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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Acoustic streaming ： ウィキペディア英語版 Acoustic streaming Acoustic streaming is a steady current in a fluid driven by the absorption of high amplitude acoustic oscillations. This phenomenon can be observed near sound emitters, or in the standing waves within a Kundt's tube. It is the less-known opposite of sound generation by a flow. There are two situations where sound is absorbed in its medium of propagation: * during propagation.〔see video on http://www.lmfa.ec-lyon.fr/perso/Valery.Botton/english/videos_streaming.html〕 The attenuation coefficient is $\backslash alpha=2\backslash eta\backslash omega^2/(3\backslash rho\; c^3)$, following Stokes' law (sound attenuation). This effect is more intense at elevated frequencies and is much greater in air (where attenuation occurs on a characteristic distance $\backslash alpha^$~10 cm at 1 MHz) than in water ($\backslash alpha^$~100 m at 1 MHz). In air it is known as the ''Quartz wind''. * near a boundary. Either when sound reaches a boundary, or when a boundary is vibrating in a still medium. A wall vibrating parallel to itself generates a shear wave, of attenuated amplitude within the Stokes oscillating boundary layer. This effect is localised on an attenuation length of characteristic size $\backslash delta=()^$ whose order of magnitude is a few micrometres in both air and water at 1 MHz. == Origin: a body force due to acoustic absorption in the fluid == Acoustic streaming is a non-linear effect. 〔Sir James Lighthill (1978) "Acoustic streaming", 61, 391, Journal of Sound and Vibration〕 We can decompose the velocity field in a vibration part and a steady part $=v+\backslash overline$. The vibration part $v$ is due to sound, while the steady part is the acoustic streaming velocity (average velocity). The Navier–Stokes equations implies for the acoustic streaming velocity: :$$ \overline_i}+\overline \overline_j _i}=-}+\eta _i}-(\overline ). The steady streaming originates from a steady body force $f\_i=-(\backslash overline\; )/$ that appears on the right hand side. This force is a function of what is known as the Reynolds stresses in turbulence $-\backslash overline$. The Reynolds stress depends on the amplitude of sound vibrations, and the body force reflects diminutions in this sound amplitude. We see that this stress is non-linear (quadratic) in the velocity amplitude. It is non vanishing only where the velocity amplitude varies. If the velocity of the fluid oscillates because of sound as $\backslash epsilon\backslash cos(\backslash omega\; t)$, the quadratic non-linearity generates a steady force proportional to $\backslash scriptstyle\; \backslash overline=\backslash epsilon^2/2$. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Acoustic streaming」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.