Johnsen Eric, Colonius Tim
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA.
J Acoust Soc Am. 2008 Oct;124(4):2011-20. doi: 10.1121/1.2973229.
The shock-induced collapse of a pre-existing nucleus near a solid surface in the focal region of a lithotripter is investigated. The entire flow field of the collapse of a single gas bubble subjected to a lithotripter pulse is simulated using a high-order accurate shock- and interface-capturing scheme, and the wall pressure is considered as an indication of potential damage. Results from the computations show the same qualitative behavior as that observed in experiments: a re-entrant jet forms in the direction of propagation of the pulse and penetrates the bubble during collapse, ultimately hitting the distal side and generating a water-hammer shock. As a result of the propagation of this wave, wall pressures on the order of 1 GPa may be achieved for bubbles collapsing close to the wall. The wall pressure decreases with initial stand-off distance and pulse width and increases with pulse amplitude. For the stand-off distances considered in the present work, the wall pressure due to bubble collapse is larger than that due to the incoming shockwave; the region over which this holds may extend to ten initial radii. The present results indicate that shock-induced collapse is a mechanism with high potential for damage in shockwave lithotripsy.
研究了在碎石机聚焦区域中，靠近固体表面的预先存在的气核因冲击波而发生的崩溃。使用高阶精确的激波和界面捕捉格式模拟了单个气泡在碎石机脉冲作用下崩溃的整个流场，并将壁面压力视为潜在损伤的一个指标。计算结果显示出与实验中观察到的相同的定性行为：在脉冲传播方向上形成一个折返射流，在气泡崩溃过程中穿透气泡，最终撞击远端并产生水击波。由于该波的传播，对于靠近壁面崩溃的气泡，壁面压力可达1吉帕量级。壁面压力随初始间距和脉冲宽度减小而增大，随脉冲幅度增大而增大。对于本研究中考虑的间距，气泡崩溃引起的壁面压力大于入射冲击波引起的壁面压力；这种情况成立的区域可能延伸到十个初始半径。目前的结果表明，冲击波诱导的崩溃是冲击波碎石术中具有高损伤潜力的一种机制。
