Loading on a Horizontal Cylinder in Irregular Waves at Large Scale

Measurements of forces on a horizontal cylinder submerged with its axis parallel to the crests of irregular waves reveal nonlinearities that cannot be attributed to diffraction or to drag loading. Laboratory experiments were undertaken using a 0.5 m diameter cylinder in waves of significant height, 1.5 m, giving maximum Keulegan Carpenter numbers of about 10. Inertia coefficients derived on a wave-by-wave basis display considerable scatter, but the median value of Cm drops to about unity as Kc approaches 5. There is also a large reduction in the median value of Cm at Keulegan Carpenter numbers below 0.2. These results suggest that the loading on a cylinder in orbital flow at low Keulegan Carpenter numbers is strongly affected by a recirculating current generated by viscosity, and is much influenced by the history of the flow.