This paper deals with prediction of cavitation noise of full scale ship's propeller from model experiment and its comparison with full scale measurements performed on two ships, a cargo liner and a training ship. It is proposed to estimate separately the tonal noise and the broadband noise because of their different mechanisms of noise generation. The acoustic-mechanical reciprocity principle is applied for estimating the tonal noise, and for the broadband noise a semi-empirical formula is applied for estimation in low frequencies. Full scale measurements on actual ship were arranged to acquire far-field noise and to eliminate extraneous noise reflected from sea surface. The comparison between predictions and full scale measurements has shown agreement amply proving that the proposed method of cavitation noise prediction is valid for practical purposes.
As the first step to estimate the underwater noise radiation from ships, experimental study on the underwater acoustic radiation efficiency of a ribbed rectangular panel is studied. It is clearly shown through the study that the radiation efficiency depends primarily on the point of excitation, and the radiation efficiency based on the input power has a similar trend to the general radiation efficiency.
In the design of a low frequency source array and evaluation of its radiation power, it is necessary to consider the mutual interaction effect between many source elements. The radiation power of a source is a function of the radiation impedance which is considerably affected by neighboring sources in low frequency ranges. The expression for the radiation impedance of each element in cylindrical line array with m elements is derived. The radiation impedance and radiation power are calculated for various array spacing, source radius and source length. The results indicate that the radiation power is significantly influenced by the mutual radiation impedance and the effects are increased as the neighboring sources vibrate inversely.