Numerical prediction of hydrodynamic coefficients for a semi-sub platform by using large eddy simulation with volume of fluid method and Richardson extrapolation

Abstract

Hydrodynamic coefficients for predicting hydrodynamic loading is significant for the design of offshore wind turbine floaters. In this paper, hydrodynamic coefficients for a semi-submersible floating offshore wind turbine are investigated experimentally and numerically. In the water tank test, added mass and drag coefficients of the semi-submersible model are identified by the forced oscillation tests. In numerical simulation, large eddy simulation (LES) with volume of fluid method (VOF) is adopted to predict added mass and drag coefficients. Firstly, numerical errors in the predicted hydrodynamic coefficients are systematically studied, and Richardson extrapolation is employed to obtain the grid independent solution. The predicted added mass and drag coefficients varying with KC number are then validated by the water tank tests and the mechanism of the hydrodynamic force are clarified by vortex shedding patterns. The hydrodynamic coefficients for each element are also investigated. Finally, effect of free surface on the hydrodynamic forces is discussed and the predicted added mass and drag coefficients are compared with those obtained from the water tank tests.