3.2.5.      Creating a Modal TAM

A modal TAM requires the modal_tam alter and the FEM mode shapes in DMIG, OUTPUT2 or OUTPUT4 format. No other parameters or input are required.

A sample input file to create a Modal TAM is shown in Figure 3-5. This also includes the ortho alter to calculate pseudo- and cross-orthogonality. Note that in the case of the modal TAM the FEM mode shapes are required whether or not the orthogonality calculations are made.

gpsc_mtam.dat

 

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

ASSIGN MASTER ='gpsc_mtam.MASTER', DELETE

ASSIGN DBALL  ='gpsc_mtam.DBALL',  DELETE

$

SOL     103     $ Normal modes

INCLUDE 'ortho.v2001'

INCLUDE 'modal_tam.v2001'

CEND

TITLE    =GENERAL PURPOSE SPACECRAFT (GPSC)

SUBTITLE =TAM - MODAL REDUCTION AND ORTHOGONALITY

$

SPC    = 10             $ Constrain booster interface points

METHOD = 70             $ Modes to 70 Hz

$

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

$

BEGIN BULK

$

$  PARAMeter cards

$  ---------------

$

PARAM   GRDPNT  0

PARAM   USETPRT 0

PARAM   WTMASS  .00259

PARAM     OMODES    13

$

$  Compute eigenvalues using the Lanczos method

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

$

EIGRL   70              70.

$

$  Spacecraft bulk data

$  --------------------

$

INCLUDE 'gpsc.blk'

INCLUDE 'gpsc.prp'

$

$  Static reduction data

$  ---------------------

$

INCLUDE 'gpsc_rke1.aset'

$

ENDDATA

Figure 3-5. An alter and FEM mode shapes are required for a modal TAM.

For this example, the pseudo-orthogonality of the FEM mode shapes with respect to the modally reduced mass matrix is presented in Table 3-7. The cross-orthogonality between the TAM and FEM mode shapes is presented in Table 3-8. The modal TAM generates “exact” pseudo- and cross-orthogonality as expected[15].

Table 3-7. Pseudo-orthogonality of FEM modes w.r.t. modally reduced mass matrix.

Table 3-8. Cross-orthogonality of TAM/FEM modes w.r.t. modally reduced mass matrix.