General Mechanical

General Mechanical

Truss of beam elements do not converge

    • Nokunaator

      Hello community,

      I have struggle quite a time to get simple truss to work, but no results. 

      It all seems to be fine when large deflections are turned off, but when I turn them on, it could not converge the results.

      Truss has upper and bottom chord which are connected with beams and joints at the end of the bar. Joints are fixed any direction and rotation also truss ends are fixed all directions and rotations, it should not have any degree of freedom. 

      For comparison I have smaller truss, which works fine. 2/3 of the length of problem truss. I do not get it why longer truss dosen't work.

      In future, I wish to but some stiffness in the joints and compare the results, however right now I wish to get my model to work as it is in the attachment. 

      I hope someone finds a little time to check my problem. You will be much appreciated. 



    • Aniket
      Ansys Employee

      Ansys staff are not allowed to download anything from the forum, can you please post the problem as inline images? Also, what errors do you get?


      Guidelines on the Student Community

      How to access ANSYS help links

    • Nokunaator

      Unfortunately I am not able to insert any pictures. Browser says "Sorry error occured".

      Despite this, workbench shows following messages 

      • The solver engine was unable to converge on a solution for the nonlinear problem as constrained.  Please see the Troubleshooting section of the Help System for more information. (error)

      • The unconverged solution (identified as Substep 999999) is output for analysis debug purposes. Results at this time should not be used for any other purpose.(warning)

      In file0.err I have tons of following warnings 

       *** WARNING ***                         CP =       1.984   TIME= 191:55

       Coefficient ratio exceeds 1.0e8 - Check results.                        


       *** WARNING ***                         CP =       2.000   TIME= 191:55

       Pivoting has been activated for the Distributed Sparse Matrix Solver .  

       The memory required may greatly exceed the predicted amount.  In that   

       event, use the DSPOPTION command to change the memory mode and/or       

       memory size used by the Distributed Sparse Matrix Solver

      At the end of file0.err

       *** ERROR ***                           CP =       4.625   TIME= 191:59

       Solution not converged at time 1.E-03 (load step 1 substep 1).          

        Run terminated.

      Also there is warning, which I couldn't find any answers. All my beam elements are made of structural steel. 

       *** WARNING ***                         CP =       0.500   TIME= 191:53

       Material number 27 (used by element 228) should normally have at least  

       one MP or one TB type command associated with it.  Output of energy by  

       material may not be available. 

      Thanks in advance


    • Nokunaator

      Now I can insert pictures and I try to explain my problem through pictures. 

      I have a truss like this - upper and bottom chord is made of beams and made into component in spaceclaim with shared topology (different components). Braces are just beams and in spaceclaim they are in differentcomponents with none topology.

      Every brace is connected with joints(general) to chords, because in future I would like to add some rotational stiffness(in-plane and out-plane) to connection. Right now all freedoms are fixed, just to get my model to work. 

      In general joint I use direct attachment, it means that I choose one vertex from chord and other from brace. 

      Truss has 2 point loads and both ends are fixed totally. 

      In my mind it should be solveable, but what I know. 

      I will appriciated all kind of help


    • Aniket
      Ansys Employee

      I would recommend you to do a Modal analysis (include fixed supports and joints in it that you are applying in structural analysis) first to see if your model is properly constrained. If it is, then fundamental frequency should not be zero or near-zero one.

      Modal analysis can show if there are any rigid body modes in your setup.

    • Nokunaator

      Thank you very much. I got my model to work. I think my model wasn't correct. In Spaceclaim, under component properties, shared topology to set shared may not make beams into one element - I had to use share tool(workbench --> sharing--> share). It wasn't totally clear for me. 

      I have another question, in modal analyse, i could not see modal shapes. Values seems correct, even colors of deformation are correct, but it wouldn't take any shape. Here is a picture of it. 

      Huge thanks for your time. 


      EDIT: Shape problem involves also eigenvalue analyse - mode deformation shapes won't appear.

      EDIT2: Got shapes right. Scale was just wrong to me. Thanks again for a help - modal analyse helped to understand problem.


Viewing 5 reply threads
  • You must be logged in to reply to this topic.