The collapse of a bubble against infinite and finite rigid boundaries for underwater laser propulsion

Abstract

In order to investigate the influence of a bubble on underwater laser propulsion, the analytical formula of the bubble collapse time near rigid boundary is deduced from Rayleigh collapse time and Rattray prolongation factor. Experiments and numerical simulations are employed to validate the collapse time formula. The collapsing features of a bubble, including the maximum bubble radius Rmax, the collapse time of the bubble TCR, the shock wave and liquid jet emitted during the bubble collapse, are obtained near infinite and finite rigid boundaries. The theoretical, numerical and experimental results for the dimensionless distance γ > 1 all illuminate that TCR increases with Rmax near the rigid boundary. Rmax and TCR increase with the laser energy first, then begin to level out as the laser energy continues to increase, thus it is impossible to increase the propelling force just through increasing the laser pulse energy continuously. In addition, TCR is smaller, and the shock wave pressure and the liquid jet velocity are larger near the finite rigid boundary than that near the infinite rigid boundary, which means that the bubble collapses fiercer in the former case, in other words the finite rigid boundary gets more propelling force.

Formation and dynamics of a toroidal bubble during laser propelling a cavity object in water

“…To verify the mechanism of formation of the toroidal bubbles and the microbubble cluster, simulations are used to calculate the pressure variation when a plasma shockwave propagates in the cavity. The simulation method we used is reported in a previous paper from our group [19]. Simulation results are shown in Fig.…”

Shock Wave Emission and Cavitation Bubble Generation in Laser Surgery

“…16 Figure 6 shows that shock wave's peak pressure decrease rapidly, and generally attenuates in proportion to 1/r, which is consistent with Refs. [18], [21] and [22]. But there are also some fluctuations in Figure 6, the reason maybe the existence of a reflected shock wave, which is caused by the rigid boundary.…”

“…The spherical shock wave changes to two hemispherical shock waves, and the pressures of these two shock wave attenuates differently with increasing time. 22 By tracking the arrival times of the bubble walls during its expanding and contracting stages at the corresponding detection distance, the temporal oscillation characteristics of a cavitation bubble oscillation can be obtained, which is shown in Figure 7. The vertical axis represents the bubble radius and corresponds to the position of the probe beam relative to the breakdown site.…”

Numerical Simulation for Cavitation Bubble Near Free Surface and Rigid Boundary

“…1,2) On the other hand, some researchers have tried to use the cavitation effect for the material surface processing. 3,4) The impact of a collapsing cavitation bubble can give a compressive residual stress at the material surfaces.…”

“…6) Cavitation bubble dynamics were investigated using an experimental facility such as laserinduced and spark-generated bubbles as well as acoustically generated cavitation bubbles. 2,7) Besides, many kinds of numerical methods have been performed to simulate a bubble dynamics. 8,9) However the large deformation of the bubble shape during the collapse made it difficult to simulate the cavitation phenomena using a traditional mesh-methods such as the finite differential method (FDM), the finite element method (FEM) and finite volume method (FVM).…”