Dissertations / Theses on the topic 'Aircraft Noise'

Aircraft noise is one of the most controversial environmental concerns in the aviation industry, partly due to the difficulty in harmonizing countries' regulation regarding this issue. The purpose of this thesis is to analyze the ways in which aircraft noise is regulated at the national and international levels, and to compare the legislative responses to aircraft noise issues in Europe and North America. Each of the four main chapters of the thesis takes into consideration a different aspect of the problem. The first chapter describes the objective and subjective ways of measuring aircraft noise. This process is necessary in order to allow the legislation to meet its purpose, namely, to protect the environment, the sources of the aircraft noise, and the effects of the aircraft noise on people. The second chapter describes the evolution of aircraft noise issues at the national levels in the US and throughout the EU, respectively, as well as at the international level, such as at the ICAO. The third chapter analyses the EU Regulation 925/1999, which created tension between the EU and the US due to its alleged discriminatory nature. This thesis examines the arguments of both sides. Finally, the fourth chapter analyses the noise certification standards developed by ICAO, namely the "balanced approach".

Airframe noise is currently of a comparable level to engine noise for an aircraft on approach with high-lift devices and landing gears deployed. The landing gears are a large contributor to the overall airframe noise in this situation. Main landing gears are typically installed beneath a lifting wing. The wing surfaces act as scattering surfaces for the noise generated by these landing gears, and the non-uniform flow around the wing affects both the propagation and strength of the noise. This thesis focuses on investigating the propagation and scattering of installed landing gear noise sources. Boundary element methods are capable of computing acoustic scattering by large and complex geometries, such as a complete aircraft geometry. However, due to their use of Green’s functions, flow effects can only be approximated. As a result, the refraction of acoustic waves due to a non-uniform flow is not accounted for. A uniform flow formulation based on a Lorentz-type transform is typically employed with boundary element methods. The effect of neglecting refraction on the propagation and scattering of landing gear noise sources is determined in this thesis. Investigations are conducted using computational aeroacoustic methods that solve the linearised Euler equations, which account for the refraction of acoustic waves due to non-uniform flow. Using computational aeroacoustic methods, the effect of non-uniform flow due to circulation on the acoustic scattering is quantified as the difference in acoustic scattering over uniform and non-uniform base flows. These investigations are conducted using both single frequency and broadband monopole sources, and both single-element and multi-element airfoils. Increasing the angle of attack, increasing the Mach number, and deploying flaps all increase the circulation around the airfoil. The effect of varying these parameters is investigated systematically. It is shown that for a source in the approximate position of a landing gear with flow conditions similar to that of an airliner on approach, the largest difference observed is at single frequencies for an airfoil configuration with a deployed flap. Otherwise, the differences are small, and in some cases so small that they can be considered negligible. It is shown that moving the source to a position above the airfoil and using a higher Mach number gives a larger difference, although this is not representative of a landing gear source. A new method is proposed to generate a broadband input signal for use with a computational aeroacoustic solver that gives a specified power spectral density at a given radial distance from a monopole source. A signal that is equal in power across a specified range of frequencies is generated using this method. The effect on the frequency content of the scattered noise from a broadband source installed beneath a lifting wing is investigated using this generated signal. It is shown for a single-element airfoil that the major contributor to the obtained power spectral density is the distance of the source from the airfoil. Varying the angle of attack and Mach number has only a small additional effect on the power spectral density. It is then shown that flap and slat deployment has a larger effect on the computed power spectral density due to the additional reflective surfaces. Existing boundary element method formulations that estimate uniform and nonuniform flow effects are evaluated for their suitability for landing gear noise scattering predictions. It is shown that the uniform flow formulation is more suitable due to a simplifying assumption made in the derivation of the non-uniform flow formulation. An existing realistic landing gear noise model is coupled with a three-dimensional acoustic boundary element method solver. The landing gear noise model applies scaling laws to directional databases for isolated landing gear components in order to estimate the total far-field noise. The implemented coupling methodology is used to compute the sound pressure level on a ground plane beneath a realistic scattering aircraft geometry. The geometrical effect of flap deployment is investigated using sources of constant strength for each configuration. It is shown that the effect of flap deployment is to increase the sound pressure level directly below and in the region immediately surrounding the aircraft. The effect of source strength reduction due to circulation around a lifting wing is then included in the predictions. This results in a large decrease in the predicted sound pressure level on the ground plane with flap deployment.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.
Includes bibliographical references (p. 45).
An experimental study was perfonned to determine which materials are best suited for internal aircraft noise reduction. An impedance tube with dimensions of a scaled aircraft was constructed and evaluated, and eleven materials were tested and compared based on their noise reduction properties, weight, and thickness. Polyvinylidene Fluoride was tested for use in active noise control for a large space.
by Djuna S. Copley-Woods.
S.B.

Appraisal of the noise produced at the combustion stage in a jet engine is becoming more important, as fan and jet noise have been significantly reduced over many years. Therefore, combustion noise is contributing more to overall noise, especially at low jet velocities. Environmental regulations stipulate that gas emissions from a jet engine should be reduced. Thus, new techniques have been introduced in their operation, especially concerning the combustion process. Accordingly, there is a need for improved processing methods in order to extract combustion noise from other sources in new build engines. A novel processing technique to extract turbofan engine combustion noise called 3S-Array is presented. It has been developed using a multiple coherence technique with data acquired in the in-duct and external sound fields of a jet engine. In-duct sensors are located in the combustion chamber and in the nozzle of the engine, and external data is acquired using an array of microphones. A beamformed signal focused on the nozzle of the engine is generated with the data from the external array. Jet noise and in influences of the room on the array output are reduced using this focusing technique, which is referred to as Focused Beamformed Output (FBO). Results show that using this new 3S-Array technique with two of the in-duct sensors and the focused beamformed signal as the third one, provides a better estimator of combustion noise than the 3-signal coherence technique alone, or the Coherence-Output Power Spectra (COP), both of which are reported in the literature as methods for the extraction of combustion noise from the radiated noise spectrum.

Thesis (Ph. D.)--University of Sydney, 2003.
Title from title screen (viewed Apr. 29, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Public Health, Faculty of Medicine. Includes bibliography. Also available in print form.

The purpose of the study was to examine the existence of an association between child blood pressure (BP) and exposure to domestic jet aircraft noise in the context of the construction of a new parallel north-south runway at Sydney (Kingsford-Smith) Airport. The baseline study was commissioned and funded by the Federal Airports Corporation (FAC), with measurements conducted in 1994 and 1995. A follow-up longitudinal component to the study was subsequently commissioned and funded by the FAC in 1997, and measurements conducted in the same year. As the same individuals were measured and re-measured over changing conditions of exposure to aircraft noise, the quasiexperimental nature of the study allowed inferences to be made regarding exposure to aircraft noise and child BP. The main hypotheses for testing were that BP, and within-subject longitudinal changes in BP, are positively related to domestic jet aircraft noise exposure and longitudinal changes in domestic jet aircraft noise exposure respectively. Subsidiary hypotheses tested for evidence of short- and long-term BP adaptation effects where BPs were related to prior changes to aircraft noise exposures. A sample of 75 primary schools within a 20 km radius of Sydney Airport under various noise exposure conditions, both existing and those projected with the advent of the new runway, participated in the study. The baseline cohort comprised 1,230 Year 3/4 children attending the schools in 1994 and 1995, and the follow-up participants comprised 628 of the original baseline sample re-measured in 1997. Study participants were enrolled by active parental consent. The baseline response rate was approximately 40% of children in the participating schools. Systolic (SBP) and diastolic (DBP) blood pressure readings of the children were taken using automated BP measuring equipment along with anthropometric measurements (heights, weights, skinfold thicknesses and waist measurements). Parental surveys captured items pertaining to the child�s ethnic background as measured by the country of birth of the child and parent(s), residential address and housing structure, child eating habits and activity levels, along with family and child history of high blood pressure. Aircraft noise exposure data were collected by the National Acoustic Laboratories and processed into the energy-averaged noise metric used in Australia for aircraft noise exposure assessment called the Australian Noise Exposure Index (ANEI). Mean exposures for a given calendar month were used in the analysis. ANEI values were geocoded to exact geographic locations using digitised street maps from which values for each house and school address, also geocoded, were interpolated. A child BP measured in a given month was matched to a aircraft noise exposure value both at their school and residential address for that month for analysis. After adjusting for confounding and other factors, the cross-sectional relationship between BP and aircraft noise exposure was found to be inconsistent. SBP was nonsignificantly negatively associated with school aircraft noise exposure at baseline (0.05 mmHg/ANEI, cluster-sampling-adjusted p>0.05), but positively and non-significantly associated with school aircraft noise exposure at follow-up (0.05 mmHg/ANEI, p>0.05). As for SBP, baseline DBP was significantly negatively related to school aircraft noise exposure at (0.09 mmHg/ANEI, p<0.001) and non-significantly positively associated with school aircraft noise exposure at follow-up (0.05 mmHg/ANEI, p>0.05). Within-subject BP changes, occurring from baseline to follow-up, regressed on corresponding longitudinal changes in aircraft noise exposures produced inconsistent results. SBP change was positively and non-significantly (0.027 mmHg/ANEI, p>0.05) associated with corresponding school aircraft noise exposure change, while SBP change was negatively associated total aircraft noise exposure change (statistically nonsignificant, 0.06 mmHg/ANEI, p>0.05). DBP changes were similarly and nonsignificantly related to corresponding aircraft noise exposure changes. Some evidence for short-term BP adaptation to recent changes in aircraft noise exposure was found. Consistent negative associations between systolic and diastolic BP and recent changes in school aircraft noise exposure were found. This association was statistically significant at study baseline (SBP: 0.19 mmHg/ANEI, p<0.001; DBP: 0.12 mmHg/ANEI, p<0.001), and of similar magnitude although not statistically significant at follow-up (SBP: 0.14 mmHg/ANEI; DBP: 0.10 mmHg/ANEI, p>0.05). In the presence of inconsistent cross-sectional BP-aircraft noise exposure associations, this finding is consistent with evidence of a homoeostatic BP response to recent changes in aircraft noise exposure, where resting BP returns to pre-existing levels unrelated to aircraft noise exposure. The public health implication of this finding appears to be benign.

The purpose of the study was to examine the existence of an association between child blood pressure (BP) and exposure to domestic jet aircraft noise in the context of the construction of a new parallel north-south runway at Sydney (Kingsford-Smith) Airport. The baseline study was commissioned and funded by the Federal Airports Corporation (FAC), with measurements conducted in 1994 and 1995. A follow-up longitudinal component to the study was subsequently commissioned and funded by the FAC in 1997, and measurements conducted in the same year. As the same individuals were measured and re-measured over changing conditions of exposure to aircraft noise, the quasiexperimental nature of the study allowed inferences to be made regarding exposure to aircraft noise and child BP. The main hypotheses for testing were that BP, and within-subject longitudinal changes in BP, are positively related to domestic jet aircraft noise exposure and longitudinal changes in domestic jet aircraft noise exposure respectively. Subsidiary hypotheses tested for evidence of short- and long-term BP adaptation effects where BPs were related to prior changes to aircraft noise exposures. A sample of 75 primary schools within a 20 km radius of Sydney Airport under various noise exposure conditions, both existing and those projected with the advent of the new runway, participated in the study. The baseline cohort comprised 1,230 Year 3/4 children attending the schools in 1994 and 1995, and the follow-up participants comprised 628 of the original baseline sample re-measured in 1997. Study participants were enrolled by active parental consent. The baseline response rate was approximately 40% of children in the participating schools. Systolic (SBP) and diastolic (DBP) blood pressure readings of the children were taken using automated BP measuring equipment along with anthropometric measurements (heights, weights, skinfold thicknesses and waist measurements). Parental surveys captured items pertaining to the child�s ethnic background as measured by the country of birth of the child and parent(s), residential address and housing structure, child eating habits and activity levels, along with family and child history of high blood pressure. Aircraft noise exposure data were collected by the National Acoustic Laboratories and processed into the energy-averaged noise metric used in Australia for aircraft noise exposure assessment called the Australian Noise Exposure Index (ANEI). Mean exposures for a given calendar month were used in the analysis. ANEI values were geocoded to exact geographic locations using digitised street maps from which values for each house and school address, also geocoded, were interpolated. A child BP measured in a given month was matched to a aircraft noise exposure value both at their school and residential address for that month for analysis. After adjusting for confounding and other factors, the cross-sectional relationship between BP and aircraft noise exposure was found to be inconsistent. SBP was nonsignificantly negatively associated with school aircraft noise exposure at baseline (0.05 mmHg/ANEI, cluster-sampling-adjusted p>0.05), but positively and non-significantly associated with school aircraft noise exposure at follow-up (0.05 mmHg/ANEI, p>0.05). As for SBP, baseline DBP was significantly negatively related to school aircraft noise exposure at (0.09 mmHg/ANEI, p<0.001) and non-significantly positively associated with school aircraft noise exposure at follow-up (0.05 mmHg/ANEI, p>0.05). Within-subject BP changes, occurring from baseline to follow-up, regressed on corresponding longitudinal changes in aircraft noise exposures produced inconsistent results. SBP change was positively and non-significantly (0.027 mmHg/ANEI, p>0.05) associated with corresponding school aircraft noise exposure change, while SBP change was negatively associated total aircraft noise exposure change (statistically nonsignificant, 0.06 mmHg/ANEI, p>0.05). DBP changes were similarly and nonsignificantly related to corresponding aircraft noise exposure changes. Some evidence for short-term BP adaptation to recent changes in aircraft noise exposure was found. Consistent negative associations between systolic and diastolic BP and recent changes in school aircraft noise exposure were found. This association was statistically significant at study baseline (SBP: 0.19 mmHg/ANEI, p<0.001; DBP: 0.12 mmHg/ANEI, p<0.001), and of similar magnitude although not statistically significant at follow-up (SBP: 0.14 mmHg/ANEI; DBP: 0.10 mmHg/ANEI, p>0.05). In the presence of inconsistent cross-sectional BP-aircraft noise exposure associations, this finding is consistent with evidence of a homoeostatic BP response to recent changes in aircraft noise exposure, where resting BP returns to pre-existing levels unrelated to aircraft noise exposure. The public health implication of this finding appears to be benign.

Thesis (MScEng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Active noise reduction (ANR) is a method of cancelling acoustic noise in a defined enclosure. Two methods exist to implement ANR, they are the analog feedback method and the digital feedforward method. Commercial ANR systems employing feedback methods have been around since the 1980's. Feedforward methods have however only become practically implemental with the age of fast real time digital signal processing. In current systems, feedback ANR is used to attenuate broadband noise whilst feedforward methods are used to attenuate narrow band or tonal noise [2]. This thesis investigates feedforward ANR to cancel broadband acoustic noise in aircraft headsets. Different adaptive filters, optimal configuration of adaptive filters and practical limitations to broadband attenuation for headsets are addressed. Results from this thesis show that at least 10dS noise energy attenuation is attainable over a bandwidth of 2.5kHz. A number of areas for further research are also identified.
AFRIKAANSE OPSOMMING: Aktiewe geraas beheer (AGS) is 'n metode om akoestiese geraas te kanselleer in 'n gedefinieerde omgewing. Twee metodes bestaan om AGS te implementeer. Hulle is die analoog terugvoer en digitale vorentoevoer metode. Kommersiële AGS wat die terugvoer metode gebruik is al in gebruik van die 1980's. Vorentoevoer metodes is egter eers sedert vinnige intydse digitale sein prosessering moontlik. In huidige stelsels word terugvoer AGS gebruik vir die attenuasie van wyeband geraas terwyl vorentoevoer metodes gebruik word om nouband of enkel toon geraas te kanselleer [2]. Die tesis ondersoek vorentoevoer AGS om wyeband akoestiese geraas te kanselleer in vliegtuig kopstukke. Verskillende aanpasbare filters, optimale opstelling van aanpasbare filters en praktiese beperkings tot wyeband attenuasie vir kopstukke word ondersoek. Resultate van die tesis wys dat ten minste 10dS geraas energie attenuasie behaal kan word oor 'n bandwydte van 2.5kHz. 'n Aantal areas vir verder navorsing is ook geïdentifiseer.

Thesis (MTech (Environmental Health))--Cape Peninsula University of Technology, 2006
Airport operations have become a major source of concern due to aircraft nOIse, particularly in areas close to airports and aircraft flight tracks. Public opposition to aircraft noise is a threat to the continued growth of civil aviation in South Africa. This study investigated the psychological effects of aircraft noise on residents and school activities at a neighbourhood close to the airport, particularly the area located under the flight tracks or adjacent to the landing and departure pattern of aircraft. Bishop Lavis was chosen as the experimental area and Kensington, about 17km away from the airport, was chosen as a control area. Questionnaires coupled with oral interviews and observations were used to gather information. The findings are focused on annoyance and disturbance. The study revealed that noise exposure caused annoyance, activity disturbance and some mild effects on school results, when compared with the control area. Disturbances were experienced in some activities that need concentration. Aircraft noise also caused communication interference, sleep deprivation and affected the teaching process. The community at the experimental area indicated some non-acoustical effects, such as fear of aircraft crashing over their homes but they indicated no willingness to leave the area. As such, it becomes essential when locating and designing airports to optimise flight paths in a way to reduce noise exposure to nearby communities. Recommendations for mitigation of noise exposure are proposed, which include operational procedure, banning chapter I and 2 aircraft, restricting night flights, proper land use planning and enforcing international environmental regulations.

Aviation noise pollution in urban areas can be considered as a major problem and source of conflict between airport infrastructure and residents. Its effects could significantly limit the growth of aviation as well as affect public health, mainly when airports are located near residential areas. Noise control measures both at the source and at the receivers are often expensive and limited. Nevertheless, they represent the most viable solutions for contrasting this phenomenon due to the difficulty of finding suitable measures to reduce aircraft noise along its propagation path. This work is focused on the development, the assessment, and the management of mitigation actions regarding the noise action plan of Pisa’s “Galileo Galilei” International Airport. This airport has recently presented its noise action plan in order to give itself the possibility of expansion without incurring in air traffic limitations. The action plan includes both the construction of a runway link to increase the take-off run length and the introduction of a noise-abatement departure procedure. The effectiveness of these actions against noise pollution has been evaluated by means of noise numerical modelling. In particular, the noise impact produced by the airport and the related exposed population have been estimated by using the Integrated Noise Model (INM). New strategies to ensure an effective noise reduction as a response to the growing aircraft traffic have been proposed. Noise maps calculated for present and future scenarios, including those following the application of noise reduction measures, are shown. For many situations, people’s exposure and the percentages of highly annoyed and highly sleep-disturbed people have been determined also including military aircraft noise. Moreover, a novel methodology for managing airport noise in the closest urban areas based on the Automatic Dependent Surveillance-Broadcast (ADS-B) technology is presented. ADS-B helps to track the 3D-flight paths with high data resolution and then to verify both the effectiveness of the action plan and the compliance with its provisions. A penetration gate has been strategically set considering the departures towards the city. The vertical distribution of the traffic crossing the gate and the correlation between take-off conditions and noise-related events have been investigated in order to establish rules for penalties due to the lack of compliance with the action plan requirements. The relationships between the operational characteristics of flight departures and aircraft noise by means of a statistical approach have been identified. Principal Component Analysis and Multiple Linear Regression were performed in order to extrapolate a simplified predictive model at a specific point on the ground. The findings may be useful to point out the operational characteristics causing the noisiest aircraft flyovers. Consequently, scheduled flight departures could be re-organized by introducing departure-direction and departureprocedure restrictions in order to minimize noise impact on the urban areas. The results confirm that ADS-B system may be considered a smart tool providing cost-effective solutions for the airport noise management in urban areas and its sustainable development, particularly when the radar tracks are not available.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 89-92).
Hybrid wing-body aircraft noise generation and boundary layer ingestion (BLI) performance trends with increased fan face Mach number inlet designs are investigated. The presented topics are in support of the NASA subsonic fixed wing project, which seeks to lower noise and increase performance by improving prediction methods and technologies. The aircraft configurations used for study are the N2A, using conventional podded engines, and the N2B, using an embedded propulsion system. Preliminary FAR Part 36 noise certification assessments are completed using the NASA Aircraft Noise Prediction Program (ANOPP). The limitations of applying current ANOPP noise prediction methods to hybrid wing-body aircraft are investigated. Improvements are made to the landing gear and airfoil self-noise modules, while a diffraction integral method is implemented in a companion thesis to enhance noise shielding estimates. The N2A overall takeoff and landing noise estimate is found to be 5.3 EPNdB higher than the N+2 goal. The dominant noise sources are the fan rearward and jet on takeoff and the main landing gear and elevons on approach. A lower fan pressure ratio and advanced landing gear fairings are recommended to decrease N2A overall noise levels. The available engine noise estimation tools were inadequate to model the N2B distributed propulsion system and rectangular exhaust nozzle; therefore, overall N2B aircraft noise results are presented for reference only. A simplified embedded propulsion system integration study is carried out to explore the N2B fan design space. A 2-D computational domain with contoured slip boundaries around the centerbody is used to replicate the effects of 3-D relief on the airframe and inlet aerodynamics. The domain includes the S-shaped inlet duct and is extended far downstream for a Trefftz plane power balance analysis to determine the propulsive power required for steady level flight. A fan actuator volume is included to couple the airframe external and the engine internal flows. Aircraft power savings, fan efficiency, and boundary layer thickness trends are examined to determine if increasing fan face Mach number improves system performance while mitigating the total pressure distortion risk of boundary layer ingestion. A fan face Mach number near 0.7 is found to increase aircraft power savings 12% relative to the baseline design and to reduce centerbody boundary layer kinetic energy thickness by 4.7%. In addition, power balances at lower fan pressure ratios as fan face Mach number increases suggesting that high-flow low pressure ratio fans are desirable for BLI.
by Philip Andrew Weed.
S.M.

The objective of this research is to examine how to design low-noise transport aircraft using Multidisciplinary Design Optimization (MDO). The subject is approached by designing for low-noise both implicitly and explicitly. The explicit design approach involves optimizing an aircraft while explicitly constraining the noise level. An MDO framework capable of optimizing both a cantilever wing and a Strut-Braced-Wing (SBW) aircraft was developed. The framework employs aircraft analysis codes previously developed at the Multidisciplinary Design and Analysis (MAD) Center at Virginia Tech (VT). These codes have been improved here to provide more detailed and realistic analysis. The Aircraft Noise Prediction Program (ANOPP) is used for airframe noise analysis. The objective is to use the MDO framework to design aircraft for low-airframe-noise at the approach conditions and quantify the change in weight and performance with respect to a traditionally designed aircraft. The results show that reducing airframe noise by reducing approach speed alone, will not provide significant noise reduction without a large performance and weight penalty. Therefore, more dramatic changes to the aircraft design are needed to achieve a significant airframe noise reduction. Another study showed that the trailing-edge (TE) flap can be eliminated, as well as all the noise associated with that device, without incurring a significant weight and performance penalty. To achieve approximately 10 EPNdB TE flap noise reduction the flap area was reduced by 82% while the wing reference area was increased by 12.4% and the angle of attack increased from 7.6 degrees to 12.1 degrees to meet the required lift at approach. The wing span increased by approximately 2.2%. Since the flap area is being minimized, the wing weight suffers only about a 2,000 lb penalty. The increase in wing span provides a reduction in induced drag to balance the increased parasite drag due to a lower wing aspect ratio. As a result, the aircraft has been designed to have minimal TE flaps without any significant performance penalty. If noise due to the leading-edge (LE) slats and landing gear are reduced, which is currently being pursued, the elimination of the flap will be very significant as the clean wing noise will be the next 'noise barrier'. Lastly, a comparison showed that SBW aircraft can be designed to be 10% lighter and require 15% less fuel than cantilever wing aircraft. Furthermore, an airframe noise analysis showed that SBW aircraft with short fuselage-mounted landing gear could have similar or potentially a lower airframe noise level than comparable cantilever wing aircraft. The implicit design approach involves selecting a configuration that supports a low-noise operation, and optimizing for performance. A Blended-Wing-Body (BWB) transport aircraft has the potential for significant reduction in environmental emissions and noise compared to a conventional transport aircraft. A BWB with distributed propulsion was selected as the configuration for the implicit low-noise design in this research. An MDO framework previously developed at the MAD Center at Virginia Tech has been refined to give more accurate and realistic aircraft designs. To study the effects of distributed propulsion, two different BWB configurations were optimized. A conventional propulsion BWB with four pylon mounted engines and two versions of a distributed propulsion BWB with eight boundary layer ingestion inlet engines. A 'conservative' distributed propulsion BWB design with a 20% duct weight factor and a 95% duct efficiency, and an 'optimistic' distributed propulsion BWB design with a 10% duct weight factor and a 97% duct efficiency were studied. The results show that 65% of the possible savings due to 'filling in' the wake are required for the 'optimistic' distributed propulsion BWB design to have comparable $TOGW$ as the conventional propulsion BWB, and 100% savings are required for the 'conservative' design. Therefore, considering weight alone, this may not be an attractive concept. Although a significant weight penalty is associated with the distributed propulsion system presented in this study, other characteristics need to be considered when evaluating the overall effects. Potential benefits of distributed propulsion are, for example, reduced propulsion system noise, improved safety due to engine redundancy, a less critical engine-out condition, gust load/flutter alleviation, and increased affordability due to smaller, easily-interchangeable engines.
Ph. D.

Since the 1950s the jet aeroacoustics community has been involved in predicting and measuring the noise distribution in jets. In this work, cylindrical and planar Fourier near-field acoustical holography are used to investigate radiation from a full-scale, installed jet engine. Practical problems involving measurement aperture and the highly directional nature of the source are addressed. Insights from numerical simulations reveal usable reconstruction regions. A comparison of cylindrical and planar NAH for the respective measurement apertures shows cylindrical NAH outperforms planar NAH on reconstructions both towards and away from the source.

Tot i que en les últimes dècades la reducció del soroll emès pels avions ha estat substancial, el seu impacte a la població ubicada a prop dels aeroports és un problema que encara persisteix. Contenir el soroll generat per les operacions d'aeronaus, tot assumint al mateix temps la creixent demanda de vols, és un dels principals desafiaments a que s'enfronten les autoritats aeroportuàries, els proveïdors de serveis per a la navegació aèria i els operadors de les aeronaus. A part de millorar l'aerodinàmica o les emissions sonores de les aeronaus, l'impacte acústic de les seves operacions es pot reduir també gràcies a la definició de nous procediments de vol més òptims. Aquests procediments s'anomenen generalment Procediments d'Atenuació de Soroll (PAS) i poden incloure rutes preferencials de vol (a fi d'evitar les zones poblades) i també perfils de vol verticals optimitzats.

Els procediments actuals per a la reducció de soroll estan molt lluny de ser els òptims. En general, la seva optimització no és possible a causa de les limitacions d'avui en dia en els mètodes de navegació, els equips d'aviònica i la complexitat present en alguns espais aeris. D'altra banda, molts PAS s'han dissenyat de forma manual per un grup d'experts i amb l'ajuda de diverses iteracions. Tot i això, en els propers anys s'esperen nous sistemes d'aviònica i conceptes de gestió del trànsit aeri que permetin millorar el disseny d'aquests procediments, fent que siguin més flexibles. En els pocs casos on s'optimitzen PAS, se sol utilitzar una mètrica acústica en l'elaboració de les diferents funcions objectiu i per tant, no es tenen en compte les molèsties sonores reals. La molèstia és un concepte subjectiu, complexe i que depèn del context en que s'usa i la seva integració en l'optimització de trajectòries segueix essent un aspecte a estudiar.

La present tesi doctoral es basa en el fet que en el futur serà possible definir trajectòries més flexibles i precises. D'aquesta manera es permetrà la definició de procediments de vol òptims des d'un punt de vista de molèsties acústiques. Així doncs, es considera una situació en que aquest tipus de procediments poden ser dissenyats de forma automàtica o semi-automàtica per un sistema expert basat en tècniques d'optimització i de raonament aproximat. Això serviria com una eina de presa de decisions per planificadors de l'espai aeri i dissenyadors de procediments.

En aquest treball es desenvolupa una eina completa pel càlcul de PAS òptims. Això inclou un conjunt de models no lineals que tinguin en compte la dinàmica de les aeronaus, les limitacions de la trajectòria i les funcions objectiu. La molèstia del soroll es modela utilitzant tècniques de lògica difusa en funció del nivell màxim de so percebut, l'hora del dia i el tipus de zona a sobrevolar. Llavors, s'identifica i es formula formalment el problema com a un problema de control òptim multi-criteri. Per resoldre'l es proposa un mètode de transcripció directa per tal de transformar-lo en un problema de programació no lineal. A continuació s'avaluen una sèrie de tècniques d'optimització multi-objectiu i entre elles es destaca el mètode d'escalarització, el més utilitzat en la literatura. No obstant això, s'exploren diverses tècniques alternatives que permeten superar certs inconvenients que l'escalarització presenta. En aquest context, es presenten i proven tècniques d'optimització lexicogràfica, jeràrquica, igualitària (o min-max) i per objectius. D'aquest anàlisi es desprenen certes conclusions que permeten aprofitar les millors característiques de cada tècnica i formar finalment una tècnica composta d'optimització multi-objectiu. Aquesta última estratègia s'aplica amb èxit a un escenari real i complex, on s'optimitzen les sortides cap a l'Est de la pista 02 de l'aeroport de Girona. En aquest exemple, dos tipus diferents d'aeronaus volant a diferents períodes del dia són simulats obtenint, conseqüentment, diferents trajectòries òptimes.
Aunque en las últimas décadas la reducción del ruido emitido por los aviones ha sido sustancial, su impacto en la población ubicada cerca de los aeropuertos es un problema persistente. Contener este ruido, asumiendo al mismo tiempo la creciente demanda de vuelos, es uno de los principales desafíos a que se enfrentan las autoridades aeroportuarias, los proveedores de servicios para la navegación y los operadores. Aparte de mejorar la aerodinámica o las emisiones sonoras de las aeronaves, su impacto acústico se puede reducir también gracias a la definición de nuevos procedimientos de vuelo optimizados. Éstos, se denominan generalmente Procedimientos de Atenuación de Ruido (PAR) y pueden incluir rutas preferenciales de vuelo (a fin de evitar las zonas pobladas) y también perfiles de vuelo optimizados.

Los procedimientos actuales para la reducción de ruido están muy lejos de ser los óptimos. En general, su optimización no es posible debido a las limitaciones de hoy en día en los métodos de navegación, los equipos de aviónica y la complejidad presente en algunos espacios aéreos. Por otra parte, muchos PAR se han diseñado de forma manual por un grupo de expertos y con la ayuda de varias iteraciones. Sin embargo, en los próximos años se esperan nuevos sistemas de aviónica y conceptos de gestión del tráfico aéreo que permitan mejorar el diseño de estos procedimientos, haciendo que sean más flexibles. En los pocos casos donde se optimizan PAR, se suele utilizar una métrica acústica en la elaboración de las diferentes funciones objetivo y por lo tanto, no se tienen en cuenta las molestias sonoras reales. La molestia es un concepto subjetivo, complejo y que depende del contexto en que se usa y su integración en la optimización de trayectorias sigue siendo un aspecto a estudiar.

La presente tesis doctoral se basa en el hecho de que en el futuro será posible definir trayectorias más flexibles y precisas. De esta manera se permitirá la definición de procedimientos de vuelo óptimos desde un punto de vista de molestias acústicas. Se considera una situación en que este tipo de procedimientos pueden ser diseñados de forma automática o semi-automática por un sistema experto basado en técnicas de optimización y de razonamiento aproximado. Esto serviría como una herramienta de toma de decisiones para planificadores del espacio aéreo y diseñadores de procedimientos.

En este trabajo se desarrolla una herramienta completa para el cálculo de PAR óptimos. Esto incluye un conjunto de modelos no lineales que tengan en cuenta la dinámica de las aeronaves, las limitaciones de la trayectoria y las funciones objetivo. La molestia del ruido se modela utilizando técnicas de lógica difusa en función del nivel máximo de sonido percibido, la hora del día y el tipo de zona a sobrevolar. Entonces, se identifica y se formula formalmente el problema como un problema de control óptimo multi-criterio. Para resolverlo se propone un método de transcripción directa para transformarlo en un problema de programación no lineal. A continuación se evalúan una serie de técnicas de optimización multi-objetivo y entre ellas se destaca el método de escalarización, el más utilizado en la literatura. Sin embargo, se exploran diversas técnicas alternativas que permiten superar ciertos inconvenientes que la escalarización presenta. En este contexto, se presentan y prueban técnicas de optimización lexicográfica, jerárquica, igualitaria (o min-max) y por objetivos. De este análisis se desprenden ciertas conclusiones que permiten aprovechar las mejores características de cada técnica y formar finalmente una técnica compuesta de optimización multi-objetivo. Esta última estrategia se aplica con éxito en un escenario real y complejo, donde se optimizan las salidas hacia el Este de la pista 02 del aeropuerto de Girona. En este ejemplo, dos tipos diferentes de aeronaves volando a diferentes periodos del día son simulados obteniendo, consecuentemente, diferentes trayectorias óptimas.
Despite the substantial reduction of the emitted aircraft noise in the last decades, the noise impact on communities located near airports is a problem that still lingers. Containing the sound generated by aircraft operations, while meeting the increasing demand for aircraft transportation, is one of the major challenges that airport authorities, air traffic service providers and aircraft operators may deal with. Aircraft noise can be reduced by improving the aerodynamics of the aircraft, the engine noise emissions but also in designing new optimised flight procedures. These procedures, are generally called Noise Abatement Procedures (NAP) and may include preferential routings (in order to avoid populated areas) and also schedule optimised vertical flight path profiles.

Present noise abatement procedures are far from being optimal in regards to minimising noise nuisances. In general, their optimisation is not possible due to the limitations of navigation methods, current avionic equipments and the complexity present at some terminal airspaces. Moreover, NAP are often designed manually by a group of experts and several iterations are needed. However, in the forthcoming years, new avionic systems and new Air Traffic Management concepts are expected to significantly improve the design of flight procedures. This will make them more flexible, and therefore will allow them to be more environmental friendly. Furthermore, in the few cases where NAP are optimised, an acoustical metric is usually used when building up the different optimisation functions. Therefore, the actual noise annoyance is not taken into account in the optimisation process. The annoyance is a subjective, complex and context-dependent concept. Even if sophisticated noise annoyance models are already available today, their integration into an trajectory optimisation framework is still something to be further explored.

This dissertation is mainly focused on the fact that those precise and more flexible trajectories will enable the definition of optimal flight procedures regarding the noise annoyance impact, especially in the arrival and departure phases of flights. In addition, one can conceive a situation where these kinds of procedures can be designed automatically or semi-automatically by an expert system, based on optimisation techniques and approximate reasoning. This would serve as a decision making tool for airspace planners and procedure designers.

A complete framework for computing optimal NAP is developed in this work. This includes a set of nonlinear models which take into account aircraft dynamics, trajectory constraints and objective functions. The noise annoyance is modelled by using fuzzy logic techniques in function of the perceived maximum sound level, the hour of the day and the type of over-flown zone. The problem tackled, formally identified and formulated as a multi-criteria optimal control problem, uses a direct transcription method to transform it into a Non Linear Programming problem. Then, an assessment of different multi-objective optimisation techniques is presented. Among these techniques, scalarisation methods are identified as the most widely used methodologies in the present day literature. Yet, in this dissertation several alternative techniques are explored in order to overcome some known drawbacks of this technique. In this context, lexicographic, hierarchical, egalitarian (or min-max) and goal optimisation strategies are presented and tested. From this analysis some conclusions arise allowing us to take advantage of the best features of each optimisation technique aimed at building a final compound multi-objective optimisation strategy. Finally, this strategy is applied successfully to a complex and real scenario, where the East departures of runway 02 at the airport of Girona (Catalonia, Spain) are optimised. Two aircraft types are simulated at different periods of the day obtaining different optimal trajectories.

Tot i que en les últimes dècades la reducció del soroll emès pels avions ha estat substancial, el seu impacte a la població ubicada a prop dels aeroports és un problema que encara persisteix. Contenir el soroll generat per les operacions d'aeronaus, tot assumint al mateix temps la creixent demanda de vols, és un dels principals desafiaments a que s'enfronten les autoritats aeroportuàries, els proveïdors de serveis per a la navegació aèria i els operadors de les aeronaus. A part de millorar l'aerodinàmica o les emissions sonores de les aeronaus, l'impacte acústic de les seves operacions es pot reduir també gràcies a la definició de nous procediments de vol més òptims. Aquests procediments s'anomenen generalment Procediments d'Atenuació de Soroll (PAS) i poden incloure rutes preferencials de vol (a fi d'evitar les zones poblades) i també perfils de vol verticals optimitzats. Els procediments actuals per a la reducció de soroll estan molt lluny de ser els òptims. En general, la seva optimització no és possible a causa de les limitacions d'avui en dia en els mètodes de navegació, els equips d'aviònica i la complexitat present en alguns espais aeris. D'altra banda, molts PAS s'han dissenyat de forma manual per un grup d'experts i amb l'ajuda de diverses iteracions. Tot i això, en els propers anys s'esperen nous sistemes d'aviònica i conceptes de gestió del trànsit aeri que permetin millorar el disseny d'aquests procediments, fent que siguin més flexibles. En els pocs casos on s'optimitzen PAS, se sol utilitzar una mètrica acústica en l'elaboració de les diferents funcions objectiu i per tant, no es tenen en compte les molèsties sonores reals. La molèstia és un concepte subjectiu, complexe i que depèn del context en que s'usa i la seva integració en l'optimització de trajectòries segueix essent un aspecte a estudiar.La present tesi doctoral es basa en el fet que en el futur serà possible definir trajectòries més flexibles i precises. D'aquesta manera es permetrà la definició de procediments de vol òptims des d'un punt de vista de molèsties acústiques. Així doncs, es considera una situació en que aquest tipus de procediments poden ser dissenyats de forma automàtica o semi-automàtica per un sistema expert basat en tècniques d'optimització i de raonament aproximat. Això serviria com una eina de presa de decisions per planificadors de l'espai aeri i dissenyadors de procediments. En aquest treball es desenvolupa una eina completa pel càlcul de PAS òptims. Això inclou un conjunt de models no lineals que tinguin en compte la dinàmica de les aeronaus, les limitacions de la trajectòria i les funcions objectiu. La molèstia del soroll es modela utilitzant tècniques de lògica difusa en funció del nivell màxim de so percebut, l'hora del dia i el tipus de zona a sobrevolar. Llavors, s'identifica i es formula formalment el problema com a un problema de control òptim multi-criteri. Per resoldre'l es proposa un mètode de transcripció directa per tal de transformar-lo en un problema de programació no lineal. A continuació s'avaluen una sèrie de tècniques d'optimització multi-objectiu i entre elles es destaca el mètode d'escalarització, el més utilitzat en la literatura. No obstant això, s'exploren diverses tècniques alternatives que permeten superar certs inconvenients que l'escalarització presenta. En aquest context, es presenten i proven tècniques d'optimització lexicogràfica, jeràrquica, igualitària (o min-max) i per objectius. D'aquest anàlisi es desprenen certes conclusions que permeten aprofitar les millors característiques de cada tècnica i formar finalment una tècnica composta d'optimització multi-objectiu. Aquesta última estratègia s'aplica amb èxit a un escenari real i complex, on s'optimitzen les sortides cap a l'Est de la pista 02 de l'aeroport de Girona. En aquest exemple, dos tipus diferents d'aeronaus volant a diferents períodes del dia són simulats obtenint, conseqüentment, diferents trajectòries òptimes.
Aunque en las últimas décadas la reducción del ruido emitido por los aviones ha sido sustancial, su impacto en la población ubicada cerca de los aeropuertos es un problema persistente. Contener este ruido, asumiendo al mismo tiempo la creciente demanda de vuelos, es uno de los principales desafíos a que se enfrentan las autoridades aeroportuarias, los proveedores de servicios para la navegación y los operadores. Aparte de mejorar la aerodinámica o las emisiones sonoras de las aeronaves, su impacto acústico se puede reducir también gracias a la definición de nuevos procedimientos de vuelo optimizados. Éstos, se denominan generalmente Procedimientos de Atenuación de Ruido (PAR) y pueden incluir rutas preferenciales de vuelo (a fin de evitar las zonas pobladas) y también perfiles de vuelo optimizados.Los procedimientos actuales para la reducción de ruido están muy lejos de ser los óptimos. En general, su optimización no es posible debido a las limitaciones de hoy en día en los métodos de navegación, los equipos de aviónica y la complejidad presente en algunos espacios aéreos. Por otra parte, muchos PAR se han diseñado de forma manual por un grupo de expertos y con la ayuda de varias iteraciones. Sin embargo, en los próximos años se esperan nuevos sistemas de aviónica y conceptos de gestión del tráfico aéreo que permitan mejorar el diseño de estos procedimientos, haciendo que sean más flexibles. En los pocos casos donde se optimizan PAR, se suele utilizar una métrica acústica en la elaboración de las diferentes funciones objetivo y por lo tanto, no se tienen en cuenta las molestias sonoras reales. La molestia es un concepto subjetivo, complejo y que depende del contexto en que se usa y su integración en la optimización de trayectorias sigue siendo un aspecto a estudiar. La presente tesis doctoral se basa en el hecho de que en el futuro será posible definir trayectorias más flexibles y precisas. De esta manera se permitirá la definición de procedimientos de vuelo óptimos desde un punto de vista de molestias acústicas. Se considera una situación en que este tipo de procedimientos pueden ser diseñados de forma automática o semi-automática por un sistema experto basado en técnicas de optimización y de razonamiento aproximado. Esto serviría como una herramienta de toma de decisiones para planificadores del espacio aéreo y diseñadores de procedimientos.En este trabajo se desarrolla una herramienta completa para el cálculo de PAR óptimos. Esto incluye un conjunto de modelos no lineales que tengan en cuenta la dinámica de las aeronaves, las limitaciones de la trayectoria y las funciones objetivo. La molestia del ruido se modela utilizando técnicas de lógica difusa en función del nivel máximo de sonido percibido, la hora del día y el tipo de zona a sobrevolar. Entonces, se identifica y se formula formalmente el problema como un problema de control óptimo multi-criterio. Para resolverlo se propone un método de transcripción directa para transformarlo en un problema de programación no lineal. A continuación se evalúan una serie de técnicas de optimización multi-objetivo y entre ellas se destaca el método de escalarización, el más utilizado en la literatura. Sin embargo, se exploran diversas técnicas alternativas que permiten superar ciertos inconvenientes que la escalarización presenta. En este contexto, se presentan y prueban técnicas de optimización lexicográfica, jerárquica, igualitaria (o min-max) y por objetivos. De este análisis se desprenden ciertas conclusiones que permiten aprovechar las mejores características de cada técnica y formar finalmente una técnica compuesta de optimización multi-objetivo. Esta última estrategia se aplica con éxito en un escenario real y complejo, donde se optimizan las salidas hacia el Este de la pista 02 del aeropuerto de Girona. En este ejemplo, dos tipos diferentes de aeronaves volando a diferentes periodos del día son simulados obteniendo, consecuentemente, diferentes trayectorias óptimas.
Despite the substantial reduction of the emitted aircraft noise in the last decades, the noise impact on communities located near airports is a problem that still lingers. Containing the sound generated by aircraft operations, while meeting the increasing demand for aircraft transportation, is one of the major challenges that airport authorities, air traffic service providers and aircraft operators may deal with. Aircraft noise can be reduced by improving the aerodynamics of the aircraft, the engine noise emissions but also in designing new optimised flight procedures. These procedures, are generally called Noise Abatement Procedures (NAP) and may include preferential routings (in order to avoid populated areas) and also schedule optimised vertical flight path profiles. Present noise abatement procedures are far from being optimal in regards to minimising noise nuisances. In general, their optimisation is not possible due to the limitations of navigation methods, current avionic equipments and the complexity present at some terminal airspaces. Moreover, NAP are often designed manually by a group of experts and several iterations are needed. However, in the forthcoming years, new avionic systems and new Air Traffic Management concepts are expected to significantly improve the design of flight procedures. This will make them more flexible, and therefore will allow them to be more environmental friendly. Furthermore, in the few cases where NAP are optimised, an acoustical metric is usually used when building up the different optimisation functions. Therefore, the actual noise annoyance is not taken into account in the optimisation process. The annoyance is a subjective, complex and context-dependent concept. Even if sophisticated noise annoyance models are already available today, their integration into an trajectory optimisation framework is still something to be further explored. This dissertation is mainly focused on the fact that those precise and more flexible trajectories will enable the definition of optimal flight procedures regarding the noise annoyance impact, especially in the arrival and departure phases of flights. In addition, one can conceive a situation where these kinds of procedures can be designed automatically or semi-automatically by an expert system, based on optimisation techniques and approximate reasoning. This would serve as a decision making tool for airspace planners and procedure designers.A complete framework for computing optimal NAP is developed in this work. This includes a set of nonlinear models which take into account aircraft dynamics, trajectory constraints and objective functions. The noise annoyance is modelled by using fuzzy logic techniques in function of the perceived maximum sound level, the hour of the day and the type of over-flown zone. The problem tackled, formally identified and formulated as a multi-criteria optimal control problem, uses a direct transcription method to transform it into a Non Linear Programming problem. Then, an assessment of different multi-objective optimisation techniques is presented. Among these techniques, scalarisation methods are identified as the most widely used methodologies in the present day literature. Yet, in this dissertation several alternative techniques are explored in order to overcome some known drawbacks of this technique. In this context, lexicographic, hierarchical, egalitarian (or min-max) and goal optimisation strategies are presented and tested. From this analysis some conclusions arise allowing us to take advantage of the best features of each optimisation technique aimed at building a final compound multi-objective optimisation strategy. Finally, this strategy is applied successfully to a complex and real scenario, where the East departures of runway 02 at the airport of Girona (Catalonia, Spain) are optimised. Two aircraft types are simulated at different periods of the day obtaining different optimal trajectories.

Aircraft noise has a negative environmental impact. One of the ways in which it can be mitigated is by placing acoustic liners inside the aircraft's engines. These liners can be optimised for noise reduction. A cost effective way to optimise acoustic liners is to make use of numerical modelling. However, there is room for improvement of the efficiency of current modelling methods. This thesis is concerned with the efficient numerical prediction of noise emitted from modern aircraft engines. Four high order finite element methods are used to solve the convected wave equation, and their performances are compared. The benefit of using the hierarchic Lobatto finite element method to solve this type of problem is demonstrated. A scheme which optimises the efficiency of the high order method is developed. The scheme automatically chooses the most efficient order for a given element, depending on the element size, and the problem parameters on that element. The computational cost of using the standard quadratic finite element method to solve a typical engine intake noise problem, is compared to the cost of the proposed adaptive-order method. A significant improvement in terms of efficiency is demonstrated when using the proposed method over the standard method. Furthermore, a new formulation based on potential flow theory for the solution of vortex sheet problems (typically encountered when dealing with exhaust noise problems) is presented.

This study involves the modeling and optimization of heterogeneous (HG) blankets for improved reduction of the sound transmission through double-panel systems at low frequencies. HG blankets consist of poro-elastic media with small, embedded masses, operating similar to a distributed mass-spring-damper system. Although most traditional poro-elastic materials have failed to effectively reduce low-frequency, radiated sound from structures, HG blankets show significant potential. A design tool predicting the response of a single-bay double panel system (DPS) with, acoustic cavity, HG blanket and radiated field, later a multi-bay DPS with frames, stringers, mounts, and four HG blankets, was developed and experimentally validated using impedance and mobility methods (IMM). A novel impedance matrix formulation for the HG blanket is derived and coupled to the DPS using an assembled matrix approach derived from the IMM. Genetic algorithms coupled with the previously described design tool of the DPS with the HG blanket treatment can optimize HG blanket design. This study presents a comparison of the performance obtained using the genetic algorithm optimization routine and a novel interactive optimization routine based on sequential addition of masses in the blanket. This research offers a detailed analysis of the behavior of the mass inclusions, highlighting controlled stiffness variation of the mass-spring-damper systems inside the HG blanket. A novel, empirical approach to predict the natural frequency of different mass shapes embedded in porous media was derived and experimentally verified for many different types of porous media. In addition, simplifying a model for poro-elastic materials for low frequencies that Biot and Allard originally proposed and implementing basic elastomechanical solutions produce a novel analytical approach to describe the interaction of the mass inclusions with a poro-elastic layer. A full-scale fuselage experiment performed on a Gulfstream section involves using the design tool for the positions of the mass inclusions, and the results of the previously described empirical approach facilitate tuning of the natural frequencies of the mass inclusions to the desired natural frequencies. The presented results indicate that proper tuning of the HG blankets can result in broadband noise reduction below 500Hz with less than 10% added mass.
Ph. D.

Active noise control is a key technology to enhance aircraft cabin comfort. This reflects the view of a vast amount of research aimed at reducing cabin noise levels by tackling structural vibration of the fuselage sidewalls. Aircraft interior trim panels and windows are characterized by poor sound transmission loss behaviour at low frequencies as a result of the mass-air-mass resonance phenomena. For next-generation transport aircraft, their impact on the cabin vibroacoustic environment is expected to become increasingly important with the upcoming use of larger passive windows providing a weak link in protecting aircraft interior from outside noise. This thesis presents a novel active structural acoustic control (ASAC) concept to reduce sound transmission through aircraft-type windows at low frequencies. The structural control inputs are achieved by piezoelectric actuators applied to the structure while the radiating pressure field is minimized. The control concept is developed by means of numerical and experimental investigations. A theoretical analysis of the fluid-structure interaction of vibrating structures is presented. A simulation procedure for the numerical evaluation of the sound transmission loss behaviour of plate-like multi wall structures is developed. The method is based on a hybrid FEM/Rayleigh methodology and utilises numerically calculated sound transmission loss of flat multi panel partitions and box like cavities with idealized boundary conditions. Several examples are presented to demonstrate the accuracy of the proposed technique. A suitable control algorithm based on an adaptive feed-forward Multi-Input Multi- Output control strategy is developed and implemented on a real-time Digital Signal Processing control board. The control strategy is based on the minimization of the sum of square outputs of a number of field microphones. Active noise control experiments are conducted for tonal and narrowband excitations by mounting the structure on a reference test suite. The sound power transmitted through the structure is determined by intensity measurements in anechoic chamber. Focus is finally given to the potential impact of active noise and vibration reduction on passengers from the point of view of comfort perception.

Buildings located near airports may be subjected to significant noise levels due to aircraft flyovers. Aircraft noise is particularly annoying when compared to other traffic noises due to its intermittent nature. While noise control is typically performed at the source, sound insulation programs are in place to improve the acoustic performance of a residence affected by the flyovers. Noise Level Reduction (NLR) is a common metric used in the United States to determine whether a residence qualifies for such programs. Sound insulation programs are available to houses that have an indoor Day Night Average Sound Level (DNL) greater than 45 dBA. NLR is a single-number metric used to quantify the ability for a building or building element to reduce the transmission of external sound pressure levels generated by aircraft. In addition to determining whether a residence qualifies, NLR can be used to quantify the effectiveness of the modifications performed as a result of the sound insulation program. NLR measurements with a loudspeaker offer an alternative method to those performed with aircraft flyovers, offering flexibility to the consultants that perform these measurements in the field. The purpose of this research was to better understand and improve the loudspeaker test for measuring NLR, providing a resource to the aircraft noise industry. Testing was completed on a "test house" that was constructed on campus with construction methods typical of a mixed-humid climate. The angular dependency, repeatability, and reproducibility of NLR, among other factors, were evaluated with field measurements. Significant NLR variations were observed with changes in lateral and vertical angles of incidence.

Environmental factors, such as noise and emissions have begun to play a significant role in the design of new aircraft. Although advances in propulsion technology have reduced source noise levels significantly over the past few decades, it is becoming increasingly difficult to project similar advances for the next few decades. It is likely however that some noise benefits may come from improvements in aircraft performance and from changes in operational procedures. In order for such developments to be analysed at the conceptual design stage, an integrated conceptual aircraft design and aircraft noise model is required that enables the designer to rapidly assess the effect of key design parameters on reference noise levels and noise contour area.

The focus of this thesis is to develop and evaluate a cutback noise minimization process - also known as dynamic cutback optimization - that considers engine spool down during thrust cutback and is consistent with ICAO and FAR Part 36 noise certification procedures. Simplified methods for flyover EPNL prediction used by propulsion designers assume instantaneous thrust reduction and do not take into account the spooling down of the engine during the cutback procedure. The thesis investigates if there is an additional noise benefit that can be gained by modeling the engine spool down behavior. This in turn would improve the margin between predicted EPNL and Stage 4 noise regulations. Modeling dynamic cutback also impacts engine design during the preliminary and detailed design stages. Reduced noise levels due to cutback may be traded for lower engine fan diameter, which in turn reduces weight, fuel burn, and cost.

With increased exposure to transportation noise, there have been continued efforts to help insulate homes from aircraft noise. Current aircraft noise guidelines are based primarily on outdoor sound levels. As people spend the majority of their time indoors, however, human perception is evidently more related to indoor sound levels. Investigations are being made to provide further insight into how typical residential constructions affect indoor response. A pilot study has built a single-room "test house", according to typical construction for mixed-humid climate regions, and has directly measured outdoor-to-indoor transmission of sound - with specific focus on continuous commercial aircraft signatures. The results of this study are being used to validate and improve modelling software that simulates a wide range of construction types and configurations for other US climate regions. The improved models will allow for increased flexibility in simulating the impacts of acoustic and energy retrofits. Overall, the project intends to improve the ability to predict acoustic performance for typical US construction types as well as for any possible design alterations for sound insulation.

Air transportation, while having many benefits, has raised numerous environmental concerns, one of the most contentious being aircraft noise. Thus, the national and international communities have been forced to take measures to cope with this problem, seeking to balance the needs of all interested parties.
The purpose of this thesis is to analyze the aircraft noise problem on the national and international levels. Each chapter highlights a distinct area of the problem. Chapter 1 covers the technical aspects of aircraft noise measurement, as well as recounts the general history, sources and effects of aircraft noise. Chapter 2 focuses specifically on the noise certification standards developed by the United States and the International Civil Aviation Organization. Chapter 3 discusses the liability issues of aircraft noise on the international level, concentrating primarily on the 1952 Rome Convention and on attempts to formulate an international instrument dealing with Liability for Damage Caused by Noise and Sonic Boom. Chapter 4 examines liability issues in the United States, defining various legal theories available. Finally, Chapter 5 articulates some methods that have helped to reduce or to mitigate the effects of aircraft noise in noise-sensitive areas.

Noise generated by low-altitude aircraft movements reaches levels higher than many other anthropogenic noise sources. How birds respond to these acute noise levels is, to date, poorly understood. This thesis provides some of the first data on how noise generated by aircraft affects avian communities and communication. Firstly, point counts conducted around Manchester airport show there is no effect of increasing noise levels on beta diversity. In addition, results show the density and abundance of the two most abundant species and the number of detections for the five most common species was also unaffected. Secondly, comparisons of the songs of the abundant chiffchaff reveal that airport birds use lower frequency songs than control birds. This finding was replicated in two countries. Additionally, the songs of airport birds in the UK are longer and slower than control birds. These findings may be explained by birds that are found close to airports are suffering from Noise Induced Hearing Loss (NIHL). This was supported when comparing the responses of airport and control chiffchaffs to territorial songs; airport chiffchaffs were more aggressive, attacking the speaker 5 times more than control birds. An explanation for this is that as an artefact of NIHL, airport birds perceive songs differently to those in the control site. Finally, physiological stress induced by aircraft noise was investigated. There were no differences in corticosterone levels, a proxy for measuring stress levels, between 11-day old blue tit chicks exposed to noise treatments and control chicks. These findings suggest that pre-fledging blue tit chicks do not perceive anthropogenic noise as an environmental stressor. Whilst the work in this thesis does not detect an effect of aircraft noise on the species community or corticosterone levels, it does provide evidence consistent with the loss of hearing in birds as a consequence of anthropogenic noise exposure.

Air traffic demand is forecast to significantly grow during the next few years. To compensate for the associated potential increase of aviation environmental impact, ambitious aircraft noise and emissions reduction goals have been set by several organisations worldwide. Accommodating these goals requires planning new mitigation strategies involving technological advances, optimised flight operations, and novel aircraft concepts. Methods for predicting the impact of potential mitigation strategies is vital to support effective planning. This thesis presents a new framework for estimating the noise impact of mitigation strategies (i.e. involving each or both of technological and operational changes) aspiring to: a) bypass the dependance on empirical flyover data and hence enable impact assessment of novel aircraft and operations, b) be independent of specific noise prediction methods and confidential inputs that are normally required by many noise prediction tools, c) have low computational requirements and thus be efficient in parametric studies, and d) provide inputs to emissions prediction tools, facilitating a more holistic strategic mitigation that considers various environmental concerns. The crux of the framework developed is that rather than seeking absolute noise values, it computationally estimates the noise impact of mitigation strategies, starting from a baseline scenario for which noise levels are known. This eliminates the need for measurements whilst minimising complexity and dependance on confidential inputs. Noise and emissions interdependencies are incorporated by expressing noise changes as a function of thrust, which is a common influencing parameter. In addition, the framework provides means for deriving purely computational NPD curves, enabling the construction of noise exposure contour maps for future aircraft and contemporary operations. The framework’s applicability on innovative flight operations and its capability of including the interdependencies between noise and emissions is demonstrated by estimating the environmentally-optimum approach and takeoff angles for civil aircraft of different sizes. The applicability to novel aircraft is displayed through noise estimations (including noise exposure contours) for various electric aircraft featuring Distributed Electric Propulsion (DEP), as well as for a Blended-Wing-Body (BWB) aircraft. The results obtained for future scenarios generally conform with the expected trends (deriving from e.g. higher-fidelity tools or historical trends) highlighting the framework’s great potential and usefulness in contributing in effective planning and decision-making.

Prediction of Supersonic Fan Noise Generated by Turbofan Aircraft Engines was focussed on improving the capability of predicting supersonic fan noise from modern high-bypass-ratio turbofan aero-engines. The shift from single core jet engines to highbypass-ratio turbofan engines brought about a reduction in the overall aircraft engine noise principally by reducing the jet-broadband noise. However, this new design meant the size of the fan of a high-bypass-ratio turbofan engine, over subsequent years, has increased in diameter. This increase allowed for the speed of the tips of the fan blades to reach and exceed the speed of sound. At high power engine operation conditions, especially at take-off conditions, the noise levels observed from such engines is very high. A major component of this noise is the supersonic fan noise which is also referred to as buzz-saw noise. Shocks are produced at the fan blade tips at this high power engine operation condition. These shocks propagate upstream, against the inflow, following a helical path dictated by the rotation of the fan. The pressure field produced at the tip of the fan is represented as a series of shock waves and expansion waves. As this pressure field advances, it interacts with the incoming flow and acoustic treatment in the intake duct. The shocks in the pressure field are all unique and are of different amplitudes. This is because the fan blades, although manufactured to tight tolerances, are not perfectly alike. Also, the arrangement of these fan blades on the fan hub will also lead to unavoidable differences among the fan blades. These minute differences are reflected in the amplitudes of the shocks, making each shock slightly different from the others. Shocks in the pressure field propagate with respect to the magnitude of their pressure amplitude. Therefore, the shocks travel at different speeds. In the course of propagation, faster shocks catch up with slower ones, and they merge into a single shock, even as the shocks’ amplitudes are attenuated. The difference in speeds and the interactions among the shocks ensure a transfer of energy among the harmonics of the pressure field. This process is nonlinear; the work in this thesis is focussed on modelling the nonlinear propagation of the shocks pressure pattern. These interactions greatly enhance the lower frequency harmonics of the pressure field shifting the dominance from the blade passage frequency and its harmonics. Further upstream, the dominance of the low frequency harmonics is unmistakable. Subsequently the pressure field is radiated from the aircraft intake duct. The resultant radiated pressure field is that which is perceived by an observer in the far-field. The models presented in this thesis capture the main features of this nonlinear propagation and radiation of the pressure field generated at the fan blade tips, and generates predictions for supersonic fan noise levels in the intake duct and in the far-field. A time domain model named SPRID (Sawtooth Propagation in Rigid Intake Ducts) developed is presented. This model predicts the supersonic fan noise levels in ducts without any acoustic treatment, and has been validated against a benchmark frequency domain nonlinear propagation model (FDNS), and also measured data from a modelscale fan rig test provided by Rolls-Royce PLC. The need to incorporate the effect of acoustic liners in the modelling led to the development of a new model which employs the combined time-frequency domain approach. In this model, the nonlinear propagation of the pressure field is simulated in the time domain, while the acoustic liner effects are implemented in the frequency domain. This model also has been validated with measured data. The combined time-frequency domain prediction method was improved to incorporate more complex features of supersonic fan noise propagation. Features such as the change in duct radius along the duct axis and the consequent change in mean flow speeds, and boundary layer effects on the liner absorption have been included in a more advanced model. The advanced nonlinear model is a more representative model of real aircraft intake duct. Also, a theoretical radiation model (GX-Munt) was utilized to predict supersonic fan noise in the far-field. In this thesis, a whole study of supersonic fan noise, starting from source generation at the fan plane up to the radiation to the farfield is presented. The thesis includes an extensive literature review, research on the generation of a source sawtooth for propagation utilizing measured data, and development of equations for nonlinear propagation in axisymmetric intake ducts. Results of the parametric studies using the advanced nonlinear propagation model reliably show all the effects of nonlinear distortion of the shock waves, variation in intake geometry, flow speeds, and variations in the acoustic liner absorption as a consequence of changes in boundary-layer thickness. Comparisons made against measured data, from modelscale fan rig tests conducted by Rolls-Royce PLC, show good and reasonable agreement. The advanced nonlinear propagation model achieves improved prediction capability for supersonic fan noise.

Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The main purpose of this dissertation is to develop a process to improve actual policy-making procedures in terms of aviation environmental effects. This research work expands current practices with physics based publicly available models. The process herein proposed provides information regarding the interdependencies between the environmental effects of aircraft. These interdependencies are also tied to the actual physical parameters of the aircraft and the engine, making it more intuitive for decision-makers to understand the impacts to the vehicle due to different policy scenarios. These scenarios involve the use of fleet analysis tools in which the existing aircraft are used to predict the environmental effects of imposing new stringency levels. The aircraft used are reduced to a series of coefficients that represent their performance, in terms of flight characteristics, fuel burn, noise, and emissions. These coefficients are then utilized to model flight operations and calculate what the environmental impacts of those aircraft are. If a particular aircraft does not meet the stringency to be analyzed, a technology response is applied to it, in order to meet that stringency. Depending on the level of reduction needed, this technology response can have an effect on the fuel burn characteristic of the aircraft. The proposed alternative is to create a fleet of replacement aircraft to the current fleet that does not meet stringency. These replacement aircraft represent the achievable physical limits for state of the art systems. In addition, the replacement aircraft show the linkage between environmental effects and fundamental aircraft and engine characteristics, something that has been neglected in previous policy making procedures. Another aspect that has been ignored is the creation of the coefficients used for the fleet analyses. In current literature, a defined process for the creation of those coefficients does not exist, but this research work develops a process to do so and demonstrates that the characteristics of the aircraft can be propagated to the coefficients and to the fleet analysis tools.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 133-137).
Aircraft planform design, takeoff operations, and airfoil design are examined as a complete system in order to quantify tradeoffs that can result in a quiet aircraft. An aircraft design model was developed to generate blended-wing-body-type designs using simple-physics models and empirical scaling from a reference design. This model generates a scaled airframe and engine, an estimate of aircraft weights and center of gravity, a takeoff trajectory, outer wing airfoil profiles, and takeoff noise predictions. Integrating the model with a single-level optimization framework, it was found that optimization for minimum noise can result in a significant noise reduction on takeoff, primarily due to changes in aircraft design and operations. There exists a design-operations coupling between the departure flight path angle and the engine size which must be exploited. Low-noise designs resulting from the single-level optimization require more fuel to complete the design mission. Modifications to the airfoil profiles do not significantly contribute to further reductions in takeoff noise, but do mitigate the fuel burn increase without adversely affecting noise levels.
(cont.) A distributed optimization framework was constructed from a problem decomposition into three subspaces: aircraft planform and engine design, aircraft operations, and wing design. In this framework, a system level optimizer is responsible for minimizing the system noise while subspace optimizers control the disciplinary models individually. This setup allowed for the exploration of different areas of the design space. As a result, the distributed optimization converged to a fundamentally different design solution with the same minimum noise value as in the single-level optimization, but with a much lower fuel burn. The key contributions of this thesis are the development and quantitative analysis of a weight and center of gravity model for an unconventional aircraft configuration, a distributed optimization framework, and a low noise aircraft design with competitive fuel burn.
by Anya Rachel Jones.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2005.
Includes bibliographical references (p. 116-119).
Advanced aircraft noise abatement approach procedures -- characterized by decelerating, continuous descent approaches using idle thrust, and enabled by flight guidance technologies such as GPS and FMS -- have been shown to reduce operational aircraft noise on communities surrounding airports. However, implementation in the near future presents two challenges. The first is to mitigate the adverse effects on aircraft performance of uncertainties in pilot response, weather, and other system components. The second is to enhance the ability of air traffic controllers to separate aircraft that are decelerating at different rates. The work in this thesis primarily addresses the first challenge by developing, first, a methodology to determine the optimum design parameters for a continuous descent approach, and, second, a new pilot cueing system. The methodology involved: 1) conducting a simulator-based, human factors experiment to obtain models of pilot delay in extending flaps/gear in conditions with and without turbulence; 2) formulating the procedure's parameters as strategic and tactical control variables; 3) using the pilot delay models and the parameter formulation to perform a Monte Carlo Simulation to resolve the conflicting objectives of reducing noise and increasing probability of target achievement. Simulation results showed that the flap schedule has to be designed for a 50-ft- higher-than the target altitude without turbulence, and a 200-ft for turbulence; 4) determining the feasibility space of the parameters in different wind conditions. Results showed that when the wind uncertainty is large, accounting for the uncertainty in the procedure design significantly reduces the effectiveness of the procedure.
(cont.) A new pilot cueing system that does not require additional aircraft automation was developed to help pilots manage the deceleration of aircraft and achieve target conditions in a changing environment. The cueing system, consisting of gates (i.e., altitude/speed checkpoints) and a recommended flap schedule, was designed and evaluated in a second experiment using a desktop simulator which showed that gates reduce target error to within five knots and provide comparable performance to that of more automated systems without increasing pilot workload. Because the gates have the potential of enabling aircraft to fly consistent speed profiles, it is hypothesized that their implementation would address the second challenge by enhancing the controller's ability to predict aircraft trajectories and their future separation.
by Nhut Tan Ho.
Ph.D.

In the last decade acoustic noise has become more and more regarded as a problem. In cars, boats, trains and aircraft, low-frequency noise reduces comfort. Lightweight materials and more powerful engines are used in high-speed vehicles, resulting in a general increase in interior noise levels. Low-frequency noise is annoying and during periods of long exposure it causes fatigue and discomfort. The masking effect which low-frequency noise has on speech reduces speech intelligibility. Low-frequency noise is sought to be attenuated in a wide range of applications in order to improve comfort and speech intelligibility. The use of conventional passive methods to attenuate low-frequency noise is often impractical since considerable bulk and weight are required; in transportation large weight is associated with high fuel consumption. In order to overcome the problems of ineffective passive suppression of low-frequency noise, the technique of active noise control has become of considerable interest. The fundamental principle of active noise control is based on secondary sources producing ``anti-noise.'' Destructive interference between the generated and the primary sound fields results in noise attenuation. Active noise control systems significantly increase the capacity for attenuating low-frequency noise without major increase in volume and weight. This doctoral dissertation deals with the topic of active noise control within the passenger cabin in aircraft, and within headsets. The work focuses on methods, controller structures and adaptive algorithms for attenuating tonal low-frequency noise produced by synchronized or moderately synchronized propellers generating beating sound fields. The control algorithm is a central part of an active noise control system. A multiple-reference feedforward controller based on the novel actuator-individual normalized Filtered-X Least-Mean-Squares algorithm is introduced, yielding significant attenuation of such period noise. This algorithm is of the LMS-type, and owing to the novel normalization it can also be regarded as a Newton-type algorithm. The new algorithm combines low computational complexity with high performance. For that reason the algorithm is suitable for use in systems with a large number of control sources and control sensors in order to reduce the computional power required by the control system. The computational power of the DSP hardware is limited, and therefore algorithms with high computational complexity allow fewer control sources and sensors to be used, often with reduced noise attenuation as a result. In applications, such as controlling aircraft cabin noise, where a large multiple-channel system is needed to control the relative complex interior sound field, it is of great importance to keep down the computational complexity of the algorithm so that a large number of loudspeakers and microphones can be used. The dissertation presents theoretical work, off-line computer experiments and practical real-time experiments using the actuator-individual normalized algorithm. The computer experiments are principally based on real-life cabin noise data recorded during flight in a twin-engine propeller aircraft and in a helicopter. The practical experiments were carried out in a full-scale fuselage section from a propeller aircraft.
Buller i vår dagliga miljö kan ha en negativ inverkan på vår hälsa. I många sammanhang, i tex bilar, båtar och flygplan, förekommer lågfrekvent buller. Lågfrekvent buller är oftast inte skadligt för hörseln, men kan vara tröttande och försvåra konversationen mellan personer som vistas i en utsatt miljö. En dämpning av bullernivån medför en förbättrad taluppfattbarhet samt en komfortökning. Att dämpa lågfrekvent buller med traditionella passiva metoder, tex absorbenter och reflektorer, är oftast ineffektivt. Det krävs stora, skrymmande absorbenter för att dämpa denna typ av buller samt tunga skiljeväggar för att förhindra att bullret transmitteras vidare från ett utrymme till ett annat. Metoder som är mera lämpade vid dämpning av lågfrekvent buller är de aktiva. De aktiva metoderna baseras på att en vågrörelse som ligger i motfas med en annan överlagras och de släcker ut varandra. Bullerdämpningen erhålls genom att ett ljudfält genereras som är lika starkt som bullret men i motfas med detta. De aktiva bullerdämpningsmetoderna medför en effektiv dämpning av lågfrekvent buller samtidigt som volymen, tex hos bilkupen eller båt/flygplanskabinen ej påverkas nämnvärt. Dessutom kan fordonets/farkostens vikt reduceras vilket är tacksamt för bränsleförbrukningen. I de flesta tillämpningar varierar bullrets karaktär, dvs styrka och frekvensinnehåll. För att följa dessa variationer krävs ett adaptivt (självinställande) reglersystem som styr genereringen av motljudet. I propellerflygplan är de dominerande frekvenserna i kabinbullret relaterat till propellrarnas varvtal, man känner alltså till frekvenserna som skall dämpas. Man utnyttjar en varvtalssignal för att generera signaler, så kallade referenssignaler, med de frekvenser som skall dämpas. Dessa bearbetas av ett reglersystem som generar signaler till högtalarna som i sin tur generar motljudet. För att ställa in högtalarsignalerna så att en effektiv dämpning erhålls, används mikrofoner utplacerade i kabinen som mäter bullret. För att åstadkomma en effektiv bullerdämpning i ett rum, tex i en flygplanskabin, behövs flera högtalare och mikrofoner, vilket kräver ett avancerat reglersystem. I doktorsavhandlingen ''Active Control of Propeller-Induced Noise in Aircraft'' behandlas olika metoder för att reducera kabinbuller härrörande från propellrarna. Här presenteras olika strukturer på reglersystem samt beräkningsalgoritmer för att ställa in systemet. För stora system där många högtalare och mikrofoner används, samt flera frekvenser skall dämpas, är det viktigt att systemet inte behöver för stor beräkningskapacitet för att generera motljudet. Metoderna som behandlas ger en effektiv dämpning till låg beräkningskostnad. Delar av materialet som presenteras i avhandlingen har ingått i ett EU-projekt med inriktning mot bullerundertryckning i propellerflygplan. I projektet har flera europeiska flygplanstillverkare deltagit. Avhandlingen behandlar även aktiv bullerdämpning i headset, som används av helikopterpiloter. I denna tillämpning har aktiv bullerdämpning används för att öka taluppfattbarheten.

Nonlinear propagation and shock formation are shown in noise radiated from full-scale military jet aircraft. Perception of sound is not only affected by the overall sound pressure level of the noise, but also characteristics of the sound itself. In the case of jet noise, acoustic shocks within the waveforms result in a characteristic commonly referred to as"crackle." The origin of shocks in the far-field of jet noise is shown to be through nonlinear propagation. Metrics characterizing the shock content of a waveform are explained and given physical significance, then applied to jet noise at various distances and engine conditions to show areas where shock formation is significant. Shocks are shown to develop at different distances from the aircraft, dependent on the amplitude and frequency, and nonlinear propagation is shown to be important in determining time and frequency characteristics of jet noise at distances of up to 1220 m from the aircraft. The shock content is also characterized during flyover experiments, and the shock content between the two scenarios is compared. While some reduction in overall level and shock content is seen in the maximum radiation region, level increases in the forward direction during flight result in increased shock content. Variation at distances of 305 m and beyond is considered and shown as a result of small atmospheric changes. Finally, a nonlinear numerical propagation scheme is used to model the propagation, showing accuracy in predicting frequency-domain and time-domain features that are evidence of nonlinear propagation.

Crackle is a perceptual feature of supersonic jet noise that is related to the presence of acoustic shocks. The skewness of the time-derivative of the pressure waveform, or derivative skewness, is used as a metric indicative of crackle perception. The three main objectives of this work are: 1) Determine the potential spatial origin of crackle-related events in the near field of a high-performance military aircraft via an event-based beamforming method. 2) Investigate the potential for nonlinear, irregular shock reflections occurring along the near-field ground array and their implications on derivative skewness. 3) Relate the near-field, crackle-related events to far-field crackle perception by comparing nonlinearly propagated waveforms with measured far-field data. The event-based beamforming method used to determine source and far-field relationship of shock-like events utilizes the cross correlation between adjacent microphone waveform segments to determine the angle of propagation for an ensemble of crackle-related events within the waveform. The angle of propagation is traced towards the source for each event to find its apparent origin along the jet lipline. Beamforming results indicate that crackle-related events appear to originate anywhere from 2 to 14.5 m downstream along the jet lipline, with distributions that shift downstream and broaden with increasing engine power. The shock reflection classification method builds on the event-based beamforming method to calculate angle of incidence relative to the ground for an ensemble of shock events. The combination of angles of incidence and the measured shock strengths of the events reveal that irregular reflections are likely to occur over the majority of the array, which likely elevates the derivative skewness values due to steeper shocks with greater peak-to-peak pressures relative to off-ground measurements. Near-field, crackle-related events are extrapolated to the far field using a nonlinear propagation model to determine their prevalence in the far field. Cross-correlation coefficients of waveform segments centered about the propagated events indicates that for farther aft angles, near-field events are more related to far-field measurements. Waveform observations show that shock-like events in the near field that are more spiked in nature tend not propagate into the far field. However, near-field, large-derivative events with broader, high-pressure peaks nonlinearly steepen and form shocks in the far field that are likely contribute to crackle perception.

Current aircraft noise guidelines are based primarily on outdoor sound levels. However, human perception is highly related to indoor response, particularly for residences. A research project has been conducted that provides insight into how typical residential dwelling envelopes affect sound transmitted indoors. A focus has been placed on the effect of residential dwelling envelopes on subsonic civil aircraft noise. Typical construction types across the United States have been identified and used to develop model predictions of outdoor-to-indoor transmission loss. While it was initially hypothesized that these construction types could be grouped by climate region, it was found that these constructions are better grouped according to their outermost construction layer. Further, the impact of systematically altering construction variables (such as the construction materials used and the ratio of window area to wall area) has been investigated. Results will be used to better understand trends for expected noise reduction for typical construction types around the United States. Additionally, comparisons have been made between the effect of older and more modern wall construction techniques on whole-house performance.

Este trabalho expõe e analisa resultados de medições acústicas de aeronaves; realizadas dentro da Área II do Plano Específico de Zoneamento de Ruído- PEZR. O plano restringe o uso do solo em decorrência das emissões sonoras, oriundas da movimentação das aeronaves para cada um dos 66 aeroportos brasileiros administrados pela INFRAERO. As medições acústicas foram realizadas entre segunda e sexta feira, no período diurno (entre 7 e 22 horas) registrando um total de 697 eventos sonoros aeronáuticos, gerados por 62 modelos diferentes de aeronaves. Os procedimentos de aquisição de dados atendem a ISO 3891 (Procedimentos para descrever o ruído aeronáutico percebido no solo), e o Guia de Monitoramento de Ruído Aeronáutico, Francês, elaborado pelo Serviço Técnico da Navegação Aérea- STNA. Com o uso de softwares, discriminaram-se os Eventos Aeronáuticos (passagem de aviões) do Ruído de Fundo. Assim, quantificou-se, com razoável precisão, o impacto sonoro causado por ruído aeronáutico e definiram-se os índices: L50 (Ruído de Fundo) e o índice L1 (Eventos Aeronáuticos). São apresentados os níveis de ruído (SEL, LMáx, LMín e Leq em dB (A)) e as análises espectrais (de 10 a 20.000 Hz, relacionados às curvas NCB, presentes na NBR 12314(ABNT, 1997)), para cada tipo de aeronave registrada. Verificou-se que o Fluxo Geral tem significativa influência nos níveis de ruído emitidos e deve ser levado em consideração nas abordagens de cunho acústico, para este aeródromo. Os níveis diários de exposição ao ruído aeronáutico não atendem aos níveis recomendados pela NBR 10151 (ABNT, 2000). Também foi verificado que, no caso de se utilizar o descritor LMáx (recomendado pelas instituições internacionais, consagradas, de aviação), os índices de isolamento acústico requeridos na NBR 8572 (ABNT, 1984), não atendem aos níveis de conforto acústico, dentro de edificações, estabelecidos pela NBR 10152 (ABNT, 1987), dependendo do tipo de procedimento (pouso ou decolagem) e aeronave analisada.
The present work presents and analyzes results of acoustic measurements of aircraft, carried out within Area II of the Specific Noise Zoning Plan (PEZR). This plan restricts the use of land as a result of sound emissions originated from aircraft movement for each one of the 66 Brazilian airports administered by INFRAERO. The acoustic measurements have been taken between Monday and Friday, in the day period (between 07:00 AM and 10:00 PM), registering a total of 697 aircraft sound events, caused by 62 different aircraft models. The data acquisition procedures meet ISO 3891 (Procedures for describing the aircraft noise perceived on land), and the French Aeronautic Noise Monitoring guidebook, elaborated by STNA – Air Navigation Technical Service. By using software, the “aircraft events” (flying by aircraft) were discriminated from the background noise. Thus, with a reasonable degree of precision, the sound impact caused by aircraft noise has been quantified, and the rates have been defined: L50 (background noise) and rate L1 (aircraft events). Noise levels are presented (SEL, Lmax, Lmin and Leq in dB(A)), and the spectral analyses (from 10 to 20,000 Hz), related to NCB curves present in NBR 12314 (ABNT, 1997) for each type of registered aircraft. It has been verified that the general flow has a significant influence on the levels of issued noise, and it must be taken into consideration in the acoustic area approaches, for this airport. The daily levels of exposure to aircraft noise do not meet the levels recommended by NBR 10151 (ABNT 2000a). It was also verified that if the Lmax describer is utilized (recommended by the international aviation institutions), the acoustic insulation levels required by NBR 8572 (ABNT, 1984), do not fully meet the levels of acoustic comfort inside buildings, as set by NBR 10152 (ABNT, 1987), according to the type of analyzed aircraft.

Acoustic experiments were conducted in an anechoic chamber with a 1/14th scale model of a supersonic aircraft engine inlet using Trailing Edge Blowing (TEB) to reduce the engine fan noise from a turbofan propulsion simulator (TPS). The TPS is 4.1 in. (10.4 cm) in diameter and is powered by compressed air. The supersonic inlet is connected to the TPS and is geometrically and acoustically scaled from a working design. The supersonic inlet is operated in a takeoff or landing operating condition where the inlet core flow is subsonic. TEB is the process of ejecting high pressure air to re-energize the wakes of upstream fan disturbances such as struts or inlet guide vanes (IGV). The elimination of the wakes will provide a uniform flow field at the engine fan face and reduce noise at the blade passing frequency. The TEB was implemented on six non-uniformly spaced support struts in the inlet. Acoustic tests were then performed at 40%, 60% and 88% of the fan design speed (PNC) to measure the reduction in the blade passing tone (BPT) due to TEB from the struts with and without the presence of IGV. The noise reductions without IGV at 40 PNC show the best results with the blade passing tone (BPT) being reduced by an average of 3.1 dB. The first harmonic of the BPT and the overall Sound Pressure Level (SPL) were also reduced by 1 dB. The addition of the IGV in the inlet reduced the effectiveness of the TEB. The addition of IGV changed the reduction in BPT at 40 PNC by 0.5 dB and the overall SPL was unchanged. At 60 PNC the addition of IGV reduced the reduction due to TEB in the BPT from an average of 2 dB to an average of 1 dB. The tests performed at 88 PNC showed negligible effects due to TEB. Aerodynamic experiments performed on the inlet that showed that the wakes of the IGV have a larger velocity defect than the struts, thus making the IGV a greater noise source.
Master of Science

The aim of this research work was to develop an Acoustic Emission (AE) source location method suitable for Structural Health Monitoring (SHM) of composite aircraft structures. Therefore useful key signal features and sensor configurations were identified and the proposed method was validated using both artificially generated AE as well as actual AE resulting from damage. Acoustic Emission is a phenomenon where waves are generated in stressed materials. These waves travel through the material and can be detected with suitable sensors on the surface of the structure. These stress waves are attributed to propagating damage inside the material and can be monitored while the structure is in service. This makes AE very suitable for SHM, in particular for aircraft structures. In recent years composite materials such as carbon fibre reinforced epoxy (CFRP) are increasingly being used for primary and secondary structures in aircraft. The anisotropic layup of CFRP can lead to different failure mechanisms such as delamination, matrix cracking or fibre breakage which affects the remaining life time of the structure to different extents. Accurate damage location is important for SHM systems to avoid further inspections and allows for a maintenance scheme which considers the severity of the damage, due to damage type, extent and location. This thesis presents a novel source location method which uses a small triangular AE sensor array. The method determines the origin of an AE wave by a combination of time of arrival and modal analysis. The small footprint of the array allows for a fast and easy installation in hard-to-reach areas. The possibility to locate damage outside and at a relatively far distance from the array could potentially reduce the overall number of sensors needed to monitor a structure. Important wave characteristics and wave propagation in particular in CFRP were investigated using AE simulated by an artificial source and actual damage in composite specimens.

This diploma thesis captures the three-dimensional implementation of noise-reducing high-liftsystems. A parametric CAD model is developed for the FNG aircraft and different high-lift configurationsare built up. In the course of research, these configurations are designed based onformerly obtained two-dimensional results of DLR’s LEISA project featuring the design of a verylong chord slat (VLCS), whose slat shape resulted in a favourable aeroacoustic behaviour at noiserelevantapproach conditions. The high-lift systems derived in this thesis differ in the spanwisevariation of the slat geometry planform as well as in the applied high-lift settings described bygap, overlap and deflection angle.The aerodynamic performance is computed via CFD RANS simulations and the results arecompared to a reference high-lift system of the FNG aircraft, which has been designed in previousstudies. The observed CFD results are further evaluated in the reference wing section of the FNGaircraft in order to display the agreement between the implemented 3D high-lift configurationsand the 2D LEISA reference data. Besides the aerodynamic performance, aeroacoustic aspects arealso considered in this diploma thesis. By means of the obtained CFD results, indirect statementsabout the success of the 3D low-noise implementation approach are made.The geometrical concordance of the derived reference wing section of the 3D CAD model isfound in general to be very high in comparison to the 2D-optimized LEISA design wing section.With regard to the observed pressure distributions of the initial four designed high-lift systemshowever, small geometry deviations are noticed to affect the obtained pressure distributions in asignificantly unintended way. The requirements of a low-noise high-lift system are thus not metfor these high-lift configurations. In the 3D implementation, the 2D-optimized slat settings haveto be modified in order to maintain the favourable aeroacoustic behaviour of the 2D considerations.Based on a reduced slat deflection angle, a further derived 3D VLCS high-lift system isobtained to match the 2D-optimized pressure distributions in the reference wing section more accurately.A significant pressure increase at the VLCS trailing edge is noticed for this configuration,which shows the noise-reducing potential of the derived VLCS device. However, the aerodynamicdegradations obtained for the designed low-noise high-lift system are found to be too high in orderto still provide improved aeroacoustic behaviour during conditions of increased approachspeed. A 3D noise-reducing high-lift system is therefore not achieved, although the 2D-optimizedLEISA pressure distributions are well captured in the reference wing section of the implemented3D high-lift system featuring modified high-lift setting parameters.

Providing a comfortable environment is the fundamental aim in Architecture. Comfortable environment mainly refers to a surrounding atmosphere which is thermally, acoustically, visually, aesthetically, etc. comfortable. Generally, environmental comfort is assessed by environmental factors such as thermal, acoustic and lighting comfort as well as air quality. There is a significant relationship between various environmental factors and students' academic achievements as well as health. Providing all of the environmental factors together is critical as they are interrelated and could conflict if they are considered separately, if the conditions over the life of the building change or relaxed benchmarks are used for design at the first stage. One of the conflicts reviewed in this study, is the conflict between acoustic comfort with thermal comfort and air quality. The hypothesis of this research is that the naturally ventilated schools located in noisy areas (e.g. Heathrow airport) suffer from overheating and poor air quality as well as a high level of background noise during summer periods, due to the lack of ventilation. The main means of ventilation in majority of the UK schools is window. In noisy areas, the classrooms' occupants (i.e. pupils, teachers) often tend to shut windows especially during silent (such as exams and readings) and lecturing activities to reduce the aircraft noise, which varies from 57dB-75dB according to their distances to Heathrow airport. On an average, as a result of closing windows, the aircraft noise drops by 15dB (depending on the type of windows) which makes the inside noise to be around 42dB-60dB. This is still higher than the 35dB which is the acceptable limit for background noise for primary school classrooms as recommended by Building Bulletin 93. The results of the study show that closing of windows does not reduce the high level of background noise to the recommended level, but it also has two negative impacts on classrooms' environments. Firstly it increases the potential for classrooms to experience overheating and secondly it causes poor air quality due to the lack of sufficient ventilation in the building. Through objective and subjective surveys, classrooms' indoor temperatures, air quality and background noise levels were evaluated and it was learnt that those schools located in the vicinity of Heathrow Airport are more likely to experience overheating and poor air quality. This has a negative impact on students' achievements. In addition, one of the reasons for the lack of environmental comfort is the use of relaxed benchmarks. It is shown in this study that overheating and air quality benchmarks which are proposed by 'Department for Education and Skills' in Building Bulletin 101 and used to design and refurbish the UK schools, are relaxed benchmarks in comparison with the others which are proposed by different organisations and researchers. The overall findings of this thesis have been developed to draw the attention of school designers' to the current and future potential conflicts between the comfort factors in schools' classrooms. To prevent failure, extra care should be taken to select a suitable ventilation strategy for providing both air quality and thermal comfort during summer for the schools located under the flights paths. For such schools, it would be beneficial that the solar gain and internal gain are controlled and heavy thermal mass materials are used for their construction. Such strategies would counterweigh the lack of ventilation in protecting the classrooms from overheating. It is also suggested that a further section is incorporated to the comfort section of the school design assessment tools to evaluate the current and future potential conflict between comfort issues in the schools' buildings. In addition, air quality and summer thermal comfort guidelines incorporated to BB 101 are recommended to be revised (similar to the acoustic section of this guideline which was revised to stringent benchmarks for background noise level and reverberation time and included in BB93).