Pre_stressed normal mode using sol 103

[Iley]

thread561-337439

Hello,

I want to use your first method with SOL103 using statsub .... when you talk about gravity load what is it? I saw that you were able to do this using FEMAP. can you send me the FEMAP program from your example?

You can also read my .bdf and tell me if a do a mistake.

Best Regards

 

[BlasMolero]

Dear Ikey,
In fact, pre-stiffened modal analysis is a great feature of NX NASTRAN modal (SOL103) solver, but I don't know if other "nastran flavour" solvers are allowed to do it.
Since modal analysis is essentially solving the differential equation of free-vibration, the load is not in the equation. So in SOL 103, the load is ignored. There are two method to take into account the gravity load effect, one is the use of STATSUB, the other is using nonlinear analysis (SOL106) with preload.

Here you are the procedure in the case of the gravity load: you need to specify the gravity load in a static subcase and including the STATSUB case control in the dynamic subcase will cause the differential stiffness to be computed and included in the normal mode solution (a similar procedure could be followed to include linear surface-to-surface contact in a modal analysis)
Here is an example with general load, inlcuding gravity load:

$
$ Preloaded Modal Analysis
$
SOL 103
TIME	  60
CEND
$*
TITLE	 = Axial Loading on a Rod - stress stiffening
ECHO	 = SORT 
$*
SUBCASE = 1 
$*
SPC = 1 
LOAD = 1
$*
SUBCASE = 2 
$*
SPC = 1 
$DISPLACEMENT(PRINT,PUNCH) = ALL 
METHOD = 1
$ take load 1 into account in modal analysis
STATSUB = 1 
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
BEGIN BULK
$*
$*  PARAM CARDS
$*
PARAM	AUTOSPC YES 
PARAM	COUPMASS      -1
PARAM	GRDPNT	      -1
PARAM	OUGCORD GLOBAL
PARAM	POST	      -2
PARAM	POSTEXT YES 
$*
EIGRL	       1		      10       0       7	MASS
$*
$*  GRID CARDS
$*
GRID	       1       0     0.0     0.0     0.0       0
GRID	       2       0 2.00000     0.0     0.0       0
GRID	       3       0 .200000     0.0     0.0       0
GRID	       4       0 .400000     0.0     0.0       0
GRID	       5       0 .600000     0.0     0.0       0
GRID	       6       0 .800000     0.0     0.0       0
GRID	       7       0 1.00000     0.0     0.0       0
GRID	       8       0 1.20000     0.0     0.0       0
GRID	       9       0 1.40000     0.0     0.0       0
GRID	      10       0 1.60000     0.0     0.0       0
GRID	      11       0 1.80000     0.0     0.0       0
$*
$*  ELEMENT CARDS
$*
CBAR	       1       1       1       3     0.01.000000     0.0
CBAR	       2       1       3       4     0.01.000000     0.0
CBAR	       3       1       4       5     0.01.000000     0.0
CBAR	       4       1       6       5     0.0-1.00000     0.0
CBAR	       5       1       7       6     0.0-1.00000     0.0
CBAR	       6       1       8       7     0.0-1.00000     0.0
CBAR	       7       1       9       8     0.0-1.00000     0.0
CBAR	       8       1      10       9     0.0-1.00000     0.0
CBAR	       9       1      11      10     0.0-1.00000     0.0
CBAR	      10       1      11       2     0.01.000000     0.0
$*
$*  MATERIAL CARDS
$*
$*
$*  I-DEAS Material: 7	name: MATERIAL7
MAT1	       7200.00+9	.29000007800.0001.1700-521.85000     0.0+ 
+	1.5000+91.5000+96.8000+7
$*
$*  PROPERTY CARDS
$*
$*
$*  I-DEAS property: 1	name: LINEAR BEAM1
$*  Fore Section   : 1	name: CARRE
PBAR	       1       72.5000-35.2083-75.2083-78.8020-7     0.0	+ 
+	.0250000.0250000.0250000-.025000-.025000-.025000-.025000.0250000+ 
+	.8333333.8333333
$*
$*  RESTRAINT CARDS
$*
SPC	       1       2    2345     0.0
SPC	       1       1   12345     0.0
$*
$*  LOAD CARDS
$*
FORCE	       1       2       01.000000-100000.     0.0     0.0
$*
ENDDATA

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

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