Morison coefficients for a circular cylinder oscillating with dual frequency in still water: an analysis using independent-flow form of Morison’s equation

Abstract

In this study, a set of experimental results for wave forces acting on a cylinder oscillating with dual frequency in still water are reported. The experiment was designed to mimic a cylinder slowly oscillating in regular waves, with the high-frequency oscillation representing the wave motion and the low-frequency oscillation, the slow drift motion. The inline forces acting on the cylinder were analyzed using the independent-flow form of Morison’s equation. Our experimental results showed that it was not appropriate to simply use in the independent-flow form of Morison’s equation the added-mass and drag coefficients obtained for the cylinder oscillating with a single frequency in still water. A new dimensionless parameter was introduced to describe each of the wave force coefficients used in the independent-flow form of Morison’s equation, and empirical expressions for the wave force coefficients were proposed using the new dimensionless parameters.