Investigation of Collapse Features of a Bubble near Target Surface of Different Sizes for Underwater Laser Propulsion

In order to investigate the underwater laser propulsion, the collapse features of a laser-induced bubble near target surface of three different sizes are studied by the experiment based on the optical beam deflection method and the numerical simulation based on VOF method. The propelling force F and the impulse IB generated by the collapse bubble are calculated. The results show that the smaller the target surface is, the smaller the maximum bubble radius is. In addition, the smaller the target surface is, the more fiercely the bubble collapses, and the larger the pressure generated by the collapse bubble is. However, the smaller the target surface is, the smaller the peak value of F is. This occurs because F is the integral of the pressure over the area, where the impact of area is greater than the pressure. Furthermore, F decreases to negative after the maximum as a result of the shock wave generated by the collapse bubble propagating along the target surface.