Fischer, T: Mitigation of Aerodynamic and Hydrodynamic Induc

enhancing the effect of aerodynamic damping and thus achieve reductions in support structure fore-aft excitation. If in contrast, the misalignment of wind and wave direction imposes design-driving loads in the sideways direction, individual pitch control or an active generator torque controller are more powerful means. In addition or as alterative to the above-mentioned control concepts of the rotornacelle-assembly, structural damper devices (either passive or semi-active) are promising solutions. Such concepts have the benefits of mitigating both directions of the support structure movements with the same efficiency and of being largely independent from the availability of the electro-mechanical system of the turbine.The state-of-the-art is an integrated design approach where rotor-nacelle-assembly and structure are considered as one entire unit and where aero-elastic and hydrodynamic load effects are analysed simultaneously. In the current research this approach is even further extended by implementing the selection of suitable load mitigation concepts and the tailoring of turbine control and design in the design iteration process. The design objective is to improve the overall cost-performance of the entire offshore wind farm. Therefore a final demonstration of the developed design methodology is performed. The study considers a standard 5 MW turbine on a monopile support structure in 25 m (MSL) water depth at exposed North Sea conditions. Such a design configuration is currently considered to be beyond the current design depth limit. A reference design of the support structure is made following a standard integrated design approach. Subsequently, the combination of four different load mitigation concepts, which did not require expensive new control hardware, leads to a significant reduction in the design driving fatigue loads at mudline of 13 %. A structural re-design for the design load envelope show considerable material savings of 9 % in the support structure and additional energy yield due to the extended cut-out. Undesired collateral effects, such as increased loads and wear of other machinery components, are rather low since overall system loads and characteristics remain within acceptable ranges. In general, the research points out that the integrated design process, extended by using offshore-specific controls to face the design-driving load events, is able to provide technically robust and cost-effective design solutions.For the future it is foreseen that turbines are getting even larger and sites with higher water depth are to be exploited. This will imply the need for new design concepts as well as further development of specific load mitigation concepts in order to achieve cost effective designs.