A combined volume of fluid and immersed boundary method for simulations of ship bow breaking waves

Abstract

The study of breaking bow waves has significant benefits due to its influence in many aspects. The consequences caused by breaking bow waves include, but are not limited to, the increase of resistance, increased detectability and damage to port facilities. Analytic studies are not suitable for this problem because of over-simplified model. Present experimental studies are costly and not robust. This thesis presents a new two-phase flow solver for the analysis and prediction of complex ship flows through an investigation of bow breaking waves and builds an air-water boundary layer model to overcome the discontinuity over the two-phase interface. A combined volume of fluid and immersed boundary method is developed to simulate two-phase flows with high density ratio. The problems of discontinuity of density and momentum flux are known to be challenging to handle in simulations. In order to overcome the numerical instabilities encountered near the interface, an extra velocity field is designed to extend the velocity of the heavier phase into the lighter phase and to enforce a new boundary condition near the interface, which is similar to non-slip boundary conditions in Fluid-Structure Interaction (FSI) problems. The interface is captured using a Volume of Fluid (VOF) method, and a new boundary layer is built on the lighter phase side by an immersed boundary method. The accuracy of the new method is validated by a wide range of test cases relevant to ship wave flows. The results of the new solver are compared with the original VOF solver, analytical solutions and single-phase flow solver results. The designed boundary layer helps to reduce the spurious velocity caused by the imbalance of dynamic pressure gradient and density gradient and to prevent the tearing of the interface due to the tangential velocity between the two phases across the interface. It is shown to improve the robustness and stability of two-phase flow simulations, and higher accuracy can be obtained on a relatively coarse grid compared to the original VOF method. The new solver is used to study bow breaking waves generated by a wedge-shape bow and KRISO Container Ship (KCS). The numerical results of velocity components and axial vorticity at different locations in the vicinity of the bow show that the new solver can predict well the vortical cross flow associated with the overturning bow wave.

More information

Identifiers

ORCID for Dominic Hudson: orcid.org/0000-0002-2012-6255

Catalogue record

Export record