Comparison of Simulation and Tank Test Results of a Semi-Submersible Floating Wind Turbine Under Wind and Wave Loads

Abstract

A model of the Dutch Tri-floater semi-submersible platform equipped with the NREL 5MW wind turbine has been tested in the hydrodynamic and ocean engineering tank of École Centrale Nantes under wind and wave loads. This paper aims at comparing the results obtained with numerical simulations with these experimental results. The numerical model is based on the FAST design code from NREL and a user defined platform load model for calculating hydrodynamic and mooring loads. This hydrodynamic model includes non linear hydrostatic and Froude-Krylov forces, diffraction/radiation forces obtained from linear potential theory and Morison forces to take into account viscous effects on the braces and heave plates. First the hydrodynamic model is calibrated against the results of free decay tests without wind. A good agreement is achieved by calibrating mooring properties and heave plates properties of the numerical model. Then a comparison of regular wave cases without wind is realised, and a fair agreement is observed for surge, heave and pitch motions of the floating system. Finally comparisons are realised for regular wave cases with a constant wind speed. A good agreement is observed for the steady state surge and pitch offset. Surge and heave motions also shown a good agreement, these degrees of freedom are not being strongly influenced by wind loading. For pitch motion, numerical simulations show differences around 0.4 rad/s wave frequency, for which model tests have shown a significant influence of wind loading on system motion.

Offshore Wind Turbines – Research and Development

“…Comparison between simulation results and model test results for two sea states without wind was presented. Similar comparison of a semi-submersible floater is reported in [19].…”

An investigation of the effects of wind-induced inclination on floating wind turbine dynamics: heave plate excursion

“…Such adverse effects, observable if the plates have a limited submergence compared to their size, have been observed experimentally by Cermelli and Roddier (2005) on a low-draft offshore platform model. Another experimental study by Philippe et al (2013b) has shown pitch motion amplification on a FWT, which was orientatively attributed to heave plate excursion.…”

Measurements and modelling of the power performance of a model floating wind turbine under controlled conditions

“…Numerous studies involving both the development of computational models and experimental work have been undertaken to date on floating horizontal‐axis wind turbines. Yet these were mainly aimed at investigating the dynamic response of the floating structure . Experimental studies on scaled floating turbines were commonly limited to wave tank tests with the wind generated using upstream air fans .…”

“…Yet these were mainly aimed at investigating the dynamic response of the floating structure . Experimental studies on scaled floating turbines were commonly limited to wave tank tests with the wind generated using upstream air fans . The flow quality is thus inferior to that normally found in wind tunnels dedicated for aerodynamic studies.…”

“…[4][5][6][7][11][12][13]19,29,35 Experimental studies on scaled floating turbines were commonly limited to wave tank tests with the wind generated using upstream air fans. 5,7,19,29 The flow quality is thus inferior to that normally found in wind tunnels dedicated for aerodynamic studies. Data from such experiments have very limited value for assessing the power performance characteristics of OFWTs.…”