Effect of bathymetry irregularities on the energy dissipation of a mooring line

Abstract

With the aim of analysing the dynamic performance of a conventional chain catenary line and the impact that bathymetry irregularities may have on mooring dynamics, its fairlead is forced to oscillate under different accelerations in both regular and irregular displacements in surge direction. The experimental setup is specifically designed to realistically assess the energy dissipation through the mooring line. The importance of the interaction with the seabed is evident from the resulting video images and the tensions at both ends of the line. The differences between fairlead tensions of different seabed configurations increase under snap loading, peak tensions reaching values in some dynamic cases almost 0.5 times lower with a steep slope than with no slope. This supports the need to consider the bathymetry when designing a mooring system. Moreover, the period for which the dissipated energy abruptly increases due to snap loading is longer as the offset and amplitude enlarge, demonstrating the effect of mean drift on the all chain mooring line. How platform drift increases the dissipated energy through the mooring system depends largely on the local bathymetry, with this increase in some cases being 5.55 times greater with a steep slope than with no slope.