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When the bubble moves in the vicinity of a free surface, the movement will be affected by the buoyancy and the Bjerknes effect. Blake and Gibson proposed the criterion which determined the motion direction of the jet and the dynamics of bubble. They proposed the jet wouldn’t be formed in the condition that . Based on the potential flow theory, boundary element method (BEM) is used to calculate three typical examples in this paper in order to study the dynamics of the bubble under the combined action of the Bjerknes effect of the free surface and the buoyancy. It is found out during the analysis that the Blake criterion is applicable to predict the conditions that and .

Comparing with many modern signal processing methods in the bearing fault diagnosis, Hilbert-Huang transform is proposed which has good resolving power, and is adapt to process non-stationary, nonlinear and no cross-interference signals. Experimental bearing vibration signals have been analyzed by using this method, whose impulse response waveform was effectively separated from the signals. The results show that the sensitivity and reliability of the method are satisfactory.