Preface Acknowledgements Introductory comments 1. Mechanical vibrations: a review of some fundamentals 2. Sound waves: a review of some fundamentals 3. Interactions between sound waves and solid structures 4. Noise and vibration measurement and control procedures 5. The analysis of noise and vibration signals 6. Statistical energy analysis of noise and vibration 7. Pipe flow noise and vibration: a case study 8. Noise and vibration as a diagnostic tool 9. Worked examples Appendices Problems Answers to problems Index.

Fundamentals of noise and vibration analysis for engineers

We studied the mechanisms by which turbulent flow induces tracheal wall vibrations detected as tracheal breath sounds (TRBSs). The effects of flow rate at transitional Reynold's numbers (1300–10,000) and gas density on spectral patterns of TRBSs in eight normal subjects were measured. TRBSs were recorded with a contact sensor during air and heliox breathing at four flow rates (1.0, 1.5, 2.0, and 2.5 l/s). We found that normalized TRBSs were proportional to flow to the 1.89 power during inspiration and to the 1.59 power during expiration irrespective of gas density. The amplitude of TRBSs with heliox was lower than with air by a factor of 0.33 ± 0.12 and 0.44 ± 0.16 during inspiration and expiration, respectively. The spectral resonance frequencies were higher during heliox than air breathing by a factor of 1.75 ± 0.2—approximately the square root of the reciprocal of the air/heliox wave propagation speed ratio. In conclusion, the flow-induced pressure fluctuations inside the trachea, which cause tracheal wall vibrations, were detected as TRBSs consist of two components: (1) a dominant local turbulent eddy component whose amplitude is proportional to the gas density and nonlinearly related to the flow; and (2) a propagating acoustic component with resonances whose frequencies correspond to the length of the upper airway and to the free-field sound speed. Therefore, TRBSs consist primarily of direct turbulent eddy pressure fluctuations that are perceived as sound during auscultation.

Measurements and theory of normal tracheal breath sounds.

Mechanisms of the generation of external acoustic radiation from pipes due to internal flow disturbances

Aeroacoustics of duct junction flows merging at different angles

Les diaphragmes utilises comme organes de perte de charge a l'interieur des tuyauteries de centrales electriques ont ete mis en cause dans la creation de sifflement. Les consequences de ces phenomenes sont des niveaux de bruit et de vibration pouvant depasser les valeurs admissibles. L'objectif de la these est d'etudier le sifflement sur la base d'experimentations et de calculs numeriques afin de proposer des outils de comprehension et de prediction. Un resultat de la these correspond a l’identification experimentale et numerique des conditions d’amplification acoustique au niveau de diaphragmes, phenomene necessaire au sifflement. Les experiences montrent que les plages de sifflement, exprimees sous la forme d’un nombre de Strouhal fonction de l’epaisseur du diaphragme et de la vitesse dans l’orifice, s’etendent de 0,2 a 0,4 et de 0,7 a 0,9 et sont independantes du nombre de Reynolds. Le potentiel de sifflement de diaphragmes est egalement caracterise a l’aide de simulations numeriques. Deux approches sont utilisees avec des calculs U-RANS incompressibles et des simulations LES compressibles. Il apparait que la simulation numerique permet de reproduire l’effet d’amplification acoustique a l’origine du sifflement, pour des pas de discretisation spatial au coin amont de l’orifice suffisamment petit. Un autre resultat de la these est la definition des parametres controlant les caracteristiques du sifflement en presence de reflexions acoustiques. Une analyse de stabilite lineaire predit l’apparition d’un sifflement et sa frequence. L’amplitude de sifflement est maximum pour un nombre de Strouhal autour de 0,25 et augmente avec le taux de reflexion autour du diaphragme.

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M.P. Norton

Papers

On the hydrodynamic and acoustic wall pressure fluctuations in turbulent pipe flow due to a 90° mitred bend