Search for: finite-element-models
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    Biophysical implications of lipid bilayer rheometry for mechanosensitive channels

    , Article Proceedings of the National Academy of Sciences of the United States of America ; Vol. 111, Issue. 38 , 2014 , Pages 13864-13869 Bavi, N ; Nakayama, Y ; Bavi, O ; Cox, C. D ; Qin, Q. H ; Martinac, B ; Sharif University of Technology
    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... 

    A poroelastic finite element model to describe the time-dependent response of lumbar intervertebral disc

    , Article Journal of Medical Imaging and Health Informatics ; Volume 1, Issue 3 , 2011 , Pages 246-251 ; 21567018 (ISSN) Nikkhoo, M ; Haghpanahi, M ; Wang, J. L ; Parnianpour, M ; Sharif University of Technology
    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.... 

    Prediction of machining chatter in milling based on dynamic FEM simulations of chip formation

    , Article Advances in Manufacturing ; Volume 6, Issue 3 , 2018 , Pages 334-344 ; 20953127 (ISSN) Jafarzadeh, E ; Movahhedy, M. R ; Khodaygan, S ; Ghorbani, M ; Sharif University of Technology
    Shanghai University Press  2018
    Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to investigate the effects of various machining parameters on this phenomenon. The dynamic properties of the machine tool at the tool tip are obtained based on experimental modal analysis, and are used in the model as the cutter dynamics. The model allows for the natural development of vibration as the result of the chip-tool engagement, and accounts for various phenomena that occur at the chip-tool interface ultimately leading to stable or unstable cutting. The... 

    An integrated software environment for finite element simulation of powder compaction processes

    , Article Journal of Materials Processing Technology ; Volume 130-131 , 2002 , Pages 168-174 ; 09240136 (ISSN) Khoei, A. R ; Sharif University of Technology
    In this paper, an integrated software environment is demonstrated for computational simulation of powder forming processes. The powder compaction software, PCS_SUT, is designed in both popularity and functionality with the development of user-friendly pre- and post-processing software. Pre-processing software is used to create the model, generate an appropriate finite element grid, apply the appropriate boundary conditions, and view the total model. Post-processing provides visualization of the computed results. In PCS_SUT, a numerical model is developed based on a Lagrangian finite element formulation for large deformations, a cap plasticity theory for non-linear behaviour of material, and... 

    Muscle force evaluation and the role of posture in human lumbar spine under compression

    , Article European Spine Journal ; Volume 11, Issue 6 , 2002 , Pages 519-526 ; 09406719 (ISSN) Shirazi Adl, A ; Sadouk, S ; Parnianpour, M ; Pop, D ; El-Rich, M ; Sharif University of Technology
    Using two nonlinear finite element models of the lumbar spine, the concept of optimal posture is explored by minimizing the segmental sagittal moments required for the equilibrium of the passive lumbar spine under a total of 2800 N axial compression while varying the pelvic tilt and lumbar lordosis. The redundant active-passive system is subsequently solved for this posture using a novel kinematics-based muscle calculation algorithm along with minimization approach. Some flattening in the lumbar spine substantially reduces the required moments and internal passive shear forces under 2800 N axial compression force. Small muscle forces are calculated for this optimal posture. The role of... 

    A new analysis method of the dry sliding wear process based on the low cycle fatigue theory and the finite element method

    , Article Journal of Materials Engineering and Performance ; Vol. 23, issue. 3 , 2014 , pp. 1096-1106 ; ISSN: 10599495 Abdi, M ; Taheri, A. K ; Bakhtiarydavijani, A ; Sharif University of Technology
    In the present work, a combination of a dynamic explicit finite element model and the low cycle fatigue theory is used to simulate the steady-state abrasive wear occurring between an as-cast eutectoid steel and a carbide-tungsten disk. While the low cycle fatigue theory has been used to model wear in softer non-ferrous alloys, this work shows its applicability and accuracy for use in harder alloys, such as the eutectoid steel used in this research which is strengthened with added chromium. The novelty of this work lies in calculating the Manson-Coffin relation constants from a coupled finite element model with experimental tests instead of the previously used Slip line method. The D... 

    Nonlinear finite element modeling of shear-critical reinforced concrete beams using a set of interactive constitutive laws

    , Article International Journal of Civil Engineering ; Volume 14, Issue 8 , 2016 , Pages 507-519 ; 17350522 (ISSN) Broujerdian, V ; Kazemi, M. T ; Sharif University of Technology
    Iran University of Science and Technology  2016
    Complex nature of diagonal tension accompanied by the formation of new cracks as well as closing and propagating preexisting cracks has deterred researchers to achieve an analytical and mathematical procedure for accurate predicting shear behavior of reinforced concrete, and there is the lack of a unique theory accepted universally. Shear behavior of reinforced concrete is studied in this paper based on recently developed constitutive laws for normal strength concrete and mild steel bars using the nonlinear finite element method. The salient feature of these stress-strain relations is to account the interactive effects of concrete and embedded bars on each other in a smeared rotating crack... 

    Stress softening and permanent deformation in human aortas: Continuum and computational modeling with application to arterial clamping

    , Article Journal of the Mechanical Behavior of Biomedical Materials ; Volume 61 , 2016 , Pages 600-616 ; 17516161 (ISSN) Fereidoonnezhad, B ; Naghdabadi, R ; Holzapfel, G. A ; Sharif University of Technology
    Elsevier Ltd  2016
    Inelastic phenomena such as stress softening and unrecoverable inelastic deformations induced by supra-physiological loading have been observed experimentally in soft tissues such as arteries. These phenomena need to be accounted for in constitutive models of arterial tissues so that computational models can properly predict the outcome of interventional procedures such as arterial clamping and balloon angioplasty that involve non-physiological tissue loading. Motivated by experimental data, a novel pseudo-elastic damage model is proposed to describe discontinuous softening and permanent deformation in arterial tissues. The model is fitted to experimental data and specific material... 

    Experimental and finite element study of the reverse faulting effects on buried continuous steel gas pipelines

    , Article Soil Dynamics and Earthquake Engineering ; Volume 86 , 2016 , Pages 1-14 ; 02677261 (ISSN) Hojat Jalali, H ; Rahimzadeh Rofooei, F ; Khajeh Ahmad Attari, N ; Samadian, M ; Sharif University of Technology
    Elsevier Ltd 
    Permanent ground displacement (PGD) caused by surface faulting is considered as one of the most significant hazards affecting buried pipelines. Pipelines crossing reverse-slip faults are subjected to compressive actions (stresses and strains) which can result in buckling of the pipe. In current work, the results obtained from the full-scale laboratory testing and finite element analyses of 4″ (114.3 mm) and 6″ (168.3 mm) steel gas pipes (without internal pressure) buried inside a split box and subjected to a reverse faulting of 0.6 m (pure dip-slip) are presented. These pipes are commonly used in gas distribution lines and networks. The experimental setup, procedure and instrumentation as... 

    Numerical parametric investigation of hysteretic behavior of steel-reinforced elastomeric bearings under large shear deformation

    , Article Structures ; Volume 26 , August , 2020 , Pages 456-470 Khaloo, A ; Maghsoudi Barmi, A ; Ehteshami Moeini, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Steel Reinforced Elastomeric Bearings (SREB) are mostly designed and used for providing different supporting conditions under service loads; while recent studies have shown remarkable characteristics which help them as a cost-effective isolation system. However, little investigation has been carried out to indicate the influence of parameters affecting the mechanical properties of the bearings under large shear deformations (i.e., the seismic performance as an isolation system). A comparative parametric study was conducted herein through finite element modeling of SREBs. The implemented model was also verified by experimental test results. The hysteretic behavior was studied in both cases of... 

    Finite Element Simulation of Nanoindentation and Nanoscratch Tests on Nanocoatings

    , M.Sc. Thesis Sharif University of Technology Nazemian, Mohsen (Author) ; Farrahi, Gholamhossein (Supervisor) ; Fallah Rajabzadeh, Famida (Co-Advisor)
    Coatings are used in order to prevent wear, corrosion, thermal gradient reduction, surface strength improving and many other applications in industries. One of the common applications of coatings, is to prevent wear and surface abrasion. Hardness and friction coefficients are two parameters that determine the wear properties of a coating. Determining these parameters in very thin films is only possible by nanoindentation and nanoscratch tests. Surface hardness, young modulus and fracture toughness can be obtained using nanoindentation and friction coefficient is calculated from nanoscratch.
    Finite element method is widely used for simulating the nanoindentation and nanoscratch... 

    Parametric Finite Element Modeling of a Lumbar Motion Segment

    , M.Sc. Thesis Sharif University of Technology Ramezanzadeh Koldeh, Masoud (Author) ; Assempour, Ahmad (Supervisor) ; Kasra, Mehran (Supervisor)
    Spinal Column is one of the most important parts of musculoskeletal system. Injuries in this region are so rampant and causing vast expense. Risk factors related to spine injuries included personal related ones such as age, sex, muscles’ strength and career related ones such as body positions at work place and loads.
    Since in vivo measurements have many restrictions, developing biomechanical models that simulate the response of a person to given loads and conditions have important role in preventing injuries and improving working conditions.
    In the present study, the parametric model of lumbar motion segment is presented, for this purpose, 12 different CT scan pictures were analyzed... 

    An Investigation into the Wear of an Eutectoid Steel Based on the Low-Cycle Fatigue Theory with the Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Abdi, Mohammad (Author) ; Karimi Taheri, Ali (Supervisor)
    In sliding wear, the process of making debris takes place with different mechanisms. Previous works estimating the wear rate have been carried out based on contact mechanics and material failure mechanisms. In present work, the possibility of existence of low-cycle fatigue as the dominant mechanism in the wear of an as-cast eutectoid steel is investigated. Moreover, wear coefficient and the the volume loss per distance of that steel was predicted. At first, wear tests were done in order to obtain the wear trend of the steel in different loads. Then, regarding the roughness of the disk surface, a finite element model was built to simulate the sliding of the pin surface over the asperities... 

    Design and Modelling of a Piezoelectric Accelerometer and Fabricating a Single Axis Accelerometer Prototype

    , M.Sc. Thesis Sharif University of Technology Ghorbani, Mohamad (Author) ; Vossoughi Vahdat, Gholamreza (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
    Nowadays, in many of industrial processes, it’s necessary to measure acceleration of a moving object. Among the different type of accelerometers, the piezoelectric type are most useful and the most widely used. These sensors come in various configurations.
    In the past, analytical and semi-empirical models have been used to design piezoelectric accelerometers. In these methods, based on some assumptions, the accelerometer nonlinear model is replaced with a linear model and the equivalent circuit model has been used to model accelerometer behavior. In these methods, the behavior of accelerometer become different from the expected one.
    Recently, with the invention of efficient computing... 

    Analytical investigation on fundamental electrical characteristics of large air-gap superconducting synchronous machine

    , Article Journal of Magnetics ; Volume 18, Issue 3 , 2013 , Pages 260-267 ; 12261750 (ISSN) Yazdanian, M ; Elhaminia, P ; Zolghadri, M. R ; Fardmanesh, M ; Sharif University of Technology
    In this paper a general 2-D model of a large air-gap synchronous machine either with non-magnetic or magnetic core rotor is investigated and electrical characteristics of the machine are analytically calculated. Considering the general model, analytical equations for magnetic field density in different regions of the large air-gap machine are calculated. In addition, self and mutual inductances in the proposed model of the machine have been developed, which are the most important parameters in the electromagnetic design and transient analysis of synchronous machines. Finite element simulation has also been performed to verify the obtained results from the equations. Analytical results show... 

    Corrigendum to: "parametric analyses on the initial stiffness of flush end-plate splice connections using FEM" [J. construct. steel res. 64 (2008) 1129-1141] (DOI:10.1016/j.jcsr.2007.09.010)

    , Article Journal of Constructional Steel Research ; Volume 65, Issue 3 , 2009 , Pages 749- ; 0143974X (ISSN) Mohamadi shooreh, M. R ; Mofid, M ; Sharif University of Technology

    A comparison between disturbance observer-based and model-based control of needle in percutaneous applications

    , Article IECON Proceedings (Industrial Electronics Conference), 25 October 2012 through 28 October 2012 ; October , 2012 , Pages 2104-2108 ; 9781467324212 (ISBN) Maghsoudi, A ; Jahed, M ; The Institute of Electrical and Electronics Engineers (IEEE); IEEE Industrial Electronics Society (IES) ; Sharif University of Technology
    In this paper, model-based and distrbance observer (DOB)-based control of needle in precautious applications are compared. In the model-based approach, the force acting on the needle is calculated by evaluating the finite element model (FEM) of the tissue with the tissue deformation. In DOB-based method, the force acting on the needle is considered as an external disturbance and it is estimated using position and velocity of the needle. In both approaches, the calculated/estimated force is used in a sliding mode control scheme to steer the needle to the target. A dynamics equation for the movement of the needle is proposed which includes the force applied by the tissue to the needle. The... 

    Studying the Behaviour and Performance of an Innovative Floating Offshore Platform

    , M.Sc. Thesis Sharif University of Technology Moradkhan, Esmaeil (Author) ; Khonsari, Vahid (Supervisor)
    The objective of this project is to study the behaviour and performance of an innotative floating offshore platform. Such Platform not only can be used for exploring oil from offshore fields, but for creating artificial islands, where land is in short supply. Due to its specific and, at the same time, simple geometry (symmetric), its fabrication does ont involve much complexity. Studies carried out on this platform include the investigation into its structural behaviour under gravitational (including self weight) and bouyancy forces. Studied cases include a number of platforms with different (geometrical) sizes and under 3 various bouyancy conditions (percentage), namely 1) 50% of the height... 

    Comparison of Approximate Methods for Analysis of Arch Dams with Finite Element Methods

    , M.Sc. Thesis Sharif University of Technology Pakzad, Alireza (Author) ; Ghaemian, Mohsen (Supervisor)
    Dams are huge structures in which safety is a very important issue because a failure will result in loss of lives and finance. Several approximate equations for the approximate analysis of arch dams already exist. These equations are usually obtained by considering the behavior of the dam as a shell. Approximate methods are much faster in comparison to the exact methods and give young design engineers who do not have the experience of designing inside view of displacements, stresses and strains. The aim of this project is to compare the results of approximate analysis of arch dams with the results of finite element models and clarify the points of dams in which approximate analysis methods... 

    An Investigation Into Residual Stresses Formed by Bending and Quenching Processes

    , M.Sc. Thesis Sharif University of Technology Ja’afari Bahramabadi, Mohammad (Author) ; Karimi Taheri, Ali (Supervisor)
    Various forms of springs are applicable, among which spiral and leaf springs can be named. Definition of leaf springs is conventionally applied to constant-width springs and is consisted of step-like leaves, each leaf having constant width. Leaf springs are largely used in vehicles, where they act as a part of suspension system supporting the weight of the vehicle along with connecting spots axles to the chassis. Springs so installed are capable of handling starting and stopping torques as well as sudden vibrations due to load carrying. Most Conventional method of manufacturing leaf springs is to bend strips of appropriate steel between curved dies, quench the strip while held between the...