Model Tests on a Radial Wellbay Spar in Gulf of Mexico, Norwegian Sea and Offshore Brazil Environments

A model test campaign on a 1:50 scale model of a Radial Wellbay Spar (RAW) Spar was carried out at the OTRC facility in College Station, Texas. The campaign subjected the model to wind, wave, and current environments from the Central Gulf of Mexico, the Norwegian Sea, and offshore Brazil. Time traces of dynamic wind loads were predetermined from computations using drag coefficients and estimated wind load areas of the topsides. A servo controlled line mechanism was used to apply the wind load to the model topsides. Current forces were modeled using static weights connected at the appropriate elevation on the model. Ten (10) top-tensioned risers (TTRs) were modeled in terms of stiffness and top tension using four equivalent model TTRs. Horizontal restoring forces of the prototype mooring were modeled using a four-model line arrangement. The model was instrumented to measure six-degree-of-freedom rigid body motions, air gap around the deck, wave run-up, water elevation in the riser gap in the hard tank, and mooring and TTR tensions. Global loads on an internal structural component between the centerwell device and hard tank were measured in all environments. Data comparisons were based on selected time traces of various responses and Weibull distributions to predict extreme values. In general, good agreement was found between the measured and predicted values.