• Proceedings of the KSME Conference
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• 2001.06e
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• pp.69-74
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• 2001

It is well known that an air bubble trapped in water emits light at its collapse robustly with a proper forcing amplitude of ultrasound. Instability mechanism which causes deviation from sphericity of bubble wall was investigated theoretically. The rapid change of the bubble wall velocity which is both dependent on the forcing amplitude, was found to be a major factor of instability of the interface. The Rayleigh-Taylor instability which occurs when rapid acceleration is directed from the lighter towards the heavier fluid is found to be not related to the instability of the sonoluminescing gas bubble. A good agreement between the calculation results and experimental data is found.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.550-555
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• 2000

Nonlinear oscillation of a microbubble under ultrasound was investigated theoretically. The bubble radius-time curves calculated by the Rayleigh-Plesset equation with a polytropic index and by the Keller-Miksis equation with the analytical solution for the Navier-Stokes equations of the gases were compared with the observed results by the light scattering method. This study has revealed that the bubble behavior such as the expansion ratio and the bouncing motion after the first collapse under ultrasound depends crucially on the retarded time of the bubble motion to the applied ultrasound.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.487-492
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• 2001

The Multi-bubble sonoluminescence(MBSL) provides a unique environment, that is, very high temperature$(5,000\sim20,000K)$ and high pressure$(500\sim10,000\;atm)$. However, the mechanism for the MBSL has been elusive. Recently, it has been suggested that the mechanism be continuous and also of discrete peaks that are caused by molecular transitions. In this article, this mechanism has been examined for the Ar/water system by the combined hydrodynamics and molecular transition.