Papers by Keith Attenborough
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Zenodo (CERN European Organization for Nuclear Research), 2008
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The Quarterly Journal of Mechanics and Applied Mathematics
Summary Regularly spaced low walls and rectangular lattices on a hard ground have been investigat... more Summary Regularly spaced low walls and rectangular lattices on a hard ground have been investigated as a means for reducing noise levels from surface transport. Predictions of the insertion loss of such surfaces has involved the use of computationally intensive numerical methods such as the Boundary Element Method (BEM) or Finite difference techniques (FDTD and PSTD). By considering point-to-point propagation above regularly spaced acoustically hard grooves with rectangular cross sections, a modal model used hitherto to predict electromagnetic and ultrasonic surface waves is adapted to derive an effective impedance for such a grooved surface. When this effective impedance is used in the classical theory for propagation from a point source above an impedance plane, the modal model enables predictions of excess attenuation spectra that compare closely with those obtained by numerical methods but take a fraction of the time. Also the modal method is extended to predict excess attenuati...
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Zenodo (CERN European Organization for Nuclear Research), 2008
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Above-ground propagation modelling at the JAPE (Joint Acoustic Propagation Experiment) site requi... more Above-ground propagation modelling at the JAPE (Joint Acoustic Propagation Experiment) site requires a reasonably accurate model for the acoustical properties of the ground. Various models for the JAPE site are offered based on theoretical fits to short range data and to longer range data obtained with random noise and pure tones respectively from a loudspeaker under approximately quiescent isothermal conditions.
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The porous structure and near-surface layering of ground influences propagation of acoustic and s... more The porous structure and near-surface layering of ground influences propagation of acoustic and seismic pulses originating from above-surface sound sources. Snow cover modifies the acoustical properties and frozen ground adds to the layering effect. A numerical model, Pulse Fast Field Program for Layered Air Ground Systems (PFFLAGS), developed originally (as FFLAGS) for continuous sound sources, is outlined. It is used to fit radial and vertical seismic signals recorded by a geophone and resulting from above-ground explosions over three types of ground including ‘hard’ and ‘soft’ soil and snow cover. An effective linear source pulse has been determined assuming that non-linear effects are small at the ranges of interest. The resulting deduction of parameters describing the near-surface ground structure is based first on fitting pore-related parameters to the above-ground acoustic waveforms received by microphones and then fitting the other parameters including elastic constants and ...
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The Journal of the Acoustical Society of America, 2020
A modal model for diffraction by a contiguous array of rectangular grooves in an acoustically-har... more A modal model for diffraction by a contiguous array of rectangular grooves in an acoustically-hard plane is extended to predict the free space acoustic field from a point source above such a structure. Subsequently, an approximate effective impedance model for grooved surfaces is presented. Measurements have shown that these ground surfaces can be used for outdoor noise reduction but accurate modelling has required the use of computationally expensive numerical methods. The extended modal model and approximate impedance model inspired by it yield equivalent results in a fraction of the time taken by the boundary element method, for example, and could be used when designing grooved surfaces to reduce noise from road traffic.
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Transport noise is an ever present concern in urban areas affecting the quality of life for milli... more Transport noise is an ever present concern in urban areas affecting the quality of life for millions of people. The traditional noise barrier is not always a convenient method of noise control and can divide communities. Deliberate introduction of small scale (0.3 m high or less) periodic roughness on otherwise acoustically-hard ground has been investigated as a way of reducing noise near to a surface transport corridor. The roughness alters the effective surface impedance of the ground and thereby creates a 'soft' ground effect. Moreover the effectiveness if the rough surface is not reduced significantly if there are pathways through it. However the rough ground also creates surface waves that must be absorbed for the noise reduction to be effective. An alternative way of reducing surface waves may be to alter the periodicity. The effects of altering the periodicity of circular rods placed on a hard surface in the laboratory have been investigated. Predictions of multiple s...
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HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Diffraction-assisted rough ground effects Imran Bashir, Shahram Taherzadeh, T.J Hill, Keith Attenborough
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A surface composed of regularly-spaced rectangular strips is known to produce airborne acoustic s... more A surface composed of regularly-spaced rectangular strips is known to produce airborne acoustic surface waves that travel slower than the speed of sound and attenuate in the propagation direction with the square root of distance. Further laboratory measurements of propagation over a regular array are reported which seem to indicate the possibility of more than one surface wave. A code based on the Boundary Element Method has been extended to the time domain. It has been used to compare the data and to explore the surface wave effects. Varying the spacing, thickness and height of the strips is shown to affect the magnitude and frequency content of the air-borne surface waves generated by the periodic strip surface.
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WIT Transactions on the Built Environment, 1970
Sound propagation from multiple dipole and monopole sources in a system comprising of a horizonta... more Sound propagation from multiple dipole and monopole sources in a system comprising of a horizontally stratified fluid above a horizontally stratified porous elastic solid is modelled using the global matrix method to solve the wave equation. A modified Biot-Stoll model is used for wave propagation in the porous elastic solid. Predictions of sound pressure level in the fluid are compared with other numerical routines to validate the program. Predicted radiation fields due to dipole and monopole sources are compared. Numerical techniques to ensure the accuracy and stability of the solution are described.
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Soil and Tillage Research, 2021
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The Journal of the Acoustical Society of America, 2019
Propagation of an airborne acoustic pulse from a point source above an array of regularly spaced ... more Propagation of an airborne acoustic pulse from a point source above an array of regularly spaced rigid cylinders on a rigid plane has been investigated using a two-dimensional multiple scattering theory. Time domain simulations show a main arrival and a separate delayed “tail.” Fourier analysis of the tail shows that, for a sufficiently sparse array of cylinders, it is composed of a series of spectral peaks resulting from constructive interference consistent with Bragg diffraction theory and amplitudes depending on the spacing and size of the cylinders. For increasingly compact distributions of cylinders, the lowest frequency peak is dominated by a quarter wavelength “organ pipe” or “gap” resonance in the space between the cylinders. Simulated pressure maps show that there is a transition region in the acoustic field with an extent that depends on the spacing and size of the cylinders. Beyond this region, individual gap resonances combine to create a field that declines exponentiall...
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Environmental Methods for Transport Noise Reduction, 2014
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Environmental Methods for Transport Noise Reduction, 2014
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The potential use of forests or narrow belts of trees alongside surface transport corridors to re... more The potential use of forests or narrow belts of trees alongside surface transport corridors to reduce noise is often dismissed. This may be a consequence of conflicting experimental evidence and incomplete understanding of the various attenuation mechanisms involved. Important mechanisms include (a) destructive interference between sound travelling directly between source and receiver and reflected from the ‘acoustically-soft’ ground formed by decaying leaf litter, (b) the influence on this interference of loss of coherence due to the reverberant scattering by trunks and branches and (c) visco-thermal scattering by foliage. First the paper lists experimental evidence of significant attenuation due to forests and tree belts. Subsequently models for predicting the various contributions to overall attenuation are outlined. Predictions of the ‘soft’ ground effect are made using physically admissible ground impedance models. Incoherence due to trunk and branch scattering is modelled as e...
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Papers by Keith Attenborough