The present paper describes the results of an experimental study of impact forces due to plunging wave action on a horizontal circular cylinder located near the still water level. The vertical and horizontal components of the Impact force on the cylinder due to a single plunging wave have been measured for 3 elevations of the cylinder, and 6 locations of wave breaking relative to the horizontal location of the cylinder. A video record of the Impact process has been used to estimate the kinematics of the wave and plunging Jet prior to impact. The force measurements have been corrected for the dynamic response of the cylinder, and analyzed to obtain slamming coefficients and rise times. It is observed that the cylinder elevation and its horizontal location have a significant effect on the peak impact force. The magnitude of the Impact force due to a breaking wave is 4 to 20 times greater than that due to a regular non-breaking wave of similar height and period. In addition to the fluid velocity, the curvature of the water surface has a noticeable effect on the peak impact force.
Forces on coastal and offshore structures due to wave impact are often critical In the design of such structures. Important features of wave impact include the rapidly varying hydrodynamic load and the consequent dynamic response of the structure. Fatigue stressing of structural members and joints which are subjected to such loads can lead to structural failure. Wave slamming on horizontal structural members may be due to non-breaking wave impact associated with a rising water surface, or to breaking wave impact associated with a plunging water jet. The resulting impact force is predominantly vertical in the former case, whereas a plunging wave can produce significant horizontal and vertical impact force components.
