During Continuous Descent Approaches (CDAs) aircraft glide towards the runway resulting in reduced noise and fuel usage. Here, we investigated whether such landings cause less noise annoyance than a regular stepwise approach. Both landing types were compared in a controlled laboratory setting with a Virtual Community Noise Simulator (VCNS), using four audio samples: an overflight during a regular approach (2000ft altitude) and three aircraft performing CDAs at respectively 3000, 4000 and 5000ft. The samples at 2000ft and 4000ft were recorded at a countryside road, a 360° photo of which was used for the virtual visuals. The other two CDA samples were derived from the recording at 4000ft. Participants were asked to rate all flyover samples twice while being immersed in the virtual environment. The CDA at 3000ft was rated as most annoying, likely due to a longer overflight duration, followed by the regular descent and then the CDAs at 4000 and 5000ft. As CDAs follow a fairly steady trajectory, it was estimated that they will increase annoyance within an area of approximately 2.5km2, as compared to regular landings. Outside of this area, CDAs may instead result in less annoyance than regular landings.

Local effects of noise mitigation are preferably researched with high-fidelity tools rather than standardized noise models. The added advantage is that it is even possible to actually listen to the audible results from these tools. Such an audible result can be generated with the help of noise synt hesis techniques. Aircraft noise synthesis, based on separate modeling of airframe and engine noise components, is described in this study for the use in a virtual reality noise simulator. The present study also shows the effect of atmospheric wind to a synthesized take-off procedure. This was studied in order to quantify the role of the wind in a previous comparison between measurements and synthesized results. The present analysis shows that there is an impact of the wind on the audible result. Hence, the modeling of wind effects can be important to bring measurements and simulation more inline. However, given the current mild wind case, the impact is relatively small. Therefore it is concluded that the observations from the previous research, the comparison without wind effects, will still hold.

The development of Personal aerial vehicles and unmanned aerial vehicles are expected to have a considerable influence on the development of future airspace design around large cities. In the Metropolis project, four different concepts for airspace design are assessed for a (metropolitan) city of the future. The different noise impact on the ground is addressed in this paper. The noise model is based on the maximum allowable source noise levels as proposed by the Federal Aviation Authority, as actual noise data from the considered aircraft is not available. Transmission loss has been modelled using Noise-Power-Distance relations from the Integrated Noise Model. The resulting noise model shows remarkable different noise footprints between the four concepts and between different traffic patterns, which included both converging and diverging flows. The layered airspace structure provided the lowest noise impact on the ground.

Variability in noise levels for flyovers of the same aircraft type can be as large as 12dB, hampering noise assessment around airports. The variable atmosphere (affecting the acoustic propagation) and variations in the aircraft emitted noise are considered as the two main contributors to the noise level variability. This paper presents two experiments aimed at quantifying these contributions. First, the atmospheric contribution was determined with a loudspeaker (100m height) sending signals to microphones on the ground, indicating a sound level variability of less than 2dB. Second, noise levels from Boeing 737 flyovers (landings) were measured with an acoustic camera. The observed noise level variability was 6-8dB. The acoustic camera imaging capabilities eliminated variations due to ground reflections and ambient noise, and identified the turbofan engines as the dominant noise source. Assuming the two contributions to be independent statistical processes, with the atmosphere contributing 2dB maximally, it is concluded that the total noise level variability (6-8dB) as measured for the flyovers was entirely due to the source. Correlating the engine noise levels to the fan rotational speed (from the spectrograms) shows that variations in engine setting explain over 70% of the observed total noise level variation.

A joint initiative of NLR, DLR, and TU Delft has been initiated to streamline the process of generating audible impressions of novel aircraft configurations. The integrated approach adds to the value of the individual tools and allows predicting the sound of future aircraft before they actually fly. Hence, an existing process for the aircraft design and system noise prediction at DLR has been upgraded to generate the required input data for an aircraft auralization framework developed by NLR and TU Delft. This paper presents the new process and an initial application towards the fully automated auralization of novel aircraft configurations within the conceptual aircraft design phase. Such an early auralization of the new designs enables the aircraft designer to assess the success of selected low-noise measures in an intuitive way in addition to the conventional measures, e.g. noise isocontour areas. The auralization result is able to capture all the predicted noise shielding measures used in the current application and indicates that, for an approach condition, drastically reduced ground noise exposure can be achieved.

This paper describes a new framework for the synthesis of aircraft flyover noise through a nonstandard atmosphere. Central to the framework is a ray-tracing algorithm that defines multiple curved propagation paths, if the atmosphere allows, between the moving source and listener. Because each path has a different emission angle, synthesis of the sound at the source must be performed independently for each path. The time delay, spreading loss, and absorption (ground and atmosphere) are integrated along each path and applied to each synthesized aircraft noise source to simulate a flyover. A final step assigns each resulting signal to its corresponding receiver angle for the simulation of a flyover in a virtual reality environment. Spectrograms of the results from a straight path and a curved path modeling assumption are shown. When the aircraft is at close range, the straight path results are valid. Differences appear especially when the source is relatively far away at shallow elevation angles. These differences, however, are not significant in common sound metrics. Although the framework used in this work performs off-line processing, it is conducive to real-time implementation.

A method to include the effect of coherence loss due to turbulence is proposed for real-time auralization of aircraft noise. By modifying the direct ray contribution relative to the ground reflected ray, using filters, the coherence loss effect can be included in a propagation scheme. The results of this approach match with the theoretical predictions thereby verifying the ability of the method. Furthermore, the modulation of aircraft tonal components, due to changing ground interference during a flyover, is diminished as a result of the proposed method. Application to an auralization and comparing to a measurement shows that auralizations can benefit from this method. Therefore the current method forms an essential addition to the techniques currently used in the auralization of aircraft noise.

Annoyance reactions to different types of landing procedures were addressed in a controlled laboratory setting using a Virtual Community Noise Simulator (VCNS) with a head mounted display.Participants, standing on a virtual countryside road, experienced four types of descentflyovers by an A330 aircraft: A regular descent flyoverat 2000ft and CDAs at respectively 3000, 4000 and 5000ft. These types of landing procedures are representative of flights approaching Amsterdam AirportSchiphol(AAS)in the Netherlands. Sound recordings for the VCNS were made on acountryside road and adjusted to match the indicated altitudes. After each flyover, participants were asked to rate their noise annoyance during the previous minute. Preliminary results showed that the 3000ft CDA was rated as the most annoying, followed by the ratings of the regular landing procedure and higher CDAs.These results could indicate that aCDA procedure, despite having lower LAmax and similar SEL levels, may still reach higher annoyance ratings due to longer flyover durations.

The most frequently used excess attenuation method for noise contour models is called the lateral attenuation correction. This empirical method disregards varying atmospheric conditions. It is known that varying atmospheric conditions can lead to large discrepancies for single-event cases. This paper studies these atmospheric effects for a longer period, thus involving multi-event calculations. A European Civil Aviation Conference Document 29 compliant noise model is used with the extended functionality to apply results from a ray-tracing excess attenuation calculation. Results are shown for monthly and yearly noise contours around an example airport using three different modeling options: the standard Document 29 methodology, the standard methodology augmented by varying atmospheric absorption, and the ray-tracing excess attenuation method. The differences found in excess attenuation between the standard Document 29 method and ray tracing are small. It is argued that the main differences are related to varying atmospheric absorption and ground attenuation. For the case considered, wind effects are of minor importance when modeling monthly or yearly contours. In conclusion, the empirical lateral attenuation model, used to estimate the average excess attenuation in a varying atmosphere, provides a practical and realistic estimate for yearly and monthly noise contours for the used atmosphere.

Traditionally aircraft flyover noise is assessed by displaying contours of noise metrics. These models can be used to study noise mitigation measures but they lack the possibility to play-back the audible sound as predicted by their calculations. To that end, noise synthesis is an option that allows to experience differences due to noise abatement procedures or new aircraft designs. A noise synthesis technique for aircraft noise is demonstrated by predicting the noise at a noise monitoring location near an airport. By comparing the synthesized results to a recorded measurement, an indication on the capability of this technique has been acquired. Differences between the synthesized and measured sound remain. A large part of that difference is believed to be caused by the inherent uncertainty when using predictive empirical source noise models. It is shown that differences between departure routes can be captured, thereby illustrating the potential of this method to listen to different take-off procedures. Future improvements in source noise prediction and the inclusion of the effects of turbulence on propagation will further aid to the realism of synthesized aircraft noise.

Heterogeneous platforms integrating different processors like GPUs and multi-core CPUs become popular in high performance computing. While most applications are currently using the homogeneous parts of these platforms, we argue that there is a large class of applications that can benefit from their heterogeneity: massively parallel imbalanced applications. Such applications emerge, for example, from variable time step based numerical methods and simulations. In this paper, we present Glinda, a framework for accelerating imbalanced applications on heterogeneous computing platforms. Our framework is able to correctly detect the application workload characteristics, make choices based on the available parallel solutions and hardware configuration, and automatically obtain the optimal workload decomposition and distribution. Our experiments on parallelizing a heavily imbalanced acoustic ray tracing application show that Glinda improves application performance in multiple scenarios, achieving up to 12x speedup against manually configured parallel solutions.

When measuring aircraft noise, variations of up to 12 dB occur for identical aircraft types flying the same procedure directly over the same microphone position. It is assumed that these variations are the combined effect of variations at the source and in the atmospheric propagation, both not accounted for in standard noise calculations. This paper presents experimental results of the variation in noise levels due to a varying atmosphere. In 2010, an experiment was started to study the atmospheric effects on vertical propagation. A sound source was installed up in a weather-measurement-tower. This setup simultaneously recorded the atmospheric conditions and the variation in sound attenuation over an extended period of time. More than a year later, all measurement results were collected and multiple linear regression analysis was applied with the intention of deriving weather dependent correction factors to improve aircraft noise predictions methods. However, the result of the regression analysis shows that the obtained relations are weak and a significant part of the excess transmission loss remains unexplained. The main question, which part of the 12 dB can be attributed to variations in atmospheric conditions, could therefore not be answered.

This paper expands recent work on a standard aircraft noise model with an advanced excess attenuation method. The most frequently used excess attenuation method for noise contour models is called the lateral attenuation correction and this empirical method disregards varying atmospheric conditions. However, it is known that for single-event cases varying atmospheric conditions can lead to large discrepancies in results. This paper studies these effects for a longer period, involving multi-event calculations. An ECAC Doc.29 compliant noise model is utilized which is extended with the functionality to apply results from a ray tracing excess attenuation calculation. Results are shown for monthly and yearly noise contours around a fictive airport using different modeling options. In the end the differences in results between the three modeling options are small. However, some differences can be distinguished for both the 58 LDEN and 48 LDEN contour. The most prominent difference is a smaller 58 LDEN contour area and a larger 48 LDEN contour area. Based on the results, it is argued that the effects of refraction, ground attenuation and atmospheric absorption each play a distinctive role in the found differences. In conclusion, the lateral attenuation model, used to estimate the average excess attenuation in a varying atmosphere, provides a practical and realistic estimate for a yearly and monthly noise contour.