1,720,970 research outputs found
An integrated approach to the direct simulation of brasses in the performance environment
No full textThe present work deals with the synthesis of sounds produced by brass instruments through the direct physical modelling. The purpose is the development of an integrated methodology for the evaluation of the response of a wind instrument taking into account the properties of the surrounding environment. The identification of the frequency response of the resonator and the performing environment is obtained by means of a Boundary Integral Equation approach. The formulation produces the matrix transfer function between the inflow at the input section of the instrument bore and the signal evaluated at an arbitrary location, and can account for the response of any boundary and object present in the surroundings. The reflection function obtained from the above model is coupled to a simplified model of valve, used to represent the excitation mechanism behaviour. The exploited algorithm has demonstrated to be accurate and efficient in offline calculation, and the observed performance discloses the possibility to implement real–time applications
DECISION MAKING BASED ON COMMUNITY NOISE ANNOYANCE IN THE MULTI-OBJECTIVE OPTIMIZA- TION OF A COMMERCIAL AIRCRAFT
No full textThe present paper deals with an innovative decision making approach for the selection of air- craft design concepts and operational procedures aimed at the reduction of the community noise annoyance. Specifically, the least annoying solutions pertaining to the Pareto front re- sulting from a multidisciplinary, multi-objective design and procedure optimization process, are selected on the basis of psychoacoustic requirements. The need of such an approach stems from the fact that the environmental requirements imposed to the commercial aviation are be- coming stricter and stricter, as the trend of the traffic increase is rapidly growing following the market demand. The fulfillment of these requirements often leads to design decisions that can be conflicting, thus forcing the designer to look for trade-off solutions since the early con- ceptual phase of the design process. The multi-objective optimization is the methodological approach most suited to cope with this kind of problems. Using this approach, the Pareto optimality is achieved as the set of non-dominated solutions (the Pareto front), i.e., the solu- tions such that none of the objectives can be improved without deteriorate at least one of the others. The criterion used to select one of the non-dominated solutions along the Pareto front represents a key point. Within the EC-funded project COSMA, the outcomes of an extensive campaign of psychometric tests aimed at the identification of the most annoying characteristics of the aircraft noise are used to rank the points on the Pareto fronts with respect to the level of annoyance produced on the residential community. The approach is highly innovative, being the first time that psychoacoustic considerations are directly used in the design and procedural optimization process. The results obtained for different classes of aircraft in several operating conditions are presented
Noise shielding metamodels based on stochastic radial basis functions
No full textThis paper deals with the development of suitable surrogate models for the acoustic assessment of the shielding effects due to engine installation on top of unconventional aircraft configurations. The interest of the aeronautic community towards finding solutions to reduce the environmental impact has increased tremendously in the last decade, in particular to reduce acoustic emissions. The Advisory Council for Aviation Research and Innovation in Europe (ACARE) has in fact set ambitious noise reduction targets for 2050, which can only be reached through important technological advances such as the development of highly innovative configurations. Among solutions proposed in literature, one of the most promising and most investigated is the Blended Wing Body (BWB) aircraft configurations. Because of the peculiar center-body shape of this concept, the engines can be installed on top of the aircraft, making its noise shielding properties particular appealing. Therefore, the choice of the optimal position of the engines to maximize the masking effect represents a crucial aspect that must be taken into account from the early design stages. However, as experimental and historical data are not available in this context, there are no alternative to perform direct simulations for the acoustic assessment needed in conceptual design phase, which would lead to an unacceptable increase of computational resources for optimization purposes. A possible solution is to limit the number of performed simulation by using them to develop metamodels based on stochastic radial basic functions for the evaluation of the acoustic shielding factor, instead of calculating the actual value at each call of the objective functions. Specifically, starting from few high-fidelity simulations by means of a bidimensional integral solver based on the convective Helmholtz equation, an adaptive metamodel is developed for the evaluation of the shielding factor of airfoils, which takes into account the variation of crucial design variable
Noise shielding models for the conceptual design of unconventional aircraft
No full textAir traffic growth and the expansion of urban areas around airports make the aviation community noise a key aspect of aircraft design. The analysis of innovative configurations is becoming activity of primary interest within the scientific community. The current effort to attain the strict noise–abatement targets imposed by the authorities risks to be profitless without a significant technological breakthrough. A promising innovative configuration in terms of noise reduction is the Blended–Wing–Body aircraft. Indeed, the installation of the propulsion system above the centre–body surface ensures a significant masking effect of the engine noise components. The lack of experimental data needed to validate the advantages introduced by these technologies, and therefore carry out parametric analysis, can only be overcome by formulating reliable and cost–effective models to predict the noise shielding induced by engines installation on unconventional geometries. The present work introduces the development of tailored models for the correction of the existing semi-empirical prediction techniques. Such models are embedded within the modules of the existing conceptual design framework FRIDA. Without excluding other disciplines, the introduction of a noise prediction tool allows to cast a wide net in the research of optimal configuration in the future aviation context
Optimized metamaterials for enhanced noise shielding of innovative aircraft configurations
No full textMetasurfaces that exploit the so-called generalized Snell's law are suitable for the manipulation of acoustic waves in the subwavelength regime, exhibiting extraordinary refracting and reflecting behaviours. This attracted the interest of the aeroacoustic community for their potential as a disruptive technology for noise abatement and acoustic field control. New acoustic treatments have, hence, been imagined for highly innovative aircraft configurations, to be placed also in unconventional positions over the airframe, fully exploiting their characteristics. However, the direct simulation of metamaterials and metasurfaces in the aeroacoustic context can be computationally very expensive, even when involved geometries are not particularly complex, limiting the possibility to include metamaterial effects into multidisciplinary design process for applications of aeronautical interest. In this paper a generalized Snell law-based lining installed on the upper side of an airfoil is explored as a way to enhance its shielding of the noise emitted by a point source. This shall be seen as a 2 dimensional schematization of the center body of a Blended Wing Body configuration with the propulsion system mounted on top of it. A model of metafluid is used to reduce the computational burden, allowing a simulation-based optimization process to be conducted, maximizing the shielding factor of the airfoil
Multi-objective, multi-disciplinary optimization of take-off and landing procedures to minimize the environmental impact of commercial aircraft: the noise vs fuel consumption trade-off within the EC project COSMA
No full textThe approach exploited within the the EC funded project COSMA (Community Oriented Solu-
tions to Minimize Aircraft Annoyance, FP7) for multi-objective optimization aimed at optimal
take-off and landing trajectories (minimizing noise emissions and fuel burn) is presented. The
methodology has been recently extended to include aircraft design variables, performing a si-
multaneous design/procedure optimization. As noise indicator, the area bounded by the SEL
60dBA contour is chosen, whereas the fuel burn refers to the specified procedure. A binary
coded multi-objective genetic algorithm (MOGA) is applied to find the front of non-dominated
solutions (Pareto front) and an optimal compromise solution is selected. The trajectory is par-
titioned into segments, and the 3D spatial coordinates of each segment extreme, along with
the aircraft speed and high-lift devices settings are taken as optimization variables. Aircraft
performance and noise emissions are evaluated through the multidisciplinary simulation, de-
sign and optimization tool FRIDA (Framework for Innovative Design in Aeronautics). The
approach is applied to three classes of aircraft, from mid to long range and the relevant results
for mid range aircraft are presented herein
Innovative acoustic treatments of nacelle intakes based on optimised metamaterials
Full text linkModern turbofans with high bypass ratios, low blade passage frequencies and short nacelles require continuous development of acoustic linings to achieve the noise reductions expected by the international aviation authorities. Metamaterials and metafluids have been recently proposed as promising technologies for designing innovative acoustic treatments dedicated to reducing aeronautic turbofan noise emissions. In this work, a phase-gradient metasurface treatment is investigated as a way to tackle the noise radiation from an axially symmetric nacelle. This paper aims to study the potential benefits of the mentioned technology, and is not an attempt to design a complete new liner or nacelle. The metasurface is modelled through an equivalent metafluid, and a simulation-based optimisation is used in defining the design parameters. The tonal contribution of the blade passage frequency is considered, and the numerical results with the metafluid optimised on one azimuthal mode at a time show a significant effect in terms of acoustic levels and directivity over an arc of virtual receivers
Multi-objective optimization of takeoff and landing procedures: level abatement vs quality improvement of aircraft noise
No full textMultiobjective optimisation of flight paths for noise level mitigation and sound quality improvement
Full text linkThe present work deals with the multiobjective, multidisciplinary optimisation of takeoff and approach operations of a commercial aircraft aimed at the mitigation of the impact of aviation noise on the population. The innovative approach used here couples the minimisation of the aircraft noise level at the certification points with the improvement of the sound quality. The latter objective represents the main novelty of the present work and is addressed using a spectral–matching approach to make the aircraft noise as close as possible to a target sound. The rationale underlying the research is the development of a community–oriented approach to the assessment airport operations in view of the complete redefinition of the future airport scenarios. Indeed, the air traffic growth, the rapid expansion of urban areas around airports, and the expected advent of urban air mobility, are transforming the aviation noise into a serious hazard to the sustainable development of society. The sound–quality–based objective imposes a comprehensive multidisciplinary approach also in the procedural optimisation, due to the detail required to estimate the noise spectrum composition. Two merit factors are minimised, specifically the EPNL at the noise certification points and the Lp–norm of the difference between the noise produced by the configuration under analysis and a target sound. The target sounds are obtained by using sound engineering techniques aimed at the sound quality improvement, on the basis of the results of the psychometric tests campaigns performed within the projects SEFA and COSMA. The minimisation is achieved adopting a global evolution method, and the results are presented in terms of approximated Pareto frontiers for a single–aisle aircraft in both takeoff and landing conditions
Steering of acoustic reflection from metasurfaces through numerical optimization
No full textSpace–coiling metamaterials that exploit the generalized Snell’s law are suitable for the subwavelength manipulation of acoustic waves, leading to extraordinary refraction and reflection properties. Typically, space–coiling metasurfaces are characterized by a narrow operating range in frequency due to the intrinsic connection between the design wavelength and the characteristic dimensions of the metasurface. The main goal of the present work is to design a broadband and modular metasurface based on space–coiling cells by extending the range of frequency where the effective metabehaviour is achieved through numerical optimization. The metasurface module is composed by eight different unit cells, each introducing a tailored phase shift in the field, that can be combined side by side to produce the desired acoustic effect. The design parameters of each cell are selected as the result of an optimization process that minimizes the dependency on the operating frequency of the metabehaviour, keeping the overall thickness below a quarter of the design wavelength. Preliminary results are obtained for a benchmark problem
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