Speaker
Description
Between December 2024 and January 2025 around 550 seismic stations were deployed in and around two wind turbines (WTs) at the WINSENT test field on the Swabian Alp. In this work, the focus is on the stations deployed in the foundation of the southern turbine and on the stations in distances of less than 100 meters from it. A plane is fitted to the vertical displacement measurements of 6 stations arranged inside the foundation at the same height. Bandpass filters are applied around two eigenfrequencies of the WT tower, these eigenfrequencies are located at 0.5 Hz and near 3.45 Hz respectively. The fitted plane is described by the azimuth and incidence of its normal vector. Wind data is compared to the time series of these angles. For times without WT operation, wind speed and incidence are highly correlated. During times with high wind speeds a tilting motion is identified as the most common motion type for the frequency range 0.4 Hz to 0.6 Hz, overall the highest incidences are observed during such a tilting motion. This tilting motion features a stable azimuth during the longest part of each period. For average wind speeds above 6 m/s the preferred azimuth of such a motion is, for both considered eigenfrequencies, close to perpendicular to the wind direction. The vertical amplitudes of the stations with distances of up to 100 meters to the WT are studied during a tilting motion of the foundation. Only a narrow frequency band centered around 0.5 Hz is used for this purpose. A dipol like radiation pattern emerges, positive amplitudes are radiated from parts of the foundation where positive amplitudes are measured inside the foundation and vice versa.