Dos Arbolitos Wind Farm 70MW
Seismic hazard wind farm
Dos Arbolitos is one of the biggest wind farms in Mexico. This wind farm is located in Juchitán de Zaragoza, in Oaxaca State, one of the areas in the country most vulnerable to earthquakes and high wind. This wind farm, in operation since 2014, is capable of providing 70 Megawatts of power and is the third biggest wind farm in Mexico, where the total power coming from wind farms is 278 MW. Due to this farm, Iberdrola, the Spanish electrical company, will provide electricity to 150,000 Mexican homes and will avoid the emission of 560,000 tons of CO2 per year.
Dynamis was enlisted in the design phase of the wind turbine tower and the foundation. Our first objective was to define the seismic input that will be used in the tower design. A set of synthetic accelerograms was obtained from a set of natural accelerograms, in accordance with the Regulatory Guide of the NRC.
After the definition of the seismic input, Dynamis performed the design of the tower through a non-linear analysis. A very recent technology called “macro-element” was used. The macro-element is an in-house tool that we developed, which allows to take into account non-linear phenomena occurring in the soil-structure interface (near field effects): sliding, soil bearing capacity loss, uplift. Moreover, this calculation module allows to consider soil-structure interaction (including material damping and radiative damping), using the substructure method through a set of dynamic impedances (far field effects).
The result of the non-linear analysis consists of the time history of the set of forces developed within the wind turbine tower, and the time history of the displacements of the head of the tower.
This non-linear analysis was compared to a previous modal spectral linear analysis and proved a high reduction of the forces generated in the tower and the foundation, essentially because of the yielding of the soil (main source of dissipation of energy). An absence of uplift was also found.
The State of Oaxaca in Mexico is one of the regions in Mexico registering the strongest winds and the highest sismicity (ao = 0.5g).