Three Dimensional Numerical Simulation Of Local Scour Around The Piles Supporting Offshore Wind Turbine In Steady Current

The local scour around the offshore wind turbine foundation is critical to thestability of the structure, and it is an important issue of the investigation on theoffshore wind turbine foundation. To study the scour around the pile-based offshorewind turbine structure, a three dimensional numerical model for the flow simulation isdeveloped based on the open source code OpenFOAM, and a local scour modelaround the structure is established based on the equilibrium of bed shear stress. Themodel is applied to simulate the scour around the piles. The main contents and resultsare summarized as follows.(1) A three-dimensional numerical model for the flow simulation, whosegoverning equations are three-dimensional Reynolds-averaged Navier-Stokesequations, is developed on the basis of OpenFOAM. The RNG k model is used tosolve the turbulence, and the VOF method is chosen to capture the free surface. Thecharacteristics of the flow around the cylinder are studied through the modelsimulation, and the velocity profile and the velocity distribution in the forward andleeward of the cylinder are analyzed. The flow model is verified by the comparisonbetween numerical and experimental results.(2) Based on the flow simulation model, a numerical model for the local scouraround the structure under current is established using the idea of the equilibrium ofbed shear stress. The bed shear stress is calculated according to the definition of theshear stress, and the dynamic mesh method is used to describe the change of bedelevation due to the scour.(3) The scour of the cohesive sediment bed around the cylinder for thelaboratory scale is simulated, and the equilibrium scour hole and the maximum depthof the hole are obtained. The numerical results compare well with the experimentaldata, indicating the validity of the local scour model.(4) The three-dimensional local scour model is used to simulate the scour aroundthe multi-pile foundation of the offshore wind turbine structure near the DonghaiBridge in Shang Hai. Because of the instability of the dynamic mesh computation, theequilibrium scour hole is not obtained and the scour simulation for the field scaleshould be further investigated.