Interaction Of Laser-induced Cavitation Bubbles And Mechanical Effects From The Nonspherical Bubble Collapse

In order to understand the influences from the different non-symmetric constraints on the bubble dynamics and the evolution of the mechanical effect from the oscillating and collapsing bubble on the nearby object, interactions between laser-induced cavitation bubbles and differently shaped rigid boundaries and colloid-liquid interface or free liquid surface, as well as laser-induced double bubble and multi bubble interactions are investigated in this work.As the first step for developing the model of bubble-interface interactions, the theoretical model for single spherical bubbles located in the bulk is modified to describe the laser-induced cavitation bubbles through modifications to the equation of state of the bubble interior substance. Through fitting of the numerical solution of the model to the experimental results, the evolution of the substance inside the laser-induced bubble can be investigated. The Keller-Miksis model of a bubble in compressible viscous liquid is solved numerically. It is found that the nonlinearity in the oscillating bubble grows as the oscillating amplitude grows. Thus, more bubble energy transforms into sound radiation and participates the momentum coupling between the bubble and the target.Three dimensional simulation models for the interactions of the single bubble and the differently shaped rigid boundaries have been developed through ALE (Arbitrary Lagrangian-Eulerian method) based on FEM (finite element method) and FVM (finite volume method). The momentum transfer from the bubble to the object has been analyzed and optimized through the highly nonlinear explicit numerical simulations. The insight gained from the numerical simulations of the design on the rigid surface profile has been implemented in guiding the further experimental investigations. Detailed kinetic energy and momentum coupling coefficients gained by the objects have been recorded after implementation of single laser pulses of different pulse energy, through means of a fiber-optic sensor based on optical beam deflection. The investigations show that the propelling force comes from the laser induced plasma shock wave, the laser induced bubble oscillation shock waves and the collapse impact induced by the collapsing bubble. The momentum coupling coefficient of the hemispherical shell is the highest.Interactions between two laser-induced bubbles and interactions within a small population bubble group are investigated, for the possible implementations of the laser propulsion effect enhanced by the strengthened jetting from the bubble collapsing. Three dimensional simulation models for the interactions between two laser-induced bubbles have been developed through VOF (Volume of Fluid) method based on FVM. It is shown that the bubble collapse jet can be strengthened and directionally controlled through manipulation of the relative bubble positions, the time difference between bubble generation, and the laser pulse energies determining the bubble sizes. Furthermore, dynamics of the bubble pairs would change but predictable as the bubble size drops from millimeter range to micrometer range, which would further influence the propulsion effects on the objects. Especially, the interactions between bubbles in a bubble cluster with arbitrary number of bubbles are investigated through the dynamical equations deducted from Hamiltonian mechanics, where the translations and pulsations of each bubble can be obtained.The outcomes from this work will be helpful in guiding further investigations for Lab on a chip based on MFEMS (Micro Fluidic Electro Mechanical System), which is recently developed as an important technique in Life Science and Biochemical researches, where laser-induced bubbles will contribute as a micro-pump, micro-mixer, a micro-propeller, or a micro-injector.