Element Results Representation for Models

Elemental results (namely stresses, strains, element forces, flux and gradients) may be provided with reference to either the material system or the elemental system.

For the HM, PUNCH, and OPTI output formats, results are provided with reference to the material system; for first order shell element results, PARAM, OMID may be used to output with either representation. The H3D and OUTPUT2 output formats, to which these elemental results are written as tensors, always contain results with reference to the elemental systems (unaffected by PARAM, OMID).

Since OptiStruct 10.0 optimization responses always match with the results written to the HM, PUNCH, and OPTI formats and first order shell responses are consistent with the PARAM, OMID setting.

PSDF and RMS Random Response Stress, Strain results are output in the Element Coordinate system.

First Order Shell Elements

For first order shell elements (CQUAD4 and CTRIA3), the material system is defined as follows:
  1. With blank MCID/THETA (default behavior), stresses, strains and plate forces are presented in the default element material system, which has x-axis aligned with line G1-G2, and other axis built accordingly to make an orthonormal triad.
  2. With MCID > 0, results are presented in the material system CID projected onto the element plane (projected material system).
  3. With MCID = 0, results are presented in the basic coordinate system projected onto the element plane (projected basic system).
  4. With THETA specified (including zero), results are presented in a rotated element material system, which is rotated by angle THETA from the edge G1-G2.
The elemental system is the bi-sector system for CQUAD4 elements (Figure 1) and the G1-G2 system for CTRIA3 elements.
Figure 1. Bi-sector Coordinate System

For the H3D and OUTPUT2 formats this representation allows HyperView to perform coordinate system transformations on stress and strain tensors.

Second Order Shell Elements

The results for second order shells (CQUAD8 and CTRIA6), including shell strains, stresses and forces, are always presented in the local material coordinate system, as described in the manual for CQUAD8 and CTRIA6 elements.

Composite Shells

Shell-type strains and stresses for composite shells use the same representation as homogeneous shells. By shell-type results, strains and stresses calculated at Z1 and Z2 using homogenized shell properties. Strains and stresses for individual plies are always presented in the respective ply coordinate system.

Solid Elements

For solid elements (CHEXA, CTETRA, CPENTA and CPYRA), the results are always provided in the material coordinate system.
  1. With blank CORDM on the PSOLID card (default behavior), strains and stresses are presented in the basic coordinate system.
  2. With CORDM > 0, strains and stresses are presented in the material system CID.
  3. With CORDM = -1, stresses are presented in the local element coordinate system (described in detail on respective solid element manual pages).

Gap Elements

For gap elements, gap forces are represented in the gap coordinate system, as described on respective gap element manual pages (CGAP and CGAPG). Compression is positive.