Littérature scientifique sur le sujet « Infrasound, acoustics, density current »
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Articles de revues sur le sujet "Infrasound, acoustics, density current"
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Millet, Christophe, Francois Lott et Alvaro de la Camara. « How does knowledge of acoustics guide the parameterizations of gravity waves ? » Journal of the Acoustical Society of America 151, no 4 (avril 2022) : A160. http://dx.doi.org/10.1121/10.0010974.
Texte intégralRésumé :
Describing the statistics of gravity wave (GW) fields represents a major motivation for both current research on atmospheric GWs and long-range infrasound propagation. In practice, the probability density functions (PDF) of the momentum fluxes are estimated combining observations, numerical modelling, and theory. Numerical models (such as WRF) show that the PDFs vary in a robust way relative to the background local wind speed. For non-orographic GWs, these PDFs are approximated as lognormal distributions, with characteristics found to depend on the background wind speed. Studies show that some trends are not observed using a state-of-the-art stochastic parameterization of GWs, unless the phase velocities of GW sources (essentially tropospheric) are dramatically changed. As the vertical wavelength and the phase velocity are related to each other, such changes also affect the interaction between infrasound and lower-stratospheric GWs. Consequently, significant efforts have been made to use ground-based acoustic sensors for characterizing the GW sources, including the use of neural networks. This approach provides a promising way to describe the statistics of GW sources from ground-truth infrasound events and an additional constraint to tune stochastic parameterizations of GWs.
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Dannemann Dugick, Fransiska, Nora Wynn, Elijah Bird, Daniel Bowman, Melissa Wright, Douglas Seastrand et Jonathan Lees. « The Las Vegas infrasound array : Long term deployments for the characterization of urban environments ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A165. http://dx.doi.org/10.1121/10.0015901.
Texte intégralRésumé :
The Las Vegas Infrasound Array (LVIA) is a network of eleven infrasound sensors deployed from November 2019 through September 2022. While ambient infrasound noise in high and low-noise rural environments has been well characterized, little attention has focused on similar characterization in urban areas with presumed higher background noise levels. The LVIA long-term deployment provides an unprecedented opportunity to study urban infrasound and low frequency audio (20–500 Hz). In addition, large scale shutdowns due to the COVID-19 pandemic provide the ability to discriminate between background noise sources as closures reduced human-generated noise while natural signals remained stable. Within this presentation we will provide an overview of the LVIA installation, focusing on data quality. In addition, we will discuss comprehensive background noise models in urban regions, focusing on presenting probability density functions (PDFs) and median, 5th percentile, and 95th percentile amplitude values to evaluate variations in frequency and amplitude. We will summarize observed trends in background noise over time, highlighting sharp declines in acoustic power following COVID-19 shutdowns. Both sets of analyses will be combined to evaluate periodicities in urban acoustics throughout the city of Las Vegas. [ SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.]
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Donskoy, Dimitri M., et Benjamin A. Cray. « Eddy-current non-inertial displacement sensing for underwater infrasound measurements ». Journal of the Acoustical Society of America 129, no 6 (juin 2011) : EL254—EL259. http://dx.doi.org/10.1121/1.3577576.
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Van Zon, Arnout Tim, et Laeslo G. Evers. « A high‐density infrasound array of particle velocity sensors in the Netherlands ». Journal of the Acoustical Society of America 123, no 5 (mai 2008) : 3153. http://dx.doi.org/10.1121/1.2933178.
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Smith, Chad M., Thomas B. Gabrielson et B. J. Merchant. « Coherent infrasound generation using an air-propane burner ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A191. http://dx.doi.org/10.1121/10.0015989.
Texte intégralRésumé :
An invaluable tool in characterization of any receiver, propagation path, or detection system, is a source with known and repeatable signal characteristics. This talk will discuss development and evaluation of a coherent (non-explosive, periodic, with controlled duration) infrasound source with frequency capabilities in the sub-hertz to several hertz band. Design of a practical sound source within this band is a difficult engineering challenge. The simple source equation, which will govern any portable human-fabricated infrasound source due to the long wavelengths, shows this fundamental difficulty. As frequency decreases volume displacement must increase by the squared inverse factor of frequency in order to maintain an equal pressure amplitude at equal range. For this reason, the authors investigate utilizing the high energy density available in gas combustion to periodically displace large volumes of air within the open atmosphere. Prototype testing has verified the capability of generating continuous signals at a fundamental frequency of 0.25–1.5 Hz in the farfield—or ranges from the source where pressure and particle velocity are roughly in-phase. Harmonics of this fundamental are also generated throughout the 0.25–4.0 Hz band with reasonable signal-to-noise ratio. Development of the infrasound source prototype as well as experimental testing and results will be discussed.
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Green, David N., et Alexandra Nippress. « Investigating infrasonic signal amplitudes at the lateral edges of propagation ducts ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A164. http://dx.doi.org/10.1121/10.0015895.
Texte intégralRésumé :
Azimuthal variation in expected infrasonic signal strength is often modelled using Nx2D finite-frequency acoustic propagation models. Such simulations frequently exhibit rapid changes in transmission loss (>30 dB across 5°) at the lateral edges of stratospheric propagation ducts, due to the sensitivity of acoustic ducting to the along-path windspeed. The inclusion of microbarometers in the USArray Transportable Array, with an inter-station separation of ∼70 km, has provided improved resolution across the lateral extent of tropospheric and stratospheric ducts within which infrasound is propagated over local and near-regional distances (10s to 100s km). We analyse signals from two explosions that generated infrasound across a broad swath of USArray microbarometers. Signals from the October 2012 Camp Minden Ammunition Plant explosion, Louisiana, show smoothly varying amplitudes across the stratospheric duct edge while those from the October 2011 Atchison Grain Elevator explosion, Kansas, exhibit less azimuthal variation. These signals provide a basis for comparison with current numerical modelling methods. Understanding infrasonic amplitudes at the lateral duct edge is important for both accurate signal interpretation from events of interest and for detection capability assessments of infrasound sensor networks. UK Ministry of Defence © Crown Owned Copyright 2022/AWE
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Nippress, Alexandra, et David N. Green. « Updates to global empirical models for infrasonic signal celerity and backazimuth from ground truth data ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A191. http://dx.doi.org/10.1121/10.0015988.
Texte intégralRésumé :
Global empirical models for infrasonic signal celerity (the epicentral distance divided by the total travel time) and backazimuth deviation (the difference between the measured and predicted backazimuth assuming great circle propagation), are used for the association of infrasound automatic detections, event location and acoustic propagation simulation validation. Following a previous methodology to develop a regional celerity-range model (Nippress et al., 2014), we developed a software suite for consistent analysis of a global ground truth database, allowing estimation of empirical models for celerity and backazimuth. We observe 304 detections in the 0.32–1.28 Hz passband, with propagation path lengths of between 25 and 6280 km. Models derived from these observations suggest the backazimuth deviation distribution is range-independent, 92% of the detections studied have a deviation ≤ ±5º. However, the celerity model, produced through fitting the travel-times with a linear regression model, is range-dependent. The celerity model bounds are determined using a quantile regression fit to the travel-time residuals, and are consistent with the current understanding of infrasound propagation. At 10 + years since the publication of the last global celerity-range model, this study provides a timely update.UK Ministry of Defence © Crown Owned Copyright 2022/AWE
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Costantino, L., et P. Heinrich. « Tropical deep convection and density current signature in surface pressure : comparison between WRF model simulations and infrasound measurements ». Atmospheric Chemistry and Physics Discussions 13, no 6 (14 juin 2013) : 15993–6046. http://dx.doi.org/10.5194/acpd-13-15993-2013.
Texte intégralRésumé :
Abstract. Deep convection is a major atmospheric transport process in the tropics, affecting the global weather and the climate system. In the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project, we combine model simulations of tropical deep convection with in-situ ground measurements, from a IMS (International Monitoring System) infrasound station in Ivory Coast, to analyse the effects of density current propagation. The WRF (Weather Research and Forecasting) model is firstly run in a simplified (referred to as "idealized case") and highly resolved configuration, to explicitly account for convective dynamics. Then, a coarser threedimensional simulation (referred to as "real") is nudged towards meteorological re-analysis data, to compare the real case with the idealized model and in-situ observations. In the 2-D run, the evolution of a deep convective cloud generates a density current, that moves outward up to 30 km away from storm center. The increase in surface density (up to 18 g m−3 larger than surrounding air) is mostly due to the sudden temperature decrease (down to −2 °C, with respect to domain averaged value), from diabatic cooling by rain evaporation near ground level. It is accompanied by a dramatic decrease in relative humidity (down to −50%), buoyancy (down to −0.08 m s−2), equivalent potential temperature (25 °C lower than the PBL) and the rapid enhancement of horizontal wind speed (up to 15 m s−2). If temperature and density changes are strong enough, surface pressure gets largely affected and high frequency disturbances (up to several tens of Pa) can be detected, at the leading edges of density current. The moister and warmer air of subcloud layer is lifted up and replaced by a more stable flow. The resulting thermodynamical instabilities are shown to play a key role in triggering new convection. If the initial environment is sufficiently unstable, they can give rise to continuous updrafts that may lead to the transition from single-cell to multi-cell cloud systems, even without the presence of an initial wind shear. The overall consistence and similarity between idealized and real simulation, and the good agreement of real case with in-situ retrievals of temperature, pressure, wind speed and direction, seem to confirm the ability of 2-D and 3-D model to well reproduce convective dynamics. Surface pressure disturbances, simulated in both idealized and real cases as a consequence of cold pool propagation, are very similar to those recorded in Ivory Coast. Present results stress the direct link between mesoscale convective system activity and high-frequency surface pressure variations, suggesting the possibility of developing a new method for real-time rainstorm tracking, based on the ground-based infrasound monitoring of pressure field.
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Costantino, L., et P. Heinrich. « Tropical deep convection and density current signature in surface pressure : comparison between WRF model simulations and infrasound measurements ». Atmospheric Chemistry and Physics 14, no 6 (28 mars 2014) : 3113–32. http://dx.doi.org/10.5194/acp-14-3113-2014.
Texte intégralRésumé :
Abstract. Deep convection is a major atmospheric transport process in the tropics, affecting the global weather and the climate system. In the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project, we combine model simulations of tropical deep convection with in situ ground measurements from an IMS (International Monitoring System) infrasound station in the Ivory Coast to analyze the effects of density current propagation. The WRF (Weather Research and Forecasting) model is firstly run in a simplified (referred to as "idealized case") and highly resolved configuration to explicitly account for convective dynamics. Then, a coarser three-dimensional simulation (referred to as "real") is nudged towards meteorological reanalysis data in order to compare the real case with the idealized model and in situ observations. In the 2-D run, the evolution of a deep convective cloud generates a density current that moves outward up to 30 km away from storm center. The increase in surface density (up to 18 g m−3 larger than surrounding air) is mostly due to the sudden temperature decrease (down to −2 °C, with respect to the domain-averaged value) from diabatic cooling by rain evaporation near ground level. It is accompanied by a dramatic decrease in relative humidity (down to −50%), buoyancy (down to −0.08 m s−2), equivalent potential temperature (25 °C lower than the planetary boundary layer (PBL)) and the rapid enhancement of horizontal wind speed (up to 15 m s−2). If temperature and density changes are strong enough, surface pressure becomes largely affected and high-frequency disturbances (up to several tens of Pa) can be detected at the leading edges of density current. The moister and warmer air of subcloud layer is lifted up and replaced by a more stable flow. The resulting thermodynamical instabilities are shown to play a key role in triggering new convection. If the initial environment is sufficiently unstable, they can give rise to continuous updrafts that may lead to the transition from single-cell to multicell cloud systems, even without the presence of an initial wind shear. The overall consistence and similarity between idealized and real simulation, and the good agreement of the real case with in situ retrievals of temperature, pressure, wind speed and direction, seem to confirm the ability of 2-D and 3-D models to well reproduce convective dynamics. Surface pressure disturbances, simulated in both the idealized and real cases as a consequence of cold pool propagation, are very similar to those recorded in the Ivory Coast. Present results stress the direct link between mesoscale convective system activity and high-frequency surface pressure variations, suggesting the possibility of developing a new method for real-time rainstorm tracking based on the ground-based infrasound monitoring of pressure field.
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Poole, Michael, Pierre Weiss, Hector Sanchez Lopez, Michael Ng et Stuart Crozier. « Minimax current density coil design ». Journal of Physics D : Applied Physics 43, no 9 (15 février 2010) : 095001. http://dx.doi.org/10.1088/0022-3727/43/9/095001.
Texte intégralThèses sur le sujet "Infrasound, acoustics, density current"
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Barfucci, Giulia. « Modeling infrasonic sources related to density currents ». Doctoral thesis, 2019. http://hdl.handle.net/2158/1170483.
Texte intégralRésumé :
Pyroclastic Density Currents (PDCs) are among the most impressive, and hazardous phenomena of volcanic activity. Understanding their dynamics remains a major challenge. Gravity driven flows, dominated by the fluidparticles interaction, are in fact difficult to access for field measurements and complex to model and describe numerically. To date, the use of infrasonic arrays has shown to be able to detect and track PDC’s run-out automatically and in real-time, strongly improving the monitoring of this dangerous volcanic activity. However, relying only infrasonic (or seismic) signal we are not able yet to quantify physical parameters of the PDC, strongly limiting our ability to timely assess the correct volcanic hazard. We here present a new integrated approach that, by the aid of computational modeling, aims to find theoretical and empirical relations between the geophysical signal and the dynamical properties of the flow. In particular we show that, for a dilute PDC the upper and turbulent part of the flow is well developed and coupled with the atmosphere and thus is very effective in generating infrasound. We use the ASHEE model to simulate the dynamic evolution of the gas-particle density current, including the infrasound generation and propagation process. The relationship between PDCs dynamics and acoustic wave-field is explored by varying both numerical and initial conditions in a stratified atmosphere. Comparing synthetic signal with real infrasound
recorded associated with density currents activity, we find a strong correlation between the frequency content of the signal and the dimensions of the density current. Our study may have strong implication in terms of hazard assessment. Infrasonic signals could be used to remotely estimate physical properties of PDCs dynamics providing data to constrain observations and improve our ability to monitor such phenomena.
Actes de conférences sur le sujet "Infrasound, acoustics, density current"
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Costley, R. Daniel, Henry Diaz-Alvarez et Mihan H. McKenna. « Vibrational and Acoustical Analysis of Trussed Railroad Bridge Under Moving Loads ». Dans ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ncad2012-1490.
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A Finite Element model has been developed for a Pratt truss railroad bridge located at Ft. Leonard Wood, MO. This model was used to investigate the vibration responses of a bridge under vehicle loading. Modeling results have been obtained for a single axle with two wheels traversing the bridge at different speeds. The current model does not include the effects of vehicle suspension. Superposition of multiple axles has been used to represent a locomotive transiting the bridge. The output of the vibration response was used as an input to an acoustic FE model to determine which vibrational modes radiate infrasound. The vibration and acoustic models of the railroad bridge will be reviewed, and results from the analysis will be presented. Measurements from an accelerometer mounted on the bridge agree reasonably well with model results. Infrasound could potentially be used to remotely provide information on the capacity and number of the vehicles traversing the bridge and to monitor the bridge for significant structural damage.
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Harwood, Adrian R. G., et Iain D. J. Dupère. « Numerical Evaluation of the Compact Green’s Function for the Solution of Acoustic Flows ». Dans ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ncad2012-0785.
Texte intégralRésumé :
Due to the relatively tiny length scales involved, complex acoustic flows are not always suitable for traditional CFD codes. This paper develops a robust, semi-analytical numerical method for predicting sound fields based on the calculation of the compact Green’s function over a grid of source-observer positions. These calculations often involve singular functions, hence variations of the method are applied to several different 2D problems to investigate the impact of any singularities on the solution. The effect of grid point density and other parameters on execution time and accuracy are explored including the effects of approximating curved geometries using a number of straight lines. Comparison to known analytical solutions for the 2D problems is used to assess the accuracy of the method. For a typical application, we compute the far-field sound generated by a simple source in the vicinity of a compact, ‘2D’ fan blade in a duct. The current method demonstrates calculation of the compact Green’s function both accurately and robustly by avoiding the mapping from unbounded domains and the evaluation of potential models containing singularities. Both are seen as sources of error which have a widespread impact.
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Lee, Seok Woo, et Seung S. Lee. « PDMS Membrane Microactuator for Focal Tunable Microlens ». Dans ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14278.
Texte intégralRésumé :
In this paper, PDMS membrane for a large displacement is fabricated by new fabrication process which can be integrated with electrical components on substrates fabricated by conventional microfabrication processes and the performance of the membrane using electromagnetism was evaluated. Rectangular PDMS membranes are designed as 2mm and 3mm in width, respectively and are actuated by Lorentz force induced by current paths spread on the membrane. The PDMS membrane is fabricated by reducing a viscosity of uncured PDMS with dilution and spin coating on the substrate on which electric components generating Lorentz force. Finally, PDMS membrane including electric components is opened by a bulk micromachining. The device is tested in magnetic field induced by Nd-Fe-B magnet whose magnetic flux density is 90G. When applied currents are 20, 25, and 30mA, the maximum deflections of membranes are 1.21, 3.07, and 20.2μm for 1.5mm width membrane and 3.34, 31.0, and 50.9μm for width 3mm membrane, respectively. The large displacement PDMS membrane actuator has potentially various applications such as fluidics, optics, acoustics, and electronics. Currently, we are planning to measure the optical performance of the actuator as a focal tunable liquid lens.