Environmental Engineering Reference
In-Depth Information
Fig. 12.13 RMS-values of
tower deflection of onshore
reference wind turbine with
and without TMD
frequency spectra. TMD can suppress especially the resonant vibrations. There-
fore, the efficiency of TMD at cut-in wind speed is much higher than at rated and
cut-out speeds.
The efficiency of the TMD is evaluated by means of RMS-values of the turbine
tower displacement in fore-aft direction. From the results with and without TMD, a
reduction factor is calculated using Eq.
12.18
. This factor is equivalent to the
vibration energy, which is dissipated by TMD. From the total 1,000 s simulation
time of the turbine response, the last 600 s is used for evaluation. Hereby, the
specified time step of the simulations equals 0.0125 s. To eliminate the static
tower deflection, which cannot be reduced by TMD, a high-pass filter is applied
with a cutoff frequency at 0.1 Hz.
R
¼
1
RMS
with TMD
RMS
without TMD
ð
12
:
18
Þ
Figure
12.13
shows the resulting RMS-values. Figure
12.14
shows the differ-
ence between the RMS-values with and without TMD. The reduction factors for
the analyzed wind speeds can be found in Fig.
12.15
. As these graphs also sum-
marize, the designed TMD mitigates the vibrations of the reference wind turbine,
especially at wind speeds lower than 5 m/s. The reduction factor varies between 20
and 80 % (Fig.
12.15
). At higher wind speeds, the tower vibrations are reduced
slightly by means of the additional structural damping caused by TMD. Hereby,
the reduction factor varies between 5 and 20 % (Fig.
12.15
).
12.4.3.2 Onshore Reference Wind Turbine with a Tuned Liquid
Column Damper
As described in Sect.
12.3.4.2
by means of the analogy, similar results can also be
obtained using TLCD [
4
]. Table
12.7
lists the calculated optimum parameters of
TLCD. Hereby, the active damper mass is, as for TMD, about 5 %. For the chosen
