Sensitivity and Cost Analysis of Mooring Solutions for Large Renewable Energy Structures

Mooring of offshore structures is a well-known concept in the naval and offshore Oil & Gas sectors, but has been proven to cause complications and be infeasible in the newer wave and wind energy sectors when applying the traditional solutions and experience. Early-stage wave energy concepts are often planned for deployment in shallow to intermediate water depths, where the traditional catenary systems are insufficient, and have experienced several failures due to large line loads. As a result, considerable amount of line and anchor material is often required and causes undesirably high mooring cost. A need for applying more novel systems and materials is present in order to increase durability and decrease the cost. This study focusses on three different mooring systems, which have been considered in earlier studies and makes direct comparison between the lifetime cost using existing cost databases and design procedures stated in design standards from certification companies. All systems are primarily composed of synthetic lines, and are designed using validated numerical models together with a surrogate based optimization routine. Furthermore, the study investigates the sensitivity on line tensions from varying environmental loads in order to quantify the sensibility and the importance of pre-assessment of the conditions at the expected deployment site.