ABSTRACT:

This paper describes Tension-Leg-Buoy (TLB) wind turbine floaters, in comparison with the OC3-HYWIND Spar-Buoy (SB). Wave tank experiments with TLB and SB conducted in a student project at the NTNU/MARINTEK MCLab are supplemented with computations with the models 3Dfloat and ANSYS. Although the small model scale of 1:100 and the scope of the test make quantitative comparisons between experiment and models difficult, the experiment and models agree reasonably well qualitatively. The main differences between TLB and SB in both experiments and computations are the smaller motions and the higher anchor loads of the TLB.

INTRODUCTION

The wind turbine technology has developed tremendously over the last three decades. The rated power for a large wind turbine has increased with a factor of 100, from 50 kW in the eighties to more than 5 MW in 2011. With a hub height of around 100 m, and a rotor diameter of more than 120m, a wind turbine is among the larger of mass-produced structures. Recent years, wind energy has been among the fastest growing energy technologies. With ambitious targets for renewable energy, the vast wind energy resource and available areas offshore are getting increased attention by energy planners and the wind energy community. This development was suggested first by Professor Bill Heronemus of Massachusetts Insititute of Technology (MIT) (Heronemus, 1972). After commercial wind turbines reached a size suitable for offshore applications around 2000, development of conceptual designs and computational tools started accelerating. Examples of floating wind turbine designs for areas with water depths in excess of 50m include 1) ballast stabilized Spar-Buoy (SB) floater with catenary mooring lines, 2) mooring line stabilized Tension Leg Platform (TLP), 3) buoyancy stabilized barge with catenary mooring lines, 4) semi-submersible platforms with one to four vertical columns, and finally the MIT double taut leg.

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