Nonlinear nonequilibrium acoustics in nanoscales

Research Project

Project/Area Number	16H04267
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	Fluid engineering
Research Institution	Osaka University
Principal Investigator	Yano Takeru 大阪大学, 工学研究科, 教授 (60200557)
Project Period (FY)	2016-04-01 – 2019-03-31
Project Status	Completed (Fiscal Year 2018)
Budget Amount *help	¥6,760,000 (Direct Cost: ¥5,200,000、Indirect Cost: ¥1,560,000) Fiscal Year 2018: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000) Fiscal Year 2017: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000) Fiscal Year 2016: ¥3,770,000 (Direct Cost: ¥2,900,000、Indirect Cost: ¥870,000)
Keywords	分子動力学 / 非線形音響学 / ボルツマン方程式 / 希薄気体 / 音波 / 気液界面 / 希薄気体力学 / 超音波 / 分子流体力学 / 非線形非平衡音響学
Outline of Final Research Achievements	Sound waves can convey the momentum and energy in gases without unidirectional flows. We can examine the transport properties of sound by solving the system of Navier-Stokes equations, if the wavelength is sufficiently large compared with the mean free path of gas molecules and the frequency is sufficiently small compared with the mean collision frequency of gas molecules. The propagation properties of short-wavelength sound have been studied by the kinetic theory of gases based on the Boltzmann equation and several discrepancies have been found between the predictions by Navier-Stokes and Boltzmann equations. However, the kinetic theory is subject to the crucial constraint that a molecule must be negligibly small compared with any other length scales concerned, and hence sound waves with wavelength of nanometers cannot be treated in the kinetic theory. We therefore consider the application of molecular dynamics to the problems of propagation of sound with wavelength of nanometers.
Academic Significance and Societal Importance of the Research Achievements	ナノメートル程度の波長をもつ超音波による運動量輸送とエネルギー輸送の予測と制御が可能となれば、非接触で微粒子の位置を精密に制御する技術や微細で精巧な加工技術の新しい発展を導くことが予想される。また、ナノメートル程度の波長をもつ超音波とナノメートル程度の厚さをもつ気液界面との非平衡な相互作用の過程が明らかになれば、超音波霧化だけでなく、新しい界面化学現象の発見やその応用技術への発展なども期待される。このように、音波による運動量輸送とエネルギー輸送をナノスケールの世界に導入すること、すなわち「非線形非平衡音響学」を創出することは、流体力学的応用研究の新展開を刺激し得るという意味でその意義は大きい。