No description available.

No description available.

This thesis is the result of over 2 years research on the ef f ects of aircraf t noise on human health of the residents around Mehrabad Airport (Tehran). other studies in England, Germany, France, Netherlands, Switzerland, Hong Kong, U. S. A., Australia, Nigeria and Canada show a positive correlation between the extent of social and psychological disorders and aircraft noise. Social survey data from questionnaires translated into Farsi highlight relationships -between noise and psychological problems. The Noise and Number Index (NNI) for aircraft noise assessment was derived from noise measurements and correlated with questionnaires. The results were computed by SPSS PC" software. The analysis of questionnaires data demonstrates that aircraft noise exposure causes annoyance and increases tiredness and affects the efficiency and performance of school teachers. Aircraft noise effects are the most severe of noises experienced by residents. It causes psychological and physiological disorders, sleep disturbance and communication difficulties. Noise is a very important factor which needs more attention and further study on its effects on human health and the impact of aircraft noise on different sections of society.

- / -

No description available.

Fluid-borne noise is one of the main components of hydraulic noise. Its attenuation may have a significant effect on the cost of hydraulic systems. Standard passive silencers and dampers can be useful in reducing it in certain frequency ranges; however, these tend to be heavy, bulky and expensive. Active control algorithms, which are a comparatively recent means of reducing fluid-borne noise, can be applied to overcome this compromise. The work presented in this thesis is the development of some active control algorithms utilized in a simple hydraulic system to cancel a number of harmonic orders of fluid-borne noise generated by a servo valve or a real pump. To realize cancellation the filtered reference least mean square (FXLMS) adaptive control method is mainly presented. Furthermore, a fast response servo valve is applied as an actuator to generate a proper anti-noise flow signal in real-time. For simplicity, an off-line identification method for the secondary path is applied in the time invariant working condition. Moreover, ripple reflection from both ends of the hydraulic circuit can produce different effects under different working conditions. In order to execute the cancellation without any prior information about the dynamics of hydraulic systems, the on-line secondary path identification method is discussed. However, in this algorithm an auxiliary white-noise signal applied to an on-line method may contribute to residual noise and an extra computation burden may be added to the whole control system. The performance of these control algorithms is firstly investigated via simulation in a hydraulic pipe model and the real-time application on a test rig using a servo valve as a noise source. Finally, these schemes are realized in a simple hydraulic system with a real pump noise source. The fluid-borne noise can be attenuated by about 20 dB in normal working conditions.

No description available.

Modern high-bypass turbofan engines produce high levels of nuisance noise that has a significant impact on the environment near airports as well as the crew and passengers inside the aircraft. Significant research is being undertaken to understand the aeroacoustic noise source mechanisms and to accurately predict engine noise levels. High-performance computers and advanced numerical techniques are now taking an active role in this research area. In this work, a numerical solver is developed to accurately and efficiently predict noise radiation from ducts. The solver is based upon a hybrid methodology whereby only the acoustic near-field is solved using the developed numerical solver, with the resultant far-field directivity determined from an integral solution of the Ffowcs Williams - Hawking equation. Particular emphasis has been placed on the radiation of duct modes from a realistic bypass engine intake geometry. The performance of the numerical schemes employed in the solver is analysed, with particular attention to the dispersion and dissipation qualities. A study into the determination of a suitable non-reflecting boundary condition for duct acoustics is also undertaken. Using a novel formulation of the linearised Euler equations, the solver is applied to noise radiation from a realistic engine intake geometry with background mean flow. The accuracy of the scheme is validated by comparison with analytic solutions for the unflanged duct case. For the unflanged duct case the effect of an acoustic liner is modelled using a time-domain impedance boundary condition. The effect of a locally supersonic inflow on radiation from the engine intake is examined. Finally, the solver is extended to determine multimode radiation from generic engine intakes, with the possibility to incorporate swirling mean flows and asymmetric duct geometries.

Dans beaucoup de cas les nuisances sonores auxquelles nous sommes quotidiennement exposés sont dues à la vibration d'une structure (machine industrielle, véhicule, appareil ménager …). Néanmoins, tous les bruits que nous percevons ne sont pas forcément dûs à la vibration d'une structure, par exemple, les bruits aérodynamiques, les bruits de turbine ou les bruits de jet … La recherche en vibroacoustique est étroitement liée avec des applications industrielles, car l'industrie a besoin des nouveaux outils numériques, développés dans les centres de recherche, pour concevoir de nouveaux produits silencieux. En effet, les démarches purement expérimentales sont en général longues, compliquées et coûteuses, elles peuvent être, de plus, très peu efficaces. Puisque l'objectif ultime est la conception d'une structure qui permet de réduire le bruit pour un très bon confort acoustique, les simulations numériques peuvent être incluses dans l'optimisation de la conception avec des techniques de conception optimales de forme et l'optimisation des matériaux. Une fois les simulations validées par les résultats expérimentaux, elles peuvent être utilisées comme outil de conception pour l'amélioration de la structure du système concerné. L'objectif principal de mon travail de thèse est le développement des outils de prédiction numériques permettant la réduction des nuisances sonores dues à la vibration des structures. Pour ce faire, des formulations théoriques originales ont été formulées, puis implantées afin de favoriser la conception de produits silencieux. D'une manière plus spécifique, deux parties vont être traitées : La première partie aborde le problème bien connu des fréquences irrégulières de la méthode des éléments finis de frontière, la BEM, pour le rayonnement acoustique dans un domaine extérieur. Dans la deuxième partie de cette thèse la formulation de la méthode multipôlaire rapide FMM couplée à la BEM, ainsi que sa mise en œuvre et validation ont été effectuées afin de repousser les limites de la BEM en terme de temps de calcul ainsi que de mémoire. / In many cases the noise which we are daily exposed are due to the vibration of a structure (industrial machinery, vehicle, appliance...). Nevertheless, all the sounds we perceive are not necessarily due to the vibration of a structure, for example, wind noise, the sounds of turbine or jet noise...The vibroacoustic research is closely linked with industrial applications because the industry needs new numerical tools, developed in research centers to develop new silent products. Indeed, purely experimental approaches are generally lengthy, complicated and expensive they can be, again, very inefficient. Since the ultimate objective is to design a structure that reduces noise for a good acoustic comfort, numerical simulations can be included in the design optimization techniques to design optimum shape and optimizationmaterials. Once the simulations validated by experimental results, it can be used as a design tool for improving the structure of the affected system. The main aim of my thesis is the development of numerical predictive tools for the noise reduction due to the vibrationof structures. To do this, the original theoretical formulations have been developed and implemented to encourage the design of silent products. In a more specific way, both parties will be addressed : the first part addreeses the familiarproblem of irregular frequencies of the finite element boundary, the BEM for acoustic radiation in an external field. In the second part of this thesis the formulation of the fast multipole method FMM coupled with BEM, as well asits implementation and validation were carried out to push the boundaries of the BEM in terms of computation time and memory.

Pandrol Rail Fastenings Limited are a designer and manufacturer of railway rail-fastening systems. As an organisation they have the capability to reduce the noise impact of bridges using resilient track components. They also have a commercial interest in providing such technology. Knowledge of the processes behind bridge noise is important to Pandrol in two ways; to aid the engineers within the organisation in the design of fastening systems and to demonstrate a state-of-the-art understanding of the problem of railway bridge noise to customers, as this will aid in the sale of Pandrol products. The fitting of new rail components to an existing track form, or failure to meet noise regulations with a new track form, can be costly. It is important to be able to predict accurately the effectiveness of noise reduction techniques. Currently, Pandrol’s knowledge of the problem consists almost entirely of experience gained and data gathered while working on existing bridge projects. To expand their knowledge base, Pandrol perform noise and vibration measurements on railway bridges and viaducts and then use the measured data to predict the performance of their systems on other bridges. This completely empirical approach to predicting bridge noise is both costly and situation specific results cannot be provided before the installation of the fastening system. ii Another approach to predicting bridge noise is through the application of analytical models. Limited analytical modelling in the context of bridge noise is currently conducted within the organisation. For these reasons, Pandrol are sponsoring research into bridge noise in the form of this EngD project. Here an existing rapid calculation approach is identified that relies less on the exact geometry of the bridge and more on its general characteristics. In this approach an analytical model of the track is coupled to a statistical energy analysis (SEA) model of the bridge. This approach forms a suitable basis from which to develop a better model here by concentrating on its weaknesses. A mid-frequency calculation for the power input to the bridge via a resilient track system has been developed by modelling the track-bridge system as two finite Timoshenko beams continuously connected by a resilient layer. This has resulted in a power input calculation which includes the important effects of coupling between the rail and bridge and the resonance effects of the finite length of a bridge. In addition, a detailed study of the frequency characteristics of deep I-section beams has been performed using Finite Element, Boundary Element and Dynamic stiffness models. It is shown that, at high frequencies, the behaviour of the beam is characterised by in-plane motion of the beam web and bending motion in the flange. This knowledge has resulted in an improved calculation for the mobility of a bridge at high frequencies. The above improvements are included in an improved model for use by Pandrol in their general activities. Data from real bridges is compared to predictions from the improved model in order to validate different aspects of the model. The model is then used to study the effect on noise of varying many bridge design parameters. It is shown that the parameter that has most influence on the noise performance of a bridge is the dynamic stiffness of the resilient rail fastening system. Additionally it is demonstrated that for a given bridge and noise receiver location, an optimum fastener stiffness exists where the noise radiated by the bridge and track is at a minimum.