Many of the methods to check and edit mesh are based around determining mesh quality, but others check for mesh penetration,
detect holes, and locate edges or features.
Use the Normals tool to display and reverse the normals of elements or surfaces. The orientation of element normals can also be adjusted.
The normal of an element is determined by following the order of nodes of the element using the right-hand rule.
The quality of elements in a mesh can be gauged in many ways, and the methods used often depend not only on the element
type, but also on the individual solver used.
HyperWorks includes some alternate methods of calculating certain element types, which only apply to quads or rectangular faces
of solids, and only include alternate checks for Aspect Ratio, Skew, Taper and Warpage.
For the most part, OptiStruct uses the same checks as HyperMesh. However, OptiStruct uses its own method of calculating Aspect Ratio, and it does not support 3D element checks.
Use the Criteria legend to investigate the model via individual criteria and view a breakdown of all failed and worst
elements based on a set QI range. This is useful when you want to resolve criteria violations and evaluate the overall
quality of a mesh.
Use the Replicate tool to replicate a mesh from one location to another, with options to keep the original mesh, as
well as to replicate into multiple copies. The replicated elements replace the original elements, maintaining relevant
information like properties, thicknesses, and other solver attributes.
Locally refine 2D elements and attached 1D elements using either the Auto Quads tool, the Box tool, or the Manual tool. These are most useful for aerospace and marine applications, where specific transition patterns are required
from the refined mesh to the existing mesh.
Use the Detach tool to detach elements from the surrounding structure. You can detach elements from a portion of your model so that
it can be translated or moved, or you can offset the new nodes by a specified value. You can also use this panel
to detach and remove elements from your model.
Use the Imprint/Extend tool to extend a mesh to meet another mesh and form a good connection between them, or to imprint overlapping meshes
so that they match one another.
Associate nodes to a point, line, or surface/solid face; move nodes along a surface; place a node at a point on a
surface; remap a list of nodes to a line; or project nodes to an imaginary line passing through two nodes.
Use the Split panel to split plates or solid elements. In addition, hexa elements can also be split using a technique
that moves progressively through a row of elements in the model
Stitch two unconnected meshes by adding elements between them, split elements at weld locations, and combine and split
elements to fix connectivity in the transitional area between fine and coarse mesh areas.
Perform a model-based CAD-CAD, CAD-FE or FE-FE comparison between two models, or two selections of entities, and find
and report geometrical/shape differences.
Many of the methods to check and edit mesh are based around determining mesh quality, but others check for mesh penetration,
detect holes, and locate edges or features.
The quality of elements in a mesh can be gauged in many ways, and the methods used often depend not only on the element
type, but also on the individual solver used.
When possible, HyperWorks 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"). HyperWorks uses the same method
used for the Length (min) check.
For 3D elements, each face of the element is treated as a 2D element and
its aspect ratio determined. The largest aspect ratio among these faces
is returned as the 3D element’s aspect ratio.
Aspect ratios should rarely exceed 5:1
Chordal Deviation
Largest distance between the centers of element edges and the associated
surface.
Second order elements return the same chordal deviation as first order,
when the corner nodes are used due to the expensive nature of the
calculations. Figure 1. Chordal Deviation
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.
The Jacobian value ranges from 0.0 to 1.0, where 1.0 represents a
perfectly shaped element. The determinant of the Jacobian relates the
local stretching of the parametric space which is required to fit it
onto the global coordinate space.
HyperWorks evaluates the determinant of the Jacobian
matrix at each of the element’s integration points (also called Gauss
points) or at the element’s corner nodes, and reports the ratio between
the smallest and the largest. In the case of Jacobian evaluation at the
Gauss points, values of 0.7 and above are generally acceptable. You can
select which method of evaluation to use (Gauss point or corner node)
from the Check Element settings.
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".
Figure 2. Length Check
You can choose which method to use in the Check Element
settings.
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.
For triangular elements, for each corner node (i), HyperWorks calculates the closest
(perpendicular) distance to the ray including the opposite
leg of the triangle, h(i). MNH = min(hi) * 2/sqrt(3.0). The
scaling factor 2/sqrt(3.0) ensures that for equilateral
triangles, the MNH is the length of the minimum side. Figure 3. Minimal Normalized Height for Triangular
Elements
For quadrilateral elements, for each corner node, HyperWorks calculates the closest
(perpendicular) distances to the rays containing the legs of
the quadrilateral that do not include this node. The figure
above depicts these lengths as red lines. Minimal normalized
height is taken to be the minimum of all eight lines and the
four edge lengths, thus, the minimum of 12 possible
lengths. Figure 4. Minimal Normalized Height for Quadrilateral
Elements
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. Figure 5. Skew of Triangular Elements
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. Figure 6. Taper for Quadrilateral Element
These areas are then compared to one half of the area of the
quadrilateral.
HyperWorks then finds the smallest ratio of each of
these triangular areas to ½ the quad element’s total area (in the
diagram above, "a" is smallest). The resulting value is subtracted from
1, and the result reported as the element taper. This means that as the
taper approaches 0, the shape approaches a rectangle.
Triangles are assigned a value of 0, in order to prevent HyperWorks from mistaking them for highly-tapered
quadrilaterals and reporting them as "failed".
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.
Warpage of up to five degrees is generally acceptable. Figure 7. Warpage
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.
HyperWorks calculates the closest
(perpendicular) distances to the planes formed by the
opposite faces for each corner node. Figure 8.
The resulting minimum length/size is the minimum of all such measured
distances.
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. Figure 9.
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 HyperWorks 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.
The shape factor for a tetrahedral element is determined by dividing the
element’s volume by the volume of an ideal (equilateral) tetrahedron of
the same circumradius. In the case of tetrahedral elements, the
circumradius is the radius of a sphere passing through the four vertices
of the tetrahedron. Figure 10.