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Modal computation of a tank in NX Nastran using the MFLUID feature

Hi,

 

I am trying to run a 103 modal computation of a filled tank.

The computation run without problem without the fluid content.

 

Now added the fluid including following entries in the deck file

(the attached image helps to understand the entries):

 

$RSMETHOD for dry modes

RSMETHOD = 13100

$METHOD for wet modes

METHOD = 13200
MFLUID=200

...

BEGIN BULK
$*  NX Modeling Object: EIGRL 1
EIGRL      13100        200.0000
EIGRL      13200         50.0000

...

PARAM      VMOPT       2

...

$ Entry for the outer shells (only wetted on one side, inside)

$ red part and outside yellow parts in the attached image

MFLUID       200       1 3.0e+02 1.0e-06      11               N       N

$ Entry for 2 inner shells (wetted on both sides)

$ inside yellow parts in the attached image
MFLUID       200       1 3.0e+02 1.0e-06              12       N       N

$

$ coordinate system for the MFLUID entries

CORD2R         1       0 5325.26-788.274520.6972 5325.26-788.274521.6972+

+        5326.26-788.274520.6972

...

$ Element list for the wetted on one side elements
ELIST         11     639     641     644     646     650     653     655+
+            657     658     662     665     666     667     669     670+

...

$ Element list for the both wetted side elements
ELIST         12   29058   29060   29061   29062   29063   29064   29065+
+          29070   29073   29074   29075   29077   29078   29079   29082+

 

 

The computation is not running and following error message appears:

 

 *** SYSTEM FATAL MESSAGE 3034 (LNNHERR)
     INTERNAL FAILURE IN THE LANCZOS PROCEDURE:
     M-ORTHOGONAL QR PROCEDURE FAILED TO CONVERGE.  PROBABLE CAUSE:
     MASS MATRIX IS INDEFINITE (MODES) OR STIFFNESS MATRIX IS INDEFINITE (BUCKLING).
     USER ACTION: CONTACT SIEMENS PLM SOFTWARE CUSTOMER SUPPORT.
 *** SYSTEM FATAL MESSAGE 7340 (LNNHERR)
     WARNING REPORTED BY SUBROUTINE LNNDRVD  (IER=   728)
     USER INFORMATION:  GRAM-SCHMIDT DID NOT CONVERGE.

 TABLE OF SHIFTS:  (LNNRIGL)
 SHIFT #        SHIFT VALUE         FREQUENCY, CYCLES     # EIGENVALUES BELOW    # NEW EIGENVALUES FOUND
     1.        9.8696039E+04          5.0000000E+01                31                        9
     2.       -4.1670943E-04         -3.2489032E-03                 0                       10
     3.        4.9348020E+04          3.5355335E+01                31                        0

 *** SYSTEM FATAL MESSAGE 7340 (LNNRIGL)
     TRIDIAGONAL QL DID NOT CONVERGE.
     THIS RUN IS TERMINATED. PARAM,BAILOUT,-1 MAY BE USED TO CONTINUE THE RUN.

0FATAL ERROR
1                                        * * * END OF JOB * * *
 

 

Maybe I made an error in the MFLUID definition?

I used for example the same coordinate system 1 for both MFLUID definition.

 

Thank you in advance for any hints.

Best regards

Sébastien

 

 

3 REPLIES

Re: Modal computation of a tank in NX Nastran using the MFLUID feature

You can try one of the following to see if that helps to get around the error

 

1. Add "sys426=1" to the nastran command line (selects REDMULT performance method)

2. Add "sys263=6" or "sys263=15" (changes the MAXSET of the EIGRL card from the default of 7)

 

Let us know if this resolves your issue


Thanks

Re: Modal computation of a tank in NX Nastran using the MFLUID feature

 

Re: Modal computation of a tank in NX Nastran using the MFLUID feature

Hi,

thank you very much for your quick answer and the hints.

In the meantime I could run the computation without error message (reviewing the MFLUID deck entries like coordinate systems, etc).

 

Kind regards

Sébastien