Environmental Engineering Reference
In-Depth Information
Z(t)
wind
wind
m*
k
*
EI(x)
m(x)
EI(x)
m(x)
Fig. 13.2
Structural model of the reference wind turbine [
12
]. Dimensions in milimeters
elasticity 206,000 MPa, Poisson ratio 0.3, yielding stress 345 MPa), with a vari-
able hollow circular cross section with external diameter variable from 2.30 m
(top) to 4.15 m (bottom). The weight of the tower, including the flanges and
internals, is 3,713 kN (body) and 1,210 kN (nacelle, including the rotor blades).
Chen and Georgakis [
12
,
13
] showed the equivalence, from a dynamic point of
view, of this structure with a single degree of freedom (DOF) system made up of a
tapered tubular cantilever beam with a concentrated mass at the top. In the same
studies, the development of a 1/20-scale model of the prototype structure is pre-
sented. This test model is characterized by a 5.12 m high vertical tube with uni-
form cross section U133/4 (i.e., a hollow circular one with 133 mm of external
diameter and 4 mm in thickness), chosen according to the principle of the
equivalent flexural stiffness, with a lumped mass of 280 kg placed at the top
(Fig.
13.3
).
The base of the model is realized so as to be stiff enough, by means of two
parallel, horizontal steel C profiles (UPN 240 cross section) whose top and bottom
flanges are firmly bolted to stiff, horizontal steel plates. It is connected in the
middle to the shaking table through a cylindrical steel hinge, with interposed a
small, stiff steel frame. On both sides of the base, one cylindrical spring (89 kN/m
stiff) and one MR damper (described in the next section) are installed.
The shaking table facility used for the test consists of a platform made of
20 mm thick aluminum plates 1.5 9 1.5 m in plan. The table can be moved in a
single horizontal direction by a 100 kN hydraulic actuator MTS 244.22. Stiffness
grid plates of 300 9 300 mm are welded to the top and bottom plates. Further-
more, in the areas where the forces are transmitted, additional stiffeners have been
added.
