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Continuous underwater noise from shipping has received increased attention recently. The work presented in this report, focuses on the issues and our ability to predict the underwater radiated noise (URN) from a ship, during the design phase as well as assessing the performance of an existing vessel. Although standards and procedures are improving, it is not straight-forward to provide a fair assessment across different techniques and locations. 

In PUB, we performed measurements of URN for a coastal tanker in (1) a controlled sea trial, (2) cavitation tunnel model scale experiments, and (3) CFD simulations in both model and full-scale. The results were compiled and jointly analyzed to identify, describe, and understand discrepancies between the various techniques. Using CFD, we also analyzed effects of scale and confinement (blockage) in the cavitation tunnel experiments in relation to full-scale conditions. Further, a technique to compute URN in CFD were developed with the ambition to find a reliable and relatively cost-efficient method compared to what is often used in literature today. 

We can see large discrepancies in the outcome from the different methods and in the two scales. A main uncertainty in the comparison is the contribution of URN from the machinery system on the vessel, captured in the sea trial measurements but not considered in the cavitation tunnel experiments or the CFD. It is anticipated that machinery-generated URN is large in relation to propeller induced URN in this case as the cavitation extent is rather limited in the experiments and CFD. In the model tests, part of the discrepancies is related to intermittency in the cavitation dynamics. For the CFD, we are not resolving the flow dynamics in the ship wake and tip vortex cavitation is only captured to a limited extent, leading to under-predicted URN. The scale and blockage effects are noted to be significant, and they cannot be accurately represented by recommended scaling procedures. The new procedure to compute URN from CFD appears to perform well and give similar level of accuracy with a higher robustness than previous method. 

A final useful outcome of the project worth highlighting is the network developed between participating partners. We have through PUB developed a small but active community working with URN from shipping in Sweden with a high international recognition.