• What if towers swing?

Wind turbines and seismological stations – passive dampers for the reduction of seismic emissions

Seismometer stations in Germany
Source: BGR

In Germany, there are more than 150 so-called „Seismological stations“, operated by the Federal Institute of Geosciences and Natural Resources (BGR) as well as by university institutes and regional earthquake services. The high density of the seismic stations in the Lower Rhine bay, the Rhine valley and the Vogtland reflect the location of seismic zones in Germany.

The seismological stations form networks that are to be subdivided into:

  • Emission networks to observe seismic activities,
  • immission networks to assess the vibration impact on the earth’s surface,
  • exploration networks for the so-called reservoir-monitoring.

Vibration producers

Wind turbines (WT) produce vibrations in the foundation soil subsoil, which can spread primarily as surface waves and detrimentally affect the functional capability of adjacent seismic stations. The North Rhine-Westphalian wind power decree of November 4, 2015 (no. 8.2.12) deals with this potential conflict between wind turbines and seismic stations.

“There can be a conflict regarding the use of wind turbines and measuring stations of the Geological Service. The Geological Service NRW is responsible for the monitoring of seismic activities and seismic hazard in North Rhine-Westphalia. Moreover, North Rhine-Westphalia has installed a seismic warning system as a measure of hazard prevention and civil protection. In planning and approval processes for wind turbines, it is compulsory that the Geological Service NRW be involved for wind turbine sites within a radius of 10 km around the sites of the seismic measuring stations indicated on the website of the Geological Service.” http://www.lee-nrw.de/wp-content/uploads/2015/10/Rechtl_seismologisches-Gutachten_Endfassung.pdf (retrieved July 28, 2016)

Vibration reduction

Vibration damper on WT (scheme)
Vibration damper on WT (scheme)

Vibration absorbers are a long-known and established tool for reducing vibrations in towers, buildings, bridges, machines, plants and vehicles. Taking into account the technical constraints, resonant vibrations can be reduced using vibration absorbers. For the reduction of the seismic emissions of wind turbines passive dampers can be used. Depending on frequencies and amplitudes which have detrimental effect, it is already with little damper masses that substantial vibration reductions can be achieved.

Our range of services includes:

  • Simulations-based design (using FE-model of WT-tower, nacelle and rotor) of a vibration absorber,
  • detection of the vibration modes which are critical with respect to the seismic emissions, if necessary: supplementary comparison with vibration measurement data,
  • definition of the functional parameters of a vibration absorber and their implementation in a plant-specific design, if necessary,
  • simulation-based prognosis of the absorber’s efficacy,
  • production, delivery and commissioning.