研究者業績
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 特任教授
- 学位
- 博士(工学)(1993年3月 東京大学)
- 研究者番号
- 30421861
- ORCID ID
https://orcid.org/0009-0003-1983-0418
- J-GLOBAL ID
- 202501003875861850
- researchmap会員ID
- R000090222
研究キーワード
1経歴
3-
2025年4月 - 現在
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2000年4月 - 2025年3月
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1996年3月 - 2025年3月
論文
33-
Physics of Fluids 36(3) 2024年3月Fluid-rigid body interaction is a significant topic in research on particle methods. This study developed a fluid-rigid body coupling method based on a physically consistent particle method, i.e., the moving particle hydrodynamics (MPH) method, incorporating the passively moving solid (PMS) model. When the discrete particle system satisfies the fundamental laws of physics, i.e., mass conservation, linear and angular momentum conservation, and the second law of thermodynamics, the method is asserted physically consistent, and this feature is important for robust dynamic calculations. The PMS model is a pioneering approach that is practical for particle methods in which fluid and rigid-body particles are initially calculated as a fluid. Then, only rigid-body particles are modified to restore the initial shape by applying rigid-body constraints. Thus, combining the MPH method and the PMS model realizes a fluid-rigid body coupling method that satisfies fundamental physical laws. The proposed method was first verified via the fundamental rigid body and fluid-rigid body coupling problems: the Dzhanibekov effect on a T-shaped rigid body, a floating rectangular solid, a floating cylinder, and water entry of a two-dimensional cylinder. Second, the proposed method was validated via calculating a cylinder rolling on a liquid film as a fluid-rigid body coupling problem with rotation. By using a potential-based surface tension model, the computed results showed reasonable agreement with the experimental data obtained in this study. Overall, it was confirmed that the proposed method is a promising fluid-rigid body coupling approach, in which the surface tension and wettability can be considered as well.
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トライボロジスト 69(11) 763-772 2024年New bearing units having lubricant supply structure were devised for realizing longer lifetime and better performance of rotation mechanisms of space machineries. The spacer sandwiched by two bearings was filled with grease and porous body was established between grease and the bearing for both preventing thickener transferred into bearings and supplying only oil for bearings. The oil supply function was verified by friction tests and bearing tests using fluorescent agent. The contribution for long lifetime of the oil supply system was confirmed by the lifetime tests under a vacuum which showed stable rotation for 2×10⁸ revolutions at a room temperature and 1×10⁹ revolutions at a temperature of 60℃. Moreover, large size bearing units with the oil supply structure were evaluated under high rotation speed for utilized in larger spacecraft requiring larger attitude control torque and observation systems requiring agile attitude control. Using larger size bearings and rotating with higher speed would cause to promote oil scattering by centrifugal force and oil evaporation by temperature rise, whereas the oil supply structure was conducted the feasibility to realize both larger size bearings, higher rotation speed, longer lifetime and low torque.
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Journal of Fluid Science and Technology 18(4) JFST0035-JFST0035 2023年The Bingham fluid simulation model was constructed and validated using a physically consistent particle method, i.e., the Moving Particle Hydrodynamics (MPH) method. When a discrete particle system satisfies the fundamental laws of physics, the method is asserted as physically consistent. Since Bingham fluids sometimes show solid-like behaviors, linear and angular momentum conservation is especially important. These features are naturally satisfied in the MPH method. To model the Bingham feature, the viscosity of the fluid was varied to express the stress-strain rate relation. Since the solid-like part, where the stress does not exceed the yield stress, was modeled with very large viscosity, the implicit velocity calculation was introduced so as to avoid the restriction of the time step width with respect to the diffusion number. As a result, the present model could express the stopping and solid-like behaviors, which are characteristics of Bingham fluids. The proposed method was verified and validated, and its capability was demonstrated through calculations of the two-dimensional Poiseuille flow of a Bingham plastic fluid and the three-dimensional dam-break flow of a Bingham pseudoplastic fluid by comparing those computed results to theory and experiment.
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Computational Particle Mechanics 9(3) 421-441 2021年6月21日In this study, we improve a multiresolution method to reduce the computation time of fluid lubrication simulation based on a particle method by applying an implicit algorithm for viscosity calculation. The present method is based on the moving particle simulation (MPS) method and the overlapping particle technique (OPT), which is a multiresolution method for particle methods under unsteady states. The MPS method is used to solve the Navier–Stokes equation. The OPT is used to reduce the number of required particles and reduce the computation time. We improve the OPT by applying an implicit method for viscosity calculation to eliminate restrictions regarding time increment due to the diffusion number. In addition, we enable the particle size to be changed significantly between subdomains in the OPT. To validate the proposed method, we simulate the fluid lubrication of line contact in two dimensions until the flow reached a steady state. Consequently, it is shown that the pressure obtained using the proposed method agrees well with that obtained using the Reynolds equation. The computation time of a particle simulation using the improved multiresolution method is significantly shorter than that of a single-resolution simulation. In addition, the effects of particle size and subdomain size are validated in the fluid lubrication simulation using the OPT.
MISC
194-
日本航空宇宙学会誌 69(5) 180-186 2021年超低高度衛星技術試験機「つばめ」(以降,SLATS : Super Low Altitude Test Satellite)の姿勢制御用搭載機器である国産新型ホイール・タイプS は,10Nms以下クラスの国産リアクションホイール(RW)として開発された.本ホイールは,それまで輸入品に頼っていた小型RWに関して,高信頼性,高品質な国産品に対するユーザからのニーズにこたえるために開発を行ったものであり,SLATSに搭載され軌道上実証することとなった.本ホイールの地上での開発は順調に進み,2017年12月のSLATS打ち上げ後も約2年弱の運用期間にわたり軌道上で順調に動作し続け,機器特性や健全性等に関する貴重な結果をもたらした.本解説記事では,国産新型ホイール・タイプSの開発結果と軌道上での実証結果について紹介する.
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日本航空宇宙学会誌 69(4) 140-144 2021年宇宙機のアンテナや太陽電池パドルなどの保持解放機構は,動作時に数千GSRS(SRS : Shock Response Spectrum)の衝撃を発生させるため,宇宙機搭載機器には高い耐衝撃性が要求される.また,既存の保持解放機構は使い捨てであるか,または再使用のために製造工場へ返送してリファービッシュが必要となる.これらの課題を解決するため,宇宙航空研究開発機構(JAXA)と三菱電機株式会社(MELCO)は保持軸力10 kN級の保持解放機構である「低衝撃保持解放機構(LSRD : Low Shock Release Device)」を共同で開発した.このデバイスは保持エネルギを内部機構の運動エネルギに変換することにより,動作時の衝撃レベルを極めて低くすることができる.また,再使用時は部品交換の必要がなく,現場でのリセットが可能である.2017年12月23日に打ち上げられた超低高度衛星技術試験機「つばめ」(SLATS)の太陽電池パドル保持部に8台のLSRDが搭載され,軌道上実証に成功した.今後,本デバイスの活躍が期待される.