4 - Memorial University of Newfoundland DAI

n new valucof FPB(M) or AIC[M) excecda the previous one; the iteration
is then lerminatod. (Both eritcria are "red in this trealiro.)
6.3 Estimating Modal Parameters
R~timnting rcnonnnt frcqoency and damping ratio. from the MEM spectral
vs~imntc (i.. . oquation (6.22) does no1 immediatelyappear to have any great
advnntngc over convrntional methods (PFT). But when the expression is re-
oxamincd, it i. ohscrved that the ~peclml estimate is axtually a closed-form
egtrnatian lor the re3pon.c rprrtrum. This ~ni~ucfestureol the MEM spectral
cstim;sc provides the key to formulating the nlodal pnran~eterertimators and
their s1ntistics.
6.3.1 Resonant Frequencies
Itesonnd fqucncics can be estimated as the selection of frequencies corn
sponding to relative maximum of the corresponding spectrum. This search
for t~~aximnem be expressed in s mathematical form using the result of dif-
fcrotltinl calculations which slates: the derivative of s function is zero at an
extrema. Thus, as the spectrum is avnilable in the functional form, the rela-
livc cvtrenla of the spectral density spectrum can be abtsined rn the solution
or:
-- dC*.
df - O.
(6.29)
To obtain an expression which satisfiesequation (6.29), the following steps
are lskcn:
Let