Time Stepping Adjustment in Transient Simulations-Enhancement request

1

Hello Group/Developers,
Thank you for the great tool!!.

While working with transient simulation, the program complains that the step size has exceeded. After looking through, it appears that the file time step becomes less than the next increment which will reach the final time.
For example if the end time is 25 sec and the minimum time step is specified as 0.25 sec and max time step allowed is 1.0 sec, the time integration proceeds as if the last but one time is 24.8 sec (For the sake of explanation) the next increment will be 24.8+0.25 which is 25.05 exceeding the final time of 25 sec and the program complains and stops before final step. There is nothing wrong but, it is expected as the final time step should trim to 0.2 sec than 0.25 which is specified.

This problem does not occur when Min and max time step is not specified. But in this case since time steps are allowed to scale, the number of solution points are less and it is difficulty in obtaining more smoother solution points. Some times, knowing the correct time step would be iterative and predetermine the time points is not possible. We feel an easier option would be to provide flexibility in trimming the time step to reach end time when the calculation reaches last time step,overriding the minimum time step. if we opt to choose constant time stepping, it is leading to very fine and too many time points, ending up significant penalty in run time.

This problem was encountered when we did a transient thermal simulation for composite discs.
Transient Thermal Analysis of Composite Brake Disks || FreeCAD, Salome & Calculix || Fluid Network

we are using self compiled latest version on ubuntu 20.04.

Could you consider this as enhancement request?

Regards,
CAE4U

2

Interesting. I set a simple transient heat transient problem where convergence is not an issue and any increment size can be used. I forced CalculiX to use increments of 0.3 s (by setting initial, max and min increment size to this value) while the total time was 25 s. CalculiX went with 0.3 s until the last increment where it cut the increment size to 0.1 s.

3

Thank you. When you say any increment, we understand setting different max and min step size also work and Calculix indeed has the feature of adjusting the time step. We will look at other possible contributor for the behavior.