Sound Radiation From Beams Under the Action of Moving Line Forces

Abstract

The topic of sound radiation from beams under the action of harmonic line forces moving at subsonic speeds is studied. The nondimensional sound power is formulated through integration of the surface acoustic intensity distribution over the entire beam. Asymptotic expressions for the sound power in the low frequency region are derived depending upon the characteristics of the fluid loading and the spatial extent of the applied forces. Numerical integrations have been performed to determine the effects on the radiated sound power of the Mach number, M , the acoustic length of line force, Ko L , and the wavenumber ratio, γ. The results show that for beams under heavy fluid loading, the effect of the speed of the moving force is not pronounced, while for beams under light fluid loading, the unique coincidence radiation peak at γ ∼ 1 for a stationary force (M = 0̸) is split into two coincidence peaks (located in the frequency regions γ<1 and γ>1 respectively) due to the effects of the Doppler shift. The values of Ko L that suppress the coincidence peaks are also changed due to the motion of the line force.