4.2.1. Tank

A trimmed mesh has been chosen due to the possibility to create anisotropic cells which provide a predominantly hexahedral mesh with minimal cell skewness, it results as the best discretization at the interface between the two fluids. It is worthwhile to remark that wave reflection can occur also when the mesh size suddenly changes. To avoid this problem, usually three different volumetric sea surface refinements are used in order to gradually coarsen the mesh, as shown from a prospective-side view in Figure 4 and side-view in Figure 5.

**Figure 4.** Sea surface refinements in prospective view.

**Figure 5.** Sea surface refinements in side-view.

The wave damping should start before the coarsest grid level is reached since such a change in cell size is a potential source of reflection that should be included in the damping zone [28].
