Sharif Digital Repository

The purpose of this project is modeling and solving equation of an open cycle system based on MHD generator in order to achiving geometrical properties of generator shuch as length and cross sections of channel and extractable electrical power. In this work hydrogen is used as initial fuel and it’s combustion product near oxygen as working fluid in an open cycle system concluding of combustion chamber, convergence nozzle, farady generator with separated electrod’s and constant mach number and also diffuser. Motion of fluid is considered one dimentional and direction of magnetic field with magnitude of 2 tesla is assumed to be perpendicular to motion and electrical current directs. For... 

Due to the high level abstraction inherent in most formal specifications and the need to formally specify and develop nondeterministic systems, such as concurrent, probabilistic, and game-like ones, nondeterminism comes into formal specifications inevitably. As it will be shown in this thesis, after developing programs constructively from implicitly nondeterministic specifications, which have been written in the CZ (constructive Z) specification language, only one of the allowable, specified behaviors will appear in final programs. In this way, the implementer will be provided with only one of the possible implementations that is not necessarily the best one. When the nondeterminism involved... 

One of the most crucial methods to Ensure correct software performance is testing. On this ground, one of the most critical discussions regarding software testing is the effectiveness of a test suite. Program state coverage is a criterion for determining the effectiveness of a test suite. This criterion indicates the number of program states that are executed for the lines. Since the total number of program states cannot be calculated to measure coverage, this criterion proposes a fixed number of 10 to measure program state coverage. Also, according to calculations for the program state in the execution of each line, the time complexity of this criterion is high. In this thesis, providing... 

In order to isolate the engine from the body of the car and chassis to reduce transient vibrations, an engine mount system is used. Using its flexible rubber components, the engine grip keeps the car's engine suspended, allowing it to shift power to the body and chassis. The purpose of this project is to optimize the geometry of the engine mount to achieve the desired static and dynamic stiffness values simultaneously. In this regard, by defining the hyperlastic and viscoelastic properties of the material used in the engine mount, we simulated the static stiffness and dynamic stiffness values of one of the most common engine mounts in the automotive industry. Then we investigate the effect... 

In this study, high frequency vibration analysis of two connected plates by a beam interface is carried out using Energy Finite Element Analysis (EFEA). In structural vibration analysis at low frequencies, classical methods such as Finite Element Method or Boundary Element Method present accurate results. But, using these methods at high frequencies requires expense of high calculation cost and time. Therefore, using of statistical methods that are based on average estimates of vibrations, at high frequencies is most popular. EFEA is a method that gives average response of structure at a certain point and frequency band. This method is developed on the basis of finite element analysis of... 

This dissertaion deals with the vibration and aeroelasticity analysis of a turbomachinery cascade with Magnetorheological Elastomer (MRE) based sandwich blades. At first, bending vibration of the rotary blades equipped with an MRE core based on the three-layered sandwich beam theory have been studied in the flexural and edgewise directions. Further, the torsional vibration is investigated and the effects of different parameters such as the intensity of the magnetic field, rotating speed and the MRE layer thickness on the natural frequencies and loss factors of the system are studied. On the basis of the modeling obtained for the structural dynamics and based on the Whitehead's unsteady... 

One of the key issues in the design of vessels is their proper stability and performance in waves. Therefore, the use of twin-hull vessel designs such as conventional catamaran and SWATH is suitable for improving stability and seakeeping quality. Although SWATH has a better seakeeping quality than a conventional catamaran, it has been observed that at high forward speeds, especially in head waves, the vertical motions of the vessel is greatly enhanced. Various methods such as correction of the hull form and the use of fin stabilizers can be used to modify SWATH vessel motion behavior. These control surfaces can respond appropriately to the dynamic forces from the waves, reducing the motions... 

Humans can take lots of advantages from influencing on small particles. Since manipulation of micro sizes by humans or macro robots, due to their precession and size, is not possible, a new field of study, called Microrobotics, has been introduced. To better understand the working principles in small dimensions, we first need to know the governing physics laws. This step helps us to identify the dominant forces in the small dimensions, which, in turn, leads to better actuation of miniature robots. Because of the size of the miniature robots, one of the best actuation methods is the interaction of the magnetic field on magnetic dipoles. To use the magnetic field as an actuation force, the... 

Market heterogeneity is an essential element in the strategic decision making of firms. Today, differences in urban structures, product varieties, and information availability have created new heterogeneities that deviate from the ones in the classic literature of marketing and industrial organization. Thus a new perspective is needed for analyzing the firms' decisions in these markets. In this thesis, we study the effect of heterogeneous markets on the pricing, location, quality, and product line introduction strategy of a firm to find the optimal reaction of a firm entering these markets. In this regard, we first assume that consumers are not only located at different places in the market... 

In the present study, the nonlinear vibrations of the rotor on the nonlinear bearing have been studied by the multiple scale method. To achieve this goal, Jeffcott models, two degrees of freedom and rotating Euler-Bernoulli beam have been used as rotors and insulators and nonlinear tilting-bearing bearings have been used as supports.To better understand the importance of the supports in the analysis of rotating systems, the rotor joints with isolates with high static stiffness and low dynamic stiffness have been considered and the dynamic behavior of the system has been studied using the multiple scale method. The results of this study showed that this type of nonlinear isolator has a good... 

In many industries, including oil and gas industries, power plants, refineries, petrochemicals, steel and cement industries, industrial complexes and consumer industries, there are tanks for storing materials. It is necessary to measure level of products while they are stored in tanks of different sizes. Ultrasonic is one of the non-contact and accurate measurement technologies that can provide a suitable solution for liquid tank monitoring. The purpose of this thesis is to design and build the electronic parts (transmitter and receiver circuits) of an ultrasonic system that is capable of detecting levels at a distance of less than 5 meters with an accuracy of 0.5 % full scale. In this... 

This research investigates the possibility of using the component mode synthesis (CMS) method in experimentation. It should be noted that the original idea for this project originated from an industrial problem. The main issue in this problem was the lack of sufficient equipment to conduct tests on very large structural modes and the high computational cost for their analysis. Therefore, a test platform was constructed using a scaled-down sample (approximately 1:25) with connections that closely resembled real connections. This assembly was then tested separately, and the results were compared with analytical analyses. After updating and correcting the model in several stages, the structure... 

In this thesis, the high frequency random vibrations analysis of a reinforced plate with a cutout is carried out using Energy Finite Element Analysis (EFEA) and the final results are validated with experimental results. EFEA method uses the average energy density as the primary variable to form the governing differential equations of energy flow in the structure. In this method the equations of space and time averaged energy density are derived in the Far Field and the energy intensity is considered as continues variable over the structure. In this work, at first for simple beam and plate an EFEA code is developed. Then the relationships for joints are derived using structural dynamics. Some... 

Due to the importance of recognizing the underwater and the existence of danger to human life in this environment, the use of AUVs has greatly expanded. To build and use these vehicles, we need to model dynamic behavior, and control these systems. The nonlinear dynamics of the AUV makes it difficult to use common linear controllers. On the other hand, the coefficients used in dynamic equations have uncertainty and changes, and as a result, dynamic analysis may be probably un-accurate. If the controller is designed, the controller must be self-tuning and robust to be able to withstand changes and uncertainty. Adaptive control is an approach for controlling such systems. The main idea in... 

Fuel sloshing plays a direct and pivotal role in the tracking control tasks of liquid-propellant satellites. To address this problem, existing works have considered some simplifying assumptions on fuel motion, such as fuel rigidity and potential ideal fluid. On the other hand, most studies have used the ODE discretized model-based control schemes to stabilize the infinite-dimensional satellite-fuel system, which can cause spillover instability and lead to a significant loss of accuracy. To overcome these issues, we generally solve the PDE-based control problem for rigid bodies with partially liquid cavities. In this regard and based on the governing PDEs of the liquid motion, the... 

In recent years, there have been many studies aimed at finding program defect using information of previous ones. These studies, by using the program text, previous bugs, and information related to version control and project management systems create an defect prediction model to find other defect prone areas in the program. The output of defect prediction methods is part of the program’s text, which is likely to have defects. Considering that the result of this method is just the text of the program and does not provide any extra information for finding defects to the user, these methods have not yet been applied to the software industry. On the other hand, by spreading the use of Q & A... 

Modeling and Controlling of a satellites fuel slosh is considered a vital problem in the field of satellite attitude control. In this paper modeling and control of the attitude of a satellite carrying a partially filled spherical fuel tank, which uses the diaphragm as a propellant management device (PMD), has been studied. The fuel slosh dynamics is modeled using a spherical pendulum with two degrees of freedom and a rigid arm, which represents the first mode of sloshing. The effects of the diaphragm that surround the fuel surface, are considered as torsional springs and dampers attached to the satellite body. The combined dynamics equations of the satellite rigid motion and the fuel slosh... 

In the past few decades, with the advancement of technology, using autonomous robots has been receiving growing interest. Autonomous semi-submersible vehicles are a subset of autonomous underwater vehicles (AUV). This type of vehicle operates near the surface of the water and is semi-submerged. Nonlinear coupled dynamics, structural uncertainties, model parameters dependency to robot velocity, external disturbances, and model constraints are AUV’s workspace challenges. For this reason, depth control of these vehicles in the presence of environmental disturbances is crucial. However, MPC as one of the advanced control methods in the field of robotics is increasingly developing. This control... 

Precise adjustment of orientation is vital in many important applications of satellites. Besides, in order to have sustainable power source and to reduce heavy costs of launching deployable solar arrays with large area to mass ratio are utilized. The vibrations in these flexible parts and attitude dynamics of the main hub influence eachother mutually. Thus, simultaneous attitude and vibrations control is of noticeable significance. In this thesis considering new details such as multi-section solar panels, the governing dynamic partial differential equations (PDE) are derived via Hamilton principle. In order that errors arised from discretized models be eliminated and just using regular...