Published papers that you’re welcome to download

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Tonal Noise Mitigation On Wind Turbines

Jutta M. Stauber, Brett A. Marmo and Donald Black

Free layer damping tiles were applied to the tower of a wind turbine, whose problematic tone of ~350 Hz was amplified by resonant vibrations of the tower. IEC 61400 measurements before and after the installation of the damping tiles showed that the audibility of the problematic tone was reduced by 3 dB and a broadband noise reduction of 3 dB was also observed. Several steps were carried out to determine that free layer damping was a suitable solution for this wind turbine. Firstly, acoustic and vibration surveys were carried out to ensure that the problematic tone was, indeed, amplified by the tower. Secondly, as a means of de-risking the application of the solution, structural-acoustic finite element models were created. These were used to predict the modal shape of the tower and consequently to determine the number and placement of tiles necessary to reduce the tone. After the installation of the tiles on the tower, acoustic and vibration measurements were carried out to determine their effectiveness on both reducing the amplitude of the resonant vibrations of the tower and the tonal and broadband noise of the turbine. Keywords: Tonality, Mitigation, Wind turbine, Free layer damping

Acoustic Modelling For The Environmental Impact Assessment Of Tidal Turbine Arrays

Dr Brett Marmo

Usually the first time that the operational sound from new tidal turbines can be measured is after they have been installed and are already interacting with animals in the marine environment. A modelling solution is therefore required to estimate whether marine animals will be able to hear and avoid contact with tidal turbines. An acoustic-structural interaction model is used calculate the acoustic output of tidal turbines. The cumulative sound of an array of tidal turbines and its dependence on bathymetry is calculated using a parabolic equation code. Modelled and measured sound pressure levels give infor-mation on potential upstream warning distances/times for animals which in turn helps to consider collision risk. Keywords: Tidal turbine, porpoise, structural-acoustic model

Seismic vibrations from wind turbines and their effects on the seismometer array at Eskdalemuir

The CTBTO (Comprehensive Nuclear Test Ban Treaty Organisation) IMS seismometer array station located at Eskdalemuir in Scotland has been operating since 1962. It is vital that the government and MoD safeguard the array from excessive seismic vibration noise. The presentation reviews the work undertaken by the EWG (Eskdalemuir Working Group) a cross government/industry group, in reviewing a vibration budget in relation to seismic vibration from wind turbines. The work outlines measurement analysis and modelling to develop an understanding of how wind turbines generate seismic waves. In turn this work was used to develop a model to predict seismic ground waves that could be used to refine and define the wind turbine exclusion and 50km consultation zone around the array.

Tidal turbine device modeling, simulation and vibration analysis

Barry Carruthers, Dr Brett Marmo

The marine sector is inherently populated by pioneering technologies and innovative device designs. Therefore there is minimal track record or experience upon which to evaluate the robustness and reliability of a marine renewable device. Holistic modelling, simulation and analysis is the most cost-effective method of prediction and identifying engineering issues as early in the design life as possible. This paper will summarise the methods by which Xi Engineering have modelled and analysed a tidal stream device in order to determine vibration throughout operational conditions. The objective of this is to highlight fatigue concerns, predict maintenance cycles, and implement appropriate design changes early in the development.

Wind Turbine Noise Reduction

Xi Engineering Consultants Ltd., using COMSOL Multiphysics.

Noise from wind farms falls into two categories: aerodynamic noise is created by the blades of a turbine swishing through the air, while mechanical noise is associated with the machinery housed in the nacelle of a turbine. As mechanical noise tends to be tonal, it is this that is most often a nuisance factor for residents living nearby. As a result, there are strict regulatory standards throughout Europe and North America, and when operators do not meet these requirements, they face potentially heavy penalties.

Software assists quieting noisy turbine

Brett A. Marmo and Barry J. Carruthers

Wind turbines occasionally get a bad rap for noise. At times, it’s not the turbine’s fault but rather an internal problem that amplifies the noise. For instance, a recent set of megawatt-scale wind turbines were emitting noise in the 800-830-Hz band. The manufacturer identified 820 Hz as the frequency at which the gear teeth mesh in the gearbox’s last stage. All conventional wind turbine gearboxes have gear-meshing frequencies but do not cause problematic noise, indicating the vibration was being amplified structurally. A vibration survey using a set of accelerometers identified the vibration pathway between the gearbox,nacelle, and tower walls.

Modelling of Noise Effects of Operational Offshore Wind Turbines including noise transmission through various foundation types

Dr Brett Marmo, Dr Iain Roberts, Dr Mark-Paul Buckingham

This report presents modelling of the acoustic output of operational off-shore wind turbines and its dependence on the type of foundation structure used. Three foundation types are examined: jacket, monopile and gravity foundation. The acoustic output from each of these foundation types is then compared to curves representing the hearing and behavioural response of marine species likely to come into contact with off-shore wind farms in Scottish Waters. The marine species examined are minke whales, harbour porpoise, grey seals, harbour seals, bottlenose dolphins, European eels, allis shad, sea trout and Atlantic salmon.

Monitoring and Mitigation of Low Frequency Noise from Wind Turbines to Protect Comprehensive Test Ban Seismic Monitoring Stations

Styles P., Westwood R.F., Toon S.M., Buckingham M.-P.,Marmo B., Carruthers B.

The first work which described the harmonic tonal nature of vibrations from windfarms was carried out at St Breock's Down, Cornwall, UK and is described in Legerton et al (1996) and more fully in Snow, and Styles (1997). This has since raised concerns about the possible effect of wind farms on sensitive installations. Styles et al (2005) describe an extensive monitoring programme to characterise the low frequency vibration spectra produced by wind turbines of various types, both fixed and variable speed. They demonstrated that small but significant harmonic vibrations controlled by the modal vibrations of the towers and excited by blade passing, tower braking and wind loading while parked, can propagate tens of kilometres and be detected on broadband seismometers.

Wind Turbine Noise Reduction

Jennifer Hand

Modeling of a megawatt wind turbine system enabled Xi Engineering Consultants to address a problematic tonal resonance with an innovative solution that minimized the cost of remedial work for their client. Noise from wind farms falls into two categories: aerodynamic noise is created by the blades of a turbine swishing through the air while mechanical noise is associated witht he machinery housed in the nacelle of a turbine. As mechanical noise tends to be tonal, it is this that is most often a nuisance factor for residents living nearby. As a result there are strict regulatory standards throughout Europe and North America and when operators do not meet these requirements they face potentially heavy penalties.