Generation of flexural waves in infinite plates by laser-initiated air shock waves

Controlled explosions that take place above ground surface during military testing generate not only shock waves in air but also strong ground vibrations. It is convenient and much less expensive to study the associated sound and vibration phenomena using reduced-scale laboratory simulations, with a laser as a source of air shock waves interacting with large elastic plates modelling the ground1,2. Earlier, a semi-analytical model describing interaction of air shock waves with an elastic half space has been suggested by one of the present authors to describe generation of Rayleigh surface waves by electric spark discharge near the surface3. The aim of the present paper is to further develop the above-mentioned semi-analytical model3 and to apply it to the interaction of laser-initiated air shock waves with an infinite elastic plate. The impact of the incident shock wave is to be approximated by an equivalent cylindrically diverging surface force resulting from the surface pressure of the incident and reflected shock waves. The well-known analytical expressions for air particle velocity and pressure in the front of a shock wave are used to describe this surface force as a function of time and distance from the epicentre. The problem is then solved using the Green’s function method applied to an infinite plate. The resulting frequency spectra and time shapes of the generated flexural wave pulses are calculated for different values of the height of the laser-generated spark above the plate surface. The obtained theoretical results for time histories and frequency spectra of generated flexural waves are compared with the results of the reduced-scale model experiments on shock wave interaction with a large plastic plate.