Chordal error

Chordal error
This set of parameters control the chordal error of the surface and line meshes of the whole model. They are always considered when using the MinElem surface unstructured mesher (Structuration type), and they are used with the other meshers (Rfast and Rsurf, as well as line meshes) if 'Use with lines, RFast and RSurf meshers' is set.

• Minimum element size: it has to be considered that, in some geometries, the element size to achieve a given limit chordal error may be very small. This option allows the user to fix a minimum element size not to refine too much the mesh in this situations.
• Maximum chordal error in model: this limits the maximum chordal error in the meshes of the model:
  • Relative(%): the surface and line elements in the mesh won't present more chordal error than this percentage of their size. If the value is zero, it is not considered.
  • Absolute: the maximum chordal error (distance) allowed in the model. If the value is zero, it is not considered.

If both relative and absolute chordal error limit is set, the more restrictive is applied depending on each element. If the value is 0, it is not considered.

• Angular tolerance (degrees): this angle limits the difference between normals from adjacent elements.

Considering all these parameters, after generating the initial meshes, GiD refines the mesh until the chordal error is inside the defined limits.
The recommendation is to use the angular tolerance (more intuitive parameter), and the absolute value in case you know the characteristic sizes of your model.