## General Mechanical

#### Auto Time Stepping in Transient Structure

• i.tamunodienye2
Subscriber

Hi,

I am having issue with Analysis Settings" in Transient Structural.

I have the following in the tabular data.

Total "End Time" = 20.25 s

Total "Steps" = 405

I have tried to set up the "Analysis Settings" for the simulation but this has been difficult.

Please how do i set the "Auto Time Stepping"

Thanks

Inima

• peteroznewman
Subscriber

Hello Inima,

It’s often better to use a single step with the End Time of 20.25s. You can have a two column, 405 row spreadsheet with Time in the first column and load in the second column (or three components in 3 columns) to paste into the load Tabular Data. Make the Initial Time Step 0.05s, the Minimum Time Step 0.001s and the Maximum Time Step 0.05s. That will give you at least 405 substeps.

You should run a Modal analysis to learn the Natural Frequencies of the structure. You should also run the time-history of the load through an FFT operation to learn the frequency content in the load.

Once you learn the frequencies, you need to evaluate if the 0.05s max time step is too large. The max time step should be less than 1/20th of the period of the highest frequency of interest.

• i.tamunodienye2
Subscriber

Hello @peternewmancsh

Thank you so much for your help.

Please can you help me again in understanding how the Initial Time Step (0.05s), the Minimum Time Step (0.001s) and Maximum Time Step (0.05s) can give  405 substeps. Is this based on calculation, estimation... Please let me know how you arrived at these values.

Thanks

• peteroznewman
Subscriber

Hello Inima,

End Time/Max Time Step = Minimum possible number of substeps. In your case, 20.25/.05 = 405.

You are guaraneed to get at least that many substeps. Because you have allowed a Minimum Time Step of 0.001s, you could get a lot more substeps if the autostepping algorithm decides it needs more substeps.

The initial time increment can’t be larger than the maximum time step or smaller than the minimum time step.

• i.tamunodienye2
Subscriber

Thank you @peteroznewman

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