Sharif Digital Repository

The theory of resonant wave interaction has found considerable applications in meteorology, oceanography and limnology. It is known that the mechanism serves as an effective means of energy transfer in the atmosphere, oceans and lakes. In this project, the three-dimensional resonant interaction of a surface wave with two pairs of interfacial waves in a stratified fluid is studied theoretically. Witham’s variational method is formulated in order to apply to weak resonant interaction among waves whose amplitudes and phase angles vary slowly with position and time. The method is applied to a surface-interfacial wave interaction in a horizontally infinite two layer fluid. Combination of two... 

Flame Response to acoustic excitation which plays an important role in combustion chamber stability state may be found through numerical simulation. A finite volume code of higher order accuracy developed for compressible flows was adopted. Species equations along with a single-step irreversible reaction model were added to this non-reacting program. Changes were also made to the energy equation. Premixed methane/air flame in tubes was studied and the same problem was solved with FLUENT software. It was found that whether the Lewis number is considered constant or temperature dependent has a strong effect on flame structure and shape and that using mean values for gas properties yields out... 

Using Variational Method, two important hydrodynamic phenomena, “internal gravity waves” and “gravity currents”, are modelled theoretically in this research. Variational method as a robust technique for modelling complicated problems related to fluid mechanics gives us the ability of finding closed-form formula for predicting the behavior of the flow in an ideal fluid system. In the first part of this research, focusing on the nonlinear resonant interaction between surface and internal waves, we model the evolution of interfacial waves on the interface of a two-layer fluid system. This phenomenon play an important role in the mixture of the fluid and cascade of energy in the environment.... 

In this project, multi objective optimization (MOO) approach is used to optimize the SOFC/MGT integrated system performance in two strategies. In order to improve the performance and increase of Micro Gas Turbine (MGT) efficiency, it can be combined with Solid Oxide Fuel Cell (SOFC) which it has high operating temperature.The multi-objective optimisation method used allows to generate Pareto curves that represent the trade-off between conflicting thermo-economic objectives of SOFC/MGT integrated system, like, electrical efficiency, output power and electricity cost. The results of the thermo-economic optimization offer a basis for decision making and engineering improvement. SOFC capacity... 

Online searching for product information or buying some certain goods online has become increasingly popular during the last few years. Despite this fact there is still little empirical evidence about the relationship between in-store shopping and e-shopping. The substitution effect between these two types of shopping can have significant outcomes in urban transportation. Hence Analyzing different aspects of this new phenomenon and using its potential substitution effect on in-store shopping to decrease the amount of mobility in transportation system can be an attractive subject for urban transportation planners. The main purpose of this study is to reveal the relationship between the... 

Nanoparticles can be applied as chemical agent in enhnaced oil recovery like surfactants and polymers. One of nanoparticles usefull capabilities is modification of their surface. This research investigates this capabilty of nanoparticles in enhanced oil recovery. Surface modification of nanoparticles with both agents can bring new abilities to these materials. Here surface of silica nanoparticles is modified by hydrophilic agent comprising PEG groups, hydrophobic agent comprising propyl group and both agents. FT-IR tests showed that grafting of modifiyng agents on surface of nanoparticles is well done. To investigate effect of nanoparticles surface modification on nanoparticles capability in... 

In this project, a comprehensive methodology is developed to present the lifetime management and optimization framework for hybrid renewable energy systems. The main purpose of this work is to minimize the lifetime cost and improve the system reliability based on the interaction between different optimization levels related to different steps in the system lifetime. The proposed methodology is generally presented by providing a connection between the three specified optimization levels: 1) Planning: including design and long-term optimization models which is performed before system operation, 2) Real-time operation: By employing the receding horizon optimization which is applied from the... 

Renewable energies and their various types have been recognized as sustainable solutions to address the challenges arising from increasing energy consumption and environmental issues. The use of wind energy as one of the renewable energy sources has particular advantages, considering it as one of the most sustainable energy sources. One of the key factors in wind turbine development is the diversity and multiplicity in their structural designs. Therefore, the design of wind turbine structures with characteristics such as suitable strength, high energy efficiency, optimal cost, and high reliability is of great importance. By employing various sciences such as vibrations and optimization in... 

Air-cooled condenser is widely used in thermal power plants as its main cooling system. However, the thermal capacity of air-cooled condensers reduces considerably in environmental wind drafts. So, the purpose of this study is to find practicable solutions to minimize the mal-performance of air-cooled condensers in windy conditions in either design or off-design conditions and consequently prevent the related steam turbines power reduction. The target combined cycle power plant consists of 4*160 MW steam turbines and 4 air-cooled condensers in its steam cycle part. This research presents two general and practical remedies, which are also applicable to many different powerplants irrespective...