Sharif Digital Repository

The leads with heavy current passing through the covering plates, and the winding in a transformer, are sources of eddy current losses. Due to this loss some regions of tank wall are subject to serious local overheating. It affects the safety and reliability of this expensive bject and power delivery.Heavy current in large power transformers and special type transformers give rise to a concentrated passage of eddy currents which in turn cause high local losses and overheating in the metallic parts especially in the steel tank walls of transformer.This local overheating is dangerous for transformer oil and the solid insulations. Therefore the calculation of losses and proper design of... 

In the recent years, medical application of robots has been widely developed. Transforming open surgeries to close surgeries has distinguished this novel method to decrease limitations in this type of surgery. In this procedure, two or three small incisions on the skin are used as guides for robotic instruments to enter the cavity, to improve the surgeon’s manipulation and function in surgery. One of challenges in this field is surgeon’s training for laparoscopic surgery. Surgical simulators are used to solve this problem. Lack of instrument for large organs gripping and tissue palpation loss are existing difficulties in available surgical simulators in such a manner that surgeons has no... 

This thesis aims to discuss matters in the area of non-symmetrical contact. Problems have been solved by the use of different numerical methods and their precision has been determined. In most projects which have been conducted in regards with contact's studies, Indenter has been considered vertical on the other object and particles of two objects are moving in the vertical direction of the free surface. This matter has resulted in obtaining symmetrical functions relevant to the point of beginning contact which helps distributing contact pressure, stresses and movements. In addition, mostly profiles of two involved objects are considered symmetrical that this matter greatly contributes... 

In this study, the thermal buckling behavior of thin metal liner reinforced by composite shell in present of the initial imperfection is investigated. For this purpose, the Ryzener – Myndlyn shear-deformation theory & the virtual work method are used to extract equilibrium equations. In this work, the conical shell with c-c, s-s, c-f boundary conditions has been studied. The outer layer of reinforced composite is exposed to constant ambient temperature and iner layer is exposed to heat. Metal liner and reinforced composite shell are merged with together. In other words, the degrees of freedom at each node for both shells are assumed to be equal. Solution method is finite element method using... 

In this research, distribution of stress, strain and temperature fields in the strip and workroll were determined during steady state cold rolling process. To do this, first an initial guess based on the approach proposed by Hill for the velocity field was taken and accordingly, the real velocity distribution and then the strain rate and stress fields in the strip were calculated. Then, using the obtained stress and strain rate fields, the deformation power was determined and used as a boundary condition for solving the thermal behavior of the strip. By considering the Streamline Upwind Petrov-Galerkin method and solving the finite element relations, the temperature distribution within the... 

Various theoretical studies have been developed to obtain a deeper understanding of concrete behavior lead to the concrete constitutive models in the macroscale. In these models, however, the microstructure of the concrete and its effects on the concrete behavior has not been taken into account.Several numerical approaches have been incorporated to determine the effects of concrete mesostructure on the overall behavior of concrete. They may be classified at least in three main groups. In the first group, Continuum finite element methods (FEM) equipped with interface elements is incorporated. Second group is to incorporate more efficient elements, such as lattice or truss elements, instead of... 

In this research, molecular structural mechanics method is employed to calculate the Young’s modules of a two-layered carbon graphene sheet. For this purpose, covalent bonds are modeled using non-linear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered from all other atoms located in its cut-off radius. Young’s modulus, bending modules and Poisson’s ratio of single and two-layered graphene sheets were calculated and the results revealed that Young’s modulus decreases... 

Since it is important to obtain the suitable cutting conditions for machining and investigate the effect of various parameters on this process, the simulation of this process has been developed extensively by using the finite element method in recent years. Due to very large plastic deformation and also continuous chip flow, one of the most appropriate techniques in modeling chip formation is the arbitrary Lagrangian-Eulerian (ALE) finite element method which has been used in several papers using some traditional codes like ABAQUS or personal codes in recent years. However, one of the limitations in this method is the use of a continuous mesh retains with no change in connectivities which is... 

Bearing capacity of foundations is one of the most controversial issues in foundation engineering. In this study regarding to the previous researches which has done by the other researchers the bearing capacity factors of a footing has calculatedusing finite element method. On the next step of this study some footings has modeled on different positions near slopes with different angles and bearing capacity of them has calculated, then some strip foundation has modeled and bearing capacity of them has calculated and compared with the values of the footings in this study and strip foundations of the other researches. Furthermore some foundations have modeled on the solpe and bearing capacity... 

Minimally Invasive Surgery (MIS) is a modern surgical technique in which the operation is performed through small incisions in the body. Therefore, the surgeon looses his/her sense of touch which is of high importance in any medical operation. In the present work, a novel smart grasper is presented in which the surgeon can virtually acquire a feeling of force/momentum experienced by the organ/tissue. The smart grasper uses piezoelectric sensors bonded at desired locations to detect the applied force/momentum applied by surgeon and to measure the transmitted force/momentum to the tissue/organ. First, an accurate electro-mechanical model of the smart grasper is developed and the relations...