Journal articles on the topic 'Dynamic meteorology Air entrainment'
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1
Vandre, E., M. S. Carvalho, and S. Kumar. "Characteristics of air entrainment during dynamic wetting failure along a planar substrate." Journal of Fluid Mechanics 747 (April 14, 2014): 119–40. http://dx.doi.org/10.1017/jfm.2014.110.
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AbstractCharacteristic substrate speeds and meniscus shapes associated with the onset of air entrainment are studied during dynamic wetting failure along a planar substrate. Using high-speed video, the behaviour of the dynamic contact line (DCL) is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above some critical substrate speed. Meniscus confinement within a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a wide range of liquid viscosities, expanding upon the findings of Vandre, Carvalho & Kumar (J. Fluid Mech., vol. 707, 2012, pp. 496–520). A pressurized liquid reservoir controls the meniscus position within the confinement gap. It is found that liquid pressurization further postpones air entrainment when the meniscus is located near a sharp corner along the stationary plate. Meniscus shapes recorded near the DCL demonstrate that operating conditions influence the size of entrained air films, with smaller films appearing in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, suggesting that strong air stresses near the DCL trigger the onset of air entrainment.
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Kamal, Catherine, James E. Sprittles, Jacco H. Snoeijer, and Jens Eggers. "Dynamic drying transition via free-surface cusps." Journal of Fluid Mechanics 858 (November 12, 2018): 760–86. http://dx.doi.org/10.1017/jfm.2018.794.
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We study air entrainment by a solid plate plunging into a viscous liquid, theoretically and numerically. At dimensionless speeds $Ca=U\unicode[STIX]{x1D702}/\unicode[STIX]{x1D6FE}$ of order unity, a near-cusp forms due to the presence of a moving contact line. The radius of curvature of the cusp’s tip scales with the slip length multiplied by an exponential of $-Ca$. The pressure from the air flow drawn inside the cusp leads to a bifurcation, at which air is entrained, i.e. there is ‘wetting failure’. We develop an analytical theory of the threshold to air entrainment, which predicts the critical capillary number to depend logarithmically on the viscosity ratio, with corrections coming from the slip in the gas phase.
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Andre´s, Luis San, and Sergio E. Diaz. "Flow Visualization and Forces From a Squeeze Film Damper Operating With Natural Air Entrainment." Journal of Tribology 125, no. 2 (March 19, 2003): 325–33. http://dx.doi.org/10.1115/1.1510878.
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Measurements of dynamic film pressures and high-speed photographs of the flow field in an open-ended Squeeze Film Damper (SFD) operating with natural free air entrainment are presented for increasing whirl frequencies (8.33–50 Hz), and a range of feed pressures to 250 kPa (37 psig). The flow conditions range from lubricant starvation (air ingestion) to a fully flooded discharge operation. The test dynamic pressures and video recordings show that air entrainment leads to large and irregular gas fingering and striation patterns. This is a natural phenomenon in SFDs operating with low levels of external pressurization (reduced lubricant through flow rates). Air ingestion and entrapment becomes more prevalent as the whirl frequency raises, and increasing the feed pressure aids little to ameliorate the loss in dynamic forced performance. As a result of the severity of air entrainment, experimentally estimated damping forces decrease steadily as the whirl frequency (operating speed) increases.
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Sprittles, James E. "Air entrainment in dynamic wetting: Knudsen effects and the influence of ambient air pressure." Journal of Fluid Mechanics 769 (March 25, 2015): 444–81. http://dx.doi.org/10.1017/jfm.2015.121.
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Recent experiments on coating flows and liquid drop impact both demonstrate that wetting failures caused by air entrainment can be suppressed by reducing the ambient gas pressure. Here, it is shown that non-equilibrium effects in the gas can account for this behaviour, with ambient pressure reductions increasing the mean free path of the gas and hence the Knudsen number $\mathit{Kn}$. These effects first manifest themselves through Maxwell slip at the boundaries of the gas, so that for sufficiently small $\mathit{Kn}$ they can be incorporated into a continuum model for dynamic wetting flows. The resulting mathematical model contains flow structures on the nano-, micro- and millimetre scales and is implemented into a computational platform developed specifically for such multiscale phenomena. The coating flow geometry is used to show that for a fixed gas–liquid–solid system (a) the increased Maxwell slip at reduced pressures can substantially delay air entrainment, i.e. increase the ‘maximum speed of wetting’, (b) unbounded maximum speeds are obtained, as the pressure is reduced only when slip at the gas–liquid interface is allowed for, and (c) the observed behaviour can be rationalised by studying the dynamics of the gas film in front of the moving contact line. A direct comparison with experimental results obtained from a dip-coating process shows that the model recovers most trends but does not accurately predict some of the high viscosity data at reduced pressures. This discrepancy occurs because the gas flow enters the ‘transition regime’, so that more complex descriptions of its non-equilibrium nature are required. Finally, by collapsing onto a master curve experimental data obtained for drop impact in a reduced pressure gas, it is shown that the same physical mechanisms are also likely to govern splash suppression phenomena.
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Esmail, M. N., and M. T. Ghannam. "Air entrainment and dynamic contact angles in hydrodynamics of liquid coating." Canadian Journal of Chemical Engineering 68, no. 2 (April 1990): 197–203. http://dx.doi.org/10.1002/cjce.5450680203.
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Zhang, Wei, Bingbing Han, Kunpeng Zhang, and Qian Ding. "Dynamic Analysis of a Rotor System Supported on Squeeze Film Damper with Air Entrainment." International Journal of Bifurcation and Chaos 27, no. 14 (December 30, 2017): 1750212. http://dx.doi.org/10.1142/s0218127417502121.
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Squeeze film dampers (SFDs) are widely used in compressors and turbines to suppress the vibration while traversing critical speeds. In practical applications, air ingestion from the outside environment and cavitation may lead to a foamy lubricant that weakens oil film damping and dynamic performance of rotor system. In this paper, a rigid rotor model is established considering both lateral and pitching vibration under different imbalance excitations to evaluate the effect of air entrainment on rotor system. Tests with three different imbalances are carried out on a rotor-SFD apparatus. Volume controlled air in mixture ranging from pure oil to all air are supplied to the SFD. The transient response of rotor is measured in the experiments. The results show that two-phase flow produces significant influence on the system stability and dynamical response. The damping properties are weakened by entrained air, such as the damping on high frequency components of rolling ball bearing. Super-harmonic resonance and bifurcation are observed, as well as the low frequency components due to air entrainment.
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Wang, Yan, Xiao-dong Ren, Xue-song Li, and Chun-wei Gu. "Numerical investigation of subsynchronous vibration in floating ring bearings." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, no. 11 (January 19, 2018): 1390–401. http://dx.doi.org/10.1177/1350650117753915.
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Floating ring bearings are popular among turbochargers due to their simplicity and reliability. The disappearance of subsynchronous vibration with the increase of shaft speed in a low oil-supplied pressure floating ring bearing is reported by Hatakenaka and Yanai. This finding may help eliminate the noise and decrease the loss of turbochargers. This work aims to explain this phenomenon in the low oil-supplied floating ring bearing using computational fluid dynamic. Steady computational fluid dynamic calculation is conducted to validate the effect of air entrainment. Transient computational fluid dynamic calculation method with mesh motion method is established. The subsynchronous vibration of the shaft can be obtained by discrete Fourier transform analysis. The results are validated by comparing them with those in the literature. It is found that the disappearance of the subsynchronous vibration is the result of the change in lubricant properties caused by the air entrainment.
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San Andre´s, Luis, and Oscar De Santiago. "Forced Response of a Squeeze Film Damper and Identification of Force Coefficients From Large Orbital Motions." Journal of Tribology 126, no. 2 (April 1, 2004): 292–300. http://dx.doi.org/10.1115/1.1611503.
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Experimentally derived damping and inertia force coefficients from a test squeeze film damper for various dynamic load conditions are reported. Shakers exert single frequency loads and induce circular and elliptical orbits of increasing amplitudes. Measurements of the applied loads, bearing displacements and accelerations permit the identification of force coefficients for operation at three whirl frequencies (40, 50, and 60 Hz) and increasing lubricant temperatures. Measurements of film pressures reveal an early onset of air ingestion. Identified damping force coefficients agree well with predictions based on the short length bearing model only if an effective damper length is used. A published two-phase flow model for air entrainment allows the prediction of the effective damper length, and which ranges from 82% to 78% of the damper physical length as the whirl excitation frequency increases. Justifications for the effective length or reduced (flow) viscosity follow from the small through flow rate, not large enough to offset the dynamic volume changes. The measurements and analysis thus show the pervasiveness of air entrainment, whose effect increases with the amplitude and frequency of the dynamic journal motions. Identified inertia coefficients are approximately twice as large as those derived from classical theory.
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Katta, V. R., and W. M. Roquemore. "Numerical Studies on Trapped-Vortex Concepts for Stable Combustion." Journal of Engineering for Gas Turbines and Power 120, no. 1 (January 1, 1998): 60–68. http://dx.doi.org/10.1115/1.2818088.
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Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.
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Diaz, S. E., and L. A. San Andre´s. "Air Entrainment Versus Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of Their Fundamental Differences." Journal of Engineering for Gas Turbines and Power 123, no. 4 (October 1, 1998): 871–77. http://dx.doi.org/10.1115/1.1383258.
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Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in air-breathing engines and process gas compressors. However, SFDs are prone to develop a flow regime where the ingestion of air leads to the formation of a bubbly lubricant. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling, although actual practice demonstrates that it greatly reduces the damper force response. Measurements of film pressures in a test SFD describing circular centered orbits at whirl frequencies varying from 0 to 100 Hz are presented for fully flooded and vented discharge operating conditions. The experiments demonstrate that operation with low levels of external pressurization, moderate to large whirl frequencies, and lubricant discharge to ambient leads to the entrapment of air within the damper film lands. The experiments also elucidate fundamental differences in the generation of film pressures and forces for operation in a flooded condition that evidences vapor cavitation. Damping forces for the vented end with air entrainment are just 15 percent of the forces measured for the flooded damper. Further measurements at constant whirl frequencies demonstrate that increasing the lubricant pressure supply retards the onset of air entrainment. Classical fluid film cavitation models predict well the pressures and forces for the lubricant vapor cavitation condition. However, prevailing models fail to reproduce the dynamic forced response of vented (open-ended) SFDs where air entrainment makes a foamy lubricant, which limits severely the damper film pressures and forces.
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Kalmus, Peter, Matthew Lebsock, and João Teixeira. "Observational Boundary Layer Energy and Water Budgets of the Stratocumulus-to-Cumulus Transition." Journal of Climate 27, no. 24 (December 10, 2014): 9155–70. http://dx.doi.org/10.1175/jcli-d-14-00242.1.
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Abstract The authors estimate summer mean boundary layer water and energy budgets along a northeast Pacific transect from 35° to 15°N, which includes the transition from marine stratocumulus to trade cumulus clouds. Observational data is used from three A-Train satellites, Aqua, CloudSat, and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO); data derived from GPS signals intercepted by microsatellites of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC); and the container-ship-based Marine Atmospheric Radiation Measurement Program (ARM) Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI) Investigation of Clouds (MAGIC) campaign. These are unique satellite and shipborne observations providing the first global-scale observations of light precipitation, new vertically resolved radiation budget products derived from the active sensors, and well-sampled radiosonde data near the transect. In addition to the observations, the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) fields are utilized to estimate the budgets. Both budgets approach within 3 W m−2 averaged along the transect, although uncertainty estimates from the study are much larger than this residual. A mean entrainment rate along the transect of mm s−1 is also estimated. A gradual transition is observed in the climatological mean from the stratocumulus regime to the cumulus regime characterized by an increase in boundary layer height, latent heat flux, rain, and the horizontal advection of dry air and a decrease in entrainment of warm dry air.
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Cai, Lin, Jin Li Wang, and Hong Tao Zheng. "Experiment and Numerical Study of Annular Flow Entrainment Mechanism in Oil-Air Lubrication Pipe." Advanced Materials Research 189-193 (February 2011): 1782–85. http://dx.doi.org/10.4028/www.scientific.net/amr.189-193.1782.
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Annular flow is a based flow pattern of two-phase in the pipe, and oil air flow in delivery pipe of Oil-Air lubrication (OAL) system is one of them. In order to learn the entrainment mechanism of annular flow in OAL pipe, both experiment adopted observational method and numerical simulation used Computational Fluid Dynamic (CFD) were carried out. The pipe diameter is 4mm and Volume of Fluid (VOF) model was used for two phase flow in simulation. The results shows that: it is a wave-annular flow in OAL pipe, and the oil wave in pipe is affected by air, when air velocity is low, the wave is clearly and regularly, but when air velocity increases, the wave become turbulent. When oil or air flow rate increases, the shear stress of pipe wall will be increased, the wave height will be increased as air velocity increases.
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Otte, T. L., and J. E. Pleim. "The Meteorology-Chemistry Interface Processor (MCIP) for the CMAQ modeling system." Geoscientific Model Development Discussions 2, no. 2 (December 15, 2009): 1449–86. http://dx.doi.org/10.5194/gmdd-2-1449-2009.
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Abstract. The Community Multiscale Air Quality (CMAQ) modeling system, a state-of-the-science regional air quality modeling system developed by the US Environmental Protection Agency, is being used for a variety of environmental modeling problems including regulatory applications, air quality forecasting, evaluation of emissions control strategies, process-level research, and interactions of global climate change and regional air quality. The Meteorology-Chemistry Interface Processor (MCIP) is a vital piece of software within the CMAQ modeling system that serves to, as best as possible, maintain dynamic consistency between the meteorological model and the chemical transport model. MCIP acts as both a post-processor to the meteorological model and a pre-processor to the CMAQ modeling system. MCIP's functions are to ingest the meteorological model output fields in their native formats, perform horizontal and vertical coordinate transformations, diagnose additional atmospheric fields, define gridding parameters, and prepare the meteorological fields in a form required by the CMAQ modeling system. This paper provides an updated overview of MCIP, documenting the scientific changes that have been made since it was first released as part of the CMAQ modeling system in 1998.
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Morrison, Hugh. "An Analytic Description of the Structure and Evolution of Growing Deep Cumulus Updrafts." Journal of the Atmospheric Sciences 74, no. 3 (March 1, 2017): 809–34. http://dx.doi.org/10.1175/jas-d-16-0234.1.
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Abstract New theoretical analytic expressions are derived for the evolution of a passive scalar, buoyancy, and vertical velocity in growing, entraining moist deep convective updrafts. These expressions are a function of updraft radius, height, convective available potential energy (CAPE), and environmental relative humidity RH. They are quantitatively consistent with idealized three-dimensional moist updraft simulations with varying updraft sizes and in environments with differing RH. In particular, the analytic expressions capture the rapid decrease of buoyancy with height due to entrainment for narrow updrafts in a dry environment despite large CAPE. In contrast to the standard entraining-plume model, the theoretical expressions also describe the effects of engulfment of environmental air between the level of free convection (LFC) and height of maximum buoyancy (HMB) required by mass continuity to balance upward acceleration of updraft air (i.e., dynamic entrainment). This organized inflow sharpens horizontal gradients, thereby enhancing smaller-scale lateral turbulent mixing below the HMB. For narrow updrafts in a dry environment, this enhanced mixing leads to a negatively buoyant region between the LFC and HMB, effectively cutting off the region of positive buoyancy at the HMB from below so that the updraft structure resembles a rising thermal rather than a plume. Thus, it is proposed that a transition from plume-like to thermal-like structure is driven by dynamic entrainment and depends on updraft width (relative to height) and environmental RH. These results help to bridge the entraining-plume and rising-thermal conceptual models of moist convection.
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Liu, Chen-Yu, Eric Vandre, Marcio S. Carvalho, and Satish Kumar. "Dynamic wetting failure in surfactant solutions." Journal of Fluid Mechanics 789 (January 19, 2016): 285–309. http://dx.doi.org/10.1017/jfm.2015.739.
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The influence of insoluble surfactants on dynamic wetting failure during displacement of Newtonian fluids in a rectangular channel is studied in this work. A hydrodynamic model for steady Stokes flows of dilute surfactant solutions is developed and evaluated using three approaches: (i) a one-dimensional (1D) lubrication-type approach, (ii) a novel hybrid of a 1D description of the receding phase and a 2D description of the advancing phase, and (iii) an asymptotic theory of Cox (J. Fluid Mech., vol. 168, 1986b, pp. 195–220). Steady-state solution families in the form of macroscopic contact angles as a function of the capillary number are determined and limit points are identified. When air is the receding fluid, Marangoni stresses are found to increase the receding-phase pressure gradients near the contact line by thinning the air film without significantly changing the capillary-pressure gradients there. As a consequence, the limit points shift to lower capillary numbers and the onset of wetting failure is promoted. The model predictions are then used to interpret decades-old experimental observations concerning the influence of surfactants on air entrainment (Burley & Kennedy, Chem. Engng Sci., vol. 31, 1976, pp. 901–911). In addition to being a computationally efficient alternative for the rectangular geometries considered here, the hybrid modelling approach developed in this paper could also be applied to more complicated geometries where a thin air layer is present near a contact line.
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Barth, M. C., J. Lee, A. Hodzic, G. Pfister, W. C. Skamarock, J. Worden, J. Wong, and D. Noone. "Thunderstorms and upper troposphere chemistry during the early stages of the 2006 North American Monsoon." Atmospheric Chemistry and Physics Discussions 12, no. 7 (July 4, 2012): 16407–55. http://dx.doi.org/10.5194/acpd-12-16407-2012.
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Abstract. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is applied at 4 km horizontal grid spacing to study the meteorology and chemistry over the continental US and Northern Mexico region for the 15 July to 7 August 2006 period, which coincides with the early stages of the North American Monsoon. Evaluation of model results shows that WRF-Chem reasonably represents the large-scale meteorology and strong convective storms, but tends to overestimate weak convection. In the upper troposphere, the WRF-Chem model predicts ozone and carbon monoxide (CO) to within 10–20% of aircraft and sonde measurements. However, the frequency distribution from satellite data indicates that WRF-Chem is lofting too much CO from the boundary layer (BL). Because ozone mixing ratios agree well with these same satellite data, it suggests that chemical production of O3 in the model is overpredicted and compensates for the excess convective lofting of BL air. Analysis of different geographic regions (West Coast, Rocky Mountains, Central Plains, Midwest, and Gulf Coast) reveals that much of the convective transport occurs in the Rocky Mountains, while much of the UT ozone chemical production occurs over the Gulf Coast and Midwest regions where both CO and volatile organic compounds (VOCs) are abundant in the upper troposphere and promote the production of peroxy radicals. In all regions most of the ozone chemical production occurs within 24 h of the air being lofted from the boundary layer. In addition, analysis of the anticyclone and adjacent air indicates that ozone mixing ratios within the anticyclone region associated with the North American Monsoon and just outside the anticyclone are similar. Increases of O3 within the anticyclone are strongly coincident with entrainment of stratospheric air into the anticyclone, but also are from in situ O3 chemical production. In situ O3 production is up to 17% greater within the anticyclone than just outside the anticyclone when the anticyclone is over the Southern US indicating that the enhancement of O3 is most pronounced over regions with abundant VOCs.
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Sun, D. C., and D. E. Brewe. "Two Reference Time Scales for Studying the Dynamic Cavitation of Liquid Films." Journal of Tribology 114, no. 3 (July 1, 1992): 612–15. http://dx.doi.org/10.1115/1.2920925.
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Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.
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San Andres, Luis, and Oscar C. De Santiago. "Dynamic Response of Squeeze Film Dampers Operating With Bubbly Mixtures." Journal of Engineering for Gas Turbines and Power 126, no. 2 (April 1, 2004): 408–15. http://dx.doi.org/10.1115/1.1690770.
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Squeeze film dampers (SFDs) aid to attenuate vibrations in compressors and turbines while traversing critical speeds. In actual applications, gas ingestion from the environment may lead to the formation of a foamy lubricant that degrades the rotor/bearing system dynamic performance. Impact and imbalance response tests conducted on a rigid rotor supported on SFDs, and aimed to emulate the pervasive effect of air ingestion into the damper film lands, are reported. Two types of squeeze film damper support the test rotor, one is a conventional cylindrical design with a squirrel cage-type elastic support, and the other is a compact four-pad damper with integral wire EDM elastic supports. Both dampers have identical diameter and radial clearance. Controlled (air in oil) mixtures ranging from pure oil to all air conditions are supplied to the SFDs, and measurements of the transient rotor response to calibrated impact loads are conducted. System damping coefficients, identified from acceleration/load transfer functions, decrease steadily as the air content in the mixture increases. However, measurements of the rotor synchronous imbalance response conducted with a lubricant bubbly mixture (50% air volume) show little difference with test results obtained with pure lubricant supplied to the dampers. The experimental results show that air entrainment is process and device-dependent, and that small amounts of lubricant enable the effective action of SFDs when the rotor traverses a critical speed.
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Fang, Xiang, Anthony Chun Yin Yuen, Guan Heng Yeoh, Eric Wai Ming Lee, and Sherman Chi P. Cheung. "Capturing the Swirling Vortex and the Impact of Ventilation Conditions on Small-Scale Fire Whirls." Applied Sciences 10, no. 10 (May 15, 2020): 3428. http://dx.doi.org/10.3390/app10103428.
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The fundamental flow structure and temperature distribution of small-scale fire whirls, including tangential and axial velocities, temperature variation, and air entrainment in the lower boundary layer, were successfully captured using a generic fire field model with large eddy simulation (LES) turbulence closure. Numerical predictions were validated thoroughly against two small-scale experimental measurements, where detailed temperature and velocity distributions were recorded. Good agreement between numerical and experimental results was achieved. Normalization was also performed to compare the numerical predictions with the empirical correlations by Lei et al. (2015) developed from medium-scale fire whirl measurements. The transient development stages of small-scale fire whirls and the impact of air entrainment on the stability of the fire whirls were also investigated based on the validated numerical results. The numerical validations showed the potential of the current LES fire field model in capturing the dynamic behaviour of the fire whirl plume and performing a quantitative analysis on its onset criteria and combustion dynamics in future.
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Diaz, Sergio, and Luis San Andre´s. "A Model for Squeeze Film Dampers Operating With Air Entrainment and Validation With Experiments." Journal of Tribology 123, no. 1 (September 19, 2000): 125–33. http://dx.doi.org/10.1115/1.1330742.
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Squeeze film dampers (SFDs) reduce vibrations and aid in suppressing instabilities in high performance rotor-bearing systems. However, air ingestion and entrapment, pervasive in open-ended dampers with low supply pressures, leads to a bubbly lubricant that severely reduces the dynamic film forces and the overall damping capability. Analyses based on conventional film rupture models, vapor or gaseous lubricant cavitation, fail to predict the actual performance of SFDs, and thus lack credibility in engineering practice. A modified Reynolds equation for prediction of the pressure in a homogeneous bubbly mixture flow is advanced along with an empirical formula for estimation of the amount of air entrained in an open-ended damper. Careful experimentation in a test SFD operating with controlled bubbly mixtures and freely entrained air evidenced similar physical behavior, guided the analytical developments, and provided the basis for validation of the model forwarded. Comparisons of predictions and test results show a fair correlation. A simple equation to predict the amount of air ingestion is also advanced in terms of the damper geometry, supplied flow and operating conditions. The criterion may lack practical implementation since the persistence of air entrainment increases with the frequency and amplitude of journal motions, unless enough lubricant is supplied at all operating conditions.
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Otte, T. L., and J. E. Pleim. "The Meteorology-Chemistry Interface Processor (MCIP) for the CMAQ modeling system: updates through MCIPv3.4.1." Geoscientific Model Development 3, no. 1 (April 7, 2010): 243–56. http://dx.doi.org/10.5194/gmd-3-243-2010.
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Abstract. The Community Multiscale Air Quality (CMAQ) modeling system, a state-of-the-science regional air quality modeling system developed by the US Environmental Protection Agency, is being used for a variety of environmental modeling problems including regulatory applications, air quality forecasting, evaluation of emissions control strategies, process-level research, and interactions of global climate change and regional air quality. The Meteorology-Chemistry Interface Processor (MCIP) is a vital piece of software within the CMAQ modeling system that serves to, as best as possible, maintain dynamic consistency between the meteorological model and the chemical transport model (CTM). MCIP acts as both a post-processor to the meteorological model and a pre-processor to the emissions and the CTM in the CMAQ modeling system. MCIP's functions are to ingest the meteorological model output fields in their native formats, perform horizontal and vertical coordinate transformations, diagnose additional atmospheric fields, define gridding parameters, and prepare the meteorological fields in a form required by the CMAQ modeling system. This paper provides an updated overview of MCIP, documenting the scientific changes that have been made since it was first released as part of the CMAQ modeling system in 1998.
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Jia, Hailing, Xiaoyan Ma, and Yangang Liu. "Exploring aerosol–cloud interaction using VOCALS-REx aircraft measurements." Atmospheric Chemistry and Physics 19, no. 12 (June 18, 2019): 7955–71. http://dx.doi.org/10.5194/acp-19-7955-2019.
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Abstract. In situ aircraft measurements obtained during the VAMOS (Variability of the American Monsoons) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field campaign are analyzed to study the aerosol–cloud interactions in the stratocumulus clouds over the southeastern Pacific Ocean (SEP), with a focus on three understudied topics (separation of aerosol effects from dynamic effects, dispersion effects, and turbulent entrainment-mixing processes). Our analysis suggests that an increase in aerosol concentration tends to simultaneously increase both cloud droplet number concentration (Nd) and relative dispersion (ε), while an increase in vertical velocity (w) often increases Nd but decreases ε. After constraining the differences of cloud dynamics, the positive correlation between ε and Nd becomes stronger, implying that perturbations of w could weaken the aerosol influence on ε and hence result in an underestimation of dispersion effect. A comparative analysis of the difference of cloud microphysical properties between the entrainment and non-entrainment zones suggests that the entrainment-mixing mechanism is predominantly extremely inhomogeneous in the stratocumulus that capped by a sharp inversion, whereby the variation in liquid water content (25 %) is similar to that of Nd (29 %) and the droplet size remains approximately constant. In entrainment zone, drier air entrained from the top induces fewer cloud droplets with respect to total in-cloud particles (0.56±0.22) than the case in the non-entrainment zone (0.73±0.13) by promoting cloud droplet evaporation. This study is helpful in reducing uncertainties in dispersion effects and entrainment mixing for stratocumulus, and the results of this study may benefit cloud parameterizations in global climate models to more accurately assess aerosol indirect effects.
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Kulessa, A. S., A. Barrios, J. Claverie, S. Garrett, T. Haack, J. M. Hacker, H. J. Hansen, et al. "The Tropical Air–Sea Propagation Study (TAPS)." Bulletin of the American Meteorological Society 98, no. 3 (March 1, 2017): 517–37. http://dx.doi.org/10.1175/bams-d-14-00284.1.
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Abstract The purpose of the Tropical Air–Sea Propagation Study (TAPS), which was conducted during November–December 2013, was to gather coordinated atmospheric and radio frequency (RF) data, offshore of northeastern Australia, in order to address the question of how well radio wave propagation can be predicted in a clear-air, tropical, littoral maritime environment. Spatiotemporal variations in vertical gradients of the conserved thermodynamic variables found in surface layers, mixing layers, and entrainment layers have the potential to bend or refract RF energy in directions that can either enhance or limit the intended function of an RF system. TAPS facilitated the collaboration of scientists and technologists from the United Kingdom, the United States, France, New Zealand, and Australia, bringing together expertise in boundary layer meteorology, mesoscale numerical weather prediction (NWP), and RF propagation. The focus of the study was on investigating for the first time in a tropical, littoral environment the i) refractivity structure in the marine and coastal inland boundary layers; ii) the spatial and temporal behavior of momentum, heat, and moisture fluxes; and iii) the ability of propagation models seeded with refractive index functions derived from blended NWP and surface-layer models to predict the propagation of radio wave signals of ultrahigh frequency (UHF; 300 MHz–3 GHz), super-high frequency (SHF; 3–30 GHz), and extremely high frequency (EHF; 30–300 GHz). Coordinated atmospheric and RF measurements were made using a small research aircraft, slow-ascent radiosondes, lidar, flux towers, a kitesonde, and land-based transmitters. The use of a ship as an RF-receiving platform facilitated variable-range RF links extending to distances of 80 km from the mainland. Four high-resolution NWP forecasting systems were employed to characterize environmental variability. This paper provides an overview of the TAPS experimental design and field campaign, including a description of the unique data that were collected, preliminary findings, and the envisaged interpretation of the results.
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Liu, Ze Qin, Ling Yu Liu, and Xiao Jian Li. "Numerical Simulation of Flow Field Characteristics of Free Falling Particle Plume Affected by Particle Diameter and Density." Advanced Materials Research 894 (February 2014): 163–66. http://dx.doi.org/10.4028/www.scientific.net/amr.894.163.
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The study of flow field characteristics of free falling particle plume is part of the basic application research of gas-solid two phase flow. The Computational Fluid Dynamic Software FLUENT was adopted in this paper. The numerical simulation was carried out to study the influence of particle diameter and particle density to the particle flow field characteristics of free falling particle plume. The results of the numerical simulation showed that, with the increasing of particle diameter and the increasing of particle density, the disturbance of ambient air to the particle plume decreased, and the entrainment ability of particle plume to the ambient air was diminished.
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Huang, Chunli, Xu Zhao, Weihu Cheng, Qingqing Ji, Qiao Duan, and Yufei Han. "Statistical Inference of Dynamic Conditional Generalized Pareto Distribution with Weather and Air Quality Factors." Mathematics 10, no. 9 (April 24, 2022): 1433. http://dx.doi.org/10.3390/math10091433.
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Air pollution is a major global problem, closely related to economic and social development and ecological environment construction. Air pollution data for most regions of China have a close correlation with time and seasons and are affected by multidimensional factors such as meteorology and air quality. In contrast with classical peaks-over-threshold modeling approaches, we use a deep learning technique and three new dynamic conditional generalized Pareto distribution (DCP) models with weather and air quality factors for fitting the time-dependence of the air pollutant concentration and make statistical inferences about their application in air quality analysis. Specifically, in the proposed three DCP models, a dynamic autoregressive exponential function mechanism is applied for the time-varying scale parameter and tail index of the conditional generalized Pareto distribution, and a sufficiently high threshold is chosen using two threshold selection procedures. The probabilistic properties of the DCP model and the statistical properties of the maximum likelihood estimation (MLE) are investigated, simulating and showing the stability and sensitivity of the MLE estimations. The three proposed models are applied to fit the PM2.5 time series in Beijing from 2015 to 2021. Real data are used to illustrate the advantages of the DCP, especially compared to the estimation volatility of GARCH and AIC or BIC criteria. The DCP model involving both the mixed weather and air quality factors performs better than the other two models with weather factors or air quality factors alone. Finally, a prediction model based on long short-term memory (LSTM) is used to predict PM2.5 concentration, achieving ideal results.
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Huang, Chunli, Xu Zhao, Weihu Cheng, Qingqing Ji, Qiao Duan, and Yufei Han. "Statistical Inference of Dynamic Conditional Generalized Pareto Distribution with Weather and Air Quality Factors." Mathematics 10, no. 9 (April 24, 2022): 1433. http://dx.doi.org/10.3390/math10091433.
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Air pollution is a major global problem, closely related to economic and social development and ecological environment construction. Air pollution data for most regions of China have a close correlation with time and seasons and are affected by multidimensional factors such as meteorology and air quality. In contrast with classical peaks-over-threshold modeling approaches, we use a deep learning technique and three new dynamic conditional generalized Pareto distribution (DCP) models with weather and air quality factors for fitting the time-dependence of the air pollutant concentration and make statistical inferences about their application in air quality analysis. Specifically, in the proposed three DCP models, a dynamic autoregressive exponential function mechanism is applied for the time-varying scale parameter and tail index of the conditional generalized Pareto distribution, and a sufficiently high threshold is chosen using two threshold selection procedures. The probabilistic properties of the DCP model and the statistical properties of the maximum likelihood estimation (MLE) are investigated, simulating and showing the stability and sensitivity of the MLE estimations. The three proposed models are applied to fit the PM2.5 time series in Beijing from 2015 to 2021. Real data are used to illustrate the advantages of the DCP, especially compared to the estimation volatility of GARCH and AIC or BIC criteria. The DCP model involving both the mixed weather and air quality factors performs better than the other two models with weather factors or air quality factors alone. Finally, a prediction model based on long short-term memory (LSTM) is used to predict PM2.5 concentration, achieving ideal results.
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Lecœur, È., and C. Seigneur. "Dynamic evaluation of a multi-year model simulation of particulate matter concentrations over Europe." Atmospheric Chemistry and Physics Discussions 13, no. 1 (January 8, 2013): 475–526. http://dx.doi.org/10.5194/acpd-13-475-2013.
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Abstract. A nine-year air quality simulation is conducted from 2000 to 2008 over Europe using the Polyphemus/Polair3D chemical-transport model (CTM) and then evaluated against the measurements of the European Monitoring and Evaluation Programme (EMEP). The spatial distribution of PM2.5 over Europe shows high concentrations over northern Italy (36 μg m−3) and some areas of eastern Europe, France, and Benelux, and low concentrations over Scandinavia, Spain, and the easternmost part of Europe. PM2.5 composition differs among regions. The operational evaluation shows satisfactory model performance for ozone (O3). PM2.5, PM10, and sulfate (SO42−) meet the performance goal of Boylan and Russell (2006). Nitrate (NO3−) and ammonium (NH4+) are overestimated, although NH4+ meets the performance criteria. The correlation coefficients between simulated and observed data are 63% for O3, 57% for PM10, 59% for PM2.5, 57% for SO42−, 42% for NO3−, and 58% for NH4+. The comparison with other recent one-year model simulations shows that all models overestimate nitrate. The performance of PM2.5, sulfate, and ammonium is comparable to that of the other models. The dynamic evaluation shows that the response of PM2.5 to changes in meteorology differs depending on location and the meteorological variable considered. Wind speed and precipitation show a strong negative day-to-day correlation with PM2.5 and its components (except for sea salt, which shows a positive correlation), that tends towards 0 as the day lag increases. On the other hand, the correlation coefficient is near constant for temperature, for any day lag and PM2.5 species, but it may be positive or negative depending on the species and, for sulfate, depending on the location. The effects of precipitation and wind speed on PM2.5 and its components are better reproduced by the model than the effects of temperature. This is mainly due to the fact that temperature has different effects on the PM2.5 components, unlike precipitation and wind speed which impact most of the PM2.5 components in the same way. These results suggest that state-of-the-science air quality models reproduce satisfactorily the effect of meteorology on PM2.5 and, therefore, are suitable to investigate the effects of climate change on particulate air quality.
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Lecœur, È., and C. Seigneur. "Dynamic evaluation of a multi-year model simulation of particulate matter concentrations over Europe." Atmospheric Chemistry and Physics 13, no. 8 (April 25, 2013): 4319–37. http://dx.doi.org/10.5194/acp-13-4319-2013.
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Abstract. A 9 yr air quality simulation is conducted from 2000 to 2008 over Europe using the Polyphemus/Polair3D chemical-transport model (CTM) and then evaluated against the measurements of the European Monitoring and Evaluation Programme (EMEP). The spatial distribution of PM2.5 over Europe shows high concentrations over northern Italy (36 μg m−3) and some areas of Eastern Europe, France, and Benelux, and low concentrations over Scandinavia, Spain, and the easternmost part of Europe. PM2.5 composition differs among regions. The operational evaluation shows satisfactory model performance for ozone (O3). PM2.5, PM10, and sulfate (SO4=) meet the performance goal of Boylan and Russell (2006). Nitrate (NO3−) and ammonium (NH4+) are overestimated, although NH4+ meets the performance criterion. The correlation coefficients between simulated and observed data are 63% for O3, 57% for PM10, 59% for PM2.5, 57% for SO4=, 42% for NO3−, and 58% for NH4+. The comparison with other recent 1 yr model simulations shows that all models overestimate nitrate. The performance of PM2.5, sulfate, and ammonium is comparable to that of the other models. The dynamic evaluation shows that the response of PM2.5 to changes in meteorology differs depending on location and the meteorological variable considered. Wind speed and precipitation show a strong negative day-to-day correlation with PM2.5 and its components (except for sea salt, which shows a positive correlation), which tends towards 0 as the day lag increases. On the other hand, the correlation coefficient is near constant for temperature, for any day lag and PM2.5 species, but it may be positive or negative depending on the species and, for sulfate, depending on the location. The effects of precipitation and wind speed on PM2.5 and its components are better reproduced by the model than the effects of temperature. This is mainly due to the fact that temperature has different effects on the PM2.5 components, unlike precipitation and wind speed, which impact most of the PM2.5 components in the same way. These results suggest that state-of-the-science air quality models reproduce satisfactorily the effect of meteorology on PM2.5 and therefore are suitable to investigate the effects of climate change on particulate air quality, although uncertainties remain concerning semivolatile PM2.5 components.
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Barth, M. C., J. Lee, A. Hodzic, G. Pfister, W. C. Skamarock, J. Worden, J. Wong, and D. Noone. "Thunderstorms and upper troposphere chemistry during the early stages of the 2006 North American Monsoon." Atmospheric Chemistry and Physics 12, no. 22 (November 21, 2012): 11003–26. http://dx.doi.org/10.5194/acp-12-11003-2012.
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Abstract. To study the meteorology and chemistry that is associated with the early stages of the North American Monsoon, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is applied for the first time at high resolution (4 km grid spacing, allowing for explicit representation of convection) over a large region (continental US and northern Mexico) for a multi-week (15 July to 7 August 2006) integration. Evaluation of model results shows that WRF-Chem reasonably represents the large-scale meteorology and strong convective storms, but tends to overestimate weak convection. In the upper troposphere, the WRF-Chem model predicts ozone (O3) and carbon monoxide (CO) to within 10–20% of aircraft and sonde measurements. Comparison of UT O3 and CO frequency distributions between WRF-Chem and satellite data indicates that WRF-Chem is lofting CO too frequently from the boundary layer (BL). This excessive lofting should also cause biases in the WRF-Chem ozone frequency distribution; however it agrees well with satellite data suggesting that either the chemical production of O3 in the model is overpredicted or there is too much stratosphere to troposphere transport in the model. Analysis of different geographic regions (West Coast, Rocky Mountains, Central Plains, Midwest, and Gulf Coast) reveals that much of the convective transport occurs in the Rocky Mountains, while much of the UT ozone chemical production occurs over the Gulf Coast and Midwest regions where both CO and volatile organic compounds (VOCs) are abundant in the upper troposphere and promote the production of peroxy radicals. In all regions most of the ozone chemical production occurs within 24 h of the air being lofted from the boundary layer. In addition, analysis of the anticyclone and adjacent air indicates that ozone mixing ratios within the anticyclone region associated with the North American Monsoon and just outside the anticyclone are similar. Increases of O3 within the anticyclone are strongly coincident with entrainment of stratospheric air into the anticyclone, but also are from in situ O3 chemical production. In situ O3 production is up to 17% greater within the anticyclone than just outside the anticyclone when the anticyclone is over the southern US indicating that the enhancement of O3 is most pronounced over regions with abundant VOCs.
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Curry, G., H. C. Hughes, D. Loseby, and S. Reynolds. "Advances in cubicle design using computational fluid dynamics as a design tool." Laboratory Animals 32, no. 2 (April 1, 1998): 117–27. http://dx.doi.org/10.1258/002367798780600070.
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As part of a recent animal facility refurbishment, a cubicle containment system was designed to increase the amount of experimental space and also provide containment facilities to support the holding and use of specialized animal models. In order to achieve this, a series of computational fluid dynamic (CFD) studies was undertaken to evaluate the effects of different airflows and in order to optimize ventilation, a variety of exhaust/supply arrangements and animal loads was employed. These studies showed that air delivered via two, opposed, low level ducts, at a rate of 20 air changes per hour and exhausted high in the cubicle above the rack, was the optimal configuration resulting in minimal turbulence, stagnation and entrainment.
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Liu, Xueying, Amos P. K. Tai, and Ka Ming Fung. "Responses of surface ozone to future agricultural ammonia emissions and subsequent nitrogen deposition through terrestrial ecosystem changes." Atmospheric Chemistry and Physics 21, no. 23 (December 3, 2021): 17743–58. http://dx.doi.org/10.5194/acp-21-17743-2021.
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Abstract. With the rising food demands from the future world population, more intense agricultural activities are expected to cause substantial perturbations to the global nitrogen cycle, aggravating surface air pollution and imposing stress on terrestrial ecosystems. Much less studied, however, is how the terrestrial ecosystem changes induced by agricultural nitrogen deposition may modify biosphere–atmosphere exchange and further exert secondary feedback effects on global air quality. Here we examined the responses of surface ozone air quality to terrestrial ecosystem changes caused by year 2000 to year 2050 changes in agricultural ammonia emissions and the subsequent nitrogen deposition by asynchronously coupling between the land and atmosphere components within the Community Earth System Model framework. We found that global gross primary production is enhanced by 2.1 Pg C yr−1, following a 20 % (20 Tg N yr−1) increase in global nitrogen deposition by the end of the year 2050 in response to rising agricultural ammonia emissions. Leaf area index was simulated to be higher by up to 0.3–0.4 m2 m−2 over most tropical grasslands and croplands and 0.1–0.2 m2 m−2 across boreal and temperate forests at midlatitudes. Around 0.1–0.4 m increases in canopy height were found in boreal and temperate forests, and there were ∼0.1 m increases in tropical grasslands and croplands. We found that these vegetation changes could lead to surface ozone changes by ∼0.5 ppbv (part per billion by volume) when prescribed meteorology was used (i.e., large-scale meteorological responses to terrestrial changes were not allowed), while surface ozone could typically be modified by 2–3 ppbv when meteorology was dynamically simulated in response to vegetation changes. Rising soil NOx emissions, from 7.9 to 8.7 Tg N yr−1, could enhance surface ozone by 2–3 ppbv with both prescribed and dynamic meteorology. We, thus, conclude that, following enhanced nitrogen deposition, the modification of the meteorological environment induced by vegetation changes and soil biogeochemical changes are the more important pathways that can modulate future ozone pollution, representing a novel linkage between agricultural activities and ozone air quality.
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Gilliland, Alice B., Christian Hogrefe, Robert W. Pinder, James M. Godowitch, Kristen L. Foley, and S. T. Rao. "Dynamic evaluation of regional air quality models: Assessing changes in O3 stemming from changes in emissions and meteorology." Atmospheric Environment 42, no. 20 (June 2008): 5110–23. http://dx.doi.org/10.1016/j.atmosenv.2008.02.018.
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Yang, Bin, and Chandra Sekhar. "“Conventional” and “Ceiling Mounted” Personalized Ventilation – The Dynamic Effects of a Moving Person on Personal Exposure Effectiveness." Advanced Materials Research 935 (May 2014): 333–36. http://dx.doi.org/10.4028/www.scientific.net/amr.935.333.
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Ceiling mounted personalized ventilation (PV) aims to provide clean outdoor air into breathing zone of occupants directly without affecting indoor aesthetics. High momentum, at outlet of PV air terminal device (ATD), is utilized in order to avoid inducing more ambient air and let more personalized air come into breathing zone. In steady state, its performance depends much on the ceiling mounted ATD because supply air momentum, other than buoyancy effects and ambient air flow, is the major driving force in the micro-environment of occupied zone. In dynamic state, the movement of a person near PV ATD causes entrainment or detrainment effect, which can be regarded as another comparable factor influencing ceiling mounted PV performance. A typical office workplace consisting of either ceiling mounted PV ATD or conventional PV ATD and ambient air supply diffuser is simulated. One person is assumed to be seated and another moving person is simulated by dynamic meshes in computational fluid dynamics (CFD). Simulations at moving person velocities of 0.5, 1 and 1,5 m/s and distance between seated person and moving person of 0, 0.2, 0.4m are performed. A new index, computational personal exposure effectiveness, is utilized to assess the performance of the PV ATD in regard to inhaled air quality under the influence of moving person. According to numerical results, the stability of ceiling mounted PV, under dynamic environment with moving person, is better than that of conventional PV although the personal exposure effectiveness (PEE) is lower than that of conventional PV with the same personalized air flow rate in steady state.
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Huang, Xin, Aijun Ding, Lixia Liu, Qiang Liu, Ke Ding, Xiaorui Niu, Wei Nie, et al. "Effects of aerosol–radiation interaction on precipitation during biomass-burning season in East China." Atmospheric Chemistry and Physics 16, no. 15 (August 9, 2016): 10063–82. http://dx.doi.org/10.5194/acp-16-10063-2016.
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Abstract. Biomass burning is a main source for primary carbonaceous particles in the atmosphere and acts as a crucial factor that alters Earth's energy budget and balance. It is also an important factor influencing air quality, regional climate and sustainability in the domain of Pan-Eurasian Experiment (PEEX). During the exceptionally intense agricultural fire season in mid-June 2012, accompanied by rapidly deteriorating air quality, a series of meteorological anomalies was observed, including a large decline in near-surface air temperature, spatial shifts and changes in precipitation in Jiangsu province of East China. To explore the underlying processes that link air pollution to weather modification, we conducted a numerical study with parallel simulations using the fully coupled meteorology–chemistry model WRF-Chem with a high-resolution emission inventory for agricultural fires. Evaluation of the modeling results with available ground-based measurements and satellite retrievals showed that this model was able to reproduce the magnitude and spatial variations of fire-induced air pollution. During the biomass-burning event in mid-June 2012, intensive emission of absorbing aerosols trapped a considerable part of solar radiation in the atmosphere and reduced incident radiation reaching the surface on a regional scale, followed by lowered surface sensible and latent heat fluxes. The perturbed energy balance and re-allocation gave rise to substantial adjustments in vertical temperature stratification, namely surface cooling and upper-air heating. Furthermore, an intimate link between temperature profile and small-scale processes like turbulent mixing and entrainment led to distinct changes in precipitation. On the one hand, by stabilizing the atmosphere below and reducing the surface flux, black carbon-laden plumes tended to dissipate daytime cloud and suppress the convective precipitation over Nanjing. On the other hand, heating aloft increased upper-level convective activity and then favored convergence carrying in moist air, thereby enhancing the nocturnal precipitation in the downwind areas of the biomass-burning plumes.
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Echendu, S. O. S., H. R. Tamaddon-Jahromi, and M. F. Webster. "Modelling polymeric flows in reverse roll coating processes with dynamic wetting lines and air-entrainment: FENE and PTT solutions." Journal of Non-Newtonian Fluid Mechanics 214 (December 2014): 38–56. http://dx.doi.org/10.1016/j.jnnfm.2014.09.013.
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Costantino, L., and F. M. Bréon. "Aerosol indirect effect on warm clouds over South-East Atlantic, from co-located MODIS and CALIPSO observations." Atmospheric Chemistry and Physics Discussions 12, no. 6 (June 7, 2012): 14197–246. http://dx.doi.org/10.5194/acpd-12-14197-2012.
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Abstract. In this study, we provide a comprehensive analysis of aerosol interaction with warm boundary layer clouds, over South-East Atlantic. We use MODIS retrievals to derive statistical relationships between aerosol concentration and cloud properties, together with co-located CALIPSO estimates of cloud and aerosol layer altitudes. The latter are used to differentiate between cases of mixed and interacting cloud-aerosol layers from cases where the aerosol is located well-above the cloud top. This strategy allows, to a certain extent, to isolate real aerosol-induced effect from meteorology. Similar to previous studies, statistics clearly show that aerosol affects cloud microphysics, decreasing the Cloud Droplet Radius (CDR). The same data indicate a concomitant strong decrease in cloud Liquid Water Path (LWP), in evident contrast with the hypothesis of aerosol inhibition of precipitation (Albrecht, 1989). Because of this water loss, probably due to the entrainment of dry air at cloud top, Cloud Optical Thickness (COT) is found to be almost insensitive to changes in aerosol concentration. The analysis of MODIS-CALIPSO coincidences also evidenced an aerosol enhancement of low cloud cover. Surprising, the Cloud Fraction (CLF) response to aerosol invigoration is much stronger when (absorbing) particles are located above cloud top, than in cases of physical interaction, This result suggests a relevant aerosol radiative effect on low cloud occurrence. Heating the atmosphere above the inversion, absorbing particles above cloud top may decrease the vertical temperature gradient, increase the low tropospheric stability and provide favorable conditions for low cloud formation. We also focus on the impact of anthropogenic aerosols on precipitation, through the statistical analysis of CDR-COT co-variations. A COT value of 10 is found to be the threshold beyond which precipitation mostly forms, in both clean and polluted environments. For larger COT, polluted clouds showed evidence of precipitation suppression. Results suggest the presence of two competing mechanisms governing LWP response to aerosol invigoration: a drying effect due to aerosol enhanced entrainment of dry air at cloud top (predominant for optically thin clouds) and a moistening effect due to aerosol inhibition of precipitation (predominant for optically thick clouds).
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Chen, Fang, Xi Chen, and Xinjian Zhang. "An Empirical Study on System Dynamics Model for Sustainable Development of Air Traffic Control Units." Ecological Chemistry and Engineering S 28, no. 1 (March 1, 2021): 101–16. http://dx.doi.org/10.2478/eces-2021-0009.
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Abstract With the rapid growth of flight volume, the contradiction between insufficient support capability of air traffic control (ATC) units and large demand for development ultimately hinders their sustainable and safe development. The article aims at the leverage point of the contradiction between supply and demand so as to provide scientific safety policies. Based on the system archetype “growth and underinvestment”, from the perspective of the feedback relationships between support capability, safety, and development, the causality of the dynamic factors of control, communication, navigation, and surveillance, as well as meteorology and information subsystems was studied. Then, a system dynamics model for the sustainable and safe development of ATC units was established. Taking the Tianjin ATC sub-bureau as an example, policy suggestions for sustainable and safe development were put forward according to the scenario simulation results.
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Pinsky, Mark, Eshkol Eytan, Ilan Koren, and Alexander Khain. "Convective and Turbulent Motions in Nonprecipitating Cu. Part II: LES Simulated Cloud Represented by a Starting Plume." Journal of the Atmospheric Sciences 79, no. 3 (March 2022): 793–813. http://dx.doi.org/10.1175/jas-d-21-0137.1.
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Abstract The dynamic structure of a small trade wind cumulus (Cu) is analyzed using a novel approach. Cu developing in a shear-free environment is simulated by 10-m-resolution LES model with spectral bin microphysics. The aim is to clarify the dynamical nature of cloud updraft zone (CUZ) including entrainment and mixing in growing Cu. The validity of concept stating that a cloud at developing state can be represented by a parcel or a jet is tested. To investigate dynamical entrainment in CUZ performed by motions with scales larger than the turbulence scales, the modeled fields of air velocity were filtered by wavelet filter that separated convective motions from turbulent ones. Two types of objects in developing cloud were investigated: small volume ascending at maximal velocity (point parcel) and CUZ. It was found that the point parcel representing the upper part of cloud core is adiabatic. The motion of the air in this parcel ascending from cloud base determines cloud-top height. The top-hat (i.e., averaged) values of updraft velocity and adiabatic fraction in CUZ are substantially lower than those in the point parcel. Evaluation of the terms in the dynamical equation typically used in 1D cloud parcel models show that this equation can be applied for calculation of vertical velocities at the developing stage of small Cu, at least up to the heights of the inversion layer. Dynamically, the CUZ of developing cloud resembles the starting plume with the tail of nonstationary jet. Both the top-hat vertical velocity and buoyancy acceleration linearly increase with the height, at least up to the inversion layer. An important finding is that lateral entrainment of convective (nonturbulent) nature has a little effect on the top-hat CUZ velocity and cannot explain the vertical changes of conservative variables qt and θl. In contrast, entrained air lifting inside CUZ substantially decreases top-hat liquid water content and its adiabatic fraction. Possible reasons of these effects are discussed. Significance Statement (i) The study improves the understanding of the effects of lateral entrainment and mixing. (ii) The study shows the dominating role of the convective-scale motions in cloud microphysics and dynamics. (iii) The comparison of results of 10-m-resolution large-eddy simulations with a simple cloud model allows evaluating validity of current schemes of convective parameterization.
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Liao, Zhiheng, Jiaren Sun, Jialin Yao, Li Liu, Haowen Li, Jian Liu, Jielan Xie, Dui Wu, and Shaojia Fan. "Self-organized classification of boundary layer meteorology and associated characteristics of air quality in Beijing." Atmospheric Chemistry and Physics 18, no. 9 (May 15, 2018): 6771–83. http://dx.doi.org/10.5194/acp-18-6771-2018.
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Abstract. Self-organizing maps (SOMs; a feature-extracting technique based on an unsupervised machine learning algorithm) are used to classify atmospheric boundary layer (ABL) meteorology over Beijing through detecting topological relationships among the 5-year (2013–2017) radiosonde-based virtual potential temperature profiles. The classified ABL types are then examined in relation to near-surface pollutant concentrations to understand the modulation effects of the changing ABL meteorology on Beijing's air quality. Nine ABL types (i.e., SOM nodes) are obtained through the SOM classification technique, and each is characterized by distinct dynamic and thermodynamic conditions. In general, the self-organized ABL types are able to distinguish between high and low loadings of near-surface pollutants. The average concentrations of PM2.5, NO2 and CO dramatically increased from the near neutral (i.e., Node 1) to strong stable conditions (i.e., Node 9) during all seasons except for summer. Since extremely strong stability can isolate the near-surface observations from the influence of elevated SO2 pollution layers, the highest average SO2 concentrations are typically observed in Node 3 (a layer with strong stability in the upper ABL) rather than Node 9. In contrast, near-surface O3 shows an opposite dependence on atmospheric stability, with the lowest average concentration in Node 9. Analysis of three typical pollution months (i.e., January 2013, December 2015 and December 2016) suggests that the ABL types are the primary drivers of day-to-day variations in Beijing's air quality. Assuming a fixed relationship between ABL type and PM2.5 loading for different years, the relative (absolute) contributions of the ABL anomaly to elevated PM2.5 levels are estimated to be 58.3 % (44.4 µg m−3) in January 2013, 46.4 % (22.2 µg m−3) in December 2015 and 73.3 % (34.6 µg m−3) in December 2016.
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Makar, P. A., W. Gong, C. Mooney, J. Zhang, D. Davignon, M. Samaali, M. D. Moran, et al. "Dynamic adjustment of climatological ozone boundary conditions for air-quality forecasts." Atmospheric Chemistry and Physics 10, no. 18 (September 28, 2010): 8997–9015. http://dx.doi.org/10.5194/acp-10-8997-2010.
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Abstract. Ten different approaches for applying lateral and top climatological boundary conditions for ozone have been evaluated using the off-line regional air-quality model AURAMS, driven with meteorology provided by the GEM weather-forecast model. All ten approaches employ the same climatological ozone profiles, but differ in the manner in which they are applied, via the inclusion or exclusion of (i) a dynamic adjustment of the climatological ozone profile in response to the model-predicted tropopause height, (ii) a sponge zone for ozone on the model top, (iii) upward extrapolation of the climatological ozone profile, and (iv) different mass consistency corrections. The model performance for each approach was evaluated against North American surface ozone and ozonesonde observations from the BAQS-Met field study period in the summer of 2007. The original daily one-hour maximum surface ozone biases of about +15 ppbv were greatly reduced (halved) in some simulations using alternative methodologies. However, comparisons to ozonesonde observations showed that the reduction in surface ozone bias sometimes came at the cost of significant positive biases in ozone concentrations in the free troposphere and upper troposphere. The best overall performance throughout the troposphere was achieved using a methodology that included dynamic tropopause height adjustment, no sponge zone at the model top, extrapolation of ozone when required above the limit of the climatology, and no mass consistency corrections (global mass conservation was still enforced). The simulation using this model version had a one-hour daily maximum surface ozone bias of +8.6 ppbv, with small reductions in model correlation, and the best comparison to ozonesonde profiles. This recommended and original methodologies were compared for two further case studies: a high-resolution simulation of the BAQS-Met measurement intensive, and a study of the downwind region of the Canadian Rockies. Significant improvements were noted for the high resolution simulations during the BAQS-Met measurement intensive period, both in formal statistical comparisons and time series comparisons of events at surface stations. The tests for the downwind-Rockies region showed that the coupling between vertical transport associated with troposphere/stratosphere exchange, and that associated with boundary layer turbulent mixing, may contribute to ozone positive biases. The results may be unique to the modelling setup employed, but the results also highlight the importance of evaluating boundary condition and mass consistency/correction algorithms against three-dimensional datasets.
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Berkes, F., P. Hoor, H. Bozem, D. Kunkel, M. Sprenger, and S. Henne. "Airborne observation of mixing across the entrainment zone during PARADE 2011." Atmospheric Chemistry and Physics Discussions 15, no. 20 (October 27, 2015): 29171–212. http://dx.doi.org/10.5194/acpd-15-29171-2015.
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Abstract. This study presents the analysis of the structure and air mass characteristics of the lower atmosphere during the field campaign PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) on Mount Kleiner Feldberg in southwestern Germany during late summer 2011. We analysed measurements of meteorological variables (temperature, moisture, pressure, wind speed and direction) from radio soundings and of chemical tracers (carbon dioxide, ozone) from aircraft measurements. We focus on the thermodynamic and dynamic properties, that control the chemical distribution of atmospheric constituents in the boundary layer. We show that the evolution of tracer profiles of CO2 and O3 indicate mixing across the inversion layer (or entrainment zone). This finding is supported by the analysis of tracer–tracer correlations which are indicative for mixing and the relation of tracer profiles in relation to the evolution of the boundary layer height deduced from radio soundings. The study shows the relevance of entrainment processes for the lower troposphere in general and specifically that the tracer–tracer correlation method can be used to identify mixing and irreversible exchange processes across the inversion layer.
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Berkes, Florian, Peter Hoor, Heiko Bozem, Daniel Kunkel, Michael Sprenger, and Stephan Henne. "Airborne observation of mixing across the entrainment zone during PARADE 2011." Atmospheric Chemistry and Physics 16, no. 10 (May 18, 2016): 6011–25. http://dx.doi.org/10.5194/acp-16-6011-2016.
Full textAbstract:
Abstract. This study presents the analysis of the structure and air mass characteristics of the lower atmosphere during the field campaign PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) on Mount Kleiner Feldberg in southwestern Germany during late summer 2011. We analysed measurements of meteorological variables (temperature, moisture, pressure, wind speed and direction) from radio soundings and of chemical tracers (carbon dioxide, ozone) from aircraft measurements. We focus on the thermodynamic and dynamic properties that control the chemical distribution of atmospheric constituents in the boundary layer. We show that the evolution of tracer profiles of CO2 and O3 indicate mixing across the inversion layer (or entrainment zone). This finding is supported by the analysis of tracer–tracer correlations which are indicative for mixing and the relation of tracer profiles in relation to the evolution of the boundary layer height deduced from radio soundings. The study shows the relevance of entrainment processes for the lower troposphere in general and specifically that the tracer–tracer correlation method can be used to identify mixing and irreversible exchange processes across the inversion layer.
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Duarte, Rafael, Anton J. Schleiss, and António Pinheiro. "Effect of pool confinement on pressures around a block impacted by plunging aerated jets." Canadian Journal of Civil Engineering 43, no. 3 (March 2016): 201–10. http://dx.doi.org/10.1139/cjce-2015-0246.
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The erosion caused by jets issued from hydraulic structures progressively develops a confined scour-hole on the riverbed. A realistic scour assessment must consider both the influence of the air entrained when the jet plunges into the pool and the flow patterns induced by bottom geometry. This experimental study systematically analyzes the combined influence of jet aeration and pool confinement on the dynamic pressures affecting the water–rock interface and inside 3D fissures around a block. The results show that confinement reduces mean pressures and pressure fluctuations when the pool is relatively deep, but almost no influence is found when the pool is shallow, while air entrainment has an opposite effect. Three mechanisms are identified, two of them depend on the pool depth. Furthermore, when a block is mobile, pressures are attenuated inside the surrounding joints. The consequent block vibrations and the presence of air reduce pressure waves celerity inside the fissures.
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Hall, C. M. "On the possibility of ion-drag to induce dynamic instability in the lower thermosphere neutral gas." Annales Geophysicae 18, no. 8 (August 31, 2000): 967–71. http://dx.doi.org/10.1007/s00585-000-0967-0.
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Abstract. Strong wind shears may result in dynamic instability, often characterised by the Richardson number lying between zero and 0.25. The extent to which electric-field driven ion flow may induce such neutral wind shears is examined. Further, it is proposed that, in the ionosphere, it is possible for electric fields to drive ion winds such that the collisionally induced neutral air response may be comparable to viscous damping of neutral motion. We shall present an analogy to the Reynolds Number Re to quantify this effect. In the same way that Re may be used to evaluate the likelihood of a flow being turbulent, the analagous metric may also indicate where in the atmosphere plasma dynamics may be strong enough to destabilise the neutral dynamics.Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions) - Meteorology and atmospheric dynamics (turbulence)
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Sapit, Azwan, Mohd Azahari Razali, Mohd Faisal Hushim, M. Jaat, Akmal Nizam Mohammad, and Amir Khalid. "Dynamic Behavior of Rapeseed Oil Spray in Diesel Engine." Applied Mechanics and Materials 773-774 (July 2015): 520–24. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.520.
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Fuel-air mixing is important process in diesel combustion which significantly affects the combustion and emission of diesel engine. Due to the nature of biomass fuel that has high viscosity and high distillation temperature, the condition and furthermore the improvement of atomization process is very important. This study investigates the atomization characteristics and droplet dynamic behaviors of diesel engine spray fueled by rapeseed oil (RO). Optical observation of RO spray was carried out using shadowgraph photography technique. Single nanospark photography technique was used to study the characteristics of the rapeseed oil spray while dual nanospark shadowgraph technique was used to study the spray droplet behavior. Using in-house image processing algorithm, the images were processed and the boundary condition of RO spray also was studied. The results show that RO has very poor atomization due to the high viscosity nature of the fuel. This is in agreement with the results from spray droplet dynamic behavior studies that shows due to the high viscosity, the droplets are large in size and travel downward, with very little influence of entrainment effect due to its large kinematic energy.
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Longo, K. M., S. R. Freitas, M. Pirre, V. Marécal, L. F. Rodrigues, J. Panetta, M. F. Alonso, et al. "The Chemistry CATT-BRAMS model (CCATT-BRAMS 4.5): a regional atmospheric model system for integrated air quality and weather forecasting and research." Geoscientific Model Development 6, no. 5 (September 9, 2013): 1389–405. http://dx.doi.org/10.5194/gmd-6-1389-2013.
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Abstract. Coupled Chemistry Aerosol-Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS, version 4.5) is an on-line regional chemical transport model designed for local and regional studies of atmospheric chemistry from the surface to the lower stratosphere suitable both for operational and research purposes. It includes gaseous/aqueous chemistry, photochemistry, scavenging and dry deposition. The CCATT-BRAMS model takes advantage of BRAMS-specific development for the tropics/subtropics as well as the recent availability of preprocessing tools for chemical mechanisms and fast codes for photolysis rates. BRAMS includes state-of-the-art physical parameterizations and dynamic formulations to simulate atmospheric circulations down to the meter. This on-line coupling of meteorology and chemistry allows the system to be used for simultaneous weather and chemical composition forecasts as well as potential feedback between the two. The entire system is made of three preprocessing software tools for user-defined chemical mechanisms, aerosol and trace gas emissions fields and the interpolation of initial and boundary conditions for meteorology and chemistry. In this paper, the model description is provided along with the evaluations performed by using observational data obtained from ground-based stations, instruments aboard aircrafts and retrieval from space remote sensing. The evaluation accounts for model applications at different scales from megacities and the Amazon Basin up to the intercontinental region of the Southern Hemisphere.
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Lee, T. S., H. T. Low, D. T. Nguyen, and W. R. A. Neo. "Experimental study of check valves performances in fluid transient." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 223, no. 2 (March 18, 2009): 61–69. http://dx.doi.org/10.1243/09544089jpme228.
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An experimental set-up was introduced to study the dynamic behaviour of different types of check valves under pressure transient conditions. Three types of transient comparison methods were used, with similar results being obtained from all three methods. The experimental results show that the check valves with low inertia, assisted by springs or small travelling distance/angle, gave better performance under pressure transient conditions as compared to check valves without these features. Although different amounts of air entrainment were found to affect the experimental readings, the general characteristics of each check valve remain the same when compared between valves. This study can be applied to help in the choosing of suitable check valves for a particular pumping system.
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Estévez, J., P. Gavilán, and A. P. García-Marín. "Data validation procedures in agricultural meteorology – a prerequisite for their use." Advances in Science and Research 6, no. 1 (May 20, 2011): 141–46. http://dx.doi.org/10.5194/asr-6-141-2011.
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Abstract. Quality meteorological data sources are critical to scientists, engineers, climate assessments and to make climate related decisions. Accurate quantification of reference evapotranspiration (ET0) in irrigated agriculture is crucial for optimizing crop production, planning and managing irrigation, and for using water resources efficiently. Validation of data insures that the information needed is been properly generated, identifies incorrect values and detects problems that require immediate maintenance attention. The Agroclimatic Information Network of Andalusia at present provides daily estimations of ET0 using meteorological information collected by nearly of one hundred automatic weather stations. It is currently used for technicians and farmers to generate irrigation schedules. Data validation is essential in this context and then, diverse quality control procedures have been applied for each station. Daily average of several meteorological variables were analysed (air temperature, relative humidity and rainfall). The main objective of this study was to develop a quality control system for daily meteorological data which could be applied on any platform and using open source code. Each procedure will either accept the datum as being true or reject the datum and label it as an outlier. The number of outliers for each variable is related to a dynamic range used on each test. Finally, geographical distribution of the outliers was analysed. The study underscores the fact that it is necessary to use different ranges for each station, variable and test to keep the rate of error uniform across the region.
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Dantas, Sérgio Roberto Andrade, Ramoel Serafini, Roberto Cesar de Oliveira Romano, Fúlvio Vittorino, and Kai Loh. "Influence of polypropylene microfibre (PPMF) dispersion procedure on fresh and hardened rendering mortar properties." Ambiente Construído 20, no. 2 (June 2020): 7–23. http://dx.doi.org/10.1590/s1678-86212020000200384.
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Abstract This study was carried out to evaluate the influence of a polypropylene microfibre (PPMF) dispersion procedure on fresh and hardened state properties of rendering mortars. Specimens prepared with two different PPMF dispersion procedures were evaluated comparatively with reference specimens prepared without adding PPMF. Changes in the fresh properties were monitored using flow table, squeeze flow, and air-entrainment tests. The hardened state was characterized by capillary water absorption, air-permeability, dynamic elastic modulus (E), tensile strength according to the Brazilian test, and porosity by the Archimedes immersion method. Results show that the fresh mortar properties were not affected by dispersion procedure and all hardened mortar properties were statistically similar, except for the dimensional variation of the specimens. The study also shows that adding polypropylene microfibres in a dispersed form was more effective in terms of controlling total drying shrinkage than directly adding fibres to the cementitious matrix (as recommended by the manufacturer) or the reference mortar.
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Martano, Paolo. "Droplet Fate in a Cough Puff." Atmosphere 11, no. 8 (August 9, 2020): 841. http://dx.doi.org/10.3390/atmos11080841.
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The dynamic and thermodynamic evolution of droplets, in a size range characterizing a cough, has been analysed using basic equations of motion and coupled to the evolution of a spherical cloud puff in which they are supposed to be expired. It has been found that the maximum contamination range of the emitted droplets is controlled by two different mechanisms: surface evaporation and inertia-gravitational settling—with a switching threshold between them for a radius around a few tens of microns. For the smallest droplets, the environmental conditions (the temperature and humidity) are found to be very effective in determining the contamination range, even for weak entrainment in the cloud puff. This last fact could be of some relevance in the seasonal behaviour of air-borne epidemics.