Sharif Digital Repository

One of the major reasons causing cracks in external surfaces of concrete arch dams are thermal loads. Therofore, in order to avoid instabilities due to function of thermal loads in association with hydrostatic and hydrodynamic pressures, a precise evaluation of temperature distribution through dam body is indispensable. In this study, effects of thermal loads mostly on upstream surface of Karun-3 concrete arch dam in Iran were examined using a 3-D finite element method considering water level fluctuations. Also the influence of operatvie boundry conditions in our problem which are water temperature, air temperature and solar radiation was precisely taken into account. Moreover, nonlinear... 

In this thesis contact problem between wheel and rail has been studied. Also rolling contact fatige (RCF) has been studied in detail. Unlike previous studies that have focused on FEM solution, in this study the problem has been formulated based on analytical methods. Evaluating the loads in wheel-rail contact zone is necessary to find the defects. This thesis presents the evaluation of the stress field inside elastic rolling bodies with an elliptic area of contact. This kind of model can be applied to wheel-rail contact mechanics. The problem has been solved for two main models: with friction and without friction. The results have shown that shear stress reaches the maximum magnitude... 

The main purpose in this thesis is the finite element simulation of thermal barrier coatings (TBC), subjected to residual stresses due to the coating process followed by thermo-mechanical fatigue loadings. This finite element modeling is performed in the ABAQUS software. In order to consider the actual condition of thermal barrier coating, models are defined based on a SEM image including real roughness and porosity of coating layers using image processing technique.
Two-step residual stress taking into account both coating process of bond coat and top coat layer is performed. Pre- heating of substrate and bond coat in order to reach comperessive stresses in coating layers has been... 

The main aim of this thesis is to develop a mathematical model for vibration analysis of cracked rotors. This model should be a simple and precise model for prediction of the cracked rotor vibration behavior and suitable for vibration control. In order to create such model, the pure bending of a cracked beam is analyzed at first. This analysis is performed for two different orientations of the crack with respect to the beam and the bending vector. In this section a continuous bending model with continuous model for crack is developed which can predict the full deformation of the cracked beam in bending and can estimate the stress distribution in the beam with good approximation. Comparison... 

One of the three fundamental methods in reservoir evaluation is coring, other two methods are logging and well test. Coring is an operation during which, samples from formation rock are taken, and used for laboratory tests and examinations. Although coring presents exact information from reservoir rock, its small scale is the reason of some laboratory errors. This operation is fulfilled with special bits. Coring importance shines where it could give us an idea of reservoir conditions; however cannot be develop it, to all of the reservoir. Coring is used to identify rock properties like porosity, permeability, wettability and fluid properties like fluid density or fluid saturation. Rock... 

One of the main geotechnical phenomena that causes severe damage during earthquake is liquefaction. This incident occurs due to the undrained behavior of loose sandy soils. In this occurrence, the interaction between the solid and liquid phases in a cyclic motion leads to an increase in pore water pressure and a decrease in interactive forces (effective forces) between grains in the solid grains. Therefore, shear strength decreases. Different aspects of the aforementioned phenomenon is investigated, namely, field, laboratory, and numerical; nevertheless, the study is largely focused on the numerical modelling. Most studies in this field are carried out on a one-layer saturated sand. However,... 

The phenomenon of aging causes a great deal of damage to the airborne structures for which there is a specific maintenance instruction, or if an unexpected damage occurs in specific area of a structure, this damage must be repaired and a special repair process must be designed for it. However, due to the diversity of damages and also variations of the implemented loads, the load is transferred to other structural elements, hence, it is necessary to extend the life of the structure in order to identify these loaded elements and reinforce the applied forces. First, this phenomenon involves a design of a large number of metal patches, where a large number of drills have to be made in the body... 

Metallic implants are often used in the open reduction and internal fixation of fractures. Open reduction and internal fixation are commonly used in cases of trauma when the bone cannot be healed using external methods such as casting. The locking compression plate combines the conventional screw holes, which use non-locking screws, with locking screw holes, which use locking head screws. This allows for more versatility in the application of the plate.
In the present work, the stress (von-mises) and deformation of a locking compression plate fixed across a transverse fracture (2-mm gap) at the midshaft of femur was evaluated by Ansys software. Femur model is divided to two part... 

A finite difference technique is developed to predict the second stage creep displacement rates and stress analysis of a short fiber metal matrix composite subjecting to a constant axial load. The exponential law is adopted to describe the matrix creep behavior. Also, a method for prediction of interfacial debonding at fiber/matrix interface is developed using a stress based method. The obtained results could greatly help to better understand the flow pattern of matrix material and the load transfer mechanism between fiber and matrix. The stress components and strain rates are also validated by the available FEM and experimental results  

Turbochargers are industrial devices that widely are used in aviation, marine and automotive industry. Manufacturing cost and technology of their components vary according to their application fields. One of the most important components of these devices is turbine wheel, which needs to be solid, strong and have a high resistance in critical extraordinary conditions. In these days, it can be seen that superalloys are used remarkably in manufacturing of turbine wheels. When this part of turbine is damaged due to some different reasons, turbine wheel must be quit of circle Process according to repair instructions. In these conditions either turbine must be repaired or replaced by a new one;... 

In gas turbine industry, usually turboshaft engines are designed base on turbojet and turbofan gas generators. Hence, the overall cost of product design and manufacturing will decrease and sales and revenues will increase. It is also common to convert aerial engines with their flight life passed to industrial engines. In the present work, the conversion of an existing turbojet in the gas turbine lab of sharif university of technology to a turboshaft has been investigated. In the first step of project, the experimental data of turbojet performance are considered and the design point of the turboshaft engine will be determined. Then, nominal rotational speed of power turbine and zero to three... 

Wide lands in IRAN are covered by the “Hydro – Collapsible” soils. These types of soils possess high apparent shear strength in their natural condition but are highly susceptible to volume collapse upon wetting. This behavior is generally attributed to their open, unstable soil fabric and their weak inter-particle bonding forces, which together yield a soil void structure that is susceptible to collapse.
Previous studies rarely investigated the roles of stress state level, matric suction and stress path on the hydro-mechanical nature of the collapse phenomenon. Also most studies dealt with conducting laboratory tests on remolded soil specimens through which the role of natural soil...