Unsteady Wave-Making Resistance of an Accelerating Ship

Abstract

To measure the resistance of a ship in a towing tank, the target speed of the ship model is achieved by towing the model from the rest at a given acceleration imposed by the carriage. The fluctuations in resistance are generated because of the impulse effects during rapid acceleration. Such acceleration effects in deep water have been studied by previous works [1–3]. In shallow water, the unsteady effects are expected to be stronger, making the fluctuating resistance persisting longer. In order to predict the unsteady waves and to estimate the unsteady oscillating components in the wave resistance, a numerical method based on 3D unsteady potential-flow theory was developed. An implicit finite-difference algorithm coupled with an iterative boundary integral-equation solution procedure was used to deal with the unsteady linear and nonlinear free-surface condition. The results showed that both the acceleration intensity and water depth have a significant effect on the oscillation amplitude of the unsteady wave resistance as well as other force components. Findings of these computations and comparative evaluation of experimental observation are made where relevant. The findings in the present work can be applied to provide guidance for using the appropriate settings, e.g., magnitude and duration of carriage acceleration, when conducting ship-model resistance tests.