Sound radiation from periodically spring-supported beams under the action of a convected uniform harmonic loading

The main purpose of this paper is to investigate the effects of periodic spring supports on the acoustic response of an infinite, fluid-loaded beam subject to a harmonic moving line force. The mechanics of a fluid-loaded beam with periodic spring supports was formulated based on the Timoshenko beam theory. The main focus is to examine the effects of the spring support spacing and the travelling line force speed on the radiated sound power. The effects of the spring supports on the radiated sound power decrease as the excitation frequency and the Mach number of the travelling line force increase. When the external line force is stationary and acoustically small, it is interesting to find that the radiated sound power is seen to exhibit peaks at certain low wavenumber ratios except when the length of the external force is an integral multiple of the spring support spacing. It is shown that the locations of these peaks coincide with the lower bounding wavenumber ratios of the odd number of propagation zones. Under the circumstances, the incomplete pressure equalization is responsible for the fluctuations in radiated sound power. However, when the line force is moving, the radiated sound power fluctuates more rapidly at low wavenumber ratios even through the length of the external line force is an integral multiple of the support spacing. (C) 1999 Academic Press.