Nearfield acoustic radiation from spherical shells

In this study, the acoustic nearfield of excited spherical shells is investigated. The interaction of the acoustic medium with the vibration response of an elastic spherical shell due to an excitation by a point force or an acoustic point source is investigated analytically and experimentally. Thus, only axisymmetric, nontorsional motion of the spherical shell is considered, with a thin shell theory that includes extensional and bending deformation. The elastic spherical shell resonances were computed when in vacuo and when submerged in light (air) and heavy (water) acoustic medium. These were verified experimentally by testing two duralumin shells, a = 8 in. in radius and wall thicknesses h = 0.0514 and 0.1069 in. The measured resonance frequencies were within 5% of those predicted in air and in water for identified mode numbers up to 34. The measured mean-line driving point admittance also agreed well with the predicted ones to within 3 dB. [Work supported by NAVSEA.]