When water depth and soil conditions make it difficult to install fixed foundations for wind turbines, floating foundations may be preferred.
As a floating foundation brings new challenges to the turbine, Marin has published a paper that describes those challenges addressed by accurate numerical simulations that include the effects of the motions of the floater on the turbine’s loads and vice-versa.
Several codes have recently been developed for that purpose. To improve their accuracy, these codes need to be calibrated. This can be done in wave basins at reduced scale. Ideally, a physical model of the floater on which a turbine is mounted is used. Only then, the interaction between the hydrodynamic response of the floater and the aerodynamic loads can realistically be investigated.
Scaling Down and Rotors
The model tests of a floating structure in a wave tank aim at accurately assessing the motions of the floater. For the kind of floating foundations envisaged here, the best practise is to scale down the floater according to Froude scaling laws.
Unfortunately, this scaling does not work for the rotor. It has been observed that the aerodynamic loads of the scaled down rotor are much smaller than the equivalent loads at full scale. It was necessary to study the air flow around the rotor to understand what happens with the scaled down rotor.
In the basin, the flow separates closer to the leading edge of the blade than in real conditions. Consequently, the rotor’s thrust and torque drop and the turbine performs badly. Another scaling approach is required for the rotor to scale its performance rather than its geometry.
