Drag and Inertia coefficients of a Cylinder in Random Waves

Laboratory experiments were carried out to research drag and inertia coefficients of a vertical circular cylinder in random waves. The results were compared with those of field experiments and numerical simulations to discuss the characteristics of the random wave force. This comprehensive study showed that the drag and inertia coefficients obtained from the least squares fit on a wave-by-wave basis scattered widely as a results of shedding vortices during the previous wave cycle, the so-called history effect. Coefficients determined by least squares fit of the complete force time series of a random wave record were well ordered as a function of Keulegan-Carpenter number defined by significant orbital displacement or significant wave height and showed good agreement with the values in regular waves. This study enabled us to apply the results of extensive studies in regular waves or in harmonic flow to estimate wave forces acting on an ocean structure in random waves.