The effect of internal point masses on the radiation of a ribbed cylindrical shell

The radiation associated with complexity is examined by use of finite element–infinite element models of framed fluid loaded shells for frequencies up to ka=10. The vibro-acoustic response of the shell with no internal complexity is compared to an identical structure with point masses attached to the frames. The simple ribbed shell is seen to have pass and stop band structure with radiation physics that is dominated by supersonic components. The addition of point masses to the structure gives rise to major changes in the response that include a coupling of radiating and otherwise nonradiating circumferential orders, resulting in a significant increase in radiation (about 10 dB) over a broad frequency range. These results are in general agreement with nearfield acoustical holography (NAH) experimental results. [Work supported by ONR.]