@phdthesis{oai:muroran-it.repo.nii.ac.jp:00005113,
 author = {畠中, 和明 and HATANAKA, Kazuaki},
 month = {2016-02-15, 2016-02-15},
 note = {application/pdf, 計算機技術の発展に伴い，様々な研究分野において数値計算の果たす役割が急速に拡大している。本論文では，衝撃波を伴う超音速流れ場の物理的特性を明らかにすることを目的として，幾つかの具体的な課題について行った実験的・数値解析的研究について述べる。研究は高性能計算機の最大限の活用を目指し，流れ場の数値計算や実験データの解析手法を課題毎に最適化することに留意して行われた。研究課題は大きく分けて「数値流体力学による超音速流れ場の考察」と「光学的可視化手法における画像処理」の二つである。流れ場の基礎方程式を計算機で近似的に解く数値流体力学（Computational Fluid Dynamics: CFD）では，複雑な流れ場を厳密に模擬することは近年の高性能計算機を用いても困難であるため，問題の性質や研究の目的に応じた最適な計算機環境を準備し，許容できる精度範囲での近似計算を行うことが重要となる。本研究では，数値計算に特化した並列計算機システムの構築とその性能評価も行っている。最適化に関しては，「超音速流中の半球殻周りの非定常流れ場の研究」では，与えられたハードウェア資源を効率よく運用し，3次元の非定常計算によって衝撃波振動現象の発生と複雑な推移過程についての詳細を明らかにした。また「半球容器内での衝撃波爆縮に関する研究」では，問題の性質に合わせてプロセッサにGPUを使用するハードウェア面からの最適化を行い，価格や消費電力に対する計算性能が非常に高いシステムを実現した。また「弱い衝撃波の分子振動による緩和効果に関する研究」では，解析のアルゴリズムを根本から見直してソフトウェア面からの最適化を行い，並列計算機で数時間かけて解析していた問題を 1 CPU のPCで同等の結果を数分で得られるまでに計算速度が劇的に改善される結果を得た。また本研究では，「光学的可視化手法の画像処理」の最適化を行う対象として，Background Oriented Schlieren（BOS）法を課題に設定し，最適化手法の評価を行った。BOS法は，現象の背後に設置した背景画像が，流れ場の屈折率が変動することによって歪む（変位する）ことを利用して密度勾配を可視化する光学的可視化手法の一つである。本研究では，BOS法に使用する背景画像に複数の周波数成分を含む輝度画像を用い，単一周波数の場合に顕在化する問題を解決することに成功した。以上のように，数値解析のみならず，実験的研究に於いても計算機利用技術の最適化を行い，幾つかの学術的成果を上げる事ができた。, The role played by numerical calculation is rapidly expanding in various research fields, in sync with the progress of computational technology. In this paper, we describe an experimental and numerical analytical study conducted on a number of specific topics, for the purpose of clarifying the physical characteristics of supersonic flow fields associated with shock waves. The study aims to maximize the utility of high-performance computers and takes into consideration the optimization of analysis methods of the numerical calculations and experimental data of flow fields for each issue. This study focuses on two broad topics, namely the "consideration of supersonic flow fields using numerical fluid dynamics" and "image processing with an optical visualization method." An exact simulation of complex flow fields is difficult to achieve with computational fluid dynamics (CFD) that utilizes approximation using computers to resolve the fundamental equations of flow fields, even when high-performance computers developed in the recent years are used. Therefore, it is important to prepare an optimum computational environment suitable for the characteristics of issues or objectives of studies and to perform approximation calculations within an allowable precision range. A parallel computer system specializing in numerical calculations is built and its performance evaluated in this study. Hardware resources are managed well to clarify details on the occurrence of the shock wave vibrational phenomenon and the complex transitional process by using a three-dimensional unsteady calculation for the purpose of optimization in the "study of an unsteady flow field around a hemispherical shell in an supersonic flow." Furthermore, optimization from hardware aspects, such as the use of a graphics processing unit (GPU) as the processor to suit the characteristics of the problem, is carried out in order to achieve a system with an extremely high computational performance with respect to cost and power consumption in the "study on a shock wave implosion inside a hemispherical implosion chamber." Optimization from software aspects is carried out by conducting a fundamental review of the algorithm used for analysis in the "study on the relaxation effect of a molecular vibration for a weak shock wave," achieving a dramatic improvement in the computational speed to the extent that problems that were analyzed using parallel computer systems over several hours in the past could be solved in just few minutes using a personal computer mounted with a single central processing unit (CPU). Furthermore, a background-oriented schlieren (BOS) is focused upon as a topic of optimizing "image processing by using an optical visualization method" in this study in order to evaluate the proposed optimization method. The BOS method is one of the optical visualization methods that visualize density gradients by using the fact that the image set up in the background of a phenomenon gets distorted because of a change in the refraction index of the flow field. An intensity image that includes multiple frequency components is used as the background image in the abovementioned BOS method and successfully resolves the problems related to the cases of single frequencies. Further, computer utilization technology is optimized not only with a numerical analysis but also for experimental research as described above, and a number of academic achievements are realized.},
 school = {室蘭工業大学, Muroran Institute of Technology},
 title = {衝撃波問題における解析の最適化とその適用及び評価},
 year = {},
 yomi = {ハタナカ, カズアキ}
}