Adaptive grid refinement for unsteady ship flow and ship motion simulation

The method has been made as general and flexible as possible, so that it can be used in daily practice for the realistic applications of this commercialised flow solver.

An adaptive grid technique has been developed for the FINE™/Marine flow solver, the unstructured finite-volume RANS code created by EMN (CFD Department of the Fluid Mechanics Laboratory). The method has been made as general and flexible as possible, so that it can be used in daily practice for the realistic applications of this commercialised flow solver.

The method is based partially on earlier work by A. Hay [3], an initial version was presented at NuTTS 2008 [8].

One of the major developments with respect to last year has been the full integration of the grid refinement method in the FINE™/Marine flow solver; before, it was run as a separate program. As this integration has made the grid refinement method much faster than before, it is now feasible to adapt the grid often to a flow solution in evolution. This in turn has opened the way for a new application of the method: unsteady flows.

The principle of adaptive grid refinement is ideal for unsteady ship flows. The flow around a ship contains many phenomena that are highly localised in space: notably the water surface, but also the vorticity shed from the ship’s hull that determines the aft-body flow. These phenomena require locally fine grids to be resolved well. And for unsteady flow, their positions change in time; therefore, a non-adapted grid must be fine in all the positions

where the local phenomena will ever be during the simulation. Adaptive refinement, on the other hand, can place the fine grid only there where the flow features are now, and change the grid as the flow evolves. Thus, a great reduction of the total number of cells is possible.

This paper shows the use of our adaptive grid refinement method for unsteady flows. Section 2 gives a brief introduction to the flow solver and the refinement method. Then section 3 explains, in more detail, three aspects of the method that are fundamental for unsteady flow. Finally, in section 4, the method is applied to different unsteady flow test cases.

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