Achieving Model Stability

The most frequent faced challenges when applying the various static load groups are

  • The static analysis has not converged

  • The static analysis diverge

  • Too large incremental rotations

  • Numerical instability possibly caused by large stiffness differences

Under compression or loads that are large compared to the system’s stiffness may lead to convergence problems and possibly to the analysis failing. Both the cross-sectional stiffness and the geometric stiffness from tensions elements will contribute to the system’s stiffness and the stability of static analysis. Boundary changes may be used to hold parts of the system until the system is more stable.
Dynamic time domain analysis is in general more stable as both mass and damping contribute to effective dynamic stiffness and thus improving convergence.
Table 1. Potential reasons and remedies
Reasons Remedies

Too large incrementation steps

Increase the number of steps.
Study the static loading sequence using the visualization.
Consider to change the order of the static load group and possibly combine load groups, see Typical configurations.

Inconvenient stress free configuration

Study the static loading sequence using the visualization.
Consider to remodel the stress free configuration
Consider to change the order of the static load group and possibly combine load groups, see Typical configurations.

Values of bottom stiffness

Check if the stiffness is correct or as intended

Erroneous drag coefficients or current velocities

Check the values

Numerical instability possibly caused by large stiffness differences

Check the SIMA console and/or <*>_stamod.mpf-file for information .
Locate the affected line/segment/element and check the cross sectional properties/stiffness.
It is possible to plot intermediate static configuration and forces using the Matrix Plot Storage plot option and then study the result using the <*>_stamod.mpf-file, Storage
Open the file <*>_stamod.res-file to find additional information