A numerical study of cylinders in waves and currents

The research on combination flow of planar oscillatory flow plus an in-line steady stream is of importance to the situation of structures in waves: and current. The combination flow has not been studied extensively. There is still little information about the effect of current and about combined effect of current and waves on hydrodynamic loading of the structures. The present study investigates the combination flow around a circular cylinder using a vortex-based method incorporating vortex moving particles (discrete vortices) with a finite-difference scheme for the vorticity diffusion. The main attention is paid to the effects of a small current on in-line fluid forces and vortex patterns in the wake. Morison's equation and an equation with two drag terms are examined. The results show that the presence of a small current in an oscillatory flow can reduce the drag coefficient significantly. Morison's equation gives reasonably good predictions for the in-line forces for an oscillatory flow plus a small current. The current tends to bring the whole vortex wake downstream and tries to form the stable Karman asymmetrical form in the downstream wake. The present results show certain agreement with some previous experimental results. (C) 2000 Academic Press.