Development of design tool for statically equivalent deepwater mooring systems

Abstract

Verifying the design of floating structures adequately requires both numerical simulations and model testing, a combination of which is referred to as the hybrid method of design verification. The challenge in direct scaling of moorings for model tests is the depth and spatial limitations in wave basins. It is therefore important to design and build equivalent mooring systems to ensure that the static properties (global restoring forces and global stiffness) of the prototype floater are matched by those of the model in the wave basin prior to testing. A fit-for-purpose numerical tool called STAMOORSYS is developed in this research for the design of statically equivalent deepwater mooring systems. The elastic catenary equations are derived and applied with efficient algorithm to obtain local and global static equilibrium solutions. A unique design page in STAMOORSYS is used to manually optimize the system properties in search of a match in global restoring forces and global stiffness. Up to eight mooring lines can be used in analyses and all lines have the same properties. STAMOORSYS is validated for single-line mooring analysis using LINANL and Orcaflex, and for global mooring analysis using MOORANL and Orcaflex. A statically equivalent deepwater mooring system for a representative structure that could be tested in the Offshore Technology Research Center at Texas A&M University is then designed using STAMOORSYS and the results are discussed.