Noise emissions from wind turbines are one of the main issues that the wind energy industry must deal with nowadays. Strict noise regulations often prevent wind turbines to operate at maximum power conditions, causing large losses of power production and, hence, of revenue. Several noise reduction measures have been proposed so far, but the use of trailing-edge serrations and permeable inserts seem to be the two most promising approaches, showing broadband noise reductions of several decibels. This paper considers the noise reductions (with respect to the baseline blade) observed in previous wind-tunnel measurements featuring these two measures, and scales and synthetically applies them to an experimental recording of a full-scale Vestas V90-2.0 MW wind turbine in operational conditions. The calculated results are then auralized for the observer location used for noise certification in the IEC 61400-11 standard. State-of-the-art sound quality metrics (loudness, tonality, sharpness, roughness and fluctuating strength) are then applied to these simulated sound signals to better understand the achieved reduction in noise annoyance experienced by humans. Reductions in the maximum A-weighted sound pressure level (L_p,A,max) of about 2.4 and 1.2 dBA are observed for the serrations and permeable inserts, respectively. In general, trailing-edge serrations seem to reduce the calculated annoyance experienced (17% lower than the baseline) more efficiently than the permeable inserts (just 2% lower)

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Environmental noise caused by traffic and industrial facilities is a relevant health factor in urban areas, along major traffic routes and in the vicinity of airports. The technique of auralization helps exploring the relationships between sound and its impact on people under fully controlled conditions. Further, by directly addressing the hearing sensation, it is an intuitive tool for the assessment and communication of environmental noise scenarios. Analogous to visualization, auralization enables us to listen to situations that do not exist in reality. In this thesis research, methods for the auralization of environmental acoustical sceneries are established. The sceneries are represented by a virtual environment containing virtual sound sources that are arranged in space and time, and within which sound waves propagate to a virtual observer. To that aim, sophisticated calculation models for the synthesis and reproduction of road traffic, railway and wind turbine noise are developed. This requires investigating the relevance of the involved acoustical phenomena for perceived realism. On that basis, calculation models (i.e. synthesizer structures) are proposed that adequately reproduce source characteristics, sound propagation effects, and spatial impression. The models are accompanied by methods to derive the necessary input parameters from own measurements and data analysis. The presented calculation models are parametric and thus allow for a large versatility with respect to scenarios and sound reproduction. Because the three considered environmental noise sources feature their specific acoustical peculiarities, source-specific models are proposed. These source-specific models have in common that the sound radiated by a source is artificially generated using digital sound synthesis. For wind turbine and road traffic noise, a combination of additive and subtractive synthesis, denoted as spectral modeling synthesis, is applied. A uniqueness of the wind turbine synthesizer is the ability to reproduce and control different types of characteristic amplitude modulation. The synthesizer for road vehicles separately produces tire noise and propulsion noise. The generated propulsion sounds depend on the engine type, the instantaneous engine condition (engine speed and load), and the emission angle. An additional special feature of the propulsion sound synthesis is the fact that, besides amplitude and frequency, the phase of the engine harmonics has to and is considered. For railway rolling and impact noise, in contrast, a physically-based synthesis approach has been developed that describes the mechanical excitation and the vibration of the dynamic wheel/rail system. The corresponding model considers the microstructure of the wheels and rails, as well as structural resonances of the wheel/rail system to elicit the typical metallic sound character of railway noise. In all models, sound propagation effects, such as geometrical divergence, Doppler effect, atmospheric absorption, ground effect and amplitude fluctuations due to atmospheric turbulence, from a virtual point source to a virtual observer location are simulated by processing the synthetic source signals with time-variant filters in the time domain. Auralizations created with the presented models feature a high audio quality and are judged as plausible and realistic by expert listeners. To achieve this realism in the auralizations, it was found that variation with respect to time, frequency, space, and orientation is crucial. The presented models extend the today's body of existing auralization models and allow for new possible applications.@en

Within the research project TAURA, a traffic noise auralization system was developed that covers road traffic and railway noise. This paper focuses on an emission synthesizer for railway noise and presents a concept for rolling and impact noise. The synthesis is based on a physical approach in which the noise generation mechanism is modeled in the time domain. As a starting point, equivalent roughness patterns of each wheel and the rail are generated. These spatial signals are used to implicitly model the mechanical excitation of the wheel/rail system. Transfer paths describing the vibrational behavior and the radiation of wheels and rail are implemented as digital filters. This approach features a high degree of flexibility but requires knowledge of the detailed model parameters.

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By directly addressing the hearing sensation, auralization is an intuitive means for the assessment and communication of noise scenarios. Authenticity can be fu1iher improved by offering visual information. Currently, various auralization and visualization systems exist, that differ with respect to their sound and image signal generation as well as their reproduction strategy. Within the past few years, the entertainment indushy has launched several virtual reality (YR) products such as head-mounted displays or game engines that appear attractive for applications in environmental sound auralization. This contribution gives an overview of current VR systems and inti·oduces evaluation criteria for comparison and assessment. Focus here is on the application to different railway noise scenes. This involves the generation of stimuli for experimental studies and the use as a demonstrator. To achieve maximal flexibility with respect to scenarios and the reproduction systems, the synthesis of sound and images on the basis of on an object-based approach is suggested.@en