CFD Predictions Including Verification and Validation of Hydrodynamic Forces and Moments on Ships in Restricted Waters
Lu Zou
PhD Thesis. Chalmers University of Technology, 2012
Abstract
The evaluation of ship manoeuvrability is of significance at the initial design stage, as inappropriate manoeuvring performance may result in unstable ship motion, difficulties in steering and even marine accidents. Restricted waters, with the presence of solid boundaries of the flow field, such as a shallow seabed below the hull, a side bank in the vicinity of the hull or another hull nearby, complicate the flow field and introduce an influence on hydrodynamic forces and moments acting on the hull. Such restricted water effects are essential for the ship manoeuvring or navigation. The traditional prediction tools for ship manoeuvring, i.e. model tests, can provide direct and reliable predictions of the hydrodynamic forces and moments in restricted water, but it is expensive and time-consuming, and most importantly, the flow field is seldom measured. Computational Fluid Dynamic (CFD) on the other hand, greatly promoted in the past decade, has the capacity to provide details in the restricted flow field and can help to understand the mechanism of restricted water effects. However, the application of CFD methods is still limited and the accuracy obtained is always a concern. In this thesis, the hydrodynamic forces and moments acting on tanker hulls are predicted by a Reynolds-Averaged Navier-Stokes (RANS) solver, including the influence from asymmetric flows (drift angle), shallow water (water depth), canal banks (ship-bank distance) and a longitudinally or transversely approaching ship (ship-to-ship interaction). In addition, a formal verification and validation (V&V) procedure is applied to understand and control the numerical and modelling error in the computations. The general results are promising compared with the experimental measurements, as the current RANS method predicts the hydrodynamic quantities and trends qualitatively well. Moreover, an investigation of modelling errors indicates possible ways to obtain improved predictions. The flow field analyses further provide valuable insight into the restricted-water effects and help the understanding of the mechanism of those effects.