Abstract
Abstract. Aero-servo-elastic analyses are required to determine the wind turbine loading for a wide range of load cases as specified in certification standards. The floating reference frame (FRF) formulation can be used to model the structural response of long and flexible wind turbine blades. Increasing the number of bodies in the FRF formulation of the blade increases both the fidelity of the structural model and the size of the problem. However, the turbine load analysis is a coupled aero-servo-elastic analysis, and computation cost not only depends on the size of the structural model, but also depends on the aerodynamic solver and the number of iterations between the solvers. This study presents an investigation of the performance of the different fidelity levels as measured by the computational cost and the turbine response (e.g., blade loads, tip clearance, tower-top accelerations). The analysis is based on aeroelastic simulations for normal operation in turbulent inflow load cases as defined in a design standard. Two 10 MW reference turbines are used. The results show that the turbine response quickly approaches the results of the highest-fidelity model as the number of bodies increases. The increase in computational costs to account for more bodies can almost entirely be compensated for by changing the type of the matrix solver from dense to sparse.
Highlights
Modern wind turbine blades are large, slender and flexible composite structures with a complex pre-bent and twisted geometry
This study presents an investigation of the performance of the different fidelity levels as measured by the computational cost and the turbine response
The effects of blade structural model fidelity on the turbine response, loads, stability and computation time are investigated in this study
Summary
Modern wind turbine blades are large, slender and flexible composite structures with a complex pre-bent and twisted geometry. An aero-servoelastic code or framework is used to accurately calculate the complex dynamical response of wind turbines with large and flexible blades This has led to the implementation of geometrically nonlinear structural solvers in wind-turbinespecific aero-servo-elastic codes. The structural solver BeamDyn (Wang et al, 2017) was implemented in FAST (Jonkman and Buhl Jr., 2005) It uses the geometrically exact beam theory (Hodges, 1990) based on the Legendre spectral finite element method. Another example is a recent release of Bladed (DNV GL, 2018) that uses a multibody formulation (Shabana, 2013; Cardona and Géradin, 2001) to capture large structural deflections of the modeled structures. BHawC (Rubak and Petersen, 2005) is another nonlinear aeroelastic wind turbine simulation code which uses a corotational formulation to resolve large deflections accurately
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