Master of Science / Department of Mechanical and Nuclear Engineering / Mohammad H. Hosni / A traditional cooling/refrigeration cycle has four main system components which are an evaporator, a compressor, a condenser, and an expansion valve. This type of cycle requires use of refrigerants which have been found to be harmful to the environment, including causing damage to the atmospheric ozone layer. The main objective of the project was to investigate a water-based non-vapor compression cooling system. Water as a working fluid has the advantages of being inexpensive and environmentally safe for use, as compared to commercially available chemical refrigerants. The water-based cooling system investigated employed cavitation phenomena in converging-diverging glass nozzles. Cavitation is an important phenomenon in fluids, and is common occurring in many devices such as pumps, refrigeration expansion valves, and capillary tubes. It occurs when the static pressure of the fluid falls below the vapor pressure, into a metastable liquid state. Cavitation can be in the form of traveling bubble cavitation, vortex cavitation, cloud cavitation, or attached wall cavitation. In this thesis, the focus was first on visualizing cavitation for water flowing through converging- diverging glass nozzles. These nozzles had throat diameters between 2 mm and 4 mm. Two systems were used: (1) a continuous flow system, where water was driven by a centrifugal pump, and (2) a transient blow down system, where water flow was initiated using a suction pump. A high-speed camera was used to record videos and images of the associated cavitation phenomena. A thermal infrared camera was used in an attempt to measure temperature drop in the nozzle while the system was running The second part of this thesis focused on the understanding of the fundamental thermodynamics phenomena and on the development of practical knowledge relevant to the cavitation process. Two equations of state were used in the analysis, the van der walls equation of state, and the Peng Robinson equation of state. Equations of state were used to predict the transition from vapor to liquid. At a given temperature, the equations were solved for a pressure value corresponding to saturated liquid and saturated vapor specific volume values. Then, the equations were used to determine the spinodal liquid and vapor lines, which represent the metastabillity limits for the liquid and vapor. The characteristic equations of state, combined with implementation of the Law of Corresponding States and thermodynamic theory, were used to estimate the temperature reduction available for refrigeration.

Master of Science / Department of Mechanical and Nuclear Engineering / B. Terry Beck / Mohammad H. Hosni / Cavitation is the formation of vapor phase from the liquid phase by reduction in its absolute pressure below the saturation pressure. Unlike boiling, where the temperature of the liquid is increased to cause vaporization, the reduction in the pressure alone can cause the liquid to turn into vapor. Cavitation is undesirable in many engineering applications as it is associated with reduction in efficiency and is known to cause damage to pump and propeller components. However, the endothermic nature of cavitation could be utilized to create a region of low temperature that could be utilized to develop a new refrigeration cycle. The work presented in this thesis is part of ongoing research into the potential cooling capacity of cavitation phenomena, where the cavitation in a converging-diverging nozzle is being investigated. Due to the constricting nature of the throat of the converging-diverging nozzle, the liquid velocity at the throat is increased, obeying the continuity law. With an increase in velocity, a reduction in absolute pressure is accompanied at the throat of the nozzle according to the Bernoulli’s principle. The local absolute pressure at the throat can go lower than the saturation vapor pressure, thereby causing the fluid to cavitate. The effect of water temperature on the flowrates, the onset of cavitation within the nozzle, and the resulting length of the cavitation region within the nozzle are the subject of this thesis. Experimental results and analysis are presented which also show that near the onset of cavitation, the flowrate can go beyond the choked flowrate, causing the local pressure in the throat to go well below zero for an extended amount of time in the metastable state, before nucleating (cavitating) into a stable state. Flow visualization using a high speed digital camera under different operating conditions was aimed at investigating the region of cavitation onset, which appears to be associated with boundary layer separation just downstream of the nozzle throat. In order to delay the boundary layer separation point in the downstream section of the nozzle, the diffuser region of the nozzle was modified to enable two flow paths, where one path would suck the flow near the inner walls of the nozzle and the other would allow the bulk of the flow to pass through. This was achieved with the use of inserts. Various inserts were tested in an attempt to capture the effect of inserts on the cavitation phenomena. Their effect on the flowrates, length of two phase region, and cavitation onset are presented in this thesis.

The master´s thesis deals with the flow induced by rotation of cavitating fluid in converging-diverging nozzle, which simulates the vortex rope in impeller of water turbines. Measurement is performed on an experimental circuit in laboratory. Results from experimental measurements are compared with CFD simulation of single and two-phase flow. The main focus is to compare the difference of hydraulic losses and shapes of cavitating structures identified in the experiment and in the simulation.

Converging shocks have long been a topic of interest in theoretical fluid mechanics, and are of prime importance in inertial confinement fusion. However, tracking converging shocks in numerical schemes poses several challenges. Numerical schemes based on shock capturing inherently diffuse out shocks to multiple grid cells, making it hard to track the shock. Converging shocks are significantly harder to track, as this numerical smearing is much more significant when converging shocks approach the axis of convergence. To mitigate this problem, we transform the conservation laws to a non-inertial frame of reference in which the accelerating shock is stationary. A system of equations is derived based on the transformed conservation laws coupled to the shock speed obtained from jump conditions and a characteristic-based derivation of a relation governing shock acceleration. We solve these equations using a finite volume method. Our numerical results compare favorably with the analytical value of Guderley exponent for self-similarly converging cylindrical hydrodynamic shocks. Results for fast magnetosonic shock in MHD are also presented and compared with results from geometrical shock dynamics (GSD). Results from our shock fitting method, developed without any approximation to the original ideal magnetohydrodynamics equations, provide further credibility to GSD applied to converging fast magnetosonic shocks. This sort of shock fitting is a precursor to future multidimensional stability analysis of imploding shocks.

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No description available.

We develop and adapt absolute stability results for nonnegative Lur'e systems, that is, systems made up of linear part and a nonlinear feedback in which the state remains nonnegative for all time. This is done in both continuous and discrete time with an aim of applying these results to population modeling. Further to this, we consider forced nonnegative Lur'e systems, that is, Lur'e systems with an additional disturbance, and provide results on input-to-state stability (ISS), again in both continuous and discrete time. We provide necessary and sufficient conditions for a forced Lur'e system to have the converging-input converging-state (CICS) property in a general setting before specializing these results to nonnegative, single-input, single-output systems. Finally we apply integral control to nonnegative systems in order to control the output of the system with the key focus being on applications to population management.

<p>Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process.</p>

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Esta dissertação pretende fornecer uma contribuição acadêmica aos estudos sobre harmonização contábil em blocos econômicos. A pesquisa teve como objetivo analisar o processo de harmonização contábil nos seis países integrantes do MERCOSUL, após a refundação do IASB, em 2001. A metodologia do estudo tem caráter descritivo e natureza analítica, visando descrever as características qualitativas em relação aos aspectos contábeis e regulatórios dos países estudados. Foi realizada uma pesquisa documental em que foram analisados os relatórios sobre harmonização contábil no MERCOSUL e o método aplicado foi o de estudo de múltiplos casos. Os documentos analisados foram: (a) Report on the Observance of Standards and Codes Auditing and Accounting (ROSC A&A), do Banco Mundial; (b) relatório enviado pelos países ao IASB; (c) relatório enviado pelos países ao GLENIF, além das informações disponíveis nos sites oficiais dos próprios países. A pesquisa contribui para resgatar a história do processo de harmonização e alertar para os potenciais impactos das diferenças na preparação dos balanços das empresas que compõem o bloco. / This thesis aims to provide an academic contribution to the studies on accounting harmonization in economic blocs. The research aimed to analyze the accounting harmonization process in the six member countries of Mercosur, after rebuilding the IASB in 2001. The study methodology is descriptive and analytical nature, seeking to describe the qualitative characteristics in relation to accounting and regulatory aspects of countries studied. Documentary research was carried out in the reports on accounting harmonization were analyzed in Mercosur, and the method used was the study of multiple case. The documents analyzed were: (a) Report on the Observance of Standards and Codes - Auditing and Accounting (ROSC A & A) of the World Bank; (B) report submitted by countries to the IASB; (C) report submitted by countries to GLENIF; addition to the information available on the official websites of the countries themselves. The research contributes to rescue the history of the harmonization process and warn of the potential impacts of the differences in the preparation of balance sheets that make up the block.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Esta dissertação pretende fornecer uma contribuição acadêmica aos estudos sobre harmonização contábil em blocos econômicos. A pesquisa teve como objetivo analisar o processo de harmonização contábil nos seis países integrantes do MERCOSUL, após a refundação do IASB, em 2001. A metodologia do estudo tem caráter descritivo e natureza analítica, visando descrever as características qualitativas em relação aos aspectos contábeis e regulatórios dos países estudados. Foi realizada uma pesquisa documental em que foram analisados os relatórios sobre harmonização contábil no MERCOSUL e o método aplicado foi o de estudo de múltiplos casos. Os documentos analisados foram: (a) Report on the Observance of Standards and Codes Auditing and Accounting (ROSC A&A), do Banco Mundial; (b) relatório enviado pelos países ao IASB; (c) relatório enviado pelos países ao GLENIF, além das informações disponíveis nos sites oficiais dos próprios países. A pesquisa contribui para resgatar a história do processo de harmonização e alertar para os potenciais impactos das diferenças na preparação dos balanços das empresas que compõem o bloco. / This thesis aims to provide an academic contribution to the studies on accounting harmonization in economic blocs. The research aimed to analyze the accounting harmonization process in the six member countries of Mercosur, after rebuilding the IASB in 2001. The study methodology is descriptive and analytical nature, seeking to describe the qualitative characteristics in relation to accounting and regulatory aspects of countries studied. Documentary research was carried out in the reports on accounting harmonization were analyzed in Mercosur, and the method used was the study of multiple case. The documents analyzed were: (a) Report on the Observance of Standards and Codes - Auditing and Accounting (ROSC A & A) of the World Bank; (B) report submitted by countries to the IASB; (C) report submitted by countries to GLENIF; addition to the information available on the official websites of the countries themselves. The research contributes to rescue the history of the harmonization process and warn of the potential impacts of the differences in the preparation of balance sheets that make up the block.