Abstract: To distinguish the real modal
from the false one and to identify the modal parameters
accurately are two key problems in applying ITD as an
identification technique. The ITD method uses a confidence
factor of the modal to distinguish the real from the false, its
accuracy is significantly influenced by the noise in the
recorded signal and the numbers of the measured points, and the
results have to be judged artificially. This method also
requires to change the least square equations into the form of
normal equations to solve the matrix of the system, which makes
a worse ill-condition and instability of the equations to be
solved. In order to improve the ITD method, the real and false
modals are distinguished by means of the comparison of the
frequence values of different series, with which a quite
reasonable reliability can be assured even with less measuring
points and the influence of the recorded noise on the real modal
of the system can be reduced to a minimum extent. An improved
Gram-schmit orthogonalization approach is used to solve the
least square equations in the identification calculation for a
higher precision. An identification program is designed with the
FORTRAN77 algorithmic language. With the program several tests
are performed with satisfactory results.
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