Sharif Digital Repository

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  

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... 

Base isolation system is an efficient passive structural control approach to save the structures from the harms of earthquakes. The base isolated systems help to reduce the base shear by increasing the period of the structures, as well as dissipating the seismic input energy by its inherent damping mechanism [1]. However, the residual displacement of the base isolation systems resulted from strong ground motions would remain as a main obstacle in its regular serviceability after the main event. In that regard different isolating devices have been introduced to resolve the problem of the remaining permanent displacement. On the other hand, Shape Memory Alloys (SMAs) are among the newly... 

Seismic performance analysis is conducted for an isolated three-span continuous highway bridge, which is restrained with shape memory alloy bar. Two series of earthquake ground acceleration, known as ‘pulse records’ and ‘non-pulse records’ are applied to the bridge in three directions. Four types of pier-girder connection are used in the analysis: rigid connection (only for comparison), lead rubber bearing system (LRB), lead rubber bearing along shape memory alloy (SMA) restrainer system and high damping rubber bearing (HDRB) system. SMA bar restrainer is made of Ni-Ti. In the first step of the work, structural properties and analytical models of the bridge segments are introduced. Then, a... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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...