7.9.           ITER_RKE Alter

 

$-----------------------------------------------------------------------

$  Rigid Format 103 - Normal modes analysis

$  MSC/NASTRAN Version 2001 or NX Nastran Version 1.0

$

$

$     ******************************************************

$     *****            COPYRIGHT  (C)  2003            *****

$     *****          BY ATA ENGINEERING INC.           *****

$     *****             ALL RIGHTS RESERVED            *****

$     ******************************************************

$

$     09-03- ATA/Paul Blelloch

$

$     07-18-06 ATA/George Antoun

$        o Now writes initial user-defined ASET to punch file

$

$  Description:

$

$  This alter performs an Iterative Residual Kinetic Energy scheme to optimally

$  select A-set DOF.  It starts from a small A-set defined by the user and

$  iteratively adds DOF until it reaches a user specified number.  At

$  each iteration it add the DOF with the highest residual kinetic energy

$  across all FEM modes.

$

$  The number of DOF eliminated at each step of the iterative process is

$  controlled by the parameter GUFILT.  The default value of 1.0 will

$  eliminate one DOF at each step.  Setting GUFILT to a value less than

$  1.0 may result in a larger number of DOF eliminated at each iterative

$  step.  All DOF with a stiffness/mass ratio greater than GUFILT times

$  the largest ratio are eliminated at each step.

$

$  If the value of GUFILT results in deleting enough DOF that the

$  remaining number is less than NGUYAN at any step it is internally

$  reset to 1.0.  From this point on one DOF will be eliminated at all

$  following steps.

$

$  Currently this alter will calculate the eigenvalues for the reduced

$  mass and stiffness matrices, but will then fail.  It will write the

$  selected DOF list to the PCH file.  This can be used to create ASET

$  cards to perform a Guyan reduction.

$

$  Special instructions to use this alter:

$-----------------------------------------------------------------------

$  FILE MANAGEMENT SECTION (FMS)

$

$  If no ASET is defined, a considerable amount of scratch space may be

$  required.  This may require the addition of a card of the following

$  form

$

$  INIT SCRATCH LOGICAL=(SCR1(20GB)),

$               SCR300=(SCR300(20GB))

$

$-----------------------------------------------------------------------

$  EXECUTIVE CONTROL DECK

$

$    SOL 103

$    Include this alter immediately before the CEND statement

$

$-----------------------------------------------------------------------

$  CASE CONTROL DECK

$

$    No special input is required.

$

$-----------------------------------------------------------------------

$  BULK DATA DECK

$

$    Optional parameters:

$

$    PARAM,NGUYAN,I     : Number of DOF in final set (no default)

$

$    PARAM,GUFILT,RS    : Filter to remove DOF at each step (default = 1.0)

$

$    PARAM,OMODES,I     <0 : Read FEM modes from OUTPUT2 file UNIT = |OMODES|

$                        0 : Do not calculate orthogonality (no FEM modes)

$                       >0 : Read FEM modes from OUTPUT4 file UNIT = OMODES

$

$-----------------------------------------------------------------------

$  EXAMPLE NASTRAN DECKS

$

$

$    ASSIGN  MASTER='gpsc_aset.MASTER'

$    ASSIGN  DBALL ='gpsc_aset.DBALL'

$    $

$    SOL     103

$    INCLUDE iter_guyan.v2001

$    CEND

$    $

$    TITLE    = GENERAL PURPOSE SPACECRAFT

$    SUBTITLE = SELECT DOF

$    LABEL    = ITERATIVE GUYAN REDUCTION METHOD

$    $

$    SPC = 1

$    METHOD = 50                 $ Modes to 50 Hz

$    $

$    BEGIN BULK

$    $

$    PARAM,NGUYAN,50             $ Select best 50 DOF

$    PARAM,GUFILT,0.9            $ Eliminate DOF with > 90% of max ratio

$    $

$    EIGR,50,AHOU,1.0,50.0

$    $

$    INLCUDE 'gpsc.blk'

$    $

$    ENDDATA

$

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