A method to determine the acoustic reflection and absorption coefficients of porous media by using modal dispersion in a waveguide

The measurement of acoustic material characteristics using a standard impedance tube method is generally limited to the plane wave regime below the tube cut-on frequency. This implies that the size of the tube and, consequently, the size of the material specimen must remain smaller than a half of the wavelength. This paper presents a method that enables the extension of the frequency range beyond the plane wave regime by at least a factor of 3, so that the size of the material specimen can be much larger than the wavelength. The proposed method is based on measuring of the sound pressure at different axial locations and applying the spatial Fourier transform. A normal mode decomposition approach is used together with an optimization algorithm to minimize the discrepancy between the measured and predicted sound pressure spectra. This allows the frequency and angle dependent reflection and absorption coefficients of the material specimen to be calculated in an extended frequency range. The method has been tested successfully on samples of melamine foam and wood fiber. The measured data are in close agreement with the predictions by the equivalent fluid model for the acoustical properties of porous media

Calibrating the discrete boundary conditions of a dynamic simulation: a combinatorial approximate Bayesian computation sequential Monte Carlo (ABC-SMC) approach

This paper presents a novel adaptation of the conventional approximate Bayesian computation sequential Monte Carlo (ABC-SMC) sampling algorithm for parameter estimation in the presence of uncertainties, coined combinatorial ABC-SMC. Inference of this type is used in situations where there does not exist a closed form of the associated likelihood function, which is replaced by a simulating model capable of producing artificial data. In the literature, conventional ABC-SMC is utilised to perform inference on continuous parameters. The novel scheme presented here has been developed to perform inference on parameters that are high-dimensional binary, rather than continuous. By altering the form of the proposal distribution from which to sample candidates in subsequent iterations (referred to as waves), high-dimensional binary variables may be targeted and inferred by the scheme. The efficacy of the proposed scheme is demonstrated through application to vibration data obtained in a structural dynamics experiment on a fibre-optic sensor simulated as a finite plate with uncertain boundary conditions at its edges. Results indicate that the method provides sound inference on the plate boundary conditions, which is validated through subsequent application of the method to multiple vibration datasets. Comparisons between appropriate forms of the metric function used in the scheme are also developed to highlight the effect of this element in the schemes convergence

On the variation of the acoustic intensity vector near an open end of a pipe

A new laboratory facility for studying of the acoustic intensity field in a round 6m long, 150mm diameter pipe has been developed. It enables to control carefully the boundary conditions at the both ends, positions and the orientation of the acoustics sensors. It has been used to measure the variation of the acoustic intensity near the open end of the pipe with a triaxial intensity probe supplied by Microflown. The measured data have been used to validate a new efficient model based on the normal model decomposition and finite element methods. It is shown that even in the plane wave regime the acoustic intensity distribution near the pipe end is very complex and that the measured intensity vector sensitive to the radial and longitudinal position of the probe. It is demonstrated that a very small variation in the position of the intensity probe can result in a very large change in the intensity vector that is difficult to predict. The results of this work have a strong implication on the design of acoustic intensity sensors that have been developed to characterise the boundary conditions in a pipe

An acoustic method of blockage characterisation in a pipe based on the cross-sectional mode analysis

Copyright © (2014) by the International Institute of Acoustics & Vibration All rights reserved. This paper presents an acoustic method to characterise a blockage of an arbitrary shape in an air filled pipe. Two sets of experiments are conducted using the transient pulse signals. For the first experiment, the frequency range extends beyond the plane wave regime so that three first cross-sectional modes are excited and analysed with a horizontal microphone array in the absence and presence of a blockage. The 2D Fourier transform is then applied to transfer the acquired sound pressure data into the frequency and wavenumber space from which the modal reflection and transmission coefficients can be determined. For the second experiment, the microphone array is placed at a single position and the frequency range is below the first cross-sectional mode which makes the analysis relatively simple and robust. A set of equations is derived and employed to calculate the area ratio and the length of a blockage making use of a reflection coefficient from a blockage and a phase change between incident and reflected signals

Use of fibre-optic sensors for pipe condition and hydraulics measurements: a review

The combined length of the sewerage and clean water pipe infrastructure in the UK is estimated to be about 800,000 km. It is prone to failure due to its age and the inadequacies of the current pipe inspection methods. Fibre-optic cable sensing is an attractive way to continuously monitor this infrastructure to detect critical changes. This paper reviews the existing fibre-optic sensor (FOS) technologies to suggest that these technologies have better sensing potential than traditional inspection and performance monitoring methods. This review also discusses the requirements for retrofitting an existing pipeline with an FOS. It also demonstrates that there is a need for further research into methods applicable to non-pressurised pipelines, as there is very little existing literature that focuses on partially filled pipes and pipes with gravity fed flows

Local and international: richly contested concepts in practitioner research (a patchwork paper)

This paper is a co-written paper by masters' students at a university in the Midlands region of England. In it the authors, all practicing teachers, explore via a series of interlinked research stories how they conceptualise: 'international’ and ‘local’ in their research. This paper by focusing, sharply on this aspect of their research positioning, reveals that this was in complex, nuanced and idiographic ways. The Midlands is one of the most multi-cultural and multi-ethnic regions of Britain and is therefore one where embracing and interpreting intersectionality is at the heart of navigating personal and professional life. One interpretation of these terms that emerged therefore interwove ‘the local’ and ‘the international’ and emphasised using research that focuses on the localised detail of classroom practice to find paths towards building inclusive classrooms within a multicultural context. However, another perspective that emerged drew conceptual boundaries between these terms, seeing internationally conducted research as a distinct but illuminating route into understanding local issues; while a third took as its starting point ‘the local’ and from this built an aspirational goal that good practice grounded in locally conducted research could inform international debates. These are just three illustrative examples of different ways that these teacher researchers interpreted the dichotomy of the global and the local. As is common and appropriate with patchwork presentations there is no attempt to impose a single methodological framework on the multiple authors and the research vignettes are rich and varied. This paper reveals that to practitioner researchers the concepts of international and local are richly contested and are utilized in varied ways. It will contribute to building an understanding of how practitioner research, too often perceived as localised and distinct from international research, can define its place in the international research community

Local and international: richly contested concepts in practitioner research (a patchwork paper)

This paper is a co-written paper by masters' students at a university in the Midlands region of England. In it the authors, all practicing teachers, explore via a series of interlinked research stories how they conceptualise: 'international’ and ‘local’ in their research. This paper by focusing, sharply on this aspect of their research positioning, reveals that this was in complex, nuanced and idiographic ways. The Midlands is one of the most multi-cultural and multi-ethnic regions of Britain and is therefore one where embracing and interpreting intersectionality is at the heart of navigating personal and professional life. One interpretation of these terms that emerged therefore interwove ‘the local’ and ‘the international’ and emphasised using research that focuses on the localised detail of classroom practice to find paths towards building inclusive classrooms within a multicultural context. However, another perspective that emerged drew conceptual boundaries between these terms, seeing internationally conducted research as a distinct but illuminating route into understanding local issues; while a third took as its starting point ‘the local’ and from this built an aspirational goal that good practice grounded in locally conducted research could inform international debates. These are just three illustrative examples of different ways that these teacher researchers interpreted the dichotomy of the global and the local. As is common and appropriate with patchwork presentations there is no attempt to impose a single methodological framework on the multiple authors and the research vignettes are rich and varied. This paper reveals that to practitioner researchers the concepts of international and local are richly contested and are utilized in varied ways. It will contribute to building an understanding of how practitioner research, too often perceived as localised and distinct from international research, can define its place in the international research community