Current/Wind Loads and Thruster-Hull Interaction
Calculation of the current and wind loads coefficients and assessment of the thruster efficiency degradation due to thruster-hull interaction using CFD.
Jan De Nul Group required a study of the station-keeping capabilities of two sister supply vessels. For this, blueOASIS calculated the current and wind loads and assessed the thruster efficiency degradation due to thruster-hull interaction using Computational Fluid Dynamics (CFD). All the calculations were made using the CFD solver ReFRESCO.
The current load calculations are carried out for two loading conditions with a constant uniform current velocity of 0.5144 m/s (1 knot), for 19 headings ranging from 0 to 180 degrees, in steps of 10 degrees. In total 38 current load calculations are carried out.
Before proceeding to the final computations, a sensitivity study was carried out to assess the impact on the load coefficients of different wind velocities and the method used to resolve the viscous layer. Taken into account the lessons learned from these sensitivity tests, the wind load calculations were then calculated for the most wind-exposed loading condition with a constant uniform wind velocity of 10 m/s, for 37 headings ranging from 0 to 360 degrees, in steps of 10 degrees.
The thruster-hull interaction calculations were carried out for 36 azimuthal angles ranging from 0 to 350 degrees, in steps of 10 degrees. To simplify the simulations and achieve reasonable CPU time and costs, an Actuator Disk (AD) model was used to replace the rotating blades of the thruster. This model requires a set of calibration simulations using higher fidelity models, which were carried out in open water conditions using only the thruster unit (no vessel hull present).
The resulting coefficients were used as input by Jan De Nul Group on a Dynamic Positioning software for the studied vessels.