著者

佐藤 康晴 清野 文雄 小笠原 啓一 山本 佳孝 佐藤 徹 平林 紳一郎 清水 賀之

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.129, no.4, pp.124-131, 2013-04-01 (Released:2014-04-14)

参考文献数

20

被引用文献数

5 9

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The motion of a single MH-bubble in quiescent fluid was examined experimentally. If a methane-gas bubble is placed under the condition that hydrates nucleation can initiate, typically at high pressure and low temperature, a thin methane hydrate film is formed on the bubble surface and it alters the motion of the bubble in the fluid drastically. It behaves as if solid did.To clarify the fluid dynamics of MH-bubbles, we devised the special apparatus which enabled us to observe the three dimensional behaviours of the MH-bubbles under high pressure condition. The three dimensional motions of the MH-bubbles were captured by two high-speed cameras whose resolution was 1024*1024 pixel at 500Hz. To analyze the motions of the MH-bubbles, Direct Linear Transformation Method was adopted.Equivalent diameter of the MH-bubble was altered from 3.8 to 7.8 mm, which corresponded to the range from 555 to 1155 in Reynolds number, by replacing the nozzles with different diameters.The MH- bubbles in this range exhibited the zigzag motion, while methane bubbles the spiral motion. Main findings in this research are as follows:(1) The aspect ratio, the height to width ratio, decreased linearly with the increment of the equivalent diameter of a MH-bubble. This reflects the fact that the shape of the MH-bubble shifts from spherical to ellipsoidal. (2) Strouhal number which characterizes the zigzag motion of the MH-bubbles increased with Reynolds number. (3) The drag coefficients were measured up to the Reynolds number of about 1000. The drag coefficient of a MHbubble departs from the standard drag curve when the shape deformation become notable. After that, it rise in accordance with the progress of the deformation. These phenomena also have been observed in the behaviour of a bubble with a surfactant.

著者

鈴木 英之 柴田 創 藤岡 弘幸 平林 紳一郎 石井 希実子 菊池 紘樹

出版者

The Japan Society of Naval Architects and Ocean Engineers

雑誌

日本船舶海洋工学会論文集 (ISSN:18803717)

巻号頁・発行日

vol.18, pp.81-90, 2013

被引用文献数

3

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Rotor-floater-mooring coupled response analysis is essentially important for design of Rotor Nacelle Assembly (RNA) and floating support structure of Floating Offshore Wind Turbine (FOWT). The authors have developed an analysis code UTWind for the analysis of the coupled response. Blades and floater are modeled as frame structure with beam elements. Lumped mass model is use for mooring. Aerodynamic load on blade is calculated by Blade Element Momentum Theory (BEM), and hydrodynamic load is calculated by Hooft's method, and Morison equation was modified to be applicable to cylindrical element with cross section with two axes of line symmetry. The equations of motion of rotor, floater and mooring are solved in time domain by weak coupling algorithm.The numerical results by the code were compared with experimental results in wave and wind-wave coexisting condition with/without blade pitch control and showed good agreement. Response by negative damping was reproduced by the code and showed good agreement with experiments.