Dynamic Tension Analysis Of The Mooring Line Of The Offshore Floating Wind Turbine

Floating offshore wind turbines(FOWT) is the most protential wind power technology. Mooring lines are used to locate the wind turbine, and transmitted the wind load and wave load to the sea floor, which is the guarantee of the safe of wind turbines. Under the aerodynamic and hydrodynamic loads, the offshore wind turbine will produce large motions, and the dynamic tension of the mooring line shows significant nonlinear characteristic due to its station of slack and taut alternations. The high dynamic tension will lead to fatigue fracture of the mooring line. This paper focuses on mooring line dynamic tension characteristics to carry out theory and simulation modeling and analysis, the study of typical wind load dynamic tension variation and its influencing factors, so as to provide a theoretical basis for the mooring system of floating offshore wind turbine design. The main work are as follows:(1) Based on blade element momentum theory(BEM), a wind turbine blade aerodynamic loads calculation model was established, calculation obtained by programming impeller thrust, torque and wind turbine power, used of the spectrum described Jonswap wave loads, and radiation diffracted wave of computing hydrodynamic floating wind turbine loads; the motion equations of the wind turbine were established. The separation of slack and taut regions was determined by the damping ratio, the frequency ratio and the displacement ratio. Based on the NREL 5-MW offshore wind turbine, the displacement of the wind turbine and the dynamic tension of the mooring line under three different cases were analyzed, and the influence of the pretension force on the dynamic tension of the mooring line was investigated.(2) Deduced the catenary equation of mooring line, and the initial position of mooring line was given according to the parameters; An equivalent dynamic model of mooring line was established by using the method of multi rigid body discretization, The discrete rigid segment was regarded as a flexible cantilever beam, and the detailed derivation of the discrete element model of line was given, The calculating formula of spring stiffness coefficient between adjacent rigid body and rigid body was derived. The offshore floating wind turbine flexible coupling dynamic model was established in ADAMS. Concerned the influence of the aerodynamic and hydrodynamic loads on the whole turbine, the dynamic characteristics of turbine and the dynamic tension of mooring line were studied.(3) Effects of the arrangement of the mooring lines and the arrangement of the mooring lines on the dynamic tension of the mooring lines were analyzed. Effects of dynamic tension of the mooring line failure fracture of single or a plurality of the mooring cables were studied, and a method for judging the fracture failure of the mooring line was presented.