The Eulerian part instance that is used by the volume fraction tool must be the same instance to which materials are assigned. The Eulerian part must be meshed before using the volume fraction tool. You should not edit the part mesh after creating the discrete field, as the element numbering in the discrete field may not conform to the elements in the updated mesh.

The reference part instance used by the volume fraction tool can include unmeshed geometry, a native mesh, or orphan elements; deformable, Eulerian, and discrete rigid parts are all allowed. The volume fraction tool always uses the mesh representation (if available) of the reference part instance when calculating the discrete field; if the reference instance is partially meshed, only the meshed portion of the instance is considered in the volume fraction calculation. The mesh on the reference instance should be fine enough to capture all important geometric details in the subsequent material assignment.

The reference part instance must be either a three-dimensional solid or a fully enclosed three-dimensional shell. The faces of a shell enclosure must define a single, continuous surface; features that create T-intersections with the surface faces (such as ribs or interior dividing panels) are not allowed (see Figure 28–9). An Eulerian element is considered to be inside a shell reference instance if it lies within the volume enclosed by the shell surface.