Chimera RANS simulation of unsteady three-dimensional flows induced by berthing ships

A chimera Reynolds Averaged Navier-Stokes (RANS) method has been developed for the simulation of unsteady fluid flow induced by a ship approaching a berthing structure. The method solves the mean flow and turbulence quantities on embedded, overlapped, or matched grid blocks. The unsteady RANS equations are formulated in an earth-fixed reference frame and transformed into general curvilinear, moving coordinate systems. A chimera domain decomposition technique is employed to handle relative motions among different grid blocks, including free surface grids. This generalized method can be used to evaluate two and three-dimensional, laminar and turbulent unsteady flows, with free surface and relative motions among different components of a system.; The mean flow and turbulence quantities along the block boundaries are interpolated using the interpolation coefficients. Relative motions between the ship and the harbor lead to the changes of interpolation coefficients. The PEGSUS program is used to find the interpolation coefficients for interpolations among different grid blocks at each time step. In order to reduce CPU time, the independent PEGSUS program is extensively modified and integrated into the RANS solver as a subroutine, resulting in an at least ten fold saving in CPU time for a CRAY supercomputer, compared with that of the separate executions of the PEGSUS and the RANS programs. This is obtained through improved efficiency in data exchanges between the integrated PEGSUS program and the RANS solver. When executed separately, it leads to excessive CPU time for data communications between these two programs through the hard disk.; To account for free surface effects, a free surface solver is incorporated into the chimera RANS program. A user defined, free surface connection table is introduced for specifying the arrangement of free surface grids, which are taken from the volume grids, and associated boundary conditions. A two-dimensional chimera scheme is developed for free surface chimera grids, using the linking information provided by the user defined, free surface connection table.; To demonstrate the feasibility of the method, the berthing behavior of a 2D barge hull form is first investigated with prescribed translational motion. Good results are obtained. The method is then extended to simulate the berthing behavior of a 3D barge in translational motion, excluding and including free surface effects. Comparison is made between the numerical and experimental results for a model-scale barge to further validate the method for predicting ship berthing behavior, and good agreement is achieved. Finally, the method is employed to simulate the berthing operation of a practical ship, DDG-51 guided missile destroyer, in combined lateral, oblique and rotational motions.; The numerical solutions obtained successfully capture several important phenomena of unsteady flows around a berthing ship, such as the underkeel flow acceleration, separation in the wake region behind the ship path, cushioning effect between the ship and the harbor quay wall, and the complex interaction among the bow, shoulder, and stem wave systems.