7.3.           EFFIND Alter

 

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$  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            *****

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

$

$     06-04- ATA/Paul Blelloch

$

$  Description:

$

$  This alter performs an effective independence scheme to optimally select

$  A-set DOF.  It starts from a candidate set defined by the user on USET

$  cards and iteratively removes DOF until it reaches a user specified number.  At

$  each iteration it eliminates the DOF lowest contribution to the

$  determinant of the Fisher Information Matrix.

$

$  This alter optionally allows the user to premultiply the mode shapes by the

$  square root of the mass matrix.  However it does not do a mass weighted

$  effective independence since it does not reduce the mass matrix.  Because

$  no reduction of the mass matrix is required it is possible to start with

$  a very large candidate set (>100,000 DOF).  This can be a useful method to

$  come up with a smaller candidate set for the Iterative Guyan Reduction or

$  Mass Weighted Effective Independence methods.

$

$  If the mass weighting option is not used the mode are initially scaled so

$  that the diagonal values of the Fisher Information Matrix are 1.0.  This

$  results in an initial determinant of close to 1.0.

$

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

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

$  eliminate one DOF at each step.  Setting EFFILT 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 EFFILT times

$  the largest ratio are eliminated at each step.

$

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

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

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

$  following steps.

$

$  The alter calculates and outputs the determinant of the Fisher

$  Information Matrix at each step.

$

$  At each step the alter writes the number of DOF removed, the number

$  of DOF remaining and the determinant of the Fisher Information Matrix

$  to the .f06 file.  It also writes the DOF removed at that step to the

$  .pch file.  At completion of the alter, the retained DOF are written

$  to both the .f06 and .pch files.

$

$  Special instructions to use this alter:

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

$  FILE MANAGEMENT SECTION (FMS)

$

$    No special input is required.

$

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

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

$

$    PARAM,MWEIGHT,CHAR8 'YES' : Weight modes by square root of mass matrix (default)

$                         'NO' : Use unweighted modes

$

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

$

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

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

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

$

$    PARAM,N1,I         : 1st FEM mode to use in error norm calculation (default = 1)

$

$    PARAM,N2,I         : Last FEM mode to use in error norm calculation (default = all)

$

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$  EXAMPLE NASTRAN DECKS

$

$

$    ASSIGN  MASTER='gpsc_aset.MASTER'

$    ASSIGN  DBALL ='gpsc_aset.DBALL'

$    $

$    SOL     103

$    INCLUDE effind.v2001

$    CEND

$    $

$    TITLE    = GENERAL PURPOSE SPACECRAFT

$    SUBTITLE = SELECT DOF

$    LABEL    = EFFECTIVE INDEPENDANCE METHOD

$    $

$    SPC = 1

$    METHOD = 50                 $ Modes to 50 Hz

$    $

$    BEGIN BULK

$    $

$    PARAM,NDOF,50             $ Select best 50 DOF

$    PARAM,MWEIGHT,YES         $ Mass weight modes

$    $

$    EIGR,50,AHOU,1.0,50.0

$    $

$    INLCUDE 'gpsc.blk'

$    $

$    ENDDATA

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