Studies on the Initial Stability of an Air-Cushion Supported Floating Platform for Offshore Wind Turbine

Hao, Hongbin (Harbin Engineering University) | Guo, Zhiqun (Harbin Engineering University) | Liao, Kangping (Harbin Engineering University) | Xu, Guochun (Ningbo University)

OnePetro 

ABSTRACT

The next large scale exploitation of wind energy will gradually move to the seas with the depth of 30-100m, in which only the semi- submersible and barge type foundation are suitable. Compared with the semi-submersible foundation, the barge type has simpler structure and is more adaptable to water depth, however, suffers larger seakeeping motions in waves. In order to improve the seakeeping performance of the barge foundation for offshore wind turbines, the present work proposes a concept of Air-cushion Supported Floating Platform (ASFP), and integrates the air cushion into barge foundations, which can buffer the wave loads acting on the foundation and reduce the motions. The air cushion makes the new floating foundation very different, and this paper presents a method to estimate the initial stability of the air- cushioned floating offshore wind turbine foundation

NOMENCLATURE

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INTRODUCTION

The next generation of wind energy exploitation in China will move to the seas with the depth of 30-100m. Generally, the fixed offshore wind turbine is used in shallow water, and the cost increases very quickly with the increase of water depth. It is considered that the fixed one is not suitable for the water of depth more than 30m (Zhou, 2013), in which the floating one should be considered. Besides, the floating one could be built and assembled in shipyard, which is very useful to reduce the cost. So the floating offshore wind turbine should be used when the water depth is within 30-100m.

Some types of platforms have been employed for floating offshore wind turbines (Ewea, et al, 2013), which can mainly be classified into four types (Wang, et al, 2010): Spar-buoy type, Tension-leg platform (TLP) type, Semi-submersible type and Pontoon type (Barge type). The Spar-buoy type needs a long body to lower the center of gravity and the required water depth should be more than 100m. The TLP type needs a certain water depth to adapt the tidal range and the required water depth should be more than 70m. So only the Semi-submersible and Barge type platforms are suitable for the seas with depth of 30-100m. Compared with the Semi-submersible platforms, the Barge type is more adaptable to water depth, and the simpler structure makes it possible to be built by concrete, which can reduce the cost and overcome the seawater corrosion effectively. But it suffers larger seakeeping motions in waves. So if the motion response of Barge type platforms in waves can be reduced, it will be very desirable to be used in the seas with depth of 30-100m.