# HyperMesh

When possible, HyperMesh CFD checks strive to maintain compatibility with popular solvers.

## 2D and 3D Element Checks

The following checks apply to both types of elements, but when applied to 3D elements
they are generally applied to each face of the element. The value of the worst face
is reported as the 3D element’s overall quality value.

- Aspect Ratio
- Ratio of the longest edge of an element to either its shortest edge or the shortest distance from a corner node to the opposing edge ("minimal normalized height"). HyperMesh CFD uses the same method used for the Length (min) check.
- Chordal Deviation
- Largest distance between the centers of element edges and the associated surface.
- Interior Angles
- Maximum and minimum interior angles are evaluated independently for triangles and quadrilaterals.
- Jacobian
- Deviation of an element from its ideal or "perfect" shape, such as a triangle’s deviation from equilateral.
- Length (min)
- Minimum element lengths are calculated using one of two methods.
- The shortest edge of the element. This method is used for non-tetrahedral 3D elements.
- The shortest distance from a corner node to its opposing edge (or face, in the case of tetra elements); referred to as "minimal normalized height".

Note: This setting affects the calculation of the Aspect Ratio check. - Minimum Length / Size
- Minimum element size is calculated using:
- Shortest edge
- Length of the shortest edge of each element is used.
- Minimal normalized height
- Is a more accurate, but more complex height.
- Minimal height
- The same as minimal normalized height, but without a scaling factor.

- Skew
- Skew of triangular elements is calculated by finding the minimum angle
between the vector from each node to the opposing mid-side, and the
vector between the two adjacent mid-sides at each node of the
element.The minimum angle found is subtracted from ninety degrees and
reported as the element’s skew.Note: Skew for quads is part of the HyperMesh-Alt quality check.
- Taper
- Taper ratio for the quadrilateral element is defined by first finding the area of the triangle formed at each corner grid point.These areas are then compared to one half of the area of the quadrilateral.
- Warpage
- Amount by which an element, or in the case of solid elements, an element face, deviates from being planar. Since three points define a plane, this check only applies to quads. The quad is divided into two trias along its diagonal, and the angle between the trias’ normals is measured.

## 3D Element Only Checks

- Minimum Length / Size
- Two methods are used to calculate the minimum element size.
- Shortest edge
- Length of the shortest edge of each element is used.
- Minimal normalized height
- More accurate, but more complex.

- Tetra Collapse
- The height of the tetra element is measured from each of the four nodes to its opposite face, and then divided by the square root of the face’s area.The minimum of the four resulting values (one per node) is then normalized by dividing it by 1.24. As the tetra collapses, the value approaches 0.0, while a perfect tetra has a value of 1.0. Non-tetrahedral elements are given values of 1 so that HyperMesh CFD will not mistake them for bad tetra elements.
- Vol. Aspect Ratio
- Tetrahedral elements are evaluated by finding the longest edge length and dividing it by the shortest height (measured from a node to its opposing face). Other 3D elements, such as hex elements, are evaluated based on the ratio of their longest edge to their shortest edge.
- Volume Skew
- Only applicable to tetrahedral elements; all others are assigned values of zero. Volume Skew is defined as 1-shape factor, so a skew of 0 is perfect and a skew of 1 is the worst possible value.