秋永 剛 (アキナガ タケシ)

AKINAGA Takeshi

写真a

所属

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 

研究分野・キーワード

流体工学,生物流体物理

出身大学 【 表示 / 非表示

  • 1993年04月
    -
    1997年03月

    同志社大学   工学部   機械工学科   卒業

出身大学院 【 表示 / 非表示

  •  
    -
    2005年03月

    同志社大学  工学研究科  機械工学専攻  博士後期課程  単位取得満期退学

取得学位 【 表示 / 非表示

  • 同志社大学 -  博士(工学)

職務経歴(学内) 【 表示 / 非表示

  • 2020年04月
    -
    継続中

    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  

  • 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  

 

学位論文 【 表示 / 非表示

  • Stability and transition of flow past bluff bodies

    Takeshi Akinaga

      2007年03月

    単著

論文 【 表示 / 非表示

  • Tertiary and Quaternary States in the Taylor-Couette System

    Takeshi Akinaga, Sotos C. Generalis, Friedrich H. Busse

    Chaos, Solitons & Fractals   109   107 - 117   2018年04月  [査読有り]

    国内共著

    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.

    DOI

  • 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]

    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.

    DOI

  • 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]

    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.

    DOI

  • 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]

    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.

    DOI

  • The charge effect on the hindrance factors for diffusion and convection of a solute in pores: II

    Takeshi Akinaga, Hideyuki O-tani, Masako Sugihara-Seki

    Fluid Dynamics Research   44 ( 6 ) 065504 - 065504   2012年09月  [査読有り]

    国内共著

    The diffusion and convection of a solute suspended in a fluid across porous membranes are known to be reduced compared to those in a bulk solution, owing to the fluid mechanical interaction between the solute and the pore wall as well as steric restriction. If the solute and the pore wall are electrically charged, the electrostatic interaction between them could affect the hindrance to diffusion and convection. In this study, the transport of charged spherical solutes through charged circular cylindrical pores filled with an electrolyte solution containing small ions was studied numerically by using a fluid mechanical and electrostatic model. Based on a mean field theory, the electrostatic interaction energy between the solute and the pore wall was estimated from the Poisson–Boltzmann equation, and the charge effect on the solute transport was examined for the solute and pore wall of like charge. The results were compared with those obtained from the linearized form of the Poisson–Boltzmann equation, i.e. the Debye–Hückel equation.

    DOI

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