7 Replies Latest reply on Nov 23, 2011 9:05 AM by Bill McEachern

Error message "Status code 3: Negative diagonal of matrix"

Ian Bonesteel Nov 22, 2011 10:36 AM

I get this error when I try to run my analysis using a high quality mesh. It runs fine with a draft quality mesh, so I am thinking it is some issue related to the mid-side nodes. I have an SPR for this (586951), but am wondering if anyone else has encountered this and has a work around.

My analysis is an assembly containing surface models, since I am analyzing carbon fiber composite parts. Let me know if anymore information would be helpful.

Re: Error message "Status code 3: Negative diagonal of matrix"

Bill McEachern Nov 22, 2011 10:44 AM (in response to Ian Bonesteel)

run it with iterative solver for awhile so you see whats moving. Then attach it with a manual bonded contact. Sometime the auto bonding loses its mind.
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- Re: Error message "Status code 3: Negative diagonal of matrix"
  
  Ian Bonesteel Nov 22, 2011 11:27 AM (in response to Bill McEachern)
  
  I am using the FFEPlus (Iterative) solver. The problem is it doesn't even get to iteration. It gets through "Forming surface to surface bonding", and then most of the way through "establishing stiffness matrix", and then it gives me the error message and stops the analysis saying it failed.
  
  I tried turning on the soft springs option too, and that didn't help.
  
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  - Re: Error message "Status code 3: Negative diagonal of matrix"
    
    Bill McEachern Nov 22, 2011 11:42 AM (in response to Ian Bonesteel)
    
    how many DOF? Does it work with isotropic shells instead of laminated?
    
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    - Re: Error message "Status code 3: Negative diagonal of matrix"
      
      Ian Bonesteel Nov 22, 2011 1:29 PM (in response to Bill McEachern)
      
      It has 251,574 DOF. If I define the shell as "thin" at 0.1" thickness with the same material, the analysis runs with the high quality mesh. I guess it only has trouble with laminates.
      
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      - Re: Error message "Status code 3: Negative diagonal of matrix"
        
        Bill McEachern Nov 22, 2011 1:33 PM (in response to Ian Bonesteel)
        
        I would check all the definitions for the lamianted materials and the ply schedule. could be an error in there. Of course this does not explain why it would run with tria 3s and not with tria 6's.
        
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        Re: Error message "Status code 3: Negative diagonal of matrix"
        
        Ian Bonesteel Nov 22, 2011 1:51 PM (in response to Bill McEachern)
        
        I redefined that surface and checked the composite orientation. I rotated the orientation where I had sections of the surface coming together and the axes for the material orientation were 90 degrees to one another. This seems to have done the trick, it now runs with a high quality mesh.
        
        Thank you very much for your help Bill.
        
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        Re: Error message "Status code 3: Negative diagonal of matrix"
        
        Bill McEachern Nov 23, 2011 9:05 AM (in response to Ian Bonesteel)
        
        Your welcome.
        
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