Abstract

Wave loads on a small scale vertical cylinder can be calculated by the Morison's equation and much work has been done on variations of the drag coefficient and the inertia force coefficient with KC number and Reynolds number. Recent concerns on wave loads on a cylinder include the hydrodynamic forces induced by waves of large amplitude or breaking waves. The present work focuses on the study of the hydrodynamic forces induced by nonlinear regular waves on a free surface piercing cylinder. A numerical wave tank is established to compute the wave forces acting the cylinder for the cases of different KC number. Analyzing spectra of transverse force coefficient, it turns out that the frequency spectra of the transverse force coefficient changes from one single peak pattern to the multi-peak pattern as the KC number increases. In order to understand the mechanism of generation of the transverse force coefficient, the flow field around the cylinder is simulated carefully and analyzed. The asymmetric flow patterns of flow separation and vortex shedding from the cylinder generate the transverse force.

Introduction

In recent years, numerous fixed offshore wind farms have been built to meet the demand for clean energy. The first large-scale offshore wind farm in the world named Homs Res was built in Denmark in 2002. In 2005, the first Chinese large-scale offshore wind farm was constructed in the East China Sea coast nearby Shanghai city. By now, most offshore wind farms have been built in the shallow water region, in which the foundation is commonly single cylinder or cylinders deep- going into the sea bed. Because of that, a good investigation of the hydrodynamic characteristics induced by waves on a vertical cylinder is important for the structure designing of offshore wind turbine.

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