WindSea A/S has developed a concept for large wind turbines offshore. The structure is a moored, free floating platform and can thus be positioned at very large depths.

Full scale project

The WindSea is a triangular wind turbine platform with a turret mooring system allowing the entire platform to yaw into a position where the wind turbines are facing the oncoming wind. The three turbine nacelles are therefore fixed and have no yaw actuators.

The WindSea platform will have a total installed output of around 10 MW per platform. A wind farm consisting of e.g. 30 platforms (90 turbines) will be capable of producing more than 1200 GWh of energy a year, enough electricity for more than 60,000 households.

We were contracted to carry out model tests of the WindSea concept. The concept was tested both in wind tunnel and in the towing tank. Preliminary CFD calculations were also carried out in co-operation with National Laboratory for Sustainable Energy – RISØ DTU.

Wind tunnel tests

The wind tunnel tests were carried out with the purpose of documenting the efficiency of the aft wind turbine, which is partly in the shadow of the two front wind turbines. Furthermore, the global loads and moments where measured and documented in order to evaluate mooring forces and turning moments.

Towing tank tests

The towing tank model test should document and investigate the stability of the platform, both with and without rotating wind turbine wings. The towing tank tests should also test the general functionality of the platform movements, such as the capability to rotate the platform in changing wind directions.

In order to perform the tests in the towing tank, a unique wind generation system was developed. The new wind rack can accurately model the wind field including the wind profile in a sectional area of approximately 4 x 6m. The system is comprised of a large high-pressure compressor and a rack of tubes fitted with high speed nozzles.

The rack efficiently transforms the towing tank into a very large wind tunnel. The system showed very good results and will now be tuned and finalised for use in future projects. For both the wind tunnel tests and towing tank tests, a large effort was put into constructing ultra-light wind turbine wings to ensure the correct stabilization contribution from the rotating wings. The wind turbine wings were made as a composite of glass fibre and foam to ensure the ultra-low weight.

Three wind turbines are placed on a single structure, giving an expected total capacity of 10 MW for one platform. 
WindSea model exposed to wind and waves in our towing tank