It is not uncommon for the mesh to become folded (or tangled) during the mesh deformation process. When this occurs, a message indicating the existence and location of either negative sector volumes or negative (that is, topologically invalid) elements is written to the CFX-Solver Output file. Notification of negative sector volumes highlights the existence of non-convex mesh elements that still have a positive volume. Although the existence of negative sector volumes is not a fatal condition, it does indicate that:
Mesh elements are only barely positive
Further mesh deformation is likely to yield elements with negative volumes, which is a fatal condition
Some of the most common causes for mesh folding during deformation are identified in the following sections.