Environmental Engineering Reference
In-Depth Information
Table 13.1 Fixed base con-
dition: peak response of the
tower under both load cases
input
max|r| [MPa]
max|x| [mm]
EOG
51
39
PRK
29
25
imposing the MR dampers to work as rigid links, feeding them with a constant
current of 3 A during the overall duration of the tests. Actually the expected (then
registered) maximum force applied to the dampers for the two FB tests were less
than 5 kN, therefore much less than the threshold value for the ''friction'' force F
dy
of the devices (about 27 kN for 3 A, according to Eq.
13.3
). Table
13.1
summa-
rizes the peak absolute value for displacement x (top of the tower relative to the
base) and for base stress r for both load cases.
The structural model has been tested first using the CLES control algorithm.
The higher value of the dimensionless parameter n involved in the procedure, as
previously said, gives smoother variations of command voltage in time. According
to the results of three pre-tests, the values n = 15 for the EOG load case and n = 1
for PRK load case were selected.
Subsequently, various tests have been performed with the 2VAR control
algorithm to evaluate and compare the effects, in terms of reduction of the
structural response, of different couples of stress (r
lim
) and displacement (x
lim
)
limits chosen within the ranges [10, 40] MPa and [16, 46] mm respectively. The
best combination of limit values resulted to be (r
lim
, x
lim
) = (30 MPa, 46 mm) for
the EOG load case, and (r
lim
, x
lim
) = (12 MPa, 20 mm) for the PRK input.
For each of the above-mentioned tests the reduction of the base stress has been
monitored as the first objective to be achieved. Moreover, the effectiveness in
controlling top displacement has been evaluated, even if a moderate increase has
been considered acceptable. In particular, peak top displacement less than 1.3
times the peak registered in the FB condition have been tolerated, not causing
significant detrimental second order effects to the tower.
The main experimental results related to the four tests (two load cases, two
controllers) are described in the next sections, first with reference to the EOG, then
to the PRK load cases.
In the following, the command voltage has to be intended as a 0-10 V voltage
signal in output from the controller (PC) and in input to the power supplies, the
latter having, when adopted as current driver, a control loop gain 0.4 A/V. The
maximum intensity of current inside the dampers for all the tests has been set equal
to 1 A. Therefore, the maximum command signal is 2.5 V.
