$-----------------------------------------------------------------------
$ 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)
$
$-----------------------------------------------------------------------
$ 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
$ $-----------------------------------------------------------------------