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Keith Attenborough - One of the best experts on this subject based on the ideXlab platform.
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Outdoor Ground Impedance models
The Journal of the Acoustical Society of America, 2011Co-Authors: Keith Attenborough, Imran Bashir, Shahram TaherzadehAbstract:Many models for the acoustical properties of rigid-porous media require knowledge of parameter values that are not available for outdoor Ground surfaces. The relationship used between tortuosity and porosity for stacked spheres results in five characteristic Impedance models that require not more than two adjustable parameters. These models and hard-backed-layer versions are considered further through numerical fitting of 42 short range level difference spectra measured over various Ground surfaces. For all but eight sites, slit-pore, phenomenological and variable porosity models yield lower fitting errors than those given by the widely used one-parameter semi-empirical model. Data for 12 of 26 grassland sites and for three beech wood sites are fitted better by hard-backed-layer models. Parameter values obtained by fitting slit-pore and phenomenological models to data for relatively low flow resistivity Grounds, such as forest floors, porous asphalt, and gravel, are consistent with values that have been obtained non-acoustically. Three Impedance models yield reasonable fits to a narrow band excess attenuation spectrum measured at short range over railway ballast but, if extended reaction is taken into account, the hard-backed-layer version of the slit-pore model gives the most reasonable parameter values.
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A revised standard method for Ground Impedance measurement.
Journal of the Acoustical Society of America, 2009Co-Authors: Keith Attenborough, Shahram TaherzadehAbstract:ANSI S1.18 (1998) for Ground Impedance measurement has been revised to combine the previously existing template method with direct deduction of Impedance from data for the complex level difference between vertically separated microphones. It has been found that, despite the improved sensitivity at low frequencies that should be achievable through use of a longer range, the combined approach ceases to give reliable information for horizontal source‐receiver separations of more than 1 m. The revised standard contains four worked examples: three grass‐covered Ground surfaces and a gravel road. The first example has been used to show that although use of consecutive measurements with a single microphone produces data that is usable with the template method, the phase information is not sufficiently robust to allow direct Impedance deduction. In the three grassland examples, the widely used single parameter model is found to overpredict the real and imaginary parts of Ground Impedance at lower frequencies. The...
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The influence of Hank Bass on Ground effect research between 1981 and 1995.
Journal of the Acoustical Society of America, 2008Co-Authors: Keith AttenboroughAbstract:In 1981 Bolen and Bass published a paper on Ground effect which included a pioneering effort to deduce Ground Impedance from propagation data. This study can be regarded as a basis for current revision of the ANSI S1 1998 standard for measuring Ground Impedance. The author's first interaction with Henry Bass (Hank) in the same year stemmed from mutual interest in observations of buried geophone responses to airborne sound sources. Our initial experiments involved understanding such responses and the relationship of Ground properties to the phenomenon of Ground effect. Subsequent work by Hank and colleagues initiated modeling of the Ground as a layered poroelastic medium. In this paper are highlighted the several pioneering efforts and observations in the Bolen and Bass 1981 paper. Most remarkable of these were their deductions of values of Ground Impedance at low frequencies. But other important observations concerned the assumption of local reaction, the spatial variability of Ground properties, the adequacy of a popular one-parameter Ground Impedance model and the mechanisms by which sound penetrates the Ground. Some of the issues raised by Bolen and Bass are the subject of continuing research and recent related developments are reviewed.
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Sources and potential influences of uncertainty in Ground Impedance measurements and estimations
Journal of the Acoustical Society of America, 2008Co-Authors: Shahram Taherzadeh, Keith AttenboroughAbstract:Knowledge of acoustic Impedance of Ground surface is essential for determining noise levels outdoors. At distances up to a few hundred metres from the source Ground effect may be the dominant factor. The short‐range measurement of sound level spectra from an omni‐directional source has been used as a standard method to deduce the acoustic Impedance spectrum of Ground surfaces (e.g. ANSI S1.18, 1999). However, there remain a number of uncertainties in such measurement methods. For example, at low frequencies the difficulties in fitting theoretical or phenomenological models to short range data may result is a large uncertainty in predictions of sound levels at larger distances. Another source of uncertainty is the variability of the acoustic Impedance of apparently uniform Ground. Another potential influence on predictions of long term equivalent noise levels is seasonal variation. This paper discusses the extent and potential influences of such uncertainties in measured and deduced Ground Impedance spectra.
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Aspects of direct deduction of Ground Impedance
Journal of the Acoustical Society of America, 2007Co-Authors: Keith Attenborough, Shahram Taherzadeh, Gilles A. Daigle, Roland KruzeAbstract:ANSI S1.18 1998 offers a method for determining Ground Impedance by fitting data to templates of the magnitude of level difference obtained using a point source and two vertically separated microphones with specified geometries according the ‘‘acoustical‐softness’’ of the Ground. The ANSI working group on Ground Impedance is seeking to revise the current template method for deducing Ground Impedance by developing a practical method, based in fitting complex level difference spectra and without assuming any particular Impedance model. Both minimization and root finding techniques have been used in published laboratory experiments. The results of trial outdoor measurements in the UK, USA, Germany, and Canada are presented. Issues have arisen concerning phase matching of microphones, the signal processing instrumentation, the site and meteorological constraints, and the smoothness of the resulting data.
Shahram Taherzadeh - One of the best experts on this subject based on the ideXlab platform.
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Outdoor Ground Impedance models
The Journal of the Acoustical Society of America, 2011Co-Authors: Keith Attenborough, Imran Bashir, Shahram TaherzadehAbstract:Many models for the acoustical properties of rigid-porous media require knowledge of parameter values that are not available for outdoor Ground surfaces. The relationship used between tortuosity and porosity for stacked spheres results in five characteristic Impedance models that require not more than two adjustable parameters. These models and hard-backed-layer versions are considered further through numerical fitting of 42 short range level difference spectra measured over various Ground surfaces. For all but eight sites, slit-pore, phenomenological and variable porosity models yield lower fitting errors than those given by the widely used one-parameter semi-empirical model. Data for 12 of 26 grassland sites and for three beech wood sites are fitted better by hard-backed-layer models. Parameter values obtained by fitting slit-pore and phenomenological models to data for relatively low flow resistivity Grounds, such as forest floors, porous asphalt, and gravel, are consistent with values that have been obtained non-acoustically. Three Impedance models yield reasonable fits to a narrow band excess attenuation spectrum measured at short range over railway ballast but, if extended reaction is taken into account, the hard-backed-layer version of the slit-pore model gives the most reasonable parameter values.
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A revised standard method for Ground Impedance measurement.
Journal of the Acoustical Society of America, 2009Co-Authors: Keith Attenborough, Shahram TaherzadehAbstract:ANSI S1.18 (1998) for Ground Impedance measurement has been revised to combine the previously existing template method with direct deduction of Impedance from data for the complex level difference between vertically separated microphones. It has been found that, despite the improved sensitivity at low frequencies that should be achievable through use of a longer range, the combined approach ceases to give reliable information for horizontal source‐receiver separations of more than 1 m. The revised standard contains four worked examples: three grass‐covered Ground surfaces and a gravel road. The first example has been used to show that although use of consecutive measurements with a single microphone produces data that is usable with the template method, the phase information is not sufficiently robust to allow direct Impedance deduction. In the three grassland examples, the widely used single parameter model is found to overpredict the real and imaginary parts of Ground Impedance at lower frequencies. The...
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Sources and potential influences of uncertainty in Ground Impedance measurements and estimations
Journal of the Acoustical Society of America, 2008Co-Authors: Shahram Taherzadeh, Keith AttenboroughAbstract:Knowledge of acoustic Impedance of Ground surface is essential for determining noise levels outdoors. At distances up to a few hundred metres from the source Ground effect may be the dominant factor. The short‐range measurement of sound level spectra from an omni‐directional source has been used as a standard method to deduce the acoustic Impedance spectrum of Ground surfaces (e.g. ANSI S1.18, 1999). However, there remain a number of uncertainties in such measurement methods. For example, at low frequencies the difficulties in fitting theoretical or phenomenological models to short range data may result is a large uncertainty in predictions of sound levels at larger distances. Another source of uncertainty is the variability of the acoustic Impedance of apparently uniform Ground. Another potential influence on predictions of long term equivalent noise levels is seasonal variation. This paper discusses the extent and potential influences of such uncertainties in measured and deduced Ground Impedance spectra.
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Aspects of direct deduction of Ground Impedance
Journal of the Acoustical Society of America, 2007Co-Authors: Keith Attenborough, Shahram Taherzadeh, Gilles A. Daigle, Roland KruzeAbstract:ANSI S1.18 1998 offers a method for determining Ground Impedance by fitting data to templates of the magnitude of level difference obtained using a point source and two vertically separated microphones with specified geometries according the ‘‘acoustical‐softness’’ of the Ground. The ANSI working group on Ground Impedance is seeking to revise the current template method for deducing Ground Impedance by developing a practical method, based in fitting complex level difference spectra and without assuming any particular Impedance model. Both minimization and root finding techniques have been used in published laboratory experiments. The results of trial outdoor measurements in the UK, USA, Germany, and Canada are presented. Issues have arisen concerning phase matching of microphones, the signal processing instrumentation, the site and meteorological constraints, and the smoothness of the resulting data.
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Air¿Ground interaction in long range propagation of low frequency sound and vibration¿field tests and model verification
Applied Acoustics, 2005Co-Authors: Christian Madshus, Keith Attenborough, Finn Løvholt, Amir M. Kaynia, Lars R. Hole, Shahram TaherzadehAbstract:Abstract An extensive program of intermediate and long range impulsive sound propagation field tests have been conducted. The test program and the performed measurements are presented. Particular focus is given on the air–Ground interaction and its effect on low frequency sound and vibration propagation. It is found that the pressure wave interaction with the viscoelastic Rayleigh wave in the Ground may have a significant effect on the Ground Impedance and the sound and vibration propagation. This introduces an important mechanism not covered in commonly used Ground Impedance models. Numerical simulation models have been developed and verified against the test data. The Ground Impedance does not only effect the sound pressure propagation. If either acoustically induced Ground vibration, or Ground to building transmitted vibration, is to be considered, the acousto-seismic Impedance has a dramatic effect on the level of Ground vibration induced by a given sound pressure. For a site where Rayleigh wave interaction appears at the dominant frequencies of the sound pressure, the Ground vibration may be greater than a factor 100 (40 dB) than at a site with Ground conditions not making the interaction happen.
Kenneth E. Gilbert - One of the best experts on this subject based on the ideXlab platform.
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Application of the Beilis–Tappert parabolic equation method to sound propagation over irregular terrain
Journal of the Acoustical Society of America, 2012Co-Authors: Santosh Parakkal, Kenneth E. Gilbert, Xiao DiAbstract:The Beilis–Tappert (1979) parabolic equation method is attractive for irregular terrain because it treats surface variations in terms of a simple multiplicative factor (“phase screen”). However, implementing the exact sloping-surface Impedance condition is problematic if one wants the computational efficiency of a Fourier parabolic equation algorithm. This article investigates an approximate flat-Ground Impedance condition that allows the Beilis–Tappert phase screen method to be used with a Fourier algorithm without any added complications. The exact sloping-surface Impedance condition is derived and applied to propagation predictions over hills with maximum slopes from 5° to 22°. The predictions with the exact Impedance condition are compared to predictions using the approximate flat-Ground Impedance condition. It is found that for slopes less than 15°–20°, the flat-Ground Impedance condition is sufficiently accurate. For slopes greater than approximately 20°, the limiting factor on numerical accuracy is...
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Application of the Beilis and Tappert parabolic equation to long-range sound propagation over irregular terrain
Journal of the Acoustical Society of America, 2011Co-Authors: Santosh Parakkal, Kenneth E. Gilbert, Xiao DiAbstract:The Beilis and Tappert parabolic equation method is studied in the applications of sound propagation over irregular terrain. The exact Ground Impedance condition for porous Ground is derived and applied to propagation over hills with slopes from 5 ° to 22 °. It is found that for slopes less than approximately 20 °; the flat-Ground Impedance condition is sufficiently accurate. For slopes greater than about 20 °, the limiting factor on numerical accuracy becomes the narrow-angle approximation used in the Beilis and Tappert method. The generalized polar coordinate parabolic equation method (Polar-PE method) was developed partly to provide a very solid numerical benchmark to the Beilis and Tappert PE method.
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A direct method for measuring acoustic Ground Impedance in long-range propagation experiments
Journal of the Acoustical Society of America, 2010Co-Authors: Kenneth E. Gilbert, Carrick L. Talmadge, Garth Frazier, Roger WaxlerAbstract:A method is reported for determining Ground Impedance in long-range propagation experiments by using the definition of Impedance directly. The method is envisioned as way of measuring the impedence at multiple locations along the propagation path, using the signals broadcast during the experiment itself. In a short-range (10 m) test, the direct method was in good agreement with a more conventional model-based least-squares method. The utility of the direct method was demonstrated in a 400 m propagation experiment in a agricultural field. The resulting Impedance was consistent with the Impedance measured previously in the same field.
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Low‐frequency Ground Impedance from the surface mode
Journal of the Acoustical Society of America, 2005Co-Authors: Roger Waxler, Carrick L. Talmadge, Kenneth E. GilbertAbstract:At the last meeting of the Acoustical Society of America we presented data and theoretical analysis showing that pulse arrivals in downward refracting atmospheres have a universal low‐frequency tail. This tail was identified with the surface mode. In this presentation we discuss the possibility of obtaining low‐frequency Ground Impedance from the surface mode arrival. Signals received on a 10‐m vertical array are analyzed. The vertical waveform of the surface mode is obtained as a function of frequency and used to infer a Ground Impedance. The inferred Ground Impedance is compared to Impedances predicted by Ground Impedance models.
Alberto Borghetti - One of the best experts on this subject based on the ideXlab platform.
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Inverse Laplace Transform of Sunde’s Formula for the Ground Impedance of Buried Cables
2019 IEEE International Conference on Environment and Electrical Engineering and 2019 IEEE Industrial and Commercial Power Systems Europe (EEEIC I&CPS, 2019Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:The time-domain calculation of electromagnetic transients in multi-conductor lossy overhead lines and buried cables requires the evaluation of the transient Ground resistance matrix. For the case of overhead lines, analytical expressions for the transient Ground resistance obtained by solving the inverse Laplace transform of Sunde's formula have been recently presented. This paper presents the expressions obtained by the analytical inverse Laplace transform of Sunde's formula for the case of buried cables. The results provided by the proposed analytical expressions agree with those given by the numerical inverse transform of Sunde's formula. The new expressions are adopted for the calculation of the per-unit-length voltage drop in a multiconductor underGround line. The voltage drop waveforms are compared with those given by recently proposed time-domain analytical expressions that neglect displacement currents.
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Inverse Laplace Transform of the Ground Impedance Matrix of Overhead Lines
IEEE Transactions on Electromagnetic Compatibility, 2018Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:This letter deals with the calculation in time domain of the transient Ground resistance matrix of an overhead transmission line (TL). Each element of the matrix is evaluated by solving analytically the inverse Laplace transform of the general integral expressions of the Ground Impedance in frequency domain proposed by Sunde. The presented expressions are suitable for the direct implementation in an electromagnetic transient program (e.g., EMTP-like ones) based on a time domain solution of the TL's equations.
Fabio Tossani - One of the best experts on this subject based on the ideXlab platform.
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Inverse Laplace Transform of Sunde’s Formula for the Ground Impedance of Buried Cables
2019 IEEE International Conference on Environment and Electrical Engineering and 2019 IEEE Industrial and Commercial Power Systems Europe (EEEIC I&CPS, 2019Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:The time-domain calculation of electromagnetic transients in multi-conductor lossy overhead lines and buried cables requires the evaluation of the transient Ground resistance matrix. For the case of overhead lines, analytical expressions for the transient Ground resistance obtained by solving the inverse Laplace transform of Sunde's formula have been recently presented. This paper presents the expressions obtained by the analytical inverse Laplace transform of Sunde's formula for the case of buried cables. The results provided by the proposed analytical expressions agree with those given by the numerical inverse transform of Sunde's formula. The new expressions are adopted for the calculation of the per-unit-length voltage drop in a multiconductor underGround line. The voltage drop waveforms are compared with those given by recently proposed time-domain analytical expressions that neglect displacement currents.
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Inverse Laplace Transform of the Ground Impedance Matrix of Overhead Lines
IEEE Transactions on Electromagnetic Compatibility, 2018Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:This letter deals with the calculation in time domain of the transient Ground resistance matrix of an overhead transmission line (TL). Each element of the matrix is evaluated by solving analytically the inverse Laplace transform of the general integral expressions of the Ground Impedance in frequency domain proposed by Sunde. The presented expressions are suitable for the direct implementation in an electromagnetic transient program (e.g., EMTP-like ones) based on a time domain solution of the TL's equations.
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An Improved Approach for the Calculation of the Transient Ground Resistance Matrix of Multiconductor Lines
IEEE Transactions on Power Delivery, 2016Co-Authors: Fabio Tossani, Fabio Napolitano, F. Rachidi, C. A. NucciAbstract:The general integral expressions for the elements of the Ground Impedance matrix do not have an analytical inverse transform in the time domain. Therefore, the Ground transient resistance of a multiconductor line is commonly evaluated in the time domain by means of approximated expressions in order to avoid the numerical inverse fast Fourier transform burden. In this paper, we propose a new analytical approach for calculating the transient Ground resistance in the time domain that stands on the very accurate Sunde logarithmic expression for the Ground Impedance matrix of an overhead multiconductor line. The proposed analytical approach is adopted for calculating lightning induced voltages in a multiconductor overhead line. The results show that the proposed analytical formula is in perfect agreement with the numerical inverse Fourier transform of the general Sunde expression and, therefore, is more accurate than the approximated expressions available in the literature.
