应用时空守恒元和解元方法数值研究冲击波碎石的力学机理

To maximize stone comminution and minimize tissue damage with the combined effect of cavitation and shock wave, the damage and destruction mechanisms of shock wave lithotripsy have to be studied. Based on a series of in vitro and in vivo experiments, it has been ascertained that the wave structure of pressure following a tension with large positive and negative peak produced stone spall, fatigue and cavitation in the wake of the shock wave is a crucial element in the stone comminution process. The numerical simulation of cavitation bubbles dynamical theory of shock wave lithotripsy based on the experimental data and the results of the numerical simulation is established. The model can elaborate the mechanisms of stone breakage and tissue damage, the relation with the shock wave waveform and firing frequency and other parameters. The model also can test the usability of usually bubble dynamics used on shock wave lithotripsy. The model also can evaluate the destructive effects of high-speed micro-jet, strong shock wave, high temperatures and other factors. The numerical simulation of the bubble dynamic process, which is non-symmetrical collapse induced by shock wave lithotripsy, in stones and near the surface of the tissue describes the evolutionary process for velocity field, deformation speed, stress wave, temperature field and at the interface coupling and other factors on the gas - liquid - solid phase regions. The model also involves in the study of cavitation mechanism medical for ultrasound and laser.

进一步研究冲击波碎石中空化的损伤和破坏机制，为达到空化和冲击波共同作用下组织损伤的最小化及碎石疗效的最优化提供科学数据和改进建议。基于一系列生物体外以及体内的实验，已经验证了先压力后拉力，且正负峰值都很大的波形结构，正是引起结石层裂、疲劳和空化的主因。利用实验数据以及数值模拟结果，建立冲击波碎石的空泡动力学理论进行数值模拟，进一步阐明其中空化的组织损伤和结石破坏机制，及其与冲击波波形和击发频率等参数的关系，检验通常的空泡动力学对冲击波碎石的适用度，评价高速微射流、强冲击波、高温及其他因素的破坏作用。特别是通过对冲击波碎石时诱发的空泡在结石和组织表面附近非对称坍塌的动力学过程的数值模拟，详细描述在气-液--固三相各区域内的速度场、变形速度场、应力波、温度场、及界面处各自的耦合等因素的时间演化过程。也涉及医用超声波、激光等的空化机制的研究。

利用时空守恒元和解元方法建立了ESWL中的水下聚焦冲击波的二维数学模型，分别数值模拟了球面压电陶瓷型和液电式机型ESWL的在单侧和双侧波源情况下，冲击波传播过程。成功地模拟了单侧波源与双侧波源ESWL中的聚焦流场。并比较了单侧波源和双侧波源碎石机在第二焦点处及其前后位置的压力值。模拟了聚焦超声波在人体组织中的发热现象。在水和组织中模拟了静态声场，得到组织中的声学强度分布，计算得到吸收的声能，用来作为组织域中的生物传递物理场接口中的热源，通过瞬态求解模拟组织暴露在超声场中1S内的加热和冷却过程。推导了高阶精度的CE/SE格式并且模拟了激波绕流现象。模拟了在传统的液电式碎石器上附加了一对反射器的流场以及焦区附近的压强。数值模拟结果表明，最大正、负压力值随着附加反射器的角度的增加而逐渐减少，负压的减少幅度相较于正压的减少幅度来说更大。