This paper presents new experimental and numerical evidence that perforations in a pipe wall resu... more This paper presents new experimental and numerical evidence that perforations in a pipe wall result in a low-frequency bandgap within which sound waves rapidly attenuate. These perforations are modelled as an acoustically soft boundary condition on the pipe wall and show that a low frequency bandgap is created from 0 Hz. The upper bound of this bandgap is determined by the dimensions and separation of the perforations. An analytical model based on the transfer matrix method is proposed. This model is validated against numerical predictions for the pipe with varying perforation geometries. A numerical study is undertaken to model the effect of perforations with ideal acoustically soft boundary conditions and surrounded with an air gap. Close agreement is found between the numerical and analytical models. Experimental evidence shows that the width of the bandgap is accurately predicted with the numerical and analytical models.
INTER-NOISE and NOISE-CON Congress and Conference Proceedings
The attenuation of acoustic waves by silencers is typically achieved through the employment of ri... more The attenuation of acoustic waves by silencers is typically achieved through the employment of rigidly backed cavities, connected to a main waveguide by a perforated panel. This invokes a resonant response at frequencies determined by the dimensions of the perforation and the rigidly backed cavity. A limiting factor in this approach is that to achieve low frequency attenuation, either large cavity depths are required, which is often impractical, or narrow neck regions need to be used, where performance is limited due to the viscothermal losses. Within this paper, a non-rigidly backed perforated pipe is presented where the pressure release condition at each perforation creates an acoustic sound-soft boundary condition. By the introduction of sound-soft boundary conditions, a low frequency band gap is created as the first order mode is shifted to a non-zero value, the frequency of which is determined by the dimensions and separation of the perforations. Experimental results displaying...
The combined length of the sewerage and clean water pipe infrastructure in the UK is estimated to... more 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.
Acoustic insulation for pipelines has been historically constructed from mineral wool layers that... more Acoustic insulation for pipelines has been historically constructed from mineral wool layers that are surrounded by aluminium or steel jacketing. The thickness of the mineral wool and the cladding determines the overall acoustic performance of the insulation. Unfortunately, this system has a number of disadvantages related to its weight and corrosive properties. In addition re-radiation effects, acoustic energy transference into pipe supports and poor compliance resulting from the metal cladding, often reduces the performance of the insulation system. The desire to find an alternative system that will meet the required acoustic performance criteria is evident. Recent studies carried out by Bradford University and Armacell UK Ltd have shown that a new type of elastometric insulation composite can offer improved performance over traditional types of noise insulation used in the marine and offshore segments. It has been shown that a new, high performance, sound absorption material and ...
Denna artikel ger en kort oversikt av bulleratgarder, resulterande fran EU-projektet HOSANNA, for... more Denna artikel ger en kort oversikt av bulleratgarder, resulterande fran EU-projektet HOSANNA, for minskning av buller fran vag- och spartrafik under ljudets utbredning. Dessa verktyg inkluderar anvandning av ny skarmdesign, plantering av trad, forbattringar av mark- och vagytor samt vegetation pa byggnadsfasader och tak, med hjalp av naturmaterial, sasom vegetation, jord och andra substrat i kombination med atervunnet material och artificiella element. De akustiska insattningsdampningarna bedoms genom numeriska berakningar, perceptuella effekter och kostnadsnyttoanalys. En betydande minskning av buller fran vag- och spartrafik forutsags for ett 1-m-hogt urbant bullerskydd. Detta kan forbattras, upp till ca 10 dB insattningsdampning, genom att placera ytterligare skydd mellan korfalten. Ett 3 m brett och 0,3 m hogt rutnat, ett omsorgsfullt planterat 15 m brett tradbalte samt att ersatta 50 meter asfalterad mark med grasmark forutspas ge bullerminskningar om 5–8 dB, medan anvandning a...
The Journal of the Acoustical Society of America, 2021
Available data suggests that granulated aerogels can be of interest in terms of their sound absor... more Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter ...
Combined sewer overflow structures (CSO) play an important role in sewer networks. When the local... more Combined sewer overflow structures (CSO) play an important role in sewer networks. When the local capacity of a sewer system is exceeded during intense rainfall events, they act as a “safety valve” and discharge excess rainfall run-off and wastewater directly to a natural receiving water body, thus preventing widespread urban flooding. There is a regulatory requirement that solids in CSO spills must be small and their amount strictly controlled. Therefore, a vast majority of CSOs in the UK contain screens. This paper presents the results of a feasibility study of using low-cost, low-energy acoustic sensors to remotely assess the condition of CSO screens to move to cost-effective reactive maintenance visits. In situ trials were carried out in several CSOs to evaluate the performance of the acoustic sensor under realistic screen and flow conditions. The results demonstrate that the system is robust within ±2.5% to work successfully in a live CSO environment. The observed changes in th...
Journal of the Acoustical Society of America, 2016
Greening of urban spaces provides a number of environmental benefits. Living Green Walls (LGW) is... more Greening of urban spaces provides a number of environmental benefits. Living Green Walls (LGW) is a most typical example of greening which is also known for its ability to absorb unwanted noise. However, this ability of LGW to absorb noise is rather hard to quantify, because there is a lack of reliable experimental methods to measure it in-situ. This work reports on a new method to measure the absorption coefficient of LGW which makes use of a highly directional parametric transducer and acoustic intensity method. This method is tested under controlled laboratory conditions and in a typical street environment. The results of these experiments demonstrate the ability of the method to measure the absorption of a LGW. It also enables us to quantify the effects of the plant type and moisture content in the soil on the ability of the LGW to absorb sound. The proposed method has certain benefits over ISO354-2003 and CEN/TS 1793-5:2003 standard methods.
Data on the frequency-wavenumber spectra and dispersion relation of the dynamic water surface in ... more Data on the frequency-wavenumber spectra and dispersion relation of the dynamic water surface in an open channel flow are very scarce. In this work, new data on the frequency-wavenumber spectra were obtained in a rectangular laboratory flume with a rough bottom boundary, over a range of subcritical Froude numbers. These data were used to study the dispersion relation of the surface waves in such shallow turbulent water flows. The results show a complex pattern of surface waves, with a range of scales and velocities. When the mean surface velocity is faster than the minimum phase velocity of gravity-capillary waves, the wave pattern is dominated by stationary waves that interact with the static rough bed. There is a coherent three-dimensional pattern of radially propagating waves with the wavelength approximately equal to the wavelength of the stationary waves. Alongside these waves, there are freely propagating gravity-capillary waves that propagate mainly parallel to the mean flow,...
The Journal of the Acoustical Society of America, Feb 1, 2017
There is a considerable number of research publications on the characterization of porous media t... more There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of Science(TM) (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory mea...
The importance of sustainability in all aspects of procurement is gaining momentum in many countr... more The importance of sustainability in all aspects of procurement is gaining momentum in many countries and recently the EC has awarded a contract (QUIESST) to develop not only improved evaluation techniques for acoustic performance of noise reducing devices but also to examine optimisation and sustainability issues. This paper examines some options for “natural” forms of screening surface transport noise that might on the face of it be considered sustainable but until a number of factors are fully considered it is not clear how they compare with manufactured noise barriers. It also considers the psychological benefits of using natural solutions based on the “tranquillity rating prediction tool” recently developed at the University of Bradford.
This paper presents new experimental and numerical evidence that perforations in a pipe wall resu... more This paper presents new experimental and numerical evidence that perforations in a pipe wall result in a low-frequency bandgap within which sound waves rapidly attenuate. These perforations are modelled as an acoustically soft boundary condition on the pipe wall and show that a low frequency bandgap is created from 0 Hz. The upper bound of this bandgap is determined by the dimensions and separation of the perforations. An analytical model based on the transfer matrix method is proposed. This model is validated against numerical predictions for the pipe with varying perforation geometries. A numerical study is undertaken to model the effect of perforations with ideal acoustically soft boundary conditions and surrounded with an air gap. Close agreement is found between the numerical and analytical models. Experimental evidence shows that the width of the bandgap is accurately predicted with the numerical and analytical models.
INTER-NOISE and NOISE-CON Congress and Conference Proceedings
The attenuation of acoustic waves by silencers is typically achieved through the employment of ri... more The attenuation of acoustic waves by silencers is typically achieved through the employment of rigidly backed cavities, connected to a main waveguide by a perforated panel. This invokes a resonant response at frequencies determined by the dimensions of the perforation and the rigidly backed cavity. A limiting factor in this approach is that to achieve low frequency attenuation, either large cavity depths are required, which is often impractical, or narrow neck regions need to be used, where performance is limited due to the viscothermal losses. Within this paper, a non-rigidly backed perforated pipe is presented where the pressure release condition at each perforation creates an acoustic sound-soft boundary condition. By the introduction of sound-soft boundary conditions, a low frequency band gap is created as the first order mode is shifted to a non-zero value, the frequency of which is determined by the dimensions and separation of the perforations. Experimental results displaying...
The combined length of the sewerage and clean water pipe infrastructure in the UK is estimated to... more 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.
Acoustic insulation for pipelines has been historically constructed from mineral wool layers that... more Acoustic insulation for pipelines has been historically constructed from mineral wool layers that are surrounded by aluminium or steel jacketing. The thickness of the mineral wool and the cladding determines the overall acoustic performance of the insulation. Unfortunately, this system has a number of disadvantages related to its weight and corrosive properties. In addition re-radiation effects, acoustic energy transference into pipe supports and poor compliance resulting from the metal cladding, often reduces the performance of the insulation system. The desire to find an alternative system that will meet the required acoustic performance criteria is evident. Recent studies carried out by Bradford University and Armacell UK Ltd have shown that a new type of elastometric insulation composite can offer improved performance over traditional types of noise insulation used in the marine and offshore segments. It has been shown that a new, high performance, sound absorption material and ...
Denna artikel ger en kort oversikt av bulleratgarder, resulterande fran EU-projektet HOSANNA, for... more Denna artikel ger en kort oversikt av bulleratgarder, resulterande fran EU-projektet HOSANNA, for minskning av buller fran vag- och spartrafik under ljudets utbredning. Dessa verktyg inkluderar anvandning av ny skarmdesign, plantering av trad, forbattringar av mark- och vagytor samt vegetation pa byggnadsfasader och tak, med hjalp av naturmaterial, sasom vegetation, jord och andra substrat i kombination med atervunnet material och artificiella element. De akustiska insattningsdampningarna bedoms genom numeriska berakningar, perceptuella effekter och kostnadsnyttoanalys. En betydande minskning av buller fran vag- och spartrafik forutsags for ett 1-m-hogt urbant bullerskydd. Detta kan forbattras, upp till ca 10 dB insattningsdampning, genom att placera ytterligare skydd mellan korfalten. Ett 3 m brett och 0,3 m hogt rutnat, ett omsorgsfullt planterat 15 m brett tradbalte samt att ersatta 50 meter asfalterad mark med grasmark forutspas ge bullerminskningar om 5–8 dB, medan anvandning a...
The Journal of the Acoustical Society of America, 2021
Available data suggests that granulated aerogels can be of interest in terms of their sound absor... more Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter ...
Combined sewer overflow structures (CSO) play an important role in sewer networks. When the local... more Combined sewer overflow structures (CSO) play an important role in sewer networks. When the local capacity of a sewer system is exceeded during intense rainfall events, they act as a “safety valve” and discharge excess rainfall run-off and wastewater directly to a natural receiving water body, thus preventing widespread urban flooding. There is a regulatory requirement that solids in CSO spills must be small and their amount strictly controlled. Therefore, a vast majority of CSOs in the UK contain screens. This paper presents the results of a feasibility study of using low-cost, low-energy acoustic sensors to remotely assess the condition of CSO screens to move to cost-effective reactive maintenance visits. In situ trials were carried out in several CSOs to evaluate the performance of the acoustic sensor under realistic screen and flow conditions. The results demonstrate that the system is robust within ±2.5% to work successfully in a live CSO environment. The observed changes in th...
Journal of the Acoustical Society of America, 2016
Greening of urban spaces provides a number of environmental benefits. Living Green Walls (LGW) is... more Greening of urban spaces provides a number of environmental benefits. Living Green Walls (LGW) is a most typical example of greening which is also known for its ability to absorb unwanted noise. However, this ability of LGW to absorb noise is rather hard to quantify, because there is a lack of reliable experimental methods to measure it in-situ. This work reports on a new method to measure the absorption coefficient of LGW which makes use of a highly directional parametric transducer and acoustic intensity method. This method is tested under controlled laboratory conditions and in a typical street environment. The results of these experiments demonstrate the ability of the method to measure the absorption of a LGW. It also enables us to quantify the effects of the plant type and moisture content in the soil on the ability of the LGW to absorb sound. The proposed method has certain benefits over ISO354-2003 and CEN/TS 1793-5:2003 standard methods.
Data on the frequency-wavenumber spectra and dispersion relation of the dynamic water surface in ... more Data on the frequency-wavenumber spectra and dispersion relation of the dynamic water surface in an open channel flow are very scarce. In this work, new data on the frequency-wavenumber spectra were obtained in a rectangular laboratory flume with a rough bottom boundary, over a range of subcritical Froude numbers. These data were used to study the dispersion relation of the surface waves in such shallow turbulent water flows. The results show a complex pattern of surface waves, with a range of scales and velocities. When the mean surface velocity is faster than the minimum phase velocity of gravity-capillary waves, the wave pattern is dominated by stationary waves that interact with the static rough bed. There is a coherent three-dimensional pattern of radially propagating waves with the wavelength approximately equal to the wavelength of the stationary waves. Alongside these waves, there are freely propagating gravity-capillary waves that propagate mainly parallel to the mean flow,...
The Journal of the Acoustical Society of America, Feb 1, 2017
There is a considerable number of research publications on the characterization of porous media t... more There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of Science(TM) (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory mea...
The importance of sustainability in all aspects of procurement is gaining momentum in many countr... more The importance of sustainability in all aspects of procurement is gaining momentum in many countries and recently the EC has awarded a contract (QUIESST) to develop not only improved evaluation techniques for acoustic performance of noise reducing devices but also to examine optimisation and sustainability issues. This paper examines some options for “natural” forms of screening surface transport noise that might on the face of it be considered sustainable but until a number of factors are fully considered it is not clear how they compare with manufactured noise barriers. It also considers the psychological benefits of using natural solutions based on the “tranquillity rating prediction tool” recently developed at the University of Bradford.
Uploads