Studies of blast sound propagation and passive absorption using laser-generated shock waves and a semi-analytical method

以往的野外工作已经显示了在接近地面的室外爆炸声传播中的几个现象，这些现象可能与声震耦合有关，但至今仍未得到解释。此外，仍然需要进一步研究被动方法，以吸收在空中爆炸附近产生的声音。然而，现场爆炸试验既昂贵又困难。申请者和同事已经在实验室模拟爆炸声传播中使用声冲击方面获得了经验，声冲击可以是电产生的，也可以是通过透镜聚焦高功率脉冲YAG激光器的光束而产生的。激光产生的冲击被发现比电火花源产生的冲击具有更高的强度和重复性。基于以前在赫尔的经验，由EPSRC激光贷款计划产生，建议开展一项系统的研究方案，研究地面弹性、粗糙度和曲率对线性和非线性近地表传播的影响。这将涉及使用专门建造的宽带麦克风、设计和开发麦克风定位系统以进行详细的声场测绘和麦克风挡板，以减少麦克风周围反射的声音与感兴趣的入射信号之间的干扰影响。建议与拉夫堡大学合作，研究和验证半分析方法的应用，而不是进一步开发完全数值方法来模拟震源附近的爆炸声传播。除了比完全数值方法的计算成本更低之外，所得到的模型应该能更好地理解与声诱导瑞雷波的产生相关的参数和几何结构。激光产生的冲击的高强度和良好的重复性也使它们成为实验室研究通过由相对较大的颗粒或纤维组成的厚的刚性或弹性多孔层的传输的有用来源，这些层可能有助于被动吸收低频声波冲击。因此，本文还对此类材料的线性和非线性声学特性进行了系统的实验研究。

Previous field work has shown several phenomena in outdoor blast sound propagation near to the ground surface that may be related to acoustic-to-seismic coupling but as yet are unexplained. Moreover there remains a need for further work on passive methods for absorbing sound generated near to airborne blasts. However field experiments with explosions are expensive and difficult. Experience has been gained by the applicants and coworkers in the use of acoustic shocks, either electrically-produced or caused by focussing the beam of a high powered pulse YAG laser through a lens, in laboratory simulations of blast sound propagation. The laser-generated shocks have been found to have higher intensity and repeatability than those from an electrical sparker source. Based on this previous experience at Hull, resulting from the EPSRC laser loan scheme, it is proposed to carry out a systematic programme of research on the effects of ground elasticity, roughness and curvature on linear and nonlinear near-surface propagation. This will involve use of specially-constructed wide-band microphones, design and development of microphone positioning systems for detailed sound field mapping and microphone baffles to reduce the effects of the interference between sound reflected around the microphone and the incident signals of interest. Rather than further development of completely-numerical methods for modelling blast sound propagation near the source, in conjunction with Loughborough University it is proposed to investigate and validate the application of a semi-analytical method. Apart from being less computationally-expensive than a completely numerical method, the resulting model should improve understanding of the parameters and geometry associated with creation of acoustically-induced Rayleigh waves. The high intensity and good repeatability of laser-generated shocks also make them a useful source for laboratory investigations of transmission through thick rigid- or elastic-porous layers composed of relatively large grains or fibres that are potentially useful for passive absorption of low-frequency acoustic shocks. Consequently a systematic experimental investigation of the linear and nonlinear acoustrical properties of such materials is proposed also.