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  2. 大山 聖

大山 聖

オオヤマ アキラ  (Akira Oyama)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 教授
東京大学大学院 教授
東京理科大学 理工学研究科機械工学専攻 客員教授
学位
博士（工学）(2000年3月 東北大学大学院)
研究者番号
10373440
J-GLOBAL ID
200901044748363926
researchmap会員ID
5000069161
外部リンク
宇宙科学航空研究開発機構宇宙科学研究所の大山です．
自分の研究分野にとらわれず，新しい研究分野にも挑戦していきたいと考えています．

研究キーワード

 17

研究分野

 6

経歴

 13
もっとみる

学歴

 5

委員歴

 7
もっとみる

受賞

 13
もっとみる

論文

 132
  • Yoshikatsu FURUSAWA, Keiichi KITAMURA, Tsubasa IKAMI, Hiroki NAGAI, Akira OYAMA
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 67(1) 12-22 2024年  
  • Yohanes Bimo Dwianto, Pramudita Satria Palar, Lavi Rizki Zuhal, Akira Oyama
    146(4) 2023年11月7日  
  • Shigetaka Kawai, Kengo Asada, Akira Oyama
    60(5) 1721-1727 2023年9月  
  • 岩瀬拓, 十川直幸, 川鍋友宏, 磯野勝朝, 山出吉伸, 大山聖, 金子公寿
    ターボ機械 728-741 2022年12月  査読有り
  • Shigetaka Kawai, Wataru Yamazaki, Akira Oyama
    Journal of Computational Physics 468 111505-111505 2022年11月  査読有り
  • Daiki Terakado, Taku Nonomura, Soshi Kawai, Hikaru Aono, Makoto Sato, Akira Oyama, Kozo Fujii
    Physical Review Fluids 7(8) 2022年8月19日  査読有り
  • Taku Nonomura, Takuma Ibuki, Yuta Ozawa, Keisuke Asai, Akira Oyama
    Measurement Science and Technology 32(12) 125306-125306 2021年12月1日  査読有り
    The methods that measure the turbulence statistics distribution of high-speed flow with high spatial resolution using particle-image-velocimetry images are proposed, and their performances are verified. Two methods are proposed, and the problems caused by blurring the particle shape due to the high-speed movements are resolved. While the conventional method approximates the unique particle shapes with a circular distribution for image pairs, the first proposed method approximates the different particle shapes with an ellipse for first and second images of pairs and reduces the effects of the blur in the flow direction of the particles. Meanwhile, the second proposed method treats the general particle shapes such as the blur of temporally changing laser intensity and adopts the deconvolution analysis using a Fourier transform. Synthetic particle images were created and a supersonic jet test was performed, and the proposed methods were evaluated to be superior to the previous method for the estimation of turbulent fluctuation using those data.
  • Shuichi Hiramatsu, Masayuki Anyoji, Koji Fujita, Hiroki Nagai, Akira Oyama, Hiroyuki Kato
    Engineering Research Express 3(1) 015035-015035 2021年3月1日  査読有り
    <title>Abstract</title> A fixed-wing aircraft called Mars Airplane Balloon Experiment −2 (MABE2) developed by the authors was the subject of high-altitude flight demonstration test in this paper, which can simulate the near-actual environment of a Martian atmospheric flight. Although the flight condition is in the low-Reynolds-number region due to low density at high altitude, the wing suffers from aeroelastic deformation given the relatively high dynamic pressure load in the pull-up phase. Stereophotogrammetry was applied in the 6.5 m × 5.5 m low-speed wind tunnel at the Japan Aerospace Exploration Agency (JAXA), aiming to optically measure MABE2’s aeroelastic deformation under dynamic pressure loads equivalent to high-altitude flight test, with the MABE2’s reinforced structural strength. The results of the accuracy test indicated that stereophotogrammetry measures aeroelastic deformation at high accuracy of ±0.1 mm around the image center and ±0.3 mm around the edge. A slight deflection of up to 4 mm was observed on the main wing, whereas both the main and tail wings were hardly twisted. Compared with flight-simulation-assumed errors, these deformations are extremely small and have a negligible effect on the high-altitude flight test. The study results confirmed the practicality and efficiency of this optical measurement technique in aeroelastic deformation measurement for a real light aircraft.
  • Shigetaka Kawai, Wataru Yamazaki, Akira Oyama
    AIAA Scitech 2021 Forum 1-8 2021年  
    This paper investigates the applicability of a multi-element polynomial chaos method based on edge detection for uncertainty quantification of discontinuous responses in aerodynamic problems. This paper presents numerical experiments for the supersonic flow problem of Busemann’s biplane airfoil, which exhibits a discontinuous response of the drag coefficient to the uncertainty associated with the freestream Mach number caused by the flow choking. The numerical experiments show that the proposed method can sharply and efficiently capture the discontinuous response by accurately locating the discontinuity, while the conventional polynomial chaos method yields spurious oscillatory solutions.
  • Matthew P. Richardson, Hiroaki Kobayashi, Yuki Sakamoto, Yusuke Maru, Shinichiro Tokudome, Satoshi Nonaka, Shujiro Sawai, Akira Oyama, Daisaku Masaki, Satoshi Takada, Hiromitsu Kakudo, Toru Kaga, Kiyoshi Kinefuchi, Tetsuya Sato
    Accelerating Space Commerce, Exploration, and New Discovery conference, ASCEND 2021 2021年  
    The Japan Aerospace Exploration Agency, in partnership with academia and industry, are developing the Air Turbo Rocket for Innovative Unmanned Mission (ATRIUM) engine: an air turboramjet + rocket combine cycle propulsion system intended to replace conventional liquid rocket engines in Vertical Takeoff Vertical Landing applications, such as reusable sounding rockets. A subscale Flight Test Bed (FTB) vehicle is also being developed to demonstrate the ATRIUM engine in a flight environment. In this paper, the ATRIUM engine and FTB vehicle are introduced, and current progress in their development is summarized. Future test plans and practical applications are also discussed.
  • 谷口翔太, 大山聖
    航空宇宙技術 20 52-58 2021年  査読有り
  • 藤田昂志, 久保大輔, 大山聖, 永井大樹
    航空宇宙技術 20 101-104 2021年  査読有り
  • Yohanes Bimo Dwianto, Hiroaki Fukumoto, Akira Oyama
    GECCO 2020 - Proceedings of the 2020 Genetic and Evolutionary Computation Conference 690-698 2020年6月25日  
    In the present work, we propose some new modifications of an existing constraint handling technique (CHT) for single-objective optimization problems. The base CHT is generalized multiple constraint ranking (G-MCR), which is already a modified version of the original CHT, MCR. Despite that G-MCR significantly outperformed the original MCR in the previous study, it is found that G-MCR tends to generate very few feasible individuals on a certain real-world like engineering design problem. In the present work, G-MCR is further modified to strike a better balance between feasible and infeasible individuals on each generation in an adaptive way so that the interaction between feasible and infeasible regions can be maintained, thus providing more efficient search towards constrained global optimum. Based on the investigation on 78 benchmark problems, we obtain that some of the proposed modifications produce more robust convergence performance by obtaining significant superiority on many types of problems. On real-world like engineering design problems, we also observe that the feasibility ratio generated on each generation might have an important role in improving the convergence performance.
  • Yuta Ozawa, Taku Nonomura, Akira Oyama, Keisuke Asai
    Physics of Fluids 32(4) 2020年4月1日  査読有り
  • Shigetaka Kawai, Akira Oyama
    Journal of Verification, Validation and Uncertainty Quantification 5(4) 041004 2020年  査読有り
  • Shigetaka Kawai, Akira Oyama
    Transactions of the Japan society for aeronautical and space sciences 63(4) 172-184 2020年  査読有り
  • Yohanes, Bimo Dwianto, Hiroaki Fukumoto, Akira Oyama
    進化計算学会論文誌 11(2) 2020年  査読有り
  • Hiroshi Tokutake, Koji Fujita, Akira Oyama, Hiroki Nagai
    Aerospace technology Japan 18(2) 17-24 2020年  査読有り
  • Satoshi Shimomura, Satoshi Sekimoto, Akira Oyama, Kozo Fujii, Hiroyuki Nishida
    AIAA Journal Vol. 58(No. 10) 4260-4270 2020年  査読有り
    The effectiveness of closed-loop flow control using a deep Q network (DQN), such as deep reinforcement learning algorithm, was experimentally researched for a NACA0015 airfoil. The system used a dielectric barrier discharge plasma actuator as the flow control device, and the experiment was conducted at the chord Reynolds number of 6.3 x 10(4). The closed-loop control system selected a nondimensional burst frequency of the actuator by analyzing the time series of the surface pressure data. The neural network of the DQN was sequentially trained at the angles of attack of 12 and 15 deg. As a result, the closed-loop control successfully generated a higher control gain compared with the open-loop control using a fixed burst frequency. Particularly, at 15 deg there was a significant control gain that could not be obtained by the open-loop control. The closed-loop control keeps the flow attached and preserves it for a longer time by periodically switching the actuator on and off.
  • Hikaru Aono, Katsutoshi Kondo, Taku Nonomura, Masayuki Anyoji, Akira Oyama, Kozo Fujii, Makoto Yamamoto
    Transactions of the Japan Society for Aeronautical and Space Sciences 63(1) 8-17 2020年  査読有り
    © 2020 The Japan Society for Aeronautical and Space Sciences Aerodynamics of an owl-like wing model at low Reynolds numbers (Re = O(104-5)) are investigated using large-eddy simulations with high-resolution computational schemes. The airfoil shape of the owl-like wing model is constructed based on a cross-sectional geometry of the owl wing at 40% wingspan from the root. The chord-based Re ranges from 1.0 © 104 to 5.0 © 104 and the angle of attack (¡) varies from 0 to 14 deg. The time-averaged lift (Cl) and drag coefficients computed are in reasonable agreement with the results of force measurement. The results computed clarify a nonlinear change in the Cl curve slope, which is due to an increase in the suction peaks in conjunction with the change in type of separation, the formation of a laminar separation bubble (LSB), and pressure recovery on the pressure side. The generation of the LSB on the suction and/or pressure sides at the Re of 2.3 © 104 and 4.6 © 104 are seen, while reattachments are observed only on the pressure side at the Re of 1.0 © 104 due to the camber of the wing. Furthermore, the owl-like wing model demonstrates favorable aerodynamic performance in terms of a maximum lift-to-drag ratio in comparison with several airfoils at the Re range considered. This is due to the strong suction peaks and distribution of surface pressure on the pressure side. It is emphasized that the concave lower surface enhances the time-averaged aerodynamic performance at all of the ¡ even though the LSB is generated and fluctuation in lift history is induced at low ¡.
  • Hiroaki Fukumoto, Akira Oyama
    2019 IEEE Symposium Series on Computational Intelligence, SSCI 2019 2138-2145 2019年12月1日  
    To apply MOEAs to industrial problems, the estimation of the ideal and nadir points becomes crucial in order to handle the differently scaled objectives by normalization and to handle the unknown Pareto Front. In this paper, the impact of the estimation methods of the ideal and nadir points for decomposition-based multi-objective evolutionary algorithms is examined on some constrained optimization problems whose constraints are explicitly designed to have the characteristics of the practical problems. The numerical experiments show that the estimation method has great impact on the performance of MOEAs.
  • Yohanes Bimo Dwianto, Hiroaki Fukumoto, Akira Oyama
    GECCO 2019 - Proceedings of the 2019 Genetic and Evolutionary Computation Conference 762-770 2019年7月13日  
    This work presents a new rank-based constraint handling technique (CHT) by implementing a modification on Multiple Constraint Ranking (MCR), a recently proposed rank-based constraint handling technique (CHT) for real-world engineering design optimization problems solved by evolutionary algorithms. The new technique, namely MCR-mod, not only maintains MCR's superior feature, i.e. balanced assessment of constraints with different orders of magnitude and/or different units, but also adds some more good features, such as more proper rank definition that the best feasible solution in the population always has better rank than the best infeasible solution, involvement of good infeasible solution, and easier way of implementation. Numerical experiments on benchmark problems from IEEE-CEC 2006 competition and engineering design are conducted to assess the accuracy and robustness of MCR-mod. From 25 independent runs on each problem, MCR-mod has proven its robustness compared to MCR, by its ability to produce better feasible optimal solution in most problems. Based on nonparametric statistical tests, there are indications that MCR-mod yields significant superiority in terms of accuracy compared with MCR on problems whose most constraints are inequality and active constraints, indicating that all added features of MCR-mod produce some improvements on the constraint-handling performance.
  • Tatsumasa Ishikawa, Hiroaki Fukumoto, Akira Oyama, Hiroyuki Nishida
    GECCO 2019 Companion - Proceedings of the 2019 Genetic and Evolutionary Computation Conference Companion 209-210 2019年7月13日  
    Several studies report that the solutions obtained by indicator-based evolutionary algorithm (IBEA) with the binary additive epsilon indicator are biased to specific regions in the objective space. This paper reveals the reason of the bias is due to the asymmetricity of the epsilon indicator without considering the dominance relationship. This paper also proposes a modified epsilon indicator to obtain uniformly distributed solutions in the objective space. The proposed indicator uses indicator value based on Chebyshev distance when the dominance relationship does not exist between two solutions. The results of the experiments show that the diversity of IBEA is enhanced by the proposed indicator on WFG5 problem.
  • Koji Fujita, Akira Oyama, Hiroshi Tokutake, Hiroki Nagai
    Trans. JSASS Aerospace Tech. Japan 17(4) 512-518 2019年7月  査読有り
  • Hiroaki Fukumoto, Akira Oyama
    2019 IEEE Congress on Evolutionary Computation, CEC 2019 - Proceedings 1734-1741 2019年6月1日  
    To enhance the coverage performance of MOEA/DM2M, we propose a modified nadir point called a dystopian point and propose to use the dystopian point as the origin of the direction vectors of MOEA/D-M2M. The performance of the proposed algorithm is tested on 16 artificial test problems and a real-world-like problem, which have the feature of difficultto- approximate PF boundaries. The experimental results show that the existing MOEAs, including the standard MOEA/DM2M, performs not very well with respect to coverage while the proposed algorithm performs well. The results on the real-worldlike problem indicate that the balance between convergence, diversity, coverage, and feasibility is all important.
  • Fujita, K, Oyama, A, Kubo, D, Kanazaki, M, Nagai, H
    Journal of Flow Control, Measurement & Visualization, Science Research Publishing 7(2) 2019年4月  査読有り
    This paper reports the results of the aerodynamic deformation measurements of the meter-scale, entire shape, actual UAV in the wind tunnel using a video grammetry technique. The measured airplane was the airplane for Mars exploration being developed by Japan Aerospace Exploration Agency (JAXA) and Japanese universities. Its main wing span length was 2.4 m. The video grammetry measurement was performed using VICON’s system. Retroactive markers and stickers were put on the airplane. JAXA’s 6.5 m × 5.5 m Low-Speed Wind Tunnel was used. The airplane was mounted on the strut support with pitch-free or pitch-locked conditions. The deformations of the main wing bending, the main wing twisting, the tail boom bending, and the elevator deflection angle change were revealed quantitatively. The bending stiffness of a main wing spar that was designed as a safety factor of 2.8 at load factor of 5 was sufficient. The main wing spar was located around a center of pressure of an airfoil and it showed enough stiffness for twisting at nominal condition. The effects of the main wing bending and twisting, and the tail boom bending on the aerodynamic performance were estimated but they were in an acceptable range from the standpoint of the controllability of the aerodynamic performance using control surfaces. Even though the servo motor was located near the elevator and the linkage between the servo motor and the elevator was short, the measured elevator deflection angle was at most 4% smaller than the angle at no-wind condition. The obtained results and presented method are useful for control, flight data analysis, and design of lightweight airplanes.
  • Hiroaki Fukumoto, Akira Oyama
    Proceedings of the 2018 IEEE Symposium Series on Computational Intelligence, SSCI 2018 1180-1187 2019年1月28日  
    Multi-objective evolutionary algorithms (MOEAs) are an active research topic for multi-objective design problems. MOEAs are population-based global optimization algorithms and it is said that the performance of the MOEAs depends on the population size. It is well-known that the population size should be large enough to guarantee the diversity of the solution while the large population size makes the convergence slow. This study is on the trade-off of the convergence speed and the diversity of the solutions and the trade-off is visualized from the view point of the efficiency of the algorithms against the population size. It is clearly shown that there is an optimal population size with regard to the efficiency for each problem and for a target quality of the solutions. To shift the optimal population size toward larger, i.e, to make the convergence fast with good diversity property, two methods are employed. First method is the multi-objective-to-multi-objective (M2M) decomposition and the other is a newly proposed elitist mate selection based on binary tournament (termed EBT). Experimental studies on MOP test instances show that NSGA-II incorporated with the M2M decomposition and the EBT (NSGA-II-EM2M in short) shows the highest and fastest performance with better efficiency over NSGA-II and NSGA-II-M2M with different mate selection schemes.
  • Yohanes Bimo Dwianto, Hiroaki Fukumoto, Akira Oyama
    AIAA Aviation 2019 Forum 1-17 2019年  
    In the present work, we propose an efficient infill criterion of surrogate model specifically for computationally expensive, severely-constrained optimization problems. Basing on a rank-based constraint handling technique (CHT) called multiple constraint ranking (MCR), we devise a rank-based infill criterion to overcome the drawbacks of the widely-known infill criterion called constrained expected improvement (CEI), namely CEI-MCR. In the framework of efficient global optimization (EGO), we conduct optimization on various kinds of benchmark problems to investigate the performance of the proposed infill criterion, CEI-MCR, compared with other currently existing infill criteria, CEI and EGOcons. Results of statistical significance tests on the optimization of the benchmark problems bring about a indication that the performance of CEI-MCR is either significantly more superior or equivalent compared with CEI and EGOcons by the end of EGO on all problems selected in the present work. In the last part of the present work, we conduct an airfoil design optimization and notice that CEI-MCR also performs with significant superiority or equivalently compared with CEI and EGOcons.
  • Yuta Ozawa, Taku Nonomura, Akira Oyama, Makoto Yamamoto
    25th AIAA/CEAS Aeroacoustics Conference, 2019 2019年  
    The flow structure and near field acoustic profile of a supersonic jet at a Mach number of 2.0 and Reynolds numbers of 105 and 106 were investigated by particle imaging velocimetry, schlieren visualization and acoustic measurement using a microphone. The effect of the disturbance in the shear layer was also investigated. In the case of higher Reynolds number jet, the presence of disturbance does not significantly affect the flow and acoustic fields because the shear layer state has already been turbulent even without the disturbance. However, presence of disturbance significantly affects the flow and acoustic fields in the case of moderate Reynolds number jet (Re=105) because the initial condition of the shear layer without disturbance is laminar and disturbance promotes the turbulent transition which has the strong influence on flow and acoustic fields. The sound pressure level decreases with adding disturbance because the promoted turbulent shear layer is smoothly growing instead of rapid growth in the vicinity of the transition which leads to strong acoustic wave emission.
  • Shigetaka Kawai, Kengo Asada, Akira Oyama
    AIAA Scitech 2019 Forum 2019年  
    Freestream turbulence effects on laminar separation bubbles in low-Reynolds-number flow over a flat plate are investigated using large eddy simulations. To this end, the framework of the Fourier-series-based synthesized turbulence is introduced to make inflow turbulent fluctuation. The results show that the freestream turbulence accelerates the laminar-turbulent transition and the length of the separation bubble decreases. Consequently, the pressure distributin of the simulations with the freestream turbulence shows closer distributions to an experimental result than the simulation without freestream turbulence. Moreover, a parametric study shows that the length scale of turbulence, as well as the intensity of turbulence, affects the flow reattachment point. This fact may indicate that we have to pay attention to the turbulent length scale in addition to the turbulent intensity on wind tunnel tests.
  • Nonomura, T., Nakano, H., Ozawa, Y., Terakado, D., Yamamoto, M., Fujii, K., Oyama, A.
    Shock Waves 2019年  査読有り
  • 大山聖, 小平剛央, 立川智章, 渡辺毅, 剱持寛正
    日本機械学会論文集 85(879) 19-00293-19-00293 2019年  査読有り
  • KANAZAKI Masahiro, TOMISAWA Kai, FUJITA Koji, OYAMA Akira, NAGAI Hiroki
    Journal of Fluid Science and Technology 14(3) JFST0017-JFST0017 2019年  査読有り
    <p>We redesigned the Mars Airplane Balloon Experiment Two (MABE-2) based on MABE-1 to improve the vehicle's stability and controllability. Following the redesign, the MABE-2 vehicle had a larger horizontal tail volume than that of MABE-1 for improved stability performance. In addition, to further improve the stability and control characteristics, a rectangular planform was employed for the horizontal tail wing; in contrast, MABE-1 had a tapered planform. The vertical tail position of MABE-2 was moved to the end of the horizontal tail wing, because the vertical tail of MABE-1, which was positioned at the mid span of the horizontal tail wing, showed aerodynamic interaction with the horizontal tail wing. In this paper, we discussed the aerodynamic performance of a control surface based on computational fluid dynamics with variation in the deflection angle between the control surface and the horizontal tail (elevator), and we examined the effects of this redesign on longitudinal control characteristics. Numerical investigations confirmed the linear variation in the pitching moment and the aerodynamic force with the changing elevator deflection angle in MABE-2. Surface pressure observations indicated that MABE-2 shows a smooth variation in the pressure distribution with changing elevator deflection angle, while MABE-1 does not. These results demonstrate that the aerodynamic control characteristics of MABE-2 were improved in comparison to those of MABE-1.</p>
  • Theoretical and Computational Fluid Dynamics 32 805-820 2018年12月  査読有り
  • Takehisa Kohira, Oyama Akira, Hiromasa Kemmotsu, Tomoaki Tatsukawa
    GECCO 2018 Companion - Proceedings of the 2018 Genetic and Evolutionary Computation Conference Companion 183-184 2018年7月6日  
    A benchmark problem based on a real-world car structure design optimization1 is proposed. The benchmark problem is constructed by using a response surface method from the design optimization result of a car structure design optimization problem. Because this benchmark problem bases on actual car structure design optimization result conducted by Mazda, it contains features of real-world design optimization problems. Objectives are the minimization of the total weight of the different type of cars and maximization of the number of common gauge (standard plate thickness) parts among the different type of cars. This benchmark problem has 148 discrete design parameters and 36 design constraints for simultaneous design optimization of two types of cars and 222 discrete design parameters and 54 design constraints for simultaneous design optimization of three types of cars. Thus, it is a scalable and multiobjective design optimization problem with many and discrete design parameters and many and severe constraints. The benchmark problem is available on our website (http://ladse.eng.isas.jaxa.jp/benchmark/).
  • Hiroaki Fukumoto, Akira Oyama
    GECCO 2018 Companion - Proceedings of the 2018 Genetic and Evolutionary Computation Conference Companion 177-178 2018年7月6日  
    While many of real-world industrial design problems involve several constraints, researches on multiobjective evolutionary algorithms (MOEAs) for problems with many constraints or the benchmark problems themselves are limited. The novel constrained multiobjective optimization benchmark problem based on a real-world car structure design optimization problem, termed Mazda CdMOBP, has more desirable characteristics as a constrained benchmark problem than the existing ones. The experimental results with 12 constrained MOEAs on this problem suggest the importance of balancing all of three factors of convergence, diversity, and feasibility and knowledge of proper settings of not only MOEA and CHT but also these parameters are imperative for application of MOEAs to industrial design problems.
  • Akira Oyama, Takehisa Kohira, Hiromasa Kemmotsu, Tomoaki Tatsukawa, Takeshi Watanabe
    2017 IEEE Symposium Series on Computational Intelligence, SSCI 2017 - Proceedings 2018- 1-4 2018年2月2日  
    A design tool for simultaneous structure design optimization of multiple car models is developed and applied to simultaneous design optimization of MAZDA CX-5 (SUV car), MAZDA6 wagon (large car), and MAZDA3 hatchback (small car) to demonstrate feasibility of the developed design tool. This problem is a multiobjective design optimization problem where the objectives are minimization of total weight of three car models and maximization of number of common thickness parts. To find the nondominated designs efficiently, an evolutionary multiobjective optimization algorithm named Cheetah is adopted. For analysis of the obtained nondominated and dominated designs, an interactive data mining tool iSPM is used. To evaluate crash performances accurately, a finite-element software LS-DYNA is used for each crash mode. To overcome difficulty in computational time, the K computer is used, where the required computational time is more than 360 hours using 73,728 cores of the K computer. As a result, many designs that outperform the initial design developed by Mazda Motor Corporation are found. In addition, the obtained nondominated designs reveal the trade-off between the two design objectives of the simultaneous structure design optimization problem of multiple car models.
  • Shigetaka Kawai, Akira Oyama
    10th International Conference on Computational Fluid Dynamics, ICCFD 2018 - Proceedings 2018年  
    The stochastic behaviors of airfoil characteristics at low Reynolds numbers under uncertain flow conditions are investigated. The potential importance of considering multiple uncertainties including the Reynolds number effect on the stochastic response of the airfoil characteristics is highlighted at low Reynolds numbers.
  • Hiroaki Fukumoto, Akira Oyama
    Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 10784 634-649 2018年  
    A generic framework for incorporating constraint handling techniques (CHTs) into multi-objective evolutionary algorithms (MOEAs) is proposed to resolve the differences between MOEAs from algorithmic and implementation perspective with respect to the incorporation of CHTs. To verify the effectiveness of the proposed framework, the performances of the combined algorithms of five CHTs and four MOEAs on eight constrained multi-objective optimization problems are investigated with the proposed framework. The experimental results show that the outperforming CHT can vary by constrained multi-objective optimization problems, as far as examined in this study.
  • Hiroaki Nakano, Taku Nonomura, Akira Oyama, Hiroya Mamori, Naoya Fukushima, Makoto Yamamoto
    AIAA Aerospace Sciences Meeting, 2018 *(210059) *-* 2018年  査読有り
    © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The numerical analysis of the supersonic jet is conducted using large eddy simulations (LES) with high order schemes and the grid of approximately 650 million points. A Mach number and a Reynolds number are set to be 2.0 and 9.0×105, respectively. At first, we confirm the azimuthal grid resolution. As a result, it seems that the flow field and the acoustic field near the jet flow are slightly affected by changing the grid resolution, while the sound pressure level at far-field converges sufficiently with the present grid number. The computational flow field shows good agreement as compared with the experimental data. Moreover, it is shown that the sound pressure level at far-field can be predicted within 4dB difference as compared to the experimental data. Next, the effect of the jet temperature of the supersonic jet on the acoustic waves is investigated. The temperature ratio of the chamber to ambient air is set to be 1.0, 2.7, and 4.0 for the cold, mid-hot and hot jets, respectively. Mach waves are radiated from the supersonic jet toward downstream. we confirmed that the shorter potential core length, the higher sound pressure level, the larger angle of Mach waves with increasing jet temperature.
  • Shigtaka Kawai, Thijs Bouwhuis, Yoshiaki Abe, Aiko Yakeno, Taku Nonomura, Akira Oyama, Harry W.M. Hoeijmakers, Kozo Fujii
    AIAA Aerospace Sciences Meeting, 2018 (210059) 2018年  査読有り
    © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The relation between the parameters of the body-force field generated by a plasma actuator and the maximum induced velocity in quiescent air is investigated by expressing the body-force distribution as the Gaussian function of the spatial coordinates. The aim of this study is to identify the dominant parameters for modeling of the body-force distribution. For that purpose, the parametric study using numerical simulations and dimensional analysis are conducted to derive the nondimensional key parameters. It is found that the nondimensional maximum induced velocity is determined by the Reynolds number calculated by three parameters: the total induced momentum per unit time, the height of the center of gravity of the body-force distribution, and the standard deviation from the center of gravity. In addition, the relation for the Gaussian body-force distribution turns out to be applicable to a conventional model, i.e, the Suzen model, even though the shapes of the distribution differ. Thus, we conclude that the three body-force parameters above are the key parameters for the maximum velocity induced by a plasma actuator.
  • Takuya Harada, Koji Fujita, Akira Oyama, Hiroya Mamori, Makoto Yamamoto
    AIAA Aerospace Sciences Meeting, 2018 (210059) 2018年  査読有り
    Aerodynamics optimization of airfoil for flying-wing type Mars airplane is conducted to show tradeoff between maximization of aerodynamic performance and stability requirement. To see the tradeoff between the two objectives, a multiobjective evolutionary algorithm is used where aerodynamic performance of each airfoil is evaluated with a two-dimensional laminar Navier-Stokes flow solver. Some design constraints are applied to obtain feasible airfoil shapes. The obtained Pareto-optimal airfoils show tradeoff between the two design objectives. Analysis of the flow field of the obtained airfoils leads to some useful knowledge in designing airfoil for flying-wing type Mars airplane.
  • Morizawa Seiichiro, Nonomura Taku, Oyama Akira, Fujii Kozo, Obayashi Shigeru
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 61(6) 258-267 2018年  査読有り
  • Yuta Ozawa, Taku Nonomura, Masayuki Anyoji, Hiroya Mamori, Naoya Fukushima, Akira Oyama, Kozo Fujii, Makoto Yamamoto
    Transactions of the Japan Society for Aeronautical and Space Sciences 61(6) 281-284 2018年  査読有り
  • M. Anyoji, M. Okamoto, K. Fujita, H. Nagai, A. Oyama
    Fluid Mechanics Research International Journal 1(3) 2017年11月  査読有り
  • Satoshi Shimomura, Takuto Ogawa, Satoshi Sekimoto, Taku Nonomura, Akira Oyama, Kozo Fujii, Hiroyuki Nishida
    Volume 1C, Symposia: Gas-Liquid Two-Phase Flows; Gas and Liquid-Solid Two-Phase Flows; Numerical Methods for Multiphase Flow; Turbulent Flows: Issues and Perspectives; Flow Applications in Aerospace; Fluid Power; Bio-Inspired Fluid Mechanics; Flow Manipulation and Active Control; Fundamental Issues and Perspectives in Fluid Mechanics; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes 2017年7月30日  
    This paper experimentally investigates the effectiveness of a closed-loop flow control method using a DBD plasma actuator for a NACA0015 airfoil, in which the surface pressure fluctuation is fed back to the system; the actuator was driven when the pressure fluctuation exceeds the setup threshold. The Reynolds number based on the chord length is set to 63,000 and the angle of attack is in the range from 12 to 15 degrees. The actuator was installed on the surface at 5% of the chord length from the leading edge. The results show that the closed-loop control worked better than the continuous operation. In the angle of attack of 12 and 14 degrees, the complete attached flow was attained by setting the appropriate threshold value of the pressure fluctuation. On the other hand, in 15 degrees, although the complete attached flow was not attained, the flow separation was partially suppressed.
  • Takeshi Watanabe, Tomoaki Tatsukawa, Takayuki Yamamoto, Akira Oyama, Yasuhiro Kawakatsu
    JOURNAL OF SPACECRAFT AND ROCKETS 54(4) 796-807 2017年7月  査読有り
    The present study focuses on exploring optimal transfer solutions for the Demonstration and Experiment of Space Technology for INterplanetary voYage (DESTINY) mission, which was proposed as an Institute of Space and Astronautical Science (ISAS) Epsilon-class small program in 2013 based on the "Space Science & Exploration Roadmap" proposed by the ISAS and later approved by the government committee on space policy. During the DESTINY mission, the spacecraft will first be injected into a low elliptical orbit by an Epsilon rocket, and its altitude will then be increased to approach the Moon using an ion engine system. Next, the spacecraft will be injected via a transfer orbit to the L2 Halo orbit of the Sun-Earth system by way of gravity assist from the Moon. As the spacecraft revolves around the Earth several hundred times, it gradually increases its altitude. Thus, the launch time and thrust profile must be chosen properly. Note that there are several conflicting requirements, including the reduction of fuel consumption, total flight time, and maximum eclipse time, that must be taken into consideration. To satisfy these requirements, many-objective evolutionary computation is applied to find better orbital designs.
  • Vinay Ravindra, Prilando Rizki Akbar, Miao Zhang, Jiro Hirokawa, Hirobumi Saito, Akira Oyama
    IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 65(5) 2144-2156 2017年5月  査読有り
    This paper investigated the possibility of using an X-band traveling-wave antenna for application in synthetic aperture radar (SAR) on a small-satellite platform. A rectangular slotted parallel-plate antenna panel capable of radiating dual polarization over the same physical aperture was selected for this purpose. The design procedure, which provides for an optimal antenna pattern in a SAR application, is described. A metaheuristic multiobjective optimization algorithm was applied to synthesize an appropriate far-field pattern, which enhances the quality of the SAR image. Subsequently, the optimization results were used to build a more realistic model of the antenna panel in electromagnetic simulation software. An antenna panel was fabricated, and its electrical characteristics were measured. The fabricated prototype weighed 1310 g and measurements showed nearly 50% aperture efficiency for both circular polarizations [34.6-dBic right-hand circular polarized (RHCP), 34.5-dBic left-hand circular polarized (LHCP), and peak gain at 9.65 GHz], with low side-lobes. A beam shift of 2.1 degrees was observed between the RHCP and LHCP beams at the design center frequency and was later analyzed to be the result of an error in the modeling of the adhesive layer.
  • Toshiki Kondoh, Tomoaki Tatsukawa, Akira Oyama, Takeshi Watanabe, Kozo Fujii
    2016 IEEE Symposium Series on Computational Intelligence, SSCI 2016 2017年2月9日  
    In this paper, we describe how discretizing design variables on real-coded genetic algorithms (RCGAs) can influence the convergence and the diversity of Pareto optimal solutions. We use Non-dominated Sorting Genetic Algorithm II (NSGA-II) as an RCGA based on Pareto dominance, changing the number of significant digits after the decimal point for each design variable. Test problems and engineering problems are investigated. Computational results show that the use of a smaller number of significant figures instead of larger ones achieves better convergence that a larger number in many cases. In the DTLZ3 test problem, low applied precision avoids dominance-resistant solutions (DRSs) and improves both the generational distance (GD) and the inverted generational distance (IGD). On the other hand, in the DTLZ4 test problem, low digit precision improves GD, whereas it worsens IGD. This indicates that a minimum digit precision is required to maintain the diversity of Pareto optimal solutions in some problems. When we use RCGAs, it is critical to set the number of significant digits after the decimal point to realistically represent actual engineering problems.
  • 井上 翔太, 大山 聖, 守 裕也, 福島 直哉, 山本 誠
    日本機械学会関東支部総会講演会講演論文集 2017.23 211 2017年  

MISC

 59
  • 森穂高, 大山聖, 丸祐介, 坂本勇樹, 小林弘明, 江口光
    日本航空宇宙学会年会講演会講演集(CD-ROM) 54th 2023年  
  • 遠藤桜, 大山聖, 山田和彦
    宇宙科学技術連合講演会講演集(CD-ROM) 67th 2023年  
  • 岸, 祐希, 金崎, 雅博, 杉浦, 正彦, 田辺, 安忠, 大山, 聖, 佐藤, 允, KISHI, Yuki, KANAZAKI, Masahiro, SUGIURA, Masahiko, TANABE, Yasutada, Oyama, Akira, SATO, Makoto
    宇宙航空研究開発機構特別資料: 第53回流体力学講演会/第39回航空宇宙数値シミュレーション技術シンポジウム論文集 = JAXA Special Publication: Proceedings of the 53rd Fluid Dynamics Conference / the 39th Aerospace Numerical Simulation Symposium JAXA-SP-21-008 149-155 2022年2月14日  
    第53回流体力学講演会/第39回航空宇宙数値シミュレーション技術シンポジウム (2021年6月30日-7月2日. 日本航空宇宙学会 : 宇宙航空研究開発機構(JAXA)オンライン会議) The 53rd Fluid Dynamics Conference / the 39th Aerospace Numerical Simulation Symposium (June 30 - July 2, 2021. The Japan Society for Aeronautical and Space Sciences : Japan Aerospace Exploration Agency (JAXA), Online meeting) In this paper, aerodynamic characteristics around the blade of the hexacopter ''HAMILTON (HexAcopter for Martian pIt crater exploraTiON)'' for Mars exploration are investigated to obtain design knowledge regarding multicopter drone flying in Martian atmosphere. Reynolds-averaged Navier-Stokes simulation with the moving overlapped grid was employed for aerodynamic evaluation of two cases; one is hexa-rotor case and the other is single rotor case in order to compare single rotor case and hexa-rotor case and reveal unique characteristics of multirotor case. According to computational results, in both cases, hexa-rotor and single rotor, the maximum figure of merit could be observed at higher hovering thrust conditions. It is suggested that the baseline blade geometry could generate thrust efficiently at higher thrust conditions. The flow structure around the hexa-rotor can be classified into three groups; turn-in side where the flow was drawn the inside by blades rotation, turn-out side where the flow was put out to the outside by blades rotation, and the center side which was located between the turn-in and turn-out sides. The rotors of the center side took the low figure of merit compared with the other rotors because of aerodynamic interference from the turn-in side and the turn-out side rotors. Therefore, the total figure of merit of all rotors increased when the distance among rotors is increased. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA2130027012 レポート番号: JAXA-SP-21-008
  • 大山聖
    計算工学 27(2) 2022年  
  • 大山聖
    自動車技術 75(4) 2021年  招待有り
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書籍等出版物

 1
  • Akira Oyama
    Springer Verlag 2009年  Refereed
    Constraint-handling techniques for evolutionary multiobjective aerodynamic and multidisciplinary designs are focused. Because number of evaluations is strictly limited in aerodynamic or multidisciplinary design optimization due to expensive computational fluid dynamics (CFD) simulations for aerodynamic evaluations, very efficient and robust constraint-handling technique is required for aerodynamic and multidisciplinary design optimizations. First, in Section 2, features of aerodynamic design optimization problems are discussed. Then, in Section 3 constraint-handling techniques used for aerodynamic and multidisciplinary designs are overviewed. Then, an efficient constraint-handling technique suitable to aerodynamic and multidisciplinary designs is introduced with real-world aerodynamic and multidisciplinary applications. Finally, an efficient geometry-constraint-handling technique commonly used for aerodynamic design optimizations is presented. © 2009 Springer-Verlag Berlin Heidelberg.

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共同研究・競争的資金等の研究課題

 7
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