Numerical study on a hybrid mooring system with clump weights and buoys

• The buoys attached to the lines could reduce the tension on the lines.
• There is only horizontal component of the loads at the anchor point.
• The new hybrid mooring system can be applied in wide range of water depth.

A new hybrid mooring system based on the traditional taut mooring lines was proposed in the present study. A series of clump weights were attached to the lower end of each mooring line to form a catenary shape. Some buoys were connected to the upper ends of the lines to reduce the top tension on each mooring line. In order to verify the advantages of this new hybrid system, we investigated the motion responses of a semi-submersible platform moored by the proposed hybrid mooring system. The top tension on the lines was also calculated by using the time domain method. Comparing the results from the taut mooring system, it can be found that the tension on the lines could be reduced by using the present hybrid mooring system, while the motion responses were hardly influenced. Furthermore, a catenary shape was formed at the lower end of each mooring line, which could reduce the requirement of the anti-uplift capacity of the anchors. We also carried out the parametric study to investigate the optimal position and volume of the buoys. The discussions were highlighted on the influence of the water depth.