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Type of Document	Dissertation
Author	Johnsen, Eric
URN	etd-05092008-171346
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-05092008-171346
Title	Numerical simulations of non-spherical bubble collapse : with applications to shockwave lithotripsy
Degree	PhD
Option	Mechanical Engineering
Advisory Committee	Advisor Name Title Chris Brennen Committee Chair John Brady Committee Member Joseph Shepherd Committee Member Tim Colonius Committee Member
Keywords	Interface-capturing Shockwave lithotripsy Computational fluid dynamics Bubble dynamics Shock-capturing
Date of Defense	2007-11-29
Availability	unrestricted
Abstract Shockwave lithotripsy (SWL) is a non-invasive medical procedure in which shockwaves are focused on kidney stones in an attempt to break them. Because the stones are usually immersed in liquid, cavitation occurs during the process. However, the stone comminution mechanisms and the bubble dynamics of SWL are not fully understood. In the present thesis, numerical simulations are employed to study axisymmetric Rayleigh collapse and shock-induced collapse of a single gas bubble in a free field and near a wall. A high-order accurate, quasi-conservative, shock- and interface-capturing scheme is developed to solve the multicomponent Euler equations. The primary contributions of the present work are the development of a new numerical framework to study compressible multicomponent flows, the characterization of the dynamics of non-spherical bubble collapse, and quantitative measurements of wall pressures generated by bubble collapse. Because of asymmetries in the flow field, a re-entrant jet develops and generates a large water-hammer pressure upon impact onto the distal side. Jet properties are calculated and, as an indication of potential damage, wall pressures are measured; pressures on the order of 1 GPa are achieved locally. In shock-induced collapse, the wall pressure is amplified by the presence of bubbles within several initial radii from the wall. Thus, the pressure generated by the bubble collapse is larger than the incoming shock. The results extended to SWL show that shock-induced collapse has tremendous potential for damage along the stone surface. Furthermore, the simulations are coupled to an elastic wave propagation code to show that bubble collapse may cause damage within kidney stones as well.
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