<p dir="ltr">The computational campaign reported in this thesis focuses on a series of experiments at Mach 2.85 carried out in the 1980s at NASA Ames Research Center on a set of cylinder / skewed flare configurations designed to produce highly three-dimensional shockwave / boundary-layer interactions in the absence of end-wall effects. Computations carried out in that era were unable to match the experimental results using the numerical techniques, turbulence models, and grid resolution available at the time. In the present work, newer Reynolds-averaged Navier-Stokes and detached eddy simulation methods have been applied to these flows, and relatively good agreement has been obtained with the experimental data. Difficulty in capturing the correct separation bubble size was encountered with initial detached eddy simulations, but the introduction of resolved turbulence via a boundary layer trip produced much better results. This thesis reports on results obtained for four inclination angles (0 deg, 5 deg, 10 deg, and 23 deg) of the skewed flare. Detached eddy simulation is seen to be an economical alternative to large eddy simulation for capturing many features of large-scale separation unsteadiness over long time intervals at true Reynolds number.</p>

Electrical wiring on board aircraft has raised serious weight and safety concerns in the aerospace industry. Wires are antenna. It may also cause interference to radio-based systems on the aircraft, or, in the case of military aircraft, create a "signature" that can be detected by enemy receivers. Wireless application in avionic system helps reducing the total weight and reconfigurable of the aircraft; hence, lower the fuel costs, installation cost and maintenance costs, as well as the “signature” of the aircraft. The focus of this thesis, therefore, is to study the feasibility of different wireless standards, namely Wi-Fi, Bluetooth and ultra-wide band (UWB), on replacing the wired data connection in the EW countermeasure or chaff/flare dispenser systems. The study was constructed under the supervision of the department of Electronic Defense System, Saab AB in Järfalla, Stockholm. The discussion will be based on the resource availability, the reliability, the stability and the security of the wireless system relative to an avionic application; i.e., whether wireless links will negatively affect the overall reliability and safety of the aircrafts. Due to the theoretical studies and results from the simulation, we studied the feasibility issue and concluded that UWB is the most appropriate choice of wireless communication for non-critical aerospace applications, comparing with Wi-Fi and Bluetooth. UWB links can have reasonable immunity to interferences, low interference to other on-board wireless systems, and good security performance.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 211-214.

Magnetic reconnection is an important mechanism for the restructuring of magnetic fields, and the conversion of magnetic energy into plasma heating and non-thermal particle kinetic energy in a wide range of laboratory and astrophysical plasmas. In this thesis, reconnection is studied in two semi-collisional plasma environments: flares in the solar corona, and the start-up phase of the Mega-Ampere Spherical Tokamak (MAST) magnetic confinement device. Numerical simulations are presented using two different plasma descriptions; the test-particle approach combined with analytical magnetohydrodynamic fields is used to model populations of high-energy particles, and a two-fluid approach is used to model the bulk properties of a semi-collisional plasma. With the first approach, a three-dimensional magnetic null-point is examined as a possible particle acceleration site in the solar corona. The efficiency of acceleration, both within the external drift region and in the resistive current sheet, is studied for electrons and protons using two reconnection models. Of the two models, it is found that the fan-reconnection scenario is the most efficient, and can accelerate bulk populations of protons due to fast and non-uniform electric drifts close to the fan current-sheet. Also, the increasing background field within the fan-current sheet is shown to stabilise particle orbits, so that the energy gain is not limited by ejection. With the second approach, the effects of two-fluid physics on merging flux-ropes is examined, finding fast two-fluid tearing-type instabilities when the strength of dissipation is weak. The model is then extended to the tight-aspect ratio toroidal-axisymmetric geometry of the MAST device, where the final state after merging is a MAST-like spherical tokamak with nested flux-surfaces and a monotonically increasing q-profile. It is also shown that the evolution of simulated 1D radial density profiles closely resembles the Thomson scattering electron density measurements in MAST. An intuitive explanation for the origin of the measured density structures is proposed, based upon the results of the toroidal Hall-MHD simulations.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21575号 / 理博第4482号 / 新制||理||1643(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 柴田 一成, 准教授 岩室 史英, 教授 一本 潔 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19359号 / 理博第4121号 / 新制||理||1593(附属図書館) / 32373 / 新制||理||1593 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 一本 潔, 教授 柴田 一成, 准教授 野上 大作 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Yes / Flaring is a combustion process commonly used in the oil and gas industry to dispose flammable waste gases. Flare flameout occurs when these gases escape unburnt from the flare tip causing the discharge of flammable and/or toxic vapor clouds. The toxic gases released during this process have the potential to initiate safety hazards and cause serious harm to the ecosystem and human health. Flare flameout could be caused by environmental conditions, equipment failure, and human error. However, to better understand the causes of flare flameout, a rigorous analysis of the behavior of flare systems under failure conditions is required. In this article, we used fault tree analysis (FTA) and the dynamic Bayesian network (DBN) to assess the reliability of flare systems. In this study, we analyzed 40 different combinations of basic events that can cause flare flameout to determine the event with the highest impact on system failure. In the quantitative analysis, we use both constant and time-dependent failure rates of system components. The results show that combining these two approaches allows for robust probabilistic reasoning on flare system reliability, which can help improving the safety and asset integrity of process facilities. The proposed DBN model constitutes a significant step to improve the safety and reliability of flare systems in the oil and gas industry.

No / In the last few years, there has been growing interest in near-real-time solar data processing, especially for space weather applications. This is due to space weather impacts on both space-borne and ground-based systems, and industries, which subsequently impacts our lives. In the current study, the deep learning approach is used to establish an automated hybrid computer system for a short-term forecast; it is achieved by using the complexity level of the sunspot group on SDO/HMI Intensitygram images. Furthermore, this suggested system can generate the forecast for solar flare occurrences within the following 24 h. The input data for the proposed system are SDO/HMI full-disk Intensitygram images and SDO/HMI full-disk magnetogram images. System outputs are the “Flare or Non-Flare” of daily flare occurrences (C, M, and X classes). This system integrates an image processing system to automatically detect sunspot groups on SDO/HMI Intensitygram images using active-region data extracted from SDO/HMI magnetogram images (presented by Colak and Qahwaji, 2008) and deep learning to generate these forecasts. Our deep learning-based system is designed to analyze sunspot groups on the solar disk to predict whether this sunspot group is capable of releasing a significant flare or not. Our system introduced in this work is called ASAP_Deep. The deep learning model used in our system is based on the integration of the Convolutional Neural Network (CNN) and Softmax classifier to extract special features from the sunspot group images detected from SDO/HMI (Intensitygram and magnetogram) images. Furthermore, a CNN training scheme based on the integration of a back-propagation algorithm and a mini-batch AdaGrad optimization method is suggested for weight updates and to modify learning rates, respectively. The images of the sunspot regions are cropped automatically by the imaging system and processed using deep learning rules to provide near real-time predictions. The major results of this study are as follows. Firstly, the ASAP_Deep system builds on the ASAP system introduced in Colak and Qahwaji (2009) but improves the system with an updated deep learning-based prediction capability. Secondly, we successfully apply CNN to the sunspot group image without any pre-processing or feature extraction. Thirdly, our system results are considerably better, especially for the false alarm ratio (FAR); this reduces the losses resulting from the protection measures applied by companies. Also, the proposed system achieves a relatively high scores for True Skill Statistics (TSS) and Heidke Skill Score (HSS).

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24415号 / 理博第4914号 / 新制||理||1702(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 浅井 歩, 教授 一本 潔, 教授 横山 央明 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Laser flare can often be a major issue in particle image velocimetry (PIV) involving solid boundaries in a flow or a gas-liquid interface. The use of fluorescent light from dye-doped particles has been demonstrated in water applications, but reproducing the technique in an airflow is more difficult due to particle size constraints and safety concerns. The following thesis is formatted in a hybrid manuscript style, including a full paper presenting the applications of fluorescent Kiton Red 620 (KR620)-doped polystyrene latex microspheres in PIV. These particles used are small and monodisperse, with a mean diameter of 0.87 μm. The KR620 dye exhibits much lower toxicity than other common fluorescent dyes, and would be safe to use in large flow facilities. The first sections present a general introduction followed by a validation experiment using a standard PIV setup in a free jet. This work was the first to demonstrate PIV using fluorescent KR620-doped microspheres in an airflow, and results from the experiment were compared to similar data taken using standard PIV techniques. For the free jet results, Mie-scattered and fluorescent PIV were compared and showed average velocities within 3% of each other at the nozzle exit. Based on the PIV validation requirements used, this was deemed to be more of an indication of nozzle unsteadiness rather than an error or bias in the data. Furthermore, fluorescent PIV data obtained vector validation rates over 98%, well above the standard threshold of 95%. The journal article expands on the introductory work and analyzes testing scenarios where fluorescent PIV allows for velocity measurements much closer to a solid surface than standard, Mie-scattered PIV. The fluorescent signal from the particles is measured on average to be 320 ± 10 times weaker than the Mie scattering signal from the particles. This fluorescence-to-Mie ratio was found to be nonuniform, with the typical signal ratio for a single particle expected to fall between 120 and 870. This reduction in signal is counterbalanced by greatly enhanced contrast via optical rejection of the incident laser wavelength. Fluorescent PIV with these particles is shown to eliminate laser flare near surfaces, in one case leading to 63 times fewer spurious velocity vectors than an optimized Mie scattering implementation in a region more than 5 mm from an angled surface. In the appendix, a brief summary of an experiment to characterize the temperature sensitivity of the KR620 dye is included. This experiment concluded that the KR620 particles did not exhibit sufficient temperature sensitivity to warrant further investigation at the time. / Master of Science