3.5.           Comparing Test and Analysis Models

The TAMKIT ortho alter can be used to evaluate test self-orthogonality and FEM-test cross-orthogonality.  It will also calculate test self MAC and FEM-test cross MAC. To do this the test mode shapes and frequencies must be converted to DMIG and DMI cards respectively. The method for doing this depends on the format of the test data, but if the user is using IMAT he can use the shp2dmig function provided with TAMKIT to write an IMAT shape structure to DMIG and DMI format. The test mode shape matrix must be written to a DMIG matrix named PHITEST and the test frequencies are written to a DMI matrix name LAMAT. The calculation of test orthogonalities by the ortho alter is triggered by the existence of the test mode shapes and frequencies. The default behavior of the ortho alter does not renormalize the FEM modes, so to get a more true comparison of your test and FEM modes PARAM,NORMFEM should be set to ‘YES.’  The procedure for using the ortho alter is described in Section 3.3. An example Nastran input that uses ortho to compare test and analysis modes is listed in Figure 3-22.  The read_tam and rpt_tam Matlab functions read and report test/FEM orthogonalities and MAC values as well as TAM/FEM.

gpsc_tortho.dat

 

ASSIGN INPUTT4='gpsc_fem.op4', UNIT=13

ASSIGN MASTER ='gpsc_tortho.MASTER', DELETE

ASSIGN DBALL  ='gpsc_tortho.DBALL', DELETE

$

DIAG 8 $

SOL     103     $ Normal modes

$

$  Write modal data

$

INCLUDE 'ortho.v2001'

$

CEND

TITLE    =GENERAL PURPOSE SPACECRAFT (GPSC)

SUBTITLE =TEST-ANALYSIS CORRELATION

$

SPC    = 10             $ Constrain booster interface points

METHOD = 70             $ Modes to 70 Hz

$

DISP(PUNCH)   = ALL     $ Recover but do not print mode shapes

MEFFMASS(ALL) = YES     $ Calculate modal effective mass

$

BEGIN BULK

$

PARAM   WTMASS  .00259

PARAM   POST    -2

PARAM   MAC     YES

PARAM   OMODES  13

$

EIGRL   70      1.0     70.0

$

$  Spacecraft bulk data

$

INCLUDE 'gpsc.blk'

INCLUDE 'gpsc.prp'

$

INCLUDE 'gpsc_ei.aset'

$

INCLUDE 'gpsc_test.dmig'

$

ENDDATA

Figure 3-22. Sample input file for test-analysis correlation using ortho alter