Stress Concentration Factors For Tubular Joints Of Support Structure Of Offshore Wind Turbine

Wind energy is a kind of clean and renewable resource. Offshore wind energy as a part of solution to the atmospheric carbon dioxide and the global warming problem is abundant in China. However, large-scale development of offshore wind energy has to face many challenges. The multi-pile foundation structures are widely used to offshore wind turbine in China. The support structure for an offshore wind turbine (OWT) is subjected to both hydrodynamic loads and aerodynamic loads. The tubular joints are the weakest component leading to fatigue failure of the whole structure.In this thesis, based on the actually multi-pile foundation structure, the types of tubular joints are determined. Stress concentration factor (SCF) for tubular joints are studied by using AN SYS. The contents of the research include:(1) Based on the theory of space geometry, the space curve equations of weld toes and weld roots for chord and brace are derived, repectively. Using Matlab, the program to calculate weld curves is developed.(2) The finite element models of a simple tubular K joint is established, using the shell elements and the solid elements, respectively. The distribution of SCFs along the weld of this tubular joint is calculated. By comparison of FE results and experimental ones, the solid elements are selected for SCF analysis.(3) Considering the load cases and their combination under fatigue limit state, two offshore wind turbines composed of Tripod and Pentapod substructures are analyzed, respectively. Then, the load types subjected to axial load, in-plane bending and out-of-plane bending of simple tubular K/Y joints and multi-planar tubular Y-joints are determined, respectively.(4) According to the geometrical parameters of actual OWT, the cases of simple tubular K/Y joints are determined. Using SOLID95of ANSYS, the FE models corresponding to each case subjected to different loading types are analyzed. The distributions of SCFs along weld are obtained. The effects of the geometrical parameters such as α, βA, βB,θA and θB on SCFs are discussed. Moreover, the numerical SCF results are compared with the empirical ones from DNV-RP-C203for simple tubular Y joints.(5) In light of the geometrical parameters of actual OWT, the cases of tubular three-planar and five-planar Y joints are determined. Using SOLID95of ANSYS, the FE models corresponding to each case subjected to different loading types are calculated. The distributions of SCFs along weld are obtained. The effects of the geometrical parameters such as α, β, γ and τ on SCFs are studied. Moreover, the numerical SCF results are compared with the empirical ones from DNV-RP-C203for simple tubular Y joints.