Modelling Thruster-Hull Interaction with CFD

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.