Search for: multiscale-models
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    Multi-scale dispersive gradient elasticity model with rotation for the particulate composite

    , Article Composite Structures ; Volume 294 , 2022 ; 02638223 (ISSN) Nouri, A ; Toufigh, V ; Sharif University of Technology
    Elsevier Ltd  2022
    Research on the characteristics of composites material has received enormous interest in recent years. The multi-scale nature of composite material leads to employing advanced techniques. Moreover, the presence of a wave with the high-frequency source adds complexity to the analysis. In this paper, a novel multi-scale elasticity model was developed to predict the wave dispersion property of particulate composites. The methodology was based on the simultaneous participation of translational and rotational degrees of freedom in motion equations. The method scheme of gaining motion equations was accomplished by using Taylor's expansion as a continualization method. The framework of the motion... 

    Multiscale modeling of coupled thermo-hydro-mechanical analysis of heterogeneous porous media

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 391 , 2022 ; 00457825 (ISSN) Saeedmonir, S ; Khoei, A. R ; Sharif University of Technology
    Elsevier B.V  2022
    This paper presents a numerical multiscale formulation for analysis of the transient heat and fluid flow in deformable heterogeneous porous media. Due to the heterogeneity of the media, the direct numerical simulation of the micro-structures leads to high computational costs. Hence, the multi-scale method can provide an efficient computational procedure. To this end, the first-order computational homogenization is adopted for two-scale simulation of THM problems. The governing equations of the problem contain a stress equilibrium equation, a mass continuity equation and an advection–diffusion equation in a fully coupled manner. Accordingly, the proper virtual power relations are defined as a... 

    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... 

    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... 

    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... 

    Multi-scale modeling of edge effect on band gap offset in polygonal cross-section Silicon nanowires

    , Article Computational Materials Science ; Volume 79 , 2013 , Pages 262-275 ; 09270256 (ISSN) Khoei, A. R ; Dormohammadi, H ; Aramoon, A ; Sharif University of Technology
    The band gap offset is an effect of coordination numbers (CNs) of atom reduction at the edge of transversal cross-section of Silicon nanowires (SiNWs). In this paper, a hierarchical multi-scale technique is developed to model the edge effect on the band gap shift of SiNWs since the geometric effect is dominant in the energy gap due to the appearance of strain in the self-equilibrium state. The multi-scale model is performed based on the molecular dynamics approach and finite element method for the micro- (atomistic) and macro-scale levels, respectively. The Cauchy-Born (CB) hypothesis is used to relate the atomic positions to the continuum field through the deformation gradient. Finally, the... 

    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... 

    Validity and size-dependency of Cauchy-Born hypothesis with Tersoff potential in silicon nano-structures

    , Article Computational Materials Science ; Volume 63 , 2012 , Pages 168-177 ; 09270256 (ISSN) Khoei, A. R ; Dormohammadi, H ; Sharif University of Technology
    Elsevier  2012
    One of the most popular constitutive rules that correlate the continuum and atomic properties in multi-scale models is the Cauchy-Born (CB) hypothesis. Based on this constitutive law of continuum media, it assumes that all atoms follow the deformation subjected to the boundary of crystal. In this paper, the validity and failure of CB hypothesis are investigated for the silicon nano-structure by comparison of the continuum and atomic properties. In the atomistic level, the stresses and position of atoms are calculated using the molecular dynamics (MD) simulation based on the Tersoff inter-atomic potential. The stresses and strains are compared between the atomistic and continuous media to... 

    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... 

    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... 

    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... 

    Investigating the effect of carbon nanotube defects on the column and shell buckling of carbon nanotube-polymer composites using multiscale modeling

    , Article International Journal for Multiscale Computational Engineering ; Volume 7, Issue 5 , 2009 , Pages 431-444 ; 15431649 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    Carbon nanotube (CNT)-reinforced polymer composites have attracted great attention due to their exceptionally high strength. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. In this article, a new three-phase molecular structural mechanics/finite element (MSM/FE) multiscale model is used to study the effect of CNT vacancy defects on the stability of single-wall (SW) CNT-polymer composites. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions... 

    Hierarchical multiscale modeling of nanotube-reinforced polymer composites

    , Article International Journal for Multiscale Computational Engineering ; Volume 7, Issue 5 , 2009 , Pages 395-408 ; 15431649 (ISSN) Ghanbari, J ; Naghdabad, R ; Sharif University of Technology
    A finite element-based hierarchical multiscale modeling scheme is presented and used for the analysis of nanotube-reinforced polymer composites. The scheme presented here consists of micro- and macroscale boundary value problems linked together using a computational homogenization scheme. Using the presented hierarchical multiscale scheme, we have studied nanotube-reinforced polymer composites, and the elastic properties are determined. Using different representative volume elements (RVEs) representing different volume fractions of aligned nanotubes, the effect of the nanotube volume fraction and the existence of an interphase layer on the effective elastic modulus of the nanocomposite are... 

    Nonlinear hierarchical multiscale modeling of cortical bone considering its nanoscale microstructure

    , Article Journal of Biomechanics ; Volume 42, Issue 10 , 2009 , Pages 1560-1565 ; 00219290 (ISSN) Ghanbari, J ; Naghdabadi, R ; Sharif University of Technology
    We have used a hierarchical multiscale modeling scheme for the analysis of cortical bone considering it as a nanocomposite. This scheme consists of definition of two boundary value problems, one for macroscale, and another for microscale. The coupling between these scales is done by using the homogenization technique. At every material point in which the constitutive model is needed, a microscale boundary value problem is defined using a macroscopic kinematical quantity and solved. Using the described scheme, we have studied elastic properties of cortical bone considering its nanoscale microstructural constituents with various mineral volume fractions. Since the microstructure of bone... 

    Computer simulation of flocs interactions: Application in fiber suspension

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Volume 292, Issue 2-3 , 2007 , Pages 99-109 ; 09277757 (ISSN) Jafari, A ; Zamankhan, P ; Mousavi, S. M ; Sharif University of Technology
    Elsevier  2007
    The present effort is the development of a multiscale modeling, simulation methodology for investigating complex phenomena arising from flowing fiber suspensions. Specific consideration was given to dynamic simulations of viscoelastic fibers in which the fluid flow is predicted by a method that is a hybrid between Direct Numerical Simulations (DNS) and Large Eddy Simulation techniques (LES), and fluid fibrous structure interactions (FSI) will be taken into account. Numerical results are presented for which focus is on fiber floc deformation by hydrodynamic forces in turbulent flows. Dynamics of simple fiber networks in a shearing flow of water in a channel flow illustrate that the... 

    Multiscale modeling of fluid turbulence and flocculation in fiber suspensions

    , Article Journal of Applied Physics ; Volume 100, Issue 3 , 2006 ; 00218979 (ISSN) Jafari, A ; Zamankhan, P ; Mousavi, S. M ; Henttinen, K ; Sharif University of Technology
    A mathematically rigorous, multiscale modeling methodology capable of coupling behaviors from the Kolmogorov turbulence scale through the full scale system in which a fiber suspension is flowing is presented. Here the key aspect is adaptive hierarchical modeling. Numerical results are presented focus of which are on fiber floe formation and destruction by hydrodynamic forces in turbulent flows. Specific consideration was given to molecular-dynamics simulations of viscoelastic fibers in which the fluid flow is predicted by a method which is a hybrid between direct numerical simulations and large eddy simulation techniques, and fluid fibrous structure interactions were taken into account. The... 

    A Thermo-Mechanical Multi-Scale Simulation for the Compaction Process of the Oxide-Coated Aluminum Nano-Powders

    , M.Sc. Thesis Sharif University of Technology Orvati Movaffagh, Amir Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    This research introduces a novel thermo-mechanical multiscale technique, utilizing machine learning, for simulating the compaction process of aluminum nanopowders with surface oxidation at various temperatures. The methodology employed involves the utilization of nonlinear thermo-mechanical Finite Element Method (FEM) for macro scale analysis, while employing the Molecular Dynamics (MD) method to calculate the mechanical and thermal characteristics of aluminum nanopowders at the nano-scale. The first part of the research presents a comprehensive study on the thermal conductivity of alumina-coated aluminum nanopowders, which is a crucial property for their application in powder metallurgy,... 

    Multi-Scale Numerical Modeling of Two Phase Flow over Flexible Surface Micro-Structures

    , Ph.D. Dissertation Sharif University of Technology Heyat Davoudian, Salar (Author) ; Javadi, Khodayar (Supervisor)
    The present thesis investigates the micro-droplet dynamics in an inclined channel covered with flexible structures. For this purpose, the DPD (dissipative particle dynamics) method is used to study the behavior of particles present in the flow, including the droplet, the fluid around the droplet, and polymeric structures. This model leads to a more accurate representation of flow hydrodynamics and indicates the way for exploring and understanding complex fluid properties in real flows. The first part of the thesis deals with the dynamics of rising bubbles attached to a vertical wall under different wettability conditions. Even though bubbles rising freely in a liquid have extensively been... 

    Multiscale Modeling of Creep Behavior of Nickel-Based Superalloys

    , Ph.D. Dissertation Sharif University of Technology Tolooei Eshlaghi, Golsa (Author) ; Khoei, Amir Reza (Supervisor)
    Nowadays, single-crystal nickel-based superalloys are widely used in the manufacture of gas turbine blades in the aerospace industry due to their high resistance to creep, fatigue and corrosion at high temperatures. The superior behavior of these materials at elevated temperatures is a result of their two-phase microstructure, which includes the matrix phase (γ) of nickel and the precipitate phase (γ') of Ni3Al intermetallic compounds with a high volume fraction. The aim of this thesis is to develop computational modeling tools to study the creep deformation of single-crystal Ni-based superalloys. At high temperatures, the creep deformation of Ni-based superalloys is determined by the atomic...