Index of content:
Volume 103, Issue 5, May 1998
- STRUCTURAL ACOUSTICS AND VIBRATION 
103(1998); http://dx.doi.org/10.1121/1.422764View Description Hide Description
A set of in-air experiments were made on two, thin, cylindrical shells to understand and control the propagation of membrane waves, which are primary determinants of target strength in the mid-frequency, high-aspect angle regimes. A circumferential source array was used to drive single modes in all wave types, compressional, shear, and flexural. Resulting waves were collected using an axial line array of laser Doppler velocimeter measurements and the wave types separated by array processing. Comparison between a clean plastic shell and a steel shell with a keel-like feature suggest on the order of 10-dB reduction of compressional wave response via coupling into higher order flexural waves by the nonaxisymmetric discontinuity. The conversion coupled with subsequent damping of the resulting flexural waves makes this a potentially useful mechanism for control of membrane waves.
103(1998); http://dx.doi.org/10.1121/1.422765View Description Hide Description
Sound radiation by a simply supported unbaffled plate is presented using a double layer integral representation of the acoustic pressure. Both the pressure jump and the plate displacement are developed in series of the simply supported plate modes. This leads to modal coupling coefficients, which are numerically calculated for this specific unbaffled problem. The unbaffled problem is then transformed in the presentation of the baffled one which allows us to define original modal radiation impedance coefficients to the unbaffled plate. Baffled and unbaffled radiation impedances are then compared versus nondimensional frequency, in real and imaginary parts for a set of representative modes. An approximate expression for the direct unbaffled radiation impedance is presented, which is useful for light fluid loading. Finally, the influence of the baffle on sound radiation both in light and in heavy fluid, on the acoustic radiated power, the plate velocity, and the radiation factor is investigated.