Estimation of broadband power radiated from ribbed plates under turbulent boundary layer excitation

Abstract

‘‘Exact’’ calculation of the acoustic power radiated due to the vibration of ribbed underwater panels driven by a turbulent boundary layer (TBL) requires consideration of the interactions among ribs and end supports. This paper shows that the power radiated in broad frequency bands may be directly estimated by considering the discontinuities to act independently. Analysis of a string loaded with identical masses or springs, and subjected to a wave-number-white forcing spectral density, is first used to demonstrate that the mean-squared attachment force within a broad frequency band may be estimated by ignoring coupling among attachments. A water-loaded membrane having parallel line mass attachments is then used to show that each attachment can be considered to radiate independently of the others when the acoustic wavelength is less than the spacing between them. These simple models are generalized and combined to develop an estimate of the vibration-related power radiated by finite ribbed steel plate sections in water driven by TBL-like surface pressures. The approximation is compared to results based on an exact formulation for a doubly periodic plate that represents ribs and end supports, and found to agree within 3 dB. [Work supported by ONR.]