Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Evaluation of Selection Algorithms for Simultaneous Layout and Pipe Size Optimization of Water Distribution Networks
2981
EN
M.H.
Afshar
Department of Civil Engineering,Iran University of Science and Technology
Journal Article
2009
06
01
In this paper, a genetic algorithm is presented for the simultaneous layout and pipe size
optimization of water distribution networks and its eciency is evaluated and compared using
dierent selection mechanisms. An engineering concept of reliability is used, in which the number
of independent paths from source nodes to each of the demand nodes is considered as a measure
of reliability. The method starts with a predened layout, which includes all possible links. The
method is capable of designing a layout of predened reliability, including tree-like and looped
networks. It is shown that a layout optimization of a network, followed by size optimization, does
not lead to an optimal or a near-optimal solution. This emphasizes the need for simultaneous
layout and size optimization of networks, if an optimal solution is desired. The performance of
the method for layout optimization of pipe networks is tested against two benchmark examples
in the literature and the results are presented.
https://scientiairanica.sharif.edu/article_2981_2da9dc749a59bfcd486ddd95053b6fbc.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
A Methodology for Analyzing the Transient Reliability of Systems with Identical Components and Identical Repairmen
2982
EN
M.
Amiri
Department of Industrial Engineering,Sharif University of Technology
Journal Article
2009
06
01
In this paper, the Markov models, eigenvectors and eigenvalue concepts are used to propose
a methodology for analyzing the transient reliability of a system with identical components
and identical repairmen. The components of the systems under consideration can have two
distinct congurations, namely; they can be arranged in series or in parallel. A third case is also
considered, in which the system is up (good) if k-out-of-n components are good. For all three
cases, a procedure is proposed for calculating the transient probability of the system availability
and the duration of the system to reach the steady state.
https://scientiairanica.sharif.edu/article_2982_cb4b36f5d23168eba06f5f1504b93888.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Project Completion Time in Dynamic PERT Networks with Generating Projects
2983
EN
M.
Modarres
Department of Industrial Engineering,Sharif University of Technology
A.
Azaron
Department of Industrial Engineering,University of Bu-Ali-Sina
Journal Article
2009
06
01
In this paper, an analytical method is developed to compute the project completion time
distribution in a dynamic PERT network, where the activity durations are exponentially
distributed random variables. The projects are generated according to a renewal process and
share the same facilities. Thus, these projects cannot be analyzed independently. The authors'
approach is to transform this dynamic PERT network into a stochastic network and, then, to
obtain the project completion time distribution by constructing a proper continuous-time Markov
chain. This dynamic PERT network is represented as a network of queues, where the service
times represent the durations of the corresponding activities and the arrival stream to each node
follows a renewal process. Finally, the proposed methodology is extended to the generalized
Erlang activity durations.
https://scientiairanica.sharif.edu/article_2983_59bd05a6d953a8d10db750682f3d8e4c.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
A Multiple Scale Method Solution for the Nonlinear Vibration of Rectangular Plates
2984
EN
A.
Shooshtari
Department of Mechanical Engineering,Tarbiat Modares University
Journal Article
2009
06
01
In this paper, rst, the equations of motion for a rectangular isotropic plate have been derived.
This derivation is based on the Von Karmann theory and the eects of shear deformation
have been considered. Introducing an Airy stress function, the equations of motion have been
transformed to a nonlinear coupled equation. Using the Galerkin method, this equation has been
separated into position and time functions. By means of the dimensional analysis, it is shown
that the orders of magnitude for nonlinear terms are very small, with respect to linear terms.
Then, for the rst time, the invariant manifold theory has been applied to the plate problem
and it is proved that the nonlinearities are stiness and inertia types. Finally, the multiple
scale method is applied to the equations of motion and closed-form relations for the nonlinear
natural frequencies and mode shapes of the plate are derived. The obtained results are in good
agreement in comparison with numerical methods. Using the obtained relation, the eects of
initial displacement, thickness and dimensions of the plate on nonlinear natural frequencies and
displacements have been investigated. These results are valid for a special range of the ratio of
thickness to dimensions of the plate, which is a characteristic of the multiple scale method.
https://scientiairanica.sharif.edu/article_2984_4518497989ac417528af17057a3041fe.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Modeling of Metal-Mold Interface Resistance in the Al-11.5 wt% Si Alloy Casting Process
2985
EN
P.
Davami
Department of Materials Science and Engineering,Sharif University of Technology
Journal Article
2009
06
01
In this investigation, a computational model has been developed, including heat transfer and
the eects of the resistance of a metal-mold interface and pressure, for simulation of the
solidication process. Simulation of the interface resistance is based on the Zero Thickness
Element (ZTE), utilizing the Finite Element Method (FEM). Solid boundary conditions, including
contact resistances, have been modied by a pressure gradient in each of the ZTE. The pressure
gradient has been modeled, based on experimental data. In order to verify the computational
results, an Al-11.5 wt% Si alloy was poured into a permanent mold and the temperature of
the interface was measured by a data acquisition system. Then, the eect of metalo-static
pressure on overall heat transfer in the interface resistance was modeled. Comparison between
the experimental and simulation results during the solidication process shows a good consistency,
which conrms the accuracy of the model for the eects of interface resistance on solidication
time.
https://scientiairanica.sharif.edu/article_2985_927b3f3567b84bebca295bfec3cb8aba.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Direct Discrete Method (DDM) and its Application to Neutron Transport Problems
2986
EN
A.A.
Salehi
Department of Mechanical Engineering,Sharif University of Technology
Journal Article
2009
06
01
The objective of this paper is to introduce a new direct method for neutronic calculations.
This method, called Direct Discrete Method (DDM), is simpler than the Neutron Transport
Equation and more compatible with the physical meanings of the problem. The method, based
on the physics of the problem, initially runs through meshing of the desired geometry. Next,
the balance equation for each mesh interval is written. Considering the connection between the
mesh intervals, the nal discrete equation series are directly obtained without the need to rst
pass through the set-up of the neutron transport dierential equation. In this paper, a single and
multigroup neutron transport discrete equation has been produced for a cylindrical shape fuel
element with and without the associated clad and the coolant regions, each with two dierent
external boundary conditions. The validity of the results from this new method are tested against
the results obtained by the MCNP-4B and the ANISN codes.
https://scientiairanica.sharif.edu/article_2986_bbeac0747001f09b95515e36484e713f.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Evaluation of the Vertical Distribution of Base Shear Force in Base-Isolated Structures
2987
EN
F.R.
Rofooei
Department of Civil Engineering,Sharif University of Technology
Journal Article
2009
06
01
Application of the base-isolation systems, as a means to limit the seismic-induced response
of structures, has attracted the attention of many engineers and researchers. Due to their
importance, the Uniform Building Code (UBC) has incorporated a special section for the
seismic analysis and design of base-isolated structures since its 1991 edition. The present
work investigates the vertical distribution of the lateral seismic force for base-isolated structures
provided by the 1997 edition of UBC (UBC97). Dierent 6 and 8-story, 3-D base-isolated
structural models with LRB isolators are considered, having a variety of eective periods and
eective damping ratios. The UBC97 analysis procedure for the base-isolated structures is used
to determine the minimum lateral seismic force and its vertical distribution for dierent
oors.
Since the number of stories above the isolation interface is more than four for the considered
isolated structural models, the response spectrum analysis is used, considering the equivalent
linear properties for isolation systems. Also, the UBC97 recommended that the 5%-damped
design spectra be properly modied to account for the actual modal damping ratios of an
isolated structure. Extensive nonlinear dynamic analyses were performed for 8 types of LRB
isolators, using appropriately normalized earthquake accelerograms recorded on SA and SB soil
proles. Both the superstructure and the isolators are allowed to behave nonlinearly, in order to
evaluate the seismic induced demand shear force on dierent
oors. The peak base center and
corner displacements, maximum base and story shear forces and the maximum inter-story drifts
are determined for dierent base-isolation systems and earthquake records. The results, together
with their mean and mean plus one standard deviation values, are used for the evaluation of
UBC97 response spectrum analysis procedures for these buildings. The results indicate that
the UBC97 suitably predicts the seismic lateral forces for base-isolated buildings. However, it
does not provide a good estimate of the shear force distribution over the height, especially for
the highly damped base-isolation systems. Furthermore, the number of columns per story that
behaved nonlinearly during the time history analyses is included for comparison.
https://scientiairanica.sharif.edu/article_2987_9f5d1a14ee78cc8181a72cd9e68edd59.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Modeling Highway Congestion Index for a Developing Country: The Iran Experience
2988
EN
M.
Vaziri
Department of Civil Engineering,Sharif University of Technology
Journal Article
2009
06
01
This paper describes an attempt to develop congestion indices for a developing country with
a limited sampling. Speed and
ow rate information was collected from urban highway trac
ow videotaping in Iran. Video display provided information for trac modeling when, similar to
most of the developing nations, Iran does not have locally developed highway capacity manuals.
Processing of the extracted data and trac modeling provided free and capacity
ow information
for the selected freeway and principal arterial sections for the capital city of Tehran. The
congestion indices were associated, in simple and logical models, with ve trac descriptive
variables of travel speed, travel rate, delay rate, travel rate ratio and delay ratio, respectively.
To calibrate the congestion index models, specic congestion levels were assessed by the index
values under free and capacity
ow conditions. The functional forms used in congestion index
modeling were derived from the congestion rate of change, simple, reasonable and relevant
assumptions. For comparison, index models, based on the US Highway Capacity Manual, HCM,
speed and
ow rate information, were also developed. The developed indices were suggested
as feasible and included quick response measures for congestion monitoring and control when
trac management resources are often limited and scarce. Based on the preferences of a group
of transportation professionals and university students, the relative importance of each of the
individual indices, as average weighting value, was identied. Using the average weighting values,
an overall congestion index was also developed. The overall congestion index was suggested as
a complimentary or alternative measure for congestion intensity assessment and evaluation. The
study ndings were based on a rather limited database and were location specic; nevertheless,
for quick response congestion index development, the applied methodology could be used by any
developing country. The suggested indices have potential in trac management and congestion
mitigation.
https://scientiairanica.sharif.edu/article_2988_02649b554da95a1cf8f2651ddc162589.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
14
1
2007
02
01
Impedance Control of a Flexible Link Robot for Constrained and Unconstrained Maneuvers Using Sliding Mode Control (SMC) Method
2989
EN
G.R.
Vossoughi
Department of Mechanical Engineering,Sharif University of Technology
Journal Article
2009
06
01
In this paper, the modeling and impedance-control of a one link
exible robot is presented. The
concept of impedance control of
exible link robots is rather new and is being addressed for the
rst time. The control algorithm is valid for both constrained and unconstrained maneuvers.
First, equations of motion and the associated boundary conditions are derived using Hamilton's
principle. A linear nite dimensional model is, then, generated in the Cartesian coordinates, using
the assumed mode method and by introduction of a proper coordinate transformation. The target
impedance is, then, introduced in the Cartesian coordinate system and a control law is designed
to realize the proposed target impedance for a given frequency range, using the Sliding Mode
Control Theory. A set of computer simulations are carried out to demonstrate the eectiveness
of the proposed control law. Simulations are carried out with various contact stiness. As the
results show, when the environmental surface stiness is smaller than, or comparable to, that of
the link, the control system is able to achieve stable behavior and the link vibration diminishes
rather rapidly. However, when the environmental stiness is much greater than that of the
stiness of the link, although the robot achieves stable behavior during contact, the vibrations
tend to increase.
https://scientiairanica.sharif.edu/article_2989_68c8b445e351971beba90a21b300b770.pdf