Predicting underwater-radiated noise, new paper
Pollution in the ocean is also about the ambient noise closely related to maritime shipping and seismic exploration by the oil/gas industry. 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 are contributing with more research in this area. In August, a new paper will be published in the well-known journal Ocean Engineering.
In the paper, the authors present a characterization of the measured noise signal from a chemical tanker with propeller in non-cavitation and cavitating conditions respectively. This is followed by a validation study of the underwater-radiated noise predicted by model testing technique and by a hybrid computational fluid dynamics (CFD) method (DDES-URANS in combination with the Ffowcs-Williams Hawkings acoustic analogy). The capabilities and limitations of the methods are also discussed.
About the paper
The paper; “Predicting underwater radiated noise of a full scale ship with model testing and numerical methods”, published in Ocean Engineering, Volume 161, 1 August 2018, Pages 121–135. Co-authored by Da-Qing Li, Jan Hallander and Torbjörn Johansson.
The work was carried out within project AQUO (Achieve Quieter Oceans by shipping noise footprint reduction), funded by the European Commission. Project Reference: 314227 under FP7-SST-2012-RTD-1.
Full-scale measurement, model testing and a hybrid CFD method were used to characterize the Underwater Radiated Noise (URN) of a ship at design speed. The CFD method consists of a multiphase Delayed Detached Eddy Simulation and the Ffowcs-Williams Hawkings acoustic analogy. The paper discusses the correlation of the noise spectra with the observed cavitation behavior and compares the measured full-scale data with those predicted by the model testing and the CFD method. The comparison shows that the sheet cavity and Tip Vortex Cavitation (TVC) predicted by the model testing are in reasonably good agreement with the full-scale observations. The pressure pulses are somewhat higher than the full-scale data. Overall, the predicted URN has a good correlation with the noise spectra obtained from the sea trial.
The CFD method shows the potential to resolve turbulence eddy structures in the wake. It captures the dynamic development of sheet cavitation and the collapse and rebound of TVC as observed in the model test and the sea trial, but under-predicts the extent of TVC. The pressure pulses and tonal noise are in close agreement with the respective measured data for the first five orders of blade passing frequency. The method underestimates the broadband noise level in the frequency range 50–112 Hz where the TVC is expected to have an important contribution. The maximum under-prediction in this range is about 28 dB at 72 Hz. At frequencies above 200 Hz, the broadband noise becomes more and more under-predicted with increasing frequency.
The article can be previewed and is available online www.sciencedirect.com