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Enhanced Frequency Domain Decomposition - EFDD |
At a Glance
-
Method:
Enhanced Frequency
Domain
Decomposition.
-
User
choices:
Peak
picking, MAC
level for
identification
of spectral
peak, time
interval for
identification
of damping
-
Mode shape
estimation:
Immediate
animation,
mode shape
estimate
improved by
frequency
domain
averaging.
-
Frequency
and damping
estimation:
Estimated
from free
decays
corresponding
to
identified
spectral
peak.
-
Detection of
harmonics
and removal
of their
influence
from
estimated
modal
parameters.
-
Patent
protected.
Still simple
peak picking
From a user
point-of-view
the enhanced FDD
works like the
simple and
efficient
peak-picking
FDD.The user
just picks a
point at a modal
peak, and
immediately the
modal estimates
are available.
A single click
on a button -
Thats what it
takes to
estimate a mode
Identification
of the modal
peak
Based on a MAC
criterion, the
enhanced FDD
algorithm
identifies the
modal peak
around the peak
point selected
by user.This
modal peak
corresponds to a
SDOF system, and
is actually the
auto spectral
density of the
SDOF system.
Normally the
peak is
identified in a
certain
frequency range
around the
spectral peak.
The red curve
indicate the
identified part
of the SDOF bell
shaped curve.
Accurate
frequency and
damping
The
corresponding
SDOF free decays
are obtained by
transforming the
identified
spectral
function back
into the time
domain by
inverse FFT.
Estimations of
natural
frequencies and
damping ratios
are then
obtained
directly from
the free decay
signals in the
time domain.This
procedure allows
for an
estimation of
the natural
frequency that
is not limited
by the frequency
resolutions of
the spectral
density
functions.
The identified
SDOF spectral
density is
transformed to
time domain and
the damping
ratio and
natural
frequency is
estimated from
the obtained
free decay.
More accurate
mode shapes
Mode shapes are
obtained by
averaging
directly in the
frequency domain
using the
identified part
of the spectral
function and the
corresponding
singular value
decomposition of
the spectral
matrix.
Estimated mode
shape.
Download movie.
Removing
influence of
harmonics
If a structure
being tested has
rotating parts
the measurements
made will not
only include the
response to the
natural input
but also the
response coming
from the
sinusodial
forced
excitation. The
influence of
these harmonics
can be
eliminated from
the modal
estimation. For
more
information, see
Dealing with
Harmonics in
EFDD.
The influence of
the harmonic,
indicated with
green color, is
eliminated from
the estimation
of the mode.
Back to
Technical
Details
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