# PTDM implementation

**URL:** <https://forums.nlr.gov/t/ptdm-implementation/4543>\
**Category:** Structural Analysis\
**Created:** [February 20, 2023, 11:00pm UTC](https://forums.nlr.gov/t/ptdm-implementation/4543 "2023-02-20T23:00:32Z")\
**Posts on this page:** 1\
**Showing post:** 16

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**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [March 17, 2023, 12:58pm UTC](https://forums.nlr.gov/t/ptdm-implementation/4543/16 "2023-03-17T12:58:42Z")

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Dear @Emanuel.Rergis,

OK, I’m glad you got the model to run now.

There are many posts on this forum that provide guidance on how to select a suitable time step (`DT`). The time step requirement is dictated by the highest full-system natural frequencies of your model (with the standard rule of thumb being `DT < 1/(10*f_max)`, which will depend on the system masses and stiffness. The full-system natural frequencies (including `f_max` in Hz) can be found through a linearization analysis followed by eigenanalysis (including MBC3 if the rotor is spinning with blade degrees of freedom enabled). There is also a balance between time step size (`DT`) and number of correction steps (`NumCrctn`); smaller `DT` can likely use smaller (or zero) `NumCrctn`, but setting `NumCrctn` to 1 or higher may allow you to use larger `DT`.

Best regards,

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