Search for: multiscale-models
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    A Multi-Scale Method for Non-Linear Mechanical Behavior of Nanostructures Based on Coarse-Grained Model

    , M.Sc. Thesis Sharif University of Technology Vokhshoori Koohi, Melika (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    The ever-increasing growth of Nanotechnology has elevated the necessity for the development of new numerical and computational methods that are better capable of evaluating systems at this scale. The existing techniques, such as Molecular Dynamics Methods, in spite of being fully capable of evaluating nanostructures, lack the ability to simulate large systems of practical size and time scales. Therefore, in order to be able to provide a realistic simulation of a large model, simulation of which is limited by the computational cost of the current molecular dynamics methods at hand, Coarse-Graining technique has recently become a very effective and beneficial method which refers to the... 

    Continuum Analysis of Defects Based on Atomistic Simulat

    , M.Sc. Thesis Sharif University of Technology Heidarzadeh, Narges (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    In this study, a new multi-scale hierarchical technique has been employed to investigate the role of temperature on nano-plates with hex atomic structure. Different number of primary edge dislocations is considered and the temperature varies from 0 up to 800 K. Primary edge dislocations are created by proper adjustment of atomic positions to resemble discrete dislocations (DD’s) and then the application of equations of motion to the relaxed configuration of this adjustment. The interatomic potential used for atomistic simulation is Finnis-Sinclair Embedded-Atom-Method (FS-EAM) as many-body interatomic potential and the Nose-Hoover thermostat has been implemented to adjust the modulation of... 

    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... 

    Multi Scale Modeling of Carbon Nano Structures Using Brenner Potential Function

    , M.Sc. Thesis Sharif University of Technology Ziapour, Rouzbeh (Author) ; Khoei, Amir Reza (Supervisor)
    Due to high cost and ineffectiveness of molecular models a new method for coupling continuum models with molecular models is used. In this method, the continuum and molecular domains are overlapped. Comparing the results obtained from the concurrent simulations and molecular dynamic simulations proves the accuracy of the method used. The method is used for modeling single layered graphene sheets, stress contours are presented for multiscale and both static and dynamic simulations of concurrent. For multiscale simulations two different carbon nano tubes are investigated and strees-bond angle and strees-bond length are also presented  

    Multiscale Modeling of Carbon Nano Structures Using Tersoff Potential Function

    , M.Sc. Thesis Sharif University of Technology Najjari, Alireza (Author) ; Khoei, Amir Reza (Supervisor)
    During the last decade, thanks to a combination of exploding computational power and improved physical insight into material behavior, continuum and atomistic simulations improved greatly. Both classes of methods are now used to solve problems, which are more complicated than ever with greater accuracy than ever before. Nevertheless, there still exist problems for which neither method alone is sufficient. In general, atomistic simulations cannot be used for such length scales due to the restrictions on the number of atoms that can be simulated, along with the time scales, which they can be simulated for. In contrast, continuum simulations tend to fail at the atomic scale, for example due to... 

    Mechanical Behavior Analysis of Carbon Nanotube-Based Polymer Composites using Multiscale Modeling

    , Ph.D. Dissertation Sharif University of Technology Montazeri Hedesh , Abbas (Author) ; Naghdabadi, Reza (Supervisor) ; Rafii Tabar, Hashem (Supervisor) ; Bagheri, Reza (Supervisor)
    In this project, two multiscale modeling procedures have been implemented to study the mechanical behavior of SWCNT/polymer composites. First, a new three-phase molecular structural mechanics/ finite element (MSM/FE) multiscale model has been introduced which consists of three components, i.e. a carbon nanotube, an interphase layer and outer polymer matrix. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. Using this model, we have investigated the macroscopic material properties of nanocomposite with and without considering the interphase and compared the results with molecular dynamics (MD) simulations.... 

    A Multi-Scale Method for Modeling and Analysis of the Creep Behavior in Composite plates

    , M.Sc. Thesis Sharif University of Technology Barzegar, Mohsen (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Polymer matrix composites, which are composed of a wide variety of short or long fibers bound together by organic polymer matrix, have been widely utilized in many engineering aeras, particularly in aerospace engineering. Recently, studying and analyzing the mechanical behavior of composites was one of the major reaserch interests. Regarding the vast variety of data drived from experimental tests, a requirement of tools that could facilitate estimating creep properties of materials is an important concern for researchers. The present work at first, introduces some major creep models and then proposes a 3D creep Burgers model for implementing in abaqus which could be used in macro phase. This... 

    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... 

    A Self-Consistence Numerical Method to Estimate Effective Mechanical Properties of Fibrous Composites

    , M.Sc. Thesis Sharif University of Technology Vasheghani, Koorosh (Author) ; Hosseini Kordkhaili, Ali (Supervisor)
    One of the most widely used methods in the study of the mechanical behavior of fiber-reinforced polymers is modeling and simulation of a unit cell behavior. According to the arrangement of composite materials, the unit cell is selected in order to include and represent actual constructions of the material. In this study a numerical self-consistence method is proposed to estimate effective properties of Carbon-epoxy composite materials. In this method, in addition of two main phases i.e. matrix and fiber, a phase of composite properties is also considered surrounding the unit cell. First using analytical and semi-empirical methods, the properties are calculated and are converged after... 

    Calculation of Heterogenous Material Properties by Using of Eshelby based and BEM Methods

    , M.Sc. Thesis Sharif University of Technology Yazdanparast, Reza (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    To days the heterogeneous material are used extensively in the engineering materials. Optimization ability is a key feature of these materials to reach desired properties. Heterogeneous materials are the materials that make up from the constituents of multiphase materials in lower length scale such as mesoscopic, microscopic or/and Nano scales. So the properties of these materials at each scale are depending on to several characteristics of heterogeneities such as geometry, material and packing. In these materials the effects of heterogeneities at the lower scales are very significant and the constitutive equations are different for each range of scale. The proper selection of this range... 

    Multi-scale Modeling of Crack Using Nano-XFEM

    , M.Sc. Thesis Sharif University of Technology Ghaffari, Reza (Author) ; Haddadpour, Hassan (Supervisor)
    In this thesis a mutliScale model based on the Cauchy-Born hypothesis and via usage of XFEM is proposed for crack modeling. By solving an example, the important of surface effects in the surface stresses region is shown. Considering not being able to model the surface effects with the Cauchy-Born method, the boundary Cauchy-Born method for modeling crack effects is used. Moreover, three Molecular Dynamics method for modeling crack will be proposed. According to the obtained results from these methods, it was deduced that for calculating the correct surface stresses in Molecular Dynamics the mutual interaction of upper and lower atoms of crack should be omitted. Finally, the validation of... 

    Hybrid Multiscale Modeling of Cancer Cell Behavior

    , Ph.D. Dissertation Sharif University of Technology Zangooei, Mohammad Hossein (Author) ; Habibi, Jafar (Supervisor)
    Cancer is a class of diseases characterized by out-of-control cell growth. Cancer is among the leading causes of death worldwide.Cancer modeling is increasingly being recognized as a powerful tool to refine hypotheses, focus experiments, and enable predictions that are more accurate.We investigate a three-dimensional multiscale model of vascular tumour growth, which couples blood flow, angiogenesis, vascular remodelling, nutrient/growth factor transport, movement of, and interactions between, normal and tumour cells. We constructed a hybrid multi- scale agent-based model that combines continuous and discrete methods.Each cell is represented as an agent. The agents have rules that they must... 

    Modelling and Simulation of Melanoma Cancer, Based on Cellular Automata Approaches

    , M.Sc. Thesis Sharif University of Technology Rad, Jaber (Author) ; Habibi, Jafar (Supervisor)
    Nowadays, M&S is critical as a powerful tool for human to fight against cancer. Skin cancer is one of the most widespread cancers and melanoma would be the most dangerous kind of it. In cancerous micro-environment, cancer cells interact with vasculature, and compete with normal cells over nutrients. This plays a major role in tumor progression pattern and speed. In recent years, a few multiscale models have been developed considering these phenomena. Such a model provides a platform for future researches, especially in drug effects prediction. A reliable simulation must satisfy the constraints and facts in the real world as much as possible. M&S credibility assessment is a major concern to... 

    A Temperature Dependant Multiscale Modeling of Crack Growth in Nano Materials

    , M.Sc. Thesis Sharif University of Technology Imani, Arman (Author) ; Khoei, Amir Reza (Supervisor)
    The fact that materials and crack behave differently under different temperatures, brings a need for further investigation in this field. Recent studies regarding this behavior are mainly based on molecular dynamic method. While this method garuntee a highpercicion, the computational costs of this method can be high when dealing with crack propagation problem. Taking advantage of multiscale methods allows us to overcome this challenge by reducing the calculation time while providing acceptable results. In this research a multi-scale method capable of considering thermal effects has been developed. A concurrent model is created by using theory of elasticity for continuum part and taking... 

    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... 

    Nondestructive Test in Geopolymer Concrete with Aid of Ultrasonic Waves

    , M.Sc. Thesis Sharif University of Technology Nouri, Ali (Author) ; Toufigh, Vahab (Supervisor)
    In recent decades, particle composite materials have a wide range of applications in engineering. Particle composites are a group of heterogeneous materials with different length scales and are characterized by particles that are randomly distributed in a matrix phase. Geopolymer concrete is a special type of concrete that its binder is made by reacting alumina and silicate carriers with an activating agent and in recent years with the expansion of its use has reduced the amount of cement consumption. In addition to the many advantages of geopolymer concrete, it has disadvantages in terms of setting time. That is why the use of cement has been proposed as a solution to the problem. This... 

    Coarse Grained-Atomistic Concurrent Multi-Scale Modeling for Numerical Simulation of Mechanical Behavior of Heterogeneous Materials in Nano-cale

    , M.Sc. Thesis Sharif University of Technology Ali Madadi Ahmadabadi, Ashkan (Author) ; Khoei, Amir Reza (Supervisor)
    In this thesis, a method has been exploited to couple the atomistic domain with the coarse-grained domain. Since molecular dynamics has a high computational cost when a large number of atoms exist, coarse-grained molecular dynamics was used in which a number of atoms are assumed as a bigger bid and interatomic potential is modified for bids so that the material’s mechanical properties remain constant. This method not only reduces the computational cost of calculating forces in molecular dynamics simulation but also, the time step used in Coarse-Grained Methods can be more than atomistic simulations as the frequency of occurring phenomena in CG scale is less than atomistic scale.The advantage... 

    Coarse-gained Multi-scale Modeling for Numerical Simulation of Nonlinear Behavior of Materials in Nano-scale

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Khashayar (Author) ; Khoei, Amir Reza (Supervisor)
    In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

    Hierarchical Multi-Scale Modeling of Large Plastic Deformation with Application in Powder Compaction

    , Ph.D. Dissertation Sharif University of Technology Rezaei Sameti, Amir (Author) ; Khoei, Amir Reza (Supervisor)
    The hierarchical multi-scale approach is one of the most powerful techniques that takes the advantage of different scales and succeeds the limitations of each method in a way that the large systems in coarse-scale can be simulated with atomic precision. In this thesis, the hierarchical atomistic-continuum multi-scale method is developed for modeling the phenomena with non-homogenous deformation, large deformation and plastic behavior. In this regard at first, an atomistic-based higher-order continuum model is formulated in the framework of nonlinear finite element method to present the geometrically nonlinear behavior of nano-structures. The efficiency of higher-order Cauchy-Born hypothesis... 

    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...