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Composites Engineering and Applications Center, University of Houston Dynamics Analysis of Offshore Wind Turbine Using Adams

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In an offshore wind turbine system, dynamic modal characteristics, hydrodynamic and aerodynamic loadings are important inputs for design considerations. In this study, the offshore wind turbine is modeled by Adams with the aid of FAST (developed by NREL). Natural frequencies and mode shapes of the offshore wind turbine are determined by Adams-LINEAR/EIGENSOL. Also the hydrodynamic and aerodynamic loadings are determined by time-domain dynamics simulation with Adams.

The geometry, mass and stiffness of an offshore wind turbine are first modeled in FAST. The Adams User-DLL (by compiling hydrodynamics, aerodynamics and aeroelastic source codes for offshore wind turbine) can be created in Adams to simulate the dynamic response of the offshore wind turbine system in time domain. The system model is shown in Figure 1.

To study baseline dynamics characteristics of the offshore wind turbine system, the wind turbine structure is cantilevered at the mud line. Its natural frequencies and mode shapes, as well as other dynamics behavior, under a specific wind, wave and current are determined. For example, the first mode shape of the mono-tower is shown in Figure 2. The wave elevation and the overturning moment of tower at mud line are shown in Figure 3 and Figure 4. The results obtained are then used for design and analysis of pile/foundation and tower interactive for supporting the wind turbine.

Figure 1. An Offshore Wind Turbine Model in Adams

Figure 2. First Mode Shape of Mono-tower

Figure 3. Wave Elevation

Figure 4. Overturning Moment of Tower at Mud line