Wind Energy Applications
There are several reasons why
for Operational Modal
Analysis (OMA) is a popular tool in wind turbine
Design Verification and Optimization
First of all, there is a growing need
to know the dynamic behavior of wind turbines under the right
operational conditions when the true environmetal forces are
acting on the structure. This need is caused by the rapid
development in the dimensions of the turbines. The larger the
dimensions get the lower the dynamic behavior in frequency gets.
This put the numerical models under pressure and there natural
becomes a need for experimental verification of these. In some
cases it is even required to follow an experimental study with
an updating of the numerical models.
Secondly, sub-parts such as blades and
tower are typically having well documented dynamic
characteristics that are provided independently of each other.
However, problems arises when these subparts are integrated with
e.g. the nacelle and the foundation. The integration of course
has a serious impact of the dynamic behaviour of the subparts.
In order to study this impact OMA is the natural tool to make
use of. See e.g. the
case study of the FE model updating of the Fuhrländer AG 2.5 MW
wind turbine. OMA will return results for the complete
turbine behavior under the right environmental conditions. This
makes it possible to update numerical models of the complete
turbine to behave correctly under the operational conditions of
A typical example of a full-scale test
is shown in the below pictures and documented in the paper
Artificial and Natural Excitation Testing of SWiFT Vestas V27
Frequency Domain Decomposition analysis.
Crystal Clear Stochastic Subspace Identification analysis.
Easier Documentation of Sub Parts
Dynamic characterization has been
applied in sub part testing in case of e.g. blades. A popular
approach has been a free response testing scheme where each mode
of the blade is determined in a single test by applying
excitation in carefully selected locations of the blade. This is
a very costly way of testing as it is time consuming, and there
is a potential risk that multiple modes are excited at the same
time which consequently will polute the results. In this case,
OMA has made life easier for several test institutions. The
reason is that all modes now accurately can be determined from a
Crystal Clear Stochastic Subspace
Identification modal analysis of a wind turbine blade.
Now it is Possible to do Modal Analysis
on Rotating Machinary during Operation
The presence of rotating components
"harmonics" in the data has for years been a nightmare to deal
with. In many applications where rotating machinary is present
in the structure being tested, it has been necessary to switch
of the rotation while doing the modal analysis or it has been
necessary to rely on the use of operating deflection shapes
(ODS). However, ARTeMIS is born with the ability to handle
"harmonics" from rotating components, such as motors, pumps,
propellers, wind turbines and generators. With its sophisticated
harmonic detection techniques and the advanced time domain
Crystal Clear Stochastic Subspace Identification (CC-SSI)
the extracted modal parameters will always describe
the true operating state of the tested structure. The latest is
harmonic peak reduction and CC-SSI techniques as a powerful
cocktail for obtaining the modal parameters in case of even very
significant harmonic peaks.