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Free keywords:
soil structure interaction, seismic metamaterials, local resonance, wind turbines,
bandgaps
Abstract:
The deflection and the control of the effects of the complex urban seismic
wavefield on the built environment is a major challenge in earthquake
engineering. The interactions between the soil and the structures and between
the structures strongly modify the lateral variability of ground motion seen
in connection to earthquake damage. Here we investigate the idea that
flexural and compressional resonances of tall turbines in a wind farm strongly
influence the propagation of the seismic wavefield. A large-scale geophysical
experiment demonstrates that surface waves are strongly damped in several
distinct frequency bands when interacting at the resonances of a set of
wind turbines. The ground-anchored arrangement of these turbines produces
unusual amplitude and phase patterns in the observed seismic wavefield, in
the intensity ratio between stations inside and outside the wind farm and
in surface wave polarization while there is no metamaterial-like complete
extinction of the wavefield. This demonstration is done by setting up a dense
grid of 400 geophones and another set of radial broadband stations outside
the wind farm to study the properties of the seismic wavefield propagating
through the wind farm. Additional geophysical equipment (e.g., an optical fiber,
rotational and barometric sensors) was used to provide essential explanatory and
complementary measurements. A numerical model of the turbine also confirms
the mechanical resonances that are responsible for the strong coupling between
the wind turbines and the seismic wavefield observed in certain frequency
ranges of engineering interest.
