The Constitution Truss Spar, operated by Anadarko Petroleum Corporation (APC), is located in Green Canyon Block 679 and 680 in a water depth of 1,500 m. It was installed in October of 2006 and has since weathered multiple hurricanes and other storms. The platform is equipped with an Environmental Platform Response Monitoring System (EPRMS) which records real-time motions, environmental parameters and loads. These measurements were used to hind-cast the platform mooring tensions and estimate fatigue damage index accrued over the short life (install to start of study, July 2010) of the platform. The study found that extreme events such as Hurricane Ike (~100 yr storm) accounted for considerably higher fatigue damage index than the total caused by other small storms likely to occur in the 20 year service life of the vessel. It is therefore a recommendation of this study that a design criterion for fatigue damage accrued during extreme events such as 100 yr hurricanes be considered in the design of station keeping systems in a similar manner to the guidelines found in API RP 2T (2010) for design of tension leg platforms.

Multiline anchors are a novel way to reduce the cost of arrays of floating offshore wind turbines (FOWTs), but their behavior is not yet fully understood. Through metocean characterization and dynamic simulations, this thesis investigates the effects of wind-wave misalignment on multiline anchor systems. Four coastal U.S. sites are characterized in order to develop IEC design load cases (DLCs) and analyze real-world misaligned conditions. Stonewall Bank, Oregon showed the highest 500-year extreme wave height, at 16.6 m, while Virginia Beach, Virginia showed the highest 500-year wind speed, at 56.8 m/s. Misalignment probability distributions, at all sites, are found to converge towards zero (aligned conditions) and become less variable as wind speed increases. This indicates that high misalignment angles are unlikely at high wind speeds. A simulation parameter study, spanning a range of wave directions, misalignment angles, and DLCs, is run in OpenFAST to explore how misalignment affects multiline anchor loading. The simulated anchor is connected to three IEA 15 MW FOWT models via a taut mooring system. The force on the multiline anchor is calculated by summing the three tension vectors from the mooring lines. The mean direction of this force is found to align closely with the wind; each mean is within 5.5° of the wind direction. Higher misalignment angles cause increases to the amount of directional variation about this mean. The magnitude of the multiline force is also examined. Mean force level is found to be nearly unaffected by misalignment. However, maximum force decreases significantly as misalignment angle increases, dropping as much as 23.3% in extreme conditions. This confirms current anchor design practice, which treats aligned metocean conditions as the peak load an anchor experiences. Standard deviation of multiline force also decreases with misalignment. The operational load case, DLC 1.6, shows a slight trend towards this, but the extreme case, SLC, shows a more pronounced drop of 32.4%. This suggests that anchor cyclic loading analyses could benefit from considering misalignment. Doing so could lead to lower estimates of the cyclic loading amplitudes that anchor designs must withstand, thus leading to smaller, cheaper anchors.