Significance of Short Crested and Diffracted Waves on Full Scale Motion Correlation of a Truss Spar

Accurate prediction of responses is critical to complete a successful design of any offshore structure. Field measurements are crucial in order to confirm the numerical modelling methods used in design. Normally, free-wave components are used as inputs for analytical predictions of responses of offshore platforms. The paper discusses a method for resolving incident free-wave components from wave elevations measured around a spar offshore platform. The importance of the process is proven using full-scale measurements of motions for the Boomvang Truss Spar. The study also presents a comparison between the full scale data and analytical predictions. Two events were selected for analysis, and particular attention was placed on responses from high frequency waves. Results reveal an excellent match between the measured and analytically predicted spar responses when the measured waves are adequately decomposed into incident free-wave components and inserted into the numerical model.