Random wave forces on horizontal cylinders

Abstract

The random wave induced in-line and transverse forces on a smooth circular cylinder, placed horizontally near a plane boundary, are analyzed in the time domain. The time histories of intantaneous water surface elevation and the corresponding in-line and transverse forces are Fourier decomposed into various frequency components. The time histories of water particle kinematics for different frequency components are generated using the linear numerical transforms. Each frequency component of the in-line force is correlated with the corresponding wave component, and the in-line hydrodynamic coefficients of inertia and drag are evaluated through the use of the Morison equation and least-squares method. In addition, the in-line root mean square (r.m.s.) coefficients are also obtained. The component transverse forces are analyzed in terms of maximum and r.m.s. transverse force coefficients. All the in-line and transverse force transfer coefficients are correlated with the component Keulegan-Carpenter number or period parameter, gap ratio of the cylinder from the plane boundary and depth parameter. The component force transfer coefficients are also compared with those obtained from regular wave force experiments, and the coefficients obtained from the time domain analysis of the entire length of the instanteneous random water surface elevation and the corresponding force records. It is found that the component force transfer coefficients compare quite well with the coefficients determined from the regular wave force experiments, and show the same trend with all the parameters mentioned above as the regular wave force results under the same cylinder and water depth conditions.