A Framework for Mooring and Anchor Design in Sand Considering Seabed Trenches Based on Floater Hydrodynamics

Abstract

Seabed trenches reduce anchor capacity. However, the adverse influence is not considered in the current design, and no guideline is found in engineering practice. This paper presents a framework for mooring and anchor design in sand considering seabed trenches based on floater hydrodynamics. First, a hydrodynamic calculation of the studied floater coupled with the mooring system was conducted. Then, the potential trench profile was assessed using a mooring line–seabed dynamic model. Third, after assessing the suction anchor performance based on its installation and capacity, a refined anchor, caisson–plate gravity anchor (CPGA), was proposed, and the capacity mechanisms were analyzed. It was found that the tensions of mooring lines l1 and l2 resist maximum loads under a 45° load condition. Due to the sand’s high strength, a trench is difficult to form in this mooring type. The suction anchor is not suitable as an anchor for the carbonate sand, considering its installation and capacity. The analyses indicate that the increase in soil stress and soil mobilized range in front of the caisson promotes the capacity of CPGA. This paper provides a framework/example to design moorings and anchors considering potential trenches and provides a solution to the anchor design in carbonate sand.