Morison wave force coefficients for application to random seas

Results are presented from the analysis of the data collected from the Christchurch Bay Tower Compliant Cylinder when tested in random waves in the De Voorst flume in The Netherlands during 1987. Attention is focused on the use of rigid and flexible member (relative motion) forms of Morison's equation for the estimation of drag and inertia forces under random wave excitation. Notwithstanding some inconsistencies, many attributable to the ill-conditioning of much of the data for C d determination, the coefficients show reasonable agreement to values obtained from earlier studies. The work suggests that C d and C m coefficients from large scale measurements may not be so sensitive to their method of estimation as has previously been thought and that they are applicable to the relative velocity form of the loading mechanism. For non-deterministic analyses, Morison's equation is found to reproduce well the probability distribution of loading associated with given sea state conditions. Furthermore, no simple expansion/extension to the equation has been forthcoming and no mechanistic allowance for history effects or vortex shedding has been found.