Noise in the ether

| Environmental Testing

Engineering challenges of noise in the ether

Andy Pye finds out how noise levels in the ether are providing engineering challenges both on the macro and micro scale.

Wind energy is to have a major share in the future renewable energy mix, so the Germany-wide TremAc project aims to develop objective criteria for measuring their emissions. Experts will study the interaction of acoustic and seismic vibrations of wind power plants and plan to generate a model to compute both emissions.

“We want to compute the complete chain of effects from the plant to the population,” said Theodoros Triantafyllidis, coordinator of TremAc. “A single chain is to be developed for modelling all vibrating plant components and the surroundings – the rotating rotor blades, drive shaft, gondola suspension and tower structure, foundation and the ground, various topographic terrains and airflows, as well as adjacent residential buildings and workplaces.”

To date, the emission and perception of noise and vibrations has been studied separately in most cases. Now, the scientists plan to measure the vibrations propagating in the atmosphere as acoustic and in the ground as seismic waves. In parallel, the neighbouring population will be interviewed using environmental medicine and psychological questionnaires. The people’s subjective complaints will be related to objective measurements in buildings, both for a single wind turbine and in a wind park.

“We need to understand why neighbours complain of inconveniences caused by wind power plants, even though the required limit values are observed and people should not hear anything physiologically,” Triantafyllidis says.

Further overhead, vibration problems of a different type afflict spacecraft, as they reduce the resolution of images and the accuracy of measurements made over great distances. Many common elements of satellites can create vibrations, such as spinning reaction wheels, solar array drives and rotating cryocoolers. The European Space Agency (ESA) needs to be able to test and correct for these jitters to improve the accuracy of its Earth observations.

To make such testing possible, NPL has developed a micro-vibration platform for ESA that can measure vibrations made by subsystems to an unprecedented degree of accuracy – so sensitive it can measure the force of a single dropped feather. The platform also generates small, controlled forces and torques to shake satellite instruments and components in six degrees of freedom. The 6DoF microvibration platform will be used by ESA at its European Space Research and Technology Centre in Noordwiijk, Netherlands.

The lower section of the platform isolates it from vibrations from the surrounding environment, such as footsteps and even waves from the nearby North Sea, allowing the upper section to measure micronewton-scale vibrations free from interference.

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About Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.

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