Validation of underwater radiated noise predictions for a merchant vessel using full-scale measurements

Underwater radiated noise (URN) was previously primarily of interest in connection with the signature of naval vessels. Recently it has become increasingly relevant for other vessel types, such as cruise and merchant ships, due to a growing concern that marine life is affected by rising anthropogenic noise levels in the oceans. Shipping is a main contributor to those noise levels, with the cavitating propeller being the dominant noise source. Marine mammals and fish use sound to communicate and to sense their environment and this requires low background noise levels. The URN of a cavitating propeller can be predicted before the ship is built by means of computations and model-scale tests. High-quality validation material is needed for the validation of computational models and model test procedures, which include the scaling of the noise levels.
Within the CRS framework (Cooperative Research Ships, http://www.crships.org/) a full-scale measurement campaign was carried out on a single-screw cargo vessel by DNV-GL, DAMEN and MARIN. Model tests for several conditions have been carried out in MARIN’s Depressurized Wave Basin. During these tests, URN was measured and cavitation patterns were observed using high-speed video cameras. Within the CRS a semi-empirical model has also been developed, which predicts the broadband pressure fluctuations and URN of cavitating tip vortices on marine propellers.
This paper discusses a validation study of the computational and model test procedures for determining URN due to cavitating propellers, using the full-scale data of the aforementioned ship. Some aspects of the analysis and scaling procedures are discussed. Results are shown for three pitch settings. The agreement between the results of the various methods is very good; mostly within 3 dB. The change in noise levels between the three tested conditions is well captured.