General Mechanical

General Mechanical

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

    • TimFethke
      Subscriber

      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

    • Sandeep Medikonda
      Ansys Employee

      Hi,


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


      Regards,


      Sandeep

    • TimFethke
      Subscriber

      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

    • Sandeep Medikonda
      Ansys Employee

      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
      Subscriber

       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
      Subscriber

      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!


       


       

    • Sandeep Medikonda
      Ansys Employee

      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


       

    • TimFethke
      Subscriber

      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
      Subscriber

      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

    • TimFethke
      Subscriber

      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
      Subscriber

      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
      Subscriber

      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
      Subscriber

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

    • peteroznewman
      Subscriber

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


      Good luck!


      Peter

    • Sandeep Medikonda
      Ansys Employee

      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
      Subscriber

      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

    • April Wang
      Ansys Employee

      Hi Tim,


      This ANSYS video might be helpful for you:


      Export the ANSYS Stiffness and Mass Matrix to Text Files


       


      Regards,


      April


       

    • LisDeb
      Subscriber

      Hi everyone, I read this discussion and have one question remaining on the extraction of the stiffness matrix as described by Sandeep. Does the stiffness matrix refer to the degrees of freedom in the nodal coordinate systems, or in the global or active local one?


      Thank you

    • Sandeep Medikonda
      Ansys Employee

      Apologies...did not see this.


      I believe these are written W.R.T. global coordinate system. I base this on a statement I find in Theory Manual.
      Refer to Section 2.2 of Theory Manual, where there is a statement about derivation of structural matrices. "It will be assumed that all effects are in the global Cartesian system."  It is a general statement...not specific to SEOPT,,,, but it is the only direct comment about CSYS that I can find.

    • xiongwanyue
      Subscriber
      hello everyone, I have a question, I export the element matrix from the .emat file with the code:n*dmat,element_k,D,import,emat,jobname.emat,stiff,elemnubern*print,element_k,out.txtnand export element stiffness matrix with the code:\debug,-1,,,1nbut the two obtained matrices are different,what is the reason?nthere many method to export the element stiffness matrix ,what is the difference between them?nthank youn
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