Analysis of Deep Water Single Point Moorings

Abstract : Analytical and numerical studies were made of single point moorings of a large disc buoy in deep water. Waves of different frequencies and winds of different magnitudes were imposed on moorings of different scopes for nylon ropes. The numerical model results compared favorably with analytical solutions for a straight vibrating string and the buoy motion was validated with the results from a hydraulic model study. Approximate calculations, based on the straight vibrating string solution, were compared to the numerical results of curved mooring lines of various scopes. The analytical prediction of line tension was from fair to poor but the prediction of the position of the nodes of tension and the natural frequencies of the modes was good. A new method of presenting mooring line tension data in dimensionless form is presented that reduces moorings of different frequencies and line diameters to a common scale. The versatility of the numerical program was illustrated with two runs for moorings in shallow water with large waves in addition to a computation of line tension, position and velocity for the condition of a wind shift of 180 degrees on the buoy. The usefulness of the numerical program as a design tool was established.