Sharif Digital Repository

Routine ultrasound calibration methods have some restrictions such as: low bandwidth, low frequency resolution, limited spatial resolution, the high cost of test and risk of damage to the transducer when exposed to high powers. In this thesis, a new technique based on microbubble resonance is proposed. Non-linear resonating microbubbles produce harmonics;the first harmonic may be masked by reflection from larger microbubbles as well as unwanted reflections which cause ambiguity in the determination of the amplitude of the excited pressure. Therefore, the second harmonic is used, with a single characteristic peak. In order to model the physical phenomenon, the second harmonic generated in the... 

In small turbojet engines, it is important to find a suitable fuel injector with good spray quality. However, the rotating fuel injection system can potentially provide high atomization quality without the high-pressure fuel pump through the centrifugal forces of the engine shaft. The spray characteristics of rotary atomization for small gas turbines can be investigated using a high-speed camera. To analyze the breakup process of the liquid column and liquid film, spray visualization tests should performed under varied test conditions.In this research, experimental study on liquid breakup process has performed in rotary atomizer of j402 turbojet engine with the name of slinger injector, to... 

The liquid breakup analysis and spray characteristics measurement of atomizers are very essential for the numerical modeling of the primary atomization in combustion chambers. The rotary atomizers are used in many applications especially in small gas turbine engines as a fuel injection system. An experimental investigation of primary breakup dynamics and spray characteristics of rotary atomizers with high aspect ratio discharge channels are described. Four different rotary atomizers with round radial, round radial-axial, round radial tangential, and square radial discharge channels are studied. The purposes of this study are to identify the effect of channel orientation and its geometry on... 

Accumulative roll bonding has been used as novel method to produce the composite with ultra fine grain microstructure. This method has two steps, impose the particles as reinforcement between the layers by roll bonding process and then distribute the particles in matrix and generat an ultra fine grain microstructure during the ARB passes. In the present work, ARB process was performed to produce the Al/SiC and Al/Al2O3 nano-composites with various particles size and different volume fraction of reinforcement. Microscopic observations such as OM, SEM and TEM and XRD analyses were used to investigate the microstructure of produced composites and the distribution of the particles in matrix... 

Restructuring and privatization in power system such as any industry leads to better market operation and more social welfare. Since two decade the power system in many countries have changed from monopoly to free market. In a restructured network the technical and economical aspects should be considered together. Ancillary services are needed for any power system to be operated in an optimal and secure manner. Reactive power and voltage regulation is one of the most important ancillary services in the network. this service should be supplied by its providers through a competitive market and system operator determines the optimal dispatch among different bids. The cost of purchasing reactive... 

This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems and issues arising in its applications. The new electric utility environment has an immedi-ate consequence of emphasis on reliability and secure operation of power systems. This requires faster and more precise methods to assess the dynamic aspect of se-curity. On the other hand, this issue is becoming challenging when the determined dispatch might not be accommodated due to violation of the limits.This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems... 

CHP (Combined Heat and Power) generates electricity and thermal energy simultaneously from input fuel. Since it has high energy efficiency and low installation time, it is an appropriate approach in energy management of residential complexes. In this project, stochastic programming based on Monte Carlo approach is used to handle uncertainties in the optimal sizing of CHP for residential complexes. Availability of CHP, boiler and AC bus as well as the electrical and thermal load forecast errors are considered as stochastic variables. Minimizing system total cost considering the probability of each scenario obtained from the scenario reduction algorithm is the objective function. The system... 

The process of deregulation that has involved electricity many markets has introduced several new interesting research topics in power system area. This thesis addresses one of the most fascinating issues among them: the study of distributed generation both renewable and conventional integration in distribution networks. From the distribution network operator (DNO)'s point of view, it is of interest to develop a comprehensive methodology which considers various distributed generation technologies as an option for supplying the demand in distribution networks. In this thesis, the planning problem has been multi-objectively modeled. This will help the planner in decision making while knowing... 

Since 1980s the electricity market has been gradually evolving from a monopoly market into a liberalized one for encouraging competition and improving efficiency. This brings the opportunity for generation companies (Gencos) to make more profits while embracing more risks of not being dispatched. Therefore, it has become a core interest for the Gencos to develop optimal bidding strategies to maximize the profits and minimize the risks while participating in such a competitive market. Error of determining day-ahead electricity price is one of the sources of the risk. Energy price has a high impact on bidding strategy optimization process. So it should be determined with low error which is not...