Environmental Engineering Reference
In-Depth Information
13.6.1 SA Control for the Extreme Operating Gust
Load Case
An extreme operating gust (EOG) is a sharp increase and then decrease in wind
speed that occurs over a short period of time while the turbine is operating. The
equivalent base acceleration time history in Fig.
13.16
has been considered herein
to assess the effectiveness of both SA control strategies, reproducing such input
signal through the DTU shaking table, properly commanding the MTS actuator.
In the following, the results obtained with the CLES controller are described
first, then those corresponding to the 2VAR logic.
13.6.1.1 CLES Controller: Response Reduction Under the EOG
Load Case
The desired control force u(t) as defined in Sect.
13.5.1
has been calculated in real
time during the entire duration of the test. The CLES controller modulated the
command signal so as to make the current vary between 0 and 1 A, aiming, at each
instant of time, at making the MR reactive force as close to u(t) as possible.
Figure
13.17
shows the results in terms of base stress, top displacement,
command voltage, and forces, desired and actual force exerted by MR dampers,
respectively. The time window 4-10 s has been plotted, i.e., that corresponding to
the most significant part of the accelerogram imposed at the base. The first two
diagrams—(a) and (b)—allow to compare the SA controlled response to that
corresponding to the FB condition, under the same input base motion.
The actual control force of the MR dampers satisfactory tracked the desired one
(Fig.
13.17
d), thanks to the modulation of the command voltage according to the
above-mentioned logic (Fig.
13.17
c). This lead, as expected, to a strong reduction
of base stress, trading off larger peak top displacement, however, within the tol-
erance assumed in respect to the one registered for the FB case. Table
13.2
helps
synthesize such findings, in terms of peak values of base stress and of top dis-
placement recorded for the whole duration of the test. The CLES controller, in
respect to the FB case, reduced the peak base stress of 67 %, even at the cost of
28 % larger peak top displacement.
13.6.1.2 2VAR Controller: Response Reduction Under the EOG
Load Case
The performance of the 2VAR controller with limit values of r
lim
and x
lim
equal to
30 MPa and 46 mm, respectively, is described in the following. Figure
13.18
shows the results in terms of base stress, top displacements, and command voltage,
allowing the comparison with the FB response under the same base input motion.
The first two diagrams—(a) and (b)—are referred to the overall duration of the
