Design And Analysis Of Catenary Mooring For The Floating Offshore Wind Turbine In Shallow Water With Its Horizontal Truncated Model

In our country,there are shallow water along the coast,the research of floating wind turbine in shallow water is becoming more and more important.In order to do experiments about scale model,we have to truncate the prototype mooring to meet the insufficient size of wave tank in laboratory and make the truncated system have same motion characteristics for prototype.Nowadays the research on mooring concentrates on deep sea water or sea water of which depth is more than 200 m.Mooring in shallow water,especially for water of which depth is less than 100 m,has some challenges such as lack of enough restoring force,severe fatigue damage.In this essay,DeepCWind floating platform and NREL-5MW wind turbine are combined with mooring system in shallow water.Three calculating methods of mooring have been compared to choose a more suitable one for mooring design.Mooring design in water of which depth is 50 m has been completed through optimization.Prototype mooring has been horizontal truncated and the truncated result has been analysed.For three mooring calculating methods,simulating with different environmental conditions,lumped-mass method has been choosed.Adopting calculating methods as quasi-static,lumped-mass,finite element to simulate under conditions of steady wind,regular wave etc.Lumped-mass method performs better.Complete mooring design in shallow water of which depth is 50 m with better characteristics.To solve the difficulties occuring in shallow water,six mooring lines composed of chain which have great gravity in water to provide larger restoring force are arranged symmetrical.Three optimization objects such as cost,persistent of fatigue damage,max horizontal displacements of platform are set.Adopting pattern search to optimize the mooring with each optimization object.Considering the optimization ratio and characteristics in shallow water,choose right one among three optimization results.Truncate the mooring line in shallow water horizontally which has great similarity with prototype.According to size of wave tank in laboratory,fix the horizontal distance from anchor to fairlead.Adopting genetic algorithm to horizontal truncate mooring line in unique mooring material with weighting optimization object consists of restoring force in surge and vertical direction,tension of NO.1 mooring line and damping coefficient in surge direction.The responses of truncated mooring under condition of free-decay,regular wave andirregular wave are pretty well.