Problems with Rotor

[Supituki]

Hi everyone,

I have a problem with a rotor dynamic analysis. I'm new with Nastran but after trying thousand of times i dropped the towel with this little issue. These are the steps i have followed:

-I define a steady rotor with all its nodes, spin direction nodes and spinning velocities. There is no problem with it.

-I define the material and shape properties of all the elements. No problems with it.

-I configure the analysis with the "Complex Eigenvalue" SOL 110 solution. Then in the subcase i have tried both "Synchronous" and "Asynchronous" options for the rotor.

-I launch the analysis and after 5seconds it stops. I get the following message in the F06 file:

*** USER FATAL MESSAGE 315 (IFPDRV)
FORMAT ERROR ON BULK DATA ENTRY RSPINR
RSPINR 1 1 21 0. RPM 300.


M O D E L S U M M A R Y

NUMBER OF GRID POINTS = 25

NUMBER OF CBAR ELEMENTS = 20
NUMBER OF CELAS1 ELEMENTS = 4

^^^
^^^ USER FATAL MESSAGE 9002 (IFPS)
^^^ ERROR(S) ENCOUNTERED IN THE MAIN BULK DATA SECTION
^^^ SEE MESSAGES ABOVE. ERROR ENCOUNTERED IN MODULE IFP,



Does somebody know what i am doing wrong? At least a clue? I really need to solve this. Although it looks simple i cannot get over it

 

[Spirit]

Supituki,

try to rewrite your card like:

RSPINR 1 1 21 RPM 300.

This should be the correct sintax, I assume numbers are correct.

Regards,

Spirit



'Ability is 10% inspiration and 90% perspiration.'

 

[Supituki]

Thanks Spirit for your answer.

If you were wondering what that 0. means, it is the Damping coefficient of the Rotor. So i think that the problem isn't that. I introduced another example with damping and i got the same line but with a .3 instead of a 0.


Now i remember that a mate had problems with the Rotor Dynamics in the Nastran2007R1 version despite having technical support. Instead of solving it, he got directly a license for the Nastran 2005 Rotor Dynamics.


Anyway, has someone any idea where the problem would be and how it could be solved? Is there any patch?

Regards,
Supituki

 

[Spirit]

Supituki,

the problem is indeed not in the number value, but in the number itself. The current syntax for the RSPINR card for the NASTRAN2008 version is:

RSPINR ROTORID GRIDA GRIDB SPDUNT SPDINT

For versions up to 2005 it was indeed:

RSPINR ROTORID GRIDA GRIDB GR SPDUNT SPEED1 ... SPEEDn

It looks like there is a mismatch between the syntax of your pre-processing and the syntax of your solver. What I would suggest is editing the bulk data according to 2008 rules and submitting it to the solver manually. Seems way better than going back to the old solver just for this single small glitch.

Regards,

Spirit





'Ability is 10% inspiration and 90% perspiration.'

 

[Supituki]

Thanks again Spirit!

As i said before i'm new with Nastran and i don't know much about it.

I have found in the .bdf file where this RSPINR array is written and i can change it but that is after the analysis is done. Before the analysis i have just the .db and .ses, where i cannot change anything of relevance.

I found a manual where how the data is introduced is explained but not where... or how....

-How or where can i introduce those values manually?
-Where can i modify the RSPINR Card?



Thanks in advance

regards,

supituki

 

[Spirit]

Supituki,

I assume you must also have NASTRAN installed on your WS. So, when you are in the 'Analysis' menu in PATRAN, choose the 'Analysis Deck' option instead of 'Full Run'.
This should produce the appropriate .bdf file without running it. At this point, you can open the .bdf, edit it by hand and submit it to NASTRAN. You can then process the results importing them back into PATRAN.

Regards.

Spirit



'Ability is 10% inspiration and 90% perspiration.'

 

[Supituki]

Thanks Spirit

It looks like that the problem is solved. I get other Error reports, but at least the "ERROR ON BULK DATA ENTRY" isn't there anymore.

I'll keep fighting with the modell.

Thank you for all

Supituki

 

[Supituki]

Hi and Happy New Year!

I've been working on simple models which just had a rotor. Nothing else. But after modifying the BDF file i get another error that i cannot solve. As i dont have any references I'm not sure if the error is from the modelling or from the Solver and the problem above described.


1-I defined The rotor as steady with Nodes 30:50. The extrem nodes are 30 and 5, and 300RPM the speed. The property of the Bar elements is a Rod with R=100 defined in the section library.

2-Afterwards i defined the bearings with a MPC Rigid(Fixed) in Nodes 30 and 50. These Nodes 30 and 50 are independent while i define other four dependent Nodes for each MPC.

I submit the calculus and i get the next error message in the .F06:

*** USER WARNING MESSAGE 4698 (DCMPD)
STATISTICS FOR DECOMPOSITION OF MATRIX KXX.
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 JOB CREATED ON 12-JAN-11 AT 15:57:34 JANUARY 12, 2011 MSC.NASTRAN 4/ 3/07 PAGE 6
0 SUBCASE 1
0
GRID POINT ID DEGREE OF FREEDOM MATRIX/FACTOR DIAGONAL RATIO MATRIX DIAGONAL

31 T1 1.00000E+15 1.25632E+08
31 T2 -1.00545E+16 3.74560E+07
31 T3 -1.67574E+15 3.74558E+07
31 R1 -1.98735E+15 2.42596E+11
31 R2 -7.57038E+13 4.07719E+11
31 R3 2.51485E+14 4.07720E+11
*** 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 9119 (MMFIND1)
^^^ 5 RIGID BODY MODE(S) AND 0 MASSLESS MECHANISM(S) ARE DETECTED.

____________________________________________________________

After analyising it, i find 2 suspicious things:

1- 5 Rigid Body Modes? When i define the MPC i have four dependent Nodes. I tried these nodes both constraint with Displacement <0,0,0> and nothing defined in them. In the Constraint option i get a warning. With the other one i get no warnings. Am I defining wrong the constraints? How could i define them correctly? I read in another Post that MPC RBE could be correct too...

2- Why do i get an error in Node 31? Just in 31? I is very strange as the model is perfectly simetric! I dont understand this fact.

Could someone help? I have tried thousand different ideas and nothing!

Thanks to everyone in advance!

Supituki