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Ship Wakes Generated in a Diffuse Internal Layer

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Technical Report

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London Research and Development Corporation Ottawa, ON

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This report describes the background, theory and simulation of the internal wave wake from ships. Realistic models of both internal layers and hulls are employed. The internal layer models are based on published vertical profiles of the Brunt-Vaeisaelae frequency. Two basic profiles are employed. The first is a profile appropriate to the Strait of Gibraltar and is modeled using a Lorentzian distribution the parameters are the peak Brunt-Vaeisaelae frequency, its depth and the width of the distribution. If required, these can be altered to apply to other situations. The second profile is appropriate to that existing during the Loch Linnhe trials in Scotland. The hull models represent warship and merchant ship hulls. The warship hull model is a modified Taylor model and the block coefficient can be adjusted continuously within suitable limits the parent model was based on a twin screwed cruiser. The merchant ship model was developed by the David Taylor Model Basin and applies to single screwed ships. There are 5 separate models covering a range of block coefficients. The Wigley model, which resembles a canoe, a single source model and a simple source and sink model doublet are available in part for diagnostics. The simulations successfully reproduce some observations of wakes during the Loch Linnhe trials, in which wakes with significant structure were generated. Wakes generated on the Gibraltar layer appear to be on the edge of detectability by airborne or space-borne high resolution radar and consist mainly of a V-shape with little structure in between the arms.

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