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Accepted Manuscripts

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research-article  
Tobias Martin, Arun Kamath and Hans Bihs
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4044289
The derivation of a discrete mooring model for floating structures is presented in this paper. The method predicts the steady-state solution for the shape of an elastic cable and the tension forces under consideration of static loads. It is based on a discretization of the cable in mass points connected with straight but elastic bars. The successive approximation is applied to the resulting system of equations which leads to a significant reduction of the matrix size in comparison to the matrix of a Newton-Raphson method. The mooring model is implemented in the open-source CFD model REEF3D. The solver has been used to study various problems in the field of wave hydrodynamics and fluid-structure interaction. It includes floating structures through a level set function and captures its motion using Newton and Euler equations in 6DOF. The fluid-structure interaction is solved explicitly using an immersed boundary method based on the ghost cell method. The applications show the accuracy of the solver and effects of mooring on the motion of floating structures.
TOPICS: Simulation, Modeling, Mooring, Tension, Floating structures, Fluid structure interaction, Cables, Hydrodynamics, Approximation, Stress, Waves, Computational fluid dynamics, Newton's method, Shapes, Steady state
research-article  
Baran Yeter, Yordan Garbatov and Carlos Guedes Soares
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4044290
The objective of the present work is to carry out the strength assessment of jacket offshore wind turbine support structures subjected to progressive rupture. A defect existing in a structure made during the fabrication may turn into a small-scale rupture and because of the high-stress concentration and low-cycle fatigue load. Therefore, the ultimate load-carrying capacity of the support structure is analysed accounting for the progress of the rupture until the leg component experiences a full rupture along its circumference. The effect of the severity of the imperfection is also investigated through three case studies that are created by varying the amplitude of the waves. The moment-curvature relationship of the structure with respect to the studied cases is presented. Furthermore, the jacket support structures, at different water depths, are also analysed and discussed. Finally, some of the leg components are removed one by one to study the redundancy of the jacket support structure at 80-m water depth.
TOPICS: Offshore wind turbines, Rupture, Accounting, Water, Stress, Waves, Redundancy (Engineering), Load bearing capacity, Low cycle fatigue, Manufacturing

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