Assessment of viscous damping of a solid heave disk for motion reduction of a floating circular cylinder

Abstract

In the present study, we developed an analytical model incorporating viscous damping of a solid heave disk for the motion reduction of a floating circular cylinder in three degrees of freedom (3DOF) (surge, heave, pitch). The matched eigenfunction expansion method (MEEM) based on a potential theory is employed for solving the diffraction and radiation problem of a floating cylinder with a solid disk. To implement viscous damping due to vortex formation at the disk edge, a novel approach using the drag force and moment in the Morison equation is presented along with the conventional method using free decay tests. The developed analytical model is validated through the comparison with the regular wave experiments and computational fluid dynamics (CFD) turbulent model. Attaching the solid heave disk to the bottom of a cylinder reduces the maximum values of the heave and pitch RAOs (Response of Amplitude Operator) to 34 % and 53 %, compared to the cylinder model with no disk. Increasing the size of the heave disk decreases heave motion accordingly and significantly, however, its radius ratio must exceed the specified value of a/b=1.5 for affecting the reduction of a pitch motion.