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RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL
4

RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

(OP)
hi all,
i am relatively new to nastran, I use patran to generate the nastran input file.i keep getting this error message

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


my FEA problem is as follows. its a 2d problem where there are 2 rectangular plates one top of another whose ends are constrained at the extreme ends as a "displacement constraint". 2 forces eual and opposite in direction are applied at the centre of the 2 plates in Y direction.


both plates were meshed using quad 4 "paver" as they were not perfect retangular plates.

a part my bulk data file looks as follows:

BEGIN BULK
PARAM    POST    0
PARAM    AUTOSPC YES
PARAM   COUPMASS 1
PARAM   PRTMAXIM YES

$ Loads for Load Case : Default
SPCADD   2       1
LOAD     2       1.      1.      1       1.      3
$ Displacement Constraints of Load Set : disp
SPC1     1       123456  1       2       3       4       5       28
         29      30      31      32      55      56      57      58
         59      82      83      84      85      86      131     132
         133     134     135     158     159     160     161     162
         185     186     187     188     189     212     213     214
         215     216     217     219     220     221     222     255
SPC1     1       123456  281     THRU    292
SPC1     1       123456  349     350     351     352     353     354
SPC1     1       123456  365     THRU    371
SPC1     1       123456  396     397     398     447     448     449
         474     475     476
$ Nodal Forces of Load Set : force_upper
FORCE    1       499     0       15000.  0.     -1.      0.
FORCE    1       502     0       15000.  0.     -1.      0.
$ Nodal Forces of Load Set : force_lower
FORCE    3       250     0       15000.  0.      1.      0.
FORCE    3       253     0       15000.  0.      1.      0.
$ Referenced Coordinate Frames




if any one could help me with this, thanks in advance

Ashish

RE: RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

Hello
I think its due to under constraints( i.e u need to provide more constraints).Go for a shell element .
You could get over this problem

RE: RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

Hello

Go for "bending element" i thnk that could help.

regards

RE: RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

3
Use the PARAM, BAILOUT, -1 Option to avoid the termination of the solution.With the result you can probably detect, what is wrong with your model, e.g. a lack of constraints.

RE: RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

If your matrix/diagonal ratio is around the order of E+08 or E+09 then you can set that as a maximum which will allow your model to run and still get good results.  NASTRAN has a smaller default ratio which wont allow it to run.  Right now, your model is "soft" as we here like to call it... Add this line...

PARAM,MAXRATIO,1.0E+09

If that doesnt work, increase the 1.0E+09 to something higher.  Hope this helps...

RE: RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

Before you do the above, make SURE you equivalence your model in PATRAN. (Elements...equivalence..)  This should solve your problem or reduce the number of failed ratios.

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