A note on the acoustic radiation from point-forced elastic beams

An exact expression for the acoustic power radiated by a point-excited damped bar is derived through direct integration of the theoretical surface acoustic intensity distribution. The effects of structural damping and wavenumber ratio on the power are presented. Expressions are obtained for the contributions to the total acoustic power arising from the propagating portion of the vibratory response and the non-propagating or flexural near field portion of the vibratory response, separately. It is shown that as the ratio of the acoustic wavenumber to the flexural wavenumber increases above 0·1, the power radiated by the propagating response increases while that radiated by the non-propagating response decreases by the same amount, so that the net power remains unchanged. When the ratio exceeds approximately 0·5, however, the propagating response power dominates. At the critical frequency, the portion of the total power contributed by the flexural near field is a minimum but begins to increase above the critical frequency. In a qualitative sense, these relative effects increase with increasing structural damping.