Mesh Quality Checks

Aspect Ratio Check

For a solid mesh, you achieve the best numerical accuracy with a mesh that has uniform perfect tetrahedral elements whose edges are equal in length. For a general geometry, you cannot create a mesh of perfect tetrahedral elements.

Because of small edges, curved geometry, thin features, and sharp corners, some of the generated elements can have much longer edges than others. When the edges of an element differ in length substantially, the results are less accurate.

The aspect ratio of a perfect tetrahedral element is used as the basis for calculating aspect ratios of other elements. The aspect ratio of an element is the ratio between the longest edge and the shortest normal dropped from a vertex to the opposite face, normalized with respect to a perfect tetrahedral.

By definition, the aspect ratio of a perfect tetrahedral element is 1.0. The aspect ratio check assumes straight edges connecting the four corner nodes. The software calculates the aspect ratio to check the mesh quality.

Example

Element with aspect ratio close to 1.0	Element with large aspect ratio

Jacobian Ratio Check

Available for second order mesh elements (high quality solid and shell mesh).

The Jacobian ratio measures the deviation of an element’s shape from an ideally shaped element (one that has straight edges with equal lengths). The Jacobian ratio of a perfect second order tetrahedral element with linear edges is 1.0. The Jacobian ratio of an element increases as the curvature of the element edges increases to map a curved geometry.

Near extremely sharp or curved boundaries, the edges of an element can cross over each other and the element becomes distorted, resulting in self-intersecting geometry. Distorted elements have a negative Jacobian ratio and produce inaccurate results.

In the Mesh PropertyManager, the Issue warning for distorted elements option alerts you if there are distorted elements in the mesh. To remove distorted elements, first check the model for any geometry irregularities. Refine the mesh in areas where distorted elements exist.

The Jacobian ratio check considers the Gaussian points located within each element. The default value in a new study is 16 Gaussian points.

A good quality mesh has a Jacobian ratio between 1 and 10 for the majority of its elements (90% and above). Create a Mesh Quality Plot to plot the Jacobian ratio.