An experimental study of mooring line damping in shallow water

The aim of this paper is to establish a simple approach toexperimentally study the mooring line damping in shallow water.Experimental measurements were conducted in a wave basin ata scale of 1:50, which corresponds to a full scale of 28 m waterdepth. A chain made by stainless steel was used and the tensionforce at the fairlead was measured by tension gauges. Moreover,the mooring line geometry and velocity were computed fromimage processing technique. Series of horizontal motions atfairlead were driven from a programmable wavemaker. Regularsurges with different frequency and pretensions were tested inthis system to investigate the quasi-static and dynamic behaviorsof the mooring chain. In the quasi-static test, mooring line keepsa typical catenary shape and its indicator diagram exhibits asmooth-closed curve. In the dynamic test, the mooring line isfully lifted from the seabed and it cyclically goes through thestage of semi-taut and fully taut. We successfully reproduced asnap event in the laboratory scale and the resulting mooring linedamping can considerably increase in this manner. Themechanism of snap load is investigated by the measured tension,surge and mooring line velocities.