Study On Local Scour Around Composite Bucket Foundation Of Offshore Wind Turbines

Local scour of offshore wind turbine foundations may affect the stability of thewhole wind turbines. Scour depth is one of the critical factors in design of foundationsfor the offshore structures. Bidireational currents are generated in a water basin.Series models are carried out on the local scour around composite bucket foundations.Furthermore, a three dimensional numerical water basin based on FLOW-3D isestablished to study the flow characters and shear stresses around foundations. Themain contents and results are summarized as follows.(1) A bidirectional current system is developed, which can generate positiveconstant currents, negative constant currents and bidirectional currents according tothe sinusoidal singals. The current can be controled by the computer softwareautomatically, and also can be corrected to achieve the real-time one. The highprecision system canmeet the physical test requirements.An underwater topographicsurvey system is developed based on the high precision positioning mechanism.Aterminal is controlled automaticly by the computer remote control software. Thesystem is easy to operate and is proved stable after tests, and has been successfullyapplied to study local scour around composite bucket foundations.(2) Based on the series models tests, the local scour around composite bucketfoundation of offshore wind turbines situated in the Xiang-shui is studied. Themorphology of the scour hole around foundations, equilibrium scour time andmaximum scour scour depthare investigated based on a series of scale model of1:20,1:40and1:70. The maximum scour depth of the composite bucket foundations on-siteabout2.8m according to the physical tests.(3) A three-dimensional numerical model is established using the softwareFLOW-3D, distributions of the wake vortex and velocity profile of composite bucketfoundations are analyzed. Based on the turbulent kinetic energy method, the bed shearstress amplification factors are studied. The scour area and maximumlocalscour depthfor the piles and the composite bucket foundation are compared.KEY WORDS：Composite bucket foundation, Bidirectional current basin, Localscour, Series models, FlOW-3D...