2010
17
5
5
0
http://scientiairanica.sharif.edu/3157.html
Prediction of Longitudinal Dispersion Coefficient in Natural Channels Using Soft Computing Techniques
2
2
Accurate estimate of longitudinal dispersion coefficient is essential in many hydraulic
and environmental problems such as intake designs, modeling
ow in esturies and risk assessment of
injection of hazardous pollutants into river
ows. Recent research works show that in the absence of
knowledge about explicit relationships concerning longitudinal dispersion coefficient and its in
uencing
parameters, data driven techniques can be used to predict it with reasonable degree of accuracy. In this
paper, the usefulness of Support Vector Machines (SVM) and Genetic Programming (GP) are examined
for predicting longitudinal dispersion coefficient in natural channels. The hydraulic variables such as
ow depth (H),
ow velocity (U) and shear velocity (u) along with the width of channel (B) are used
as input variables to predict longitudinal dispersion coefficient (Kx). The performance evaluation based
on multiple error criteria confirm that GP shows remarkably good performance in capturing nonlinear
relationship between the predictors and predictant in the estimation of longitudinal dispersion coefficient
when compared with empirical approaches, the traditional Artificial Neural Networks (ANN) and SVM.
Hence GP can be used as an eficient computational paradigm in the prediction of longitudinal dispersion
coeficient in natural channels.
2
Accurate estimate of longitudinal dispersion coefficient is essential in many hydraulic
and environmental problems such as intake designs, modeling
ow in esturies and risk assessment of
injection of hazardous pollutants into river
ows. Recent research works show that in the absence of
knowledge about explicit relationships concerning longitudinal dispersion coefficient and its in
uencing
parameters, data driven techniques can be used to predict it with reasonable degree of accuracy. In this
paper, the usefulness of Support Vector Machines (SVM) and Genetic Programming (GP) are examined
for predicting longitudinal dispersion coefficient in natural channels. The hydraulic variables such as
ow depth (H),
ow velocity (U) and shear velocity (u) along with the width of channel (B) are used
as input variables to predict longitudinal dispersion coefficient (Kx). The performance evaluation based
on multiple error criteria confirm that GP shows remarkably good performance in capturing nonlinear
relationship between the predictors and predictant in the estimation of longitudinal dispersion coefficient
when compared with empirical approaches, the traditional Artificial Neural Networks (ANN) and SVM.
Hence GP can be used as an eficient computational paradigm in the prediction of longitudinal dispersion
coeficient in natural channels.
Keywords: Longitudinal dispersion coefficient; Natural channels; Artificial neural networks; Support
vector machines; Genetic programming.
0
0


S.
Adarsh
Department of Civil Engineering,Santa Cruz
Iran
aocrszva@scientiaunknown.non
Longitudinal dispersion coefficient
Natural channels
Artificial Neural Networks
support vector machines
Genetic programming
http://scientiairanica.sharif.edu/3158.html
Computational Earthquake Engineering of Bridges
2
2
A review of major research performed in the eld of earthquake engineering of bridges
during the past decade is presented with a focus on computational modeling. Topics covered include
nonlinear simulation, hazard analysis, passive, active, and hybrid control of bridges, bridge damage
studies, health monitoring of bridges, bridge management, and retrotting of bridges. Important
conclusions of interest to the bridge engineering community reported in the articles are noted.
2
A review of major research performed in the eld of earthquake engineering of bridges
during the past decade is presented with a focus on computational modeling. Topics covered include
nonlinear simulation, hazard analysis, passive, active, and hybrid control of bridges, bridge damage
studies, health monitoring of bridges, bridge management, and retrotting of bridges. Important
conclusions of interest to the bridge engineering community reported in the articles are noted.
Keywords: Bridge engineering; Bridge management; Earthquake engineering; Seismic hazard analysis;
Health monitoring; Impact; Nonlinear simulation; Retrotting; Vibrations control.
0
0


Hojjat
Adeli
Department of Civil Engineering,Oakland University
Iran
wfqelize@scientiaunknown.non


Thomas
Less
Department of Civil Engineering,Berakly
Iran
cpvwhtqm@scientiaunknown.non
Bridge engineering
Bridge management
Earthquake Engineering
Seismic Hazard Analysis
Health monitoring
impact
Nonlinear simulation
Retrotting
Vibrations control
http://scientiairanica.sharif.edu/3159.html
SteadyState Stresses in a HalfSpace Due to Moving WheelType Loads with Finite Contact Patch
2
2
In this paper, the steadystate stresses in a homogeneous isotropic halfspace under a
moving wheeltype load with constant subsonic speed, prescribed on a nite patch on the boundary, are
investigated. Navier's equations of motion in 2D case were modied via StokesHelmholtz resolution
to a system of partial dierential equations. A double FourierLaplace transformation procedure was
employed to solve the system of partial dierential equations in a new moving reference system, regarding
the boundary conditions. The eects of force transmission from the contact patch to the halfspace
have been considered in the boundary conditions. Utilizing a property of Laplace transformation leads
to transformed steadystates stresses for which inverse Fourier transformation yielded the steadystate
stresses. Considering two types of uniform and parabolic force transmission mechanism and a comparison
between the pertaining results demonstrated that the parabolic load transmission induce lower stresses
than the uniform one. Results of the problem for various speeds of moving loads showed that the stresses
increase as the moving loads' speeds increase to an extremum speed known as CIS. After the CIS speed,
stresses' absolute values decrease for higher speeds. Eventually CIS values for homogeneous halfspaces
with dierent material properties were obtained.
2
In this paper, the steadystate stresses in a homogeneous isotropic halfspace under a
moving wheeltype load with constant subsonic speed, prescribed on a nite patch on the boundary, are
investigated. Navier's equations of motion in 2D case were modied via StokesHelmholtz resolution
to a system of partial dierential equations. A double FourierLaplace transformation procedure was
employed to solve the system of partial dierential equations in a new moving reference system, regarding
the boundary conditions. The eects of force transmission from the contact patch to the halfspace
have been considered in the boundary conditions. Utilizing a property of Laplace transformation leads
to transformed steadystates stresses for which inverse Fourier transformation yielded the steadystate
stresses. Considering two types of uniform and parabolic force transmission mechanism and a comparison
between the pertaining results demonstrated that the parabolic load transmission induce lower stresses
than the uniform one. Results of the problem for various speeds of moving loads showed that the stresses
increase as the moving loads' speeds increase to an extremum speed known as CIS. After the CIS speed,
stresses' absolute values decrease for higher speeds. Eventually CIS values for homogeneous halfspaces
with dierent material properties were obtained.
Keywords: Moving load; Halfspace; Wave propagation; Contact patch.
0
0


M.
Mofid
Department of Civil Engineering,Sharif University of Technology
Iran
mofid@sharif.edu


A.
Vafai
Department of Civil Engineering,Sharif University of Technology
Iran
osapjweb@scientiaunknown.non


M.
Dehestani
Department of Civil Engineering,Sharif University of Technology
Iran
lswugkwt@scientiaunknown.non
Moving load
Halfspace
wave propagation
Contact patch
http://scientiairanica.sharif.edu/3160.html
Numerical Study on Reinforcing of Thin Walled Cracked Metal Cylindrical Columns Using FRP Patch
2
2
In this paper a new technique was proposed for the repair of defected metal columns. The
finite element method was chosen to find out the adequacy of the proposed method, regarding, the load
carrying capacity of two types of thin walled cylindrical columns with L=D = 10 and 20 along with
circumferential and longitudinal cracks. The study considers the non linearity behavior in both material
as well as geometrical characteristics. Various configurations of the composite patches made from carbonepoxy
were assumed on the cracked region and the in
uence of a patch on the load carrying capacity of the
columns was examined. The obtained results indicate that composite material can not only compensate
the effect of damage on column buckling load, but also increase buckling strength to a level even greater
than in an intact one.
2
In this paper a new technique was proposed for the repair of defected metal columns. The
finite element method was chosen to find out the adequacy of the proposed method, regarding, the load
carrying capacity of two types of thin walled cylindrical columns with L=D = 10 and 20 along with
circumferential and longitudinal cracks. The study considers the non linearity behavior in both material
as well as geometrical characteristics. Various configurations of the composite patches made from carbonepoxy
were assumed on the cracked region and the in
uence of a patch on the load carrying capacity of the
columns was examined. The obtained results indicate that composite material can not only compensate
the effect of damage on column buckling load, but also increase buckling strength to a level even greater
than in an intact one.
Keywords: Repair; Cracked metal column; Buckling load; FRP patch; Compression loading
0
0


M.Z.
Kabir
Department of Civil Engineering,Amirkabir University of Technology
Iran
m.z.kabir@aku.ac.ir


A. R.
Nazari
Department of Civil Engineering,Amirkabir University of Technology
Iran
psneeljr@scientiaunknown.non
repair
Cracked metal column
Buckling load
FRP patch
Compression loading
http://scientiairanica.sharif.edu/3161.html
Tuned Genetic Algorithms for Finding pMedians of a Weighted Graph
2
2
There are various engineering applications dealing with the prototype problem of nding the
best pmedians in a weighted graph. However, the heuristic developments are still of concern due to their
complexity. This paper utilizes genetic algorithm as a wellknown reliable evolutionary search for such
a purpose. Problem formulation is studied, introducing a characteristic graph and specialized genotype
representation called Direct Index Coding". The genetic operators are also modied due to problem
requirements, and further tuned using a simulated annealing approach. Such an enhanced evolutionary
search tool is then applied to a number of examples to show its eectiveness regarding the exact results,
and to compare eciency between tuned and nontuned GA.
2
There are various engineering applications dealing with the prototype problem of nding the
best pmedians in a weighted graph. However, the heuristic developments are still of concern due to their
complexity. This paper utilizes genetic algorithm as a wellknown reliable evolutionary search for such
a purpose. Problem formulation is studied, introducing a characteristic graph and specialized genotype
representation called Direct Index Coding". The genetic operators are also modied due to problem
requirements, and further tuned using a simulated annealing approach. Such an enhanced evolutionary
search tool is then applied to a number of examples to show its eectiveness regarding the exact results,
and to compare eciency between tuned and nontuned GA.
Keywords: Genetic algorithm; pmedian problem; Direct index coding; Simulated annealing; Parameter
tuning.
0
0


A.
Kaveh
Department of Civil Engineering,Iran University of Science and Technology
Iran
kaveh@iust.ac.ir


M.
Shahrouzi
Department of Engineering,Building and Housing Research Center
Iran
goaineec@scientiaunknown.non


Y.
Naserifar
Department of Engineering,Building and Housing Research Center
Iran
govctlkh@scientiaunknown.non
Genetic Algorithm
pmedian problem
Direct index coding
Simulated annealing
Parameter tuning
http://scientiairanica.sharif.edu/3162.html
3D Modeling of Damage Growth and Crack Initiation Using Adaptive Finite Element Technique
2
2
In this paper, the continuum damage mechanics model originally proposed by Lemaitre
(Journal of Engineering Materials and Technology. 1985; 107: 8389) is presented through an adaptive
nite element method for threedimensional ductile materials. The macrocrack initiationpropagation
criterion is used based on the distribution of damage variable in the continuum damage model. The microcrack
closure eect is incorporated to simulate the damage evolution more realistic. The ZienkiewiczZhu
posteriori error estimator is employed in conjunction with a weighted Superconvergence Patch Recovery
(SPR) technique at each patch to improve the accuracy of error estimation and data transfer process.
Finally, the robustness and accuracy of proposed computational algorithm is demonstrated by several 3D
numerical examples.
2
In this paper, the continuum damage mechanics model originally proposed by Lemaitre
(Journal of Engineering Materials and Technology. 1985; 107: 8389) is presented through an adaptive
nite element method for threedimensional ductile materials. The macrocrack initiationpropagation
criterion is used based on the distribution of damage variable in the continuum damage model. The microcrack
closure eect is incorporated to simulate the damage evolution more realistic. The ZienkiewiczZhu
posteriori error estimator is employed in conjunction with a weighted Superconvergence Patch Recovery
(SPR) technique at each patch to improve the accuracy of error estimation and data transfer process.
Finally, the robustness and accuracy of proposed computational algorithm is demonstrated by several 3D
numerical examples.
Keywords: Damage mechanics; Crack initiation; Crack closure; Adaptive mesh renement; Weighted
SPR technique.
0
0


A.R.
Khoei
Department of Civil Engineering,Sharif University of Technology
Iran
arkhoei@sharif.edu


H.
Moslemi
Department of Civil Engineering,Sharif University of Technology
Iran
mabpkszx@scientiaunknown.non
Damage Mechanics
Crack initiation
Crack closure
Adaptive mesh renement
Weighted SPR technique
http://scientiairanica.sharif.edu/3163.html
Fundamental Frequency of Tapered Plates Using Modied Modes
2
2
The fundamental frequency of a rectangular orthotropic plate having an arbitrary thickness
variation is computed by using the method of Modied Vibrational Mode (MVM) shapes. The change of
thickness within a plate is characterized by introducing a tapering index. It is shown that the vibrational
mode shapes of a tapered plate is in fact a linear combination of various mode shapes of intact plates.
This phenomenon is used to estimate the vibrational mode shapes of stepped plates. In turn, these mode
shapes are incorporated to evaluate their fundamental frequency. Many numerical analyses are carried
out to represent the accuracy and robustness of the proposed method by comparing the results to the works
presented by other researchers. The major advantage of the present method over the existing ones is its
simplicity for handling the problem of force vibration of tapered plates.
2
The fundamental frequency of a rectangular orthotropic plate having an arbitrary thickness
variation is computed by using the method of Modied Vibrational Mode (MVM) shapes. The change of
thickness within a plate is characterized by introducing a tapering index. It is shown that the vibrational
mode shapes of a tapered plate is in fact a linear combination of various mode shapes of intact plates.
This phenomenon is used to estimate the vibrational mode shapes of stepped plates. In turn, these mode
shapes are incorporated to evaluate their fundamental frequency. Many numerical analyses are carried
out to represent the accuracy and robustness of the proposed method by comparing the results to the works
presented by other researchers. The major advantage of the present method over the existing ones is its
simplicity for handling the problem of force vibration of tapered plates.
Keywords: Fundamental frequency; Stepped plate; Dynamic equation of motion; Modied Vibrational
Mode shape (MVM)
0
0


F.
Khoshnoudian
Department of Civil Engineering,Amirkabir University of Technology
Iran
vunzkkfe@scientiaunknown.non


S.
kazemi
Department of Civil Engineering,Amirkabir University of Technology
Iran
pvyuxyfj@scientiaunknown.non
Fundamental frequency
Stepped plate
Dynamic equation of motion
Modied Vibrational Mode shape (MVM)
http://scientiairanica.sharif.edu/3164.html
Solution of ConvectionDominated Problems on Irregular Meshes by Collocated Discrete Least Squares MeshLess (CDLSM) Method
2
2
In this paper, a study is performed on the eect of irregularity of domain discretization on
the performance of the CDLSM method for the solution of convectiondominated problems. The method is
based on minimizing a least squares functional of the residuals of the governing dierential equations and
its boundary conditions over a set of collocation points. Four convectiondominated benchmark examples
are solved using CDLSM method on three dierent sets of nodal distribution with dierent levels of
irregularity and the results are presented. These experiments show that CDLSM method is capable of
producing stable and accurate results for hyperbolic problems with shocked or high gradient solutions even
on highly irregular mesh of nodes. Meshless methods as alternative numerical approaches to eliminate
the wellknown drawbacks of meshbased methods have attracted much attention in the past decade due
to their
exibility and their potentiality in negating the need for the humanlabor intensive process of
constructing geometric meshes in a domain. Exploiting this ability, however, requires that the method
could solve the problem under consideration on unstructured distribution of nodes. This is particularly
important when a renement strategy is to be used to improve the performances of these methods.
2
In this paper, a study is performed on the eect of irregularity of domain discretization on
the performance of the CDLSM method for the solution of convectiondominated problems. The method is
based on minimizing a least squares functional of the residuals of the governing dierential equations and
its boundary conditions over a set of collocation points. Four convectiondominated benchmark examples
are solved using CDLSM method on three dierent sets of nodal distribution with dierent levels of
irregularity and the results are presented. These experiments show that CDLSM method is capable of
producing stable and accurate results for hyperbolic problems with shocked or high gradient solutions even
on highly irregular mesh of nodes. Meshless methods as alternative numerical approaches to eliminate
the wellknown drawbacks of meshbased methods have attracted much attention in the past decade due
to their
exibility and their potentiality in negating the need for the humanlabor intensive process of
constructing geometric meshes in a domain. Exploiting this ability, however, requires that the method
could solve the problem under consideration on unstructured distribution of nodes. This is particularly
important when a renement strategy is to be used to improve the performances of these methods.
Keywords: CDLSM; Meshless; Irregular mesh; Convectiondominated problems; Renement strategy.
0
0


M. H.
Afshar
Department of Civil Engineering,Iran University of Science and Technology
Iran
mhafshar@iust.ac.ir


G.
Shobeyri
Department of Civil Engineering,Iran University of Science and Technology
Iran
ugwyvhpq@scientiaunknown.non
CDLSM
Meshless
Irregular mesh
Convectiondominated problems
Renement strategy