Overset Topology

If overset boundary is not closed, overset hole-cutting algorithm requires an additional guidance to detect which parts should remain active.

When the overset boundaries form a closed surface, the algorithm can detect the overset assembly automatically. However, when the overset boundary does not form a closed outer surface, you set up an additional overset topology for the overset regions.

The following overset topology methods are available:

Automatic

The default option rely on the overset hole-cutting process to assemble the regions connected through overset interfaces.

Piston

Select this option to simulate a piston within a cylinder configuration where only an open piston surface is defined as an overset boundary. The option requires you to provide a direction in which the background mesh remains active, in the perspective of the overset boundary. A typical topology of such a configuration is shown below:

Viewed from the overset boundary, the cells above the overset boundary, in the direction +z, remain active.

After assigning a translational displacement to the overset region, the mesh motion is demonstrated as follows:

Direction

This is an expert option. Select this option only if you wish to simulate a situation where the overset boundary does not completely enclose any void in the overset region and this boundary is curved strongly at the same time. The remaining parts of the enclosing surface consist of wall or symmetry boundaries coinciding with respective boundaries of the background mesh.

A typical topology of such a configuration is shown below:

Boundary Conditions in the Background Region:

Boundary Conditions in the Overset Region:

After successful hole-cutting:

After assigning a rotation around Z axis to the overset region, the mesh motion is demonstrated as follows:

Note	Here, the hole-cutting algorithm requires the direction in which the overset boundary is closed. For this example, this direction is the +Y direction.

Bounded

This is an expert option. Select this option only if you wish to simulate a situation where you have meshless space within your overset region that is bounded by a wall boundary of the background region.

The following diagram shows an example (pigging case) of such a configuration:

The overset region (grey) slides inside the background region (blue) cylinder. The overset region is bounded by overset boundaries (red) and wall boundaries. The meshless space of the overset region is bounded by the wall boundary of the background region.