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    Using Base Isolators in Bridges to Reduce the Dynamic Forces of Piers and Abutments

    , M.Sc. Thesis Sharif University of Technology Kohani Khoshkbijari, Reza (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In recent years, the application of base isolation as a seismic design strategy for reducing the effects of earthquake ground motion has become an advantageous method and much effort has been devoted to base isolation research and there has been a growing acceptance of this approach. In this research, the effect of using base isolators in reducing the dynamic forces of piers and abutments of bridges is studied. More specifically double-span bridges are the target of this research. After modeling a regular bridge in a typical analysis program, it is excited by different earthquake accelerograms and then the effect of using base isolators in dissipating the earthquake energy is investigated  

    Application of Isogeometric Analysis in Determining Stress Distribution at the Tip of a Crack

    , M.Sc. Thesis Sharif University of Technology Zandinia, Meysam (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    Isogeometric Analysis is one of the new methods for solving partial differential Equations which has special advantages compared to conventional methods such as the finite Element method. Some of these benefits can be used to approximate the geometry and solving the Equations governing the behavior of materials. Calculating the stress intensity factor at the tip of the Crack using classical method such as finite element method is done as well as IGA and gives Acceptable Results in linear range. Studying how to calculate these coefficients in combination with Isogeometric analysis method and comparing results with FEM due to novelty of the approach can have considerable importance for... 

    Plastic Analysis of Two Dimensional Frames using Ant Colony Algorithms

    , M.Sc. Thesis Sharif University of Technology Pouraghajan, Marjan (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In previous decades, easy access to material and low cost human power allow the product process to be performed in a preferred way. The limit in amount of material, economy, and the efficiency of the model has not been influential like these days. Today, the effective use of material and consideration of an economic model have great importance. It is obvious that a process of designing implies optimizing which the range of its using is also continuing in many engineering sciences. Many optimization issues contain discrete nature. Many of searching spaces that we encounter in the real world applications are not necessarily continuous as a condition which has crucial importance for classic... 

    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)
    Abstract
    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... 

    Multi-scale Analysis of Dislocation Emission for Nano-crystalline Structures

    , M.Sc. Thesis Sharif University of Technology Fattahi Faradonbeh, Mehran (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In this study, a new multi-scale hierarchical technique has been employed to investigate the role of edge dislocation on nano-plates with hex atomic structure in large deformation. Two multiscale hierarchical atomistic/molecular dynamics (MD)–finite element (FE) coupling methods are proposed to illustrate the influence of temperature on mechanical properties of Magnesium in large deformation. The atomic nonlinear elastic parameters are obtained via computing second-order derivative of Representative atom’s energy and RVE’s strain energy density with respect to deformation criterions (deformation gradient and Green strain tensor) to bridge between atomistic and continuum level, the... 

    Temperature-Dependent Multiscale Simulation of Single Layer Graphene Sheet in Large Deformation

    , M.Sc. Thesis Sharif University of Technology Tanhadoust, Amin (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    Abstract
    In this study, two multiscale hierarchical atomisyic/molecular dynamics (MD)–finite element (FE) coupling methods are proposed to illustrate the influence of temperature on mechanical properties of SLGS in large deformation. The Tersoff interatomic potential is implemented, in addition, the Nose-Hoover thermostat and local harmonic approximation are employed to adjust the fluctuation of temperature in CB and MD, respectively. The atomic nonlinear elastic parameters are obtained via computing second-order derivative of Representative atom’s energy and RVE’s strain energy density with respect to deformation criterions (deformation gradient and Green strain tensor). To bridge between atomistic... 

    Multiscale Investigation of Plastic Behavior in Crystalline Metals

    , M.Sc. Thesis Sharif University of Technology Davoodi, Sina (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    Abstract
    In this study, a modern multiscale sequential molecular dynamics (MD) – finite element (FE) coupling method is proposed to represent the role of grain boundary (GB) planar defect on mechanical properties of crystalline structures at various temperatures. Different Grain Boundary misorientation angle is considered and the temperature varies from 0 up to 800 K. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the crystalline structures with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. The atomic... 

    A Temperature-Dependent Coarse-Graining Method for Nano Crystalline Materials

    , M.Sc. Thesis Sharif University of Technology Vahed Mohammad Ghasemloo, Zahra (Author) ; Khoie, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    Abstract
    The molecular dynamic (MD) method was first reported by Alder and Wainwright in the late 1950s to study the interaction of hard spheres. Molecular dynamic (MD) simulation is a technique for computing equilibrium and forwarding properties for classical many-body systems. This is a reasonable and often excellent approximation for a wide range of systems and properties. Although molecular dynamics method provide the kind of detail necessary to resolve molecular structure and localized interaction, this fidelity comes with a price. Namely, both the size and time scales of the model are limited by numerical and computational boundaries.The multi scale approach taken by the computational materials... 

    Hyperelastic Modeling of Atomistic Continuum in the Presence of Inhomogeneity

    , M.Sc. Thesis Sharif University of Technology Asadollahzadeh, Niloofar (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In this study, a pioneer multiscale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to illustrate the influence of large deformation on mechanical properties of heterogeneous nano-crystalline structures. The embedded-atom method (EAM) of many-body interatomic potential is applied to evaluate pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at room temperature. In addition, the Nose-Hoover thermostat is used to control the instability of temperature. A weight average between the lattice parameters of atomic structures is utilized in order to calculate the equivalent lattice parameter. The... 

    A Coarse -Grained Model for Molecular Dynamics Simulation of Crystalline Nano- Structures

    , M.Sc. Thesis Sharif University of Technology Ahmadzadeh, Baharan (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen ($item.subfieldsMap.e)
    Abstract
    In this work, we investigate the application of coarse graining (CG) methods to molecular dynamics (MD) simulations. These methods provide access to length and time scales previously inaccessible to traditional materials, simulation techniques. However, care must be taken when applying any coarse graining strategy to ensure that we preserve the material properties of the system we are interested in. The most prominent of these techniques is the so called multi scale coarse graining (MS-CG) method. In this study we will focus on the modeling of crystalline Nano structures using coarse graining as one of the approaches in multi scale analysis the force matching method is mainly followed to... 

    Temperature-dependent Multi Scale Large Deformation Simulation of Heterogeneous Crystals

    , M.Sc. Thesis Sharif University of Technology Gordan, Ali (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    Abstract
    In this study, a novel and unprecedented multi-scale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to demonstrate 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... 

    Mechanical Behavior of Metalic Nano-structures Using a Nonlinear Multi-scale Model Based on Coarse Graining Approach

    , M.Sc. Thesis Sharif University of Technology Pezeshkzadeh, Alireza (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Supervisor)
    Abstract
    In this thesis ،molecular dynamics simulation of structural and mechanical properties of pure aluminium and copper crystals as well as of the alloyed crystals including 10%,30%,50%,70% and 90% aluminium alloyed have been investigated using two various all-atom and coarse-grained models. Molecular dynamics simulations calculate the realistic behavior of the system and then use them in order to calculate the time average properties of the system. Embedded atom method (eam) and the numerical iterative Boltzmann Inversion method are employed to describe the interaction between atoms. The results are then compared with coarse-grained model. The demonstrated peaks in the radial distribution... 

    Multiscale Simulation of Carbon Nanotubes Using Coupled Atomistic- Continuum Modeling

    , M.Sc. Thesis Sharif University of Technology Motezaker, Mohsen (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    Carbon nanotubes are cylinders in Nano scale formed of carbon atoms with covalent bonds that contain a significant electrical and mechanical features. Carbon nanotubes are divided into two main types: multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanotubes (SWCNTs). A SWCNT is a rolled graphene sheet (graphene is in fact a single sheet of graphite). SWCNTs has lately been considered as one of most interesting research cases. The reason why researchers have been fond of investigating about graphene has been its unconventional quantum hall effects, high room-temperature electrical conductivity and its mechanical stability despite of being composed of single layer atom... 

    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)
    Abstract
    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... 

    Determination of the Plastic Zone at the Tip of a Crack in Pressure-Sensitive Materials Using RKPM

    , M.Sc. Thesis Sharif University of Technology Malgard, Afsaneh (Author) ; Mohammadi Shoja, Hossein (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    This project presents an outline of the crack tip stress fields in the presence of a plastic enclave around a growing fatigue crack using RKPM and Drucker-Prager criterion for pressure sensitive materials such as concrete and rock. Two distinguished features of RKPM are the arbitrarily high order smoothness and the interpolation property of the shape function which has kronecker delta property at the associated nodes. This method has proved to handle extreme material deformation and moving discontinuities. For the frictional materials such as rock in geotechnical engineering, a non-associated or associated Drucker- Prager plasticity model is appropriate for modeling its constitutive... 

    Properties Evaluation of Self-Consolidating Concrete Containing Rice Husk Ash

    , M.Sc. Thesis Sharif University of Technology Nourbakhsh, Ali (Author) ; Jahanshahi, Mohsen (Supervisor) ; Shams, Mohammad Reza (Co-Advisor)
    Abstract
    The Self-Consolidating (Compacting) Concrete (SCC) is a high performance concrete. Due to preventing it from segregation, SCC is known by its need to higher dosage of super plasticizer and viscose modifying agents. This increases the cost and reduces the popularity of SCC in construction industry. In this thesis, the production of Rice Husk Ash (RHA) from a controlled burning process using a special designed furnace, and cement replacement feasibility in the concrete mixture by low cost RHA, as an active pozzulanic additive have been investigated. Finding an appropriate ratio of replacement with cement for RHA and further effects on mechanical properties of SCC have been evaluated. The... 

    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)
    Abstract
    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 Combined Molecular Dynamics-Coarse Graining Technique for Modeling the Mechanical Behavior of Crystalline Nano-Structures

    , M.Sc. Thesis Sharif University of Technology Mohammad Reza, Kimia (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Supervisor)
    Abstract
    In the area of material studies, the atom structure models are the basis of all simulations and methods. With improvements in computers power, these models have become more consistent with experimental results. New theoretical methods combined with supercomputers assist to an understanding with detail and accuracy of material behavior at the atomic scale that leads to develop of the Computational Materials Science. Recently, developments in fields such as quantum mechanics, statistical physics, solid-state physics, quantum chemistry, computer science and graphics, allowed for faster computing which leads a powerful tool for material calculations and designs. New computer applications allow... 

    Numerical Investigation of Crack Propagation in Slab-Bridge System Main Beams Subjected to Moving Loads

    , M.Sc. Thesis Sharif University of Technology Morafegh, Fatemeh (Author) ; Jahanshahi, Mohsen (Supervisor) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Bridges play a vital role in road-related transport industries. Significant changes to contemporary bridge design specifications have also been mainly related to strength issues. The transitions from allowable stress design to load factor design, and more recently to load and resistance factor design (LRFD), reflect this line of thinking. It is important to note that in the early 1970s, bridge engineers developed criteria for steel bridge details to protect against fatigue and fracture failure. These were indeed service life design provisions. By industry growth and extensive need for goods transportation, there is a need for the construction of new bridges and renewal of older bridges plus... 

    The Size Effect of Coarse-Grained Modeling for Nonlinear Behavior of Nano-Structure Materials

    , M.Sc. Thesis Sharif University of Technology Khademabbasi, Navid (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    The development of Nanotechnology increasingly has elevated the urgency for the expansion of modern numerical and computational methods that have evaluating systems with capability at this scale. In spite of being fully capable of evaluating nanostructures, the existing techniques, such as Molecular Dynamics Methods, lack the ability to simulate large systems of practical size and time scales. Thus, being able to create a large model of realistic simulation, which is confined by the computational expense of the running Molecular Dynamics methods at hand, Coarse-Graining technique has recently become a very effective and beneficial method which refers to the development of simplified models of...