Validation of a distributed simulation of ship replenishment at sea with model tests

Abstract

A simulation of ship motions during replenishment at sea was validated using dedicated model test data. Motions of the supply ship and receiving ship are influenced by hydrodynamic forces and forces from replenishment gear used to transfer payloads. Simulated entities include rudders and propellers, with associated controllers. The composite simulation was implemented as a distributed simulation using the high-level architecture. An experimental model test program was developed for a tanker and destroyer conducting replenishment in head seas at a speed of 15 knots. The simulation gives generally good agreement with the model tests for heave, roll, and pitch motions, with some noted exceptions. For dynamic positioning of the destroyer relative to the tanker, there is very good agreement for mean values but underprediction of lower frequency sway and yaw motions. The variation of heave and roll motion accuracy is likely due to the hydrodynamic force prediction method using the frequency domain Green function for zero forward speed, thus not accurately modelling the propagation of radiated and diffracted waves between vessels. Prediction of viscous roll forces using semi-empirical methods likely contributed to differences between simulated and model test roll motions. The underprediction of lower frequency sway and yaw motions for the destroyer in waves could be caused by the ship motion predictions not including second-order wave drift forces.