ABSTRACT:

Based on the 5MW offshore wind turbine model developed by National Renewable Energy Laboratory (NREL), two new conceptual offshore wind turbine floating platforms with combined Tension legs- Mooring lines system were proposed in this paper. Taking the coupled dynamic responses of the top wind turbine, tower support structure and lower mooring system into consideration, the time domain hydrodynamic analysis coupled with wind loads has been done for the two offshore floating platforms: the single offshore wind turbine (SOWT) platform and the multiple offshore wind turbines (Multi-OWT) platform. According to the sea statistical historical data for China East Sea and the typical design cases in IEC61400-3 code, the motion performances of the two OWT floating platforms have been studied by numerical simulation technique, respectively. Furthermore, during the irregular wave analysis, the effects of the current force and the slow drift force on the motion responses of the two OWT platforms were also clarified. As a result, the performance of the new combined Tension legs-Mooring lines system on controlling the motion responses of the OWT floating platforms has been verified in both views of theoretical analysis and numerical simulations. In a word, the two new conceptual OWT floating platforms would play an active and instructive role in the future design of OWT floating platforms.

INTRODUCTION

At present, as the continued increase of energy demand of the whole world, more and more nonrenewable fossil fuels are consumed. Considering the supply limitation and the price volatility of conventional fossil fuels, many countries are paying more and more attentions to the exploitation of the offshore wind energy resource. Comparing with the onshore wind resource, the offshore wind resource has the advantages of high wind speed, low turbulence intensity, land saving, no noise annoyances and near the coastal developed areas.

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