Abstract
This paper describes the validation of a novel floating wind turbine simulation tool based on an existing finite element offshore structural analysis solver that recently has been extended to simulate offshore wind turbines. Given the growing importance of offshore wind in the decarbonization strategy of many countries, and particularly the predicted exponential future growth in floating offshore wind, the requirement for validated numerical modelling tools to support detailed engineering design is now greater than ever. The tool combines a unique structural analysis solver incorporating a 3D hybrid beam-column element featuring fully-coupled axial, torsional and bending deformation modes, with the open-source aerodynamic modelling software FAST, to enable it to perform fully coupled aero-hydro-structural simulation of offshore wind turbines. The validation process focuses on a floating semi-submersible platform hosting a 5MW turbine, which is the reference model used in the international research project Offshore Code Comparison Collaboration Continuation (OC4). This is a code-to-code verification project sponsored by the International Energy Agency (IEA) which benchmarks a range of simulation codes for offshore wind turbine modelling. Beginning with fundamental test cases, such as static equilibrium, eigen-analysis, and free-decay simulations, the scenarios advance in complexity to include current loading, regular and random wave excitation, in conjunction with both steady and turbulent wind inflow. The new tool generates results which exhibit a close correlation with the OC4 benchmark data, thereby validating the numerical modelling approach. Although primarily focused on the semi-submersible, the validation programme also considers the same 5MW turbine hosted by a jacket substructure in shallower water, illustrating the versatility of the modelling tool to simulate fixed support structures in addition to floating. Given the scope of the validation effort, this paper presents a representative sample of results only. A more comprehensive report covering the other load cases can be provided to interested readers by the authors. This paper complements the research work undertaken in OC4, further substantiating its insights into the dynamic responses of floating offshore wind turbines. The new tool offers advantages for non-linear structural simulation via its innovative finite element solution technique, and detailed hydrodynamic modelling via its established and proven numerical models. The combination underlines the benefits of exploiting synergies between offshore oil and gas and offshore wind.
Towards the Fully-coupled Numerical Modelling of Floating Wind Turbines
