B. M. Efimtsov
Central Aerohydrodynamic Inst. TsAGI), Moscow Branch, Acoust. Div. 17, Radio Str., Moscow, 107005, Russia
Fundamental phenomena defining thin-walled structure vibration and acoustic radiation in uniform and essentially nonuniform convecting fields of random pressure fluctuations are investigated. Investigated, in particular, are the new effects of vibration increase, which are revealed at some definite relations between spatial scales of correlation, nonuniformity, phase velocity of the pressure fluctuation field, elastic wavelengths in the structure, and their propagation velocity. The new effects of the vibration increase can be considered as latent spatial resonances. Just those resonances determine the main regularities in vibration of arbitrary thin-walled structure in the convecting field of random pressure fluctuation. Moreover, those resonances determine acoustic radiation at some moderate (usually realized) energy dissipation in the structure. In this case the radiation is associated with the resonance excitation of the structure. The well-known aerodynamic coincidence effect appears only in the case when spatial scales of correlation and nonuniformity exceed the elastic wavelength in the structure. At the high degree of vibroabsorption the acoustic radiation associated with the nonresonance excitation of the structure (their inertial behavior) can become dominant. In this case similar effects of the acoustic radiation increase become dominant. They are revealed at some definite relations between spatial scales of correlation and nonuniformity, phase velocity of pressure fluctuation, sound wavelength, and its propagation velocity in a medium, where the sound field is formed.