Methodology for Wind/Wave Basin Testing of Floating Offshore Wind Turbines

Abstract

Scale model wave basin testing is often employed in the development and validation of large scale offshore vessels and structures by the oil and gas, military and marine industries. A basin model test requires less time, resources and risk than a full scale test while providing real and accurate data for model validation. As the development of floating wind turbine technology progresses in order to capture the vast deepwater wind energy resource, it is clear that model testing will be essential for the economical and efficient advancement of this technology. However, the scale model testing of floating wind turbines requires one to accurately simulate the wind and wave environments, structural flexibility and wind turbine aerodynamics, and thus requires a comprehensive scaling methodology. This paper presents a unified methodology for Froude scale testing of floating wind turbines under combined wind and wave loading. First, an overview of the scaling relationships employed for the environment, floater and wind turbine are presented. Afterward, a discussion is presented concerning suggested methods for manufacturing a high-quality, low turbulence Froude scale wind environment in a wave basin to facilitate simultaneous application of wind and waves to the model. Subsequently, the difficulties of scaling the highly Reynolds number-dependent wind turbine aerodynamics is presented in addition to methods for tailoring the turbine and wind characteristics to best emulate the full scale condition. Lastly, the scaling methodology is demonstrated using results from 1/50th scale floating wind turbine testing performed at MARIN’s (Maritime Research Institute Netherlands) Offshore Basin which tested the 126 m rotor diameter NREL (National Renewable Energy Lab) horizontal axis wind turbine atop three floating platforms: a tension-leg platform, a spar-buoy and a semi-submersible. The results demonstrate the methodology’s ability to adequately simulate full scale global response of floating wind turbine systems.

Directionality Effects of Aligned Wind and Wave Loads on a Y-Shape Semi-Submersible Floating Wind Turbine under Rated Operational Conditions

“…Due to the complicate effects of reduced Reynolds number on the flow around turbine blades, it is almost impossible to recover all the aerodynamic forces using a geometry-scaled model [34][35][36]. Nevertheless, the average wind thrusts of the rotor had been successfully simulated by a drag disc fixed to the hub shaft [6,[37][38][39].…”

Efficient preliminary floating offshore wind turbine design and testing methodologies and application to a concrete spar design

“…[39][40][41][42][43]. Furthermore, given that the mass distribution and rotational speed are scaled correctly, the correct gyroscopic forces and 1P, 3P forcing frequencies will be reproduced [44,45].…”

Experimental comparisons of dynamic properties of floating wind turbine systems based on two different rotor concepts

“…Consequently, establishing a proper methodology for accurately designing and fabricating floating wind turbine models and emulating aerodynamic and hydrodynamic environments has proven challenging. Thus far, a series of model tests on FOWTs have been performed [15][16][17][18][19][20]. In particular, it is impossible to employ Froude and Reynolds number scaling schemes simultaneously, thus each of these basin tests involves the use of Froude scaling methods, the customary choice when employing wave basin experiments.…”