Study for computation/measurement of underwater ship radiated noise toward marine environmental protection in Japan

Abstract

USRN has been a large interest among maritime industries in terms of mariners’ comfort as well as environmental protection. This paper presents the characteristics of the measured USRN in full scale as well as the near field propeller cavitation noise estimated by viscous computational fluid dynamics (CFD) simulation. The USRN measurement was carried out according to the ISO standard protocol in deep water. The results show that the characteristics of USRN spectrum, differences of SPL in tonal noise depending on broadside and engine load are successfully captured for which the level of background noise is low enough to distinguish target noise and background noise. For the CFD simulation, two methodologies have been tested to predict frequencies and sound pressure level (SPL) of near field propeller cavitation noise, i.e., 1) direct estimation and 2) indirect estimation. The results are encouraging in that the present CFD simulation is capable of capturing sheet cavitation and resultant tonal noise. The estimation of broadband noise is still challenging by the present CFD simulation yet its application in conjunction with the semi-empirical formula is likely to be effective for predicting the upper bound level of broadband noise.