Sharif Digital Repository

Estimating the nonlinear behavior of sturctures, always have been one of the main concerns of civil engineers. One of the most recent methods for estimating behavior of structures is MIDA technique. It is a procedure that in some levels, substituted for IDA. Although this method presents the approximate results, high accuracy, fastness and inexpensive procedure made this manner to an efficient method. Indeed, this method has been presented to be exerted instead of exact IDA method which is too complicated and prolix. Up to now, no one has used this method for structures incorporating soil-structure interaction. In theMIDA manner, there is no dynamic analysis of ... 

Determining nonlinear dynamic behavior of structures is always one of the main goals of structure and earthquake engineers. The Modal Incremental Dynamic Analysis (MIDA) is one of the newest methods for analyzing the seismic behavior of structures. Indeed, this method has superseded the exact IDA method which is too complicated and prolix. Although, this method represents approximate results, high accuracy, fastness and low cost procedure made it an efficient and useful technique. Many researchers have used this method and investigated the accuracy of that and achieved proper results. Up to now no one has applied this method on structures which are equipped with dampers. In the procedure of... 

Polycarbonate (PC) and polyethylene-terephthalate (PET) are important engineering thermoplastics. During last decades these polymers and their blends have been studied extensively due to their wide range of applications. Blends of PET and PC combine mechanical properties and chemical resistance together, which make applicable in various components such as automotive, electrical and of medical parts. It has been accepted that PET/PC immiscible blends are subjected to transesterification reactions during thermal processing, which produces PET-PC copolymer chains. In fact, scissioning and substitution of ester/carbonate functional groups of PC and PET at the interface, transforms the initial... 

In the present dissertation model based grasping of soft tissue with the laparoscopic gripper, tissue deformation under the applied load and control of the tissue-instrument interaction have been studied. As the first step a cantilevered beam under bending and tension has been modeled statically and dynamically using the meshless EFG based method. Results show that an increase in the number of nodes at the displacement boundary and the area of force insertion improves the accuracy of the predicted displacement in the model compared to the analytical solution. In the second step the model is developed for a hemisphere under vertical and lateral compression. Comparison of the deformation of... 

In this thesis, the dynamic behavior of a pinned-pinned fractional viscoelastic pipe conveying fluid is examined in the external cross flow. The Galerkin method is employed to discretize the nonlinear coupled equations of motion for viscoelastic pipe conveying fluid in the external cross flow. Consequently, four modes of system are obtained. In addition, direct perturbation method of multiple scale is used to solve the governing nonlinear coupled equations of motion for the fractional viscoelastic pipe conveying pulsating fluid in the external cross flow. Moreover, time response diagrams are drawn in order to investigate under effects of the internal fluid velocity, external fluid reduced... 

Nowadays, the design of new structures and the renovation of existing buildings against earthquakes using energy absorption systems are very common. On the other hand, the near-field earthquake are characterized by directivity related velocity pulses with large accelerations. Recent studies have shown that the performance of the passive energy dissipation mechanisms are significantly depended on the characteristics of the near field velocity pulses. The efficiency of various passive dampers in damage mitigation of different building structures have been carefully evaluated under near field and far field earthquake records. In this study, the ability of viscoelastic dampers in controlling the... 

Due to adverse health problems with lumbar spine among professional drivers associated with exposure to whole body vibration (WBV), studying the effect of vibrations and parameters influencing WBV is of great importance. This study aims to simulate whole body vibration for a ground vehicle occupant and calculate loads that lumbar spine tolerate during harmonic sinusoidal vibrations. Moreover, this study determines the effect of lumbar spine angle, seat specifications (angles and materials), and vibration frequency on the results. To this end, a detailed viscoelastic lumbar spine (L1-S1) has been modeled using FE method which has been replaced with the simplified spine model in HYBRID III... 

Now a days, the ability of measuring the mechanical properties of the living cells in in experiments has been increased. Experiments shows that the stem cells could alter their faith in different mechanical situations, but an integrated model about this phenomenon in literature has not been introduced yet. In this research thesis s minimal cell model (MMC) is developed to capture the behavior of the cells on substrates with varying mechanical properties and morphologies, MMC consists of large scale models for outer membrane of the cell and nuclear envelope, cytoplasmic area, chromatin fibers and Extra cellular matrix. Each component of the MMC will be placed in an integrated software to... 

The injection process on cell is a very accurate and sensitive operation. This method is used for several new invented approaches such as tracytoplasmic Cell Injection or drug delivery. Controlling the injection force in micro scale is one of the problems of mentioned operations. Current huge and expensive laboratorial devices are helping the operators to do injection operation with :nore success. In this study a simple and novel microelectromechanical (MEMS) mechanism for doing injection process automatically on the biological cells is proposed. In order to controlling this device properly, we should model and simulate the operation condition from initial position to final condition. This... 

Tire is one component of the suspension system and has beneficial effects on reducing vibrations caused to the vehicle. This study aims to determine the factors affecting the damping and stiffness of the tire is carried out. The modeling of factors were identified. For testing the modeling effort is to be made to the instruments used to measure the damping and stiffness of the tires. To make the structural static analysis, dynamic and modal was to have sufficient structural strength and the displacements and stresses are sensibly placed. Factors that have influence on the hardness of the ring diameter, the outer diameter of the tire, tire pressure, tire tread depth, tire wall thickness,... 

In this thesis, employing the definition of an effective configuration in the Continuum Damage-Healing Mechanics (CDHM), mechanical responses of elf-healing materials are investigated. Firstly, a constitutive model is proposed to investigate damage and healing phenomena in concrete materials. In order to consider the different behavior of concretes in tension and compression, a spectral decomposition of the stress is utilized. In addition, employing the Clausius-Duhem inequality and considering the irreversible thermodynamics, conjugate forces of the damage and healing are expressed. The Gibbs potential energy is decomposed into three parts; elastic, damage and healing. In the next section,... 

In this thesis, the mechanical properties of collagen hydrogels were characterized using Finite Element method and the collagen content effect on the mechanical properties of hydrogels were investigated. Hydrogels samples with different collagen content were assessed which caused diverse mechanical behaviors. Due to the nonlinear behavior of hydrogels, using numerical methods and simulation softwars can be helpful to determine the mechanical properties of these material and save agreat deal of time. Finite Viscoelaticity theory was exploited for a UMAT Subroutine in Abaqus and an special Starin Energy Function was selected to extract the formulations. The agreement between simulation results... 

Patellofemoral joint has an important role in knee extension. Because of this joint importance and complicated mechanical behavior, a lot of mathematical models have been used, to obtain a better understand of this joint, considering this joint as a part of knee joint or as a separate joint. Although these works have comprehensively studied the patellofemoral joint but they don’t emphasis on dynamic aspects. Also there is no work to compare the experimental and theoretical results calculated from one specified subject knee.In this study, the kinematic and dynamic of patellofemoral joint has been studied, constructing a three dimensional dynamic model of patellofemoral joint and experimental... 

The numerical simulation of asphalt concrete and pavement has gained considerable attention in recent decades. Information about the response of asphalt pavements during construction and in-service traffic loading is required by pavement specialists for improvement of pavement analysis and design methods. The goal of this study was to propose a constitutive relationship and a numerical modeling method for asphalt concrete compaction in the laboratory and in situ. Asphalt binders exhibit rate-dependent viscoelastic and viscoplastic mechanical behavior in asphalt concrete. The current study examined the viscoelastic and viscoplastic mechanical behavior of asphalt concrete under various loading... 

Recent studies have shown that the injection of low-salinity water would enhance the oil recovery factor for both the core scale and the field test. The evidence obtained from laboratory studies showed that the control of salinity and the composition of injected water has successfully affected the oil release, hence enhancing the oil recovery efficiency. In this method, by changing the type and amount of dissolved ions in the injected water, the water/oil/rock interactions are altered. Based on this, extensive studies have been focused on the mechanisms for the trapped oil release at the pore scale. Several mechanisms have been proposed to explain this phenomenon, which can be divided... 

This study presents the aeroelastic stability and vibration analysis of a sandwich circular cylindrical shells with a constrained viscoelastic layer. Based on the Donnell-Moshtari theory, the structural formulation of the cylinder is obtained using Lagrange method. The Rayleigh-Ritz method is implemented to solve the discretized governing equations. To describe the mechanical properties of the viscoelastic layer, the fractional order standard solid model is applied. The effects of variation of the governing parameters such as the length to radius ratio, radius to total thickness ratio and ratio of core to facing thickness on the stability margins and frequencies of sandwich cylindrical... 

One of the best stimulation methods for oil and gas wells is matrix acidizing in order to increase the near wellbore permeability. in acidizing, good acid coverage in different layers is one the main goals. so, various methods have been presented. important part in using these methods is to not damage formation and economic matters. modern methods utilize VES acids for this purpose. viscoelastic characteristics of these materials by formation of miscellaneous, increases the apparent viscosity by a large degree. for this reason, VES fluids can be used to improve acid divergence in acid injection operation. acid system based on viscoelastic surfactants that is changed to gel instantly, can be... 

Due to the limitations on experiments in the field of cell mechanics, computational modeling of biological cells have attracted attention within two recent decades. In general, some models have been developed in two different scales, known as microstructure and continuum, both of which have their own pros and cons. Nevertheless, viscoelastic behavior of cell membrane has attracted less attention of scientists up to now. Therefore, multi-scale simulation of the viscoelastic behavior of the cell membrane has been chosen as the main goal of this thesis. Toward this goal, at first the energy of the simulation box, consisting of 128 Dipalmitoylphosphatidylcholine and 3655 water molecules, was... 

Taghizadeh Manzari, M. (In this work, a modified Smoothed Particle Hydrodynamics (SPH) method, with a new moving solid boundary treatment approach, is utilized to simulate the particulateflow problems. The renormalized first and second derivative schemes which lead tothe consistency of the method, are also used along with a modification to the continuityequation which prevents the spurious pressure oscillations. The proposed methodis validated by solving benchmark problems of solid body motion in channel flows.There is a good agreement between the obtained results and those reported in theliterature. The convergence of solutions for different domain discretizations is alsoassessed. In order... 

Composite nature of asphalt mixtures necessitates a micromechanical scheme which depends on distinctive characteristics of various constitutive phases. In this regard, discrete element method was utilized to predict the creep behavior of asphalt mixtures and strain response in primary, secondary and tertiary stages. In this research, a modified mixture modeling procedure was considered to better simulate permanent deformation response of asphalt mixtures under creep loading. A random distribution of mastic and aggregate particles with respect to a typical dense gradation was implemented to reconstruct cylindrical specimens. A bonding model represented the cohesion effect in mastic...