A comparative study of potential-flow-based numerical models to experimental tests of a semisubmersible floating wind turbine platform

Abstract

This contribution to the CCP-WSI FOWT comparative study presents numerical results from three popular potential-flow-based models, including OpenFAST, Orcaflex and WEC-Sim. The subject of the study is the VolturnUS-S semi-submersible platform with the IEA 15MW reference wind turbine. Decay tests and focused waves are simulated in the numerical models, and these are compared to experimental results, using a 1:70 scale model of the system. Comparisons between the numerical models and physical experiments are made. Results of surge motion response and line tension are presented for the decay tests and focused wave tests. The numerical models are seen to underpredict surge response in the low frequency regions of the extreme focused wave test for all three numerical models and of the operational focused wave test for WEC-Sim. Adding an empirically tuned coefficient proportional to the relative velocity between the platform and the water particles in WEC-Sim is seen to improve results in surge motion response significantly, resulting in better agreement than any of the other numerical models. Mooring line tensions are also compared in this study, and an underprediction is observed during the extreme focused wave test for the fore and aft mooring lines, including in the wave-frequency region.