Tuesday, August 30, 2005

Low-frequency noise and vibrations from windfarms

Eleanor Tillinghast of Green Berkshires recently brought to my attention the paper from which the following excerpts are taken.

P. Styles, I. Stimpson, S. Toon, R. England, and M. Wright. Microseismic and infrasound monitoring of low frequency noise and vibrations from windfarms. Applied and Environmental Geophysics Research Group, School of Physical and Geographical Sciences, Keele University, 18 July 2005:
  • Wind turbines are large vibrating cylindrical towers, strongly coupled to the ground with massive concrete foundation, through which vibrations are transmitted to the surroundings and with rotating turbine blades generating low-frequency acoustic signals which may couple acoustically into the ground. (p. 8)

  • Additionally, the blade-tower interaction is a source of pulses at a low repetition rate, which contain components in the infrasound region. The local and surrounding geology, especially layering, may play an important part in determining vibration transmission. (p. 8)

  • [W]ind farms do produce discernible harmonic signals which can be detected over considerable distances. (p. 44)

  • When the windfarm starts to generate at low wind speeds, considerable infrasound signals can be detected at all stations out to c. 10 km. (p. 66)

  • [T]he vibrations experienced on seismometers situated at considerable distances from farms propagate through the ground as high frequency Rayleigh waves and not through the air, and as such must obey the propagation modes and attenuation and absorption laws for geological materials and not air. (p. 67)

  • We have clearly shown that both fixed-speed and variable-speed wind turbines generate low-frequency vibrations which are multiples of blade-passing frequencies and which can be detected ... at considerable distances (many kilometres) from wind farms on infrasound detectors and on low-frequency microphones. (p. 76)

  • At present there are no current, routinely implemented vibration mitigation technological solutions which can reduce the vibration from wind turbines. (p. 90)
categories:  , , ,