Could someone explain me how can I do a restart from sol 106 into sol 103? The purpose is to calculate normal modes by using differential stiffness matrix from sol 106 but by changing buoundary conditions.
In other words, I have to calculate free-free normal modes with sol 103 by using the differential stiffness matrix from sol 106. This last procedure has been used to calculate a non linear static solution with a self-balanced load condition (aerodynamic + inertial + propulsive loads) by restraining the FE model grid representative of the whole airplane center of gravity.
Thanks for you help!

Hello!,

With FEMAP & NX NASTRAN SOL 106 you have an easy way to perform modal analysis with pre-load. The key is to put the METHOD command in the case control and put an eigenvalue card, such as EIRGL, in the bulk data session. Also, param LGDISP needs to be specified to compute the differential stiffness, and NMLOOP should be a value not equal to zero so that the normal modes are computed based on the updated non-linear stiffness.

Here is an example:
$
$ Normal Mode Analysis with Preload - Solution 106
$ Note that LGDISP = 1 is set to get differential stiffness matrix
$ case control METHOD = 10 calls eigenvalue module
$
SOL 106
$
CEND
$
TITLE = Normal Modes with Preload
SUBCASE 1
  NLPARM = 1
  LOAD = 1
  METHOD = 10
  SPC = 100
  DISPLACEMENT = ALL
$
BEGIN BULK
$
$------8-------8-------8-------8-------8-------8-------8-------8-------8-------
8
$
$  Param Cards
$
PARAM      WTMASS 0.00259
PARAM    COUPMASS       1
PARAM        POST      -2
$
$ Nodes
$
GRID           1       0      0.      0.      0.
GRID           2       0     10.      0.      0.
GRID           3       0     20.      0.      0.
GRID           4       0     30.      0.      0.
GRID           5       0     40.      0.      0.
GRID           6       0     50.      0.      0.
GRID           7       0     60.      0.      0.
GRID           8       0     70.      0.      0.
GRID           9       0     80.      0.      0.
GRID          10       0     90.      0.      0.
GRID          11       0    100.      0.      0.
$
$ Bar Elements
$
CBAR           1      11       1       2      0.      1.      0.
CBAR           2      11       2       3      0.      1.      0.
CBAR           3      11       3       4      0.      1.      0.
CBAR           4      11       4       5      0.      1.      0.
CBAR           5      11       5       6      0.      1.      0.
CBAR           6      11       6       7      0.      1.      0.
CBAR           7      11       7       8      0.      1.      0.
CBAR           8      11       8       9      0.      1.      0.
CBAR           9      11       9      10      0.      1.      0.
CBAR          10      11      10      11      0.      1.      0.
$
$ Bar Properties
$
PBARL          11      12           I                +
+          2.      1.      1.      .1      .1      .1
$
$ Material Properties
$
MAT1          12  1.0E+7         .33    .101
$
$ Restraints
$
SPC1         100     345       1    THRU      11
SPC1         100    1234       1
SPC1         100     234      11
$
$------8-------8-------8-------8-------8-------8-------8-------8-------8-------
8
$
$  EIGRL Card for Eigenvalue Specification
$
EIGRL          10               3
$
$  PARAM Cards: LGDISP & NMLOOP
$
PARAM      LGDISP       1
PARAM      NMLOOP       5
$
$  NLPARM Card
$
NLPARM           1       5        AUTO       5      25      PW      NO+
+           0.001  1.0E-7
$
$  FORCE Card
$
FORCE           1      11       0    500.      1.      0.      0.
$               
$
ENDDATA


Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director
 
IBERISA
48011 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

Thank you for the answer Blas.
I did as you suggest in the first time, but the problem is that this approach does not let me change the boundary conditions. More in details, I have to remove the constraint used for running the sol 106. I need to calculate normal modes for an unrestrained condition.
thank you again.
Best regards

Nicola