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Wind turbines at Inter-Noise 2013 (abstracts)  

Author:  | Noise

The 42nd International Congress and Exposition on Noise Control Engineering, Innsbruck, Austria, 15-18 September 2013

Social survey on community response to wind turbine noise in Japan
Kuwano, Sonoko (Osaka University); Yano, Takashi (Kumamoto University); Kageyama, Takayuki (Oita University of Nursing and Health Sciences); Sueoka, Shinichi (Sueoka Professional Engineer Office); Tachibana, Hideki (Chiba Institute of Technology) – Japan
A committee of Research on the Evaluation of Human Impact of Low Frequency Noise from Wind Turbine Generators conducted a serie sof physical measurements, laboratory psychological experiments and social surveys of wind turbine noise under the auspice of the Ministry of the Environment of Japan. In this paper, a design of questionnaire used in the survey and a part of the results are introduced. The questionnaire is based on the proposal of the Acoustical Society of Japan, which was planned to make the results of socialsurveys conducted by various researcherscomparable. Social surveys were conducted in 36 sites where wind turbine noise is audible and in 16sites where wind turbine noise is inaudible. The number respondents were 747 and 332, respectively. The results of the survey are introduced from various viewpoints.

Dose-response relationships for wind turbine noise in Japan
Yano, Takashi (Graduate School of Science and Technology); Kuwano, Sonoko (Osaka University); Kageyama, Takayuki (Oita University of Nursing and Health Science); Sueoka, Shinichi (Sueoka Professional Engineer Office); Tachibana, Hideki (Chiba Institute of Technology) – Japan
In order to obtain a base for wind turbine noise policy, a socio-acoustic survey was carried out throughout Japan from Hokkaido to Okinawa over three years (2010-2012). In total 747 responses were obtained with face-to-face interview method. The wind turbine noise was measured at several points in each site for successive five days. The LA,eq,n, which was precisely measured outdoor in a day, was taken as noise exposure. A representative exposure-annoyance relationship was drawn based on all data. The trend was consistent to those from Swedish and Dutch surveys. People at sites with sea wave sound were less annoyed by wind turbine noise than those at sites without. The effects of moderating factors such as interest in environmental problems, disturbance of landscape and sensitivity to noise were also investigated.

An experimental study on rating scale for annoyance due to wind turbine noise
Seong, Yeolwan; Lee, Seunghoon; Gwak, Doo Young; Cho, Yoonho (Department of Mechanical and Aerospace Engineering, Seoul National University); Hong, Jiyoung (Korea Railroad Research Institute); Lee, Soogab (Center for Environmental Noise and Vibration Research, Engineering Research Institute) – Korea
Wind turbine noise referred to as “swishing sound” causes annoyance due to the amplitude modulation of the aerodynamic noise from the blades. For that reason, many studies for rating scale realizing annoyance from the noise have been examined, but show little coherence with change of noise level. In the present study, an appropriate index for describing the annoyance tendency is suggested with jury test and correlation analysis. Twenty-eight stimuli created by numerical simulation for the test were provided and thirty-two subjects assessed noise-induced annoyance based on 7 point numerical scale. Additionally, a correlation analysis between sound descriptors and subjective annoyance was performed by using regression analysis with statistics software. This study shows that the maximum sound pressure level with fast time A-weighting (LAFmax) explains well the annoyance characteristics compared to the other descriptors considered.

Exploring underlying mechanisms for human response to wind turbine noise
Bockstael, Annelies; Van Renterghem, Timothy; De Weirt, Valentine; Botteldooren, Dick (Ghent University, INTEC, Acoustics Research Group, Belgium)
This paper investigates underlying mechanisms for human response to wind turbine noise by studying the effects in terms of source detection, recognition and annoyance with and without road traffic noise. Recordings from a single 1.8-MW wind turbine have been mixed with samples of highway noise and of local roads at different signal-to-noise ratios. These fragments have been presented to 50 normal-hearing participants in a two-stage experiment. First, annoyance and source recognition have been evaluated during quiet leisure activities in background noise, with people unaware of the actual purpose. Secondly, wind turbine noise had to be identified in a paired comparison test. The second focused identification task indicates that wind turbine noise detectability in background noise at different signal-to-noise ratios is clearly different in highway noise than in noise from local roads. Furthermore, individuals with higher detection scores are also more capable to recognize wind turbine noise in the non-focused listening experiment, and better recognition could be linked with higher annoyance reports. These findings suggest that higher level appraisal, emotional and/or cognitive processes contribute to reported wind turbine noise annoyance, but further research is needed to consolidate this hypothesis.

Large-scale calculation of possible locations for specific wind turbines under consideration of noise limits
Probst, Fabian; Probst, Wolfgang; Huber, Bernd (DataKustik, Germany)
The acoustical part of the study “Renewable Energy Potential NRW” was conducted by DataKustik GmbH. One of the major challenges of this project was the pure data size which needed to be processed. The acoustical study comprised an area of 36,540 Km², 4.2 million receivers and 136 million high-points. The wind turbines under consideration can be operated in two different modes which differ in energy production and noise emission. The final result of this automatically processed study were the possible areas suitable for wind farms, the areas of exceeding noise levels in respect to specific noise limits and the maximum possible energy production.

Identifying restorative environments and quantifying impacts
Watts, Greg; Pheasant, Rob (Bradford Centre for Sustainable Environments, University of Bradford, UK)
The UK has recently recognized the importance of tranquil spaces in the National Planning Policy Framework. This policy framework places considerable emphasis on sustainable development with the aim of making planning more streamlined, localised and less restrictive. Specifically it states that planning policies and decisions should aim to “identify and protect areas of tranquillity which have remained relatively undisturbed by noise and are prized for their recreational and amenity value for this reason”. This is considered by some (e.g. National Park Authorities) to go beyond merely identifying quiet a reas based on relatively low levels of mainly transportation noise as the concept of tranquility implies additionally a consideration of visual intrusion of man-made structures and buildings into an otherwise perceived natural landscape. This paper reports on applying a method for predicting the perceived tranquility of a place and using this approach to classify the level of tranquility in existing areas and then secondly to determine the impact of new build taking the example of the construction of a hypothetical wind farm in the countryside. For this purpose noise level measurements, photographs and jury assessments of tranquility at a medium sized land based wind farm were made. It was then possible to calculate the decrement of noise levels and visual prominence with distance in order to determine the improvement of tranquility rating with increasing distance. The point at which tranquillity was restored in the environment allowed the calculation of the position of the footprint boundary.

The overall efficiency of the windscreens used in the acoustic noise measurements on wind turbines
Buzduga, Valentin (Scantek, USA)
This paper deals with the characterization of the windscreens used in the acoustic noise measurements on wind turbine generator systems. The discussion is focused on two main aspects: determining the insertion loss introduced by windscreens in the measuring channel and evaluating the efficiency of these devices against wind effects. The International Standard IEC 61400-11:2012 only asks for characterization of the insertion loss of the secondary windscreens. For more accurate results from noise measurements, the insertion loss of the primary windscreens should be also considered. The paper highlights the advantages of the methods based on the constant divergence of the sound pressure for determining the insertion loss of the windscreens. Also, the paper proposes a new method for evaluating the sound pressure level produced by the wind turbine alone, by using the principle of the constant divergence of the sound pressure. The paper discusses the theoretical approach, experimental results and standardization aspects.

Challenges of measuring noise compliance of wind farms
Lightstone, A. D.; Du Guangsheng, (Sam) (Valcoustics Canada, Canada)
Compliant or marginally non-compliant wind farms can be expected to produce immission (receptor) sound levels at or close to the ambient. Making valid sound measurements to prove compliance, in the presence of significant wind, presents difficulties and challenges. To address the practical difficulties and standardize procedures, the Ontario Ministry of the Environment (MOE) issued a protocol for measuring noise compliance of wind farms. The sound limits are a function of wind speed and ambient sound. A major problem is that ambient sound inherently increases with wind speed and on its own may exceed the wind turbine immission limits. Thus, the measured receptor sound levels must be properly attributed to the actual source(s). Complainants (and sometimes regulatory enforcement staff), with no expertise in acoustics, usually incorrectly assume that if the measured sound levels exceed the limits, the wind farm is automatically out of compliance. Other challenges in satisfying the measurement protocol and coming to valid conclusions about compliance include choice of measurement locations, data sampling, use of secondary windscreens, total duration of the measurement campaign, dealing with other interfering sound sources and data analysis. The problems and potential solutions, expected to be applicable in any jurisdiction, will be discussed.

Loudness evaluation of general environmental noise containing low frequency components
Sakamoto, Shinichi; Yokoyama, Sakae; Tsujimura, Sohei (Institute of Industrial Science, University of Tokyo); Tachibana, Hideki (Chiba Institute of Technology) – Japan
The influence of low frequency sound in wind turbine noise has become a serious problem recently and various researches are being made in many countries. Also in Japan, a synthetic study program titled “Research on the evaluation of human impact of low frequency noise from wind turbine generators” has been performed over the three years from the 2010 fiscal year, in which field measurements, social survey on the response of nearby residents and laboratory experiments on audibility of low frequency sounds were conducted. In parallel to these studies, field measurements on general environmental noises including transportation noises inside and outside of various vehicles were performed by paying attention to low frequency components. As a result, it has been found that low frequency components are included not only in WTN but also in general environmental sounds. The environmental sounds recorded on sites were reproduced by a test facility which can reproduce low frequency components including infrasound and loudness tests were performed. As a result, it has been found that the A-weighted sound pressure level is robustly applicable to the assessment of loudness for such kinds of environmental sounds.

A longitudinal study of the impact of wind turbine proximity on health related quality of life
McBride, David (Department of Preventive and Social Medicine, University of Otago); Shepherd, Daniel (Department of Psychology, School of Public Health, Auckland University of Technology); Welch, David; Dirks, Kim N. (School of Population Health, University of Auckland) – New Zealand
Background: Wind turbine noise is known to cause annoyance and sleep disturbance, which are primary health effects. An additional risk factor is the trait of noise sensitivity, which describes individuals who are more likely to pay attention to sound, evaluate sound negatively and have stronger emotional reactions to noise. The result is chronic stress, the effects of which could be monitored through detecting stress related outcomes such as hypertension in exposed individuals. An alternative approach is to monitor health related quality of life (HRQOL). This study examines whether there is a change in this metric over time in a turbine exposed community. Methods: This is a 2 year follow up of a base-line survey carried out on individuals living within two kilometres of industrial wind turbines compared with a matched control group. We have repeated the self administered questionnaire survey in which self-reported HRQOL was measured using the abbreviated version of the WHOQOL-BREF. Results: The base-line survey found that residents living within 2 km of a turbine installation experienced significantly lower overall quality of life, physical quality of life, and environmental quality of life than a control group. The turbine group showed no change in WHOQOL or amenity scores with time, however compared to the 2012 control group, the turbine group had lower physical domain scores, and rated their overall health as being poorer. The results do not therefore support any improvement in this global health metric with time.

Psychoacoustic aspects of noise from wind turbines
Fastl, Hugo; Menzel, Daniel (AG Technische Akustik, MMK, TU München, Germany)
Wind turbines play an important role in the present discussions on sustainable generation of energy. However, sometimes the noise produced is regarded as a serious drawback. Therefore, in a pilot study some psycho-acoustic aspects of noise from wind turbines were investigated. The dependence of annoyance ratings on level and fluctuation of the digitally processed sounds was assessed in a laboratory setting. Moreover, in order to get some ideas about possible audio-visual interactions, in addition to the sounds also videos of a moving wind turbine at different distances were presented. Results show that, as expected, annoyance ratings were correlated with level and, to some degree, with fluctuation, but only three of thirteen subjects showed signs of audio-visual interaction.

A preliminary investigation on some psychological and acoustic aspects of wind farms’ noise annoyance
Maffei, Luigi; Masullo, Massimiliano; Di Gabriele, Maria (Department of Architecture and Industrial Design, Second University of Naples, Italy); Votsi, Nefta-Eleftheria P. (Department of Ecology, School of Biology, Aristotle University, Greece)
In the last years the global installed capacity of the renewable energy grew at very rapid rates. Among renewable energy wind energy is one of the typologies with the most significant growth. However the Wind Farms (WF) entail environmental impact problems specially on people. The major reasons of complaints are the acoustic and visual impact. Recent researches have concluded that noise annoyance from WFs was higher than from several other noise sources at comparable noise levels. Even though the sound levels, as heard by resident, are generally lower than 50 dB(A), many people oppose to WF concluding that they have health problems caused directly by wind turbines. In quiet environments the wind blowing is one of the main sound for inhabitants and its semantic content still exist when we consider the wind turbine noise. Wind turbine noise coexist with wind noise and their relative masking changes according to the functioning conditions. In these conditions it is very difficult to establish if the complaints of residents are due to physical rather than psychological origin. In this paper are presented the preliminary results of an auditory test in which two groups of subjects, with chronic and no-chronic exposure to wind turbine noise, have been asked to recognize, by a YES/NO questionnaire, the noise of these plants.

Nationwide field measurements of wind turbine noise in Japan
Tachibana, Hideki1; Yano, Hiroo (Chiba Institute of Technology); Sakamoto, Shinichi (Institute of Industrial Science, University of Tokyo); Sueoka, Shinichi (Institute of Noise Control Engineering) – Japan
A study program titled “Research on the evaluation of human impact of low frequency noise from wind turbine generators” has been performed in the past three years from the 2010 fiscal year sponsored by the Ministry of the Environment, Japan. In this study, noise measurements have been performed in immission areas of 34 wind farms across Japan. For the survey, measurement instrumentation was contrived in order to cover the low frequencies including infrasound and measurement techniques were investigated in order to detect wind turbine noise in ambient environmental noises. Each field measurement was performed for continuous 120 hours by unattended method and the sound pressure signal was recorded on the specially manufactured sound level meter. From the recording, A-, C-, and G-weighted and 1/3 octave band sound pressure levels were obtained during the time when the wind turbines were under the rated operation condition. The swishing sound, the most serious problem in wind turbine noise, was also analyzed by putting emphasis on the modulation period and sound pressure level fluctuation. In parallel with the measurements around wind farms, 18 control areas without wind turbine noise were chosen and the environmental noise was also measured for comparison.

Study on the amplitude modulation of wind turbine noise: Part 1 – Physical investigation
Fukushima, Akinori (NEWS Environmental Design); Yamamoto, Kazuhiro (ACT Acoustics); Uchida, Hideo (NS Environmental Science Consultant Corporation); Sueoka, Shinichi (Institute of Noise Control Engineering of Japan); Kobayashi, Tomohiro; Tachibana, Hideki (General Research Institute, Chiba Institute of Technology) – Japan
Amplitude modulation (AM) sound, so called swish sound, is generally contained in wind turbine noise (WTN) and it causes serious annoyance in the areas around wind farms. Therefore, the methods to assess the characteristics of this kind of sound should be investigated in both viewpoints, physically and psycho-acoustically. Regarding the former problem, a practical method to evaluate the magnitude of the AM using common acoustic measurement instrumentation is proposed in this paper. That is, the sound pressure level difference between the levels measured by using FAST and SLOW dynamic characteristics of a sound level meter is calculated for the measurement time interval under investigation and then the cumulative distribution function of the level difference is calculated. From the result, the value of 90% range is obtained as an indicator for assessing the AM. Statistical data evaluated by using this indicator for AM sounds contained in actual WTNs were obtained through the field measurements performed nationwide across Japan.

Study on the amplitude modulation of wind turbine noise: Part 2 – Auditory experiments
Yokoyama, Sakae; Sakamoto, Shinichi (Institute of Industrial Science, University of Tokyo); Tachibana, Hideki (Chiba Institute of Technology) – Japan
Amplitude modulation (AM) sound, so called swish sound, is generally contained in wind turbine noise (WTN) and it causes serious annoyance in the areas surrounding wind farms. Therefore, the methods to assess the characteristics of this kind of sound should be investigated in both viewpoints, physically and psycho-acoustically. Regarding the latter problem, auditory experiments were performed by using a test facility capable of reproducing low frequency sounds including infrasound. As the first experiment, the fluctuation sensation caused by AM sounds was examined by using actual WTNs recorded on sites, in which the frequency components were limited in steps by low-pass filtering processing. As a result, it has been found that the fluctuation sensation is apt to cause at frequencies higher than about 125 Hz. As the second experiment, the noisiness sensation to AM sounds were examined by using artificially synthesized sounds by changing their modulation depth in eight steps. As a result, a tendency has been seen that noisiness increases with the increase of AM depth even if the time-averaged sound pressure level is the same. [emphasis added]

Experimental study on the radiation characteristics of noise generated from a single wind turbine
Okada, Yasuaki; Koichi, Yoshihisa (Faculty of Science and Technology, Meijo University); Iwase, Teruo (Faculty of Engineering, Niigata University); Higashi, Kazuki (Kyushu Branch, Japan Weather Association); Nishimura, Naoto (Energy Use R&D Center, Kansai Electric Power Company) – Japan
Also in Japan, the wind power generation facility was added to the projects subject to the Environmental Impact Assessment Law since April 2013. The investigations on noise including low frequency components at various operating wind turbine power stations have been carried out over the country. In this paper, the field measurements of noise from a single wind turbine with a rated power of 1.5 MW were made in several terms, in order to examine the radiation characteristics of noise generated from the wind turbine. The six receiving points were set circularly around the wind turbine at a height of 1.2 m above the ground, and the four receivers were mounted at heights up to 65 m on a nearby lightning tower. We have also collected meteorological and associated wind turbine operational data at one second intervals with corresponding acoustic data. As a result of this study, it has been found that the A-weighted sound pressure levels in the upwind and downwind directions of the wind turbine are almost the same and are 5 dB larger than those in the crosswind direction. The noise level distributions at distances of 50 m to 200 m are similar to the calculated values assuming the wind turbine to be a circular plane source.

Health related guidelines for wind farms in Belgium
van den Berg, Frits (GGD Amsterdam Public Health Service); Passchier, Wim (Department of Toxicology, Faculty of Health, Medicine and Life Sciences, Maastricht University, The Netherlands); Botteldooren, Dick (Acoustics Research Group, INTEC, Ghent University); Deggoui, Naïma (Academic Hospital Saint-Luc, Université de Louvain); Fallon, Cathérine (Scientific and Public Involvement in Risk Allocations Laboratory [SPIRAL], Département de Sciences Politiques, Université de Liège); Hens, Luc (Vlaamse Instelling voor Technologisch Onderzoek [VITO]); Nemerlin, Jean (Montefiore Institute, Cedia, University of Liège); Pauluis, Jean (Faculté de Médecine); Pepermans, Yves (Faculteit Politieke & Sociale Wetenschappen, Universiteit Antwerpen, Belgium)
In 2011 the Belgian authorities have asked the Superior Health Council (SHC) to advise on the health effects of wind farms. A working group of experts with different backgrounds was put together to assess all the available literature. This group considered the request in the context of sustainable development and drafted an advice that was reviewed by two international experts. It is expected that the advice will be published in the spring of 2013. The advice mentions direct effects of operational wind turbines that may have negative consequences for the health and well-being of neighbouring people. It stresses the importance of factors such as the change in landscape, the possible intrusion on people’s attachment to their environment and the effect of local economic benefits and costs associated with a wind energy project. Also, the perception of the future quality of life will determine the social acceptance of a wind project by a local community. The advice gives a number of recommendations to better deal with all these aspects. The paper will give an overview and explanation of these recommendations.

Approaches to controlling wind turbine noise and infrasound in Japan
Fujitsuka, Tetsuro; Koyama, Takumi; Azuma, Yasuhiro; Kuwabara, Atushi (Ministry of the Environment, Japan)
In Japan, expectations are recently rising with regard to the potential of renewable energy sources as the country needs to combat global warming and reinforce the security of energy supplies. In particular, wind power is drawing attention as a renewable source of energy with great potential. In recent years, an increasing number of wind turbines have been installed. However, the number of complaints about noise generated by them, including infrasound, has also increased. This situation has required the Ministry of the Environment of Japan to assess the effects of wind turbines and accumulate knowledge on how to investigate, predict and assess such noise and infrasound generated by these installations. In FY2010, the Ministry initiated studies to achieve this. One such study is being conducted by a Ministry-commissioned study group that in March 2012 submitted an interim report on optimal methods and approaches to the environmental impact assessment (EIA) of noise generated by wind power installations based on the best available evidence, including knowledge accumulated within and outside Japan, and taking into account Japan’s topographic features and land use patterns. This submission was made before the revised Environmental Impact Assessment Law takes effect in October 2012. The revised law expands the scope to include wind turbines, among other amendments. The interim report stresses the need to assess the sound propagation characteristics due to topographical features, as many of the wind power plants in Japan are located on mountain ridges. It also emphasizes the importance of ex-post evaluations to assess, if any, the adverse health effects of wind turbine noise and infrasound. The interim report will provide a valuable resource for concerned plant operators and local governments that may be responsible for EIA. It will also serve as an important reference for compiling ordinances and handbooks that the Ministry of Economy, Trade and Industry (METI) will issue, which in turn will serve as guidelines for the EIA of future wind turbine installations under the revised law.

Assessment of low-frequency noise due to wind-turbines in relation to low-frequency background noise
de Beer, Eugène (Peutz, The Netherlands)
Assessment of low-frequency noise (LFN) is one of the aspects in the Environmental Impact Assessment for a projected wind farm at the city of Utrecht. In the Netherlands there are no legal noise limits for LFN. There are only several guidelines for the assessment of LFN. In this Environmental Impact Assessment the low-frequency noise at the dwellings due to this projected wind farm is not only calculated but also the low-frequency noise background levels has been measured during 3 months at three locations in the neighborhood of the nearby dwellings. Simultaneous the wind-speed and wind-direction have been measured. This area-specific information (low-frequency background noise at a certain wind speed and direction) has been used for the assessment of the LFN due to the projected wind farm besides a comparison with the Dutch guidelines as well as the Danish legal LFN limits. The aim of measuring the LFN is to investigate the present low-frequency background noise (due to road traffic, industry and shipping) and the possible increase of LFN annoyance due to the projected wind farm. In this paper a comparison is made between the measured background noise and the several low-frequency noise limits and guidelines.

Calculations of indoor low frequency noise from wind turbines
Backalarz, Claus; Holm Pedersen, Torben; Søndergaard, Lars Sommer (DELTA, Denmark)
In 2011 Denmark has introduced mandatory limits for low frequency noise from wind turbines. This paper reviews the experiences and studies on low frequency noise and infrasound from large and small wind turbines, Danish rules for measuring and calculating low frequency noise and an assessment of the consequences of introducing limits for low frequency noise. It is concluded that the proportion of low-frequency noise depends more on wind turbine type and operation than its size. It is usually the “normal” noise that sets limits on how close turbines can be placed to dwellings. Infrasound from modern wind turbines is not an issue. As part of the planning of a wind farm, calculations of the noise contributions from the wind farm at the nearest residences are made. By optimizing the operation of the turbines, it is possible to achieve a significant production improvement and still comply with the limits.

Wind turbine noise: an efficient and reliable method for extracting the wind turbine noise out of the background noise
Tréfois, Vincent; Dasse, Stéphane (I.C.A [Acoustic Engineers], Belgium)
Wind turbines are mostly implanted in the countryside where the background noise is usually low and at typical distances of 350 to 500 meters from the nearest neighboring dwellings. As a result, their specific noise is about the level of the background noise (typically 35 to 50 dBA) and as such difficult to extract from it. However one can take advantage of the typical wind turbine sound modulation. The method consists first in measuring and storing the time history of the short LAeq(1s) every second in continuous over the period of investigation (typically not less than 1 month if a statistical figure is to be obtained). Then the diagram of occurrences (step 0.5 dB) of these LAeq(1s) is to be plotted for each consecutive period of 10 minutes. On each graph the specific contribution of the wind turbine noise appears out of the background noise, as a group of five consecutive bands that correspond to the typical 2 to 3 dB wind turbine sound modulation. The wind turbine noise over the 10 minutes period is then the value of the fourth band. This method has been applied and validated on 5 different sites during more than 500 measuring days in continuous.

Sound from wind turbines during different weather conditions
Larsson, Conny; Öhlund, Olof (Department of Earth Sciences, Uppsala University, Sweden)
The meteorological conditions change over the day and the year and vary a lot depending of the terrain conditions. The meteorological parameters govern both the wind turbine emission sound level and the sound propagation conditions. Long-time measurements of meteorological effects on sound propagation from wind turbines have been performed at three sites in Sweden. The measurements have been performed during 2 years. Sound propagation is studied in a forest area, over a water bay and over heterogeneous terrain. The first two sites are located in the southern part of Sweden and the third is located in the northern part of Sweden. The aim of the project is to improve the knowledge about sound propagation from wind turbines and especially over varying terrain and different weather conditions. The hub height of the studied wind turbines varies from 80-138 m. Meteorological effects increase with distance and starts to be important somewhere between 400 m – 1000 m. Variations of 7-14 dBA at the immission point are found depending on ground conditions and refraction.

RoBin: meeting the requirements of the IEC 61400-11 standard for measuring the acoustic emission of wind turbines with a one-man operated system
Vaucher De La Croix, Daniel (ACOEM, France); Klaas, Timo (WÖLFEL MessSysteme Software, Germany)
Wind power becomes a real alternative to solutions based on fossil fuel as corresponding reserves diminish rapidly. Several technical challenges linked with the implementation of wind farms in numerous locations worldwide must be considered, and noise emission by wind turbines is one of these. The international standard IEC 61400-11 and German “Technische Richtlinie für Windenergieanlagen, Teil 1” of the FGW were set up in order to unify the evaluation of noise emission of wind turbines. Measurements performed according to these standards need practical challenges to be considered, such as the installation of testing equipment and an efficient evaluation of the collected data. The proposed paper will shortly review some parts of the IEC 61400-11 standard and discuss in detail operational constraint linked with on-site measurement and how modern communication technologies help in an easy system deployment and field operation for the benefits of all users.

Numerical prediction of underwater noise reduction during offshore pile driving by a Small Bubble Curtain
Göttsche Klaus, Marco; Møller Juhl, Peter (University of Southern Denmark); Steinhagen, Ulrich (MENCK, Germany)
Small Bubble Curtains are an effective technique to reduce the underwater noise being emitted during offshore pile driving. In order to protect the marine fauna, noise reduction becomes even more important, since the increasing contribution of offshore wind energy leads to a rising number of offshore construction sites in order to cover the need for clean energy. Within the Bubble Curtain air bubbles are injected into the water surrounding the pile. When these are driven by the pressure wave being emitted from the pile, reflection, scattering and absorption effects occur. Within this paper, a method is presented in order to predict the rate of noise attenuation achieved by a Small Bubble Curtain. For this purpose, the bubble distribution is determined with Computational Fluid Dynamics. The noise radiation during pile driving is simulated by Finite Element Analysis and an Effective Medium Approach considers the acoustic effects within the Bubble Curtain. The pressure level at an arbitrary distance from the pile is determined by a Parabolic Equation method. Furthermore, comparisons between simulations and offshore measurements are presented. This combination of four methods provides a flexible and efficient noise prediction tool.

This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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