Title: Mitigation of Aerodynamic and Hydrodynamic ...
Publisher: Shaker Verlag Dez 2012
Publication Date: 2012
Book Condition: Neu
Dust Jacket Condition: Dust Jacket Included
Neuware - Offshore wind energy is one of the movers in the transition of Europe's energy system. However, the further reduction of cost of offshore wind energy is the key to its future success. A significant potential for such improvements is given by the currently rather high costs associated with the design, manufacturing, installation and maintenance of the support structure. The present research proposes and demonstrates a methodology to lower the support structure investment cost by mitigation of aerodynamic and hydrodynamic induced fatigue loads through an integrated design approach as well as site and design specific wind turbine control concepts. In order to facilitate such an approach the requirements of load mitigation on three levels in the design process are analysed in detail and the most promising concepts are identified. Firstly load mitigation aspects can be included already on the design level by selecting a specific concept for the entire offshore wind turbine or the site specific design in the wind farm layout to enhance important damping effects or to reduce certain external excitations. On a next level the turbine's capabilities with respect to its operational control like by using a rotational speed window or a soft cut-out are addressed. The largest potential is found on the dynamic control level, where different advanced control concepts can be included and to damp the loads actively. The comparison of monopile and jacket designs for a typical 5MW turbine at three reference sites ranging from 10 to 50 m (MSL) water depth points out that such application of control concepts is much dependent on the selected support structure concept, offshore site, turbine type and finally the considered load effect and operational conditions. If hydrodynamic excitation of the support structure in fore-aft direction is dominant, concepts like collective pitch control with tower-feedback, active idling control or an (active) soft cut-out are promising. They all focus on 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 suppor. Bookseller Inventory # 9783844015010
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