This paper presents the results of an experimental investigation of the in-line and lift forces acting on an oscillating column with circular footing. Forced surging testes were carried out using a column with circular footing of which ratio of diameter was varied from 1.25 to 2.5. The in-line and lift force have been measured concerning both the whole model and the parts of column and footing. The drag coefficients, inertia coefficients, coefficients of root-mean-square values of the in0line fore and lift force coefficients in the range of Keulegan Carpenter number from 5 to 30 have been obtained. Those results have been compared with that of a straight finite length circular cylinder.
The prediction of the forces induced and the motion responses by wave and currents is required to design the floating marine structures. Most of the floating marine structures have been consisted of some pillar shaped material, column, column with footing and bracing. The vortex shedding of those materials is expected to have great effect on the hydrodynamic forces. Therefore, we cannot estimate the hydrodynamic forces by linear potential theory, then we need the experiential studies. Many researchers studied on the viscous forces due to vortex shedding acting on the two dimensional cylinders. Column, column with footing and bracing are finite length circular cylinder, however, and data also required on these types of cylinders. Nakamura et al.(1992) obtained the hydrodynamic coefficients of finite length circular cylinders in an oscillating flow with various ratios of length to diameter and visualized the flow fields around the cylinders in forced surging tests. Hoshino et al.(1993) obtained the hydrodynamic coefficients of finite length circular cylinder with various ratio of length to diameter on the towing condition in the in-line and transverse oscillation testes. Yagit et al.(1989) dealt with the flow around a stepped circular cylinder and the structure of the shedding vortices and measured the surface pressure distributions on cylinder in uniform flow.
