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Unsteady finite-depth effects during resistance tests on a ship model in a towing tank

Day, Alexander H. and Clelland, David and Doctors, Lawrence J. (2009) Unsteady finite-depth effects during resistance tests on a ship model in a towing tank. Journal of Marine Science and Technology, 14 (3). pp. 387-397. ISSN 0948-4280

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Abstract

This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263-273, 2008) on oscillations in wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model to the case of relatively shallow water. We demonstrate here that the unsteady effects are very prominent and that it is essentially impossible to achieve a steady-state resistance curve in a towing tank of typical proportions for a water-depth-tomodel-length ratio of 0.25. This statement is particularly true in the speed region near a depth Froude number of unity. However, on the positive side, we show here that an application of unsteady linearized wave-resistance theory provides an excellent prediction of the measured total resistance, when one accounts for the form factor in the usual manner. Finally, a simple application of the results to the planning and analysis of towing-tank tests is presented.