Contact is a nonlinear phenomenon and requires a nonlinear solution. However, contact elements can be included in a linear analysis. In this situation, the contact elements' stiffnesses are calculated based on their initial status and never change during the solution.
Linear analyses include:
Modal analysis
Any downstream analysis following a modal analysis (for example, mode superposition harmonic, PSD, and spectrum analyses)
Full harmonic analysis
The table below illustrates how the initial contact condition and the contact type determine the contact status used throughout a linear analysis.
Table 3.4: Contact Status Used in a Linear Analysis
| Contact Type | Contact Status Used Throughout the Solution | ||
|---|---|---|---|
| Initially Touching | Initially Inside Pinball Region | Initially Outside Pinball Region | |
|
Bonded (KEYOPT(12) = 3, 5, or 6) | Bonded | Bonded | Open and far-field |
|
No separation (KEYOPT(12) = 2 or 4) | No separation | No separation | Open and far-field |
|
Rough (KEYOPT(12) = 1) | Bonded | Open and near-field | Open and far-field |
| Frictionless | No separation | Open and near-field | Open and far-field |
| Frictional |
μ = 0, same as frictionless μ > 0, Bonded | Open and near-field | Open and far-field |
When viewing results from a linear analysis, keep in mind that the total forces contributed from contact elements (for example, FSUM,,CONT) do not represent the actual physical values.
Linear Perturbation Analysis
Prestress effects can be accounted for by using the linear perturbation analysis procedure, which involves a static base analysis followed by a linear perturbation analysis (for example, a linear perturbation modal analysis).
If the base analysis includes contact elements, the subsequent linear perturbation analysis uses the contact status from the restart point of the base analysis. If desired, you can adjust the contact status for specific contact pairs (CNKMOD) or globally for all contact pairs (PERTURB). See the PERTURB command for a detailed description of how to adjust contact status in a linear perturbation analysis.