This manual describes the theory and operation processes for selecting instrumented degrees of freedom (DOF) for a modal test and creating a test-analysis model (TAM) using a number of different reduction methods. A test-analysis model (TAM) is a mathematically reduced version of a finite element model (FEM). A FEM will usuÂally contain tens of thousands, hundreds of thousands, or even millions of DOF. In a TAM, only those DOF are retained which correspond to accelerometers in a modal survey, typically one or two hundred. The accuracy of the TAM is a function of the instrumented DOF and the mathematical process used to reduce the FEM to those DOF. A typical FEM and TAM are shown in Figure 1-1.
Figure 1-1. A TAM is a mathematically reduced version of a finite element model.
TAMKIT provides procedures for selecting the instrumented
DOF and for reducing the FEM matrices to these DOF. It is implemented
as a set of Nastran DMAP alters, with some Matlab functions used to read
and interpret the Nastran data. It also includes procedures for comparing
two similar models, and for comparing test and analysis modes on completion
of the modal test. The overall process covered by TAMKIT along with the
corresponding alters and MATLAB functions, is summarized in Table 1-1.
Table 1-1. Summary of Procedures and Alters/Functions Provided in TAMKIT
Step |
Alters |
MATLAB Functions |
Evaluate test article |
compare_modes |
|
Select instrumented DOF |
write_gpke residual_kinetic_energy iter_rke fast_iter_rke iter_guyan effind mass_weighted_effind |
read_ke rpt_ke pch2aset |
Create TAM |
dynamic_tam irs_tam modal_tam hybrid_tam |
|
Evaluate TAM |
ortho |
read_tam rpt_tam |
Compare test and analysis results |
ortho
|
read_tam rpt_tam |
Expand test mode shapes |
expand_modes |
|
Localize errors in the model |
expand_modes ortho |
|