Search for: multiscale-models
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    A Gradient-Enhanced Computational Homogenization Technique for Multi-Scale Modeling of Heterogeneous Materials with Softening Behavior

    , M.Sc. Thesis Sharif University of Technology Raisi, Alireza (Author) ; Khoei, Amir Reza (Supervisor)
    The use of conventional multi-scale models for materials that exhibit softening behavior is not possible due to the phenomenon of localization, because the fundamental assumptions of homogenization are no longer satisfying around the localization region, and therefore the macro-scale results depend on the size of the representative volume element and the macro-scale mesh discretization. Also, if the finite elements mesh be fine enough, the solution does not converge to acceptable physical values. This research concerns the multi-scale study of failure and proposes an appropriate method for computational homogenization of that. The main idea is to apply the enhanced homogenization method to... 

    Analysis of Delamination in Fiber-reinforced Composite Laminates Using Multiscale Modeling

    , M.Sc. Thesis Sharif University of Technology Abdolmohammadi, Nafiseh (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    This study presents delamination in fiber-reinforced composite laminates by using multiscale modeling. The meso modeling is used to derive the relationship between microcrack density and damage parameters. Next the selected failure model is applied to analyze the macroscale modeling. The progress of failure terms and the reduction of fiber and matrix properties implemented into ABAQUS/Standard, which enables an individual to create a new material behavior through the user subroutine UMAT. In the following, the contours associated with each of the damage parameters are obtained in each of the damage mode. Then for a specific material, the relationship between microcrack density and damage... 

    Temperature-dependent Multiscale Simulation of Heterogeneous FCC Crystals

    , M.Sc. Thesis Sharif University of Technology Jafarian, Navid (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    In this study, a novel multiscale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to illustrate the influence of temperature on mechanical properties of heterogeneous nano-crystalline structures. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. In order to calculate the equivalent lattice parameter, a weight average between the lattice parameters of atomic structures is utilized. The... 

    A Machine Learning-Based Atomistic-Continuum Multi-Scale Modeling of Perfect and Defective Ni-Based Superalloy in Elastoplastic Regions

    , M.Sc. Thesis Sharif University of Technology Kianezhad Tajanaki, Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    In this paper, a machine learning-based atomistic-continuum multi-scale scheme is introduced to model the materials' geometrically and materially nonlinear behavior. The kinematic and energetic consistency principles are employed to link the atomistic and continuum scales. In order to establish the kinematic consistency principle, the periodic boundary condition is implemented for the atomistic RVE. The Ni-based superalloy, including 0 to 3% porosity, is considered for the models. Several parameter analysis is done to distinguish the proper atomistic RVE to be used in multi-scale models. The data set, including the stress-strain samples, is generated through molecular dynamics analysis... 

    A multi-scale modeling of surface effect via the modified boundary Cauchy-Born model

    , Article Materials Science and Engineering C ; Volume 32, Issue 7 , 2012 , Pages 1993-2000 ; 09284931 (ISSN) Khoei, A. R ; Aramoon, A ; Sharif University of Technology
    Elsevier  2012
    In this paper, a new multi-scale approach is presented based on the modified boundary Cauchy-Born (MBCB) technique to model the surface effects of nano-structures. The salient point of the MBCB model is the definition of radial quadrature used in the surface elements which is an indicator of material behavior. The characteristics of quadrature are derived by interpolating data from atoms laid in a circular support around the quadrature, in a least-square scene. The total-Lagrangian formulation is derived for the equivalent continua by employing the Cauchy-Born hypothesis for calculating the strain energy density function of the continua. The numerical results of the proposed method are... 

    Fully coupled hydromechanical multiscale model with microdynamic effects

    , Article International Journal for Numerical Methods in Engineering ; Volume 115, Issue 3 , 2018 , Pages 293-327 ; 00295981 (ISSN) Khoei, A. R ; Hajiabadi, M. R ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    In this paper, a multiscale finite element framework is developed based on the first-order homogenization method for fully coupled saturated porous media using an extension of the Hill-Mandel theory in the presence of microdynamic effects. The multiscale method is employed for the consolidation problem of a 2-dimensional saturated soil medium generated from the periodic arrangement of circular particles embedded in a square matrix, which is compared with the direct numerical simulation method. The effects of various issues, including the boundary conditions, size effects, particle arrangements, and the integral domain constraints for the microscale boundary value problem, are numerically... 

    On the sensitivity of the nanostructural parameters on youngg"s modulus of PLSNs in fully intercalated structures

    , Article Journal of Composite Materials ; Volume 43, Issue 24 , 2009 , Pages 2921-2941 ; 00219983 (ISSN) Zehtab Yazdi, A ; Bagheri, R ; Kazeminezhad, M ; Sharif University of Technology
    Polymer-layered silicate nanocomposites have been observed to demonstrate enhanced mechanical properties particularly at low weight fractions of silicate. Experimental and theoretical investigations reveal that numerous structural parameters strongly influence the modulus of such nanocomposites. A multiscale micromechanical model is developed which considers a wide range of different affecting parameters including the particle aspect ratio, the number of silicate layers per stack, the d-spacing ratio between the layers, the penetration of polymer chains along silicate sheets, the intercalation feature, and the particle volume fraction. The developed model illustrates the accuracy and... 

    Study the effect of viscoelastic matrix model on the stability of CNT/polymer composites by multiscale modeling

    , Article Polymer Composites ; Volume 30, Issue 11 , 2009 , Pages 1545-1551 ; 02728397 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    In this article, a Molecular Structural Mechanics/Finite Element (MSM/FE) multiscale modeling of carbon nanotube/polymer composites with viscoelastic (VE) polymer matrix is introduced. The nanotube is modeled at the atomistic scale using structural molecular mechanics. The matrix deformation is analyzed by nonlinear finite element method considering VE behavior. The nanotube and matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using the MSM/FE multiscale model, we investigate the effect of carbon nanotube (CNT) on the improvement of mechanical stability of the nanocomposite. Also, the buckling behavior of these... 

    New hybrid finite volume-thermal lattice Boltzmann method, based on multi relaxation time collision operator

    , Article International Journal of Heat and Mass Transfer ; Volume 138 , 2019 , Pages 1281-1294 ; 00179310 (ISSN) Salimi, M. R ; Alizadeh Seresht, E ; Taeibi Rahni, M ; Sharif University of Technology
    Elsevier Ltd  2019
    Hybrid FVM-LBM schemes are developed in the past few years to use capabilities of both Navier-Stokes based finite volume method (FVM) and lattice Boltzmann method (LBM) to solve macro-meso multiscale problems. In this scheme, the major task is to develop some lifting relations that reconstruct distribution functions in LBM sub-domain from macroscopic variables and their derivatives. The macroscopic variables are computed using Navier-Stokes based FVM in macroscale sub-domain, while distribution functions are computed using LBM in mesoscale sub-domain. The pioneer works in this area used the single relaxation time (SRT) version of LBM. However, it is known that the numerical stability and... 

    Investigation of the interphase effects on the mechanical behavior of carbon nanotube polymer composites by multiscale modeling

    , Article Journal of Applied Polymer Science ; Volume 117, Issue 1 , March , 2010 , Pages 361-367 ; 00218995 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element... 

    Hybrid multiscale modeling and prediction of cancer cell behavior

    , Article PLoS ONE ; Volume 12, Issue 8 , 2017 ; 19326203 (ISSN) Zangooei, M. H ; Habibi, J ; Sharif University of Technology
    Public Library of Science  2017
    Background: Understanding cancer development crossing several spatial-temporal scales is of great practical significance to better understand and treat cancers. It is difficult to tackle this challenge with pure biological means. Moreover, hybrid modeling techniques have been proposed that combine the advantages of the continuum and the discrete methods to model multiscale problems. Methods: In light of these problems, we have proposed a new hybrid vascular model to facilitate the multiscale modeling and simulation of cancer development with respect to the agent-based, cellular automata and machine learning methods. The purpose of this simulation is to create a dataset that can be used for... 

    Prediction of particle deposition in the respiratory track using 3D-1D modeling

    , Article Scientia Iranica ; Volume 19, Issue 6 , December , 2012 , Pages 1479-1486 ; 10263098 (ISSN) Monjezi, M ; Dastanpour, R ; Saidi, M. S ; Pishevar, A. R ; Sharif University of Technology
    Airflow simulation of the whole respiratory system is still unfeasible due to the geometrical complexity of the lung airways and the diversity of the length scales involved in the problem. Even the new CT imaging system is not capable of providing accurate 3D geometries for smaller tubes, and a complete 3D simulation is impeded by the limited computational resources available. The aim of this study is to develop a fully coupled 3D-1D model to make accurate prediction of airflow and particle deposition in the whole respiratory track, with reasonable computational cost and efficiency. In the new proposed method, the respiratory tree is divided into three parts to be dealt with using different...