Abstract
The complexity of floating offshore wind turbine (FOWT) systems, with their coupled motions, aero-hydro-servo-elastic dynamics, as well as non-linear system behavior and components, makes modeling and simulation indispensable. To ensure the correct implementation of the multi-physics, the engineering models and codes have to be verified and, subsequently, validated for proving the realistic representation of the real system behavior. Within the IEA (International Energy Agency) Wind Task 23 Subtask 2 offshore code-to-code comparisons have been performed. Based on these studies, using the OC3 phase IV spar-buoy FOWT system, the Modelica for Wind Turbines (MoWiT) library, developed at Fraunhofer IWES, is verified. MoWiT is capable of fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems, onshore, offshore bottom-fixed, or even offshore floating. The hierarchical programing and multibody approach in the object-oriented and equation-based modeling language Modelica have the advantage (over some other simulation tools) of component-based modeling and, hence, easily modifying the implemented system model. The code-to-code comparisons with the results from the OC3 studies show, apart from expected differences due to required assumptions in consequence of missing data and incomplete information, good agreement and, consequently, substantiate the capability of MoWiT for fully-coupled aero-hydro-servo-elastic simulations of FOWT systems.
Highlights
Introduction and OutlineOffshore wind energy is becoming more and more interesting for the renewable energy industry.Depending on the location, water depth, and seabed conditions, different offshore wind turbine systems are required
An overview of the different codes, tools, and modeling approaches used by the OC3 phase IV participants [7] and described in Section 1 is given in Figure 1, including as well the color-coding, used for comparing the results from the ten OC3 phase IV
Tower-top fore-aft deflection and shear force are compared within the OC3 phase IV activities; as the tower is modeled throughout the load case (LC) together with the spar-buoy floater as rigid structure in Modelica for Wind Turbines (MoWiT), no tower-top deflections are obtained
Summary
Offshore wind energy is becoming more and more interesting for the renewable energy industry. Water depth, and seabed conditions, different offshore wind turbine systems are required. Bottom-fixed solutions, such as monopiles, jackets, tripods, gravity-based structures, or suction buckets are limited to shallow and intermediate water depths. For deeper water sites, floating platforms, such as spar-buoys, semi-submersibles, or tension leg platforms, are required to support offshore wind turbines. Spar-type floating support structures for offshore wind turbines are judged as being highly prospective for utilization in large commercial wind farms [1,2]. In comparison to onshore systems, offshore wind turbines have to deal with hydrodynamic loads in addition to wind loads. For floating offshore wind turbines (FOWTs) the system complexity increases even more. Apart from the environmental loads from wind, waves, and currents, the motion of the floating system leads to relative velocities, which have to be accounted for in the aerodynamic
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