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Showing 36 results for Finite Element Method

Afshar M.h.,
Volume 1, Issue 2 (12-2003)
Abstract

A least squares finite element method for the .solution of steady incompressible Navier Stokes equations is presented. The Navier-.Stocks equation is first recast into a system of first order partial differential equations with the velocitv. pressure and the vorticity as the main variables. Finite element discretization of the domain introduces a residual in the governing equation which is subsequently minimized in a least squares sense. The method so developed clearly. falls into the minimization category card hence circumventing the L.B.B. condition. Furthermore. the method produces symmetric positive definite matrices which makes the way for using more efficient iterative sobers. A Conjugate Gradient algorithm is, therefore, used for the solution of the resulting .system of linear algebraic equations. To improve the efficiency , of this iterative solver an incomplete Cholesky factorization of the stiffness matrix is used as ct pre-conditioner. Since the storage requirement of the Cholesky factor depends on the bandwidth of matrix. an effective algorithm for the reduction of this bandwidth has also been employed. The application of the method to solve cavity problem and .step flow with different Remolds number is presented to show the applicability of the method to solve practical flows of incompressible fluid The use of both linear and quadratic elements with selective reduced integration is also investigated and the results are presented.
Kheyr Aldin A., Mortezaei A.r.,
Volume 2, Issue 1 (3-2004)
Abstract

Structural walls are used extensively in moderate- and high-rise buildings to resist lateral loads induced by earthquakes. The seismic performance of many buildings is, therefore, closely linked to the behavior of the reinforced concrete walls. The analytical models used in this paper are developed to study the push-over response of T-shaped reinforced concrete walls andinvestigate the influence of the flange walls on laterally loaded walls and nonlinear behavior of shear walls, namely strength, ductility and failure mechanisms. A layered nonlinear finite element method is used to study the behavior of T-shaped and rectangular (barbell) shear walls. This paper introduces a computer program to practically study three-dimensional characteristics of reinforced concrete wall response by utilizing layered modeling. The program is first verified bysimulated and reported experimental response of 3-D reinforced concrete shear walls. Subsequently, a study considering eighteen analytical test specimens of T-shaped and barbell shear walls is carried out. Finally, based on analytical results, a new equation for minimum ratio of shear wall area to floor-plan area is proposed.
Ali Kheyroddin, Hosein Naderpour,
Volume 5, Issue 1 (3-2007)
Abstract

A parametric study is performed to assess the influence of the tension reinforcement index, ( ω = ρ fy /f Bc), and the bending moment distribution (loading type) on the ultimate deformation characteristics of reinforced concrete (RC) beams. The analytical results for 15 simply supported beams with different amounts of tension reinforcement ratio under three different loading conditions are presented and compared with the predictions of the various formulations and the experimental data, where available. The plastic hinge rotation capacity increases as the loading is changed from the concentrated load at the middle to the third-point loading, and it is a maximum for the case of the uniformly distributed load. The effect of the loading type on the plastic rotation capacity of the heavily reinforced beams is not as significant as that for the lightly reinforced beams. Based on the analytical results obtained using the nonlinear finite element method, new simple equations as a function of the tension reinforcement index, ω, and the loading type are proposed. The analytical results indicate that the proposed equations can be used for analysis of ultimate capacity and the associated deformations of RC beams with sufficient accuracy.
Habib Shahnazari, Hosein Salehzadeh, Amin Askarinejad,
Volume 6, Issue 1 (3-2008)
Abstract

Classical soil mechanics involves the study of fully saturated soils. However, many problems encountered in geotechnical engineering practice involve unsaturated soil, in which behavior is significantly different from classical saturated soil. Negative pore pressure and capillary forces develop a virtual cohesion between the grains of semi saturated soils. This kind of cohesion is dependent on different factors such as grain size, saturation degree, soil-water characteristic curve and relative density of the soil. In this research the virtual cohesion of fine silty sand with 5% water content and a saturation degree of 17% is estimated. A vertical slope is constructed and is accelerated in the geotechnical centrifuge until failure. During the test, the model was monitored by a wireless video camera, attached to the strong box. The cohesionless tested sand was unsaturated. Based on the scaling laws and considering parameters such as sample unit weight, failure acceleration and the sample dimensions, a slope stability analysis was performed, and the virtual cohesion generated in the sample was calculated. The factor of safety of the prototype modeled in the centrifuge is calculated either by Finite Element Method and Finite Difference Method by using the resulted virtual cohesion from physical modeling. Results of this research show the validity of physical modeling for calculating the virtual cohesion in unsaturated silty sand.
Hasan Ghasemzadeh,
Volume 6, Issue 2 (6-2008)
Abstract

Solute transport in unsaturated porous media can be viewed as a coupled phenomenon with water

and heat transport, together with mechanical behaviour of media. In this paper, solute transport is formulated

mathematically considering heat and water flow in deformable porous media. Advection, dispersion and

diffusion of chemical species in the liquid phase are considered. Convection and conduction for heat flow is

taken into account. Water flow is considered in both vapour and liquid phases. Equilibrium equation, energy

conservation, mass conservation and linear momentum for water, gas and solute are written and solved

simultaneously using finite element method. The developed model is validated by solving some examples and

comparing results with the results of experimental observation.


Kourosh Shahverdiani, Ali Reza Rahai, Faramarz Khoshnoudian,
Volume 6, Issue 2 (6-2008)
Abstract

Large capacity cylindrical tanks are used to store a variety of liquids. Their Satisfactory

performance during earthquake is crucial for modern facilities. In present paper, the behavior of cylindrical

concrete tanks under harmonic excitation is studied using the finite element method. Liquid sloshing, liquid

viscosity and wall flexibility are considered and additionally excitation frequency, liquid level and tank

geometry is investigated. The results show a value for wall thickness to tank diameter ratio which may be used

as a guide in the consideration of wall flexibility effects.


S.h. Ebrahimi, S. Mohammadi, A. Asadpoure,
Volume 6, Issue 3 (9-2008)
Abstract

A new approach is proposed to model a crack in orthotropic composite media using the extended finite element method (XFEM). The XFEM uses the concept of partition of unity in addition to meshless basic idea of approximating a field variable by its values at a set of surrounding nodes. As a result, higher order approximations can be designed with the same total number of degrees of freedom. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore mesh generating is performed without any consideration of crack conformations for elements and the method has the ability of extending the crack without any remeshing. Furthermore, the type of elements around the cracktip is the same as other parts of the finite element model and the number of nodes and consequently degrees of freedom are reduced considerably in comparison to the classical finite element method. Developed orthotropic enrichment functions are further modified to enable modeling isotropic problems.
A.r. Khaloo, I. Eshghi, P. Piran Aghl,
Volume 8, Issue 3 (9-2010)
Abstract

In this paper the response of cantilevered reinforced concrete (RC) beams with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is SuperelasticShape Memory Alloys (SE SMAs) which contains nickel and titanium elements. The SE SMA is a unique alloy that has the ability to undergo large deformations and return to their undeformed shape by removal of stresses. In this study, different quantities of steel and smart rebars have been used for reinforcement andthe behavior of these models under lateral loading, including their load-displacement curves, residual displacements, and stiffness, were discussed. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the beams and also residual deflections are created in the structure. It is found that by using SMA rebars in RC beams, these materials tend to return to the previous state (zero strain), so they reduce the permanent deformations and also in turn create forces known as recovery forces in the structure which lead into closing of concrete cracks in tensile zone. This ability makes special structures to maintain their serviceability even after a strong earthquake


D. P. Chen, C. X. Qian, C. L. Liu,
Volume 8, Issue 4 (12-2010)
Abstract

 Concrete deformation due to temperature and moisture condition will always develop simultaneously and interactively. The environmentally (hygral and thermally) induced stress and deformation are essential to concrete durability. To simulate the deformation of concrete caused by the coupling effect of temperature and moisture, a numerical simulation approach is proposed comprising analytical process and finite element analysis is proposed based on the mechanism of heat and moisture transfer in porous medium. In analytical method, Laplace transformation and transfer function were used to simplify and solve the coupled partial differential equations of heat and moisture transfer. The hygro-thermal deformation of concrete is numerically simulated by finite element method (FEM) based on the obtained temperature and moisture stress transformed from the solved moisture distribution. This numerical simulation approach avoids the complex eigenvalues, coupling difficulty and low accuracy in other solving method, and also effectively calculates the moisture induced shrinkage which is almost impossible using familiar FEM software. Furthermore, a software named Combined Temperature and Moisture Simulation System for concrete (CTMSoft) was represented and developed by a mix programming of Visual Basic, Matlab and ANSYS. CTMSoft provided a simple and more intuitive interface between user and computer by providing a graphical user interface (GUI). The validity of the numerical simulation approach was verified by two cases analysis.


Saeed Reza Sabbaghyazdi1, Tayebeh Amiri Saadatabadi,
Volume 9, Issue 3 (9-2011)
Abstract

In this research, a novel numerical algorithm is introduced for computation of temperature-induced before crack steady strainstress field in plane-stress problem. For this purpose, two dimensional heat transfer equation and force equilibrium equations are sequentially solved using Galerkin Finite Volume method on identical unstructured triangular meshes when proper convergence for each field is achieved. In this model, a proper thermal boundary condition that is suitable for unstructured triangular meshes is introduced for analysis. Two test cases are used to assess accuracy of thermal and structural modules of the developed solver and the computed results are compared with theirs analytical solution.First, thermal analysis is performed for a rectangular plate which is connected to a supporting body with constant temperature and expose to surrounding liquid at three edges.Second, structural analysis is performed for a plate under distributed loads in two directions. Having obtained acceptable results from thermal and structural modules, thermal stress analysis is performed for a plate with fixed-end condition at one of edges,due to a uniform temperature field and the computational principle stress contours are compared with the Finite Element method results which have been reported in the literatures.


R. Attarnejad, F. Kalateh,
Volume 10, Issue 1 (3-2012)
Abstract

This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.


E. Sanaei, M. Babaei,
Volume 10, Issue 3 (9-2012)
Abstract

Due to the algorithmic simplicity, cellular automata (CA) models are useful and simple methods in structural optimization. In

this paper, a cellular-automaton-based algorithm is presented for simultaneous shape and topology optimization of continuum

structures, using five-step optimization procedure. Two objective functions are considered and the optimization process is

converted to the single objective optimization problem (SOOP) using weighted sum method (WSM). A novel triangle

neighborhood is proposed and the design domain is divided into small triangle elements, considering each cell as the finite

element. The finite element formulation for constant strain triangles using three-node triangular elements is developed in this

article. Topological parameters and shape of the design space are taken as the design variables, which for the purpose of this

paper are continuous variables. The paper reports the results of several design experiments, comparing them with the currently

available results obtained by CA and genetic algorithm in the literature. The outcomes of the developed scheme show the

accuracy and efficiency of the method as well as its timesaving behavior in achieving better results


M. Mortazavi Zanjani, A. Soroush,
Volume 11, Issue 2 (11-2013)
Abstract

This paper presents results of a thorough study on the phenomenon of rupture propagation of reverse faults from the bedrock

foundation through homogeneous clayey embankments, mainly at the end of construction, with complementary analyses for the

steady state seepage through the embankment. The study is performed by means of numerical analyses with a nonlinear Finite

Element Method, verified beforehand through simulating fault propagations in an existing horizontal soil layer experiment.

Multiple cases considering three slopes & three clayey soils for the embankment and five fault dip angles, activated in several

locations of base of the embankment, are analyzed. The results show that ruptures in the embankment follow optimal paths to

reach the surface and their near-surface directions are predictable with respect to corresponding theories of classical soil

mechanics. Various types of rupture in the embankment are produced on the basis of the rupture types, the embankment base is

divided into three distinguishable zones, which can be used for interpretation of fault ruptures behavior. The effects of materials

and slope of the embankment, fault dip angle, and fault’s point of application in the bedrock-soil interface on the rupture paths

are studied in depth.


M. Fadaee, M.k. Jafari, M. Kamalian, M. Moosavi, A. Shafiee,
Volume 11, Issue 2 (11-2013)
Abstract

During past earthquakes, many instances of building damage as a result of earthquake surface fault rupture have been observed.

The results of investigating a potential mitigation scheme are presented in this paper. Such plan provides a wall in the soil with

the aim of surface displacement localization in the narrow pre-determined location. This may reduce the risk of the future rupture

downstream the wall. To evaluate the efficiency of the method, this paper (i) provides validation through successful class “A”

predictions of 1g model tests for fault deviation by weak wall and (ii) conducts sensitivity analyses on fault position, fault offset

and wall shear strength. It is shown that wall can be designed to deviate rupture path even downstream of the wall can be

protected.


A. Tarighat,
Volume 11, Issue 3 (9-2013)
Abstract

Concrete bridge deck damage detection by measurement and monitoring variables related to vibration signatures is one of the main tasks of any Bridge Health Monitoring System (BHMS). Generally damage puts some detectable/discoverable signs in the parameters of bridge vibration behavior. However, differences between frequency and mode shape before and after damage are not remarkable as vibration signatures. Therefore most of the introduced methods of damage detection cannot be used practically. Among many methods it seems that models based on artificial intelligence which apply soft computing methods are more attractive for specific structures. In this paper an Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to detect the damage location in a concrete bridge deck modeled by finite element method. Some damage scenarios are simulated in different locations of the deck and accelerations as representatives of response at some specific points are calculated. Excitement is done by applying an impact load at the center of the deck. In the proposed ANFIS damage detection model accelerations are inputs and location of the damage is output. Trained model by simulated data can show the location of the damage very well with a few training data and scenarios which are not used in training stage. This system is capable to be included in real-time damage detection systems as well.
H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)
Abstract

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
M. Afzalirad, M. Kamalian, M. K. Jafari, A. Sohrabi-Bidar,
Volume 12, Issue 1 (1-2014)
Abstract

In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
J. Nazari Afshar, M. Ghazavi,
Volume 12, Issue 1 (1-2014)
Abstract

The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)
Abstract

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
Kaustav Bakshi, Dipankar Chakravorty,
Volume 12, Issue 2 (6-2014)
Abstract

A review of literature reveals that although singly curved conical shells applicable in many fields of mechanical engineering have been studied by many researchers but doubly curved conoidal shells which are very popular as civil engineering roofing units have not received due attention. Hence relative performances of composite conoidal shells in terms of displacements and stress resultants are studied in this paper under static and dynamic loadings. Free vibration frequencies are also reported. A curved quadratic isoparametric eight noded element is used to model the shell surface. Clamped and simply supported boundary conditions are considered. Results obtained from the present study are compared with established ones to check the correctness of the present approach. A number of additional problems of composite conoidal shells are solved for eight different stacking sequences of graphite-epoxy composite for each of the edge conditions. Uniformly distributed load for static bending analysis and step load of infinite duration for solution of forced vibration problem are considered. The results are interpreted from practical application standpoints and findings that are important for a designer to note, before he decides on the shell combination he will finally adopt among a number of possible options, are highlighted.

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