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I am trying to create an mnf in Nastran. I can do it with a different model, however, one particular model is failing. Also, this model does produce modes with a sol 103, it just wont make modes for the MNF. Here is the error:

jkollma4
 *** USER WARNING MESSAGE 4645 (REIG)
  THE SHIFTED STIFFNESS MATRIX IS NOT POSITIVE DEFINITE IN MHOUSEHOLDER METHOD.
 ^^^   
 ^^^  NASTRAN/ADAMS INTERFACE DMAP INFORMATION MESSAGE: 
 ^^^   
 ^^^  DURING A-SET ORTHONORMALIZATION,  
 ^^^  A TOTAL OF  -1     MODES WERE FOUND   
 ^^^  OUT OF A POSSIBLE  47     .  
 ^^^   
 ^^^   
 ^^^  NASTRAN/ADAMS INTERFACE DMAP INFORMATION MESSAGE: 
 ^^^  NO EIGENVALUES FOUND - EXITING       
 ^^^   
  • 0
    Hi John,
     
    Can produce the 6 rigid body modes when you run the SOL103 run only? If it is not the case, then this can mean that there are modeling issues.
     
    In order to make sure that your SOL103 is well set up in general and also well set up for MNF generation, I recommend that your review the article below in full details:
     
    Thank you,
     
    Maziar Rostamian
  • 0
    Hi Maziar,
     
    Thank you for the link.  I have reviewed it.  I do get 6 rigid body modes from a SOL103 without super sets.  The f06 file shows  6 modes with eigenvalues close to 0   and they look good in hyperview.  Once I add super sets there are no longer modes with eigenvalues close to 0 in the table of the f06 file.  The tables from the f06 file  from the run with super sets is copied below.  Inclusion of the "ADAMSMNF FLEXBODY=YES" card to the deck does not change the f06 table shown below.
     
     
  • 0
     
                           R E A L  E I G E N V A L U E S
                         (BEFORE AUGMENTATION OF RESIDUAL VECTORS)
      MODE  EXTRACTION   EIGENVALUE      RADIANS       CYCLES      GENERALIZED     GENERALIZED
      NO.    ORDER                                    MASS       STIFFNESS
        1     1    1.894790E+04    1.376514E+02    2.190790E+01    1.000000E+00    1.894790E+04
        2     2    2.849922E+04    1.688171E+02    2.686808E+01    1.000000E+00    2.849922E+04
        3     3    5.506694E+04    2.346635E+02    3.734785E+01    1.000000E+00    5.506694E+04
        4     4    6.365712E+04    2.523036E+02    4.015537E+01    1.000000E+00    6.365712E+04
        5     5    7.231339E+04    2.689115E+02    4.279859E+01    1.000000E+00    7.231339E+04
        6     6    8.273514E+04    2.876372E+02    4.577888E+01    1.000000E+00    8.273514E+04
        7     7    8.997696E+04    2.999616E+02    4.774037E+01    1.000000E+00    8.997696E+04
        8     8    1.166504E+05    3.415413E+02    5.435798E+01    1.000000E+00    1.166504E+05
        9     9    1.300681E+05    3.606496E+02    5.739916E+01    1.000000E+00    1.300681E+05
        10    10    1.369057E+05    3.700077E+02    5.888856E+01    1.000000E+00    1.369057E+05
     *** USER INFORMATION MESSAGE 5458 (REIG)
       QL HOUSEHOLDER METHOD IS AUTOMATICALLY SELECTED .
     *** USER INFORMATION MESSAGE 5458 (REIG)
       QL HOUSEHOLDER METHOD IS AUTOMATICALLY SELECTED .
     *** USER INFORMATION MESSAGE 5458 (REIG)
       QL HOUSEHOLDER METHOD IS AUTOMATICALLY SELECTED .
    1                                     DECEMBER 10, 2020 MSC Nastran 9/10/18  PAGE 1004
                                                        SUPERELEMENT 1        
    0                                                      SUBCASE 1        
     
                           R E A L  E I G E N V A L U E S
                         (AFTER AUGMENTATION OF RESIDUAL VECTORS)
      MODE  EXTRACTION   EIGENVALUE      RADIANS       CYCLES      GENERALIZED     GENERALIZED
      NO.    ORDER                                    MASS       STIFFNESS
        1     1    1.894790E+04    1.376514E+02    2.190790E+01    1.000000E+00    1.894790E+04
        2     2    2.849922E+04    1.688171E+02    2.686808E+01    1.000000E+00    2.849922E+04
        3     3    5.506694E+04    2.346635E+02    3.734785E+01    1.000000E+00    5.506694E+04
        4     4    6.365712E+04    2.523036E+02    4.015537E+01    1.000000E+00    6.365712E+04
        5     5    7.231339E+04    2.689115E+02    4.279859E+01    1.000000E+00    7.231339E+04
        6     6    8.273514E+04    2.876372E+02    4.577888E+01    1.000000E+00    8.273514E+04
        7     7    8.997696E+04    2.999616E+02    4.774037E+01    1.000000E+00    8.997696E+04
        8     8    1.166504E+05    3.415413E+02    5.435798E+01    1.000000E+00    1.166504E+05
        9     9    1.300681E+05    3.606496E+02    5.739916E+01    1.000000E+00    1.300681E+05
        10    10    1.369057E+05    3.700077E+02    5.888856E+01    1.000000E+00    1.369057E+05
        11    11    1.714073E+05    4.140136E+02    6.589231E+01    1.000000E+00    1.714073E+05
        12    12    1.785389E+05    4.225386E+02    6.724911E+01    1.000000E+00    1.785389E+05
        13    13    2.075774E+05    4.556066E+02    7.251205E+01    1.000000E+00    2.075774E+05
        14    14    2.799638E+05    5.291161E+02    8.421144E+01    1.000000E+00    2.799638E+05
        15    15    3.108393E+05    5.575296E+02    8.873360E+01    1.000000E+00    3.108393E+05
        16    16    3.505898E+05    5.921062E+02    9.423663E+01    1.000000E+00    3.505898E+05
  • 0
    Hi John,
     
    It'd be very helpful to have your model to review and test it. As you may have seen, I have already communicated with your via a support case (#00910920). Please let me know by replying to the email I sent you 12/9/2020 through that case.
     
    Thank you,
    Maziar
  • 0
    Hi Maziar,

    I will look into sending you the model. If you know anything, or have documents concerning Non-disclosure agreements between MSC and Ford please let me know.

    Thanks,
    John Kollman
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