Microseismic and Infrasound Monitoring of Low Frequency Noise and Vibrations from Windfarms
Author:
In late December 2003 Atomic Weapons Establishment/Ministry of Defence recognised that many wind farm developments are planned in the vicinity of the Eskdalemuir International Monitoring Site which constitutes part of the Comprehensive Test Ban Treaty Organisation monitoring network and that the discrimination capabilities of it might be affected by possible vibration intrusion by wind turbines erected in proximity to the array and that this might have implication for its performance in discriminating nuclear weapons tests.
Wind turbines are large vibrating cylindrical towers, strongly coupled to the ground with massive concrete foundation, through which vibration are transmitted to the surrounding and with rotating turbine blades generating low-frequency acoustic signals which may couple acoustically into the ground. This may occur in several ways:
1. As a cantilever carrying the nacelle/blade mass, with frequencies typically less than 1Hz, depending on height of tower.
2. As a torsional oscillator at low frequencies.
3. As a complex distributed system at higher frequencies
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. Energy may propagate via complex paths including directly through the ground or principally through the air and then coupling locally into the ground …
Applied and Environmental Geophysics Research Group, Earth Sciences and Geography, School of Physical and Geographical Sciences, Keele University
18 July 2005
