Effect of the Beam Element Geometric Formulation on the Wind Turbine Performance and Structural Dynamics

In this paper, the original double symmetric cross section beam formulation in RIFLEX used to model the blades is compared against a newly implemented generalised beam formulation, allowing for eccentric mass, shear and elastic centres. The generalised beam formulation is first evaluated against an equivalent ABAQUS beam model (Using the generalised beam formulation implemented in ABAQUS) which consists of DTU 10MW RWT (reference wind turbine) blade in static conditions. A static displacement is applied to the tip, which is close to an operating load. The results appear very similar and ensure that the implementation is correct. The extended beam formulation is afterwards used on the Landbased 10MW turbine from DTU with external controller. This case study aims at evaluating the effect of the newly implemented formulation on realistic, flexible structure. During the study, the blades were discretised using both the old and new formulation, and dynamic simulations were performed. The effect of the beam formulation was evaluated using several wind conditions that are thought to be characteristic of operating conditions. Results show slight difference between two formulations but could be more significant for next generation flexible blades. -------------------------------------------------------------------------* corresponding author. virgile.delhaye@sintef.no **Current affiliation : Queen's University Belfast (QUB), United Kingdom (UK) 1 Earlier MARINTEK, SINTEF Ocean from 1st January 2017 through a merger internally in the SINTEF Group INTRODUCTION There is a need to improve the structural predictions of the blade in aerodynamic codes without compromising with code's efficiency. This comes from the increased complexity and size of the new blade designs. In particular, improving the aerodynamic performances of the blade by tailoring the fibre reinforced plastic layers is an important research topic (Kooijman (1996) [1]). In this context, the use of advanced beam model able to better predict blade dynamics and give a more realistic description of the load transfer into the wind turbine becomes crucial for industry. A significant contribution in this field comes from helicopter technology and was developed by Hodges et al. (1999) [2], Yu et al. (2002) [3]. The idea is to reduce a three-dimensional anisotropic elastic problem to a twodimensional cross section analysis and to a one-dimensional beam analysis (e.g. the variational asymptotic methodology by Berdichevsky (1979) [4]). These methodologies have been used to successfully describe the structural behaviour of single blade submitted to static and dynamic loadings (Otero (2010) [5]). The inclusion of such formulation in multibody codes, which are able to handle a whole wind turbine, is less common. An anisotropic beam formulation was recently implemented in the multibody aeroelastic code HAWC2 (Branner et al., 2012 [6], Kim et al., 2013 [7]), in order to simulate full wind turbine structure and to capture the bend-twist effect arising in the nextgen blades as observed by Lobitz et al. (2000) [8] (2003) [9]. In the present paper, a similar step is presented in RIFLEX with the implementation of a generalised cross-section formulation to discretize the blades. Virgile Delhaye* SINTEF Ocean1 Trondheim, Norway Madjid Karimirad** SINTEF Ocean1 Trondheim, Norway Petter Andreas Berthelsen SINTEF Ocean1 Trondheim, Norway Proceedings of the ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering OMAE2017 June 25-30, 2017, Trondheim, Norway