Cavitation tunnel at SSPA

Model-scale underwater radiated noise measurements, new paper

SSPA has been involved in numerous acoustic-related projects and continually developing various predictive tools, making them available to assist customers in solving problems related to underwater-radiated noise (URN). SSPAs experts is contributing with more research in this area. In November, the well-known journal Ocean Engineering has published a new paper.

URN from vessels is of growing environmental concern due to the potentially adverse effects on marine fauna. The increased concern has also led to a renewed interest in prediction of propeller URN from model scale measurements. Even if procedures are standardised, there are many uncertainties and some phenomena that remain to be understood.

The paper investigates the repeatability of cavitation tunnel measurements. This was done by repeating the model-scale measurements performed in the project AQUO (Achieve QUieter Oceans by shipping noise footprint reduction) 2013. New measurements were performed in 2019 with new instrumentation. The paper also studies the sensitivity to hydrodynamically based uncertainties by loading condition variations. Further on the paper compares URN predictions using measured transfer function to spherical propagation model. The URN predictions based on model-scale measurements are compared to the sea-trial measurements for the chemical tanker M/T Olympus performed in the AQUO project.

About the paper

The paper: “Model-scale underwater radiated noise measurements: A study of repeatability, sensitivity to loading condition variations and correlation to full scale data”, published in Ocean Engineering, Volume 216, 15 November 2020.

Author: Jan Hallander, SSPA Sweden

Abstract

In the European project AQUO, underwater radiated noise from the chemical tanker M/T Olympus was thoroughly investigated by measurements in full-scale as well as in model-scale. To investigate the repeatability of measurement and the sensitivity to loading condition variations, a new set of model-scale measurement was performed in 2019. The 2019 measurements have slightly lower cavitation volume than the 2013 measurements, but the difference is within normal variability considering water quality, propeller painting, pitch setting accuracy and set-up of the model. At the design speed, tip vortex cavitation dominates the noise with a hump around 70 Hz in full-scale. The tip vortex is under-predicted by the model-scale tests and the agreement with seatrial data between 30 Hz and 100 Hz is not satisfactory. At the reduced velocity conditions, leading-edge vortex cavitation dominates the noise with a hump around 150 Hz in full-scale. This type of cavitation and noise seems to be better predicted by the model-scale tests, thus the agreement with the sea-trial data is good. The improved hydrophone positions gave better signal to noise ratio while the application of transfer function measurements gave better estimates in the frequency range around 100 Hz.

The article is available online at www.sciencedirect.com