Is it possible to extract the mass, stiffness and damping matrix of a mechanical part from ansys?

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TimFethke posted this 2 weeks ago

Hello, 

I am new to working in the Ansys Workbench environment and I was wondering if it is possible to directly extract the mass, spring and damping matrix from Ansys. These matrices should be generated by Ansys in order to solve the FEM models (to my understanding) so my feeling says that they also should be available for the user.

Thanks in advance

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SandeepMedikonda posted this 2 weeks ago

Hi,

Yes, you should be able to do this using the commands described in this document.

Regards,

Sandeep

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TimFethke posted this 2 weeks ago

Hello Sandeep,

Thank you for your response! When I was looking at the document you send, I was not able to figure out how to "Enter the solution processor". Is this maybe because I am using Workbench? I understand that Ansys on its own looks a little different then the Workbench environment or is this incorrect? Can you guide me in to the right direction?

Tim

SandeepMedikonda posted this 2 weeks ago

Tim,

This document applies to an older version. But, you should see something like this in Mechanical:

Note that Mechanical is launched when you click on Model or subsequent cells in Workbench. 

~Sandeep

 

TimFethke posted this 2 weeks ago

 Sandeep,

I do see a similar picture as to what you are referring to. However, if I want to perform the steps explained I run in to problems:

2. Enter the solution processor. On the ANSYS Main Menu, select “Solution”.

3. On the “Solution” menu, select “Analysis Type”, then “New Analysis”.

4. On the “New Analysis” menu, select “Substructuring/CMS”, and click “OK”.  

The "Solution" object that you are pointing at does not have a menu where I can select Analysis type.
I do see something similar when I click on 'Static Structural' :
here

However, as you can see it is gray, and i cannot change that. Am i doing something wrong?

peteroznewman posted this 2 weeks ago

Hello Tim,

I learn about ANSYS capabilities by participation on this forum as well as share what I know. I haven't used Substructuring, but I am curious about how to do so.

First I would ask which license you are using: Student (limited) or Research (unlimited) and which version 18.2, 19.1 etc.  I have access to both a Commercial (unlimited) license on one computer and a Student license on a second computer. That way I can see when a problem exceeds the Student license limits. I suspect that Substructuring is not supported on the Student license.

Second, I would direct you to the ANSYS Help file in this area: 

I haven't read the pages and pages that are in the guide, I will do that later. I wanted to jump in with the info in Sandeep's link.

I put a Command object in a model like this:

I got a lot of errors, so I read some of the ANSYS Help on this topic and learned that Substurturing (at least in 18.2) requires Linear Elements. So I went to the Mesh Details and changed the Element Order from Program Controlled to Linear.  Then I hit Solve again and it seems like the solver started but is waiting for something and hasn't finished.  I may have to go read the ANSYS Help again!

 

 

SandeepMedikonda posted this 2 weeks ago

Hi Tim, 

As peter said, can you confirm the license and version you are using?

Also, make sure that all other instances of the Mechanical or SpaceClaim/Direct Modeller are closed.

~Sandeep

 

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TimFethke posted this 2 weeks ago

Hello Peter,

Thanks for your input, I was using student version 18.2 but I just downloaded 19.1 because I received a model that was made in 19.1. This is student version aswell. I am also currently trying to obtain the research license at this moment through my university in order to solve a different problem so my license might change in a few days. 

I have read on different fora about APDL commands but I am not familiar with them. I don't know if they are necessary to be able to use the full capabilities of Ansys but I am willing to learn if i need it to get the matrices. Because of my lack of knowledge about APDL I found the document that Sandeep posted so appealing. I will follow your advice and read the Ansys help file. 

Let me know if you manage to find why your solver wont finish and I will try to reproduce what you did.

Thanks

peteroznewman posted this 2 weeks ago

Hello Tim,

I used the same APDL code in a much smaller model and it wrote out a file, peter.txt, which I have zipped and attached. That has the load vector and the element matrix in text file format. I had a much larger model and maybe I didn't wait long enough on that.

I ran this on the Student 19.1 version and so you might get what you want.  I also attached the ANSYS Project Archive .wbpz file, which you can open by using File, Restore Archive in Workbench.

Regards,

Peter

Attached Files

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TimFethke posted this 2 weeks ago

Hello Peter,

Your results look really promising! I've investigated the .txt file and I found the solution information which included the load vector and the stiffness matrix. Can i ask why you did not get the mass matrix? Is it simply because you did not request it? maybe you could elaborate on your APDL code so that I can understand.

Tim

TimFethke posted this 2 weeks ago

By the way, I've managed to copy exactly what you did but with a different geometry and I got similar results. So this means that the method works on my version aswell. Thanks!

peteroznewman posted this 2 weeks ago

Hello Tim,

I can use APDL code that I am given, I don't know how to write it myself. Perhaps Sandeep can help with this question.

Peter

TimFethke posted this 2 weeks ago

Alright I think I will try to look in different places for the APDL code that I need! Thank you so much.

peteroznewman posted this 2 weeks ago

Also, read the entire chapter on Substructuring in the ANSYS 19.1 Help.

Good luck!

Peter

SandeepMedikonda posted this 2 weeks ago

Tim and Peter,

Nearly every button/functionality we use in Mechanical is based off on APDL commands. So whenever we hit Solve we are essentially writing an ASCII file with all the APDL commands. Sometimes, not all commands are mapped as features in Mechanical and hence warrants the use of APDL commands. 

This video by one of our Channel partners might be helpful to you:

 

For detailed learning, please refer to the command reference and the verification guide for a wide range of examples.

Hope this helps!

~Sandeep

sk_cheah posted this 2 weeks ago

Hi Tim,

Please see documentation on SEOPT. Changing it to the following should get you both stiffness and mass.

seopt, file, 2, 1

 

Kind regards,
Jason

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apwang posted this 2 weeks ago

Hi Tim,

This ANSYS video might be helpful for you:

Export the ANSYS Stiffness and Mass Matrix to Text Files

 

Regards,

April

 

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