Rigid body

Karthic_22061
Karthic_22061 Altair Community Member
edited October 2020 in Community Q&A

Hi,

I am doing modal analysis, tried to make one of the component rigid by giving a high Young's modulus value. during computation

 

A fatal error has occurred
 
  *** ERROR # 277 ***
  Jacobi method failed.
  Max. off-diagonal term in matrix = 2.74951e+295.

 

Please help me in resolving... How to make the part rigid instead of using rb2 ?

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2017

    Hi Karthik,

     

    Try with RBODY (RIgid body) and check if this helps. 

  • Karthic_22061
    Karthic_22061 Altair Community Member
    edited August 2017

    Hi Prakash,

    How to make it. where do we find RBODY card?

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2017

    hi Karthik,

     

    You can right click on Model Browser>> Create>> Rigid body. Make sure you go through the Rbody card on OptiStruct help before you create as it gives a fair idea on what is required for Rbody.

  • Karthic_22061
    Karthic_22061 Altair Community Member
    edited August 2017

    Hi,

    I dont find Rigid body in the create of model browser. I am using HM v14

     

    <?xml version="1.0" encoding="UTF-8"?>image.thumb.png.90f5c3859da0ba1cfa72f90e7bd3d7ac.png

     

  • gopal_rathore
    gopal_rathore Altair Community Member
    edited August 2017

    Hi,

    I think rbody is not available for optistruct solver. You can see it in radioss . Might have come up in 17 version.

  • Karthic_22061
    Karthic_22061 Altair Community Member
    edited August 2017

    Thank you Gopal and Prakash,

     

    How to make the part rigid instead of using rb2 ?

    I tried giving a high Young's modulus value which results in computation error

     

    A fatal error has occurred
     
      *** ERROR # 277 ***
      Jacobi method failed.
      Max. off-diagonal term in matrix = 2.74951e+295.

  • gopal_rathore
    gopal_rathore Altair Community Member
    edited August 2017

    Hi,

    The methodology seems to be correct for making part rigid i.e provide a high value of E. Are we sure that this error is due to this? I mean is the model running properly if you use rbe2 for making rigid?

    Can you share the screenshot for material properties also?

    Jacobi method solves equation using a iterative method where it makes the off-diagonal term zero. Thus this might be a convergence issue also.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2017

    Hi Gopal and Karthik,

     

    There is a RBODY in OptiStruct starting from 2017. Please see the image.

     

    But I think the problem is coming from the flexbody frequencies as the offset is tool large.

     

    Can you try to reduce the mass of the rigid body and check if there is any improvement. 

    <?xml version="1.0" encoding="UTF-8"?>RBODY.PNG

  • Karthic_22061
    Karthic_22061 Altair Community Member
    edited August 2017

    Thank you,

     

    The model running properly if i assign a realistic value for E and also with rb2.

    All i need is Rbody card for the component which i coudn't find in Hm V14.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2017

    Karthik,

     

    Can you share the modulus value used?

     

    I dont know if there is a better way to define a rigid body. 

  • Karthic_22061
    Karthic_22061 Altair Community Member
    edited August 2017

    Hi Prakash,

    I used 9e150 Mpa

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2017

    Hi karthik,


    Can you try with something like 9E20/25?

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