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Transaction on Civil Engineering

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Transaction on Civil Engineering
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Transaction on Civil Engineering
 
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Transaction on Mechanical Engineering
 
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Volume 17, Issue 5, 2010
Transaction on Civil Engineering


Prediction of Longitudinal Dispersion Coefficient in Natural Channels Using Soft Computing Techniques
 
        S. Adarsh (MSc.)

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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 non-linear 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.


Computational Earthquake Engineering of Bridges
 
        Hojjat Adeli (Professor)
  • Thomas Less [PhD.]

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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 retro tting 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
              Retro tting
                Vibrations control.


Steady-State Stresses in a Half-Space Due to Moving Wheel-Type Loads with Finite Contact Patch
 
        M. Mofid (Professor)
  • M. Dehestani [PhD.]
  • A. Vafai [Professor]

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In this paper, the steady-state stresses in a homogeneous isotropic half-space under a moving wheel-type load with constant subsonic speed, prescribed on a nite patch on the boundary, are investigated. Navier's equations of motion in 2D case were modi ed via Stokes-Helmholtz resolution to a system of partial di erential equations. A double Fourier-Laplace transformation procedure was employed to solve the system of partial di erential equations in a new moving reference system, regarding the boundary conditions. The e ects of force transmission from the contact patch to the half-space have been considered in the boundary conditions. Utilizing a property of Laplace transformation leads to transformed steady-states stresses for which inverse Fourier transformation yielded the steady-state 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 half-spaces with di erent material properties were obtained.

Keywords:
Moving load

    Half-space
      Wave propagation
        Contact patch.


Numerical Study on Reinforcing of Thin Walled Cracked Metal Cylindrical Columns Using FRP Patch
 
        M.Z. Kabir (PhD.)
  • A. R. Nazari [BSc.]

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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


Tuned Genetic Algorithms for Finding p-Medians of a Weighted Graph
 
        A. Kaveh (Professor)
  • M. Shahrouzi [PhD.]
  • Y. Naserifar [MSc.]

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There are various engineering applications dealing with the prototype problem of nding the best p-medians in a weighted graph. However, the heuristic developments are still of concern due to their complexity. This paper utilizes genetic algorithm as a well-known 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 modi ed 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 e ectiveness regarding the exact results, and to compare eciency between tuned and non-tuned GA.

Keywords:
Genetic algorithm

    p-median problem
      Direct index coding
        Simulated annealing
          Parameter tuning.


3D Modeling of Damage Growth and Crack Initiation Using Adaptive Finite Element Technique
 
        A.R. Khoei (Professor)
  • H. Moslemi [PhD.]

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In this paper, the continuum damage mechanics model originally proposed by Lemaitre (Journal of Engineering Materials and Technology. 1985

    107: 83-89) is presented through an adaptive nite element method for three-dimensional ductile materials. The macro-crack initiation-propagation criterion is used based on the distribution of damage variable in the continuum damage model. The microcrack closure e ect is incorporated to simulate the damage evolution more realistic. The Zienkiewicz-Zhu 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 re nement
            Weighted SPR technique.


Fundamental Frequency of Tapered Plates Using Modi ed Modes
 
        F. Khoshnoudian (PhD.)
  • S. kazemi [MSc.]

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The fundamental frequency of a rectangular orthotropic plate having an arbitrary thickness variation is computed by using the method of Modi ed 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
        Modi ed Vibrational Mode shape (MVM)


Solution of Convection-Dominated Problems on Irregular Meshes by Collocated Discrete Least Squares Mesh-Less (CDLSM) Method
 
        M. H. Afshar (PhD.)
  • G. Shobeyri [MSc.]

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In this paper, a study is performed on the e ect of irregularity of domain discretization on the performance of the CDLSM method for the solution of convection-dominated problems. The method is based on minimizing a least squares functional of the residuals of the governing di erential equations and its boundary conditions over a set of collocation points. Four convection-dominated benchmark examples are solved using CDLSM method on three di erent sets of nodal distribution with di erent 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. Mesh-less methods as alternative numerical approaches to eliminate the well-known drawbacks of mesh-based methods have attracted much attention in the past decade due to their exibility and their potentiality in negating the need for the human-labor 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 re nement strategy is to be used to improve the performances of these methods.

Keywords:
CDLSM

    Meshless
      Irregular mesh
        Convection-dominated problems
          Re nement strategy.