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Ship Wake Detectability in the Ocean Turbulent Environment
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2000
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The turbulent structure of ship wake and ocean upper layer is presented in this study. The authors discuss results of: 1) theory on the turbulent ship-wake and the ocean upper layer turbulence under surface waves effects including wave breaking—an analytical study; 2) based on k-e turbulent closure a couple 3-D non-steady numerical model (wake+upper layer) which includes the wave breaking; 3) experimental investigation (preliminary results) in the Davidson Laboratory towing tank on ship-wake detection by measuring turbulence in-situ. The theoretical analysis of the ship-wake turbulence uses the shear-free model, self-modeling and Kolmogorov's hypothesis for the purpose of closure. The environmental turbulence in the ocean upper layer has been formulated by the assumption of horizontally uniform hydrodynamic field and k-e group model under the existence of surface waves and its breaking. Based on k-e turbulent closure a couple 3-D non-steady numerical model (wake+upper layer) which includes the wave breaking, has been used, in the shear-free approach, to carry out numerically the ship-wake detectability in the ocean turbulent environment. Both of the analytical and numerical results show the 3-D structure of the ship wake for different wind conditions and ship speeds, and the detection range on the ocean surface and the detectability in depth of the ship wake in terms of ship parameters and the wind speed. The experimental study is destined to verify the theoretical and numerical prediction on detectability of turbulent ship wake under different experimental conditions. The wake turbulence significantly exceeds the natural level of fluctuations in the tank and the vibration noise produced by the towing system. The wake turbulent spectrums have well expressed Kolomogov's range. The ship-wake turbulence is well detectable and Kolmogorov's range can be identified even for the most remote location of the probe (~10 L sub s, L sub s is the ship length) as well under the random surface wave condition.