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Time-frequency analysis of ship wave patterns in shallow water: modelling and experiments

Pethiyagoda, R, Moroney, TJ, MacFarlane, GJ ORCID: 0000-0002-0518-430X, Binns, JR ORCID: 0000-0001-6892-0063 and McCue, SW 2018 , 'Time-frequency analysis of ship wave patterns in shallow water: modelling and experiments' , Ocean Engineering, vol. 158 , pp. 123-131 , doi: 10.1016/j.oceaneng.2018.01.108.

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A spectrogram of a ship wake is a heat map that visualises the time-dependent frequency spectrum of surface height measurements taken at a single point as the ship travels by. Spectrograms are easy to compute and, if properly interpreted, have the potential to provide crucial information about various properties of the ship in question. Here we use geometrical arguments and analysis of an idealised mathematical model to identify features of spectrograms, concentrating on the effects of a finite-depth channel. Our results depend heavily on whether the flow regime is subcritical or supercritical. To support our theoretical predictions, we compare with data taken from experiments we conducted in a model test basin using a variety of realistic ship hulls. Finally, we note that vessels with a high aspect ratio appear to produce spectrogram data that contains periodic patterns. We can reproduce this behaviour in our mathematical model by using a so-called two-point wavemaker. These results highlight the role of wave interference effects in spectrograms of ship wakes.

Item Type: Article
Authors/Creators:Pethiyagoda, R and Moroney, TJ and MacFarlane, GJ and Binns, JR and McCue, SW
Keywords: ship wakes, spectrograms, shallow water, mathematical model, interference effects
Journal or Publication Title: Ocean Engineering
Publisher: Pergamon-Elsevier Science Ltd
ISSN: 0029-8018
DOI / ID Number: 10.1016/j.oceaneng.2018.01.108
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Copyright 2018 Elsevier Ltd. All rights reserved.

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