This article describes a pressure generation technique that has been applied to the task of calibrating hydraulic pressure transducers. The technique combines principles given by the Lorentz Force and Faraday's Law of Induction to generate a hydrostatic pressure within a cavity. The time history of this pressure is given by the device without reliance on a reference transducer or knowledge of: the local gravity; thermodynamic properties of the working fluid; or acceleration of the cavity. In this way, the Pascal can be defined by reference only to the standards of the Amp, the Volt, the Meter, and -- in the case of time varying pressure -- the Second. Using this technique, a prototype device has been developed using commonly available tooling and can generate pressures in the range of 0.1 to 600 Pa with relative errors of 1.5%. / Master of Science

Although the flow of granular material in silos and the pressure acting on the silo walls have been studied for over a century, many challenges still remain in silo design. In particular, during the discharge process some dynamic phenomena in silos can often be observed to display large, self-induced and dynamic pulsations which may endanger the stability of the silo structure. The aim of this thesis is to study the flow and pressure in silos using numerical modelling and analytical methods, and to further understand the mechanical behaviour of granular material and mechanism of dynamic phenomena during silo discharge. The Finite Element (FE) method can be used to analyse the behaviour of the granular material in silos by considering the material as a continuum. In this thesis, FEM modelling of silo flow was developed using the Arbitrary Lagrangian-Eulerian (ALE) formulation in the Abaqus/Explicit program and the key parameters that affect the predictions of the flow and pressure during discharge were identified. Using the ALE technique, almost the entire silo discharge process can be simulated without mesh distortion problems. The mass flow rate and temporally averaged discharge pressure predicted by the FE model were first investigated in a conical hopper and were found to be in good agreement with those from the most commonly quoted theoretical solutions. The transient dynamic pressure fluctuations during incipient silo discharge were predicted and the causes for these dynamic events have been investigated which led to the conclusion that the stress wave propagation and the moving shear zone phenomena within the bulk solid were responsible for the dominant higher and lower frequencies effects respectively. A one-dimensional dynamic model of granular columns subject to Coulomb wall friction was developed to investigate the propagation of stress waves, focusing on the effect of geometry by examining converging and diverging tapered columns. The analytical solutions of this model are compared to the FE model based on the ALE formulation. This FE model was first validated using the known behaviour for cylindrical columns. In all cases, the stress impulse set off by incipient discharge at the silo outlet grew with the distance travelled up the column, however the rate was shown to depend on the halfangle of the taper. Over a range of small angles, the proposed analytical model was found to accurately predict this behaviour. After the successful application of the ALE technique for a conical hopper, the FE model was extended to simulate the granular flow in a flat-bottomed model silo. The FE predictions were compared with the silo pressure measurements in a model silo (Rotter et al, 2004). Pressure cells mounted along a vertical line on the silo walls were used to measure the pressure distribution in the silo tests using dry sand. The FE model was further extended to simulate the granular flow in a model silo consisting of a cylindrical section with a conical hopper. The prediction was compared with the experimental observations from a model silo (Munch-Andersen et al, 1992), together with the well-known theoretical solutions. Two numerical issues were addressed in some detail: one is the numerical treatment of the abrupt transition between the cylinder section and the conical hopper, the other is the interaction between the granular solid and the silo walls that was modelled using a dynamic friction model. In addition, the dynamic pressure events during discharge were examined and plausible explanations were given. Finally, this thesis deployed a non-coaxial elastoplastic constitutive model to explore the effect of non-coaxiality on silo phenomena. The non-coaxial FE modelling was performed on three problems: a simple shear test under various initial conditions, a steep hopper and a flat-bottomed silo. The results show that non-coaxiality did not influence the prediction of wall pressure during filling and storing, on the other hand, the discharge pressure was predicted to be larger when non-coaxiality is considered.

Submitted by Diogo Barreiros (diogo.barreiros@ufba.br) on 2017-02-17T16:41:33Z No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2017-02-21T11:56:14Z (GMT) No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / Made available in DSpace on 2017-02-21T11:56:14Z (GMT). No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / A necessidade de novas metodologias para análise e monitoramento de compressores alternativos motivou o desenvolvimento de um sistema digital multicanal com capacidade de medir diferentes grandezas simultaneamente. Como base para este trabalho escolheu-se medir pressão dinâmica, vibração e deslocamento do pistão. O desenvolvimento deste trabalho dentro de um curso de Mecatrônica produziu um sistema simples e eficiente cujos resultados experimentais, apresentados sob a forma de gráficos e dados de desempenho, confirmaram os defeitos introduzidos artificialmente. Isto permitiu validar o Sistema de Diagnóstico de Compressores Alternativos (SDCA) e demonstrou o quanto este recurso é poderoso para o diagnóstico de defeitos, tanto nos componentes da parte de compressão (fluid end) quanto nos de acionamento (power end). Estas informações, transformadas em recomendações de reparo, serão a base para uma atuação preditiva dos setores de Planejamento de Manutenção.

Este trabalho apresenta a modelagem da parte dinâmica de dois transdutores de pressão tipo piezorresistivo. Geralmente processos de calibração dinâmica usam bancadas sofisticadas, mas neste trabalho procurou-se um processo simples e de baixo custo. A metodologia baseou-se em aumentar lentamente a pressão, fornecida por um sistema hidráulico básico, até que ocorresse a explosão de um diafragma e, com isso, obteve-se um degrau de pressão, supostamente ideal. Considerado como sistemas lineares, com a resposta obtida verificou-se qual a ordem e o tipo de sistema correspondente à resposta do transdutor. Através dos dados experimentais determinou-se os parâmetros dinâmicos do modelo matemático. Foram obtidos modelos matemáticos lineares de segunda ordem de cada transdutor. As respostas dos modelos mostram ter uma concordância satisfatória quando comparadas aos dados experimentais. / This work presents a dynamic modeling method for two hydraulic piezoresistive pressure transducers. Usually the dynamic calibration processes apply sophisticated devices, but in this work a simple and low cost process was searched. The methodology was based on increasing the pressure slowly, supplied by a basic hydraulic system, up to a diaphragm explosion, assumed as an ideal step pressure variation. Considered as linear systems, the responses obtained were verified and compared with a second order linear system. Using the experimental data, the dynamic parameters of the mathematical model were determined for each of the two transducers. The theoretical responses of the models showed to have a satisfactory agreement when compared with the experimental data.

<p>A microphone has been used to measure the dynamic pressure inside a vacuum chamber during high power impulse magnetron sputtering with high enough time-resolution (~µs) to track the pressure change during the discharge pulse. An experimental measurement of the dynamic pressure is of interest since it would give information about gas depletion, which is believed to dramatically alter the plasma discharge characteristics. This investigation has shown that the magnitude of the pressure wave, which arises due to the gas depletion, corresponds to a 0.4 - 0.7Pa (3 - 5.5mTorr) pressure difference at a distance of 15cm from the target, with base pressures of 2 - 6mTorr for a peak current of 110A. It has also been shown that another pressure wave, about 250µs later, can be detected. Its explanation is suggested to be that the initial pressure wave is bouncing against the chamber walls and thereby causing another peak.</p>

A microphone has been used to measure the dynamic pressure inside a vacuum chamber during high power impulse magnetron sputtering with high enough time-resolution (~µs) to track the pressure change during the discharge pulse. An experimental measurement of the dynamic pressure is of interest since it would give information about gas depletion, which is believed to dramatically alter the plasma discharge characteristics. This investigation has shown that the magnitude of the pressure wave, which arises due to the gas depletion, corresponds to a 0.4 - 0.7Pa (3 - 5.5mTorr) pressure difference at a distance of 15cm from the target, with base pressures of 2 - 6mTorr for a peak current of 110A. It has also been shown that another pressure wave, about 250µs later, can be detected. Its explanation is suggested to be that the initial pressure wave is bouncing against the chamber walls and thereby causing another peak.

The solar wind has an important impact on the Earth and its magnetic field. Among the solar wind perturbations, there can be jumps in the solar wind dynamic pressure as well as strong magnetic excursions in the z-component of the Interplanetary Magnetic Field (IMF B_(Z )). When coronal mass ejections and other solar disturbances take place in the solar wind, there can be clear changes in the global geomagnetic field, as measured by a magnetic index called Sym-H. In this thesis some unusual events were found for which there were large fluctuations either in the solar wind dynamic pressure or in the IMF B_Z but not simultaneously in both. These events suggest that the response of the geomagnetic field to the dynamic pressure fluctuations of the solar wind is variable. In particular, it was found that the earthward component (x-component) of the IMF appeared to influence the magnitude of the Sym-H response. By contrast, there was no visible impact of the y-component of the IMF. In a second exceptional event it was found that the IMF was changing substantially while the solar wind dynamic pressure remained very constant. From this study a time delay between the IMF B_Z component and the resulting Sym-H was found to be of the order of 60 to 90 minutes.

Este trabalho apresenta a modelagem da parte dinâmica de dois transdutores de pressão tipo piezorresistivo. Geralmente processos de calibração dinâmica usam bancadas sofisticadas, mas neste trabalho procurou-se um processo simples e de baixo custo. A metodologia baseou-se em aumentar lentamente a pressão, fornecida por um sistema hidráulico básico, até que ocorresse a explosão de um diafragma e, com isso, obteve-se um degrau de pressão, supostamente ideal. Considerado como sistemas lineares, com a resposta obtida verificou-se qual a ordem e o tipo de sistema correspondente à resposta do transdutor. Através dos dados experimentais determinou-se os parâmetros dinâmicos do modelo matemático. Foram obtidos modelos matemáticos lineares de segunda ordem de cada transdutor. As respostas dos modelos mostram ter uma concordância satisfatória quando comparadas aos dados experimentais. / This work presents a dynamic modeling method for two hydraulic piezoresistive pressure transducers. Usually the dynamic calibration processes apply sophisticated devices, but in this work a simple and low cost process was searched. The methodology was based on increasing the pressure slowly, supplied by a basic hydraulic system, up to a diaphragm explosion, assumed as an ideal step pressure variation. Considered as linear systems, the responses obtained were verified and compared with a second order linear system. Using the experimental data, the dynamic parameters of the mathematical model were determined for each of the two transducers. The theoretical responses of the models showed to have a satisfactory agreement when compared with the experimental data.

Gas turbines are widely used in power generation. Monitoring pressure variations in the combustion chamber allows for real-time assessment of the turbines performance, and can be used to optimize combustion processes, leading to reduced emissions. By analyzing pressure, patterns, potential faults or degradation in critical components can be identified, enhancing the safety and reliability of the gas turbine. Measurements close to the combustion flame put high demands on the pressure sensors and their verification method. The aim of this thesis is thus to create an automated pressure sensor verification prototype capable of operating at elevated temperature.  With the intention of increasing knowledge of how high temperature influences piezoelectric dynamic pressure sensor readings, this thesis inherits and updates an existing pressure sensor verification device. A design of thermal management system for the device is presented together with a CFD model analysis for the cooling cycle, while the heating cycle and its control algorithm is studied experimentally. This thesis also focuses on sinusoidal pressure wave generation methods used in the existing verification device to achieve reliable signals at low frequencies. An experimental study to evaluate the signal quality is performed. The results propose a feasible prototype design for automated pressure sensor verification at elevated temperature. It provides insight on how the separate parts of the thermal management system could be implemented with a PID regulator. It is concluded that air heating, even with to some extent varying mass flow, can be controlled with a PID regulator. It is also concluded that stable sinusoidal pressure waves can be generated at as low as 1Hz with the gear wheel method used in the previous verification device.

Pressure measurements are required in various industrial applications, including extremely harsh environments such as turbine engines, power plants and material-processing systems. Conventional sensors are often difficult to apply due to the high temperatures, highly corrosive agents or electromagnetic interference (EMI) noise that may be present in those environments. Fiber optic pressure sensors have been developed for years and proved themselves successfully in such harsh environments. Especially, diaphragm based fiber optic pressure sensors have been shown to possess advantages of high sensitivity, wide bandwidth, high operation temperature, immunity to EMI, lightweight and long life. Static and dynamic pressure measurements at various locations of a gas turbine engine are highly desirable to improve its operation and reliability. However, the operating environment, in which temperatures may exceed 600 °C and pressures may reach 100 psi (690 kPa) with about 1 psi (6.9kPa) variation, is a great challenge to currently available sensors. To meet these requirements, a novel type of fiber optic engine pressure sensor has been developed. This pressure sensor functions as a diaphragm based extrinsic Fabry-Pérot interferometric sensor. One of the unique features of this sensor is the all silica structure, allowing a much higher operating temperature to be achieved with an extremely low temperature dependence. In addition, the flexible nature of the sensor design such as wide sensitivity selection, and passive or adaptive temperature compensation, makes the sensor suitable for a variety of applications An automatically controlled CO₂ laser-based sensor fabrication system was developed and implemented. Several novel bonding methods were proposed and investigated to improve the sensor mechanical ruggedness and reduce its temperature dependence. An engine sensor testing system was designed and instrumented. The system generates known static and dynamic pressures in a temperature-controlled environment, which was used to calibrate the sensor. Several sensor signal demodulation schemes were used for different testing purposes including a white-light interferometry system, a tunable laser based component test system (CTS), and a self-calibrated interferometric-intensity based (SCIIB) system. All of these sensor systems are immune to light source power fluctuations, which offer high reliability and stability. The fiber optic pressure sensor was tested in a F-109 turbofan engine. The testing results prove the sensor performance and the packaging ruggedization. Preliminary laboratory and field test results have shown great potential to meet not only the needs for reliable and precise pressure measurement of turbine engines but also for any other pressure measurements especially requiring high bandwidth and high temperature capability. / Ph. D.