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