Vigneswaran Sridharan
Ansys Employee
Modal Analysis is performed to evaluate the mode shapes and the natural frequencies of the system.
I guess your question is more about Mode-Superposition Transient Analysis.
The mode-superposition method scales the mode shapes obtained from a modal analysis and sums them to calculate the dynamic response. For more detailed information, seeChapter 14.8. Mode-Superposition Methodin theMechanical APDL Theory Reference.
Initial Time Step = 1/(20f) is based on several studies on the accuracy of transient dynamic solution (as 20 or more points per cycle results with good accuracy)
The accuracy of the transient dynamic solution depends on the integration time step: the smaller the value, the more accurate the solution is.
So Initial time step = 1/ 20*Frequency response.
Minimum time step = 1/(100 or 1000) times initial time step.
Maximum time step = equal to or slightly greater than the initial time step.