Abstract
This work analyses the accuracy of large-scale experimental testing procedure in ocean basin facility involving real-time hybrid model testing (ReaTHM) techniques. The analysis is based on a scaled concept for a 15MW floating offshore wind turbine (FOWT) supported by a concrete semi-submersible platform (ActiveFloat) developed within the framework of the project COREWIND. The real-time hybrid model considered includes a multi-fan system located at the aero-rotor interface, which permits to generate the aerodynamic loads, reducing the limitations typically given by scaled problems. In order to assess the uncertainties in the hardware in the loop (HIL) implementation, firstly we define the quantities of interest to be evaluated from all the possible sources liable to inaccuracy identified. Then, we quantify the systematic and random discrepancies of the selected mooring, platform and HIL parameters. Finally, we propagate the previously quantified errors, running simulations in OpenFAST under extremal and severe environmental load cases in Gran Canaria Island (Spain) site. Comparing the platform response and mooring tensions of these uncertainty propagations with the ones of the unperturbed simulation as a baseline case, we analyse the effect of each representative parameter. Thus, the reliability of the results in ocean basin testing is numerically assessed, depending on the design load case.
Highlights
The design of floating offshore wind turbines (FOWTs) to be installed in deep waters, where the greatest potential of wind resource is found, is currently one the most challenging process in offshore engineering
We focus our efforts on studying the effect of the tolerances when manufacturing the scale model and the impact of the multi-fan system limitations on the FOWT response
Wind loads seem to be dominant in platform response uncertainty as the only load case without wind presents lower mean discrepancies, above all in surge displacements
Summary
The design of floating offshore wind turbines (FOWTs) to be installed in deep waters, where the greatest potential of wind resource is found, is currently one the most challenging process in offshore engineering. The high complexity of the design process lies in the fact that it is strongly dependent on interconnected, highly non-linear dynamics, such as the hydrodynamic actions on the floater and the aerodynamic response of the turbine. As we have just said, FOWTs are complex systems due to a strong coupling between forces coming from several physical phenomena. Their aero-hydro-servo-elastic dynamical behaviour is influenced by structure flexibility, control system and aerodynamics. The problem of scale modelling is that Froude scaling laws adopted in ocean basin testing to reproduce gravity-influenced phenomena, results in too low Reynolds numbers, and in a deviated reproduction of viscous forces.
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