球在连续分层流体中的振动和悬浮
Oscillation and levitation of balls in continuously stratified fluids
摘要：
本文对有限容器内连续分层流体中球体的自由运动进行了实验研究。振荡频率被发现是非常接近当地的Brunt-Vaisala频率。附加质量的影响实际上可以忽略不计。结果表明，经典的粘性阻力将导致比实验中观察到的更强的阻尼。这被解释为来自先前激发的内波在其从边界反射之后的反馈的结果。提出了一个修正的阻力项的唯象方程，以获得与观测定性一致。我们指出，包括一个历史项将导致进一步远离观察到的数据。
英文摘要：
The free motion of balls is investigated experimentally in continously stratified fluid in a finite container. The oscillation frequency is found to be very close to the local Brunt-Vaisala frequency. The effect of added mass proves to be practically negligible. The evolution of rear jets is demonstrated, and a kind of long term levitation is found. We show that the classical viscous drag would lead to a much stronger damping than observed in the experiment. This is interpreted as a consequence of the feedback from the previously excited internal waves following their reflection from the boundaries. A phenomenological equation with a modified drag term is proposed to obtain a qualitative agreement with the observations. We point out that the inclusion of a history term would lead further away from the observed data.
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