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The application of CFD for the analysis of thruster interactions effects (or degradation effects) is still a largely unexplored area. Quantifying these effects is essential to the design of dynamic positioning (DP) vessels. Presently, thruster interactions can be quantified using data available from literature, which unfortunately is often scarce, too general or not applicable to specific designs. Dedicated model tests, on the other hand, do provide detailed results but are relatively expensive and tend to become available relatively late in the design process. Alternatively, with CFD different vessel designs and thruster layouts can be investigated for thruster interaction effects in a cost-efficient manner early in the design process. This paper presents a practical method for modelling thrusters, describing the propeller blades as an actuator disk. Numerical choices for the calculations are discussed and steady state calculations are performed. This approach is evaluated on thruster-hull interaction cases in both bollard pull and under current conditions, for a series of configurations with increasing complexity: a thruster in open water, a thruster positioned under a flat plate and a thruster under a barge. A comparison to experimental results is presented for the flow field (against PIV experimental data) and forces on the thrusters and hull of the vessel. A modern Verification and Validation procedure is used to quantify uncertainties. The results are encouraging, both in a qualitative and quantitative sense. In this context, the modelling approach employed proves to be a robust and accurate solution, with low computational effort, and therefore appropriate to be used for much more complex real applications.

Flow-Induced Motions (FIM) are an issue for floating offshore structures, such as multi-column platforms, as the phenomenon can decrease the fatigue life of the mooring, riser, and cable systems. The new concept of Floating Offshore Wind Turbines (FOWT) have a multi-column design that may be subjected to FIM. In the past, FIM was studied mainly for Oil & Gas platforms installed in deep waters. However, the FIM phenomenon of FOWT has been insufficiently explored. To rectify this, model tests were performed for the Semisubmersible (SS) Floating System design developed for the DeepCwind project (OC4 Phase II). This paper will investigate the presence of FIM and show its importance in the design process of FOWT. Three different incidence angles of the current were tested, namely 0, 90, and 180 deg. For each heading, thirty reduced velocities were tested, across the range 8,000<Re<70,000. The results showed amplitudes in the transverse direction of around 70% of the diameter of the platform column, which is similar to those observed for deep-draft (DD) SS with circular columns. Note that these amplitude values are larger for a floater with a circular column, than for a platform with square columns. The results showed that as FIM occurred for this specific FOWT SS, its effect has to be considered in the mooring system and electric cable design.