Japanese/English
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Development of flow simulation method
for high enthalpy plasma - nonionized gas coexisting systems
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Simulation of high-enthaply plasma flow such as thermal plasma flow is generally difficult. The entire flow field, in which the plasma at a high temperature and a cold gas at room temperature co-exist, must be treated simultaneously. Widely varied temperatures of 300-12,000 K cause large variations of the transport properties and the density. Meanwhile, the Mach numbers are very small in and around the plasma. When a numerical method for a compressible flow simulation is used for such a flow field, the computation takes an extremely long time to obtain a numerical solution for a practical time scale. Therefore, a thermal plasma is treated as an incompressible flow with the density as a temperatur-edependent variable. This condition, which is severe for numerical flow simulations, usually destabilizes the computation (= the computation easily breaks down). That is why thermal plasma simulations have often used differencing schemes which suppress numerical instability effectively. However, those schemes also suppress the actual physical instability simultaneously. In consequence, the numerical result does not simulate any realistic flow with vortices. On the other hand, schemes suitable for vortex capturing often cause destabilization of computations. Although these two aspects mutually conflict, a new method combining those schemes and algorithm has been long-awaited to simulate vortex motions in and around high-enthalpy plasma flows. A innovative simulation method that acheives both capturing of physical insitability (vortex motions) and numerically-stable long-time computation at the same time was developed successfully. For example, an experiment visualized that a thermal plasma jet entrained surrounding cold gas by Kelvin-Helmholtz instability, induced many vortices even far from the plasma core, and transited to a turbulent state with vortex breakup about 30 years ago. Nevertheless, such a flow had never been simulated because of the numerically severe conditions. Overcoming the difficulties, the present effort broke through that problem and obtaiend a successful result. Special thanks to Cyberscience Center, Tohoku University For more information, see ...Plasma Sources Science and Technology, Vol. 21, No. 5, (October, 2012), pp. 055029 (14 pages). Masaya Shigeta Journal of Physics D: Applied Physics, Vol. 46, No. 1, (January, 2013) 015401 (12 pages). Masaya Shigeta Journal of Physics D: Applied Physics, Vol. 49, No. 49, (November, 2016), pp. 493001 (18 pages). Masaya Shigeta Journal of Flow Control, Measurement & Visualization, Vol. 6, (April, 2018), pp. 107-123. Masaya Shigeta IEEJ Transactions on Electrical and Electronic Engineering, Vol. 14, (January, 2019), pp. 16-28. Masaya Shigeta Plasma Chemistry and Plasma Processing, Vol. 40, Issue 3, (May, 2020), pp. 775-794. Masaya Shigeta |
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Particle method simulation of molten metal flow & heat transfer
in welding processes
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The details will be provided soon. See also Web Manga (Catoon). FREE ACCESS The Japan Welding Engineering Society WE-COM Magazine "Dr. Naniwa's Welding Gatten! R". [in Japanese] Story: SHIGETA Masaya, Art: KARANO Tatsuko Special thanks to Tanaka Lab. JWRI, Osaka University For more information, see ... quarterly Journal of the Japan Welding Society, Vol. 32, No. 4, (December, 2014), pp. 213-222. [in Japanese] Masumi ITO, Seiichiro IZAWA, Yu FUKUNISHI, Masaya Shigeta Quarterly Journal of the Japan Welding Society, Vol. 33, No.2, (May, 2015), pp. 32s-38s. Masumi Ito, Yu Nishio, Seiichiro Izawa, Yu Fukunishi, and Masaya Shigeta Quarterly Journal of the Japan Welding Society, Vol. 38, No. 2, (May, 2020), pp. 84s-88s. Ryo UENO, Hisaya KOMEN, Masaya Shigeta, Manabu TANAKA |
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Experimental visualization measurements
for high-temperature manufacturing processes
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The details will be provided soon. Special thanks to Tanaka Lab. JWRI, Osaka University For more information, see ...Journal of Physics D: Applied Physics, Vol. 52, No. 35, (August, 2019), pp. 354003 (9 pages). Keigo Tanaka, Masaya Shigeta, Manabu Tanaka, Anthony B. Murphy Japanese Journal of Applied Physics, Vol. 59, (November, 2019), pp. SA0805 (12 pages). Masaya Shigeta, Manabu Tanaka Quarterly Journal of the Japan Welding Society, Vol. 38, No. 2, (April, 2020), pp. 21s-24s. Keigo TANAKA, Masaya Shigeta, Manabu TANAKA, Anthony B. MURPHY Journal of Physics D: Applied Physics, Vol. 53, No. 42, (July, 2020), pp. 425202 (8 pages). Keigo Tanaka, Masaya Shigeta, Manabu Tanaka, Anthony B. Murphy |
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Mathematical formulation & algorithm development
for nanopowder formation in plasma flows
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Plasma flow is expected as promising fluid that achieves mass-fabrication of nanometer-scale ultrafine particles (nanopowder). However, the physical phenomena are still poorly understood because it is very difficult to observe and measure directly the high-temperature flow field and nanopowder formation progressing in nano-second to milli-second time scales. Deep understanding of the physics is required to fabricate nanopowder desirable for specific purposes. To overcome that problem, we are addressing the mathematical formulations and developing the numerical algorithms. Nanoparticles have been anticipated for application in various field. Efficient and highly-accurate mass-fabrication of nanopowder leads to rapid progress of those fields; in consequence, it will bring many innovations. The final objective of this study is to develop a virtual experiment system in computer. This system will analyze the physical phenomena in detail, repeat the virtual experiments at low costs, and overcome the big problem of “high-cost equipment and running” in experimental studies. More innovative control methods of nanopowder synthesis and production of nanopowder with new characteristics will be expected as well. Special thanks to Cyberscience Center, Tohoku University For more information, see ...Journal of Applied Physics, Vol. 108, Issue 4, (August, 2010), pp. 043306 (15 pages). Masaya Shigeta and Takayuki Watanabe Modelling and Simulation in Materials Science and Engineering, Vol. 20, No. 4, (May, 2012), pp. 045017 (11 pages). Valerian A. Nemchinsky and Masaya Shigeta Powder Technology, Vol. 288, (January, 2016), pp. 191-201. Masaya Shigeta, Takayuki Watanabe Nanomaterials, Vol. 6, (March, 2016), pp. 43 (10 pages). Masaya Shigeta, Takayuki Watanabe Journal of Flow Control, Measurement & Visualization, Vol. 6, (April, 2018), pp. 107-123. Masaya Shigeta IEEJ Transactions on Electrical and Electronic Engineering, Vol. 14, (January, 2019), pp. 16-28. Masaya Shigeta Nanomaterials, Vol. 9, No. 12, (December, 2019), pp. 1736 (13 pages). Masaya Shigeta, Manabu Tanaka, Emanuele Ghedini Plasma Chemistry and Plasma Processing, Vol. 40, Issue 3, (May, 2020), pp. 775-794. Masaya Shigeta Journal of Alloys and Compounds, Vol. 873, No. 25, (August, 2021) pp. 159724 (9 pages). Y. Hirayama, M. Shigeta, Z. Liu, N. Yodoshi, A. Hosokawa, K. Takagi Journal of Alloys and Compounds, Vol. 882, No. 15, (November, 2021), ppl. 160633 (10 pages). Kwangjae Park, Yusuke Hirayama, Masaya Shigeta, Zheng Liu, Makoto Kobashi, Kenta Takagi Journal of Alloys and Compounds, Vol. 898, (March 25, 2022), pp. 162792 (7 pages). Y. Hirayama, M. Shigeta, K. Takagi and K. Ozaki |
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Simulation of landform formation of lava-modelled molten metal flow
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[Shingo TOMITA (Graduate Student, M2)] Volcanic eruptions can cause major disasters with phenomena such as pyroclastic flows, volcanic ash, and lava flows. In particular, lava flows can cause catastrophic damage in areas where they flow. To mitigate such damage, proactive measures and immediate responses are required. Proactive measures mean the preparation of hazard maps and urban planning. Immediate responses mean evacuation and construction of earthwork to protect the city after the eruption. In both cases, developing simulators that can accurately predict volcanic phenomena is necessary to enhance their effectiveness. However, previous lava flow simulators only provide broad-scale predictions and lack detailed discussion of thermo-hydrodynamic phenomena in lava and their impact on overall flow, so their predictions are not highly accurate. Therefore, we utilize our knowledge of thermo-fluid engineering and simulation to elucidate individual thermo-fluid phenomena specific to lava flows numerically. We aim to improve the prediction accuracy of the overall eruption phenomena by considering the influence of those phenomena. We have worked to reproduce the phenomena of landform formation of lava flows. One of these is called "lava levee". In flowing lava, the sides and bottom are easily cooled and solidified quickly. On the other hand, the inside lava flows without solidifying due to its low cooling rate. As a result, levee-like topography is formed. Another characteristic shape has also been reproduced: the "toe-like" structure that occurs after the tip solidifies and the accumulated lava re-flows down. These topographic formations seen during actual volcanic eruptions may affect the direction of lava flow. It is an important phenomenon for improving prediction accuracy. However, the formation process and dominant factors are not yet elucidated. We applied our knowledge of molten metal flow in welding to simulate lava flow with solidification phenomena. As a result, we successfully reproduced the lava’s landform formations, which had not been achieved in previous studies. After reproducing various phenomena, we improve the accuracy of the reproductions to elucidate these phenomena. In this way, we are working on the research toward our final goal of developing a simulator that will contribute to the mitigation of volcanic disasters. For more information, see ... Dynamics, Vol. 4, Issue 2, (April 19, 2024), pp. 287-302. Shingo Tomita, Joe Yoshikawa, Makoto Sugimoto, Hisaya Komen, Masaya Shigeta |