International Journal of Acoustics and Vibration 

About: International Journal of Acoustics and Vibration is an academic journal published by International Institute of Acoustics and Vibration (IIAV). The journal publishes majorly in the area(s): Vibration & Finite element method. It has an ISSN identifier of 1027-5851. Over the lifetime, 610 publications have been published receiving 3832 citations. The journal is also known as: IJAV.

Constructive and Destructive Interference of Acoustic and Entropy Waves in a Premixed Combustor with a Choked Exit

Abstract: Thermoacoustic instabilities are a cause for concern in combustion applications as diverse as small household burners, gas turbines or rocket engines. In this work, a feedback mechanism is analyzed, which couples combustion chamber acoustics with convectively transported fluctuations of entropy (entropy waves) generated within a premixed flame. Essential elements of this thermo-acoustic feedback loop are fluctuations in fuel concentration, induced by acoustic disturbances at the location of fuel injection, convective transport of fuel inhomogeneities through the premixing section of the burner, modulations in heat release rate and hot gas entropy resulting from the consumption of fuel/air mixture with varying fuel concentration by the flame, and the generation of sound through entropy non-uniformities at the turbine inlet. From a qualitative analysis based on relative phases, it is concluded that depending on the various convective and acoustic time lags involved, entropy waves may couple constructively as well as destructively with combustor acoustics. However, such qualitative analysis does not indicate whether the coupling between entropy and acoustic waves is strong enough to significantly influence thermo-acoustic stability. Therefore, a linear model has been constructed to estimate the effect of entropy waves on the thermo-acoustic response and stability of a combustor with a choked exit nozzle, as it might be found in a gas turbine. Note that phenomena like dispersion of convective waves, distributed heat release, vortical velocities, etc., have not been taken into account, as they would burden the presentation with unnecessary complexity. Results obtained indicate that the interaction between combustor acoustics and entropy waves can be significant, especially for the lowest non-axisymmetric modes, and even at frequencies higher than those usually associated with convective waves. As expected, it was observed that the coupling between pressure and entropy waves at the exit nozzle can enhance as well as reduce the thermo-acoustic stability of a combustor, or the responsiveness to an external or internal fluid-mechanic excitation mechanism. It is concluded that comprehensive thermo-acoustic analysis of a premixed combustor with a choked exit must in general include generation and propagation of entropy waves and coupling with combustor acoustics.

A Review of Progress in Soundscapes and an Approach to Soundscape Planning

Abstract: The soundscape approach considers the acoustic environment as a resource, focusing on sounds people want or prefer. Quiet is not a core requirement for such acoustic preference in the outdoor acoustic environment. Core requirements include congruent soundscape and landscape, and dominant wanted sounds in a place over, and not masked by, unwanted sounds. Acceptance, and further development, of the soundscape approach is facilitated by distinguishing it, both conceptually and in measurement and management approaches, from environmental noise management. Soundscape design, planning, and management, based on soundscape concepts, augment environmental noise management approaches, expanding the scope of application of the tools of acoustic specialists.

Inverse and Reciprocity Methods for Machinery Noise Source Characterization and Sound Path Quantification Part 1: Sources

Abstract: A conventional approach for the analysis of noise control problems uses the source-transmission path-receiver scheme In many situations this type of analysis is complicated by the fact that there is a multitude of simultaneous sources Moreover, even for a single noise source like a machine, there can be a multitude of partial sources and "parallel" transmission paths Therefore, the development of cost-effective noise reduction strategies often requires detailed knowledge of the contributions of the partial sources and transmission paths to the radiated sound at distant receiver positions Generally speaking, this type of analysis requires a system modelling in terms of inputs I, which genuinely characterize the sources themselves and of output-input ratios O/I These latter are transfer functions TF, which characterize the transmission paths Such an analytical approach facilitates the effective specification of required noise source quietening and of improved sound or vibration isolation in one or more paths The treatments in this article will be limited to systems with supposedly linear behaviour, ie to systems for which the output response may be modelled as a linear superposition of all contributions of the partial sources and transmission paths Then in loose mathematical terms the following model equations apply:

Evaluation of Whole-Body Vibration and Ride Comfort in a Passenger Car

Abstract: Whole-body vibration transmission influences comfort, performance, and long-term health of the driver. This current study is an objective evaluation of vehicle comfort characteristics based on standard mathematical formulae and frequency analyses. A variety of road types were selected and quantified by using the International Roughness Index (IRI). To assess vibrations transmitted to the passengers, vibration dose values (VDV), kurtosis, frequency response functions (FRF), and power spectral densities (PSD) of the compartment recorded signals were evaluated. SEAT values based on VDV outputs qualified the seat suspension as a vibration isolator, whereas the FRF and PSD quantified that behaviour through frequency analyses. Results indicate that energy concentration is at frequencies lower than 30 Hz. Such low frequency excitations are well attenuated by seat suspension in the vertical direction but are amplified (up to five times in harsh conditions) by a backrest in the fore-aft trend. Signals are amplified beyond 30 Hz, but amplitudes are still very low. It seems that backrest assembly still can be improved to become a better isolator. However, T15 (time to reach severe discomfort), even in harsh conditions, is more than three hours, which exhibits the overall good quality of the vehicle suspension systems. Kurtosis and VDV correlate with IRI and may be used as two objective metrics, together with jury evaluation, to create a vehicle vibration-comfort index in the future.