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Abstract
The ever changing structure and growing size of wind turbine blades put focus on the accuracy and flexibility of design tools. The present thesis is organized in four parts  all concerning the development of efficient computational methods for the structural modelling of composite beams which will support future growth in the rotor size.The first part presents a twonode beam element formulation, based on complementary elastic energy, valid for fully coupled beams with variable crosssection properties.The element stiffness matrix is derived by use of the six equilibrium states of the element corresponding to tension, torsion, bending, and shear. This approach avoids the need for explicit interpolation of kinematic variables and provides a direct lockingfree formulation. The formulation includes a consistent representation of distributed loads and enables recovery of the exact internal force distributions.In the second part a formulation developed for analysis of the stiffness properties of general crosssections with arbitrary geometry and material distribution is presented.The full six by six crosssection stiffness matrix is obtained by imposing simple deformation modes on a single layer of 3D finite elements. The method avoids the development of any special 2D theory for the stress and strain distributionsand enables a simple and direct representation of material discontinuities andgeneral anisotropy via their wellestablished representation in 3D elements.The third part presents an extension of the 3D crosssection analysis by an efficient Finite Element modelling approach for thin and thickwalled sections which substantially reduces the meshing effort. The approach is based on discretizing the walls of the section using a single layer of displacement based elements with the layers represented within the elements. A post processing scheme is also presented to recover inter laminar stresses via equilibrium equations of 3D elasticity derived in the laminate coordinate system.In the final part of the thesis a flexible method for analysing two types of instabilities associated with bending of thinwalled prismatic beams is presented. First, the flattening instability from the Brazier effect is modelled by representing the crosssection by twodimensional nonlinear corotating beam elements with imposed inplane loads proportional to the curvature. Second, the bifurcation instability from longitudinal stresses is modelled with a Finite Strip buckling analysis based on the deformed crosssection. The analysis is well suited for early stages of design as it only requires a simple 2D line mesh of the crosssection.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  DTU Mechanical Engineering 
Number of pages  202 
ISBN (Print)  9788774754411 
Publication status  Published  2016 
Keywords
 Crosssection stiffness analysis
 Finite elements
 Internally layered element
 Composite material
 Bifurcation instability
 Brazier effect
 Equilibrium based beam element
 Wind turbine rotor blade
 Bendtwist coupling
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Dive into the research topics of 'Structural modelling of composite beams with application to wind turbine rotor blades'. Together they form a unique fingerprint.Projects
 1 Finished

Modeling and Analysis of Coupled wind Turbine Blades
Couturier, P., Høgsberg, J. B., Legarth, B. N., Lund, E., Saravanos, D., Krenk, S. & Winther Stærdahl, J.
01/11/2012 → 07/04/2016
Project: PhD