Sharif Digital Repository

Problems with composite materials can indicate the lack of mechanical properties of the layers, especially in high temperature, which led to the expansion of functionally graded materials. The most important application of these materials is in high temperature environments .therefore the study of their behavior under mechanical and thermal loads in the range of small and large deformations is very important.The purpose of this research is to provide an analytical solution for nonlinear behavior of functionally graded circular sector plates under thermomechanical load.The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction... 

In this study, linear and nonlinear mechanical behavior of moderately thick annular sector plates made of functionally graded materials is investigated. In linear analysis, based on first order shear deformation theory, governing equation with two different approaches are derived. In first approach, by application of extended Kantorovich method (EKM), displacements field variables are expressed as separable function of and together, and two sets of ordinary differential equations (ODEs) by using the principle of minimum total potential energy are derived. In the second approach, within FSDT and using the principle of minimum total potential energy, the governing partial differential... 

In this study the free vibration of annular sector plates made of functional materials with using the extended Katrovich method is investigated for a variety of boundary conditions. For this purpose, based on the first order shear deformation theory and Hamilton's principle, equations of motion that they are five differential equations and coupled, are derived. Due to the difficulty of the equations obtained by applying extended kantrovich method on these equations, two ordinary differential equations obtained, the two categories combined fixed and simple boundary conditions will be solved by using generalized differential quadrature and in an iterative process system natural frequency is... 

The aim of this project is buckling and post-buckling analysis of laminated composite circular cylindrical shells under external pressure on the basis of different shell theories. Based on Donnell, Love, and Sanders nonlinear shell theories within the first-order shear deformation model and von Karman geometric nonlinearity, the potential energy of composite circular cylindrical shells under external pressure with simply supported edges is extracted and by minimizing of the total potential energy and implementing the Ritz method, buckling pressure, the nonlinear post-buckling analysis and the curves of static equilibrium paths are presented. Furthermore, the effect of the external energy due... 

Blood vessels are subjected to complex mechanical loads, including internal pressure, external pressure, axial stress due to connection to tissues, and the twist caused by movement of the body. The veins and venous valves, which are responsible for returning blood to the heart, become bent and twisted (tortuosity) for various reasons. This venous tortuosity causes valve insufficiency and changes the hemodynamic pattern of blood flow and varicose veins. Studies show that more than a third of old people suffer from varicose veins. These injuries have made it important to study the physical mechanism of venous tortuosity and the function of venous valves.The purpose of this study is to... 

Obtaining the mechanical properties of body tissues in a non-destructive manner is clinically important and has wide applications in the diagnosis and prevention of diseases. one of non-destructive methods is elastography, which requires proper modeling of the tissue and then analysis of the wave propagation in it and obtaining the propagation relations and the dispersion curves. Study of the literature revealed that many simplifications have been used in most modelings of arteries and so far the anisotropy of the artery and its layers with the effects of surrounding tissues and blood have not been studied Therefore, the aim of this study is to model the artery as a two-layer orthotropic... 

In this study non-linear bending of circular sandwich plates with functionally graded (FG) porous core reinforced with graphene nanoplatelets (GPL) is investigated using refined shear deformation theory (RSDT). Displacement field of this theory is considered so that different theories can be introduced to estimate transverse shear strain. Equilibrium equations and boundary conditions are derived using minimum total potential energy principle. The equations are reformulated using potential and stress functions and analytical solution is obtained using perturbation method along with Fourier series. Validations are performed for two cases of linear and non-linear bending of circular plate and... 

Coatings are used in order to prevent wear, corrosion, thermal gradient reduction, surface strength improving and many other applications in industries. One of the common applications of coatings, is to prevent wear and surface abrasion. Hardness and friction coefficients are two parameters that determine the wear properties of a coating. Determining these parameters in very thin films is only possible by nanoindentation and nanoscratch tests. Surface hardness, young modulus and fracture toughness can be obtained using nanoindentation and friction coefficient is calculated from nanoscratch.
Finite element method is widely used for simulating the nanoindentation and nanoscratch... 

To keep up with the growing demands for energy, the oil and gas industry ventures into deeper waters. This increases complexity of offshore projects. Part of this complexity is due to the resistance of a pipeline against local buckling collapse due to external pressure that is more significant in higher pipe laying depth and consequently higher external pressure. Pipeline response to external pressure is an important factor in design of marine pipeline.Local buckling of a pipeline is the buckling behaviour within the pipeline cross section. Other types of buckling behaviour such as upheaval and lateralbuckling are not in the scope of this thesis.In this thesis, the installing pipeline is... 

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,... 

Circular cylindrical shells have been widely used in many engineering structures such as spacecraft, submarines, offshores, and storage tanks. Their high stiffness-to-weight ratio and load-carrying capability make them well suited for use in civil and aerospace structures. The consecutive development of material engineering along with the increasing demands for lightweight, heat-resistant, and high strength structures have led to the usage of advanced materials namely functionally graded (FG) materials in designing such structures. In this thesis, the nonlinear static analysis of thin FG cylindrical shells is carried out using the Donnell’s shell theory with first-order approximation and the... 

Nowadays, Eye injuries caused by blunt impacts are considered among the major causes of blindness and vision problems; therefore, studying the existence of possible damages can be quite useful and effective. One of the quickest and most suitable methods in identifying damage parameters is finite-element modeling of the human eye. In this regard, in the current study, first a geometrical design was created by incorporating CT-Scan images of the eye into Mimics and later Solid works software. Afterwards, the most suitable mechanical properties for the constituents of the eye were extracted from the literature. The mechanical properties of vitreous and Sclera were obtained by experimental... 

Based on the modified couple stress and Mindlin plate theories, a Levy type solution is presented for bending and vibration analysis of rectangular isotropic micro plates with simple supports at opposite edges and different boundary conditions at the other two ones. Modified couple stress theory is taken into account to capture the size effect and the governing equations are derived using Hamilton's principle, and solved by Levy solution and space-state method. The results are verified with the existing ones in the literature. As a benchmark, additional tables for vertical deflections and free vibrations of plate with various boundary conditions are presented  

A complete understanding of high-intensity focused ultrasound-induced temperature changes in tissue requires insight into all potential mechanisms for heat deposition. Applications of therapeutic ultrasound often utilize acoustic pressures capable of producing cavitation activity. Recognizing the ability of bubbles to transfer acoustic energy into heat generation, a study of the role bubbles play in tissue hyperthermia becomes necessary. These bubbles are typically less than 50μm.
This dissertation examines the contribution of bubbles and their motion to an enhanced eating effect observed in a tissue-mimicking phantom. A series of experiments established a lationship between bubble... 

Compliant mechanisms are generally used in quasi-static condition and therefore system dynamics do not have a significant effect on their performance; But if the inertia of the links is high, the dynamics of the mechanism will affect its performance altogether. By cleverly designing the mechanism, these effects can be used to create new movement patterns. In this research, a family of compliant mechanisms is introduced whose movement patterns are a function of input speeds. This means that at low speeds, the flexibility of the mechanism does not have a significant effect on its performance, but when the speed exceeds a certain limit, this flexibility changes the configuration of the... 

In this dissertation, elasto-plastic analysis of deformation, buckling and stability of sandwich cylindrical shell panel with orthotropic core under axial compression and lateral uniform pressure is perfomed. A new study on behavior of sandwich cylindrical shell panels under elasto-plastic deformation is done. In contrast of available analyses in which the core layer assumed to be isotropic and elastic, present analysis includes the sandwich shell having orthotropic elasto-plastic core. The deformation analysis of sandwich shell is performed based on two different theories; one is adopted for sandwiches having a stiff core and the other is proper for sandwiches having a flexible core. Based... 

Quadrotors have limitation in performing fast descent maneuvers due to Vortex Ring State (VRS) region which make quadrotor unstable. In order to avoid entering VRS, a velocity constraint considered which it should be satisfied during this maneuver to guarantee a safe and stable fast descending maneuver by quadrotor. The purpose of this thesis is to overcome limitation in speed space of quadrotor in order to reduce the time of fast descending maneuvers by using Reinforcement Learning Techniques. A new cascade controller proposed which using PID in inner loop as a low level controller and DDPG as one of reinforcement learning techniques in outer loop as high level controller in order to... 

Quadrotors have limitation in performing fast descending maneuver due to entering a dangerous region in velocity space called Vortex Ring State(VRS) which cause considerable loss of lift that may lead to fall. The purpose of this project is to reduce time of fast descending maneuver without entering VRS region by using model predictive control. First, appropriate nonlinear dynamic model of quadrotor obtained by considering important aerodynamics effect. Then by considering velocity constraints in order to avoid entering the VRS region, a nonlinear model predictive controller(NMPC) has designed. This controller successfully reduce the time of the maneuver up to than ordinary descending....