Hydrodynamic forces acting on an inclined circular cylinder oscillating sinusoidally in still water and a horizontal circular cylinder with an inclined angle to the wave crests in regular deep water waves were experimentally investigated in low Kc number condition (Kc<5). The results of force measurements of the oscillating cylinder showed that the drag force and the lift force are negligible. and the dominant added mass coefficient is independent of the inclined angle and are in good agreement with the potential value. From the force measurements of the horizontally submerged circular cylinder with an inclined angle to the wave crests. it was found out that the reduction of the inertia coefficient due to viscous effect decreases with increasing the inclined angle.
In shallow water waves, the flow around a horizontally submerged cylinder is generally idealized as planer oscillatory flow as a vertical cylinder in waves. Hydrodynamic forces on a vertical cylinder in waves or a right-angled cylinder to planer oscillatory flow have been investigated by many researchers. and characteristics of the hydrodynamic coefficients of those cylinders seem to have been clarified in detail. Hydrodynamic forces acting on an inclined cylinder have been studied by several researchers. The results are, however, not always the same with each other as follows. Sarpkaya (1982) experimentally investigated the hydrodynamic forces on inclined smooth and rough circular cylinders in planer oscillatory flow, and pointed out that the hydrodynamic coefficients significantly depend on the inclined angle. Particularly inertia coefficients of the cylinders increase with increasing the inclined angle, and those tend to much larger values than the potential value as Kc number closes to zero. Cotter and Chakrabarti (1984) measured wave forces on a submerged test section which was a part of a circular cylinder inclined with respect to vertical in regular waves.
