SEMIIMPLICIT
SEMIIMPLICIT, Option,
Type, Value
Specifies parameters for a semi-implicit solution.
OptionOption to be performed:
ETOI
—
Criterion for transitioning from the semi-implicit solution phase to the implicit solution phase.
MSCA
—
Selective mass scaling factor used during the semi-implicit solution phase.
SFAC
—
Safety factor for time incrementation used during the semi-implicit solution phase.
AUTS
—
Automatic time stepping and bisection controls used during the semi-implicit solution phase.
BVIS
—
Bulk viscosity controls used during the semi-implicit solution phase.
EFRQ
—
Output and restart file frequency used during the semi-implicit solution phase.
TypeAdditional input; varies depending on the
Optionvalue. See table below.ValueAdditional input; varies depending on the
OptionandTypevalues. See table below.
Option
Label | Type
= | Value
= |
|---|---|---|
| ETOI | TIME - Time to spend in the semi-implicit phase (default) | Time value (defaults to the minimum time increment specified in the implicit run) |
| MSCA | DTIM - Initial minimum stable time increment | Time increment; defaults to (1e-4)*(total step time) [1] |
| MASS - Selective mass scaling factor | Scaling factor | |
| SFAC | (not used) | Safety factor (defaults to 0.9) |
| AUTS | DSPL - Automatic time stepping and bisections control based on displacement (default for all analysis types except static) | Maximum allowable jump in the maximum displacement increment between two substeps at which bisection will be triggered (defaults to 100) |
|
ENER - Automatic time stepping and bisections control based on energy (default for static analysis) | Maximum allowable ratio of kinetic energy to potential energy at which bisectionn will be triggered (defaults to 100). For bisection to trigger, the potential energy should be more than the program calculated reference value | |
| BVIS | LBVD - Linear bulk viscosity damping factor | Damping factor (defaults to 1.5) |
| QBVD - Quadratic bulk viscosity damping factor | Damping factor (defaults to 0.06) | |
| RBVD - Rotational bulk viscosity damping factor | Damping factor (defaults to 0.06) | |
| LIMI - Bulk viscosity force upper limit | Upper limit percentage (general default is 0.05; for PLANE182 and SOLID185 with reduced integration, the default is 0.01) | |
| NONE - Bulk viscosity is not included | (not used) | |
| EFRQ | OUTR - Solution output frequency (overwrites
Freq value on OUTRES).
SEMIIMPLICIT,EFRQ,OUTR must be issued after
OUTRES. | Frequency value (defaults to 100) [2] |
RESC - Frequency for writing restart files (overwrites
Frequency value on RESCONTROL).
SEMIIMPLICIT,EFRQ,RESC must be issued after
RESCONTROL. | Frequency value (defaults to 100) [2] |
The default time increment (1e-4)*(total step time) is based on the total step time for the load step in which the solution transitions to the semi-implicit phase.
The frequencies specified by
Option= EFRQ are based on all substeps, starting from the beginning of the analysis and spanning both the implicit and semi-implicit solution phases. For example, during the semi-implicit solution phase results are written for any substep that is divisible by the specified OUTR value.
Command Default
By default, the semi-implicit method is not used.
If the SEMIIMPLICIT command is issued with no arguments specified, the semi-implicit scheme is activated with the following defaults:
| The safety factor for time incrementation = 0.9. |
| The selective mass scaling factor is set such that the initial stable time increment in the semi-implicit phase is (1e-4)*(total step time). |
| For most analysis types, bisection is triggered if the maximum displacement increment increases more than 100 times that of the previous substep. |
| In a static analysis, bisection is triggered if the kinetic energy is more than 100 times the potential energy and the potential energy is more than the program calculated reference value. |
| Bulk viscosity is included. |
| The frequency at which the results file and restart files are written during the semi-implicit phase is every 100 substeps. |
Notes
This command triggers a semi-implicit solution scheme in which the analysis transitions to a semi-implicit solution method when the implicit solution method fails to converge. The command is valid only in the solution processor (/SOLU) and must be defined before the first SOLVE command.
The SEMIIMPLICIT command can be used in a restart, even if the base analysis did not include the command. Therefore, a problem that failed in the implicit analysis can be restarted with this command so that it can transition to the semi-implicit method and solve further.
The SEMIIMPLICIT command can overwrite the values on some commands, as described in the following table.
| Commands Affected by SEMIIMPLICIT | Behavior |
| NSUBST and DELTIM | During the semi-implicit solution phase, the time incrementation does not follow that set by the NSUBST and DELTIM commands. |
| ETCONTROL | If the SEMIIMPLICIT command is issued, the ETCONTROL command is ignored. |
| OUTRES | During the semi-implicit solution phase, the frequency for writing results specified by the OUTRES command is ignored, unless a negative number was specified on OUTRES. |
| RESCONTROL | During the semi-implicit solution phase, the restart file writing frequency specified by the RESCONTROL command is ignored, unless a negative number was specified on RESCONTROL. |
| AUTOTS | During the semi-implicit solution phase, automatic time incrementation is on, irrespective of what was specified on AUTOTS. |
| CUTCONTROL | During the semi-implicit solution phase, the CUTCONTROL command is ignored. |