7.13.       RESIDUAL_KINETIC_ENERGY 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            *****

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

$

$     09-03- ATA/Paul Blelloch

$

$  Description:

$

$  This alter calculates residual kinetic energy as a measure of DOF to

$  be added to the A-set.  This calculation requires two runs.  The first

$  is a set of FEM modes without any reduction.  The second is based on

$  a preliminary A-set selection that is a subset of the final selection.

$  The residual kinetic energy provides a "measure" of which DOF should

$  be added to A-set in order to improve the ability to measure specific

$  modes.  It is calculated as follows:

$

$  [DPHI] = [PHIO] - [GOT]*[PHIA]    - Error in expanded mode shapes

$

$  [RKE]  = [MOO]*[DPHI].^2          - Residual Kinetic energy

$

$  where

$

$  [PHIA] - A-set partition of FEM mode shapes

$  [PHIO] - O-set partition of FEM mode shapes

$  [GOT]  - Guyan shapes for preliminary A-set reduction

$

$  Two runs are required.  The first should use alter write_modes to write

$  the mode shapes of the full FEM.  The second reads those mode shapes in

$  in various formats calculate residual kinetic energy.  The

$  results are written to the .pch file in DMIG format.  Each column of the

$  residual kinetic energy matrix is normalized to a maximum value of 1.0

$  in order to make it easier to identify critical DOF.

$

$  Special instructions to use this alter:

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

$  FILE MANAGEMENT SECTION (FMS)

$

$

$    If the OUTPUT2 or OUTPUT4 options are chosen these should be assigned

$

$    ASSIGN INPUTT4=fem_modes.op4 UNIT=11

$

$    or

$

$    ASSIGN INPUTT2=fem_modes.op2 UNIT=11

$

$    Note that a formatted OUTPUT4 file can be used as follows

$

$    ASSIGN INPUTT4=fem_modes.op4 UNIT=11 FORMATTED

$

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

$                        0 : Read FEM modes from DMIG cards in bulk data

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

$

$    PARAM,KENORM,CHAR8  No: Do not normalize RKE shapes to sum of 100.0

$                       Yes: Do normalize RKE shapes to sum of 100.0 (default)

$

$    PARAM,KEFILT,RS       : Do not print terms less than KEFILT (default = 0.0)

$

$    PARAM,ORTHO,CHAR8   No: Do not calculate cross and pseudo orthogonality

$                       Yes: Calculate and print cross and pseudo orthogonality (default)

$

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$  EXAMPLE NASTRAN DECKS

$

$

$    ASSIGN  INPUTT4='gpsc_modes.op4' UNIT=11 OLD

$    ASSIGN  MASTER='gpsc_aset.MASTER'

$    ASSIGN  DBALL ='gpsc_aset.DBALL'

$    RESTART

$    $

$    SOL     103

$    INCLUDE residual_kinetic_energy.v2001

$    CEND

$    $

$    TITLE    = GENERAL PURPOSE SPACECRAFT

$    SUBTITLE = NORMAL MODES DATA RECOVERY RESTART

$    LABEL    = RESIDUAL KINETIC ENERGY CALCULATIONS

$    $

$    SPC = 1

$    METHOD = 50                 $ Modes to 50 Hz

$    $

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

$    $

$    BEGIN BULK

$    $

$    PARAM,OMODES,11             $ Calculate residual kinetic energy

$    PARAM,KENORM,0              $ Normalize RKE to maximum of 1.0

$    PARAM,KEFILT,0.01           $ Do not print terms smaller than 0.01

$    $

$    ENDDATA

$

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