Sonic-boom generated sound field under a wavy air-water interface: Analyses for incident N waves

摘要

Examples of the sonic-boom generated sound field under a wavy air-water interface based on the theory of Cheng and Lee [J. Fluid Mech. 514, 281-312 (2004)] are studied to determine the surface-wave influence on sound-pressure level, frequency range, and waveform characteristics of disturbances generated by an aerial sonic-boom N wave over water. The study substantiates that, owing to their much lower attenuation rate, the time-dependent disturbances produced by the interaction with a surface-wave train can be comparable to, and overwhelm the flat-ocean (Sawyers) wave field at large as well as moderate depth levels, depending on Mach number, surface-wave length and-height, and the alignment angle of surface waves with respect to the flight track. Computed examples, assuming a 300 ft.(91 m) signature length and a 2 psf(96 Pa) peak sea-level overpressure, show that, under a mildly wavy ocean, sonic-boom disturbances at sound-pressure level of 100-126 dB (re: 1 mu Pa) can reach a depth of 750-1500 ft.(229-457 m), where the dominant waveform evolves into an infrasound wave packet of frequency 5-40 Hz. (c) 2005 Acoustical Society of America.