Admittance-matched structures for the reduction of noise in tank making operations

Abstract

The mean-value method of predicting the dynamic response of a structure is applied to reduction of broadband noise radiated from thin, circular cylindrical shells during current tank manufacturing operations. The approach taken is twofold: first, to investigate the effectiveness of roller supports acting simultaneously as vibration absorbers, and second to assess the viability of composite beam absorbers attached directly to the cylindrical shell. Theoretical and experimental driving-point admittance curves for cylinder, roller and composite beam are presented. The results indicate that the mean-value theory is an acceptable predictor when cylindrical shells are considered, but requires minor modification for the prediction of the average admittance in the case of a transversely vibrating beam composite or sandwich. The average point input admittance of the shell is matched to that of the absorber, essentially by altering the thickness and therefore stiffness of the absorber. Sound level measurements reveal a rediction of 4·0 dB(A) in the 1 s A-weighted, L eq for the roller absorbers, while the use of composite beams is shown to produce a 3 dB(A) reduction for a doubling in the number of beams. In the latter instance, overall reductions up to 12 dB(A) have been obtained with the use of six beam absorbers.