# Check Elems Panel

Use the Check Elems pane to verify the basic quality of your elements, as well as the geometric qualities of those elements.

Location: Tool page

Each subpanel displays quality checks of a specific type, depending on dimensionality, time steps, and so forth. Each check is listed on a green command button; clicking the button performs a check and the results are summarized in the status bar.

Criteria that you edit will be preserved even if you navigate to a different subpanel and then back again. However, criteria on different subpanels do not relate to each other, so changing the length requirement on the 1-d subpanel does not change the length requirement on the 2-d subpanel.

Different checks are supplied to review the quality measurements of different types of elements. For example, if you have created a quad, it is possible that the quad has some degree of warpage. You can use the warpage function to check the element for warpage and to specify the maximum allowable warpage for that element.

Another check available is for rigid loops. Use rigid loops to determine if a group of 1D rigid elements forms a loop. After it checks for instances where this has occurred, it highlights the elements that failed the test.
Note: HyperMesh treats second-order elements just like first-order elements for the majority of these checks. However, Jacobian and Chordal Deviation checks will return slightly different results for second-order elements than they will for first-order ones. For example, second-order elements may produce less chordal deviation, but might also produce a worse Jacobian value.

## 1-d Subpanel

Use the 1-d subpanel to check for free ends in one-dimensional elements, to determine if a group of one-dimensional elements forms a loop, or to check rigid elements for conditions causing double dependency.
Option Action
free 1-d nodes Check for free nodes (not connected to another mesh) at the ends of 1D elements.
rigid loops Check 1D rigid elements for rigid loops.

1D rigid elements that build loops are highlighted. Rigid elements are detected as forming a loop if the rigid elements form a closed loop and the dependent node of one rigid serves as independent node of the next rigid in the loop.

If memory requirements are exceeded, reduce the number of displayed rigids.

dependency Check 1D weld and rigid elements for conditions causing double dependency.
include independent nodes 1D elements that share a node (dependent or independent) are considered to fail the check.

When this checkbox is cleared, 1D elements that share the same dependent node are considered to fail this check. Thus a rigid element whose dependent node is an independent node of another rigid element does not fail this check.

length < The elements that have a length less than the value specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or you select another check element function.
length > The elements that have a length greater than the value specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or you select another check element function.

## 2-d Subpanel

Use the 2-d subpanel to check elements for warpage, aspect ratio, skew, chordal deviation, and jacobian ratio. You can also check the maximum and minimum interior angles of quad and tria elements in this panel.
Option Action
warpage The amount by which an element or element face (in the case of solid elements) deviates from being planar. Warpage of up to five degrees is generally acceptable.
aspect The ratio of the longest edge of an element to its shortest edge. Aspect ratio should be less than 5:1 in most cases.
skew Skew in trias 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. Ninety degrees minus the minimum angle found is reported as the skew.

Skew in quads is calculated by finding the minimum angle between two lines joining opposite mid-sides of the element. Ninety degrees minus the minimum angle found is reported.

chord dev Check elements for chordal deviation.
cell squish Non-orthogonality of an element with respect to its faces for 3D elements or edges for 2D elements.
${\mathrm{max}}_{i}\left[1-{A}_{i}*{r}_{i}/|{r}_{i}|\right]$
2D elements
${A}_{i}$ = unit vector, normal to cell edge i
${r}_{i}$ = vector connecting the cell centroid and the middle edge i
3D elements
${A}_{i}$ = unit area vector, normal to cell edge i
${r}_{i}$ = vector connecting the cell centroid and the centroid of face i
length > The elements that have a length greater than the values specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or your select another check element function.
length < The elements that have a length less than the values specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or your select another check element function.
jacobian A measure of the deviation of an element from an ideally shaped element. The Jacobian value ranges from 0.0 to 1.0, where 1.0 represents a perfectly shaped element. However, Jacobian values of 0.7 and above are generally acceptable. The determinant of the Jacobian relates the local stretching of the parametric space required to fit it onto global coordinate space. HyperMesh evaluates the determinant of the Jacobian matrix at each of the element's integration points (also called Gauss points), and reports the ratio between the smallest and the largest.
equia skew Opens the equiangle skew utility. This utility is used to find the number of elements among those displayed that have a normalized equiangle skew larger than the value specified. The normalized equiangle skew is defined as:
area skew The deviation of an element with respect to an “optimal” element.

A circle is generated through the three corner points of the actual triangle. This circle defines a ideally shaped tria elements, from which the area is computed, A_ideal. The area from the actual triangle is computed as well, A_actual. The area skew is defined as: Area skew = (A_ideal-A_actual) / A_ideal.

taper Taper ratio for quadrilateral elements 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.
HyperMesh then finds the smallest ratio of each of these triangular areas to ½ the quad element’s total area (in Figure 1, "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.
$taper=1-{\left(\frac{{A}_{tri}}{0.5×{A}_{quad}}\right)}_{\mathrm{min}}$

Triangles are assigned a value of 0, in order to prevent HyperMesh from mistaking them for highly-tapered quadrilaterals and reporting them as "failed".

trias: min angle Minimum allowable interior angle for a tria element. Any element for which any interior angle falls below the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
trias: max angle Maximum allowable interior angle for a tria element. Any element for which any interior angle is greater than the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
quads: min angle Minimum allowable interior angle for a quad element. Any element for which any interior angle falls below the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
quads: max angle Maximum allowable interior angle for a quad element. Any element for which any interior angle is greater than the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.

## 3-d Subpanel

Use the 3-d subpanel to check tetra elements by various measures.
Option Action
warpage The amount by which an element or element face (in the case of solid elements) deviates from being planar. Warpage of up to five degrees is generally acceptable.
aspect The ratio of the longest edge of an element to its shortest edge. Aspect ratio should be less than 5:1 in most cases.
skew Skew in trias 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. Ninety degrees minus the minimum angle found is reported as the skew.

Skew in quads is calculated by finding the minimum angle between two lines joining opposite mid-sides of the element. Ninety degrees minus the minimum angle found is reported.

tet collapse Tetra elements whose collapse value falls below the value specified are highlighted when the tetra collapse function is selected. These elements remain highlighted until the Check Elems panel is exited.

Tetra collapse calculation: At each of the four nodes of the tetra, the distance from the node to the opposite side of the element is divided by the square root of the area of the opposite side. The minimum value found is normalized by dividing it by 1.24, and then reported. As the tetra collapses, this value approaches 0.0. For a perfect tetra, this value is 1.0.

cell squish Non-orthogonality of an element with respect to its faces.
$1-\left(A\cdot {r}_{c}\right)/|{r}_{c}|$
• $A$ = face unit area vector
• $|{r}_{c}|$ = 2D elements: vector connecting the adjacent cell centroids
• 3D elements: vector connecting the cell centroids and the cell face centroid
orthogonality Checks normalized orthogonality for cells. Calculated as minimum orthogonality within cell faces and across neighboring cell faces:
Within cells
Normalized dot product of the area vector of a face and ve3ctor from centroid of the face.(1)
$\frac{\stackrel{\to }{Ai}\cdot \stackrel{\to }{f}i}{\left|\stackrel{\to }{A}i\right|\left|\stackrel{\to }{fi}\right|}$
Across cells
Normalized dot product of area vector of a face and vector from centroid of cell to neighboring cell centroid.(2)
$\frac{\stackrel{\to }{Ai}\cdot \stackrel{\to }{c}i}{\left|\stackrel{\to }{A}i\right|\left|\stackrel{\to }{ci}\right|}$
The minimum of the above is considered the orthogonality value of the cell. Worst cells have orthogonality close to 0 and good cells have orthogonality close to 1.(3)
$orthogonality_3d=\mathrm{min}\left\{\frac{\stackrel{\to }{Ai}\cdot \stackrel{\to }{f}i}{\left|\stackrel{\to }{A}i\right|\left|\stackrel{\to }{fi}\right|},\frac{\stackrel{\to }{Ai}\cdot \stackrel{\to }{c}i}{\left|\stackrel{\to }{A}i\right|\left|\stackrel{\to }{ci}\right|}\right\}$
length > The elements that have a length greater than the values specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or your select another check element function.
length < The elements that have a length less than the values specified are highlighted when the length function is selected. These elements remain highlighted until you exit the Check Elems panel or your select another check element function.
jacobian A measure of the deviation of an element from an ideally shaped element. The Jacobian value ranges from 0.0 to 1.0, where 1.0 represents a perfectly shaped element. However, Jacobian values of 0.7 and above are generally acceptable. The determinant of the Jacobian relates the local stretching of the parametric space required to fit it onto global coordinate space. HyperMesh evaluates the determinant of the Jacobian matrix at each of the element's integration points (also called Gauss points), and reports the ratio between the smallest and the largest.
equia skew Opens the equiangle skew utility. This utility is used to find the number of elements among those displayed that have a normalized equiangle skew larger than the value specified. The normalized equiangle skew is defined as:
vol skew Tetra elements whose volumetric skew measurement exceeds the value specified are highlighted when the volumetric skew function is selected. These elements remain highlighted until the Check Elems panel is exited.

Volumetric skew calculation: A sphere is fit through the four nodes of the tetra. That sphere defines an ideally shaped equilateral tetra, whose volume is $8{r}^{3}/\left(9\sqrt{3}\right)$ . The actual volume of the tetra element is then calculated.

The element's volumetric skew is then (Videal -Vactual)/Videal. This measure will, normally, equal the skew measure from Tgrid, and equal 1 minus the equivalent check in Abaqus.

vol AR Elements whose Vol AR measurement exceeds the value specified are highlighted when the Vol AR function is selected. These elements remain highlighted until you exit the Check Elems panel.

Vol AR calculation for tetrahedral elements: The longest edge of the tetrahedron is found first, then the shortest altitude of the tetrahedron is found. The element's Vol AR, then, is the length of the longest edge divided by the length of the shortest altitude. For other types of 3D elements, the ratio of the longest to the shortest edge is reported.

tria faces: min angle Minimum allowable interior angle for a tria element. Any element for which any interior angle falls below the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
tria faces: max angle Maximum allowable interior angle for a tria element. Any element for which any interior angle is greater than the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
quad faces: min angle Minimum allowable interior angle for a quad element. Any element for which any interior angle falls below the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
quad faces: max angle Maximum allowable interior angle for a quad element. Any element for which any interior angle is greater than the specified value is highlighted and remains highlighted until you exit the Check Elems panel or you select another check.
neighbor size ratio Checks volume ratio to find abrupt transitions in volume mesh. Calculated as the ratio of minimum volume among a given cell and neighboring cell to maximum volume among given cell and neighboring cell. Ideal value depends on growth at which volume mesh is growing. Values less than 0.2 may indicate an abrupt transition.(4)
$\text{size_ratio_3d}={\left(\frac{\mathrm{min}\left(Vnei,Vown\right)}{\mathrm{max}\left(Vnei,Vown\right)}\right)}^{1/3}$

## Time Subpanel

Use the time subpanel to determine the approximate minimum time step for explicit solvers based on element dimensions. Additionally, the added mass required to achieve the desired minimum time step can be displayed as a contour plot on the model.

The time (timestep) subpanel includes columns for failure criteria and minimum values for each criteria. Enter the desired minimum solver timestep in the failure criteria column. When the check is performed, the calculated minimum timestep for the different element types will be displayed in the minimum value column. Rows in the table represent the different classes of elements by dimension; springs, beams, shells, solids, and thick shells.
Option Action
shells and solids, springs and beams, all types Select the type of elements to check.

Checks can be carried out separately for shell and solid elements, for spring and beam elements, or all element types.

display added mass Plot a contour indicating the amount of required added mass to achieve the minimum time step specified in the failure criteria.

To be used with the assign plot display plot.

## User Subpanel

Use the user subpanel to specify a template file that checks for any type of user quality. If an element does not pass the quality check, the template command *markfailed() is used. Any elements that fail (using *markfailed) are highlighted in the modeling window.
Option Action
template Select a template file.
filename Select an output file.
all, displayed Use this toggle to limit the check to those elements displayed on the screen, or all elements in the model.

## Command Buttons

Button Action
connectivity Test the connectivity of a group of elements.

2D elements that share more than one edge (two connecting nodes form an edge of a first order element; two corner nodes and one mid-side node form an edge of a second order element) with another two-dimensional element are highlighted.

3D elements that share more than one face with another three-dimensional element are highlighted.

Any elements where there are mid-side nodes connected to corner nodes are highlighted.

This operator can be used to find duplicate elements.

duplicates Check for duplicate elements.

If an element is duplicated, the elements involved are highlighted, except for the element with the lowest ID.

Duplicates can be deleted by clicking save failed and then retrieving the user mark (using extended entity selection) in the Delete panel. The saved (failed) elements can be accessed in any other panel using the retrieve option in the extended entity selection menu.

settings Open the Check Element Settings dialog.
save failed Save failed elements and replace them on the user mark.

When you use this function, elements that were previously on the user mark are replaced. Once the failed elements have been saved, the user mark can be loaded into other panels.

The saved (failed) elements can be accessed in any other panel using the retrieve option in the extended entity selection menu.

standard, assign plot, histogram Select a view mode, then click the green button for the desired check to activate the view.
standard (default)
Elements that exceed the specified criteria are highlighted.
assign plot
Create a color-coded view of the model, with each element or contour bearing a color based on how well or poorly it conforms to the selected check criterion. Visual options alter the rendering style (hidden line or wireframe), color method (by element or by contour), model lighting, and mesh line visibility. Create a cutting plane to view a cross-section of the model.
histogram
Graph the percentage of elements on the X axis and their deviation from the specified criterion on the Y axis. Click reset visual to clear the graph and return it to the model view.
execute Run a check based on the template and filename specified.
preview unused Locate and display all interface elements defined in the model that are not attached to any normal elements.
delete unused Delete all interface elements defined in the model that are not attached to any normal elements.
reject Undo the most recent deletion.
reset visual Clear the histogram and return to the normal view of the model.
return Exit the panel.