Sharif Digital Repository

A finite element solution procedure is presented for the simulation of transient incompressible fluid flows using triangular meshes. The algorithm is based on the artificial compressibility technique in connection with a dual time-stepping approach. A second-order discretization is employed to achieve the required accuracy in real-time while an explicit multistage Runge-Kutta scheme is used to march in the pseudo-time domain. A standard Galerkin finite element method, stabilized by using an artificial dissipation technique, is used for the spatial discretization. The performance of the proposed algorithm is demonstrated by solving a set of internal and external problems including flows with... 

Coverage is one of the most important parameters which is always used in practice to characterize a shot peening process. At the same time however, it is the most missing parameter in the finite element simulations of this process. This study aims to relate shot peening simulation to the actual coverage that is developed during the process. Accordingly, two important models from literature are re-simulated and their capability to predict an actual coverage is assessed. Results of this study illustrate that full coverage situation is not captured by these models. Thereafter, a random finite element simulation along with a step by step examination of the treated surface is adopted in order to... 

The lipid bilayer plays a crucial role in gating of mechanosensitive (MS) channels. Hence it is imperative to elucidate the rheological properties of lipid membranes. Herein we introduce a framework to characterize the mechanical properties of lipid bilayers by combining micropipette aspiration (MA) with theoretical modeling. Our results reveal that excised liposome patch fluorometry is superior to traditional cell-attached MA for measuring the intrinsic mechanical properties of lipid bilayers. The computational results also indicate that unlike the uniform bilayer tension estimated by Laplace's law, bilayer tension is not uniform across the membrane patch area. Instead, the highest tension... 

In this study, a model is developed to predict austenite phase transformation by means of Avrami's model and the finite element method. For doing so, the Avrami-type rate equation is evaluated with the modified Euler's method to handle the kinetics of phase change under non-isothermal conditions. Also, to simultaneously consider the effect of temperature variations on austenite decomposition, heat conduction equation is solved using a two-dimensional finite element approach. To establish the reliability of theoretical results, a comparison is made between simulated and experimental cooling curves for two grades of carbon steel. © 2003 Elsevier B.V. All rights reserved  

A moving finite element-based inverse method for determining the temperature on a moving surface is developed. The moving mesh is generated employing the transfinite mapping technique. The proposed algorithms are used in the estimation of surface temperature on a moving boundary with high velocity in the burning process of a homogenous low thermal diffusivity solid fuel. The measurements obtained inside the solid media are used to circumvent problems associated with sensor and the receding surface. As the surface recedes, the sensors get swept over by the thermal penetration depth. The produced oscillations occurring in certain intervals in the solution is a phenomenon associated with this... 

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis... 

The vertical stiffness of elastomeric bearing is a dominant parameter of the base isolation design. Several empirical relations have been used to calculate the vertical stiffness of the elastomeric bearing systems, although, in certain conditions such as the presence of rotation, these relations are not accurate enough. In this paper, by using a nonlinear finite element program, the effect of rotation on the vertical stiffness investigated. It was observed that the vertical stiffness of the isolator could be increased or decreased depending on the amount of rotation and the value of lateral displacement limit. © 2019 Elsevier Ltd  

In this paper, the extended finite element method is presented for large elasto-plastic deformation in 3D solid mechanics problems. The X-FEM computational algorithm is presented in the framework of Lagrangian description in order to model the arbitrary interfaces in large deformations. In X-FEM, the material interface is represented independently of element boundaries and the process is accomplished by partitioning the domain with several tetrahedral sub-elements whose Gauss points are used for integration of the domain of elements. The interface between two bodies is modeled by using the X-FEM technique and applying a modified level set enrichment function. In order to simulate the... 

Stent implantation has been regarded as a major strategy to solve gastrointestinal diseases such as biliary obstruction during the last decade. The application of nitinol superelastic stents has been recently considered for minimising such problems as restenosis after stent implantation, the ability to low stent twist, unsuitable dynamic behaviour and inadequate strength radial of stent. In the present article, the effects of material properties on mechanical performance of Z shaped nitinol wire stent under crushing test for clinical applications are studied by finite element modelling. Nitinol stent shows better mechanical and clinical performance after applying 90% crushing, less chronic... 

Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature (A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior  

Stress variations around wellbores and in the reservoirs are of much interest in subsequent drilling operations, future production, and petroleum reservoir development. Stress variations induced by in situ stresses, pore pressure, and temperature changes during drilling operations may lead to various modes of instabilities in forms of induced fractures and borehole breakouts. Previous studies of thermally induced stresses were primarily based on either assumptions of heat conduction through rock matrix or heat convection, in this case, without considering the effect of solid grain thermal conductivity. To analyze wellbore stability, in the present work, a thermo-poro-mechanical model that is... 

An enhanced unfolding inverse finite element method (IFEM) has been used together with an extended strain-based forming limit diagram (FLD) to develop a fast approach to predict the feasibility of tube hydroforming process of concept part and determine where the failure or defects can occur. In tube hydroforming, the inverse IFEM has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this study is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this article a modeling technique has been used to perform the computations in... 

The first step to locate Partial Discharge in power transformers is to find a model that can clearly explain the behavior of the winding in high-frequency. The detailed model is one of the models used for the study of PD. One of the fundamental problems of the described model is to find its parameters. And the accuracy in calculating these parameters has significant impact on reducing the simulation error and PD locating. The current paper seeks to calculate the parameters of the detailed model 20kv distribution transformer winding by using the finite element method (FEM). Comparing the results of this model with pulse waveforms obtained from the PD to the winding in the laboratory... 

The present study aims to challenge the existing finite element models in terms of one of the most important practical parameters, i.e. coverage. Important models from the literature are re-simulated and their resulted treated surfaces are carefully examined. Result of this study shows that existing finite element models could not reflect the realistic coverage. A variable dimension symmetry cell is developed in order to acquire full coverage and at the same time not increasing the computational cost. This model can successfully simulate the surface nanocrystallization by severe shot peening in which the amount of coverage is much higher than conventional shot peening  

Investigation of the relationship between different types of mechanical loading and the failure of the intervertebral disc requires a well-defined finite element model. The objective of this paper was to develop and validate a nonlinear axisymmetric poroelastic finite element model of intervertebral disc and show its capability for studying the time-dependent response. After presenting the poroelastic model of intervertebral disc, the results of prolonged (short-term and long-term creep tests) and cyclic loading were compared with in vivo and in vitro experimental data. The trends predicted by FE model agreed well with measured experimental data and showed its validity for dynamic analysis.... 

This paper presents a comprehensive design procedure of a brushless DC limited angle torque motor (LATM) based on magnetic equivalent circuit analysis which predicts its performance and magnetic characteristics. Design of toroidally wounded armature and rotor with two pole tip segments are developed using selected ferromagnetic material and rare earth permanent magnets. Derivation of airgap and other motor dimensions and design parameters with their expressions are given. A finite element analysis verification of designed LATM using a 2D modeling and simulating package is presented. Performance characteristic of analytical model and FEA model of designed LATM is compared which validates the... 

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a 3-D time-stepping finite element method. The effect of the leakage flux of the rotary transformer on the... 

Stent implantation has been regarded as a major strategy to solve gastrointestinal diseases such as biliary obstruction during the last decade. The application of nitinol superelastic stents has been recently considered for minimising such problems as restenosis after stent implantation, the ability to low stent twist, unsuitable dynamic behaviour and inadequate strength radial of stent. In the present article, the effects of material properties on mechanical performance of Z shaped nitinol wire stent under crushing test for clinical applications are studied by finite element modelling. Nitinol stent shows better mechanical and clinical performance after applying 90% crushing, less chronic... 

Gonbad-e Qabus, with a height of 52.8 m that makes it the tallest pure-brick tower in the world, located in the northern part of Iran, represents one of the most magnificent structures of the early Islamic centuries. This structure is still standing among the chaos of urban life and construction, catching the eyes of beholders even from far distances. This paper summarizes the historical and architectural background of this monumental structure and the important restorations carried out mainly in the past century. Various types of existing and potential structural and architectural damages are classified and elaborated in detail, and for each problem, a series of proposed solutions are... 

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a three-dimensional time-stepping finite element method. The effect of the leakage flux of the RT on the excitation...