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大学院理工学研究科 共同サステナブル工学専攻 |
職務経歴（学内） 【 表示 ／ 非表示 】
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2022年04月-継続中
秋田大学 大学院理工学研究科 共同サステナブル工学専攻 准教授
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2020年04月-2022年03月
秋田大学 大学院理工学研究科 システムデザイン工学専攻 機械工学コース 准教授
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2017年07月-2020年03月
秋田大学 大学院理工学研究科 システムデザイン工学専攻 創造生産工学コース 准教授
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Stability and transition of flow past bluff bodies
Takeshi Akinaga
2007年03月
単著
研究等業績 【 表示 ／ 非表示 】
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Yamashita H.
Micromachines ( Micromachines ) 12 ( 10 ) 2021年10月 [査読有り]
研究論文（学術雑誌） 国内共著
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On the Problem of Resonant Incompressible Flow in Ventilated Double Glazing
T. Akinaga, T. M. Harvey-Ball, T. Itano, S. C. Generalis, E. C. Aifantis
Lobachevskii Journal of Mathematics ( Lobachevskii Journal of Mathematics ) 42 ( 8 ) 1753 - 1767 2021年08月 [査読有り]
研究論文（学術雑誌） 国際共著
We employ a homotopy method, rather than conventional stability theory, in order to resolve the degeneracy due to resonance, which exists in fluid motion associated with a channel of infinite extent in ventilated double glazing. The introduction of a symmetry breaking perturbation, in the form of a Poiseuille flow component, alters substantially the resonant bifurcation tree of the original flow. Previously unknown resonant higher order nonlinear solutions, i.e. after the removal of the perturbative Poiseuille flow component, are discovered. A possible extension of the methodology to consider non-Newtonian gradient enhanced incompressible viscous fluids is also briefly discussed.
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Brine utilisation for cooling and salt production in wind-driven seawater greenhouses: Design and modelling
Takeshi Akinaga, Sotos Generalis, Charlie Paton, Opus Igobo, Philip Davies
Desalination 426 135 - 154 2018年01月 [査読有り]
研究論文（学術雑誌） 国内共著
Brine disposal is a major challenge facing the desalination industry. Discharged brines pollute the oceans and aquifers. Here is it proposed to reduce the volume of brines by means of evaporative coolers in seawater greenhouses, thus enabling the cultivation of high-value crops and production of sea salt. Unlike in typical greenhouses, only natural wind is used for ventilation, without electric fans. We present a model to predict the water evaporation, salt production, internal temperature and humidity according to ambient conditions. Predictions are presented for three case studies: (a) the Horn of Africa (Berbera) where a seawater desalination plant will be coupled to salt production; (b) Iran (Ahwaz) for management of hypersaline water from the Gotvand dam; (c) Gujarat (Ahmedabad) where natural seawater is fed to the cooling process, enhancing salt production in solar salt works. Water evaporation per face area of evaporator pad is predicted in the range 33 to 83 m 3 /m 2 ·yr, and salt production up to 5.8 tonnes/m 2 ·yr. Temperature is lowest close to the evaporator pad, increasing downwind, such that the cooling effect mostly dissipates within 15 m of the cooling pad. Depending on location, peak temperatures reduce by 8-16 °C at the hottest time of year.
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Convection induced by instabilities in the presence of a transverse seepage
Takeshi Akinaga, Tomoaki Itano, Sotos Generali
Chaos, Solitons & Fractals 91 533 - 543 2016年10月 [査読有り]
研究論文（学術雑誌） 国内共著
The transition of laterally heated flows in a vertical layer and in the presence of a streamwise pressure gradient is examined numerically for the case of different values Prandtl number. The stability analysis of the basic flow for the pure hydrodynamic case (Pr=0) was reported in [1]. We find that in the absence of transverse pumping the previously known critical parameters are recovered [2], while as the strength of the Poiseuille flow component is increased the convective motion is delayed considerably. Following the linear stability analysis for the vertical channel flow our attention is focused on a study of the finite amplitude secondary travelling-wave (TW) solutions that develop from the perturbations of the transverse roll type imposed on the basic flow and temperature profiles. The linear stability of the secondary TWs against three-dimensional perturbations is also examined and it is shown that the bifurcating tertiary flows are phase-locked to the secondary TWs.
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Transition of planar Couette flow at infinite Reynolds numbers
Tomoaki Itano, Takeshi Akinaga, Sotos C. Generalis, Masako Sugihara-Seki
Physical Review Letter 111 184502 - 184502 2013年10月 [査読有り]
研究論文（学術雑誌） 国内共著
An outline of the state space of planar Couette flow at high Reynolds numbers (Re<10^{5}) is investigated via a variety of efficient numerical techniques. It is verified from nonlinear analysis that the lower branch of the hairpin vortex state (HVS) asymptotically approaches the primary (laminar) state with increasing Re. It is also predicted that the lower branch of the HVS at high Re belongs to the stability boundary that initiates a transition to turbulence, and that one of the unstable manifolds of the lower branch of HVS lies on the boundary. These facts suggest HVS may provide a criterion to estimate a minimum perturbation arising transition to turbulent states at the infinite Re limit.
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プレート式熱交換器内の相変化を伴う気液二相流れ
三島 光太郎, 安永 健, 秋永 剛
熱工学コンファレンス講演論文集 ( 一般社団法人 日本機械学会 ) 2021 ( 0 ) 0069 2021年
<p>In order to comprehend fluid dynamics of gas-liquid two phase flow through plate heat exchangers flow of HFE7000 between inclined parallel plates has been numerically inverstigated based on a mixture model for gas-liquid two phase flow with the phase changes. The characteristics of the flow patterns for various flow configurations were discussed and both the Nusselt numbers and pressure drops were evaluated. As the results using plate heat exchangers, that the gas-liquid phase change could effectively enhance the heat transfer between the working fluid and the surfaces, and the prefered orientation for the installation of the plates could be identified based on the combination of the heat transfer coefficient and the pressure drop.</p>
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Tertiary and Quaternary States in the Taylor-Couette System
Akinaga T., Generalis S.C., Busse F.H.
Chaos, Solitons and Fractals ( Chaos, Solitons and Fractals ) 109 107 - 117 2018年04月 [査読有り]
国際共著
The analysis of the Taylor-Couette problem in the small gap limit is extended to the cases of tertiary and quaternary solutions. The theoretical results are compared with experimental observations. Although in the latter the small-gap approximation is not always well approximated, the comparison of theoretical results and observations yields reasonable agreements. The absence of the wavy twist mode in the observed patterns is explained by the presence of no-slip boundary conditions in the axial direction of the experimental apparatus, which differ from the periodic conditions imposed in the theoretical analysis. Quaternary solutions bifurcating from the tertiary ones through subharmonic instabilities are presented and compared with experimental observations. Reasonable agreement has been found.
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流れの線形安定性解析の数値解析法
水島二郎, 秋永剛
応用数理 16 32 - 44 2006年12月 [査読有り]
研究論文（その他学術会議資料等） 国内共著
It was shown by Ruell and Takens that fluid motion can be chaotic with three distinct frequencies being aquired due to instabilities of flow. Thus, the instability of a steady flow is the first step to chaos and hence to turbulence. After overviewing the scenario of transitions of flow to turbulence briefly, we show four numerical methods to analyze the linear stability of steady flows: numerical simulation of a set of linear equations for a disturbance, successive over relaxation method, Arnoldi method, and shift and inverse power method. We discuss the merit of each numerical method together with some issues arising in numerical stability analyses of flow past a circular cylinder, taking it as an example.