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Oscillation and levitation of balls in continuously stratified fluids

I. Biro·B. Gyure·I. M. Janosi·K. G. Szabo·T. Tel
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Abstract

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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I. Biro, B. Gyure, I. M. Janosi, K. G. Szabo, T. Tel. 2007-02-23. Oscillation and levitation of balls in continuously stratified fluids. https://doi.org/10.1063/1.2927461

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