In the design of cylinders sitting on a permeable seabed, the wave induced uplifting forces are important factors. This paper studies the nonlinear wave action on the bottom of a circular cylinder by using cnoidal wave theory. The results show that when H/d and T(g/d)½ are relatively large, the nonlinear wave force is much larger than linear one.
Circular cylinders are often used in coastal engineering. In the design of such structures, in addition to the horizontal wave forces, the wave induced uplifting forces acting on the bottom of the cylinder should be taken into account. Among the past researches of this problem, linear wave theory has been used. But in coastal regions, due to the relatively large wave height to water depth ratio, big error often occurs if linear wave theory is used to describe the real wave profile. Therefore it is needed to study the nonlinear effect of waves on the uplifting forces. In deep water regions, that is, in the regions where the values of wave length L to water depth d ratio are relatively large, for nonlinear waves with large wave height and wave steepness, good results can be achieved by using higher order Stokes wave theory to describe the wave profile. But in shallow water regions, when L/d values are larger than 8, the Stokes wave theory is no longer suitable. In such regions, when the design wave is chosen according to design specifications, the value of L/d could reach 8 to 12, and sometimes could even reach 14 to 16. In this case, it is reasonable to use cnoidal wave theory to describe the wave profile. Isaacson (1977) and Qiu (1988) conducted some research work and presented some calculating methods on horizontal cnoidal wave forces on circular cylinder.
