In the Nastran v11 release notes they say you can now do multiple random analyses in the same deck. They provide an example.
In NX Nastran 11, the ANALYSIS case control command now includes the RANDOM subcase type for SOLs 108 and 111. With the new RANDOM type, you can streamline the process of performing multiple random analyses with the RANDOM and optionally RCROSS case control commands over frequency response subcases of the same frequencies. For example, in SOL 111: SDAMPING=101 SPC=2 ACCELERATION(RPRINT)=ALL STRESS(SORT2,PSDF)=ALL RCROSS(PRINT)=1 METHOD=1 $ SUBCASE 1 $ Normal Modes ANALYSIS=MODES DISP=ALL SUBCASE 2 $ Frequency Response using FREQ set 13 FREQUENCY=13 DLOAD=111 SUBCASE 3 $ Frequency Response using FREQ set 13 FREQUENCY=13 DLOAD=211 SUBCASE 4 $ Random Response referencing FRF from subcases 2 and 3 ANALYSIS=RANDOM RANDOM=100 SUBCASE 5 $ Random Response referencing FRF from subcases 2 and 3 ANALYSIS=RANDOM RANDOM=200 $ Change frequencies SUBCASE 11 $ Frequency Response using FREQ set 23 FREQUENCY=23 DLOAD=111 SUBCASE 12 $ Frequency Response using FREQ set 23 FREQUENCY=23 DLOAD=211 SUBCASE 14 $ Random Response referencing FRF from subcases 11 and 12 ANALYSIS=RANDOM RANDOM=1100 SUBCASE 15 $ Random Response referencing FRF from subcases 11 and 12 ANALYSIS=RANDOM RANDOM=1200
Has anyone managed to do this?
Even if I structure my case control as in the example, I cannot get any output for the random analysis even though there are no FATAL errors in the f06 file.
Any ideas what I am doing wrong?
Can you run multiple random analyses in the same deck?
Have you got all the cards defined? can you post the full input deck (no model required)
Sorry, I was away for a week.
The input deck is as per listing above, but referencing my DLOAD, RANDOM, SPC and METHOD card ids.
I get no random output in f06 file. Output is only the eigenvector tables.
Not sure what you mean by random output. rms, zero crossing?
I think you only get random data if you use XYPLOT card. something like
X Y - O U T P U T S U M M A R Y ( R E S P O N S E )
SUBCASE CURVE FRAME CURVE ID./ XMIN-FRAME/ XMAX-FRAME/ YMIN-FRAME/ X FOR YMAX-FRAME/ X FOR
ID TYPE NO. PANEL : GRID ID ALL DATA ALL DATA ALL DATA YMIN ALL DATA YMAX
1 ACCE 0 101( 4) 2.000000E+00 5.020000E+02 2.500000E-01 6.438968E+00 2.500000E-01 2.000000E+00
2.000000E+00 5.020000E+02 2.500000E-01 6.438968E+00 2.500000E-01 2.000000E+00
1 ACCE 0 149( 4) 2.000000E+00 5.020000E+02 1.527553E-01 5.020000E+02 3.915089E+00 1.198768E+01
2.000000E+00 5.020000E+02 1.527553E-01 5.020000E+02 3.915089E+00 1.198768E+01
Having said that if you use say
then you should get the PSD data point
POINT-ID = 1
A C C E L E R A T I O N V E C T O R
( POWER SPECTRAL DENSITY FUNCTION )
FREQUENCY TYPE T1 T2 T3 R1 R2 R3
1.000000E+01 G 2.150474E-22 1.356574E-23 9.752309E+06 6.971814E-02 3.980307E-05 1.898200E-26
1.200000E+01 G 4.459262E-22 2.813017E-23 9.811733E+06 1.453133E-01 8.302587E-05 3.936142E-26
1.400000E+01 G 8.261416E-22 5.211516E-23 9.882576E+06 2.708569E-01 1.548983E-04 7.292264E-26
The request ACCELERATION(RPRINT)=1, where SET 1 = 100001 would give you output in the f06 for a normal random analysis
A C C E L E R A T I O N V E C T O R ( ROOT MEAN SQUARE; RMSSF SCALE FACTOR = 1.00E+00 ) POINT ID. TYPE T1 T2 T3 R1 R2 R3 1000001 G 7.589160E+01 0.0 0.0 0.0 0.0 0.0 1 IBDM VERSION 01-06 AUGUST 8, 2017 NX NASTRAN 11/ 1/16 PAGE 23 RANDOM DLL EXCITATION IN X AXIS 0 RANDOM 4000 FREQUENCY = 0.000000E+00 A C C E L E R A T I O N V E C T O R ( NUMBER OF ZERO CROSSINGS ) POINT ID. TYPE T1 T2 T3 R1 R2 R3 1000001 G 7.643273E+02 0.0 0.0 0.0 0.0 0.0
In the multiple random analysis you get nothing.
Wondering whether someone from NX Nastran would like to comment?
Does this feature work?
Sorry, we got distracted with work ( hate when this happens :-) ). Let me get to it today and I'll report back.
I have attempted to attach sample runs. One with a single case which works, and another with multiple cases which doesn't.
Maybe you can show me where I am going wrong.