Nastran and Multiphysics element quality checks

Nastran and Multiphysics perform two different categories of element geometry checks prior to and during the element matrix generation process:

• System element checks, which determine if the element’s geometry is adequate for finite element matrix generation. Nastran always issues a fatal error message if the system checks find a condition that prevents the analysis from proceeding.

• User controlled element checks, which are optional and are controlled in Nastran through the GEOMCHECK executive control statement.

In Pre/Post, you can use the Element Quality dialog box to specify options for both of these different types of Nastran checks.

Nastran system checks

Use the System Checks options in the Element Quality dialog box to set options for the system level checks that Nastran performs.

For more information, see System Element Checks in the Simcenter Nastran User’s Guide.

System Check	Applicable element types	Description
Jacobian Sign	CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8, CTETRA, CHEXA, CHEXCZ, CPYRAM, CPENTA, CPENTCZ, CQUAD4, CQUAD8, CQUADR, CTRIA3, CTRIA6, CTRIAR, CTRAX3, CTRAX6, CQUADX4, CQUADX8, CPLSTN3, CPLSTN4, CPLSTN6, CPLSTN8, CPLSTS3, CPLSTS4, CPLSTS6, CPLSTS8,	Checks the sign (positive or negative) of the Jacobian determinant at the element’s integration points. The sign of the Jacobian determinant for solid elements must be either consistently positive or consistently negative. If the sign is inconsistent, then the element fails the check.You can specify the location for the Jacobian calculation in the Customer Defaults dialog box (Simulation→Pre/Post→Element Quality Check - Nastran, on the Jacobian Integration Points page).
Jacobian Zero	CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8, CHEXA, CHEXCZ, CPENTA, CPENTCZ, CPLSTN3, CPLSTN4, CPLSTN6, CPLSTN8, CPLSTS3, CPLSTS4, CPLSTS6, CPLSTS8, CPYRAM, CQUAD4, CQUAD8, CQUADR, CQUADX4, CQUADX8, CTETRA, CTRAX3, CTRAX6, CTRIAR, CTRIA3, CTRIA6	Calculates the minimum value for the determinant of the Jacobian at all integration points for each element. A well-formed element has a positive Jacobian determinant at each integration point. The Jacobian determinant approaches zero as an element vertex angle approaches 180°.You can specify the location for the Jacobian calculation in the Customer Defaults dialog box (Simulation→Pre/Post→Element Quality Check - Nastran, on the Jacobian Integration Points page).
Volume	CTETRA, CPENTA	Ensures that the elements do not have a negative volume.
Axisymmetric Consistent Y	CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8, CPLSTN3, CPLSTN4, CPLSTN6, CPLSTN8, CPLSTS3, CPLSTS4, CPLSTS6, CPLSTS8, CTRAX3, CTRAX6, CTRIAX6, CQUADX4, CQUADX8	When axisymmetric elements are modeled in the XZ plane, this check ensures that the nodes all lie in the same Y-plane within the tolerance +/- 1.E-6.
Axisymmetric Consistent +X	CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8, CPLSTN3, CPLSTN4, CPLSTN6, CPLSTS3, CPLSTN8, CPLSTS4, CPLSTS6, CPLSTS8, CQUADX4, CQUADX8, CTRAX3, CTRAX6, CTRIAX6	When axisymmetric elements are modeled in the XZ plane, this check ensures that the X location for all nodes is ≥ 0.0.

User controlled GEOMCHECK options

Use the GEOMCHECK Options in the Element Quality dialog box to control the optional checks that Nastran performs. In Pre/Post, the Error Limit value for each option is set to the corresponding default error threshold value in Nastran. These Error Limit values are specific to each element type. For example, the default Skew Angle value is 30̊ for CQUAD4 elements and 10̊ for CTRIA3 elements. You can also specify a Warning Limit for each check.

You can use options in your customer defaults to control the default values for the error and warning limits in the Element Quality dialog box. The options to control these limits appear on the Element Quality Check-NASTRAN page of the Simulation customer defaults.

The following table lists the available checks and the element types to which they apply.

GEOMCHECK Option	Applicable element types	Description
Aspect ratio	CTETRA, CHEXA, CPYRAM, CPENTA, CQUAD4, CQUAD8, CQUADR, CTRIA3, CTRIA6, CTRIAR, CTRAX3, CTRAX6, CTRIAX6, CQUADX4, CQUADX8, CPLSTS3, CPLSTS6,CPLSTS4, CPLSTS8,CPLSTN3, CPLSTN6, CPLSTN4, CPLSTN8, CHEXCZ, CPENTCZ, CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8	Measures the ratio of the longest element edge to the shortest element edge.
Skew angle	CQUAD4, CQUAD8, CQUADR, CTRIA3, CTRIAR, CQUADX4, CQUADX8, CPLSTS4, CPLSTS8 CPLSTN4, CPLSTN8, CCHOCK4, CCHOCK8	The software creates lines between the midpoints of opposite sides of the element and then measures the angles between these lines. The angle with the greatest deviation from the ideal value is used to determine skew.
Minimum interior angle	CQUAD4, CQUAD8, CQUADR, CTRIA3, CTRIA6, CTRIAR, CTRAX3, CTRAX6, CTRIAX6, CQUADX4, CQUADX8, CPLSTS4, CPLSTS8, CPLSTN4, CPLSTN8, CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8	Measures the minimum interior angle of the element.
Maximum interior angle	CQUAD4, CQUAD8, CQUADR, CTRIA3, CTRIA6, CTRIAR, CTRAX3, CTRAX6, CTRIAX6, CQUADX4, CQUADX8, CPLSTS4, CPLSTS8 CPLSTN4, CPLSTN8, CCHOCK3, CCHOCK4, CCHOCK6, CCHOCK8	Measures the maximum interior angle of the element.
Taper	CQUAD4, CQUAD8, CQUADR, CQUADX4, CQUADX8, CPLSTS4, CPLSTS8, CPLSTN4, CPLSTN8, CCHOCK4, CCHOCK8	Measures the amount of geometric deviation of a quadrilateral element from a rectangular shape.
Warp	CQUAD4, CQUADR, CHEXA, CPYRAM, CPENTA, CHEXCZ, CPENTCZ	Measures the out-of-plane deviation of the element.
Edge point included angle	CTETRA, CHEXA, CPYRAM, CPENTA, CHEXCZ, CPENTCZ	Evaluates the included angle of midside nodes.
Edge point length ratio	CTRIA6, CQUAD8, CTETRA, CHEXA, CPYRAM, CPENTA, CHEXCZ, CPENTCZ, CTRAX6, CTRIAX6, CQUADX8, CPLSTS6, CPLSTS8, CPLSTN6, CPLSTN8, CCHOCK6, CCHOCK8	Evaluates the location of midside nodes.
Element offset length ratio	CBAR, CBEAM	Measures the offset ratio (offset length-original length/original length) for CBAR and CBEAM elements that have defined offsets.
Laminate taper ratio	CHEXA, CPENTA	Ratio of longest edge to shortest edge in stacking direction for CHEXA and CPENTA elements that reference PCOMPS entries only.
Laminate thickness ratio	CHEXA, CPENTA	Ratio of the difference between thickness in stacking direction as defined by nodes and as defined by ply thickness specification to the thickness in the stacking direction as defined by nodes for CHEXA elements that reference PCOMPS entries only.

For more information, see:

• User Controlled Checks in the Simcenter Nastran User’s Guide

• GEOMCHECK in the Simcenter Nastran Quick Reference Guide.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM, assembly FEM, or Simulation file as the work part and displayed partSimcenter Nastran, NX Design Simulation, or MSC Nastran as the specified solver
Command Finder	Element Quality

Learn more

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Nastran and Multiphysics element quality checks, Simcenter 3D 2021.1 Series

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