Featured Researcher
UC Berkeley: Jonathan Iloreta
We are using the SDSC supercomputers to study the effects of reflector geometry on the acoustic field of a shock wave lithotripter.
The simulations track the propagation and steepening of a pressure wave off an axisymmetric reflector. The model solves the Euler equations coupled with the Tait equation of state using a finite volume scheme. The reflector is modeled as an interface with a density jump. Due to the nature of our problem, we needed an extremely fine grid in order to fully resolve the shock waves (of amplitudes of ~40MPa, corresponding to thicknesses in the micron level). With the use of DataStar and its 272 nodes, we were able to capture the interesting nonlinear dynamics of the waves that our single-processor PC could not.
Two reflector geometries have been considered: an unmodified reflector and a reflector with an insert placed in it. Experimental studies have shown that the insert affects the acoustic field in such a way as to suppress strongly cavitating bubbles. However, the effect of the insert could only be experimentally tested at select locations in the flow field. On the other hand, our model allows us to determine the pressure waveforms throughout the entire domain. This is of great interest because doctors need to know how the procedure affects the entire body, not just the vicinity near the kidney stone.
Preliminary results show excellent agreement with experimental measurements. The data revealed the interaction between waves, diffraction at the reflector edge, and reflection off the lithotripter and symmetry axis. The results show significant changes between the pressure fields for the different geometries, thus hinting at the possibility of optimizing the reflector shape. We are in the process of testing new lithotripter designs in hope of determining the ideal reflector.
