7.1.           COMPARE_MODES

 

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

$  Rigid Format 103 - Normal modes analysis

$  MSC/NASTRAN Version 2001 or NX Nastran Version 1.0

$

$

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

$     *****            COPYRIGHT  (C)  2004            *****

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

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

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

$

$     05-04- ATA/Paul Blelloch

$

$  Description:

$

$  This alter compares modes from two related models.  The models are related

$  in the sense that they share a subset of nodes.  The modal comparison is

$  based on a cross-orthogonality using the mass matrix from the first model.

$  Use alter write_modes to export the modes and mass matrix for the first

$  model.  This is typically the smaller model.  Use this alter in the second

$  model to calculate the orthogonality.

$

$  The data written to the .pch file in DMI format includes the frequencies of

$  both models, the pseudo-orthogonality of the 2nd model modes w.r.t. 1st

$  model mass matrix and the cross-orthogonality between the 2nd and 1st model

$  modes w.r.t. 1st model mass matrix.

$

$  Case 1:  Model 1 is a subset of Model 2

$

$  1) Export modes and mass matrix from Model 1 using a negative value of

$     PARAM,OMODES to write data to OUTPUT2 file.

$

$  2) Include this alter in a Model 2 modes run (can be a restart) to

$     calculate cross-orthogonality between modes.  The OUTPUT2 file from

$     the first run must be assigned to the unit number identified by

$     PARAM,OMODES (positive value in this case).

$

$  Case 2:  Subset of Model 1 is a suset of Model 2

$

$  Identical to Case 1, except the shared subset of nodes must be identified

$  in the 'U1' set in the Model 1 run.

$

$  Special instructions to use this alter:

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

$  FILE MANAGEMENT SECTION (FMS)

$

$

$    ASSIGN INPUTT2=fem_modes.op2 UNIT=11

$

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

$  EXECUTIVE CONTROL DECK

$

$    SOL 103

$    Include this alter immediately before the CEND statement

$

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

$  CASE CONTROL DECK

$

$    No special input is required.  The Case Control deck must include

$    standard modal solution requests (SPC, METHOD, etc.).  Some output

$    request such as DISP(PLOT)=ALL is required to force data recovery.

$

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

$  BULK DATA DECK

$

$    Optional parameters:

$

$    PARAM,OMODES,I  : Unit number of OUTPUT2 file from 1st model

$

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

$  EXAMPLE NASTRAN DECKS

$

$

$    ASSIGN  INPUTT2='gpsc_modes1.op2' UNIT=11 OLD

$    ASSIGN  MASTER='gpsc_aset.MASTER'

$    ASSIGN  DBALL ='gpsc_aset.DBALL'

$    RESTART

$    $

$    SOL     103

$    INCLUDE compare_modes.v2001

$    CEND

$    $

$    TITLE    = GENERAL PURPOSE SPACECRAFT

$    SUBTITLE = NORMAL MODES DATA RECOVERY RESTART

$    LABEL    = COMPARE TWO SETS OF MODES

$    $

$    SPC = 1

$    METHOD = 50                 $ Modes to 50 Hz

$    $

$    DISP(PLOT) = ALL            $ Recover but don't print displacements

$    $

$    BEGIN BULK

$    $

$    PARAM,OMODES,11             $ Fortran unit number

$    $

$    ENDDATA $-----------------------------------------------------------------------