- Activate implicit by setting IMFLAG=1 on *CONTROL_IMPLICIT_GENERAL
- Set DT0 to a reasonable initial time step
- Check possible singularities in an eigenvalue analysis by requesting NEIG eigenvalues on *CONTROL_IMPLICIT_EIGENVALUE
- Find a way to constrain spurious modes
- Initially use dynamic analysis if rigid body modes are present in a static problem by setting IMASS=1 on *CONTROL_IMPLICIT_DYNAMICS
- Use TDYBIR, TDYDTH and TDYBUR
- Use numerical damping by putting GAMMA=0.6 and BETA=0.38
- Only activate geometric stiffness contribution as a last resort, except for arc length methods
- Use nonlinear solver type 12 by putting NSOLVR=12 on *CONTROL_IMPLICIT_SOLUTION
- Use default BFGS parameters ILIMIT and MAXREF on *CONTROL_IMPLICIT_SOLUTION
- Increase or decrease ILIMIT based on convergence characteristics
- Use full Newton (ILIMIT=1) for hard problems
- Keep MAXREF to a reasonably low number
- Use default convergence tolerances DCTOL, ECTOL and RCTOL on *CONTROL_IMPLICIT_SOLUTION
- ABSTOL may be set to 1.e-20 to prevent premature convergence
- Relaxing DCTOL may not necessarily result in better convergence
- Future strategy may be to focus on residual
- Activate automatic time stepping on *CONTROL_IMPLICIT_AUTO
- Set DTMAX to a number that resolves features of interest
- Frequencies
- Use default line search method on *CONTROL_IMPLICIT_SOLUTION
- Don’t use LSMTD=1 for nonlinear solver 12
- Switch to LSMTD=5 if negative volumes is an issue (typically rubbers)
- Don’t change LSTOL
- Use at least NLPRINT=2 on *CONTROL_IMPLICIT_SOLUTION to get convergence diagnostics into log files
- Use NLPRINT=3 to thoroughly track the residual norm and monitor line search behavior if debugging model is necessary
- Don’t use *CONTROL_IMPLICIT_LINEAR
- Set D3ITCTL=1 on *CONTROL_IMPLICIT_SOLUTION to get a database with Newton iterates when debugging a model
- Complement this with RESPLOT=1 on *DATABASE_EXTENT_BINARY to get the possibility to fringe the residual force vector
- For forming Mortar contact, make sure
- Tools are oriented towards the blank
- Contact on top and bottom of blank are separarated among contact interfaces
- Use part (set) definitions of slave and master in Mortar contact
- Always use weak part as slave in a Mortar contact definition to get best possible convergence
- Set SST to a reasonable characteristic length for slave side consisting of solid elements
- With this option, separate solids and shells into different contact interfaces in order to not manipulate the contact thickness for shells
- If penetrations are large, activate penetration diagnostics on *CONTROL_CONTACT
- To avoid release of contact pairs, either
- Increase stiffness scaling factor SFS
- Increase IGAP for progressive stiffness increase
- Increase SST for solids while at the same time increasing SFS
- Use IGNORE appropriately to deal with initial penetrations
- Check initial penetrations in message file
- Don’t use contact damping
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TB 2015