×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

LGMASS Problem

LGMASS Problem

LGMASS Problem

(OP)
I'm trying to run a model using NX NASTRAN 4.0 using the Large Mass Method and I keep getting garbage results. When I run the model using the enforced acceleration method I get results that make sense. I'm pretty sure that my set-up is okay because I tried using the same set-up on a different model and it works just fine. I've also run basic model checks and the model appears to check out. When I run using the enforced acceleration method I get the accelerations that match the curves I'm trying to generate. When I run the LGMASS method my accelerations do not fit to any curve that I expected and the values are 3-4 orders of magnitude too small. Any suggestions?

Here is my basic set-up:

DLOAD          1      1.      1.     102
FREQ1       1001      5.     0.1     950
RLOAD2       102     101                    1001            LOAD
FORCE        101     100       0     1.0     0.0  1.0E11     0.0
SPC            1     100     456      0.
SUPORT       100     123
CONM2        100     100       0  1.0E11
GRID         100       0      0.   -6.81      0.       0
CELAS2       101   1.E+9       1       1     100       1      0.
CELAS2       102   1.E+9       1       2     100       2      0.
CELAS2       103   1.E+9       1       3     100       3      0.
CELAS2       104  1.E+11       1       4     100       4      0.
CELAS2       105  1.E+11       1       5     100       5      0.
CELAS2       106  1.E+11       1       6     100       6      0.

RE: LGMASS Problem

My first guess would be a units mismatch, i.e. the force you are applying is not correct...  The large mass method should work just fine and should give similar results...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources