/2182
http://dx.doi.org/10.1016/j.advengsoft.2010.09.010
Habchi, W., Eyheramendy, D., Vergne, P., & Morales-Espejel, G. (2012). Stabilized fully-coupled finite elements for elastohydrodynamic lubrication problems. Advances in Engineering Software, 46(1), 4-18.
http://www.sciencedirect.com/science/article/pii/S0965997810001365
en
Advances in Engineering Software,
oai:laur.lau.edu.lb:10725/21832019-09-19T08:37:47Zcom_10725_2055col_10725_2075
A numerical investigation of local effects on the global behavior of TEHD highly loaded circular contacts
Habchi, Wassim
Vergne, P.
Bair, S.
Fillot, N.
Morales-Espejel, G. E.
This paper presents a numerical investigation of the local behavior of highly loaded thermal elastohydrodynamic contacts. The study is a continuation to a previous work of the authors where it was found that neglecting the dependence of lubricants' thermal properties on pressure and temperature leads to an underestimation of friction coefficients under high sliding regime. In this work, the local phenomena behind these observations are investigated. The results suggest that a redistribution of heat from the center of the contact towards the environment is taking place, leading to globally lower temperatures inside the contact, which leads to higher friction coefficients
2015-09-21
2015-09-21
2011
2015-09-21
Article
0301-679X
http://hdl.handle.net/10725/2183
http://dx.doi.org/10.1016/j.triboint.2011.08.010
Habchi, W., Vergne, P., Fillot, N., Bair, S., & Morales-Espejel, G. E. (2011). A numerical investigation of local effects on the global behavior of TEHD highly loaded circular contacts. Tribology International, 44(12), 1987-1996.
http://www.sciencedirect.com/science/article/pii/S0301679X11002295
en
Tribology International
oai:laur.lau.edu.lb:10725/21852019-12-17T14:12:20Zcom_10725_2055col_10725_2075
Numerical investigation of the use of machinery low-viscosity working fluids as lubricants in elastohydrodynamic lubricated point contacts
Habchi, Wassim
Vergne, P.
Eyheramendy, D.
Morales-Espejel, G. E.
This study proposes a numerical investigation of the potential use of machinery working fluids as lubricants in contacts operating under an elastohydrodynamic regime. These fluids are usually of very low viscosity and pressure–viscosity dependence. This is why, unmixed with oil, they have been of little interest for the tribological community. Hence, their rheological properties are poorly known. In fact, these are restricted to a narrow range of conditions compared to the range of interest in EHL applications. This is why some measurements are carried out in order to determine both the viscosity and density of these uncommon lubricants. Besides, their viscosity being low, high-mean entrainment speeds are required for a sufficiently thick lubricant film to build up. This leads to an important thermal dissipation within the contact. Thermal effects are included in the analysis in order to make the estimation of film thicknesses and friction coefficients in these contacts as accurate as possible. Results are discussed in the light of the peculiar properties of machinery low-viscosity working fluids.
2015-09-21
2015-09-21
2011
2015-09-21
Article
1350-6501
http://hdl.handle.net/10725/2185
http://dx.doi.org/10.1177/1350650111399373
Habchi, W., Vergne, P., Eyheramendy, D., & Morales-Espejel, G. E. (2011). Numerical investigation of the use of machinery low-viscosity working fluids as lubricants in elastohydrodynamic lubricated point contacts. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 225(6), 465-477.
http://pij.sagepub.com/content/225/6/465.short
en
IMechE Part J: Journal of Engineering Tribology
oai:laur.lau.edu.lb:10725/21842019-09-19T13:57:19Zcom_10725_2055col_10725_2075
Full Film, Boundary Lubrication and Tribochemistry in Steel Circular Contacts Lubricated with Glycerol
Habchi, W.
Matta, C.
Joly-Pottuz, L.
De Barros, M.I.
Martin, J.M.
Vergne, P.
In this article, the lubricating properties of pure glycerol are investigated under both mild and severe EHL regimes. Amazingly low friction coefficients (about 0.01) are reported by experiments in thick film regimes compared to traditional base oils. EHL calculations of film thickness and friction (including thermal effects) predict friction coefficients that are twice those actually found for glycerol. Chemical analysis of glycerol before and after the friction tests were performed by NMR and Karl Fischer methods, and they reveal that water is produced by tribochemical reaction as well as other species like aldehydes. This finding is in agreement with a corrosion pattern observed inside the wear scars of the steel samples. This study provides an explanation to the anomalously low friction observed in the thick film regime. In fact, water produced in the lubricant decreases traction forces due to the drastic decrease of the viscosity of glycerol with water addition.
2015-09-21
2015-09-21
2015-09-21
Article
1023-8883
http://hdl.handle.net/10725/2184
http://dx.doi.org/10.1007/s11249-011-9778-6
Habchi, W., Matta, C., Joly-Pottuz, L., De Barros, M. I., Martin, J. M., & Vergne, P. (2011). Full film, boundary lubrication and tribochemistry in steel circular contacts lubricated with glycerol. Tribology Letters, 42(3), 351-358.
http://link.springer.com/article/10.1007/s11249-011-9778-6
en
Tribology Letters
oai:laur.lau.edu.lb:10725/21862019-08-30T13:00:09Zcom_10725_2055col_10725_2075
High surface area electrodes in ionic polymer transducers
Akle, Barbar J.
Habchi, Wassim
Wallmersperger, Thomas
Akle, Etienne J.
Leo, Donald J.
Ionomeric polymertransducer (IPT) is an electroactive polymer that has received considerable attention due to its ability to generate large bending strain (>5%) and moderate stress at low applied voltages (±2 V). Ionic polymertransducers consist of an ionomer, usually Nafion, sandwiched between two electrically conductiveelectrodes. A novel fabrication technique denoted as the direct assembly process (DAP) enabled controlled electrode architecture in ionic polymertransducers. A DAP built transducer consists of two high surface area electrodes made of electrically conducting particles uniformly distributed in an ionomer matrix sandwiching an ionomer membrane. The purpose of this paper is to investigate and simulate the effect of these high surface area particles on the electro-chemical response of an IPT. Theoretical investigations as well as experimental verifications are performed. The model used consists of a convection-diffusion equation describing the chemical field as well as a Poisson equation describing the electrical field. The two-dimensional model incorporates highly conductive particles randomly distributed in the electrode area. Traditionally, these kinds of electrodes were simulated with boundary conditions representing flat electrodes with a large dielectric permittivity at the polymer boundary. This model enables the design of electrodes with complicated geometrical patterns. In the experimental section, several transducers are fabricated using the DAP process on Nafion 117 membranes. The architecture of the high surface area electrodes in these samples is varied. The concentration of the high surface area RuO2 particles is varied from 30 vol% up to 60 vol% at a fixed thickness of 30 μm, while the overall thickness of the electrode is varied from 10 μm up to 40 μm at a fixed concentration of 45%. The flux and charge accumulation in the materials are measured experimentally and compared to the results of the numerical simulations. Trends of the experimental and numerical investigations are in agreement, while the computational capacity is limiting the ability to add sufficient amount of metal particle to the electrode in order to match the magnitudes.
2015-09-21
2015-09-21
2011
2015-09-21
0021-8979
http://dx.doi.org/10.1063/1.3556751]
Akle, B. J., Habchi, W., Wallmersperger, T., Akle, E. J., & Leo, D. J. (2011). High surface area electrodes in ionic polymer transducers: numerical and experimental investigations of the electro-chemical behavior. Journal of Applied Physics, 109(7), 074509.
https://vtechworks.lib.vt.edu/bitstream/handle/10919/52009/2011_High_surface_area_electrodes.pdf?sequence=1&isAllowed=y
Journal of Applied Physics
oai:laur.lau.edu.lb:10725/21872019-09-20T08:44:38Zcom_10725_2055col_10725_2075
Influence of Pressure and Temperature Dependence of Thermal Properties of a Lubricant on the Behavior of Circular TEHD Contacts
Habchi, Wassim
Vergne, P.
Bair, S.
Andersson, O.
Eyheramendy, D.
Morales-Espejel, G. E.
The aim of this paper is to study the effects of pressure and temperature dependence of a conventional lubricant's thermal properties on the behaviour of heavily loaded thermal elastohydrodynamic lubrication (TEHL) contacts. For this purpose, a typical mineral oil (Shell T9) is selected and the dependence of its transport properties on pressure and temperature is investigated. Appropriate models are then developed for these dependencies. The latter are included in a TEHL solver in order to investigate their effect on the behaviour of circular EHD contacts. The results reveal the necessity of a thermal analysis including the pressure and temperature dependence of thermal properties for a good estimation of film thicknesses and mostly traction coefficients in circular EHD contacts operating under severe conditions. Numerical results are compared with experiments, showing a very good agreement over the considered ranges. This thorough validation of a thermal EHL framework for the calculation of film thickness and friction offers a previously unavailable opportunity to investigate the effects of variations in material properties.
2015-09-21
2015-09-21
2010
2015-09-21
Article
0301-679X
http://hdl.handle.net/10725/2187
http://dx.doi.org/10.1016/j.triboint.2009.10.002
Habchi, W., Vergne, P., Bair, S., Andersson, O., Eyheramendy, D., & Morales-Espejel, G. E. (2010). Influence of pressure and temperature dependence of thermal properties of a lubricant on the behaviour of circular TEHD contacts. Tribology International, 43(10), 1842-1850.
http://www.sciencedirect.com/science/article/pii/S0301679X09003028
en
Tribology International
oai:laur.lau.edu.lb:10725/21922019-08-14T06:18:44Zcom_10725_2055col_10725_2075
A numerical study of friction in isothermal EHD rolling-sliding sphere-plane contacts with spinning
Dormois, H.
Fillot, N.
Habchi, W.
Dalmaz, G.
Vergne, P.
Morales-Espejel, G. E.
Ioannides, E.
This paper presents a study of the spinning influence on film thickness and friction in EHL circular contacts under isothermal and fully flooded conditions. Pressure and film thickness profiles are computed with an original full-system finite element approach. Friction was thereafter investigated with the help of a classical Ree–Eyring model to calculate the longitudinal and transverse shear stresses. An analysis of both the velocity and shear stress distributions at every point of the contact surfaces has allowed explaining the fall of the longitudinal friction coefficient due to the occurrence of opposite shear stresses over the contact area. Moreover in the transverse direction spinning favors large shear stresses of opposite signs, decreasing the fluid viscosity by non-Newtonian effects. These effects have direct and coupled consequences on the friction reduction that is observed in the presence of spinning. They are expected to further decrease friction in real situations due to shear heating.
2015-09-28
2015-09-28
2010
2015-09-28
Article
0022-2305
http://hdl.handle.net/10725/2192
http://dx.doi.org/10.1115/1.4001104
Dormois, H., Fillot, N., Habchi, W., Dalmaz, G., Vergne, P., Morales-Espejel, G. E., & Ioannides, E. (2010). A numerical study of friction in isothermal EHD rolling-sliding sphere-plane contacts with spinning. Journal of Tribology, 132(2), 021501.
http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468459
en
Journal of Tribology
oai:laur.lau.edu.lb:10725/21932019-07-29T08:37:04Zcom_10725_2055col_10725_2075
Thermal Elastohydrodynamic Lubrication of Point Contacts Using a Newtonian/Generalized Newtonian Lubricant
Habchi, W.
Eyheramendy, D.
Bair, S.
Vergne, P.
Morales-Espejel, G.
The classical ElastoHydroDynamic (EHD) theory assumes a Newtonian lubricant and an isothermal operating regime. In reality, lubricating oils do not behave as perfect Newtonian fluids. Moreover, in most operating conditions of an engineering system, especially at high speeds, thermal effects are important and temperature can no longer be considered as constant throughout the system. This is one reason why there has always been a gap between numerical results and experimental data. This paper aims to show that this gap can be reduced by taking into consideration the heat generation that takes place in the contact and using appropriate rheological models. For this, a unique thermal ElastoHydrodynamic lubrication model is developed for both Newtonian and non-Newtonian lubricants. Pressure, film thickness and traction results are then compared to their equivalent isothermal results and experimental data. The agreement between thermal calculations and experiments reveals the necessity of considering thermal effects in EHD models.
2015-09-28
2015-09-28
2008
2015-09-28
Article
1023-8883
http://hdl.handle.net/10725/2193
http://dx.doi.org/10.1007/s11249-008-9310-9
Habchi, W., Eyheramendy, D., Bair, S., Vergne, P., & Morales-Espejel, G. (2008). Thermal elastohydrodynamic lubrication of point contacts using a newtonian/generalized newtonian lubricant. Tribology Letters, 30(1), 41-52.
http://link.springer.com/article/10.1007/s11249-008-9310-9
en
Tribology Letters
oai:laur.lau.edu.lb:10725/21942021-03-19T09:59:47Zcom_10725_2055col_10725_2075
A Full-System Approach of the Elastohydrodynamic Line/Point Contact Problem
Habchi, Wassim
Eyheramendy, D.
Vergne, P.
Morales-Espejel, G. E.
The solution of the elastohydrodynamic lubrication (EHL) problem involves the simultaneous resolution of the hydrodynamic (Reynolds equation) and elastic problems (elastic deformation of the contacting surfaces). Up to now, most of the numerical works dealing with the modeling of the isothermal EHL problem were based on a weak coupling resolution of the Reynolds and elasticity equations (semi-system approach). The latter were solved separately using iterative schemes and a finite difference discretization. Very few authors attempted to solve the problem in a fully coupled way, thus solving both equations simultaneously (full-system approach). These attempts suffered from a major drawback which is the almost full Jacobian matrix of the nonlinear system of equations. This work presents a new approach for solving the fully coupled isothermal elastohydrodynamic problem using a finite element discretization of the corresponding equations. The use of the finite element method allows the use of variable unstructured meshing and different types of elements within the same model which leads to a reduced size of the problem. The nonlinear system of equations is solved using a Newton procedure which provides faster convergence rates. Suitable stabilization techniques are used to extend the solution to the case of highly loaded contacts. The complexity is the same as for classical algorithms, but an improved convergence rate, a reduced size of the problem and a sparse Jacobian matrix are obtained. Thus, the computational effort, time and memory usage are considerably reduced.
2015-09-28
2015-09-28
2008
2016-05-09
Article
0022-2305
http://hdl.handle.net/10725/2194
http://dx.doi.org/10.1115/1.2842246
Habchi, W., Eyheramendy, D., Vergne, P., & Morales-Espejel, G. (2008). A full-system approach of the elastohydrodynamic line/point contact problem. Journal of Tribology, 130(2), 021501.
http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468009
en
ASME Journal of Tribology
oai:laur.lau.edu.lb:10725/21952021-03-19T09:59:47Zcom_10725_2055col_10725_2075
A Finite Element Approach of Thin Film Lubrication in Circular EHD Contacts
Habchi, Wassim
Demirci, I.
Eyheramendy, D.
Morales-Espejel, G. E.
Vergne, P.
So far, most of the numerical studies concerning elastohydrodynamic point contact lubrication have been realized using finite differences. This paper describes a finite element approach for the modelling of both, thick and thin film lubrication in circular contacts under isothermal elastohydrodynamic regime. Multigrid techniques are used to accelerate the convergence and reduce calculation time. The use of the finite element method (FEM) offers two advantages: first, the existence of high level ready-to-use Finite Element commercial software which reduces the time spent in implementing the method and second, the easier adaptability to different and various physical models such as lubricant rheology, starvation effects, thermal effects, non-Newtonian behaviour, etc. The numerical model is presented in detail and an example of its adaptation taking into account non-Newtonian effects is shown. Finally, a comparison is made between Newtonian and non-Newtonian solutions, exhibiting differences obtained when using both models, especially at high shear rates where the film thickness and the friction coefficients are overestimated by a Newtonian approach.
2015-09-28
2015-09-28
2016-05-06
Article
0301-679X
http://hdl.handle.net/10725/2195
http://dx.doi.org/10.1016/j.triboint.2007.01.017
Habchi, W., Demirci, I., Eyheramendy, D., Morales-Espejel, G., & Vergne, P. (2007). A finite element approach of thin film lubrication in circular EHD contacts. Tribology International, 40(10), 1466-1473.
http://www.sciencedirect.com/science/article/pii/S0301679X07000242
http://www.sciencedirect.com/science/article/pii/S0301679X07000242
en
Tribology International
oai:laur.lau.edu.lb:10725/23922022-06-01T10:25:57Zcom_10725_2055col_10725_2075
Strain response of hot-mix asphalt overlays in jointed plain concrete pavements due to reflective cracking
Ghauch, Z. G.
Abou-Jaoude, G. G.
Reflective cracks appear in asphalt overlays placed on top of a concrete pavement above the locations of joints and cracks in the concrete slab. This paper presents the results of a finite element study on the response at the bottom of the HMA overlay. The effects of subgrade and subbase strengths, vehicle speed, overlay thickness, and pavement temperature are investigated in order to identify the parameters involved in the deterioration of the overlay. An extrapolation of the strain history curve for various pavement design parameters is presented to estimate the number of load repetitions that lead to bottom–up crack initiation.
2015-10-30
2015-10-30
2013
2015-10-30
Article
0045-7949
http://hdl.handle.net/10725/2392
http://dx.doi.org/10.1016/j.compstruc.2012.12.005
Ghauch, Z. G., & Abou-Jaoude, G. G. (2013). Strain response of hot-mix asphalt overlays in jointed plain concrete pavements due to reflective cracking. Computers & Structures, 124, 38-46.
http://www.sciencedirect.com/science/article/pii/S0045794912003057
en
Computers and Structures
oai:laur.lau.edu.lb:10725/23942019-01-14T12:34:44Zcom_10725_2055col_10725_2075
Resistance Factors for Use in Load and Resistance Factor Design of Driven Pipe Piles in Sands
Abou-Jaoude, Grace
Foye, K.C.
Prezzi, M.
Salgado, R.
Load and resistance factor design of foundations is done in the offshore industry and is now being done in bridge projects in the United States. Common methods used to establish resistance factors include calibration to assumed factors of safety and reliability analysis using field load test databases. Reliability analyses are the preferred tools for this work but the needed probabilistic information regarding design method uncertainty is difficult to obtain. Furthermore, field load test databases, while relatively attractive for assessing design uncertainty, are not able to discriminate between uncertainties caused by soil variability, test methods, and model design relationships. In contrast to previous efforts, this paper illustrates an approach to uncertainty assessment that seeks to isolate the various sources of uncertainty. Using this approach, reliability analysis is used to develop resistance factors for the design of driven pipe piles in sand. The resistance factor results are used to highlight some of the differences between design methods that are exposed by the proposed uncertainty assessment technique. A brief design example is also given that illustrates the use of the resistance factors.
2015-10-30
2015-10-30
2009-01
2015-10-30
Article
1090-0241
http://hdl.handle.net/10725/2394
http://dx.doi.org/10.1061/(ASCE)1090-0241(2009)135:1(1)
Foye, K. C., Abou-Jaoude, G., Prezzi, M., & Salgado, R. (2009). Resistance factors for use in load and resistance factor design of driven pipe piles in sands. Journal of geotechnical and geoenvironmental engineering, 135(1), 1-13.
http://ascelibrary.org/doi/abs/10.1061/(ASCE)1090-0241(2009)135:1(1)
en
Journal of Geotechnical and Geoenvironmental Engineering
oai:laur.lau.edu.lb:10725/29902021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Computational modeling of flow over an ogee spillway
Chatila, Jean
Tabbara, Mazen
This paper presents an investigation into the hydraulics of regular ogee-profile spillways. The free-surfaces of the fluid for several flow heads as measured in the hydraulics laboratory are used as benchmarks. The finite element computational fluid dynamics software, ADINA, was used to predict the free surface over an ogee spillway and thus model the flow field. Since the actual flow is turbulent the k–ε flow model was used. For the cases considered in this paper, ADINA predicted reasonable free surface results that are consistent with general flow characteristics over spillways. The results are also in close agreement with measured free-surface profiles over the entire length of the spillway.
2016-02-03
2016-02-03
2004
2015-10-21
Article
http://hdl.handle.net/10725/2990
http://dx.doi.org/10.1016/j.compstruc.2004.04.007
Chatila, J., & Tabbara, M. (2004). Computational modeling of flow over an ogee spillway. Computers & structures, 82(22), 1805-1812.
http://www.sciencedirect.com/science/article/pii/S0045794904001841
en
Computers & Structures
oai:laur.lau.edu.lb:10725/29912021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Computational simulation of flow over stepped spillways
Tabbara, Mazen
Chatila, Jean
Awwad, Rita
Numerical simulations of water flow over stepped spillways with different step configurations are presented. The finite element computational fluid dynamics module of the ADINA software was used to predict the main characteristics of the flow. This included the determination of the water surface, the development of skimming flow over corner vortices, and the determination of energy dissipation. Since the actual flow is turbulent, the k–ε flow model was used. A two-phase solution process was adopted in order to optimize the overall simulation efficiency. In the first phase, a simple yet reasonable water surface consisting of three straight lines was used as an initial guess and was treated as a fixed wall. In the second phase, the results from the first phase were used as initial conditions and the water surface was treated as a free surface that evolved to attain a steady state configuration. For all the cases considered, the predicted water surface profile over the entire length of the spillway was in close agreement with the experimentally measured water surface profile. The predicted energy dissipation was also comparable to the experimentally attained values.
2016-02-03
2016-02-03
2005
2016-05-06
Article
0045-7949
http://hdl.handle.net/10725/2991
http://dx.doi.org/10.1016/j.compstruc.2005.04.005
Tabbara, M., Chatila, J., & Awwad, R. (2005). Computational simulation of flow over stepped spillways. Computers & structures, 83(27), 2215-2224.
http://www.sciencedirect.com/science/article/pii/S0045794905002014
en
Computers & Structures
oai:laur.lau.edu.lb:10725/29922021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Reclaimed Waste Water in Some Middle Eastern Countries
Chatila, Jean G.
Countries of the Middle East are increasingly suffering from shortages and mismanagement of water, a commodity that is becoming of considerable value since water demands are fast approaching the limits of availability. Efficient solutions for water-related problems necessitate the adoption of well-planned policies. The solution must be sought in the optimum use of the available water, and reuse of reclaimed waste water must play a vital part. To meet future water requirements, many countries will have no option but to increase the use of treated waste water and study the viability of waste water reuse alternatives including irrigation of agricultural lands and recharge of groundwater. The cost of waste water treatment depends on the process used and the level of treatment required for a particular use. Data on waste water in the Middle East region are scarce and scattered. The article's main aim is to provide a summary and perspective on the subject and clarify the idea that waste water is not free. This paper describes the different aspects of the waste water—quantities, treatment, potential reuse, and pricing of the treated effluent—in some countries of the Middle East. Many of these countries will have no option but to increase the use of treated waste water—an economically acceptable resource—to reduce the exploitation of scarce water sources and resources. Finally, a set of proposed regulations and recommendations has been developed.
2016-02-03
2016-02-03
2004
2016-03-07
Article
0225-5189
http://hdl.handle.net/10725/2992
http://dx.doi.org/10.1080/02255189.2004.9668990
Chatila, J. G. (2004). Reclaimed waste water in some Middle Eastern countries: Pricing and perspective. Canadian Journal of Development Studies/Revue canadienne d'études du développement, 25(3), 481-497.
http://www.tandfonline.com/doi/abs/10.1080/02255189.2004.9668990#.V6
en
Canadian Journal of Development Studies
oai:laur.lau.edu.lb:10725/29932021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Stepped Spillway as an Energy Dissipater
Chatila, Jean G.
Jurdi, Bassam R.
This paper describes an experimental investigation into the hydraulics of ogee-profile stepped spillways, examines their viability as an alternative to smooth-back spillways and investigates their efficiency in reducing the downstream energy and length of the hydraulic jump. Tests were performed in a long rectangular flume with glass walls on both sides. One smooth model was used as a benchmark for comparison with stepped models made out of a combination of crests and bottoms of different step heights. Significant reductions in terminal velocities and total energies were observed, where the stepped spillway profiles tested proved to be very effective in terms of energy dissipation for flows of the order of the design head or lower. For flows beyond the design head, the effectiveness of the stepped spillway configuration was reduced and became negligible for heads greater than one and a half times the design head. It was concluded that the number of steps is the overbearing factor in expending flow kinetic energy and, therefore, reducing the length of the downstream forming hydraulic jump.
2016-02-03
2016-02-03
2004
2016-05-09
Article
0701-1784
http://hdl.handle.net/10725/2993
http://dx.doi.org/10.4296/cwrj147
Chatila, J. G., & Jurdi, B. R. (2004). Stepped spillway as an energy dissipater.Canadian Water Resources Journal, 29(3), 147-158.
http://www.tandfonline.com/doi/abs/10.4296/cwrj147#.V6lvUJh97cs
en
Canadian Water Resources Journal
oai:laur.lau.edu.lb:10725/29942021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Modelling floodplain conveyance in compound channel flows
Chatila, Jean G.
Townsend, Ron D.
Floodplain conveyance in compound channel flows is examined through applications of the dynamic flow routing model DWOPER to both laboratory and field data sets. Three different approaches regarding the modelling of off-channel storage are considered, namely, the single-channel approach and two interface-plane methods, which artificially separate main channel flows from floodplain flows, using (i) vertical and (ii) diagonal interface planes. The single-channel method, which views composite flow fields as single units without storage, produced significant differences between simulated and observed stage and discharge hydrographs. The vertical interface method gave generally good results in the case of the laboratory data, but was less successful when applied to the field data. The diagonal interface method, which in this instance applied outward-facing diagonal interface planes at the junctions of the main channel and floodplain zones, produced superior results overal
2016-02-03
2016-02-03
1995
2016-05-10
Article
0315-1468
http://hdl.handle.net/10725/2994
http://dx.doi.org/10.1139/l95-078
Chatila, J. G., & Townsend, R. D. (1995). Modelling floodplain conveyance in compound channel flows. Canadian Journal of Civil Engineering, 22(4), 660-667.
http://www.nrcresearchpress.com/doi/abs/10.1139/l95-078#.V6lvEph97cs
en
Canadian Journal of Civil Engineering
oai:laur.lau.edu.lb:10725/29952021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Modeling of Pollutant Transport in Compound open Channels
Chatila, Jean G.
Townsend, Ron D.
In this paper we describe the development and validation of a 2-D finite-difference mathematical model for simulating inert pollutant transport in compound channels. In its formulation the model couples depth-averaged (depth-integrated) versions of the classical 3-D Navier-Stokes equations and the advection-diffusion equation with constant eddy-viscosity model. The numerical solution scheme is Platzman’s space-staggered scheme, and a double time step operation is employed in the analysis. The model is initially validated using laboratory data of continuous-injection dye tracer experiments performed in a large asymmetrical compound-shaped channel at the Hydraulics Laboratory, University of Ottawa. Comparison between predicted and observed dye concentration curves indicates generally good agreement in the overall shapes of the curves, as well as in the peak concentrations and the times to peak.
2016-02-03
2016-02-03
1998
2016-05-12
Article
0701-1784
http://hdl.handle.net/10725/2995
http://dx.doi.org/10.4296/cwrj2303259
Chatila, J. G., & Townsend, R. D. (1998). Modeling of pollutant transport in compound open channels. Canadian Water Resources Journal, 23(3), 259-271.
http://www.tandfonline.com/doi/abs/10.4296/cwrj2303259
en
Canadian Water Resources Journal
oai:laur.lau.edu.lb:10725/29962021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Laws, policy measures, standards and regulations in the water sector in Lebanon: a review and perspective
Chatila, Jean G.
Lebanon is increasingly suffering from shortage and mismanagement of water, which is becoming a commodity of considerable value due to the inadequacy of supply to meet the needs of potential users. Efficient solutions for water-related problems necessitate the adoption of well-planned policies. These policies should concentrate on improving water management, rationalizing water consumption, and augmenting and protecting water supplies. Strict water policy, wastewater treatment and disposal criteria should be in effect in order to avoid contamination and achieve proper management of water resources systems. A system of laws and policies has been developed or under development, in which the government has framed comprehensive codes and regulations including health standards. In this instance, this paper describes different aspects of the laws and applicable policies in the water sector in Lebanon. A set of proposed regulations and recommendations has been developed.
2016-02-03
2016-02-03
2003
2016-05-11
Article
1366-7017
http://hdl.handle.net/10725/2996
Chatila, J. G. (2003). Laws, policy measures, standards and regulations in the water sector in Lebanon: a review and perspective. Water policy, 5(2), 165-177.
http://wp.iwaponline.com/content/5/2/165
en
Water policy
oai:laur.lau.edu.lb:10725/29972021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Water tariffs in Lebanon
Chatila, Jean G.
Lebanon is increasingly suffering from shortage and mismanagement of water, which is becoming a commodity of considerable value owing to the inadequacy of supply to meet the needs of potential users. Water authorities and establishments fix tariffs that users have to pay to obtain water. In fact, these tariffs should represent the total costs of providing good quality water in adequate quantities. However, currently domestic water tariffs in Lebanon are mostly flat and not enough to cover the salaries of the employees and the charges of minor maintenance works. Domestic water is sold at a nominal daily flow where rates are lower for smaller towns and increase proportionally. In addition, not all subscribers are actually paying their dues and the water authorities are unable to control and limit illegal connections. As for irrigation practices, water is generally priced at a flat rate or at rates that are associated with the area that the users are allowed to invest in. This paper describes the different aspects of the water tariff structures in Lebanon, provides a review of the current water tariffs available for the different sectors and presents recommendations and ideas for a new water tariff system in the newly formed water authorities.
2016-02-03
2016-02-03
2005
2016-05-13
Article
1366-7017
http://hdl.handle.net/10725/2997
Chatila, J. G. (2005). Water tariffs in Lebanon: A review and perspective. Water policy, 7(2), 215-226.
http://wp.iwaponline.com/content/7/2/215
en
Water policy
oai:laur.lau.edu.lb:10725/29982021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Discharge estimation methods for steady Compound Channel flows
Chatila, Jean G.
Townsend, Ron D.
This study evaluates various alternatives to account for flood plain conveyance in steady compound channel flows. Evaluations are based on applying several traditional discharge estimation methods to a steady, uniform flow laboratory data set. Many of the applied techniques overestimate compound channel discharge. Six interface and two other standard methods for computing discharge in open channels were compared. Each interface method uses a particular arrangement of imaginary interface planes to artificially sub-divide the compound flow field into homogeneous zones. These methods are named for the particular interface plane arrangement adopted. The two standard methods do not involve interface planes. In general, among the methods tested, the outward-facing diagonal interface plane method and the vertical interface plane method produced the most accurate simulations.
2016-02-03
2016-02-03
1996
2016-05-13
Article
0701-1784
http://hdl.handle.net/10725/2998
http://dx.doi.org/10.4296/cwrj2102131
Chatila, J. G., & Townsend, R. D. (1996). Discharge estimation methods for steady compound channel flows. Canadian Water Resources Journal, 21(2), 131-137.
http://www.tandfonline.com/doi/abs/10.4296/cwrj2102131#.V6luhZh97cs
en
Canadian Water Resources Journal
oai:laur.lau.edu.lb:10725/29992021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Muskingum Method, EXTRAN and ONE-D for Routing Unsteady Flows in Open Channels
Chatila, Jean G.
In the present study the numerical modelling aspects of unsteady flow in simple and compound channels are examined through the application to a laboratory data set of the simple hydrologic routing method Muskingum and the unsteady flow dynamic routing models EXTRAN and ONE-D. Model simulations were compared and evaluated by applying various statistical measures to determine the degree of goodness-of-fit between simulated and observed hydrographs. In terms of overall performance, the Muskingum method proved to be a simple and reliable method avoiding complicated mathematical and numerical computations for the cases considered.
2016-02-03
2016-02-03
2003
2016-05-16
Article
0701-1784
http://hdl.handle.net/10725/2999
http://dx.doi.org/10.4296/cwrj2803481
Chatila, J. G. (2003). Muskingum Method, EXTRAN and ONE-D for routing unsteady flows in open channels. Canadian Water Resources Journal, 28(3), 481-498.
http://www.tandfonline.com/doi/abs/10.4296/cwrj2803481#
en
Canadian Water Resources Journal
oai:laur.lau.edu.lb:10725/30002021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Evaluating impact of electrified vehicles on fuel consumption and CO2 emissions reduction in Lebanese driving conditions using onboard GPS survey
Mansour, Charbel
Zgheib, Elias
Saba, Sabine
Reviewing past and current mobility assessments for the Lebanese road transport sector, road mobility demand has experienced a real explosion since 1990, and the trend is strongly upward over the decade to come. This growth is mainly attributed to the raise of daily passenger trips and the increase of car ownership. Moreover, this increase in mobility demand results in severe congestion, mostly in Greater Beirut Area (GBA), which leads to chaotic traffic conditions. As a result, Lebanese citizens are suffering from high budget required for transport, high dependence on fossil fuels, in addition to high pollution level particularly in urban areas. Therefore, reducing the fuel consumption and emissions of Lebanese road transport, particularly for passenger cars, has become a must. Electrification of conventional Internal Combustion Engine Vehicles (ICEV) nowadays appears as an effective solution of paramount importance for car manufacturers, facing the challenge of minimizing the consumption of the road transport. Therefore, the objective of this paper is to present latest technological advancements of hybrid electric vehicles and to assess their impacts in terms of fuel savings in Lebanese urban driving conditions. The logic of vehicle electrification is outlined first by presenting the technological advantages with respect to conventional vehicles. Then the paper addresses a tank-to-wheel energy consumption comparison and an operating costs comparison between several hybrid electric vehicle types and a reference conventional vehicle, on real world driving cycles, representative of GBA driving conditions. Driving cycles are collected during a survey on real route in GBA using onboard GPS devices equipped with data loggers. Finally, an assessment of fuel consumption and CO2 emissions of the Lebanese car fleet is presented, in addition to a methodology for creating mitigation scenarios serving to reduce consumption and emissions by 2020.
2016-02-04
2016-02-04
2011
2016-02-02
Article
1876-6102
http://hdl.handle.net/10725/3000
https://doi.org/10.1016/j.egypro.2011.05.030
Mansour, C., Zgheib, E., & Saba, S. (2011). Evaluating impact of electrified vehicles on fuel consumption and CO2 emissions reduction in Lebanese driving conditions using onboard GPS survey. Energy Procedia, 6, 261-276.
https://www.sciencedirect.com/science/article/pii/S187661021101441X
en
Energy Procedia
oai:laur.lau.edu.lb:10725/30012021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Optimized energy management control for the Toyota Hybrid System using dynamic programming on a predicted route with short computation time
Mansour, C.
Clodic, D.
Among the general problematic of the HEV power trains, the most critical point is the determination of the power-split ratio between the mechanical and the electrical paths, known as the energy management strategy (EMS). Many EMS are proposed in the literature, and can be grouped in two categories: the local optimization EMS and the global optimization EMS. The local optimization category corresponds to the EMS based on human expertise and the knowledge of the power train components efficiency maps. Thus, the local optimization EMS manages the power train operations by referring to predefined rules. The drawback of such strategies is that it brings an instantaneous fuel consumption optimization, and does not fully optimize the fuel consumption over the whole trip. Therefore, additional fuel savings are still possible. This paper presents an overall optimized predictive EMS for the Toyota Hybrid System (THS-II) power train of the Prius. The proposed EMS is based on Dynamic Programming (DP), where the prior knowledge of the route is required in order to predetermine the power-split ratio and optimize the fuel consumption for the whole predicted route. The DP EMS proposed for the THS-II power train is designed with a very short computation time, intended to be implemented in real-time applications. The potential of this DP-controller in reducing fuel consumption on regulatory cycles are computed and compared to a rule-based controller and to the Prius published fuel consumption results. Finally, the fuel reduction enhancements of the DP-controller are computed for real road tests achieved on a MY06 Prius in Ile-de-France, by comparing to the associated observed consumption measurements.
2016-02-04
2016-02-04
2012
2016-02-16
Article
1229-9138
http://hdl.handle.net/10725/3001
http://dx.doi.org/10.1007/s12239-012-0029-0
Mansour, C., & Clodic, D. (2012). Optimized energy management control for the Toyota hybrid system using dynamic programming on a predicted route with short computation time. International Journal of Automotive Technology, 13(2), 309-324.
http://link.springer.com/article/10.1007/s12239-012-0029-0
en
International Journal of Automotive Technology
oai:laur.lau.edu.lb:10725/30022021-02-15T12:39:31Zcom_10725_2055col_10725_2075
Dynamic modeling of the electro-mechanical configuration of the Toyota Hybrid System series/parallel power train
Mansour, C.
Clodic, D.
The hybridization of the conventional thermal vehicles nowadays constitutes a paramount importance for car manufacturers, facing the challenge of minimizing the consumption of the road transport. Although hybrid power train technologies did not converge towards a single solution, series/parallel power trains with power-split electromechanical transmissions prove to be the most promising hybrid technology. In fact, these power trains show maximum power train overall efficiency and maximum fuel reduction in almost all driving conditions compared to the conventional and other hybrid power trains. This paper addresses the model and design of the electro-mechanical configuration of one of the most effective HEV power trains: case study of the 2nd generation Prius. It presents the simulation work of the overall operation of the Toyota Hybrid System (THS-II) of the Prius, and explores not only its power-split eCVT innovative transmission system but also its overall supervision controller for energy management. The kinematic and dynamic behaviors of the THS-II power train are explained based on the power-split aspect of its transmission through a planetary gear train. Then, the possible regular driving functionalities that result from its eCVT operation and the energy flow within its power train are outlined. A feed-forward dynamic model of the studied power train is next proposed, supervised by a rule-based engineering intuition controller. The energy consumption of the THS-II proposed model has been validated by comparing simulation results to published results on European, American and Japanese regulatory driving cycles.
2016-02-04
2016-02-04
2012
2016-02-04
Article
1229-9138
http://hdl.handle.net/10725/3002
http://dx.doi.org/10.1007/s12239-012-0013-8
Mansour, C., & Clodic, D. (2012). Dynamic modeling of the electro-mechanical configuration of the Toyota Hybrid System series/parallel power train. International Journal of Automotive Technology, 13(1), 143-166.
https://link.springer.com/article/10.1007%2Fs12239-012-0013-8
en
International Journal of Automotive Technology
oai:laur.lau.edu.lb:10725/30032021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Quantitative elastohydrodynamic film forming for a gear oil with complex shear-thinning
Bair, Scott
Habchi, Wassim
Sperka, Petr
Hartl, Martin
Perhaps the most thorough characterization of the elevated pressure properties of any commercial EHL lubricant is presented here for a gear oil. Compressibility, thermal conductivity, and low-shear viscosity were measured. Of particular interest is the shear dependence of viscosity, measured across four decades of stress, which shows two transitions each with a specific value of power-law exponent. An attempt to capture a suspected third transition at very high stress resulted in mechanical degradation of the liquid in the viscometer. Numerical simulations of a point contact between a steel ball and a glass disc showed good agreement over a range of slide-to-roll ratio for the measured central thickness. The agreement for the minimum thickness was excellent. A new result is that shear-thinning of a higher molecular weight component that occurs from 3 to 200 kPa had little effect on the film thickness and could therefore be neglected in a film thickness calculation.
2016-02-04
2016-02-04
2016
2016-03-07
Article
1350-6501
http://hdl.handle.net/10725/3003
http://dx.doi.org/10.1177/1350650115600185
Bair, S., Habchi, W., Sperka, P., & Hartl, M. (2016). Quantitative elastohydrodynamic film forming for a gear oil with complex shear-thinning. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 230(3), 289-299.
https://journals.sagepub.com/doi/abs/10.1177/1350650115600185
en
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology
oai:laur.lau.edu.lb:10725/30042021-03-19T09:59:50Zcom_10725_2055col_10725_2075
A Probabilistic and Traffic-Aware Bundle Release Scheme for Vehicular Intermittently Connected Networks
Fawaz, Wissam F.
Assi, Chadi M.
Khabbaz, Maurice J.
Delay-optimal data delivery in Vehicular Intermittently Connected Networks (VICNs) is challenging since vehicular traffic is affected by numerous recurring and completely random events. Some of these events cause breakdowns and jams while others subserve traffic stability. Researchers observed that mobile vehicles might be wisely exploited to connect two isolated, Stationary Roadside Units (SRUs). In this context, the design of effective delay-minimal data relaying strategies is receiving significant attention. However, many existing such schemes either do not adequately model vehicular traffic behaviours or adapt typical Internet packet-like forwarding protocols to VICNs. In contrast, this manuscript presents a concise, yet comprehensive study of vehicular traffic states based on which a "comme-il-faut" vehicular traffic model is established. This model captures the fundamental traffic characteristics and enables the selection of appropriate distributions for vehicular flow and speeds that parallel the realistic measurements made by traffic theorists. These distributions constitute the basis of a novel Probabilistic Bundle Release Scheme with Bulk Bundle Release (PBRS-BBR) that is proposed with the objective to minimize the average bundle delivery delay. An analytical queueing model is formulated to assess the performance of PBRS-BBR under medium-to-light vehicular traffic. Extensive simulations are conducted to prove the model's validity and accuracy.
2016-02-05
2016-02-05
2012
2016-05-06
Article
0090-6778
http://hdl.handle.net/10725/3004
http://dx.doi.org/10.1109/TCOMM.2012.082712.110473
Khabbaz, M. J., Fawaz, W. F., & Assi, C. M. (2012). A probabilistic and traffic-aware bundle release scheme for vehicular intermittently connected networks. Communications, IEEE Transactions on, 60(11), 3396-3406.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6291929
en
Communications, IEEE Transactions on
oai:laur.lau.edu.lb:10725/30052021-03-19T09:59:50Zcom_10725_2055col_10725_2075
A Simple Free-Flow Traffic Model for Vehicular Intermittently Connected Networks
Fawaz, Wissam F.
Khabbaz, Maurice J.
Assi, Chadi M.
The performance of vehicular data networks (VDNs) is highly dependent on vehicular traffic. Existing studies on VDNs consider custom-developed traffic models that mimic real-life vehicular traffic behavior and prepare the ground for accurate VDN performance evaluation. Traffic evolution is affected by numerous random events. Some developed models are microscopic. They independently consider some possible factors (e.g., weather, road geometry, and drivers' skills). These microscopic models are complex, and their implementations may be costly. Other models are macroscopic. They revolve around only the following three major traffic parameters: 1) density; 2) flow; and 3) speed. The majority of such existing models are unrealistic, because they are based on restrictive assumptions tailored to their enclosing study. Comparing the performance of VDN protocols becomes adequate if and only if these protocols are all developed on top of the same traffic model. Unfortunately, the opposite is true. Hence, the design of a generic traffic model that serves as a basis for future studies on VDNs is equally urgent and important. This paper presents a comprehensive and traffic-theory-inspired macroscopic description of vehicular traffic behavior over roadway facilities that operate under free-flow traffic conditions. Accordingly, a simple and tractable macroscopic traffic model is proposed. Extensive simulations are conducted to verify the validity of the proposed model and its high accuracy.
2016-02-05
2016-02-05
2012
2016-05-09
Article
1524-9050
http://hdl.handle.net/10725/3005
http://dx.doi.org/10.1109/TITS.2012.2188519
Khabbaz, M. J., Fawaz, W. F., & Assi, C. M. (2012). A simple free-flow traffic model for vehicular intermittently connected networks. Intelligent Transportation Systems, IEEE Transactions on, 13(3), 1312-1326.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6178279&tag=1
en
IEEE Transcations on Intelligent Transportation Systems
oai:laur.lau.edu.lb:10725/30062021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Modeling and Delay Analysis of Intermittently Connected Roadside Communication Networks
Khabbaz, Maurice J.
Fawaz, Wissam F.
Assi, Chadi M.
Vehicular networks outline a challenging terrestrial application of the emerging delay-tolerant networking (DTN) paradigm where wireless links experience frequent disruptions. Thus, continuous end-to-end paths are unguaranteed. Under such conditions, mobile vehicles present opportunistic relaying capabilities that promote network connectivity, particularly between stationary and isolated roadside units. In this context, we investigate a challenging information-delivery-delay minimization problem. Information is encapsulated into bundles buffered at the source, and vehicles opportunistically transport them to the destination. Consequently, bundles undergo both queueing and transit delays. We propose a probabilistic bundle release scheme (PBRS) under which a roadside unit performs typical Internet-like forwarding where a single bundle is only released to an arriving relatively high-speed vehicle. This ensures a minimized bundle transit. In contrast, under a greedy bundle release scheme (GBRS), a bundle is released to any arriving vehicle, regardless of its speed. Two queueing models are developed to characterize a roadside unit and evaluate its performance under both schemes. A simulation framework is set up to validate these models. Results indicate the inefficiency of the typical Internet packet-like release mechanism as it incurs excessive bundle queueing delays. A bulk bundle release (BBR) extension is proposed as an effective solution. We show that GBRS-BBR outperforms PBRS-BBR.
2016-02-05
2016-02-05
2012
2016-05-10
Article
0018-9545
http://hdl.handle.net/10725/3006
http://dx.doi.org/10.1109/TVT.2012.2200001
Khabbaz, M. J., Fawaz, W. F., & Assi, C. M. (2012). Modeling and delay analysis of intermittently connected roadside communication networks. Vehicular Technology, IEEE Transactions on, 61(6), 2698-2706.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6202358
en
IEEE Transcations on Vehicular Technology
oai:laur.lau.edu.lb:10725/30072021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Disruption-Tolerant Networking
Khabbaz, Maurice J.
Assi, Chadi M.
Fawaz, Wissam F.
Nowadays, wireless networks are witnessing several deployments in various extreme environments where they suffer from different levels of link disruptions depending on the severity of the operating conditions. In all cases, their operation requirements are differently altered and their performance is negatively affected rendering them heterogeneous by nature. In the open literature, these networks are known as Intermittently Connected Networks (ICNs). The existing Internet protocols fail to operate properly in the context of ICNs, thus raising a variety of new challenging problems that are attracting the attention of the networking research community. Delay-/Disruption-Tolerant Networking emerged as a highly active area of research where networking experts compete in addressing the various ICN problems. Over time, unicast routing, one of the architectural key components common to all ICNs, became an almost independent field of research in which significant efforts continue to be invested. In contrast, network architectural designs, scheduling and forwarding issues dating from the early days of Inter-Planetary Networks (IPNs) have received relatively little attention and accumulate numerous pending challenges. Moreover, the gap caused by the lack of accurate ICN mathematical models is still large irrespective of some of the appreciated seminal works in this direction. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlight pending open issues in each of them.
2016-02-05
2016-02-05
2012
2016-05-11
Article
1553-877X
http://hdl.handle.net/10725/3007
http://dx.doi.org/10.1109/SURV.2011.041911.00093
Khabbaz, M. J., Assi, C. M., & Fawaz, W. F. (2012). Disruption-tolerant networking: A comprehensive survey on recent developments and persisting challenges. Communications Surveys & Tutorials, IEEE, 14(2), 607-640.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5770277
en
IEEE Communications Surveys & Tutorials
oai:laur.lau.edu.lb:10725/30082019-01-31T12:59:40Zcom_10725_2055col_10725_2075
Which Vehicle To Select?
Fawaz, Wissam F.
Khabbaz, Maurice J.
Assi, Chadi M.
In wireless networking, an Opportunistic Bundle Release Mechanism (OBRM) is a data bundle forwarding mechanism characterized by its ability to operate over Intermittently Connected Networks (ICNs) where end-to-end paths are not continuously available. Known for their intrinsic connectivity intermittence, vehicular networks constitute an ideal recreation ground for OBRMs. This letter, proposes the Optimal Vehicle Selection OBRM (OVS-OBRM) with the objective of minimizing the average bundle delivery delay.
2016-02-05
2016-02-05
2012
2016-02-05
Article
1089-7798
http://hdl.handle.net/10725/3008
http://dx.doi.org/10.1109/LCOMM.2012.042512.112350
Khabbaz, M. J., Fawaz, W. F., & Assi, C. M. (2012). Which vehicle to select?. Communications Letters, IEEE, 16(6), 812-815.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6205423
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30092019-01-31T12:55:58Zcom_10725_2055col_10725_2075
Enhancement of blocking performance in all-optical WDM networks via wavelength reassignment and route deviation
Fawaz, Wissam F.
This paper deals with the problem of improving the performance of all-optical Wavelength Division Multiplexing (WDM) networks in terms of blocking probability. Blocking in such network architecture is caused mainly by the so-called wavelength continuity constraint (wcc), which requires a provisioned lightpath to occupy the same wavelength on all the links along its route. To alleviate the effect of wcc on the blocking performance, a rerouting strategy is proposed. The main idea behind this strategy lies in ensuring the creation of wavelength-continuous routes for the connections that are blocked due to wcc. Particularly, the proposed rerouting strategy is built upon two main pillars, namely wavelength reassignment and route deviation. The former strives to keep the physical route followed by the lightpath intact, while the latter changes the route of the lightpath when wavelength reassignment proves to be ineffective. The performance of the rerouting strategy is studied through extensive simulations in the context of networks employing the least congested path (LCP) routing algorithm and the first-fit (FF) wavelength assignment strategy. The reported results show that the proposed rerouting strategy can guarantee significant enhancement in terms of blocking probability while achieving near-optimal performance for networks utilizing a small number of wavelengths per fiber.
2016-02-05
2016-02-05
2012
2016-02-05
Article
0140-3664
http://hdl.handle.net/10725/3009
http://dx.doi.org/10.1016/j.comcom.2012.02.003
Fawaz, W. F. (2012). Enhancement of blocking performance in all-optical WDM networks via wavelength reassignment and route deviation. Computer Communications, 35(8), 929-935.
http://www.sciencedirect.com/science/article/pii/S0140366412000503
en
Computer Communications
oai:laur.lau.edu.lb:10725/30102021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Probabilistic Bundle Relaying Schemes in Two-Hop Vehicular Delay Tolerant Networks
Fawaz, Wissam F.
Khabbaz, Maurice J.
Assi, Chadi M.
One class of Vehicular Delay-Tolerant Networks consists of two node types: stationary and mobile. Stationary nodes deployed along roadsides cannot directly communicate as they are considerably distant. Mobile nodes mounted over vehicles opportunistically entering the range of a stationary source serve as relays that carry bundles to the destination. In this letter, we introduce a novel relaying scheme that probabilistically determines a vehicle's suitability to carry bundles. Hence, bundles are released to a present vehicle if and only if that latter contributes in minimizing the mean transit delay. Extensive simulations were performed to gauge the merit of the proposed scheme.
2016-02-05
2016-02-05
2011
2016-05-12
Article
1089-7798
http://hdl.handle.net/10725/3010
http://dx.doi.org/10.1109/LCOMM.2011.011011.102512
Khabbaz, M. J., Fawaz, W. F., & Assi, C. M. (2011). Probabilistic bundle relaying schemes in two-hop vehicular delay tolerant networks. Communications Letters, IEEE, 15(3), 281-283.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5692889
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30112021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Preemption-Enabled Setup of Optical Connections Coupled with Event-Driven Rerouting
Fawaz, Wissam
Nakad, Zahi
Aad, Maroun
In an era of uncertain business tendencies, realizing profitable optical networks is emerging as the most urgent task for optical operators. This task is aggravated by the need to support quality of service (QoS) differentiation, especially with the continuous development of new applications, each having different QoS requirements. This letter proposes to tackle these challenges through the definition of a novel QoS-aware connection setup strategy. The proposed setup approach enables network operators to ensure both efficient utilization of network resources and connection blocking probability differentiation. Resource efficiency is achieved via event-driven rerouting, whereas differentiated blocking probability is realized by preemption. Specifically, high priority connections are equipped with the capability of preempting lower priority connections, which through event-driven rerouting experience smaller blocking probability. Performance of this novel connection setup strategy is analyzed in this letter by simulating its operation in the context of the National Science Foundation Network (NSFNET). The obtained simulation results show that the proposed strategy can minimize the overall blocking probability while achieving QoS differentiation.
2016-02-05
2016-02-05
2011
2016-05-13
Article
1089-7798
http://hdl.handle.net/10725/3011
http://dx.doi.org/10.1109/LCOMM.2011.122010.102058
Fawaz, W., Nakad, Z., & Aad, M. (2011). Preemption-enabled setup of optical connections coupled with event-driven rerouting. Communications Letters, IEEE, 15(2), 250-252.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5674001
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30122021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Deadline-based connection setup in wavelength-routed WDM networks
Fawaz, Wissam
Ouaiss, Iyad
Chen, Ken
Perros, Harry
This article addresses the ubiquitous topic of quality of service (QoS) aware connection provisioning in wavelength-routed WDM optical networks. The impact of the connection setup time of an optical connection has not been adequately addressed in the open literature. As such, this paper presents a novel approach that uses the optical connection setup time as a service differentiator during connection provisioning. The proposed approach utilizes the Earliest Deadline First (EDF) queueing algorithm to achieve deadline-based connection setup management with the deadline being the setup time requirement of an optical connection. The proposed EDF-based approach would allow the network operator to improve the QoS perceived by the end clients. Performance of this novel scheme is analyzed by accurately calculating various parameters, such as the fraction of connections provisioned on-time (i.e. prior to deadline expiration) and the average time it takes to successfully setup a connection. In addition, the presented approach is validated by a simulation that analyzes the performance of the proposed connection setup scheme in the specific context of the National Science Foundation Network (NSFNET). The obtained results show that a deadline-based setup strategy can minimize blocking probability while achieving QoS differentiation.
2016-02-05
2016-02-05
2010
2016-05-13
Article
1389-1286
http://hdl.handle.net/10725/3012
http://dx.doi.org/10.1016/j.comnet.2010.02.008
Fawaz, W., Ouaiss, I., Chen, K., & Perros, H. (2010). Deadline-based connection setup in wavelength-routed WDM networks. Computer Networks, 54(11), 1792-1804.
http://www.sciencedirect.com/science/article/pii/S1389128610000526
en
Computer Networks
oai:laur.lau.edu.lb:10725/30132021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Networking in E-textiles
Nakad, Z.
Jones, M.
Martin, T.
Fawaz, W.
The abundance of fabrics in our life offers immense possibilities for ubiquitous electronic integration. Electronic textiles (e-textiles) represent the merging of fabric and electronic technologies to be used in wearable and large-scale applications. The communication requirements of the computing elements of these systems will be presented along with a fault tolerant solution. The operation of the communication scheme will be studied analytically and compared to simulation results. The graceful deterioration of the performance with increasing faults will also be reported. Multiple e-textile application examples utilizing the networking scheme will be presented.
2016-02-05
2016-02-05
2010
2016-05-16
Article
0140-3664
http://hdl.handle.net/10725/3013
http://dx.doi.org/10.1016/j.comcom.2009.11.011
Nakad, Z., Jones, M., Martin, T., & Fawaz, W. (2010). Networking in E-textiles. Computer communications, 33(6), 655-666.
http://www.sciencedirect.com/science/article/pii/S0140366409003004
en
Computer Communications
oai:laur.lau.edu.lb:10725/30142021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Incorporating mutation probability into priority-aware protection in optical networks
Fawaz, Wissam
Khabbaz, Maurice
A persisting major challenge for optical network operators is to meet the various availability requirements of the different subscribed services through the deployment of effective protection strategies. Priority-aware shared protection is a promising scheme that has been proposed in the open literature as a potential approach to tackling this challenge. However, the priority-aware protection strategy is rigid in the sense that it privileges the high priority connections regardless of the low priority ones. Hence, this letter proposes to improve priority-aware protection by introducing the mutation probability parameter. This parameter expresses the likelihood that a high-priority connection be relegated temporarily to a lower priority level during recovery. In this way, the mutation-based protection strategy offers optical operators the possibility to increase the availability of their low-priority clients without violating the availability requirements of their high-priority ones. Performance of this novel protection strategy is analyzed in this letter by precisely calculating the connection availabilities resulting from its deployment.
2016-02-05
2016-02-05
2009
2016-04-11
Article
1089-7798
http://hdl.handle.net/10725/3014
http://dx.doi.org/10.1109/LCOMM.2009.091594
Fawaz, W., & Khabbaz, M. (2009). Incorporating mutation probability into priority-aware protection in optical networks. Communications Letters, IEEE, 13(11), 865-867.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5337069
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30152021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Priority-aware optical shared protection
Fawaz, Wissam
Sawah, Timothy
Abou-Rjeily, Chadi
The availability of an optical connection is considered to be a critical service differentiator in WDM optical networks. In this regard, the design of a protection scheme that improves the availability of high priority optical connections and makes efficient use of optical resources is a major challenge faced by optical network operators. In a previous study, we proposed the so-called priority-aware shared protection survivability scheme as a potential solution to this design issue.
In this paper, we complement our previous study. More specifically, we develop an offline study whose main purpose is to assess the efficiency of the priority-aware shared protection scheme. Through this study, we show that the priority-aware shared protection strategy as opposed to existing protection strategies is able to achieve the best tradeoff between optical resource usage and optical connections’ availability satisfaction.
2016-02-05
2016-02-05
2009
2017-07-27
Article
0140-3664
http://hdl.handle.net/10725/3015
http://dx.doi.org/10.1016/j.comcom.2009.06.010
Fawaz, W., Sawah, T., & Abou-Rjeily, C. (2009). Priority-aware optical shared protection: An offline evaluation study. Computer Communications, 32(15), 1677-1684.
http://www.sciencedirect.com/science/article/pii/S0140366409001534
en
Computer Communications
oai:laur.lau.edu.lb:10725/30162021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Space-Time Codes for MIMO Ultra-Wideband Communications and MIMO Free-Space Optical Communications with PPM
Abou-Rjeily, Chadi
Fawaz, Wissam
In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log2(M-1)/n log2(M).
2016-02-05
2016-02-05
2008
2017-08-10
Article
0733-8716
http://hdl.handle.net/10725/3016
http://dx.doi.org/10.1109/JSAC.2008.080810
Abou-Rjeily, C., & Fawaz, W. (2008). Space-time codes for MIMO ultra-wideband communications and MIMO free-space optical communications with PPM. IEEE Journal on Selected Areas in Communications, 26(6), 938-947.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4586310
en
IEEE Journal on selected areas in communications
oai:laur.lau.edu.lb:10725/30172019-09-30T13:22:18Zcom_10725_2055col_10725_2075
Distributed Information-Lossless Space-Time Codes for Amplify-and-Forward TH-UWB Systems
Abou-Rjeily, Chadi
Fawaz, Wissam
In this paper, we extend the non-orthogonal amplify-and-forward (NAF) cooperative scheme to the context of impulse radio ultra-wideband (UWB) systems. In particular, we consider the problem of distributed space-time (ST) coding with 2D pulse position modulations (PPM) and joint pulse position and amplitude modulations (PPAM) and we propose the first known family of full-rate codes that are information-lossless with these constellations. Being totally-real, these codes are adapted to the carrier-less nature of the UWB transmissions and they outperform all previously known totally- real constructions with any number of relays. With binary PPM, they satisfy all the construction constraints of the optimal complex-valued codes proposed in [S. Yang and J.-C. Belfore, 2007] as well as the additional constraint of being real-valued.
2016-02-05
2016-02-05
2008
2016-02-05
Article
1089-7798
http://hdl.handle.net/10725/3017
http://dx.doi.org/10.1109/LCOMM.2008.071945
Abou-Rjeily, C., & Fawaz, W. (2008). Distributed information-lossless space-time codes for amplify-and-forward TH-UWB systems. IEEE Communications Letters, 12(4), 298-300.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4489673
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30182019-01-17T13:19:09Zcom_10725_2055col_10725_2075
A Novel Connection Setup Management Approach for Optical WDM Networks
Fawaz, Wissam
Abou-Rjeily, Chadi
Wavelength Division Multiplexing (WDM) has significantly increased the transmission capacity of today's optical networks. An increase in the available bandwidth is promoting at the same time the introduction of new services, each having different Quality of Service (QoS) requirements. In this regard, QoS parameters applicable to connection setup, namely connection blocking probability and connection setup time, are expected to greatly influence the procedure of lightpath setup. In view of this, we propose to consider the connection setup time requirement as a (timely increasing) priority indicator during optical connection provisioning. In other words, we envisage in this letter the assignment of the highest setup priority to those optical connection requests having the shortest setup time requirements. To achieve this purpose, we adapt the well known Earliest Deadline First (EDF) scheduling discipline to the particular case of optical connection setup management. In order to gauge the impact of our proposal on the QoS perceived by optical clients, we introduce in this letter a computational method. This latter is used for the assessment of the percentage of optical connections that are successfully established under the proposed setup management approach.
2016-02-05
2016-02-05
2007
2016-02-05
Article
1089-7798
http://hdl.handle.net/10725/3018
http://dx.doi.org/10.1109/LCOMM.2007.071437
Fawaz, W., Chen, K., & Abou-Rjeily, C. (2007). A novel connection setup management approach for optical WDM networks. Communications Letters, IEEE, 11(12), 998-1000.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4400765
en
IEEE Communications Letters
oai:laur.lau.edu.lb:10725/30192019-01-31T11:35:59Zcom_10725_2055col_10725_2075
Priority-enabled optical shared protection
Fawaz, W.
Chen, K.
Pujolle, G.
The availability of an optical connection is considered to be a critical service differentiator in WDM optical networks. In this regard, the design of a protection scheme that is able to improve the availability of high priority connections while making efficient use of optical resources is a major concern for optical network operators. In a previous work, we proposed the so-called priority-aware shared protection as a potential survivability scheme for next generation WDM networks to deal with the previously exhibited concern.
This paper develops an online study whose main purpose is to assess the efficiency of the aforementioned protection scheme. Through this study, we show that the priority-aware shared protection strategy is able to achieve both the best efficiency in terms of resource usage and in terms of availability satisfaction rate compared to existing protection solutions.
2016-02-05
2016-02-05
2007
2016-02-05
Article
0140-3664
http://hdl.handle.net/10725/3019
http://dx.doi.org/10.1016/j.comcom.2007.07.009
Fawaz, W., Chen, K., & Pujolle, G. (2007). Priority-enabled optical shared protection: An online efficiency evaluation study. Computer Communications, 30(18), 3690-3697.
http://www.sciencedirect.com/science/article/pii/S0140366407002836
en
Computer Communications
oai:laur.lau.edu.lb:10725/30202019-01-31T11:33:08Zcom_10725_2055col_10725_2075
A novel fault management approach for DWDM optical networks
Fawaz, W.
Martignon, F.
Chen, K.
Pujolle, G.
Connection availability is considered as a critical metric when providing differentiated services in Wavelength-Division Multiplexing mesh networks. Indeed, one of the major concerns of optical network operators is related to improving the availability of services provided to their highest-class clients. Achieving this objective is possible through managing faults using the different classical protection schemes, namely the so-called dedicated and shared protection schemes. However, the majority of the work concerning protection schemes has considered the primary connections as equally important when contending for the use of the backup resources. As a main contribution in this paper, we therefore propose an improvement of the existing protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. To evaluate numerically the benefits of the service differentiation feature introduced in our proposal, we first develop a mathematical model, based on which we derive explicit expressions for the average connection availabilities that result from both the classical protection schemes and the proposed priority-aware one. Through this model, we show how the availability of the highest-class clients is improved when deploying the proposed priority-aware protection scheme. Finally, with the same objective in mind, we develop a simulation study, where a given set of connection demands with predefined availability requirements is provisioned using different protection strategies. Through this study, we show that the priority-aware protection strategy satisfies service-availability requirements in a cost-effective manner compared with the classical protection schemes.Copyright © 2006 John Wiley & Sons, Ltd.
2016-02-05
2016-02-05
2006
2016-02-05
Article
1748-1252
http://hdl.handle.net/10725/3020
http://dx.doi.org/10.1002/nem.601
Fawaz, W., Martignon, F., Chen, K., & Pujolle, G. (2006). A novel fault management approach for DWDM optical networks. International Journal of Network Management, 16(5), 337-349.
http://onlinelibrary.wiley.com/doi/10.1002/nem.601/abstract
en
International Journal of Network Management
oai:laur.lau.edu.lb:10725/30212019-01-31T12:50:29Zcom_10725_2055col_10725_2075
Service level agreement and provisioning in optical networks
Fawaz, Wissam
Daheb, Belkacem
Audouin,Olivier
Pujolle, Guy
This article proposes a service level agreement applied to the optical domain (O-SLA), which is expected to be the near- and long-term network technology of the great bandwidth capacity offered by optical devices. After an exposition of the rationale behind an optical SLA, parameters that could be included in this O-SLA, as well as their values for four classes of services are proposed. Different client (wavelength or subwavelength) and service types (from leased wavelength to bandwidth on demand) are distinguished when necessary. The last part of this article presents issues related to the provisioning of services emanating from this O-SLA.
2016-02-05
2016-02-05
2004
2016-02-05
Article
0163-6804
http://hdl.handle.net/10725/3021
http://dx.doi.org/10.1109/MCOM.2004.1262160
Fawaz, W., Daheb, B., Audouin, O., & Pujolle, G. (2004). Service level agreement and provisioning in optical networks. Communications Magazine, IEEE, 42(1), 36-43.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1262160&tag=1
en
IEEE Communications Magazine
oai:laur.lau.edu.lb:10725/30222021-03-19T09:59:50Zcom_10725_2055col_10725_2075
Service level agreement in optical networks
Du-Pond, Michel
Audouin, Olivier
Berde, Bela
Daheb, Belkacem
Fawaz, Wissam
Pujolle, Guy
Vigoureux, Martin
This article proposes a Service Level Agreement applied to the optical domain (O-sla), which is expected to be the near and long term network technology thanks, among other things, to the great bandwidth capacity offered by optical devices. After an exposition of the rationale behind an optical sla, parameters which could enter in thisO-sla, as well as their values for four classes of services, are proposed. Different client (wavelength or sub-wavelength) and services types (from leased wavelength to bandwidth on demand) are distinguished when necessary.
2016-02-05
2016-02-05
2005
2017-04-07
Article
0003-4347
http://hdl.handle.net/10725/3022
http://dx.doi.org/10.1007/BF03219847
Du-Pondd, M., Audouin, O., Berde, B., Daheb, B., Fawaz, W., Pujolle, G., & Vigoureux, M. (2005, October). Service level agreement in optical networks. In Annales des télécommunications (Vol. 60, No. 9-10, pp. 1268-1280). Springer-Verlag.
http://link.springer.com/article/10.1007/BF03219847
en
Annales Des Télécommunications
oai:laur.lau.edu.lb:10725/30252021-03-19T09:59:50Zcom_10725_2055col_10725_2075
A new method of analysis for slender columns
Zdenek, P.
Bazant, Luigi Cedolin
Tabbara, Mazen
This paper presents a simple new method to calculate column-interaction
diagrams, which takes into account slenderness effects. The
method consists of a simple incremental-loading algorithm that traces
the load-deflection curve at constant eccentricity of the axial load.
The column failure is defined for design purposes as the peak of the
diagram of axial load versus midlength bending moment at constant
load eccentricity. The tangent modulus load is found to be approximately
equal to the peak load of a column with load eccentricity 0.0}
of the cross-sectional thickness and represents a lower bound for the
maximum loads at still smaller eccentricities. Strain irreversibility at
unloading can be taken into account but its effect is very small. The
method is compared with the AC} moment magnification method and
with the CEB model column method based on moment-curvature relations.
The agreement with the CEB method is very close, but with
respect to the ACI method there are large discrepancies.
2016-02-08
2016-02-08
1991
2017-04-26
Article
0889-3241
http://hdl.handle.net/10725/3025
Bazant, Z. P., Cedolin, L., & Tabbara, M. R. (1991). New method of analysis for slender columns. ACI Structural Journal, 88(4), 391-401.
http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/276.pdf
en
ACI Structural Journal
oai:laur.lau.edu.lb:10725/30262021-03-19T09:59:50Zcom_10725_2055col_10725_2075
H-Adaptive finite element methods for dynamic problems, with emphasis on localization
Tabbara, Mazen
Belytschko, T.
H-adaptive procedures for the finite element solution of transient solid mechanics problems are studied, with particular emphasis on problems involving localization due to material instability. Various types of error criteria are examined and it is shown that for problems involving plastic response or localization, an error criterion based on an L2-projection of strains is the most effective for the constant strain elements considered here. Examples of one-dimensional and two-dimensional localization (shear band formation) problems are given.
2016-02-08
2016-02-08
1993
2017-05-23
Article
1097-0207
http://hdl.handle.net/10725/3026
http://dx.doi.org/10.1002/nme.1620362409
Belytschko, T., & Tabbara, M. (1993). H‐Adaptive finite element methods for dynamic problems, with emphasis on localization. International Journal for Numerical Methods in Engineering, 36(24), 4245-4265.
http://onlinelibrary.wiley.com/doi/10.1002/nme.1620362409/full
International Journal of Numerical methods in Engineering
oai:laur.lau.edu.lb:10725/30272016-08-24T07:55:14Zcom_10725_2055col_10725_2075
Finite element derivative recovery by moving least square interpolants
Tabbara, Mazen
Blacker, Ted
Belytschko, Ted
A simple, accurate technique for recovery of displcements and derivatives, such as strains is presented. The technique is based on local interpolation of nodal displacements using a moving least square method. The strains are then recovered by taking appropriate derivatives of this interpolant. Numerical experiments in linear elasticity and heat conduction on the convergence and accuracy of the recovered derivatives show very good results and superconvergence for strains in many cases; the technique is also effective for displacement interpolation for projection methods.
2016-02-10
2016-02-10
1994
2016-02-10
Article
0045-7825
http://hdl.handle.net/10725/3027
http://dx.doi.org/10.1016/0045-7825(94)90084-1
Tabbara, M., Blacker, T., & Belytschko, T. (1994). Finite element derivative recovery by moving least square interpolants. Computer Methods in Applied Mechanics and Engineering, 117(1), 211-223.
http://www.sciencedirect.com/science/article/pii/0045782594900841
Computer Methods in Applied Mechanics and Engineering
oai:laur.lau.edu.lb:10725/30282016-08-08T10:49:03Zcom_10725_2055col_10725_2075
Element-free galerkin methods for static and dynamic fracture
Tabbara, Marc
Belytschko, T.
Lu, Y.Y.
Element-free Galerkin (EFG) methods are presented and applied to static and dynamic fracture problems. EFG methods, which are based on moving least-square (MLS) interpolants, require only nodal data; no element connectivity is needed. The description of the geometry and numerical model of the problem consists only of a set of nodes and a description of exterior boundaries and interior boundaries from any cracks. This makes the method particularly attractive for growing crack problems, since only minimal remeshing is needed to follow crack growth. In moving least-square interpolants, the dependent variable at any point is obtained by minimizing a function in terms of the nodal values of the dependent variable in the domain of influence of the point. Numerical examples involving fatigue crack growth and dynamic crack propagation are presented to illustrate the performance and potential of this method.
2016-02-10
2016-02-10
1995
2016-02-10
Article
0020-7683
http://hdl.handle.net/10725/3028
http://dx.doi.org/10.1016/0020-7683(94)00282-2
Belytschko, T., Lu, Y. Y., Gu, L., & Tabbara, M. (1995). Element-free Galerkin methods for static and dynamic fracture. International Journal of Solids and Structures, 32(17), 2547-2570.
http://www.sciencedirect.com/science/article/pii/0020768394002822
en
International Journal of Solids and Structures
oai:laur.lau.edu.lb:10725/30292016-08-24T07:12:15Zcom_10725_2055col_10725_2075
Element-free Galerkin method for wave propagation and dynamic fracture
Belytschko, T.
Lu, Y.Y.
Tabbara, Mazen
Element-free Galerkin method (EFG) is extended to dynamic problems. EFG method, which is based on moving least square interpolants (MLS), requires only nodal data; no element connectivity is needed. This makes the method particularly attractive for moving dynamic crack problems, since remeshing can be avoided. In contrast to the earlier formulation for static problems by authors, the weak form of kinematic boundary conditions for dynamic problems is introduced in the implementation to enforce the kinematic boundary conditions. With this formulation, the stiffness matrix is symmetric and positive semi-definite, and hence the consistency, conergence and stability analyses of time integration remain the same as those in finite element method. Numerical examples are presented to illustrate the performance of this method. The relationship between the element-free Galerkin method and the smooth particle hydrodynamics (SPH) method is also discussed in this paper. Results are presented for some one-dimensional problems and two-dimensional problems with static and moving cracks.
2016-02-10
2016-02-10
1995
2016-02-10
Article
0045-7825
http://hdl.handle.net/10725/3029
http://dx.doi.org/10.1016/0045-7825(95)00804-A
Lu, Y. Y., Belytschko, T., & Tabbara, M. (1995). Element-free Galerkin method for wave propagation and dynamic fracture. Computer Methods in Applied Mechanics and Engineering, 126(1), 131-153.
http://www.sciencedirect.com/science/article/pii/004578259500804A
Computer Methods in Applied Mechanics and Engineering
oai:laur.lau.edu.lb:10725/30302019-02-01T13:43:05Zcom_10725_2055col_10725_2075
Dynamic fracture using element-free Galerkin methods
Belytschko, T.
Tabbara, Mazen
The element-free Galerkin method for dynamic crack propagation is described and applied to several
problems. This method is a gridless method, which facilitates the modelling of growing crack problems
because it does not require remeshing; the growth of the crack is modelled by extending its surfaces. The
essential feature of the method is the use of moving least-squares interpolants for the trial-and-test functions.
In these interpolants, the dependent variable is obtained at any point by minimizing a weighted quadratic
form involving the nodal variables within a small domain surrounding the point. The discrete equations are
obtained by a Galerkin method. The procedures for modelling dynamic crack propagation based on
dynamic stress intensity factors are also described.
2016-02-10
2016-02-10
2016-02-10
1996
Article
1097-0207
http://hdl.handle.net/10725/3030
http://dx.doi.org/10.1002/(SICI)1097-0207(19960330)39:6<923::AID-NME887>3.0.CO;2-W
Belytschko, T., & Tabbara, M. (1996). DYNAMIC FRACTURE USING ELEMENT‐FREE GALERKIN METHODS. International Journal for Numerical Methods in Engineering, 39(6), 923-938.
http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-0207(19960330)39:6%3C923::AID-NME887%3E3.0.CO;2-W/full
en
International Journal for Numerical Engineering
oai:laur.lau.edu.lb:10725/30312019-02-01T13:40:20Zcom_10725_2055col_10725_2075
A computational method for quasi-static fracture
Tabbara, Mazen
Stone, C.M.
A direct method for solving quasi-static, mixed-mode fracture problems is presented. The element-free Galerkin method is used in order to allow for crack growth without remeshing. An expression for the normalized, critical traction is derived in terms of the fracture resistance (R-curve) and a crack-dependent function. Sample problems demonstrate the capability of this method to accurately compute the post-peak equilibrium paths for structures with growing cracks.
2016-02-10
2016-02-10
1998
2016-02-10
Article
0178-7675
http://hdl.handle.net/10725/3031
http://dx.doi.org/10.1007/s004660050354
Tabbara, M. R., & Stone, C. M. (1998). A computational method for quasi-static fracture. Computational Mechanics, 22(2), 203-210.
http://link.springer.com/article/10.1007/s004660050354
en
Computational Mechanics
oai:laur.lau.edu.lb:10725/30322016-08-24T10:52:49Zcom_10725_2055col_10725_2075
Simulations of the penetration of 6061-T6511 aluminum targets by spherical-nosed VAR 4340 steel projectiles
Warren, Thomas
Tabbara, Mazen
In certain penetration events it is proposed that the primary mode of deformation of the target can be approximated by known analytical expressions. In the context of an analysis code, this approximation eliminates the need for discretizing the target as well as the need for a contact algorithm. Thus, this method substantially reduces the computer time and memory requirements. In this paper a forcing function which is derived from a spherical-cavity expansion (SCE) analysis has been implemented in a transient dynamic finite element code. This implementation is capable of computing the structural and component responses of a projectile due to a three dimensional penetration event. Simulations are presented for 7.11-mm-diameter, 74.7-mm-long, spherical-nose, vacuum-arc-remelted (VAR) 4340 steel projectiles that penetrate 6061-T6511 aluminum targets. Final projectile configurations obtained from the simulations are compared with post-test radiographs obtained from the corresponding experiments. It is shown that the simulations accurately predict the permanent projectile deformation for three dimensional loadings due to incident pitch and yaw over a wide range of striking velocities.
2016-02-10
2016-02-10
2000
2016-02-10
Article
0020-7683
http://hdl.handle.net/10725/3032
http://dx.doi.org/10.1016/S0020-7683(99)00148-1
Warren, T. L., & Tabbara, M. R. (2000). Simulations of the penetration of 6061-T6511 aluminum targets by spherical-nosed VAR 4340 steel projectiles. International journal of solids and structures, 37(32), 4419-4435.
http://www.sciencedirect.com/science/article/pii/S0020768399001481
en
International Journal of Solids and Structures
oai:laur.lau.edu.lb:10725/30332016-08-08T10:45:50Zcom_10725_2055col_10725_2075
Corner effects in CFRP-wrapped square columns
Tabbara, Mazen
Karam, Gebran
An experimental investigation of the corner sharpness effect in square columns with carbon fibre-reinforced polymer (CFRP) wraps is presented using traditional compressive testing of short square columns as well as an innovative set-up that allows testing directly for the CFRP strength when wrapped around the corner of a flat slab. Both types of test confirmed the observation that the confinement efficiency decreases as the corner sharpness increases, owing to stress concentrations that cause localised failure of the CFRP.
2016-02-10
2016-02-10
2015
2016-02-10
Article
0024-9831
http://hdl.handle.net/10725/3033
http://dx.doi.org/10.1680/macr.2004.56.8.461
Karam, G., & Tabbara, M. (2004). Corner effects in CFRP-wrapped square columns. Magazine of Concrete Research, 56(8), 461-464.
http://www.icevirtuallibrary.com/doi/abs/10.1680/macr.2004.56.8.461
en
Magazine of Concrete Research
oai:laur.lau.edu.lb:10725/30342019-01-14T11:15:21Zcom_10725_2055col_10725_2075
Confinement Effectiveness in Rectangular Concrete Columns with Fiber Reinforced Polymer Wraps
Tabbara, Mazen
Karam, Gebran
An innovative mechanistic based method for passive confinement efficiency estimation is proposed based on the extension to rectangular sections of the pulley model previously proposed by the writers. A refined finite element model was developed using a nonlinear concrete constitutive law in order to analyze stresses in columns passively confined with fiber reinforced polymer wraps. Rectangular and square cross sections of variable corner radii were investigated with reference to a circular cross section. Results showed an increase in corner stresses with sharper corner radii, a localization of failure at the corners, and a decrease in confinement effectiveness with an increase in the rectangularity of the cross section or an increase in corner sharpness. A rigorous numerical method for calculating geometric confinement efficiency factors is proposed and typical factors are calculated and compared with the predictions of the simple pulley model showing good agreement.
2016-02-10
2016-02-10
2005
2016-02-10
Article
1090-0268
http://hdl.handle.net/10725/3034
http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:5(388)
Karam, G., & Tabbara, M. (2005). Confinement effectiveness in rectangular concrete columns with fiber reinforced polymer wraps. Journal of Composites for Construction, 9(5), 388-396.
http://ascelibrary.org/doi/abs/10.1061/(ASCE)1090-0268(2005)9:5(388)
en
Journal of Composites for Construction
oai:laur.lau.edu.lb:10725/30352019-01-14T11:16:02Zcom_10725_2055col_10725_2075
Hoek-Brown Strength Criterion for Actively Confined Concrete
Tabbara, Mazen
Karam, Gebran
The application of the Hoek–Brown empirical strength criterion to actively confined concrete is investigated. A large database of experimental results on hydraulically and triaxially confined concrete is reviewed and analyzed. The normalized two-parameter Hoek–Brown criterion provides a simpler and more robust fit than theoretical and empirical models previously proposed in the literature for actively confined concrete. The Hoek–Brown curved failure surface is used to predict the failure angles that are experimentally observed in the brittle mode. A residual stress lower bound is proposed based on the brittle fracture mechanism. The analysis of this residual stress lower bound allows the formal identification of the transition between the brittle and the ductile failure modes in confined concrete. The modeling results are compared with the available published data and good agreement is found between the experimental observations and the predictions of the model. Recommendations for the integration of the Hoek–Brown model in the concrete design equations are also provided.
2016-02-10
2016-02-10
2009
2016-02-10
Article
0899-1561
http://hdl.handle.net/10725/3035
http://dx.doi.org/10.1061/(ASCE)0899-1561(2009)21:3(110)
Karam, G., & Tabbara, M. (2009). Hoek–Brown strength criterion for actively confined concrete. Journal of Materials in Civil Engineering, 21(3), 110-118.
http://ascelibrary.org/doi/abs/10.1061/(ASCE)0899-1561(2009)21:3(110)
en
Journal of Materials in Civil Engineering
oai:laur.lau.edu.lb:10725/30362016-08-24T05:27:26Zcom_10725_2055col_10725_2075
Comparison of various models for strain‐softening
Pijaudier‐Cabot, Gilles
Bazant, Zdenek P.
Tabbara, Mazen
This paper presents a comparison of various models for strain‐softening due to damage such as cracking or void growth, as proposed recently in the literature. Continuum‐based models expressed in terms of softening stress—strain relations, and fracture‐type models expressed in terms of softening stress—displacement relations are distinguished. From one‐dimensional wave propagation calculations, it is shown that strain‐localization into regions of finite size cannot be achieved. The previously well‐documented spurious convergence is obtained with continuum models, while stress—displacement relations cannot model well smeared‐crack situations. Continuum models may, however, be used in general if a localization limiter is implemented. Gradient‐type localization limiters appear to be rather complicated; they require solving higher‐order differential equations of equilibrium with additional bourdary conditions. Non‐local localization limiters, especially the non‐local continuum with local strain, in which only the energy dissipating variables are non‐local, is found to be very effective, and also seems to be physically realistic. This formulation can correctly model the transition between homogeneous damage states and situations in which damage localizes into small regions that can be viewed as cracks. The size effect observed in the experimental and numerical response of specimens in tension or compression is shown to be a consequence of this progressive transition from continuum‐type to fracture‐type formulations.
2016-02-10
2016-02-10
1988
2016-02-10
Article
0264-4401
http://hdl.handle.net/10725/3036
http://dx.doi.org/10.1108/eb023732
Pijaudier-Cabot, G., Bazant, Z. P., & Tabbara, M. (1988). Comparison of various models for strain-softening. Engineering computations, 5(2), 141-150.
http://www.emeraldinsight.com/doi/abs/10.1108/eb023732
en
Engineering Computations
oai:laur.lau.edu.lb:10725/30372019-02-01T13:38:57Zcom_10725_2055col_10725_2075
Bifurcation and stability of structures with interacting propagating cracks
Tabbara, Mazen
Warren, T.L.
A general method to calculate the tangential stiffness matrix of a structure with a system of interacting propagating cracks is presented. With the help of this matrix, the conditions of bifurcation, stability of state and stability of post-bifurcation path are formulated and the need to distinguish between stability of state and stability path is emphasized. The formulation is applied to symmetric bodies with interacting cracks and to a halfspace with parallel equidistant cooling cracks or shrinkage cracks. As examples, specimens with two interacting crack tips are solved numerically. It is found that in all the specimens that exhibit a softening load-displacement diagram and have a constant fracture toughness, the response path corresponding to symmetric propagation of both cracks is unstable and the propagation tends to localize into a single crack tip. This is also true for hardening response if the fracture toughness increases as described by an R-curve. For hardening response and constant fracture toughness, on the other hand, the response path with both cracks propagating symmetrically is stable up to a certain critical crack length, after which snapback occurs. A system of parallel cooling cracks in a halfspace is found to exhibit a bifurcation similar to that in plastic column buckling.
2016-02-10
2016-02-10
1992
2016-02-10
Article
0376-9429
http://hdl.handle.net/10725/3037
http://dx.doi.org/10.1007/BF00017341
Bazant, Z. P., & Tabbara, M. R. (1992). Bifurcation and stability of structures with interacting propagating cracks. International journal of fracture, 53(3), 273-289.
http://link.springer.com/article/10.1007/BF00017341#page-1
en
International Journal of Fracture
oai:laur.lau.edu.lb:10725/30382016-08-08T10:42:16Zcom_10725_2055col_10725_2075
Antiplane Shear Fracture Tests (Mode III)
Tabbara, Mazen
Bazant, Zdenek P.
Prat, PereE C.
Mode III (antiplane) shear fracture energies of concrete and mortar were measured on the basis of the size-effect law. The specimens were cylinders with a circumferential notch at midlength, subjected to pure torsion at zero axial force. The specimens were geometrically similar and their sizes varied as 1:2:4. It was observed that the mortar specimens behave closer to linear elastic fracture mechanics than the concrete specimens. The ratio of Mode III to Mode I (tensile) fracture energies was found to be about 3 for concrete and about 8 for mortar. The results indirectly indicate that a volume expansion of the sheared fracture process zone may be a significant mechanism causing transverse tensile stresses across the ligament. The size effect measurements also yield an estimate of the size of the fracture process zone, which is found to be nearly the same as for Mode I fracture.
2016-02-10
2016-02-10
1990
2016-02-10
Article
0096-7920
http://hdl.handle.net/10725/3038
Bazant, Z. P., Prat, P. C., & Tabbara, M. R. (1990). Antiplane shear fracture tests (Mode III). Materials Journal, 87(1), 12-19.
https://www.concrete.org/publications/internationalconcreteabstractsportal.aspx?m=details&ID=2302
en
Materials Journal
oai:laur.lau.edu.lb:10725/30392016-08-24T08:07:06Zcom_10725_2055col_10725_2075
Global Positioning System measurements of strain accumulation and slip transfer through the restraining bend along the Dead Sea fault system in Lebanon
Gomez, Francisco
Karam, Gebran
Khawlie, Mohamad
McClusky, Simon
Vernant, Philippe
Reilinger, Robert
Jaafar, Rani
Tabet, Charles
Khair, Kamal
Approximately 4 yr of campaign and continuous Global Positioning System (GPS) measurements across the Dead Sea fault system (DSFS) in Lebanon provide direct measurements of interseismic strain accumulation along a 200‐km‐long restraining bend in this continental transform fault. Late Cenozoic transpression within this restraining bend has maintained more than 3000 m of topography in the Mount Lebanon and Anti‐Lebanon ranges. The GPS velocity field indicates 4–5 mm yr−1 of relative plate motion is transferred through the restraining bend to the northern continuation of the DSFS in northwestern Syria. Near‐field GPS velocities are generally parallel to the major, left‐lateral strike‐slip faults, suggesting that much of the expected convergence across the restraining bend is likely accommodated by different structures beyond the aperture of the GPS network (e.g. offshore Lebanon and, possibly, the Palmyride fold belt in SW Syria). Hence, these geodetic results suggest a partitioning of crustal deformation involving strike‐slip displacements in the interior of the restraining bend, and crustal shortening in the outer part of the restraining bend. Within the uncertainties, the GPS‐based rates of fault slip compare well with Holocene‐averaged estimates of slip along the two principal strike‐slip faults: the Yammouneh and Serghaya faults. Of these two faults, more slip occurs on the Yammouneh fault, which constitutes the primary plate boundary structure between the Arabia and Sinai plates. Hence, the Yammouneh fault is the structural linkage that transfers slip to the northern part of the transform in northwestern Syria. From the perspective of the regional earthquake hazard, the Yammouneh fault is presently locked and accumulating interseismic strain.
2016-02-11
2016-02-11
2007
2016-02-11
Article
0956-540X
http://hdl.handle.net/10725/3039
http://dx.doi.org/ 10.1111/j.1365-246X.2006.03328.x
Gomez, F., Karam, G., Khawlie, M., McClusky, S., Vernant, P., Reilinger, R., ... & Barazangi, M. (2007). Global Positioning System measurements of strain accumulation and slip transfer through the restraining bend along the Dead Sea fault system in Lebanon. Geophysical Journal International, 168(3), 1021-1028.
http://gji.oxfordjournals.org/content/168/3/1021.short
en
Geophysical Journal International
oai:laur.lau.edu.lb:10725/30412016-08-24T09:34:04Zcom_10725_2055col_10725_2075
On the ovalisation in bending of Nylon and plastic tubes
Karam, Gebran
An untruncated form of the Brazier analysis is used to model the ovalisation of plastic tubes in bending over a wide range of ovalisation values. A relationship between the different geometric parameters of the problem is obtained independently of the materials modulus. Theoretical predictions are compared with some recently reported data showing good agreement.
2016-02-11
2016-02-11
1994
2016-02-11
Article
0308-0161
http://hdl.handle.net/10725/3041
http://dx.doi.org/10.1016/0308-0161(94)90077-9
Karam, G. N. (1994). On the ovalisation in bending of nylon and plastic tubes. International journal of pressure vessels and piping, 58(2), 147-149.
http://www.sciencedirect.com/science/article/pii/0308016194900779
en
International Journal of Pressure Vessels and Piping
oai:laur.lau.edu.lb:10725/30422019-01-14T11:14:42Zcom_10725_2055col_10725_2075
Biomechanical Model of the Xylem Vessels in Vascular Plants
Karam, Gebran
• Background and Aims The xylem, or water transport system, in vascular plants adopts different morphologies that appear sequentially during growth phases. This paper proposes an explanation of these morphologies based on engineering design principles.
• Methods Using microscopic observations of the different growth stages, an engineering analysis of the xylem vessels as a closed cylinder under internal pressure is carried out adopting pressure vessel design concepts.
• Key Results The analysis suggests that the xylem vessel structural morphology follows the ‘constant strength’ design principle, i.e. all of the material within the wall of the xylem is loaded equally to its maximum allowable stress capacity, and the amount of material used is therefore systematically minimized. The analysis shows that the different structural designs of the xylem vessel walls (annular, helical, reticulate and pitted) all quantitatively follow the constant strength design principle.
• Conclusions The results are discussed with respect to growth and differentiation. It is concluded that the morphology of the xylem vessel through the different phases of growth seems to follow optimal engineering design principles
2016-02-11
2016-02-11
2005
2016-02-11
Article
0305-7364
http://hdl.handle.net/10725/3042
http://dx.doi.org/ 10.1093/aob/mci130
Karam, G. N. (2005). Biomechanical model of the xylem vessels in vascular plants. Annals of botany, 95(7), 1179-1186.
http://aob.oxfordjournals.org/content/95/7/1179.short
en
Annals of Botany
oai:laur.lau.edu.lb:10725/30432016-08-25T08:12:22Zcom_10725_2055col_10725_2075
Vocational and Technical Education in Lebanon
Karam, Gebran
The current status of the Lebanese vocational and technical education (VTE) system is assessed and the strategic issues and challenges facing it are identified. In addition to the economic and social challenges that are common to many developing countries, the Lebanese system suffers from idiosyncratic problems, which may require innovative and bold reform strategies. The results of the first open consultations in the history of VTE with public and private sector stakeholders and key decision makers are analysed. These results are used to confirm the analysis of the current situation and to chart a strategic planning process for policy making, reform, and improved effectiveness in Lebanese vocational and technical education. (Contains 6 tables, 1 figure, and 1 footnote.)
2016-02-11
2016-02-11
2006
2016-02-11
Article
1443-1475
http://hdl.handle.net/10725/3043
Karam, G. (2006). Vocational and Technical Education in Lebanon: Strategic Issues and Challenges. International Education Journal, 7(3), 259-272.
http://eric.ed.gov/?id=EJ847310
en
International Education Journal
oai:laur.lau.edu.lb:10725/30442018-01-30T09:03:05Zcom_10725_2055col_10725_2075
Discussion: Strength tests on slender plain block masonry walls with veneer wythes
Karam, Gebran
2016-02-11
2016-02-11
1992
2016-02-11
Article
0315-1468
http://hdl.handle.net/10725/3044
Karam, G. N. (1992). Discussion: Strength tests on slender plain block masonry walls with veneer wythes. Canadian Journal of Civil Engineering, 19(6), 1082-1083.
en
Canadian Journal of Civil Engineering
oai:laur.lau.edu.lb:10725/30452019-01-14T11:09:45Zcom_10725_2055col_10725_2075
Discussion of “Modeling Stiffness Degradation in Filamentary Composite Materials” by Robert M. Hackett and Kerry T. Slattery
Karam, Gebran
2016-02-11
2016-02-11
1993
2016-02-11
Article
0899-1561
http://hdl.handle.net/10725/3045
http://dx.doi.org/10.1061/(ASCE)0899-1561(1993)5:4(547)
Karam, G. N. (1993). Discussion of “Modeling Stiffness Degradation in Filamentary Composite Materials” by Robert M. Hackett and Kerry T. Slattery (May, 1992, Vol. 4, No. 2). Journal of materials in civil engineering, 5(4), 547-549.
en
Journal of Materials in Civil Engineering
oai:laur.lau.edu.lb:10725/30462019-01-14T11:03:15Zcom_10725_2055col_10725_2075
Discussion of “Predictions of Thermal Characteristics for Mixed Porous Media” by Yueying Deng, Clifford B. Fedler, and James M. Gregory
Karam, Gebran
2016-02-11
2016-02-11
1993
2016-02-11
Article
0899-1561
http://hdl.handle.net/10725/3046
http://dx.doi.org/10.1061/(ASCE)0899-1561(1993)5:3(420)
Karam, G. N. (1993). Discussion of “Predictions of Thermal Characteristics for Mixed Porous Media” by Yueying Deng, Clifford B. Fedler, and James M. Gregory (May, 1992, Vol. 4, No. 2). Journal of Materials in Civil Engineering, 5(3), 420-421.
http://ascelibrary.org/doi/abs/10.1061/(ASCE)0899-1561(1993)5:3(420)
en
Journal of Materials in Civil Engineering
oai:laur.lau.edu.lb:10725/30472019-01-14T11:03:48Zcom_10725_2055col_10725_2075
Discussion of “Compressive Behavior of Glass-Fiber-Reinforced Polymer Concrete” by S. Mebarkia and C. Vipulanandan
Karam, Gebran
2016-02-11
2016-02-11
1993
2016-02-11
Article
0899-1561
http://hdl.handle.net/10725/3047
Karam, G. N. (1993). Discussion of “Compressive Behavior of Glass-Fiber-Reinforced Polymer Concrete” by S. Mebarkia and C. Vipulanandan (February, 1992, Vol. 4, No. 1). Journal of Materials in Civil Engineering, 5(1), 146-148.
http://ascelibrary.org/doi/pdf/10.1061/(ASCE)0899-1561(1993)5%3A1(146)
en
Journal of Materials in Civil Engineering
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