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Volume 15, Issue 3, 2008
Civil and Mechanical Engineering


A Methodology for Optimizing Statistical Multi-Response Problems Using Fuzzy Goal Programming
 
        M. Amiri (PhD.)
  • J. Salehi-Sadaghiani [PhD.]

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This paper presents a method for optimizing statistical multi-response problems. The method is based on fuzzy goal programming and it enjoys a strong mathematical foundation. In this method, the decision maker's comments are considered objectively. The LINGO programming environment is used to test the developed method. The method performance is evaluated by comparing the results with those of other existing methods.


Performance Evaluation of Masonry Buildings Using a Probabilistic Approach
 
        A. Bakhshi (PhD.)
  • K. Karimi [PhD.]

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In many countries, there are traditional houses made of stone, adobe and brick, which perform relatively weakly in earthquakes. To mitigate casualties in future earthquakes, it is necessary to evaluate the current status of these buildings and propose e ective methods to retro t them. One method of evaluating the performance of buildings in earthquakes is through the use of fragility curves. These diagrams show the probability of exceeding a speci c state of damage versus seismic intensity parameters, such as PGA, MMI, Ia, CAV etc. Fragility curves will provide an important basis for analytical methods, based on probabilistic approaches. Much work has been done on bridges, concrete and steel structures, while limited studies have been conducted on masonry buildings. Considering the prevalence of these buildings and the high seismic activity in some regions where they are built, fragility curves for di erent types of masonry buildings are developed in this research. The results obtained show the probable damage to those types of masonry building chosen in this research for di erent earthquake intensities and restates that, by providing horizontal and vertical ties and retro tting these buildings, by the methods proposed in some seismic code provisions (such as FEMA 356 and 357), their behavior in earthquakes are apparently e ected and structural damage reduced. Furthermore, results indicate that soil type does not signi cantly in uence the seismic behavior of masonry buildings.


Sensitivity Based Health Monitoring of Structures with Static Response
 
        S. Chakraborty (PhD.)
  • G. Aditya [PhD.]

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A sensitivity based parameter identi cation method is presented to detect the damage of existing structures, using applied sets of static forces at one subset of degrees of freedom and measured displacements at a subset of degrees of freedom that may overlap completely, partially, or not at all. The algorithm follows an output error approach, which minimizes the deviation between a measured and a theoretical displacement, in lieu of the commonly used force error function. An iterative scheme is developed utilizing a rst order Taylor series expansion to linearize the associated non linear problem. The algorithm automatically adjusts the structural element sti ness parameters, in order to improve the comparison between a measured and a theoretical response in an optimal way. The measured input required in the present study is arti cially generated. The e ect that a noisy displacement measurement has on an identi cation procedure is also studied. A procedure is also identi ed, in order to select the limited number of DOF required to perform successful parameter identi cation, reducing the impact of measurement errors on the identi ed parameters. The algorithm is elucidated by a numerical example on frame structures.


A Method for Calculation of Face Gradients in Two-Dimensional, Cell Centred, Finite Volume Formulation for Stress Analysis in Solid Problems
 
        N. Fallah (PhD.)

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In this paper, a procedure is proposed for the evaluation of displacement gradients in a twodimensional, cell centred, nite volume formulation for stress analysis in linear elastic solid problems. Temporary elements with isoparametric formulations are used for calculation of the gradients at the cell boundaries. In this way, stress continuity across the common face of the two adjacent cells will be guaranteed. The formulation is veri ed by three test cases, in which the proposed formulation shows good predictions.


Investigation of the E ect of Pad Geometry on Flat and Rounded Fretting Fatigue
 
        G.H. Farrahi (PhD.)
  • A. Mohajerani [PhD.]

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In this paper, the e ect of geometrical parameters on the fretting fatigue of a half-plane in contact with a at and rounded pad is studied. This is accomplished by calculating and comparing the stress states and stress intensity factors of fretting cracks for a number of pad geometries. The pad geometry is represented by the radius of its rounded corners and the width of its central at part. The distribution of dislocation method is employed to calculate the stress intensity factors of fretting induced cracks of di erent lengths for di erent values of geometrical parameters. The results of this study can be insightful for improving the geometrical design of an aero-engine compressor disk, as similar contact and damage are prone to occur in its dovetail region.


Numerical Simulation of Free-Surface Waves and Wave Induced Separation
 
        B. Firoozabadi (PhD.)
  • S.H. Sadathosseini [PhD.]
  • S.M. Mousaviraad [PhD.]
  • G. Ahmadi [Professor]

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The present study is concerned with the numerical simulation of free-surface waves and wave induced separation in the presence of an intrusion. The results of several simulations are reported. The rst study was performed for a NACA0024 surface piercing hydrofoil over a range of several Froude numbers (0.19, 0.37, 0.55), along with wave breaking at Fr = 1.0 The NACA0024 foil was of particular interest, as it almost has no separation at large depths

    thus the e ect of the freesurface wave and the wave induced separation could be studied. Free- surface waves and wave induced separation results were evaluated and compared with both the available experimental data and the previous numerical results. The wave breaking ow was also successfully simulated and results were presented. The second series of simulations were carried out for a circular cylinder in order to investigate the shape e ects on the wave-induced separation. Results suggest that, at high Froude numbers, the free-surface waves are a function of Froude and not the shape of a body. Flow features with regard to separation, free-surface elevations and drag coecients were also studied.


A Meshless Boundary Element Method Formulation for Transient Heat Conduction Problems with Heat Sources
 
        M.R. Hematiyan (PhD.)
  • G. Karami [PhD.]

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In the boundary element formulation of heat conduction, the heat source e ect imposes an additional domain integral term on the system of integral equations. With this term, an important advantage of the boundary element method as a boundary-only formulation will be lost. This paper presents an accurate method for the evaluation of heat source domain integrals, with no need of domain discretization. Transformation of the domain integral into the corresponding boundary integral is carried out using Green's theorem. Both time-dependent and time-independent fundamental solutions are considered. The methodology can be implemented in general and for similar situations. Numerical examples will be presented to demonstrate the accuracy and eciency of the presented method.


Comprehensive Simulation of Surface Texture for an End-Milling Process
 
        B.M. Imani (PhD.)
  • E. Layegh [PhD.]

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The analysis and simulation of the manufacturing process require extensive and complicated computations. Nowadays, computer resources and computational algorithms have reached the stage where they can model and simulate the problem eciently. One of the important processes in manufacturing is machining. In this research, the end-milling process, which is one of the most complex and widespread processes in machining, is chosen. The most important parameters in end-milling are surface roughness and surface location errors. Comprehensive simulation software is developed to model the end-milling process, in order to anticipate the nishing parameters, such as surface roughness and errors. The proposed algorithm takes into account cutting conditions, such as feed, doc, woc and tool run out etc. In addition, the dynamic simulation module of the software can accurately model the exible end-mill tool, the milling cutting forces and regeneration of the waviness e ects, in order to construct a realistic surface texture model. The software can accurately determine the most commonly used index of surface roughness parameters, such as Ra, P.T.V. and surface errors.


Quality Function Deployment, Value Engineering and Target Costing, an Integrated Framework in Design Cost Management: A Mathematical Programming Approach
 
        F. Jariri (PhD.)
  • S.H. Zegordi [PhD.]

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In this paper, the need to incorporate three famous design cost management methods, called: Quality Function Deployment (QFD), Value Engineering (VE) and Target Costing (TC) into a single model has been addressed. Each method performs very well in cost management procedures as design activities. These methods have been incorporated into a mathematical programming model, in order to achieve the maximum bene t of each method. The model, essentially, optimizes customer satisfaction subject to target cost. The tool is a mixed integer zero-one nonlinear programming. The uni ed model has been proposed to prevent a non-optimal solution when methods interact with each other. The practitioner should be con dent that the quality solution would be achieved in contrast to when the methods are applied sequentially. A simple automobile design example was formulated and solved to show the performance of the model.


Free Water Surface Oscillations in a Closed Rectangular Basin with Internal Barriers
 
        A.R. Kabiri Samani (PhD.)
  • B. Ataie-Ashtiani [PhD.]

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Thee enclosed basin has certain natural frequencies of seiche, depending on the geometry of the water boundaries and the bathymetry of water depths. Therefore, the variation in the water surface at a point becomes irregular, as caused by the combination of several natural frequencies, which may be considered as the superposition of sinusoidal frequency components of di erent amplitude. This paper is mainly concerned with the motion of an incompressible irrotational uid in a closed rectangular basin with internal impervious barriers. An analytical solution is presented for predicting the characteristic of generated waves in these types of basin. The equations of free water surface oscillations and its boundary conditions are reduced to a system of linear equations, which is solved by applying the small amplitude water wave theory. The ow potential, wave amplitude, ow patterns and the natural period of waves generated in the basin with impervious internal barriers are found, based on the basin geometry. It is shown that the natural period of the basin is strongly dependent on the location of the barriers and the size of the barrier opening.


Use of Arti cial Neural Networks in Predicting Highway Runo Constituent Event Mean Concentration
 
        M. Kayhanian (Professor)
  • A. Massoudieh [PhD.]

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In this paper, the large amount of highway runo characterization data that were collected in California, during a 3-year monitoring season (2000-2003), were assessed in order to develop an Arti cial Neural Network (ANN) model for predicting the Event Mean Concentration (EMC) of the constituent. The initial data analysis performed by a Multiple Linear Regression (MLR) model revealed that the Total Event Rainfall (TER), the Cumulative Seasonal Rainfall (CSR), the Antecedent Dry Period (ADP), the contributing Drainage Area (DA) and the Annual Average Daily Trac (AADT) were among the variables having a signi cant impact on the highway runo constituent EMC. These parameters were used as the basis for developing an Arti cial Neural Network (ANN) model. The ANN model was also used to evaluate the impact of various site and storm event variables on highway runo constituents' EMCs. The ANN model has proven to be superior to the previously developed MLR model, with an improved R2 for most constituents. Through the ANN model, one was able to see some non-linear e ects of multi variables on pollutant concentration that, otherwise, would not have been possible with a typical MLR model. For example, the results showed that copper EMC is more sensitive at higher Annual Average Daily Trac (AADT), with respect to ADP, compared with lower range AADT.


Optical and Structural Properties of Copper Doped CdS Thin Films Prepared by Pulsed Laser Deposition
 
        S.M. Mahdavi (PhD.)
  • A. Irajizad [PhD.]
  • A. Azarian [PhD.]
  • R.M. Tilaki [PhD.]

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This paper presents the study of the structural and optical properties of copper doped cadmium sul de thin lms prepared by pulsed Nd:YAG laser. The copper concentration in the targets was varied from 0.05% to 5% in weight and they were heated at a temperature of 500C in air for one hour. It was observed that annealing un-doped and doped thin lms at temperatures above 160C leads to an abrupt increase in the optical transmission, changing from dark brownish to transparent yellowish. For annealed samples at 300C, increasing Cu concentration from 0.0% to 2%, leads to an increase in the optical transmission up to 80%, at a wavelength of about 700 nm. XRD patterns showed the hexagonal phase of cadmium sul de and a number of CdO peaks relating to the partial oxidation of cadmium. The XPS spectra of the annealed samples indicate an accumulation of Cu at the surface. Therefore, Cu impurity can enhance CdS oxidation and the size of the crystallites. The highest value of the photo-current for the samples is related to the lowest Cu concentration, i.e: 0.05%.


Fuzzy Hierarchical Queueing Models for the Location Set Covering Problem in Congested Systems
 
        H. Mahlooji (PhD.)
  • H. Shavandi [PhD.]

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In hierarchical service networks, facilities at di erent levels provide di erent types of service. For example, in health care systems, general centers provide low-level services, such as primary health care, while specialized hospitals provide high-level services. Because of the demand congestion at service networks, the location of servers and their allocation of demand nodes can have a strong impact on the length of the queue at each server, as well as on the response time to service calls. This study attempts to develop hierarchical location-allocation models for congested systems by employing a queueing theory in a fuzzy framework. The parameters of each model are approximately evaluated and stated as fuzzy-numbers. The coverage of demand nodes is also considered in an approximate manner and is stated by the degree of membership. Using queueing theory and fuzzy conditions, both referral and nested hierarchical models are developed for the Location Set Covering Problem (LSCP). To demonstrate the performance of the proposed models, a numerical example is solved in order to compare the results obtained from the existing probabilistic models and the new fuzzy models developed in this paper.


Numerical Simulation of Buoyancy A ected Turbulent Air Flow in a Room
 
        A. Nouri-Borujerdi (Professor)
  • A. Fathi-Gishnegani [PhD.]

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In this paper, a three-dimensional steady state incompressible turbulent air ow is considered in a large single room. The buoyancy a ected turbulent air ow is numerically simulated by solving governing equations. The turbulence modeling includes both k 􀀀 " and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects, such as displacement of radiator system performance, temperature and ow eld distribution and comfort conditions. The results show that the best temperature distribution and comfort condition are obtained when the radiator is installed under the window and its height is equal to or greater than that of the window.


Unaxisymmetric Heat Transfer in the Axisymmetric Stagnation-Point Flow of a Viscous Fluid on a Cylinder with Simultaneous Axial and Rotational Movement Along with Transpiration
 
        A.B. Rahimi (PhD.)
  • R. Saleh [PhD.]

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The unaxisymmetric heat transfer of an unsteady viscous ow, in the vicinity of an axisymmetric stagnation-point of an in nite circular cylinder, with simultaneous axial and rotational movement, along with transpiration, Uo, is investigated, when the angular velocity, axial velocity and wall temperature or wall heat ux vary arbitrarily with time. The impinging free stream is steady and with a strain rate of k. An exact solution of the Navier-Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained by the use of appropriate transformations for the most general case, when the transpiration rate is also time-dependent. However, results are presented only for uniform values of this quantity. The general self-similar solution of unsteady unaxisymmetric heat transfer is obtained, in which unaxisymmetry is due to the sinusoidal variation of the temperature, with respect to the surface position of the rotating cylinder, and unsteadiness is because of the sinusoidal variation of the temperature of each point of the cylinder surface, with respect to time and, also the rotation of the cylinder. All the solutions are presented for Reynolds numbers, Re = ka2=2, ranging from 0.1 to 10.0 for di erent values of Prandtl number and selected values of the dimensionless transpiration rate, S = U0=ka, where a is the cylinder radius and  is the kinematic viscosity of the uid. The local coecient of heat transfer (Nusselt number) is found to be independent of time and place, though the cylinder wall temperature or wall heat ux are both functions of time and place.


Strong Ground Motion E ects on Seismic Response Reduction by TLCDs
 
        S.M. Zahrai (PhD.)
  • A. Kavand [PhD.]

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Nowadays, various types of passive control systems are being used as an e ective solution to reduce the seismic responses of structures. One type of these systems, the Tuned Liquid Column Damper (TLCD), suppresses the input seismic energy by a combined action, including the movement of liquid mass in the container, a restoring force on the liquid, due to gravity loads, and the damping, due to liquid movement through the ori ces. In this paper, the possible e ects of seismic excitation characteristics, such as frequency content and soil condition, on the seismic performance of TLCDs, are investigated, using nonlinear time-history analyses. For this purpose, a ten-story building was modeled as an elastic MDOF structure and used for numerical analyses. For the time-history analyses, among the past strong ground motion records of Iran, 16 records with di erent characteristics were selected. The results of this study show that these characteristics play a substantial role in the performance of TLCDs and they should be, accordingly, considered in the designing of TLCDs. In some cases, TLCD is able to reduce structural displacement up to 50%, while, in most cases, the e ectiveness of TLCD in reducing structural acceleration is not signi cant. However, it should be mentioned that, in real applications, de-tuning may occur, due to the inelastic behavior of structures, which can reduce e ectiveness. This study also shows that the displacement reduction capacity of TLCDs is highly dependent on excitation characteristics, while the acceleration reduction capacity is not that sensitive.