Numerical modelling of the muddy layer effect on Ship's resistance and squat

Abstract The increasing use of maritime transport has led to an increase in ship size. However, the dimensions of channels and harbours cannot follow the expansion rate of ships. Large ships will experience shallow water effects such as the bottom effect more severely, which plays an important role in the manoeuvrability and the stability of ships. To reduce navigational restriction in estuary environment and close to ports, the World Association for Waterborne Transport Infrastructure (PIANC) established the concept of the nautical bottom. Using this concept, ships can navigate with both small and negative under keel clearance (UKC) relative to the water-mud interface. Hence, the aim of this work, is to conduct a numerical investigation in order to study the influence of the muddy seabed on the ship's manoeuvrability especially on the ship's resistance and squat. Accordingly, a 3D Computational Fluid Dynamics (CFD) model based on the Volume of Fluid (VoF) method was used to simulate the multiphase flow for various setups. Four parameters were tested: the mud properties, the ship's speed, the mud thickness and the UKC value relative to the water-mud interface. The numerical results of this investigation were in reasonable agreement with experimental data. Through this investigation it was also shown the performances of the CFD method to simulate setups difficult to achieve in towing tank.