When two vessels are in a side-by-side configuration, the vessel in the wake experiences significantly lower wind forces. This phenomenon is known as shielding and can result in large varying wind forces as a function of the relative position of the vessels. Therefore, it is important to be able to predict and to include the shielding effects in simulations studies in order to ensure safe approach, offloading and departure operations. In this paper, a predictive wind shielding estimation model is applied for side-by-side configuration consisting of a FPSO next to either a shuttle tanker, a prismatic LNGC or a moss type LNGC. The same estimation model has also been successfully applied in earlier studies on vessels in tandem configuration.
The wind force of the shielded vessel alongside the FPSO is estimated by multiplying the volumetric mean wind velocity with the unshielded wind coefficients of the vessel. The volumetric mean wind velocity over the vessel is extracted from the velocity field in the wake of the FPSO when the vessel is not present. It is noticed that the velocity field in the wake is spatially non-uniform, with large differences in both velocity magnitude and direction. Therefore, the shuttle tanker is divided into multiple segments, and for each segment the local velocity and local force coefficient is taken into account. A sensitivity analysis for the number of segments is conducted, ranging from 4 segments up to 56 segments. The shielded wind coefficients from the prediction method compare well with experimental results from wind tunnel tests.
This approach works well for both the tandem and side-by-side operations. The segmented force coefficients and the velocity field in the wake can be obtained as a post processing step from CFD calculations for a single vessel. Therefore, this estimation model can be a very useful approach for time-domain simulations.