Experimental investigation on responses characteristics of a mooring line with imposed top-end motions

Abstract

Abstract A series of experiments were performed to investigate the dynamic response of a mooring line based on the catenary configuration with imposed surge and heave motions in a water flume with a considered model scale factor of 1:70. The surge and heave motions with different amplitudes and periods were driven by a programmable electrical motor at the fairlead position, respectively. The dynamic tensions and motion trajectories of the mooring line were measured to illustrate the effects of pretension and motion period on the predominant harmonic components in the dynamic response. The results show that the pretension and motion period have significant effects on the dynamic tensions and nonlinear motion trajectories of the mooring line. Multiple harmonic components of the dynamic tension are observed at the fairlead and the predominant harmonic tensions are found to be changed with variations of the pretension and motion period. A sharp increase of the maximum tension force is observed at large pretension for the mooring line with the surge and heave imposed motions. Such sharp tension increase may result in floating platform and mooring system breakage. The results of this paper revel the foundation of the further studies on the transforming mechanism of the slack and taut state of the mooring line as well as for optimism of the engineering designs in floating offshore devices mooring installations.