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Type of Document	Dissertation
Author	Tanguay, Michel
Author's Email Address	michel AT dynaflow-inc.com
URN	etd-05282004-130028
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-05282004-130028
Title	Computation of bubbly cavitating flow in shock wave lithotripsy
Degree	PhD
Option	Mechanical Engineering
Advisory Committee	Advisor Name Title Tim Colonius Committee Chair Anthony Leonard Committee Member John F. Brady Committee Member Lawrence A. Crum Committee Member Melany L. Hunt Committee Member
Keywords	lithotripsy numerical model shock wave cavitation
Date of Defense	2003-12-10
Availability	unrestricted
Abstract Lithotripsy is at the forefront of treatment of kidney stones. By firing shock waves at the stone, it can be broken down into small fragments. Although the treatment is non-invasive, both short- and long-term side effects occur. In order to understand and rectify these shortcomings, lithotripsy has been the subject of ongoing research. Based on in vitro experiments, it has been ascertained that the cloud of cavitating bubble produced in the wake of the shock wave is a crucial element in the stone comminution process. Various solutions designed to maximize stone comminution and/or decrease tissue damage have been proposed over the years. However, the particulars of the comminution mechanism(s) are still undetermined. In this work, a numerical model of the two-phase flow inside an electrohydraulic lithotripter was used to provide additional insight in the behavior of the bubble cloud. The numerical model is based on an ensemble averaged two-phase flow model for a compressible liquid. The differential equations were discretized following the WENO shock capturing scheme in prolate spheroidal and cylindrical coordinate systems. The initial conditions for the flow field are estimated based on empirical observations and then validated by comparing the predicted pressure measurements and bubble cloud behavior against experimental values. In order to gain additional insight in the mechanism for stone comminution, a variety of relevant initial conditions were modeled. The following lithotripter configurations were analyzed: free-field, dual-pulse and single-pulse with an artificial stone at the focus. The impact of parameters such as the intensity of the initial shock wave and the pulse rate frequency (PRF) has been investigated. Based on an energy argument, conclusions regarding the effciency of stone comminution are presented. In addition, based on these conclusions, avenues for improvement of the numerical model are highlighted.
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