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

以前的现场工作已经表明，在室外爆炸声传播的地面附近，可能与声震耦合，但尚未解释的几种现象。此外，还需要进一步研究吸收空气爆炸附近产生的声音的被动方法。然而，爆炸的现场实验是昂贵和困难的。本申请人及其同事在爆炸声传播的实验室模拟中，已经获得了使用声震的经验，所述声震或者是电产生的，或者是通过透镜聚焦高功率脉冲YAG激光束而引起的。已发现激光产生的冲击比电火花源产生的冲击具有更高的强度和可重复性。根据以前在船体从EPSRC激光器租借计划获得的经验，建议开展一项系统的方案，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。这将涉及使用特别构造的宽带麦克风，设计和开发用于详细声场映射的麦克风定位系统，以及麦克风挡板，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。而不是进一步发展的完全数值方法模拟爆炸声传播附近的源，与拉夫堡大学，建议调查和验证的应用程序的半分析方法。除了计算成本低于完全数值方法外，所得到的模型还应提高对与声致瑞利波产生相关的参数和几何形状的理解。激光产生的冲击的高强度和良好的可重复性，也使他们成为一个有用的源，通过厚的刚性或弹性多孔层的传输实验室调查组成的相对较大的颗粒或纤维，是潜在的有用的被动吸收低频声冲击。因此，本文还提出了对这种材料的线性和非线性声学特性进行系统的实验研究。

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.