An IRS TAM requires only the irs_tam alter. No other parameters or input are required.
A sample input file to create an IRS TAM is shown in Figure 3-4. This also includes the ortho alter to calculate pseudo- and cross-orthogonality.
gpsc_itam.dat
ASSIGN INPUTT4='gpsc_fem.op4', UNIT=13
ASSIGN MASTER ='gpsc_itam.MASTER', DELETE
ASSIGN DBALL ='gpsc_itam.DBALL', DELETE
$
SOL 103 $ Normal modes
INCLUDE 'ortho.v2001'
INCLUDE 'irs_tam.v2001'
CEND
TITLE =GENERAL PURPOSE SPACECRAFT (GPSC)
SUBTITLE =TAM - IRS 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 3-4. An alter is required for an IRS TAM.
For this example, the pseudo-orthogonality of the FEM mode shapes with respect to the IRS reduced mass matrix is presented in Table 3-5. The cross-orthogonality between the TAM and FEM mode shapes is presented in Table 3-6. For this example the IRS TAM generates pseudo- and cross-orthogonality matrices that are within 1% of the “exact” solution.
Table 3-5. Pseudo-orthogonality of FEM modes w.r.t. IRS reduced mass matrix.
Table 3-6. Cross-orthogonality of TAM/FEM modes w.r.t. IRS reduced
mass matrix.