Showing papers on "Aircraft noise published in 1997"

Rotorcraft Noise Model

Abstract: The Rotorcraft Noise Model (RNM) is an aircraft noise impact modeling computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions either on a uniform grid or at specific defined locations. The basic computational model calculates a variety of metrics. Acoustic properties of the noise source are defined by two sets of sound pressure hemispheres, each hemisphere being centered on a noise source of the aircraft. One set of sound hemispheres provides the broadband data in the form of one-third octave band sound levels. The other set of sound hemispheres provides narrowband data in the form of pure-tone sound pressure levels and phase. Noise contours on the ground are output graphically or in tabular format, and are suitable for inclusion in Environmental Impact Statements or Environmental Assessments.

Computation of aircraft noise propagation through the atmospheric boundary layer

Abstract: : Of all outdoor noise sources, aircraft probably have the largest impact on communities. As a result, the accurate prediction of aircraft noise exposure is of great interest. Nevertheless, conventional procedures for quantifying aircraft noise draw heavily on empirical data in which source and propagation effects are more or less statistically lumped together. A physically more relevant modeling of aircraft noise propagation is the ray acoustics approximation. Whereas ray acoustics techniques are well developed for stationary sources, they are not often applied to aircraft noise because the aircraft motion in principle requires many time-consuming computations to obtain the time history of a single takeoff or landing event. The present paper describes the application of the method of ray-tracing to a source moving along a three-dimensional path in a realistic atmosphere. The method is illustrated by typical examples of the effects of a non-uniform wind and temperature profile such as the formation of acoustic shadow zones without any noise and, alternatively, zones with multiple reflections. It is shown that large reductions in computation time can be obtained if the flight path is close to level, which is factual for the majority of civil aircraft movements.

Optimizing an Actuator Array for the Control of Multi-Frequency Noise in Aircraft Interiors

Abstract: Techniques developed for selecting an optimized actuator array for interior noise reduction at a single frequency are extended to the multi-frequency case. Transfer functions for 64 actuators were obtained at 5 frequencies from ground testing the rear section of a fully trimmed DC-9 fuselage. A single loudspeaker facing the left side of the aircraft was the primary source. A combinatorial search procedure (tabu search) was employed to find optimum actuator subsets of from 2 to 16 actuators. Noise reduction predictions derived from the transfer functions were used as a basis for evaluating actuator subsets during optimization. Results indicate that it is necessary to constrain actuator forces during optimization. Unconstrained optimizations selected actuators which require unrealistically large forces. Two methods of constraint are evaluated. It is shown that a fast, but approximate, method yields results equivalent to an accurate, but computationally expensive, method.

New Computational Methods for the Prediction and Analysis of Helicopter Noise

Abstract: : This paper describes several new methods to predict and analyze rotorcraft noise. These methods are 1) a combined computational fluid dynamics and Kirchholt scheme for far-field noise predictions, 2) parallel computer implementation of the Kirchhoff integrations 3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and 4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise.

Helicopter Rotor Noise Prediction: Background, Current Status, and Future Direction

Abstract: Advances in computational fluid dynamics, substantial increases in computer speeds, and robust and efficient acoustic algorithm developments have led to dramatic improvements in helicopter rotor noise prediction over the last 15 years. This talk examines the current status of helicopter rotor noise prediction. A brief history is given followed by a discussion of the status of prediction for each source mechanism. The acoustic analogy approach, and specifically, theories based on the Ffowcs Williams -- Hawkings equation are the most widely used for deterministic noise sources. Thickness and loading noise can be routinely predicted given good blade motion and blade loading inputs. Blade-vortex interaction noise can also be predicted well with measured input data, but prediction of airloads with the high spatial and temporal resolution required for BVI is still difficult. Efficient prediction of high-speed impulsive noise has just become feasible. The best broadband noise prediction currently depends on semi-empirical methods.

The theory of mental testing and the correlation between physical noise level and annoyance

Abstract: Applying the ‘‘theory of psychological testing,’’ physical noise measurement procedures are regarded as ‘‘tests’’ variables and the related annoyance as the criterion variable. The concepts of ‘‘reliability,’’ ‘‘validity’’ and ‘‘equivalence’’ then can be used to assess the precision of different noise measurements. Referring to data of an investigation on aircraft noise in the vicinity of Munich Airport in 1969, in which different physical as well as annoyance data were sampled from the same subjects, it turns out, that the measurements called Leq1, Ls, Leq3, Leq4, NNI and FB1 meet the equivalence criterions of test theory, that is, they cannot statistically be distinguished, and their coefficients of reliability are close to one. Other measurements like D10, H81, log N and Leq10, equivalent to the former six. However, even the former six are only of moderate validity (about 0.5). Regarding psychological testing, therefore, physical noise is only a poor measure when used to predict individual annoyance, b...

Sound effects: Measuring the impact of aircraft noise on residential property values around McCarran International Airport

Abstract: The airline industry is investing billions of dollars to adhere to the Airport Noise and Capacity Act of 1990. The Act requires airlines to reconfigiu'e 100% of their fleets with quieter aircraft. This regulation is based in part on studies conducted around airport facilities which indicated a negative impact from noise on residential property values. The purpose of this paper is to review the issue of aircraft noise and its impact on residential property, specifically single-family homes. It discusses the use of hedonic functional forms in measuring the effect of aircraft noise around a major airport facility. The empirical analysis concludes that a low, negative impact on single-family residences can be expected as a result of aircraft noise exposure around McCarran International Airport.

An assessment of the benefits active noise reduction systems provide to speech intelligibility in aircraft noise environments.

Abstract: The high noise levels being experienced in some military fast jet aircraft and helicopters generally result in a reduction in the intelligibility of speech communications. A study has been conducted to assess the effect of reducing noise levels at the ear, by the use of current Active Noise Reduction (ANR) systems, on speech intelligibility in aircraft noise environments. The results of this study indicate that ANR would improve speech intelligibility in both types of aircraft. The assessment has been conducted using Diagnostic Rhyme Test (DRT) and Articulation Index (AI) techniques. The study has also allowed the correlation between DRT and AI test results to be investigated. A more detailed account of the work reported in this paper is provided at [1].

Federal Interagency Committee on Aviation Noise: Report on Aviation Noise Research Conducted By U.S. Federal Agencies.

Abstract: : The Federal Interagency Committee on Aviation Noise (FICAN) was formed in 1993 to provide forums for debate over needs for future aviation noise research and to encourage new development efforts in this area. All Federal agencies concerned with aviation noise are represented on the Committee, including the Department of Defense, the Department of the Interior, the Department of Transportation, the Environmental Protection Agency, the National Aeronautics and Space Administration, and the Department of Housing and Urban Development. This report introduces current and planned research topics in aviation noise. The work summarized here represents the individual (or sometimes joint) initiatives of member agencies. Fifty-nine projects on aviation noise were identified by FICAN members. Areas of study include: investigation of new criteria for determining land use compatibility, examination of community reactions to aircraft noise, perception of aircraft noise and how it is affected by background noise, acoustic issues associated with rotary wing aircraft, noise effects on animals, development and improvement of computer models, noise reduction technologies, improved public information materials, and structural damage effects.

The Flight Track Noise Impact Model

Abstract: To meet its objective of assisting the U.S. aviation industry with the technological challenges of the future, NASA must identify research areas that have the greatest potential for improving the operation of the air transportation system. To accomplish this, NASA is building an Aviation System Analysis Capability (ASAC). The Flight Track Noise Impact Model (FTNIM) has been developed as part of the ASAC. Its primary purpose is to enable users to examine the impact that quieter aircraft technologies and/or operations might have on air carrier operating efficiency at any one of 8 selected U.S. airports. The analyst selects an airport and case year for study, chooses a set of flight tracks for use in the case, and has the option of reducing the noise of the aircraft by 3, 6, or 10 decibels. Two sets of flight tracks are available for each airport: one that represents actual current conditions, including noise abatement tracks, which avoid flying over noise-sensitive areas; and a second set that offers more efficient routing. FTNIM computes the resultant noise impact and the time and distance saved for each operation on the more efficient, alternate tracks. Noise impact is characterized in three ways: the size of the noise contour footprint, the number of people living within the contours, and the number of homes located in the same contours. Distance and time savings are calculated by comparing the noise abatement flight path length to the more efficient alternate routing.

Airport noise control through land use regulation in the vicinity of airports : the case of Kimpo International Airport

Abstract: The effect of airport noise on communities surrounding airports presents a serious problem for airport operations and expansion. In order to resolve this problem, many attempts have been made to control airport noise over recent years all over the world. Of these, land use regulation is an important method for controlling' the adverse impacts of airport noise on airport environs. The success of the prevention of noise sensitive development depends on effective land use planning and control. This study reviews effective noise control through land use regulation at Kimpo International Airport, Korea. For the purpose of a more precise understanding of the noise problem, a review of the various aspects and causes of aircraft noise, the way noise is measured, its effects on people, and the methods to alleviate the adverse impact of airport noise is presented. In addition to these, the characteristics of effective land use planning around an airport, available land use control measures, and the compatible land use planning system practised in the United States, the United Kingdom and Korea are reviewed. The role of Kimpo International Airport will change to the exclusive use for domestic flights. With the opening of the new intemational airport in 2001, the noise analysis shows a significant reduction in the noise impacted area at Kimpo Airport following this change in role, due to the decrease of the number of aircraft operations and the elimination of noisier aircraft, However, the pressure for development in less impacted areas may make the airport noise problem worse in the future. In order to prevent encroaching development in the vicinity of Kimpo Airport, the following conclusions are presented: - More objective and efficient standards for land use regulation are desirable. - Compatible land use planning through the co-operative efforts of each of the various parties involved is essential for the prevention of noise sensitive development. - Developing a community relations programme is useful for the resolution of airport noise problems and the restoration of a community's confidence. - Systematic selection of noise control measures and monitoring programmes are essential for the effective management of the noise environment.

Neural networks for modelling aircraft noise radiation

Abstract: This paper deals with a method for estimating the spectra of aircraft flyover noise radiation by means of neural network (NN) techniques. The method employs geometrical flight path data obtained by radar and one-third octave spectra of aircraft flyover noise, recorded simultaneously on the ground to train an NN-spectra model of flyover noise. The procedure uses a standard neural network backpropagation algorithm applied to minimise the error between measured and network-simulated octave or one-third octave spectra of the noise. The outputs of the NN-noise radiation model are octave or one-third octave spectra of aircraft noise (normalised to standard atmospheric/weather conditions) at some reference distance around an aircraft as a function of frequency, polar directivity angle (emission angle), azimuthal directivity angle (elevation angle), flight speed and thrust settings. Knowledge of these spectra opens up a wide range of new possibilities in the domain of aircraft noise prediction. In particular, phenomena such as radiation dirctivity of aircraft noise, atmospheric attenuation and weather conditions during the propagation, local ground effects, reflection, and conversion of received spectra to time dependent A-level or Dlevel flyover noise history can be incorporated correctly in the prediction methodology, without the need of restoring to empirical approximations like lateral attenuation correction. The proposed methodology is illustrated for the case of NN-modelling of flyover octave spectra, measured for a small body commercial aircraft.

Classification Trees and the Analysis of Helicopter Vibration Data

Abstract: : Health and Usage Monitoring Systems are receiving a great deal of interest, in an attempt to increase the safety and operational readiness of helicopters, and to minimize maintenance costs. These systems monitor (and can record) various flight parameters, pilot conversations, engine exhaust debris, metallic chip detector levels in the lubrication system, rotor track and balance, as well as vibration levels at selected locations throughout the airframe and the power drive system. Vibration levels are currently being observed on two operational SH-60B helicopters and on an H-60 power drive system installed in the Helicopter Transmission Test Facility (HTTF) at the Naval Air Warfare Center, Trenton, NJ. This paper employs classification trees to analyse vibration signatures produced in the HTTF, identifying those characteristics which distinguish normal signatures from signatures produced by known faulted parts. These trees are quite successful in separating the two types of signatures and achieve small misclassification rates for HTTF data. They are also applied to vibration data collected from an operational aircraft; assuming the tail gearbox in the operational aircraft has no faults, the trees derived from the HTTF produce a high proportion of false alarms.