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13- On-line wind farm noise control

Napisane przez admin w dniu . Opublikowano w Publikacje.

The results of wind turbines (WTs) noise calculations, calibrated with the outcomes of multi point continuous noise monitoring around the wind farm (WF) are presented in the paper. The Nord2000 noise calculation method was used to obtain contours of LAeq, taking into account instantaneous WTs parameters, its horizontal directivity and meteorological conditions . Noise contours of LAeq around a single WT are not symmetrical due to wind direction and directivity of WT. This is why sound levels in the noise protected (residential) areas around WF are not always the same. Usually, LAeq may be reduced by a few decibels by switching WT into noise reduced mode. Using an on-line -real time calibrated – calculation model this can be applied only to a selected WT influencing sound levels at a given area where current conditions might cause noise complaints (while the other WTs can operate in a normal mode). There are factors that increase the probability of noise complaints, such as amplitude modulation, as well as decrease this probability, such as masking effect of wind induced noise or high ambient noise which should also be taken into account while setting the current operation mode of individual WTs.

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12- Noise annoyance studied in different situations: a comparison of results obtained in situ and laboratory conditions

Napisane przez admin w dniu . Opublikowano w Publikacje.

Noise annoyance is one of the most common non-health effects of noise. Although related to sound levels in some way, annoyance ratings do not depend on this factor alone. Other factors are discussed, including a measurement condition. Researchers ask people to rate annoyance in their homes or in laboratory conditions. Some studies suggest that the results from these two conditions cannot be compared because different non-acoustic factors influence people’s judgments. To answer this question, we conducted a study in which people were asked to rate the annoyance of the same noise stimuli in both conditions. The results obtained so far show that there are no statistical differences for all noise levels.

Dale

11- Modelling Low-Frequency Noise of Wind Turbines

Napisane przez admin w dniu . Opublikowano w Publikacje.

The industrial noise calculation method, which includes wind farm noise, is defined in Polish regulations and Directive 2002/49/EC. According to these documents, the method described in the ISO 9613-2 covering the frequency range from 63 Hz to 8 kHz should be used. However, wind turbines are also a source of the low-frequency noise in the band from a few Hz and thus well below the lower frequency of the existing models calculation range. These sounds are described as rumbling or pulsing, which is a source of annoyance to people living near wind turbines. Therefore, propagation of the low-frequency component should be modelled at the predicting acoustic impact stage of wind turbines on the environment. The paper reviews modelling methods in the low-frequency range and verifies the suitability of ISO 9613-2, CNOSSOS-EU and NORD2000 algorithms for modelling low-frequency noise including frequencies below 63 Hz. The results of the calculations were compared with the results of measurements carried out around the wind farm.

This research has been founded by the National Centre for Research and Development – project No. NOR/POLNOR/Hetman/0073/2019 and by the Polish Ministry of Science and Higher Education – project No. 16.16.130.942.

Dalej

10- Comparison analysis of noise generated by wind turbines with the other noise source in outdoor environment13-

Napisane przez admin w dniu . Opublikowano w Publikacje.

The paper presents a comparison analysis of the noise generated by wind turbines and the one generated by a ventilation shaft of a working coal mine. The aim of the research was to compare the frequency and amplitude distribution of those sources, especially in the infra range. The ultimate aim it is evaluate possible environmental impact on human annoyance or severity. During the research noise signals were recorded utilizing low frequency microphones, shielded by windscreens. Microphones were localized at the heights of 0.0 m, 1.5 m (approximate location of a human ear in a standing position) and 4 m. Additionally, a measurement position of a microphone in relation to the ground surface was observed. Measurements at ground level were performed according to the standard PN-EN 61400-11:2013-07 and in vertical position, where the microphone was mounted „upside down” with the grid flush with the board. The possible influence of wind speed was also monitored. The results of the measurements are discussed.

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9- Wind Turbine’s Noise Annoyance Ratings Related to the Distance and Directivity of a Wind Turbine

Napisane przez admin w dniu . Opublikowano w Publikacje.

Wind turbine (WT) noise is commonly reported to be very annoying. There is a consensus in the literature that this is mainly due to the non-stationary nature of the signal, which is modulated by the movement of the blades. However, measuring and recording such noise is very difficult due to the fact that in most cases a single wind turbine is only one part of a larger complex (consisting of dozens of them). In this paper we describe a laboratory experiment in which people were asked to rate the annoyance of WT noise as a function of distance from a WT. Wind turbine noise was recorded from both sides, downwind and in line with the rotor plane. The results suggest that annoyance ratings decrease with increasing distance from a WT and that noise recorded from the side (in line with the rotor plane) is slightly more annoying than that recorded downwind. In addition, the RT used as reference noise was the least annoying source.

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8- Analysis of Wind Turbine Acoustic Signals in Terms of Detecting Amplitude Modulation and Frequency Deviation

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The operation of a wind turbine is characterized by the fluctuation in the emitted noise related to the rotational speed of the turbine – the periodical movement of the blade in variable atmospheric conditions (amplitude modulation, AM) as well as the movement towards and away from the observation point (Doppler effect – frequency modulation, FM). Amplitude modulation is one of the factors that contributes to the increased nuisance caused by wind turbines. The phenomenon of amplitude modulation has been subject of numerous scientific studies. However, the problem remains of determining the depth of AM’s impact on the increase in annoyance of wind turbine noise. The results of this research showing the characteristic features and depth of AM in different frequency bands. In addition, it has been shown that, in the recorded results, modulation (deviation) of the frequency of the modulated band occurs simultaneously with amplitude modulation. Cyclical changes in the density distribution of spectra in time and space have been demonstrated. Examples have been presented show that defined metrics to determine the variability of modulation frequency depending on the observer’s position relative to the signal source. One such parameter that can demonstrate objective frequency offset is the popular jitter indicator.

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7- Review of evaluation criteria for infrasound and low frequency noise in the general environment

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It has been suggested that infrasound (IS) and low frequency noise (LFN) may be responsible for adverse health effects in people living in the vicinity of wind farms. Many studies have indicated that the basic noise measure − an A-weighted sound pressure level (SPL) − is a less suitable descriptor for assessing the effects of IS and/or LFN. Thus, this paper reviews existing or proposed methods for evaluating infrasound and LFN in residential areas with regard with their impact on human health and wellbeing.

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6- Experimental Verification of Windshields in the Measurement of Low Frequency Noise from Wind Turbines

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Measuring noise from wind turbines is a problematic metrological task due to the significant interference caused by the wind, especially in the low-frequency range. In the audible band, especially A-weighted, the impact of interference from wind is considerably less than in the low-frequency and infrasound bands. In the audible band, especially the A-weighted curve, the impact of interference from wind is significantly less than in the low-frequency and infrasound bands. For this reason, methods are still being sought to reduce interference from wind in the lowest frequency bands effectively. Experimental tests within the scope of the work were carried out using several windshields, with a single standard windscreen at 1.5 m and 4 m height, with an additional microphone shield (tent), and on the board with a double windscreen at a ground level according to IEC 61400-11. Experimental verification of a windshield’s effectiveness and impact under real conditions was carried out using a low-frequency noise source, which was the main fan station at the salt mine shaft. This source generates noise with similar spectral characteristics to wind turbines and can operate in windless conditions. This allowed noise measurements to be made without interference from the wind. Signals were recorded in windless and windy conditions at different wind speeds using tested windshields. An effectiveness analysis of the proposed measurement methods was also carried out on the wind farm. Performed research indicates that the best of the tested variants, when measuring wind turbine noise in the low-frequency range, is to place the microphone on the board with a double windscreen according to IEC 61400-11. At wind speeds of less than 5 m/s at 1.5 m above the ground, the shield effectively eliminates disturbances in the band above 4 Hz. Still, as the wind speed increases above 6 m/s, the level of disturbance increases, and its bandwidth in the lowest frequencies expands.

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5- Evaluation of Annoyance Due to Wind Turbine Noise Based on Pre-learned Patterns

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Annoyance due to wind turbine noise is usually assessed on the basis of surveys conducted among people living in the vicinity of turbines or in the laboratory conditions. Due to the fact that the latter are very different from natural conditions, we propose a solution to reduce this difference. Prior to the surveys, 50 participants were asked to familiarize themselves with 5 environmental signals. They were informed about the annoyance rating assigned to each signal (obtained earlier in laboratory conditions), expressed as a number between 0 (not annoying signal) and 10 (extremely annoying signal). Participants were then presented with new environmental sounds and asked to rate the annoyance caused by each sound, in accordance with the previously learned method. The analysis of our results shows that the variability of answers given by respondents at their homes is similar to those obtained earlier in laboratory conditions.

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4- How to Determine the Annoyance Due to the Wind Turbine

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In the study of annoyance due to wind turbines, the dominant approach takes into account only the noise generated by these sound sources. However, there are studies which show that such value alone is not enough to explain why for the majority of people living near wind turbines their noise is extremely annoying, despite the fact that the measured sound level values are relatively low. One way of solving this problem is to introduce a correction to the one-factor noise index. This has been already done by taking into account the time variability (amplitude modulation) of the sound generated by wind turbines. Another proposal is to establish a multifactorial noise index which includes not only the noise parameters, but also non-acoustic characteristics (mainly visual), which are supposed to influence the overall perception of the annoyance associated with wind turbines. These two approaches will be discussed in this paper.

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