Hydrodynamic forces on vertical piggyback cylinders in regular waves

The wave-induced hydrodynamic forces on a pair of vertical cylinders of different diameters in close proximity are investigated experimentally. The smaller cylinder is placed at various circumferential positions around the larger one. The effects of the wall-to-wall gap between the 2 cylinders are also investigated. The wave forces, including drag, inertia forces and mean lift, are measured on each cylinder independently and at 2 different depths below the mean water level for each cylinder. The Keulegan-Carpenter numbers vary from 0.4 to 14 based upon the larger cylinder diameter, and the Reynolds numbers are in the subcritical regime. It is found that there is significant interference effect upon the cylinder drag and inertia coefficients