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Wind turbine blade design using FEM

Wind turbine blade design using FEM. Afolabi Akingbe Wei Cheng Wenyu Zhou. Outline. Basics of wind turbine blade Blade element theory Membrane & plate bending model Shell element in FEM ANSYS model. How wind turbine blades work. Essential blade concepts. chord. Twist angle.

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Wind turbine blade design using FEM

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  1. Wind turbine blade design using FEM AfolabiAkingbe Wei Cheng Wenyu Zhou

  2. Outline • Basics of wind turbine blade • Blade element theory • Membrane & plate bending model • Shell element in FEM • ANSYS model

  3. How wind turbine blades work

  4. Essential blade concepts chord

  5. Twist angle

  6. Blade element theory

  7. Membrane & plate bending • 3D structures under arbitrary loads • Split element into two types for different calculations • Membrane element for in-plane loads • Plate bending elements for transverse loads and bending

  8. FEM triangular blade model

  9. Membrane element analysis • Assume linear displacements • are 2x2 matrices

  10. Membrane element analysis

  11. Bending element analysis • Tranverse displacements and rotations are taken as degrees of freedom. • are 4x4 matrices

  12. Bending element analysis

  13. FEM for shell analysis • A combination of a plate bending and membrane element • The DOF of a plate and plane stress finite element in a local element-aligned coordinate system are considered

  14. Shell element (a) Plane deformation (b) bending deformation The finite element solution

  15. Displacement model • The displacement model for the flat shell is expressed as Ni is the bilinear shape functions associated to node i, and

  16. Strain and curvature • The membrane εm and curvature κare defined as Transverse shear strain is

  17. Approximation of strain field • The membrane deformation, the approximation of the strain field is

  18. Discrete curvature field • The discrete curvature field is

  19. Approximation of shear strain • The approximation of shear strain is written as

  20. Linear system • Combining simultaneously membrane and bending actions, a linear system for the vector of nodal unknowns q can be written where ke is the stiffness matrix composed of membrane and plate stiffness element matrices

  21. Load vector • The load vector at each node i is of the form fie = [FxiFyiFziMxiMyiMzi]T

  22. Element stiffness matrix • The element stiffness matrix at each node i

  23. ANSYS Modeling • Angular velocity • Surface pressure

  24. Deformation & stress contours • More stress at the blade root • Thicker material closer to root to endure high loads (Displacement contour) (Stress contour)

  25. Composite • Can use commercial code like ANSYS to quickly change material properties and mesh sizing.

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