In a transient analysis, a coupling step is associated with a time interval when the coupling step size (in seconds) is specified. When running a transient analysis, values must be defined for the end time and the time step size. For more information, see EndTime and TimeStepSize in the System Coupling Settings and Commands Reference manual.
With a time specified, a coupling step is the same as a time step within the transient analysis. The coupling step size used should reflect the time scales of the physics being studied. Note that unless sub-stepping is supported by the coupling participants, coupling step size is typically limited by the finest/smallest time scale of the participants.
If the analysis duration is specified using an end time, ensure that an integral number of coupling steps can be executed between the (re)start time and the specified end time. If this is not done, then the final coupling step size is reduced to respect the specified end time, and this may introduce temporal discretization error into the coupled analysis.
The minimum number of coupling iterations may be set to a value larger than one (one is the default). If the data transfers have been under-relaxed, ensure that a minimum number of coupling iterations is performed so that you iterate out the effect of the under-relaxation. Note, however, that the data transfer convergence criteria would usually make this unnecessary. The maximum number of coupling iterations should be set to allow complete convergence within each coupling step.
Steady-Transient Analyses
Mixed steady-transient solutions (in which one participant runs a steady solution and one runs a transient solution) have a Transient analysis type. By mixing steady and transient participant analyses, greater solution efficiency can be realized for transient analyses involving physics with disparate time scales. The coupled analysis remains time-accurate, provided that the physical timescales of the steady-state participant(s) are orders of magnitude faster than those of the transient participant(s).
In such steady-transient analyses, System Coupling will show the overall analysis type as Transient, while the physics with the shorter/faster timescale is solved as steady-state.
Note: For steady-transient analyses with an AEDT coupling participant:
When the AEDT participant has excitations or motion that is dependent on System Coupling time, its solution type is presented to System Coupling as Transient, even if the underlying electromagnetic solution type is Eddy Current.
You can further improve solution efficiency by moderating the update frequency for the AEDT participant. For more information, see UpdateControl in the System Coupling Settings and Commands Reference manual.
For best practices, see Improving the Accuracy of Transient Analyses.