An experimental study of the dynamics of catenary mooring lines

Abstract

This work examines the dynamic forces that are generated in catenary mooring lines when the top part of the line is subjected to a forcing function. The forcing function consists of a sinusoidal motion of fixed amplitude but varying frequency and varying angle in the vertical plane. The effect of changes in the pretension in the chain is also examined. -- Four different areas of response are classified by the response of the line and the characteristics of the force in the line observed over time. The force in each area is examined and the mechanism that generates these forces is discussed. The change of these forces with changes in the forcing function at the top end of the line is also examined. -- The model parameters for the catenary mooring system are identified and model tests performed. From these model tests it is possible to conclude that large structures such as oil rigs and large vessels will cause mooring lines to respond in a range where dynamic forces need not be taken into account. However, smaller objects such as buoys will suffer significant dynamic forces.