How to extract the OMEGA value that was used for a particular time point in an RST file.

Each time step in an RST file may have a different value of OMEGA that was used. I believe this information is available in the RST, is it possible to get the values using DPF

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James Derrick

Hey @Jim Kosloski I don't know but the @Structures-Scripting-Team might

Ryoma

@Jim Kosloski
OMEAGA you mean is rpm value, right?
If so, you can get rpm value from TimeFreqSupport.rpms

https://dpf.docs.pyansys.com/version/stable/api/ansys/dpf/core/time_freq_support/TimeFreqSupport.html#TimeFreqSupport.rpms

Jim Kosloski

@Ryoma thanks for the information. That seems like it should be the answer, but it does not work. It does not return anything for a model that has OMEGA applied. Besides not working, there are a few issues with this anyway:

RPMS is a bad name, if it is indeed intended to return the applied angular velocity. While we allow angular velocity to be entered in RPM in Mechanical, it is always sent as radians/sec to the solver. So if it did work RPMS would be confusing
The documentation states it returns 1 value per time step, but OMEGA may be applied about the X, Y and/or Z axes. So at a minimum it should return 3 values. We also allow angular acceleration (DOMEGA) and angular velocity about the CG (CGOMEGA and DCGOMEGA). It would be good if it returned all of these items

Mike.Thompson

@Jim Kosloski , @Ryoma ,
These concepts are very easy to confuse, but there are distinct things for different workflows being discussed.

You can see in the old post for what's new in mechanical ~V19, Mechanical started to support multi-RPM harmonic analysis in support of electric motor design (mostly). This allows you to setup multiple harmonic analysis steps, with a specified RPM, and do a freq. sweep at each RPM. Each RPM has a freq. range defined for it. Effectively you are doing multiple harmonic sweeps in a single harmonic analysis. The DPF operator is getting that RPM value, and the RPM terminology is correct and consistent.

What the original question is really about is a LOAD value that is an angular velocity. This is not an RPM time point, but a rotational speed applied as a body load on elements. There are a few commands and ways to apply this load, and it can be applied to all or some of the elements, or there can also be different rotational speeds for different elements (think two rotors spinning at different speeds). The rotational speed can also be synced (via SYNCHRO command) to the harmonic excitation freq. and a factor (default=1) can be used. This is typical in rotordyamics where the excitation is a mass unbalance that is a 1x excitation. As pointed out by Jim, rotational speed as a load is also a vector with 3 components, so you can theoretically have 3 values per element for any given substep.

To the original question, I do not think there is a published way in DPF to extract the load value of a rotational velocity. I am not even sure there is a good way to do this with APDL commands at current time, but if you know of an APDL way please share. In a PyAnsys domain, you could then use PyMAPDL to get the values instead of PyDPF.

https://storage.ansys.com/mbu-assets/Mech/whatsnew/WhatsNew193.htm