Predicting Wind Loads on Typical Offshore Vessels Using CFD

Within the OO1 and OO2 “Offloading Operability” JIPs, wind-tunnel measurements were carried out to determine the wind loads on a number of vessels, e.g. Membrane (Prismatic) and Moss (Spherical) type LNG Carriers, Shuttle tanker and FPSO. Furthermore, wind velocity measurements were performed in the wake of the FPSO. For all these vessels CFD calculations are carried out using MARIN’s in-house code ReFRESCO. In [9] the sensitivity of the CFD results was investigated for various parameters, such as grid resolution, grid type, flow solver and geometric simplifications. In this paper it is shown that the calculated forces are very dependent on the atmospheric velocity profile used in the calculations. Therefore, different profiles are first compared with the profile measured in the wind tunnel. Then, the development of the profile in the CFD calculations is investigated. Using the appropriate grid resolution and the correct velocity profile, the wind loads on 5 different vessels are calculated for the angles 0 to 180 degrees in steps of 10 degrees. Overall, the calculated force coefficients agree well with the measurements for all vessels. Furthermore, the wind velocity distribution in the wake of the FPSO shows a good agreement with the velocity measurements. The location and shape of the wake are predicted accurately and the calculated velocities show reasonable agreement with the measured velocity distribution. From the results presented in this paper we conclude that with ReFRESCO the wind loads on typical offshore vessels can be predicted with reasonable accuracy in a cost-efficient manner. The accuracy of the calculated velocity fields is such that these can be used in prediction methods to obtain shielding effects on vessels positioned in the wake.