Element Integration#

This section defines the positions and numbering of element Gauss points used for spatial integration. These points are the only places where material values (e.g. stress and strain) exist. If you need accurate values of material variables it is highly advised to use a **test output option to output directly at them (with the *gauss_var option), or use the **value_at_integration output for the structure.

Gauss points are defined in a local element coordinate system which is mapped to the global coordinates (real element geometry) using the element shape functions. The element is defined in the reference coordinates by 1 to 1 on the ξ and η element axis.

../../_images/integ2d.svg
../../_images/integ2d_tri.svg

To visualize Gauss points numbers and positions for one or several elements of the current visible elset, use View Show:

../../_images/visualize_gp.png

Fig. 4 Visualization of a c3d8 Gauss points.#

Additionally there is a post-processing gp_xyz to output the exact positions of the gauss points.

****post_processing
 ***global_post_processing
  **file integ
  **process gp_xyz
    screen % output directly in the screen
****return

For a c3d8, running the previous file prints:

Element 1 /  # of integration points : 8
  0 : (0.211325,0.211325,0.211325)
  1 : (0.788675,0.211325,0.211325)
  2 : (0.211325,0.788675,0.211325)
  3 : (0.788675,0.788675,0.211325)
  4 : (0.211325,0.211325,0.788675)
  5 : (0.788675,0.211325,0.788675)
  6 : (0.211325,0.788675,0.788675)
  7 : (0.788675,0.788675,0.788675)