Upstream-Cylinder and Downstream-Cylinder Influence on the Hydrodynamics of a Four-Cylinder Group

The wave interaction at low Keulegan-Carpenter numbers with a group of four large cylinders arranged in the form of a square with one diagonal along the direction of wave propagation is studied with a focus on the hydrodynamic effects of the most upstream and the downstream cylinders in the group. This is studied by removing them and comparing the wave forces and the free surface elevations around the three remaining cylinders with the four-cylinder configuration. The theoretically predicted wave near-trapping in the case of the four-cylinder group is also investigated for low- and high-steepness incident waves. The numerical results are compared with analytical formulas based on potential theory, and differences are observed between the results for high wave steepnesses. It is observed that the downstream cylinder has a significant influence on the wave forces acting on the cylinders in the four-cylinder group. It is also found that the numerical model correctly represents the wave near-trapping predicted by the analytical formula at a low incident wave steepness. For a high incident wave steepness, the diffraction regime is found to be different, with significant wave radiation from the cylinders and, consequently, the conditions for wave near-trapping breakdown