Experimental study of the influence of the rope material on mooring fatigue damage and point absorber response

摘要

The present work investigates the influence of mooring material on the hydrodynamic responses of a point absorber by experimental tests. Three taut mooring systems are considered with different materials, namely wire, nylon and polyester. In order to study the influence of mooring material on point absorber hydrodynamic responses, the other factors that may influence system dynamics are kept as unchanged as possible. During the model tests, the pretension of the three mooring systems are set to be similar and the parameters of wave conditions are identical. Decay tests are conducted to determine the system natural periods and linear damping coefficients in different modes. Totally seventeen regular wave cases and two irregular wave conditions are tested to study the motion responses of the buoy as well as mooring dynamics. The response amplitude operators of motion responses and mooring tensions are obtained by the regular wave model tests. Three wideband spectral methods as well as two simplified spectral methods are applied to study mooring fatigue damage in the random wave conditions, and the results are compared with the estimations of rainflow counting approach. It is shown that the alpha 0.75 method provides the most precise estimations of fatigue damage in most mooring cases among spectral methods discussed this study.