Sharif Digital Repository

Generally concrete dams have not been sited at location where there were faults classified as active. However, there may be sites suitable for concrete dams where there is some possibility of fault displacement occurring underneath the dam. In addition, there may be situations where an existing dam was constructed over a fault thought to be inactive and later determined to be active, due to different approaches of classification of a fault whether it is active or not. Also some discontinuities may be observed during construction. For these cases nonlinear analysis and criteria will be required to assess the capability of concrete dams to safely withstand fault displacements. In this thesis,... 

In this research, a Ground-to-Ground axisymmetric flying vehicle is studied. In this flying vehicle the warhead is replaced by a nose having simple and cheap guidance and control. Commonly such systems include axial rotation to increase stability, which results in the malfunction of the added seekers. In this research, to overcome this problem, the rotation of the vehicle’s forward part is controlled by fuzzy control method, from the beginning of the fly. In addition, a strapdown seeker, which has high accuracy and low cost is used. This provides the system with employing Integrated Guidance and Control (IGC). The IGC, used in this research is based on fuzzy logic, which directly determines... 

Disturbance rejection is one of the most important criteria that should be considered when designing control systems. The problem has been widely investigated and studied when the parameters of disturbance signal is known. However, there are still ongoing researches in the field when the parameters of disturbance signals are uncertain and/or varying with time. In some applications the disturbance signal can be modelled by special dynamics, e.g., step type disturbances with unknown magnitude, sinusoidal disturbances with unknown magnitude and frequency, and damped sinusoidal disturbances with unknown magnitude, frequency and damping factor. In such cases, an adaptive scheme for estimating the... 

One of the significant as well as fascinating utilization of thermoacoustic is combining heat pump and thermoacoustic refrigerator. By means of supplied heat from hear source, the heat pump generates acoustic power which will be absorbed by refrigerator and forwarded to the heat source afterwards. In other words, thermoacoustic systems, from the side of which heat is absorbed, produces chill in the opposite side. Due to the novelty as well as heavy and precise research requirements, these systems has been neither designed nor manufactured in our country yet. In this research a laboratory prototype from aforementioned systems has been constructed, thereby paving the way for enjoying and... 

Matrix acidizing operation is one of the popular methods of well stimulation in the oil and gas industry which is used to remove near wellbore damage, increase the permeability, hence improve the production rate from the formation. Hydrochloric acid is used in the carbonate reservoirs to remove formation damage and create wormhole deep in the rock. It has been shown that with the proper operating design, significant improvement in the production rate can be obtained. A successful acid operations involves the proper selection of the candidate wells, identify the type of formation damage, stimulation method selection, correct design acidizing scenario, implementation of the technique and... 

Asset pricing models are one of the most important tools in investment management and portfolio allocation. Multi-factor asset pricing models try to explain the relationship between risk and expected return through a limited number of macroeconomic, fundamental or statistical factors. Usually, these models are suggested based on the US market and its intrinsic qualities. Although, there are some similarities between the Iranian and the US market, these economies are structurally different and therefore, proposing a proper multi-factor model based on the Iranian market’s fundamental characteristics will greatly improve the understanding of risk-return relationship in this market. In this... 

Many improvements in the Inertance Pulse Tube Refrigerators (IPTR) have brought them to a place in which other Cryocoolers are gradually replaced. The Inertance Pulse Tube Refrigerators have high reliability, low operating and maintenance cost, low vibration and high efficiency due to lack of mobile components. These Cryocoolers are used in the cooling of infrared sensors, Cryosurgery applications, transportation, liquefaction of gases, and so on. The IPTR based on Stirling cycle and it uses helium gas as working fluid. Typically, a variety of compressors can be used as a driver, resulting in reduction in the lifetime of the IPTR. Thermoacoustic engines can be used to remove these... 

The present thesis is devoted to deeply reconsider the anti-vortex film cooling method and its undiscovered features using numerical optimization and advanced turbulence models. In this regards, a modified turbulent heat-flux model was developed to enhance the predictions in complex flow fields with highly anisotropy and non-equilibrium flow/thermal features. Next, the model was introduced to ANSYS FLUENT 16.0 package to prepare a more accurate flow solver. Then, the solver was coupled with an in-house Differential-Evolution (DE) optimization algorithm to find the optimum configurations of anti-vortex holes for several flow and geometric conditions such as flat-plate, convex/concave surfaces... 

Asset pricing models are one of the most important tools in investment management and portfolio allocation. Multi-factor asset pricing models try to explain the relationship between risk and expected return through a limited number of macroeconomic, fundamental or statistical factors. Usually, these models are suggested based on the US market and its intrinsic qualities. Although, there are some similarities between the Iranian and the US market, these economies are structurally different and therefore, proposing a proper multi-factor model based on the Iranian market’s fundamental characteristics will greatly improve the understanding of risk-return relationship in this market. In this... 

Demand for high performance components has caused a propensity towards high strength alloys, especially 7000 series, having extended applications in aerospace, automotive and medical industries. Due to high strength, heat treatability, and optimum weight, these alloys have been implemented in various conditions, specifically AA7075, being directly used in airframes. Through the years, numerous attempts have been made to improve the corrosion and formability properties of these alloys, resulting in the development of various tempering methods such as retrogression and re-ageing. Despite achiving optimal properties, it has been of less interest through literature to assess the formability of... 

Thermo-acoustic sience is the conversion of heat to power through the sound wave. Thermoacoustic engines for different reasons like easy making, not having moving parts and so high reliablibility of system is in attention for researchers. Also looped-tube thermoacoustic engines are very new in the world and sience and thechnology of them belong to a few companies and for different reasons are replacing different kinds of thermoacoustic engines.They have higher efficiency than other types. They can be made in large scales. They have a larger thermal range. In this research, the numerical study of one, two and four stage looped-tube thermoacoustic engines has investigated with the help of... 

In this research plastic deformation analysis of high carbon steel wire in one and more pass wire flat rolling process using the finite element method (FEM) has been investigated. The effects of changing rolling pass number, length of wire, mechanical property of roll, rolling speed and friction between roll and wire in calculated results have been studied and with the main process parameters are compared. Then, the damage and failure of wire and that’s steady state cross-section is examined by model of Johnson cook damage criterion (JC). The results suggested that reduction in height of the wire affects the rolling process parameters such as strain, damage and the cross-sectional geometry... 

In this research it has been attempted to suggest a modified retrogression and re- aging heat treatment on the sheet of AA7075 alloy with a thickness of 2 mm. The main aim of the research is to reduce the required duration of RRA process while maintaining the value of the conventional tensile strength achieving by the RRA process. This was performed by adding an intermediate warm rolling deformation during the RRA process. The rolling temperature was 180 °C and the rolling reductions were 30%, 40%, 50%. Moreover, the temperature of 170°C was selected as the re-aging temperature, for which the aging time of 0.5, 1, 1.5, 2, and 2.5 hours were examined. This temperature and times were chosen to... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can...