×
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

Aeroelasticity (SOL144) - Problem with constraints

Aeroelasticity (SOL144) - Problem with constraints

Aeroelasticity (SOL144) - Problem with constraints

(OP)
Hi everyone,

I have a problem running my static aeroelastic analysis problem.

It consists of one wing represented as different beam elements along the span of the wing (has a kink).
To the nodes connecting the spanwise beams also always leave a beam towards the leading edge and one to the traling edge.

I have clamped the root (Node 201) with SPC1 1 1246 201.
And nodes 101 and 301, which are the leading and trailing edge at the root with SPC1 2 246 101 301.

Further I have specified a SUPORT 35 201 to perform the TRIM analysis.

I think this should sufficiently constrain the model. However I'm getting the following error.

CODE -->

*** SYSTEM INFORMATION MESSAGE 4159 (DFMSA)
     THE DECOMPOSITION OF KLL      YIELDS A MAXIMUM MATRIX-TO-FACTOR-DIAGONAL RATIO OF    8.627062E+07
 *** USER WARNING MESSAGE 4698 (DCMPD)
     STATISTICS FOR DECOMPOSITION OF MATRIX KLL.
     THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER THAN
     1.000000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.
     USER INFORMATION:
     THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO MESSAGES APPEAR IN THE TABLE ON THE NEXT PAGE.
1    MSC.NASTRAN AEROELASTIC JOB CREATED ON 30-NOV-12 AT 18:31:27          DECEMBER   1, 2012  MD NASTRAN  12/15/10   PAGE     8
     UNTITLED.SC1                                                                                                                   
0                                                                                                            SUBCASE 1              
0                                                                                                                                   
         GRID POINT ID       DEGREE OF FREEDOM   MATRIX/FACTOR DIAGONAL RATIO        MATRIX DIAGONAL                                
                                                                                                                                    
             209                    T1                   2.32532E+07                   2.46890E+16
             212                    T1                   2.68200E+07                   2.46728E+16
             212                    T2                   8.62706E+07                   8.00587E+15
             214                    T1                   1.70589E+07                   2.46624E+16
             214                    T2                   2.53534E+07                   8.03312E+15
             217                    T1                   2.55754E+07                   2.46445E+16
             217                    T2                   5.81368E+07                   8.07818E+15
             220                    T1                   2.59770E+07                   2.46251E+16
             220                    T2                   5.01106E+07                   8.12882E+15
 *** USER INFORMATION MESSAGE 3035 (SOLVER)
                                  FOR DATA BLOCK   KLR     
    SUPPORT PT.NO.             EPSILON             STRAIN   ENERGY     EPSILONS LARGER THAN 0.001 ARE FLAGGED WITH ASTERISKS
                1          4.9240492E-14         -2.6321411E-04                 
                2          4.9240492E-14         -2.2796631E-02                 
 ^^^     
 ^^^ USER   FATAL   MESSAGE 9050 (SEKRRS)    
 ^^^ RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL. 
 ^^^ USER ACTION:  CONSTRAIN MECHANISMS WITH SPCI OR SUPORTI ENTRIES OR SPECIFY PARAM,BAILOUT,-1 TO                                
     CONTINUE THE RUN WITH MECHANISMS. 

I have tried to run a modal analysis with the same structural model and this runs without problems. I'm guessing it goes wrong
somewhere in the definition of the splines. I'm currently using SPLINE4.

What I find weird is that nodes 209 - 220 are located from the kink to close to the wing tip, along the elastic axis.
Why is there a problem only at those nodes and not the others?

I will check tomorrow if I can perform a Flutter analysis with only one aerodynamic surface and spline defined and no elevator.

I have attached the .bdf and .f06. Hopefully somebody can give me a hint.

Thanks anyway!

RE: Aeroelasticity (SOL144) - Problem with constraints

I guess the best bet is to package all your run file and contact the nastran tech support.

BTW, have you tried using param,maxratio,1.+8 on your input deck? MSC does recommend using maxratio in the order of 1.+7 to 1.+8 on most production models. I don't think the loss of one significant digit is going to affect your solution accuracy!

RE: Aeroelasticity (SOL144) - Problem with constraints

(OP)
Thank you very much for your response.

First of all, fortunately I've been able to solve it over the weekend.

I found several errors which may have caused the problem.
One is the fact that the research student of whom I got the model represented rigid beams as normal beams with a Younghs modulus of 10^20 GPa, I guess that the 10^10 order of magnitude with the other beams is not appreciated by the solver.

An other problem seemed to be the aerodynamic coordinate system which had the Z axis pointing upwards just as the reference coordinate system. This caused a negative angle of attack and negative pressures which didn't made sense.

Thanks for the proposal to contact MSC but from their site I found that only commercial customers can use the support.
However, they seem to have some support personnel on their forum.

Kind regards.

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