In this paper, a discrete vortex model based on full vortex cloud method is established to simulate the wave and wave-current flow fields around pile-groups. The variation of calculated grouping effect coefficients versus relative spacing between piles and group-configuration, as well as the flow pattern around the piles, are discussed. Though the combinations of flow field parameters and pile-group configurations are limited in this paper, the results of present model generally agree with that reported by other researchers.
Pile groups or arrays are extensively used in ocean engineering, to calculate the wave and current forces on the piles are crucial in structure design. Due to the shielding effects, the flow pattern around each pile in a group changes dramatically, which makes the hydrodynamic forces on a pile 40% or even higher than those on other piles in a group. Therefore, it is of important practical interest to study the pile grouping effect. Many studies have shown that the grouping effect coefficients, defined as the ratio of hydrodynamic forces on each pile in a group to those on an isolated pile, are affected mainly by the Keulegan-Carpenter number and the relative spacing between the piles. Though there are many literatures about the wave and current loads on isolated pile, the studies about the wave or wave-current loads on pile groups are still quite limited. So far the reported results on this subject are mainly obtained by physical model tests. Chakrabarti (1982a, 1982b) measured the wave forces on the vertical tubes arranged in line with the wave direction. The force coefficients are presented as functions of the KC number and the tube spacing. Chakrabarti reported that the inertia and drag coefficients generally decrease as the spacing decreases due to shielding effect, while the lift coefficient increases as the spacing decreases.
