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Resistance of a ship undergoing oscillatory motion

Doctors, Lawrence J. and Day, Alexander H and Clelland, David (2010) Resistance of a ship undergoing oscillatory motion. Journal of Ship Research, 54 (2). pp. 120-132. ISSN 0022-4502

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Abstract

In this paper, we describe extensions to the research of Doctors, Day and Clelland (2008) and Day, Clelland and Doctors (2008), in which the oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model were measured and predicted, in the cases of relatively deep and relatively shallow water. In the current study, the ship model was towed with a harmonic velocity component superimposed on the usual constant forward velocity. This work constitutes a ¯rst step in the understanding of the unsteady hydrodynamics of a racing shell (rowing boat). We show here that the unsteady wave resistance varies considerably from the traditional (steady) average value. Indeed, the wave resistance is frequently negative during part of the oscillatory cycle. However, the general effect is an increase in the temporal mean value of the wave resistance; this suggests that every effort should be made to reduce the unsteadiness of the motion. We also demonstrate that the unsteady wave-resistance theory provides an excellent prediction of the measured effects summarized here. These predictions are often within a few percent of the measured values of the resistance.