Reduce the Cost of Energy of offshore wind by using advanced control strategies for active loads reduction, and using an advanced integrated design approach for (automated) design optimization.
An offshore wind turbine often has a suboptimal design due to the fact that the turbine and the support structure are designed in separate design loops. Based on requirements from the wind turbine manufacturer, support structures are designed with fixed constraints regarding allowable loads, stiffness and eigenfrequencies. By integrating the design of the support structure in the overall optimization loop, a more cost-effective combined wind turbine and support structure design can be achieved.
The integrated wind turbine design tool FOCUS6 has been extended to enable an automated integral design approach, where the offshore tower and support structure design is in the same design loop as the turbine design. At each step of this integral design optimization, the parameters describing the geometry of the support structure are updated. The wind turbine controller is then fine-tuned for the current turbine parameters to ensure optimal performance with respect to the fatigue loading on the tower. The resulting configuration is checked against ultimate load constraints (maximum allowable stress and buckling under combined bending and axial loading) and fatigue damage constraints.
For the optimization, a representative (offshore) load set has been defined for North Sea conditions. The computational effort required for the optimization should be limited. This has been achieved by selecting a reduced, representative set of load cases, which includes the design-driving ultimate loads on the support structure and gives a close approximation of turbine fatigue life.
The new functionality of FOCUS6 is used to explore the potential of the integral design approach for reduction of the total cost of the XD115 offshore wind turbine.
Integral optimization is performed successfully for an offshore monopile supporting the XEMC Darwind XD115 5 MW wind turbine. To achieve this, the wind turbine design tool FOCUS6 has been extended to include features for automated integral design of the tower and support structure.
T.J.J. van der Zee, M. J. de Ruiter, R.R.H. Brood "Cost reductions using an integral design approach - Optimizing an offshore wind turbine in FOCUS6", Report WMC-2015-044
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