Model Tests for Three Floating Wind Turbine Concepts

Abstract

Floating wind turbine systems have been proposed to tap the significant energy resources found beyond fixed bottom depths. However, limited physical data exists concerning the performance of these systems. This paper presents details of a unique, comprehensive 1/50 th scale model floating wind turbine test effort which involves extensive testing of a scale model of the National Renewable Energy Laboratory (NREL) 5 MW, horizontal axis reference wind turbine atop three generic floating platforms: tension-leg platform, a spar-buoy and a semi-submersible.Design considerations are presented including scaling, instrumentation, test phases and procedures. The test models are geosyms of the full scale systems with scaled platform, tower and turbine mass properties. Froude scaling of both wind and waves is applied and the fundamental tower bending mode is also scaled. A novel, low turbulence, low swirl wind generation system incorporated into the wave basin is utilized which employs 35 fans, flow straighteners and a conditioning nozzle. The model instrumentation includes motions, accelerations and loads as well as wind turbine rpm, torque and thrust. The test matrix is presented and includes system identification tests in addition to tests representing combinations of regular or irregular seas, with static or dynamic winds in both operational and extreme conditions.Selected results from the model tests are discussed which point to the differences and similarities of the three floater concepts. The results demonstrate relatively strong interaction for the fatigue sea states between the tower and platform dynamics for the tension-leg platform system. The results also indicate large loads in the tower during extreme events for the case of the spar and the semi platforms that are due to tower bending from pitch and roll.The model tests add to the present technical knowledge base in the offshore floating wind turbine industry in terms of model test design, wind modeling, coupled response data for the floater and wind turbine and calibration of analysis tools. The results of the tests will be used for validation, calibration and potential improvements of floating wind turbine design tools such as NREL's coupled aero-hydro-elastic code, FAST.

Experimental and numerical study of hydrodynamic responses of a combined wind and wave energy converter concept in survival modes

“…The support structures for the offshore wind turbines are mostly bottom-fixed so far, but there are increasing interest in developing floating wind turbines. Several model tests for floating wind turbines have been performed: model tests on concepts with the NREL 5 MW wind turbine atop three generic floating platforms, i.e., spar, tension leg and semi-submersible (Goupee et al, 2012;Jonkman, 2010) at a 1:50 scaling ratio have been tested in Maritime Research Institute Netherlands (MARIN). Some prototypes have also been tested: Hywind with a 2.3 MW wind turbine was launched in 2009 (Stiesdal, 2009); WindFloat with a 2MW wind turbine was installed in 2011 (Principle Power Website, 2015); and two floating wind turbines were installed in Japan in late 2013, a semi-submersible with 2 MW downwind turbine (Fukushima Offshore Wind Consortium, 2013) and a spar with a 2 MW wind turbine (GOTO FOWT Website, 2015).…”

Offshore floating vertical axis wind turbines, dynamics modelling state of the art. Part III: Hydrodynamics and coupled modelling approaches

“…8. The three main classes of floating support structures currently being adopted [70]. 2 The time constant for an uncontrolled floating structure is given by…”

Dynamic response of floating substructure of spar-type offshore wind turbine with catenary mooring cables

“…This subject has been studied by experimentally using small-scale prototypes (Nielsen et al, 2006;Utsunomiya et al, 2010;Goopee et al, 2012), by analytically/numerically with the simplified wind turbine geometry and the analytically derived wind/wave loads (Tracy, 2007;Lee, 2005;Karimirad, 2010;Dodaran and Park, 2012), or by the combined use of CFD, hydro, FSI (fluid-structure interaction) or/and MBD (multibody dynamics) codes (Zambrano et al, 2006;Jonkman, 2009;Jonkman and Musial, 2010). In case of numerical simulation, 3-D full Navier-Stokes equations are rarely used because extremely long slender mooring lines not only require a large simulation domain but cause highly turbulence flow around them.…”