3D Fully Nonlinear Beam Dynamics of Offshore Wind Turbines
- Carsten Corte (Baustatik - Baudynamik - Numerische Modellierung)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- 3D fully nonlinear beam dynamics, consistent added air mass, offshore wind turbines, simultaneous wind-force and electromechanic moment equilibrium, rotorblade pitch control design
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The 3D fully nonlinear beam dynamics are presented in analytic translational and rotational force equilibrium with subsequent consistent and stable both spatial finite element and time finite difference discretization. Dynamic equilibrium of wind-force induced rotational moment onto the rotor system and electromagnetic rotational moment from the generator—nacelle assembly is described and consistently introduced into the 3D beam dynamics approach. By modeling wind forces onto the rotorblades, one-sided fluid-structure interaction is consistently performed. The approach is applied to time domain modeling of 30 minutes real time intervals for a 120 m diameter three-blade rotor system of 100 m hub height at 50 m mean water depth for i) 3.6 MW SWT-3.6 and ii) 6.0 MW SWT-6.0 wind generators. Rotorblade twist angle distribution is optimized to enforce dynamic moment equilibrium between wind-force induced moment onto the rotor system and electromagnetic rotational moment from the generator—nacelle assembly. Twist angle at rotorblade roots (pitch control) is designed to meet the manufacturer's power curve. Computational results meet the manufacturer's power curve within 0 to 2 percent deviation for average wind velocities in the operating range of 5 m/s to 25 m/s.
Offshore wind turbines are exposed to long-term combined load from stochastic sea state and stochastic turbulent wind. A realistic description of the overall structural dynamics of the complete structure is of main importance for the fatigue design of the different parts of the structure, as there are rotorblades, nacelle, machinery components, azimuth drive, tower segments, ring bolt connections, transition piece, tripod construction, underwater construction and foundation. Sea state load and wind load have up to now been modeled by at-the-time-established approaches. Gravity wave and so sea state modeling ranges back many decades from now (Wave theories by Airy 1845, Stokes 1847, 3rd order Stokes theory Skjelbreia 1959, 5th order Stokes theory Skjelbreia and Hendrickson 1960, stream function theory Dean 1965). A summary on wave theory approaches, on wave-wind correlation mechanisms and on hydrodynamic forces as well as on the dependence of structural dynamic properties of offshore wind turbines on water depth is given in Corte 2003. Extreme wave modeling including breaking waves became applicable as periodicity of waves in space and time was not demanded as assumption anymore and numerical methods (finite element method, boundary element method) were developed for the purpose of nonlinear wave modeling (Longuet-Higgins and Cokelet 1976, Vinje and Brevig 1981, Gravert 1987, Skourup 1989, Grilli, Skourup and Svendsen 1989, Grilli and Svendsen 1990, Grilli 1993, Grilli and Subramanya 1994, 1996, Grilli et al. 2001, 2005, Fochesato et al. 2005a,b,c). Local phenomena as breaking wave impact on rigid structures, e.g. 2D circular structures and 3D cylindrical structures, could be modeled by free surface flow based on potential flow assumptions as well as on viscous fluid flow assumptions (von Kármán 1929, Wagner 1932, Fabula 1957, Goda 1964, Wienke 2001, 2005, Peil and Corte 2005a,b, 2006, Corte and Grilli 2006, Corte 2006). Atmospheric boundary layer modeling was established by logarithmic or exponential average wind speed profiles (Davenport 1961, Telljohann 1998a,b, Peil and Telljohann 1996, 1997, 1999a,b) and 3D wind turbulence modeling (Davenport 1961, Kaimal et al. 1972, Telljohann 1998a,b, Peil and Telljohann 1996, 1997, 1999a,b).
|File Size||2 MB||Number of Pages||11|