ASA 124th Meeting New Orleans 1992 October

2pSA9. The effect of incomplete coating coverage on acoustic scattering from cylinders.

Christopher E. Shaw

Jerry H. Ginsberg

School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332

Scattering of a plane wave at beamwise incidence to a cylinder whose flat ends are rigid and whose curved surface is coated with a pressure release material is considered. In comparison to previous studies of complete coating coverage, the present work uses a boundary element formulation to evaluate the effect of removing regions of coating, thereby converting those regions to rigid scatterers. The study explores the dependence of the amplitude of the far-field scattered signal on several factors: the percentage of uncovered area, the ratio of axial to circumferential dimension of the missing patch, the location of the uncoated region, proximity of missing patches, and frequency. In general, the following factors tend to increase the far-field backscatter: (1) large regions of missing coating, (2) impedance discontinuities near the end of a cylinder with rigid endcaps, (3) small regions of missing coating on the shadow side of the cylinder, and (4) higher driving frequencies. [This work was supported in part by ONR.]