A 10MW reference floating offshore wind platform has been specially adapted for the TRL+ as an example of current and future trends in the floating offshore wind sector where multi-megawatt concepts are being developed.
The floating offshore wind turbine studied during the TRL+ project is an in-house upscaling of the DeepCWind platform in order to support a 10 MW wind turbine. The floater is made up of four columns, one central column which supports the wind turbine and three exterior columns that give the stability. All the four columns are joined by means of braces which have a diameter one order of magnitude lower than the four main columns. The DeepCWind platform was upscaled in order to have the necessary stability and good operability. In the upscaling process the evolution of the structural weight was taken into account.
The mooring system, in accordance with DNV-OS-J103 rule, has been recalculated in order to fit with the Bimep conditions. The mooring system is composed of 3 catenaries (link chains) placed every 120 degrees.
Wind turbine DTU 10MW
The wind turbine used is the 10 MW DTU wind turbine which has a tower of 119 meters and a rotor diameter of 178 meters and it is able to generate a thrust of 150 tons.
The TRL+ floating offshore wind concept has been fully tested at laboratory scale. The tests have been carried out in the Cantabrian Coastal and Ocean Basin (CCOB) managed by IHCantabria and part of the TRL+ consortium facilities. The test program has a very ambitious scope including coupled wave, wind and current action over the floating structure to analyse the dynamic response of the platform due to turbulent and constant wind, second order wave forces, etc.
Wind forces have been reproduced by using the IHCantabria’s technology. A multi-fan system able to reproduce the wind turbine control strategy. The hydrodynamic performance of the platform has been addressed assessing motions, loads over mooring lines, nacelle accelerations, etc. The experimental database has been used to calibrate and validate the virtual model of the floating platform including the high complexity of coupled environmental loads.
The numerical model developed to analyse the behaviour of the device consists of different submodels coupled together. These submodels analyse the main components: the floating platform, the mooring system, the wind turbine and their interaction with the environment. In summary, the submodels used are:
Rigid body model:
Newton´s second law is used to obtain the dynamic of the structure as a rigid solid with six degrees of freedom, three translations and three rotations. For this, it is necessary to know the inertia matrix of the platform and calculate all the forces and moments that act on it.
with this model, we obtain the influence of the wind turbine on the platform. We also calculate the turbine rotation, so its energy production can be obtain too.
Hydrostatic and hydrodynamic models:
with the hydrostatic model, we obtain the combination of buoyancy and gravity forces acting on the device due to the stiffness matrix. For the calculation of hydrodynamic forces, linear potential theory is used, characterizing the response of the platform with hydrodynamic coefficients obtained with the boundary element method (BEM)
Mooring system model:
to model the lines used in the mooring system two options are considered. On the one hand, a quasi-static model that ignores the dynamic effects on the lines, based on the catenary equation, significantly faster, on the other hand a more elaborate dynamic model, based on the finite element method (FEM).
Once all the submodels are defined, they are coupled together in a single model. To do this, at each time step, the position and the speed of the platform are used in the others submodels to calculate the forces on it.
R. P. F. Gomes, J. C. C. Henriques, L. M. C. Gato and A. F. O. Falcao, “Design of a floating oscillating water column for wave energy conversion,” Conference European Wave Tidal Energy (EWTEC), Proceeding 9th, Southamptom (UK) , 2011.
A. Meseguer and R. Guanche, “Wind turbine aerodynamics scale-modeling for floating offshore wind platform testing,” Journal of Wind Engineering and Industrial Aerodynamics, 2019.