Numerical Study on Hydrodynamic Force and Wave Induced Vortex Dynamics around Cylindrical Pile

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the hydrodynamic force and vortex dynamics. To do so, the rectangular wave flume and monopile is modeled on a solver; available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for four cases with different wave characteristics consequently for different Keulegan-Carpenter numbers (KC). Hydrodynamic in-line force acting upon pile was studied and the results indicated that the total in-line force increases as KC number increases. In addition, when vortex shedding develops, drag force component increases and inertia force component decreases. The vortex dynamics around the pile was investigated by means of Q criterion and vorticity field. It was seen that by increasing KC number larger than ۶, vortex shedding will be happened. Moreover, variation of bed shear stress around the pile has been investigated and it was seen that the bed shear stress is influenced by KC number which is result of existence of horseshoe vortices. The bed shear stress near the pile is negative due to existing of the horseshoe vortex. It begins when KC exceeds ۶ and by increasing KC up to ۲۰, the magnitude of negative values of bed shear stress near the pile increased which implies horse shoe vortices are completely formed. This also complies the experimental results.

Keywords:

Keulegan-Carpenter , OpenFOAM , RANS Equations , Vortex Shedding , Wave-Pile Interaction