It is well known that a cloud cavitation is one of the most destructive forms of cavitation. The set of equations for the motion of a spherical bubble cloud is formulated. Behavior of bubble clouds are simulated numerically when the surrounding pressure is decreased from 50kPa to 10kPa and then increased to 50kPa. An inward propagating shock wave is formed during the collapse of bubble cloud and the shock wave is focused at the cloud center. This creates a violent bubble collapse that causes a high emitted pressure from the bubbles, which is several hundreds times larger than the single bubble collapse and becomes more than 1GPa. The frequency of the emitted pressure is so high that it propagates with the speed of sound of liquid and the high frequency pressure disturbance is observed at the center region before the main shock reaches the center.
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