Coupled Simulations of Wind Turbines and Offshore Support Structures : Strategies based on the Dynamic Substructuring Paradigm

Abstract

Large scale offshore wind power has been recognized as a key technology to increase the share of renewable energy. However, as this energy source is currently still relatively expensive, efforts are made to significantly reduce its costs. Cost reductions are to be achieved, for instance, by installing larger turbines in larger offshore wind farms in order to benefit from economies of scale. Many of these large wind farms have to be built further offshore in deeper waters, where the waves are also higher. As a result traditional monopile foundations are not always feasible and multi-membered foundations, such as jackets and tripods, are required. The design of these foundations is generally done by a specialized company, which needs to take the loading from the wind turbine into account. In order to quantify this loading over the design lifetime, typically thousands of aero-elastic simulations are required. These aero-elastic models account for all the physical phenomena that are relevant for an offshore wind turbine, such as the structural-, aero-, hydro-, and controller dynamics. However, as models of multi-membered foundations are significantly larger than their monopile counterparts, more compact models are required to limit the computational costs of these simulations. Hence, advanced methods are required to enable the use of reduced models in wind turbine simulations. In addition, these techniques should also be used in an efficient and accurate design process involving multiple parties. In this thesis several computational approaches are proposed to fulfill these needs. It is shown that one is able to obtain accurate results, while speeding up calculations and that these methods fit perfectly into a multi-party design process.