# CHEXA Element Checks and Default Bound Values

## CHEXA 1st-order (8-noded) Element Checks

The following qualities of the CHEXA 1st-order
element are checked:

- Aspect Ratio
- The aspect ratio of a CHEXA 1st-order element is defined as the maximum aspect ratio among its six faces; each treated as a CQUAD4 element.
- Face Skew Angle
- The face skew angle of a CHEXA 1st-order element is defined as the maximum skew angle among its six faces; each treated as a CQUAD4 element.
- Vertex Angle
- The same vertex angle check is performed for all of the faces, and each is treated as a quadrilateral (CQUAD4) element. The minimum and maximum values reported for the element.
- Face Warpage
- The face warpage of a CHEXA 1st-order element is defined as the maximum warpage among its six faces; each treated as a CQUAD4 element.
- Twist Angle
- The twist angle of a CHEXA 1st-order element is defined as the maximum rotation of one face with respect to its opposite face. The calculation is done as:
- Edge Angle
- An edge angle is the absolute value of the angle between two faces sharing a common edge, subtracted from 90 degrees. For warped faces, the projected planes are used to compute the face normals used for the angle calculation. The edge angle of a CHEXA 1st-order is defined as the maximum edge angle in the element.

## CHEXA 1st-order Default Bounds

Information | Default values for warning message | Default values for error message | Default values for validity check | |||
---|---|---|---|---|---|---|

Lower Limit | Upper Limit | Lower Limit | Upper Limit | Lower Limit | Upper Limit | |

Aspect Ratio | - | 100.0 | - | 1000.0 | - | 1.0E5 |

Face Skew Angle | - | 60.0 | - | 75.0 | - | 90.0 |

Face Warp Angle | - | 30.0 | - | 60.0 | - | 180.0 |

Twist Angle | - | 30.0 | - | 90.0 | - | 180.0 |

Edge Angle | - | 60.0 | - | 85.0 | - | 90.0 |

## CHEXA 2nd-order (20-noded) Element Checks

The following qualities of the CHEXA 2nd-order
element are checked:

- Aspect Ratio
- This quality is calculated using only the corner nodes. Its definition is the same as that used for the CHEXA 1st-order element.
- Face Skew Angle
- This quality is calculated using only the corner nodes. Its definition is the same as that used for the CHEXA 1st-order element.
- Vertex Angle
- This quality is calculated using only the corner nodes. Its definition is the same as that used for the CHEXA 1st-order element.
- Face Warpage
- Twist Angle
- Edge Angle
- Hoe Normal Offset
- The hoe normal offset is the maximum of its edges normal offset values. See Hoe Normal Offset of 3-Node Edge
- Hoe Tangent Offset
- The hoe tangent offset is the maximum of its edges tangent offset values. See Hoe Tangent Offset of 3-Node Edge

## CHEXA 2nd-order Default Bounds

Information | Default values for warning message | Default values for error message | Default values for validity check | |||
---|---|---|---|---|---|---|

Lower Limit | Upper Limit | Lower Limit | Upper Limit | Lower Limit | Upper Limit | |

Aspect Ratio | - | 100.0 | - | 1000.0 | - | 1.0E5 |

Face Skew Angle | - | 60.0 | - | 75.0 | - | 90.0 |

Face Warp Angle | - | 30.0 | - | 60.0 | - | 180.0 |

Twist Angle | - | 30.0 | - | 75.0 | - | 180.0 |

Edge Angle | - | 60.0 | - | 89.0 | - | 90.0 |

Hoe Normal Offset | - | 0.30 | - | 0.60 | - | 1.0E5 |

Hoe Tangent Offset | - | 0.20 | - | 0.25 | - | 0.50 |

The values used for warning and error checks may be adjusted by the ELEMQUAL Bulk Data Entry, but validity checks are hard-coded.