Showing 29 results for Finite Element
A. F. Nateghi, A. Vasseghi, and V. L. Shahsavar,
Volume 25, Issue 1 (7-2006)
Abstract
Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake
events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage.
In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.
A. R. Safari, M. Ghayour, and A. Kabiri,
Volume 25, Issue 1 (7-2006)
Abstract
It is empirically established that, due to a number of factors involved, a classical (linear) analysis of buckling pressure is impossible. Nonlinear theories of buckling are, therefore, required that involve effective factors such as imperfections and welding effects. In this study, models are developed which are as close to allowable standard deviations as possible. In the next stage, their buckling behavior is investigated both experimentally and numerically using finite element packages ADINA, ANSYS, COSMOS, and MARC based on specific capabilities of each. Results show that reasonable estimates of real buckling pressure will become possible when material and geometrical nonlinearities and initial imperfections are introduced into the analytical system. Finally, in the light of the results obtained, a submarine pressure hull is analyzed.
S. Hatami, M. Azhari, and M.m. Saadatpour,
Volume 26, Issue 1 (7-2007)
Abstract
Based on classical plate theory, standard and spectral finite element methods are extended for vibration and dynamic stability of axially moving thin plates subjected to in-plane forces. The formulation of the standard method earned through Hamilton’s principle is independent of element type. But for solving numerical examples, an isoparametric quadrilateral element is developed using Lagrange interpolation functions. The spectral method is, in fact, the solution of motion equation for an axially moving plate. Although this method has some limitations concerning boundary condition of plate and in-plane forces, it leads to an exact solution of free vibration and stability of plates travelling on parallel rollers. The method can be used as a benchmark of accuracy of other numerical methods.
M. R. Forouzan, and I. Salehi,
Volume 26, Issue 1 (7-2007)
Abstract
In this paper, properties of slab deformation in sizing press mill as one of the slab reduction processes in hot rolling mills have been evaluated using the elastoviscoplastic finite element method with explicit formulation. Effect of prarameters such as initial slab width and thickness, reduction, feed pitch, and anvil speed on factors such as dogbone formation, head and tail fishtail profile, width necking at the leading end of slab, and slab edge quality have been studied. Furthermore, a comparison has been made between the two common width reduction methods, i.e. Vertical Rolling (Edging) and sizing Press, in order to determine their differences and the efficiency of each process. The amount of width return (back spread), one of the most important factors related to width reduction efficiency and also slab formation after the first horizontal rolling pass, has been evaluated. Also, in order to validate the applied finite element method, the results obtained have been compared with experimental ones found in the literature. The results show that deformation in sizing press is more favourable and that its efficiency is better than that of the vertical rolling mill.
M. Salimi, M. Jamshidian, A. Beheshti, and A. Sadeghi Dolatabadi,
Volume 26, Issue 2 (1-2008)
Abstract
The mechanical behavior of cold rolled sheets is significantly related to residual stresses that arise from bending and unbending processes. Measurement of residual stresses is mostly limited to surface measurement techniques. Experimental determination of stress variation through thickness is difficult and time-consuming. This paper presents a closed form solution for residual stresses, in which the bending-unbending process is modeled as an elastic-plastic plane strain problem. An anisotropic material is assumed. To validate the analytical solution, finite element simulation is also demonstrated. This study is applicable to analysis of coiling-uncoiling, leveling and straightening processes.
F. Daneshmand, M. Farid, and M.j. Kazemzadeh-Parsi,
Volume 27, Issue 2 (1-2009)
Abstract
In this paper, a modification on the fixed grid finite element method is presented and used in the solution of 2D linear elastic problems. This method uses non-boundary-fitted meshes for the numerical solution of partial differential equations. Special techniques are required to apply boundary conditions on the intersection of domain boundaries and non-boundary-fitted elements. Hence, a new method is also presented for the computation of stiffness matrix of boundary intersecting elements and boundary conditions of higher accuracy are applied. In order to examine the applicability of the proposed method, some
numerical examples are solved and the results are compared with those obtaioned from both fixed grid finite element and standard finite element methods.
E. Yari , H. Ghassemi,
Volume 34, Issue 2 (1-2016)
Abstract
The main objective of this paper is to provide an applied algorithm for analyzing propeller-shaft vibrations in marine vessels. Firstly an underwater marine vehicle has been analyzed at different speed in unsteady condition using the finite volume method. Based on the results of this analysis, flow field of marine vehicle (wake of stern) and velocity inlet to the marine propeller is extracted at different times. Propeller inlet flow field is applied in the boundary element code and using this code, marine propeller has been analyzed in unsteady state. In continue, main / lateral forces and moments over the propeller are extracted. Then the data obtained from the boundary element code alongwith exact geometry of the propeller and shaft have been studied, using finite element code. Natural and forced frequency of the propeller have been determined in various modes of vibration. According to obtained data from Finite Element Method (FEM) numerical analysis, maximum displacement of propeller is for displacement of the propeller tip in forced vibration state
E. Fazeli, F. Behnamfar,
Volume 35, Issue 1 (9-2016)
Abstract
In this paper, first the theory of Improved Applied Element Method (IAEM) is proposed and then an appropriate algorithm and software are developed for analyzing structures behavior until collapse by this method. Then, some examples of structural analysis by the above method and a software developed for this study are presented. The results show that IAEM has the ability to solve the discussed problems more accurately in less time than Finite Element Method (FEM). Moreover, the efficiency of the method for solving large displacements problems is enhanced in this research by introducing nonlinear response indicators. For modification of the stiffness matrix in the nonlinear range, a new method is presented that increases the accuracy of calculation up to 30%.
R. Naderi, A. Khademalrasoul,
Volume 35, Issue 1 (9-2016)
Abstract
This study shows how to create different types of crack and discontinuities by using isogeometric analysis approach (IGA) and extended finite element method (XFEM). In this contribution, two unique features of isogeometric analysis approach are utilized to create discontinuous zones. Discontinuities consist of crack and cohesive zone. In isogeometric analysis method NURBS is used to approximate both geometry and primary variable. NURBS can create quadratic shapes exactly. Also, stress intensity factors are calculated in the vicinity of the crack tips for two dimensional problems and are compared with corresponding analytical and numerical counterparts. Extended finite element method is the other numerical method which is used in this work. The enrichment procedure is utilized in extended finite element method to create discontinuities. The well-known path independent J-integral approach is used in order to calculate the stress intensity factors. Also, in mixed mode situation, the interaction integral (M-integral) is considered to calculate the stress intensity factors. Results show that isogeometric analysis method has desirable accuracy as it uses lower degree of freedoms and consequently lower computational efforts than extended finite element method. In addition, creating the internal cohesive zone as one of the most important issues in computational fracture mechanics is feasible due to the special features of isogeometric analysis. The present study demonstrates the capability of isogeometric analysis parametric space to control the inter-element continuity and create the cohesive zone.
M. S. Eskandarjuy , A. Baghlani,
Volume 35, Issue 2 (2-2017)
Abstract
In this paper, wave propagation method was applied to detect damage of structures. Spectral Finite Element Method
(SFEM) was used to analyze wave propagation in structures. Two types of structures i.e. rod and Euler-Bernoulli beam were
modelled using spectral elements. The advantage of spectral finite element over conventional Finite Element Method (FEM), in
wave propagation problems, is its accuracy and lower computational time. Two examples of rod and Euler-Bernoulli beam with
embeded concentrated mass were presented to illustrate the superiority of SFEM to FEM. Finally, a cracked beam was modeled
and analyzed using spectral finite elements and the location of the crack was determined using time history response of beam
structure.
M. Mohammadimehr, S. Alimirzaei,
Volume 36, Issue 2 (3-2018)
Abstract
In this research, the nonlinear buckling analysis of Functionally Graded (FG) nano-composite beam reinforced by various distributions of Boron Nitrid Nanotube (BNNT) is investigated under electro-thermodynamical loading with considering initial geometrical imperfection. The analysis is performed based on nonlocal elasticity theory and using the Finite Element Method (FEM). Various distributions of BNNT along the beam’s thickness are considered as uniform and decreasing-increasing functionally graded; and the extended mixture model is used to estimate the properties of nano-composite beam. The elastic medium around the smart nano-composite beam is modeled as elastic foundation. The governing equations of equilibrium are derived using energy method and nonlocal elasticity theory; and the critical buckling load is obtained for various boundary conditions such as simply-simply supported (S-S) and clamped-clamped (C-C) using the FEM. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of nano-composite beam increases and consequently the stability of the system increases. The effect of FG-X distribution type is more than uniform distributions. Also, the critical buckling load of nano-composite beam increases with an increase in the electric field and elastic foundation.
B. Sadeghian, M. Ataapour, A. Taherizadeh,
Volume 36, Issue 2 (3-2018)
Abstract
Friction stir welding is of the most applicable methods to join dissimilar metals. In this study, the thermal distribution during the joining of 304 stainless steel and 5083 aluminum alloy by friction stir welding method was simulated by the finite element method. Both, transient and stationary thermal solutions were used in the simulations and the two methods were compared correspondingly. To verify the model, two sheets of stainless steel and aluminum were prepared and the friction stir welding was applied. Additionally, by using thermocouples temperature, the history of points on the sheets was obtained during welding. Then, the simulation and the experimental results were compared to validate the model. Finally, an artificial neural network model was created and the effect of different input parameters on the maximum temperature under the tool was investigated.
Aliakbar Taghipour, J. Parvizian, S. Heinze, A. Duester, E. Rank,
Volume 37, Issue 1 (9-2018)
Abstract
finite cell method, are employed to compute a series of benchmark problems in the finite strain von Mises or J2 theory of plasticity. The hierarchical (integrated Legendre) shape functions are used for the finite element approximation of incompressible plastic dominated deformations occurring in the finite strain plasticity of ductile metals. The computational examples include the necking under uniaxial tension with notched and un-notched samples and the compression of a perforated plate. These computations demonstrate that the high-order finite element methods can provide a locking-free behavior with a pure displacement-based formulation. They also provide high convergence rates and robustness against high mesh distortions. In addition, it is shown that the finite cell method, on the top of the aforementioned advantages, provides easy mesh generation capabilities for highly complex geometries. The computational results are verified in comparison with the results obtained using a standard low-order finite element method known as the F-bar method. The numerical investigations reveal that both methods are good candidates for the plasticity analysis of engineering materials and structures made up of ductile materials, particularly those involving complex geometries.
F. Shirmohammadi, M. M. Saadatpour,
Volume 37, Issue 1 (9-2018)
Abstract
In this article spectral modal method is developed for studying wave propagation in thin plates with constant or variable thickness. Theses plates are subjected to the impact forces and different boundary conditions. Spectral modal method can be considered as the combination of Dynamic Stiffness Method (DSM), Fourier Analysis Method (FAM) and Finite Stripe Method (FSM). Using modeling of continuous distribution of mass and an exact stiffness causes solutions in frequency domain. Unlike the most numerical methods, in this method refining meshes is no longer necessary in which the cost and computational time is decreased. In this paper the important parameters of the method and their effects on results are studied through different examples.
M. Jafari, M. Jamshidian, S. Ziaei-Rad,
Volume 37, Issue 2 (3-2019)
Abstract
The stored deformation energy in the dislocation structures in a polycrystalline metal can provide a sufficient driving force to move grain boundaries during annealing. In this paper, a thermodynamically-consistent three-dimensional, finite-strain and dislocation density-based crystal viscoplasticity constitutive theory has been developed to describe the distribution of stored energy and dislocation density in a polycrystalline metal. The developed constitutive equations have been numerically implemented into the Abaqus finite element package via writing a user material subroutine. The simulations have been performed using both the simple Taylor model and the full micromechanical finite element model. The theory and its numerical implementation are then verified using the available data in literature regarding the physical experiments of the single crystal aluminum. As an application of the developed constitutive model, the relationship between the stored energy and the strain induced grain boundary migration in aluminum polycrystals has been investigated by the Taylor model and also, the full finite element model. The obtained numerical results indicated that the Taylor model could not precisely simulate the distribution of the stored deformation energy within the polycrystalline microstructure; consequently, the strain induced grain boundary migration. This is due to the fact that the strain induced grain boundary migration in a plastically deformed polycrystalline microstructure is principally dependent on the spatial distribution of the stored deformation energy rather than the overall stored energy value.
H. Arzani, E. Khoshbavar Rad,
Volume 37, Issue 2 (3-2019)
Abstract
In this paper, a method is proposed to improve the results of the standard finite element method. L2 norm is used to determine the nodal error. In the next step, the appropriate order of the interpolation cover is seclected to be proportional to the nodal error and the results are corrected. The error computation procedure and the use of covering enrichment functions will continue until the error reaches the specified value. Cover enrichment interpolation functions will consider the effects of the adjacent elements of each node, in addition to the values obtained from the standard interpolation for each element. Computation rules are programmed in the matlab program and considered for the same examples. Comparison of the results of the proposed method with the exact solutions and the results of the methods proposed by the other researchers in the field of linear elasticity indicates the efficiency and accuracy of the proposed method.
I. Ahmadi, D. Kouhbor, R. Taghiloo,
Volume 38, Issue 1 (8-2019)
Abstract
In this paper, a finite element model is presented for the transient analysis of low velocity impact, and the impact induced damage in the composite plate subjected to low velocity impact is studied. The failure criteria suggested by Choi and Chang and the Tsai-Hill failure criteria are used for the prediction of the damage in the composite plate; then the effect of various parameters on the impact induced damage is investigated. The first order shear deformation plate theory and the Ritz finite element method are employed for modeling the behavior of plate, and the modified Hertz contact low is used for the prediction of the contact force through the impact. In the numerical results, the time history of indentation, contact force and stress during the impact and the impact induced damage is investigated. The matrix cracking and delamination in the plies of the laminated composite plate subjected to low velocity impact are studied and the effects of various parameters are investigated.
S. A. Ghazi Mirsaeed, V. Kalatjari,
Volume 38, Issue 1 (8-2019)
Abstract
In this paper, finite element analysis of thin viscoelastic plates is performed by proposing new plate elements using complex Fourier shape functions. New discrete Kirchhoff Fourier Theory (DKFT) plate elements are constructed by the enrichment of quadratic function fields in a six-noded triangular plate element with complex Fourier radial basis functions. In order to illustrate the validity and accuracy of the presented approach and robustness of the proposed elements in viscoelasticity, finite element analysis of square and elliptical viscoelastic thin plates is performed and the results are compared to those of analytical solutions and with those obtained by discrete Kirchhoff Theory (DKT) elements and the commercial software ABAQUS. The results show that FE solutions using DKFT elements have an excellent agreement with the analytical solutions and ABAQUS solutions, even though noticeably fewer elements, in comparison to DKT and classic plate elements, are employed, which means that the computational costs are reduced effectively.
M. Jamei, H. R. Ghafouri,
Volume 38, Issue 2 (2-2020)
Abstract
In this study, we present a numerical solution for the two-phase incompressible flow in the porous media under isothermal condition using a hybrid of the linear lower-order nonconforming finite element and the interior penalty discontinuous Galerkin (DG) method. This hybridization is developed for the first time in the two-phase modeling and considered as the main novelty of this research.The pressure equation and convection dominant saturation equation are discretized using the nonconforming Crouziex-Raviart finite element (CR FEM) and the weighed interior penalty discontinuous Galerkin (SWIP) method, respectively. Utilizing the nonconforming finite element method for solving the flow equation made the pressure and velocity values be consistent with respect to the degrees of freedom arrangement at the midpoint of the neighboring element edges. The boundary condition governing the simulation is the Robin type at entrance boundaries, and the time marching discretization for the governing equations is the sequential solution scheme. An H (div) projection using Raviart-Thomas element is implemented to improve the results’ resolution and preserve the continuity of the normal component of the velocity field. At the end of each time step, the non-physical oscillation is omitted using a slope limiter, namely, modified Chavent-Jaffre limiter, in each element. Also, in this study, the developed algorithm is verified using some benchmark problems and the test cases are considered to demonstrate the efficiency of the developed model in capturing the shock front at the interface of fluid phases and discontinuities.
O. Bateniparvar, N. Noormohammadi, A. M. Salehi,
Volume 39, Issue 2 (2-2021)
Abstract
In this paper, Equilibrated Singular Basis Functions (EqSBFs) are implemented in the framework of the Finite Element Method (FEM), which can approximately satisfy the harmonic PDE in homogeneous and heterogeneous media. EqSBFs are able to automatically reproduce the terms consistent with the singularity order in the vicinity of the singular point. The newly made bases are used as the complimentary enriching part along with the polynomial bases of the FEM to construct a new set of shape functions in the elements adjacent to the singular point. It will be shown that the use of the combined bases leads to the quality improvement of the solution function as well as its derivatives, especially in the vicinity of the singularity.
