Academic literature on the topic 'Convective loading'
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Journal articles on the topic "Convective loading"
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Grabowski, Wojciech W., and Hugh Morrison. "Supersaturation, buoyancy, and deep convection dynamics." Atmospheric Chemistry and Physics 21, no. 18 (September 21, 2021): 13997–4018. http://dx.doi.org/10.5194/acp-21-13997-2021.
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Abstract. Motivated by recent discussions concerning differences of convective dynamics in polluted and pristine environments, the so-called convective invigoration in particular, this paper provides an analysis of factors affecting convective updraft buoyancy, such as the in-cloud supersaturation, condensate and precipitation loading, and entrainment. We use the deep convective period from simulations of daytime convection development over land discussed in our previous publications. An entraining parcel framework is used in the theoretical analysis. We show that for the specific case considered here, finite (positive) supersaturation noticeably reduces pseudo-adiabatic parcel buoyancy and cumulative convective available potential energy (cCAPE) in the lower troposphere. This comes from keeping a small fraction of the water vapor in a supersaturated state and thus reducing the latent heating. Such a lower-tropospheric impact is comparable to the effects of condensate loading and entrainment in the idealized parcel framework. For the entire tropospheric depth, loading and entrainment have a much more significant impact on the total CAPE. For the cloud model results, we compare ensemble simulations applying either a bulk microphysics scheme with saturation adjustment or a more comprehensive double-moment scheme with supersaturation prediction. We compare deep convective updraft velocities, buoyancies, and supersaturations from all ensembles. In agreement with the parcel analysis, the saturation-adjustment scheme provides noticeably stronger updrafts in the lower troposphere. For the simulations predicting supersaturation, there are small differences between pristine and polluted conditions below the freezing level that are difficult to explain by standard analysis of the in-cloud buoyancy components. By applying the piggybacking technique, we show that the lower-tropospheric buoyancy differences between pristine and polluted simulations come from a combination of temperature (i.e., latent heating) and condensate loading differences that work together to make polluted buoyancies and updraft velocities slightly larger when compared to their pristine analogues. Overall, the effects are rather small and contradict previous claims of a significant invigoration of deep convection in polluted environments.
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Takeishi, A., and T. Storelvmo. "Sensitivity study of the aerosol effects on a supercell storm throughout its lifetime." Atmospheric Chemistry and Physics Discussions 14, no. 17 (September 18, 2014): 24087–118. http://dx.doi.org/10.5194/acpd-14-24087-2014.
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Abstract. An increase in atmospheric aerosol loading could alter the microphysics, dynamics, and radiative characteristics of deep convective clouds. Earlier modeling studies have shown that the effects of increased aerosols on the amount of precipitation from deep convective clouds are model-dependent. This study aims to understand the effects of increased aerosol loading on a deep convective cloud throughout its lifetime with the use of the Weather Research and Forecasting (WRF) model as a cloud-resolving model (CRM). It simulates an idealized supercell thunderstorm with 8 different aerosol loadings, for three different cloud microphysics schemes. Variation in aerosol concentration is mimicked by varying either cloud droplet number concentration or the number of activated cloud condensation nuclei. We show that the sensitivity to aerosol loading is dependent on the choice of microphysics scheme. For the schemes that are sensitive to aerosols loading, the production of graupel via riming of snow is the key factor determining the precipitation response. The formulation of snow riming depends on the microphysics scheme and is usually a function of two competing effects, the size effect and the number effect. In many simulations, a decrease in riming is seen with increased aerosol loading, due to the decreased droplet size that lowers the riming efficiency drastically. This decrease in droplet size also results in a delay in the onset of precipitation, as well as so-called warm rain suppression. Although these characteristics of convective invigoration (Rosenfeld et al., 2008) are seen in the first few hours of the simulations, variation in the accumulated precipitation mainly stems from graupel production rather than convective invigoration. These results emphasize the importance of accurate representations of graupel formation in microphysics schemes.
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Aschmann, J., B. M. Sinnhuber, M. P. Chipperfield, and R. Hossaini. "Impact of deep convection and dehydration on bromine loading in the upper troposphere and lower stratosphere." Atmospheric Chemistry and Physics 11, no. 6 (March 22, 2011): 2671–87. http://dx.doi.org/10.5194/acp-11-2671-2011.
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Abstract. Stratospheric bromine loading due to very short-lived substances is investigated with a three-dimensional chemical transport model over a period of 21 years using meteorological input data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis from 1989 to the end of 2009. Within this framework we analyze the impact of dehydration and deep convection on the amount of stratospheric bromine using an idealized and a detailed full chemistry approach. We model the two most important brominated short-lived substances, bromoform (CHBr3) and dibromomethane (CH2Br2), assuming a uniform convective detrainment mixing ratio of 1 part per trillion by volume (pptv) for both species. The contribution of very short-lived substances to stratospheric bromine varies drastically with the applied dehydration mechanism and the associated scavenging of soluble species ranging from 3.4 pptv in the idealized setup up to 5 pptv using the full chemistry scheme. In the latter case virtually the entire amount of bromine originating from very short-lived source gases is able to reach the stratosphere thus rendering the impact of dehydration and scavenging on inorganic bromine in the tropopause insignificant. Furthermore, our long-term calculations show that the mixing ratios of very short-lived substances are strongly correlated to convective activity, i.e. intensified convection leads to higher amounts of very short-lived substances in the upper troposphere/lower stratosphere especially under extreme conditions like El Niño seasons. However, this does not apply to the inorganic brominated product gases whose concentrations are anti-correlated to convective activity mainly due to convective dilution and possible scavenging, depending on the applied approach.
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Cui, Z., S. Davies, K. S. Carslaw, and A. M. Blyth. "The response of precipitation to aerosol through riming and melting in deep convective clouds." Atmospheric Chemistry and Physics Discussions 10, no. 11 (November 25, 2010): 29007–50. http://dx.doi.org/10.5194/acpd-10-29007-2010.
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Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.
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Cui, Z., S. Davies, K. S. Carslaw, and A. M. Blyth. "The response of precipitation to aerosol through riming and melting in deep convective clouds." Atmospheric Chemistry and Physics 11, no. 7 (April 15, 2011): 3495–510. http://dx.doi.org/10.5194/acp-11-3495-2011.
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Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.
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Aschmann, J., B. M. Sinnhuber, M. P. Chipperfield, and R. Hossaini. "Impact of deep convection and dehydration on bromine loading in the upper troposphere and lower stratosphere." Atmospheric Chemistry and Physics Discussions 11, no. 1 (January 5, 2011): 121–62. http://dx.doi.org/10.5194/acpd-11-121-2011.
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Abstract. Stratospheric bromine loading due to very short-lived substances is investigated with a three-dimensional chemical transport model over a period of 21 years using meteorological input data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis from 1989 to the end of 2009. Within this framework we analyze the impact of dehydration and deep convection on the amount of stratospheric bromine using an idealized and a detailed full chemistry approach. We model the two most important brominated short-lived substances, bromoform (CHBr3) and dibromomethane (CH2Br2), assuming a uniform detrainment mixing ratio of 1 part per trillion by volume (pptv) for both species. The contribution of very short-lived substances to stratospheric bromine varies drastically with the applied dehydration mechanism and the associated scavenging of soluble species ranging from 3.4 pptv in the idealized setup up to 5 pptv using the full chemistry scheme. In the latter case virtually the entire amount of bromine originating from very short-lived source gases is able to reach the stratosphere thus rendering the impact of dehydration and scavenging on inorganic bromine in the tropopause insignificant. Furthermore, our long-term calculations show that the mixing ratios of very short-lived substances are strongly correlated to convective activity, i.e. intensified convection leads to higher amounts of very short-lived substances in the upper troposphere/lower stratosphere especially under extreme conditions like El Niño seasons. However, this does not apply to the inorganic brominated product gases whose concentrations are anti-correlated to convective activity mainly due to convective dilution and possible scavenging, depending on the applied approach.
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Song, Xiaoliang, Guang J. Zhang, and J. L. F. Li. "Evaluation of Microphysics Parameterization for Convective Clouds in the NCAR Community Atmosphere Model CAM5." Journal of Climate 25, no. 24 (December 15, 2012): 8568–90. http://dx.doi.org/10.1175/jcli-d-11-00563.1.
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Abstract A physically based two-moment microphysics parameterization scheme for convective clouds is implemented in the NCAR Community Atmosphere Model version 5 (CAM5) to improve the representation of convective clouds and their interaction with large-scale clouds and aerosols. The explicit treatment of mass mixing ratio and number concentration of cloud and precipitation particles enables the scheme to account for the impact of aerosols on convection. The scheme is linked to aerosols through cloud droplet activation and ice nucleation processes and to stratiform cloud parameterization through convective detrainment of cloud liquid/ice water content (LWC/IWC) and droplet/crystal number concentration (DNC/CNC). A 5-yr simulation with the new convective microphysics scheme shows that both cloud LWC/IWC and DNC/CNC are in good agreement with observations, indicating the scheme describes microphysical processes in convection well. Moreover, the microphysics scheme is able to represent the aerosol effects on convective clouds such as the suppression of warm rain formation and enhancement of freezing when aerosol loading is increased. With more realistic simulations of convective cloud microphysical properties and their detrainment, the mid- and low-level cloud fraction is increased significantly over the ITCZ–southern Pacific convergence zone (SPCZ) and subtropical oceans, making it much closer to the observations. Correspondingly, the serious negative bias in cloud liquid water path over subtropical oceans observed in the standard CAM5 is reduced markedly. The large-scale precipitation is increased and precipitation distribution is improved as well. The long-standing precipitation bias in the western Pacific is significantly alleviated because of microphysics–thermodynamics feedbacks.
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Eastin, Matthew D., William M. Gray, and Peter G. Black. "Buoyancy of Convective Vertical Motions in the Inner Core of Intense Hurricanes. Part I: General Statistics." Monthly Weather Review 133, no. 1 (January 1, 2005): 188–208. http://dx.doi.org/10.1175/mwr-2848.1.
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Abstract The buoyancy of hurricane convective vertical motions is studied using aircraft data from 175 radial legs collected in 14 intense hurricanes at four altitudes ranging from 1.5 to 5.5 km. The data of each leg are initially filtered to separate convective-scale features from background mesoscale structure. Convective vertical motion events, called cores, are identified using the criteria that the convective-scale vertical velocity must exceed 1.0 m s−1 for at least 0.5 km. A total of 620 updraft cores and 570 downdraft cores are included in the dataset. Total buoyancy is calculated from convective-scale virtual potential temperature, pressure, and liquid water content using the mesoscale structure as the reference state. Core properties are summarized for the eyewall and rainband regions at each altitude. Characteristics of core average convective vertical velocity, maximum convective vertical velocity, and diameter are consistent with previous studies of hurricane convection. Most cores are superimposed upon relatively weak mesoscale ascent. The mean eyewall (rainband) updraft core exhibits small, but statistically significant, positive total buoyancy below 4 km (between 2 and 5 km) and a modest increase in vertical velocity with altitude. The mean downdraft core not superimposed upon stronger mesoscale ascent also exhibits positive total buoyancy and a slight decrease in downward vertical velocity with decreasing altitude. Buoyant updraft cores cover less than 5% of the total area in each region but accomplish ∼40% of the total upward transport. A one-dimensional updraft model is used to elucidate the relative roles played by buoyancy, vertical perturbation pressure gradient forces, water loading, and entrainment in the vertical acceleration of ordinary updraft cores. Small positive total buoyancy values are found to be more than adequate to explain the vertical accelerations observed in updraft core strength, which implies that ordinary vertical perturbation pressure gradient forces are directed downward, opposing the positive buoyancy forces. Entrainment and water loading are also found to limit updraft magnitudes. The observations support some aspects of both the hot tower hypothesis and symmetric moist neutral ascent, but neither concept appears dominant. Buoyant convective updrafts, however, are integral components of the hurricane’s transverse circulation.
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Chen, Tianmeng, Zhanqing Li, Ralph A. Kahn, Chuanfeng Zhao, Daniel Rosenfeld, Jianping Guo, Wenchao Han, and Dandan Chen. "Potential impact of aerosols on convective clouds revealed by Himawari-8 observations over different terrain types in eastern China." Atmospheric Chemistry and Physics 21, no. 8 (April 26, 2021): 6199–220. http://dx.doi.org/10.5194/acp-21-6199-2021.
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Abstract. Convective clouds are common and play a major role in Earth's water cycle and energy balance; they may even develop into storms and cause severe rainfall events. To understand the convective cloud development process, this study investigates the impact of aerosols on convective clouds by considering the influence of both topography and diurnal variation in radiation. By combining texture analysis, clustering, and thresholding methods, we identify all convective clouds in two warm seasons (May–September, 2016/17) in eastern China based on Himawari-8 Level 1 data. Having large diurnally resolved cloud data together with surface meteorological and environmental measurements, we investigate convective cloud properties and their variation, stratified by elevation and diurnal change. We then analyze the potential impact of aerosol on convective clouds under different meteorological conditions and topographies. In general, convective clouds tend to occur preferentially under polluted conditions in the morning, which reverses in the afternoon. Convective cloud fraction first increases then decreases with aerosol loading, which may contribute to this phenomenon. Topography and diurnal meteorological variations may affect the strength of aerosol microphysical and radiative effects. Updraft is always stronger along the windward slopes of mountains and plateaus, especially in northern China. The prevailing southerly wind near the foothills of mountains and plateaus is likely to contribute to this windward strengthening of updraft and to bring more pollutant into the mountains, thereby strengthening the microphysical effect, invigorating convective clouds. By comparison, over plain, aerosols decrease surface heating and suppress convection by blocking solar radiation reaching the surface.
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Segall, A. E. "Thermoelastic Analysis of Thick-Walled Vessels Subjected to Transient Thermal Loading." Journal of Pressure Vessel Technology 123, no. 1 (August 21, 2000): 146–49. http://dx.doi.org/10.1115/1.1320818.
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A closed-form solution was derived for the transient thermal fields developed in thick-walled vessels subjected to a plausible exponential heating on the internal surface with convection to the surrounding external environment. The resulting series representation of the temperature distribution as a function of time and radial position was then used to derive new relationships for the transient thermoelastic stress states. The derived expressions allow an easy analysis of the significance of the exponential terms and convective coefficient in determining the magnitudes and distribution of the resulting stress states over time. Excellent agreement was seen between the derived temperature and stress relationships and a finite element analysis when the thermophysical and thermoelastic properties were assumed to be independent of temperature.
Dissertations / Theses on the topic "Convective loading"
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Horne, Ryan Ruben. "Thermal and Convective Loading Methods for Releasing Hydrophobic Therapeutics from Contact Lenses." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6388.
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This thesis investigates the feasibility of loading silicone hydrogel (SiHy) contact lenses with two different hydrophobic therapeutics, latanoprost and DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), for treatment of glaucoma and hyperemia respectively. The two methods of loading were 1) thermal loading in an aqueous medium and 2) convective loading in a solution of n-propanol. Dailies Total1® lenses prepared in this manner were tested for their loading and their release into artificial tears. Continuous release over 1-4 days at therapeutic levels is achievable from thermal loading of DMPC, convective loading of DMPC, and convective loading of latanoprost. The DMPC loading processes can be naturally integrated into standard manufacturing lines for Dailies Total1®. Both DMPC and latanoprost release at rates proportional to the amount loaded into a contact lens. Latanoprost loads into a contact lens strictly proportionally to the loading concentration and the time of loading. The convective loading step represents a significant improvement on both the time of loading (reduced from days to minutes) and the loading capacity of silicone hydrogel contact lenses. This thesis also compares the loading and release of latanoprost in the convective loading procedure using the SiHy contact lenses of Acuvue Advance® (Johnson & Johnson Vision Care, Jacksonville, FL) , Air Optix® (Alcon, Copenhagen, Denmark), Biofinity® (CooperVision), PureVision® (Bausch & Lomb), and Dailies Total1® (Alcon), and the polyHEMA lens, SofLens 38® (Bausch & Lomb), finding that silicone hydrogels load an order of magnitude more drug than the polyHEMA lens and release into artificial tears for an order of magnitude longer. Overall, these experiments provide a quantitative understanding of the dynamics of loading and release for both DMPC and latanoprost.
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Hergert, Randall J. "Saharan Air Layer Dust Loading: Effects on Convective Strength in Tropical Cloud Clusters." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5882.
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Numerous factors play a role in the development and maintenance of North Atlantic tropical cyclones as they originate and cross the Main Development Region. These factors include sea-surface temperatures (SSTs), relative humidity, vertical wind shear, etc. One key player in many of these factors is the Saharan Air Layer (SAL) which has been a source for study for nearly five decades.
The interplay between dust loading within the SAL and the development of African Easterly Waves (AEWs) has been repeatedly noted in many of the studies in this field. The cumulative indirect effect of the dust on AEWs however remains unknown (Evan et al., 2006a). On a case by case basis, the SAL has been shown to negatively influence the development of AEWs, i.e. entrainment of dry air into the low to mid-levels, enhanced vertical wind shear and suppression of convection within the storm (Dunion & Velden, 2004). Positive influences on AEW development have also been attributed to the SAL, namely its enhancement of the African Easterly Jet (AEJ) which in turn helps produce positive vorticity along its southern edge that AEWs tap into for energy (Karyampudi & Pierce, 2002).
Further study is indeed warranted to try to fully understand whether or not the SAL has a positive or negative influence on the development of AEWs. A polarized view may be inadequate, as the SAL’s role could very well be positive, negative or somewhere in between depending on the storm characteristics and environmental conditions present at that unique time.
This study looked into the role dust loading has on the mixing between the SAL and the moist marine boundary layer directly beneath the base of the SAL, which can range from 500 – 1500m and revealed a dynamic and varying relationship. It also demonstrated, through a decrease in cloud top temperatures, that dust levels are associated with the convective strength of AEWs by acting as cloud condensation nuclei (CCNs). However this association can be nullified through other parameters unique to each individual storm; SSTs, vertical wind shear, dry-air entrainment, etc.
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Zorzi, Gianluca. "Numerical and experimental investigation of structural stiffness influence on ratcheting convection cell in granular soils under cyclic loading." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
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Lateral cyclic loaded structures in granular soils can lead to an accumulation of irreversible strains by changing their mechanical response (densification) and forming a closed convective cell in the upper layer of the bedding. In the present thesis the convective cell dimension, formation and grain migration inside this closed volume have been studied and presented in relation to structural stiffness and different loads.
This relation was experimentally investigated by applying a cyclic lateral force to a scaled flexible vertical element embedded in dry granular soil. The model was monitored with a camera in order to derive the displacement field by means of the PIV technique.
Modelling large soil deformation turns out to be difficult, using mesh-based methods. Consequently, a mesh-free approach (DEM) was chosen in order to investigate the granular flow with the aim of extracting interesting micromechanical information.
In both the numerical and experimental analyses the effect of different loading magnitudes and different dimensions of the vertical element were considered. The main results regarded the different development, shape and dimensions of the convection cell and the surface settlements. Moreover, the Discrete Element Method has proven to give satisfactory results in the modelling of large deformation phenomena such as the ratcheting convective cell.
Conference papers on the topic "Convective loading"
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Han, Zenghu, and Bao Yang. "Natural Convective Heat Transfer of Water-in-FC72 Nanoemulsion Fluids." In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52351.
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The use of SOLID-particles has long been a common way of increasing fluid thermal conductivity. In this paper, nanoemulsion fluids—dispersions of LIQUID-nanodroplets—are proposed. As an example, water-in-FC72 nanoemulsion fluids are developed, and their thermophysical properties and impact on natural convective heat transfer are investigated experimentally. A significant increase in thermal conductivity—up to 52% for 12vol% of water nanodroplets (or 7.1 wt%)—is observed in the fluids. The enhancement in conductivity and viscosity of the fluids is found to be nonlinear with water loading, indicating an important role of the hydrodynamic interaction and aggregation of nanodroplets. However, the relative viscosity is found to be about two times the relative conductivity if compared at the same water loading. The presence of water nanodroplets is found to systematically increase the natural convective heat transfer coefficient in these fluids, in contrast to the observation in several conventional nanofluids containing solid nanoparticles.
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Platyrrachos, M. A., and S. A. Karamanos. "Finite Element Analysis of Sloshing in Horizontal-Cylindrical Industrial Vessels Under Earthquake Loading." In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71499.
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The present paper presents a finite-element formulation for earthquake-induced sloshing in horizontal-cylindrical industrial vessels. Assuming small-amplitude free-surface elevation, a linearized sloshing problem is obtained, which provides very good results in comparison with other analytical or numerical solutions, and available experimental data. The paper is aimed at calculating sloshing frequencies, as well as sloshing transient response under horizontal seismic excitation. Based on an “impulsive-convective” decomposition of the container-fluid motion, an efficient methodology is proposed for the calculation of the total seismic force, through the corresponding sloshing masses. The results from the present finite element analysis offers an efficient tool for predicting the total seismic force in horizontal cylinders and extends the current design practice for vertical cylindrical tanks stated in existing seismic design specifications.
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Saha, Sudipta, Amitav Tikadar, Jamil Khan, and Tanvir Farouk. "Numerical Analysis on Evaporation Assisted Convective Cooling: Effect of Surface Morphology." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11065.
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Abstract With an escalating need to find ways to reduce the water consumption in industrial cooling system, on-demand hybrid cooling has been a topic of great interest. The main concept of this cooling method is centered upon the utilization of huge exchange of enthalpy associated with phase change process in a conventional convective cooling system. In this study, a multidimensional multi-physics model has been employed to study a system that undergoes this dual mode cooling process where both convection and evaporation contribute to the heat transfer process. The computational domain considered is comprised of a thin liquid film that undergoes evaporation with constant heat flux provided from the bottom and a convective loading of laminar air flow above it. Evaporation takes place at the liquid-gas interface and the evaporated mass is being carried away by the incoming air, hence augmenting the convective cooling through the phase change process. This is an extension of our prior work where the surface structure modification (i.e. undulated surface) on the performance of this proposed hybrid cooling method is numerically investigated. Array of hemispherical structures have been introduced as the surface introducing the heat flux to the liquid film. The objective is to increase the surface to volume ratio and decrease the thermal resistance across the liquid film. The predictions indicate that with the increase in the height of the undulated surface the thermal resistance across the liquid film tends to decrease. Results from these simulations show that a ∼50% reduction in the thermal resistance can be achieved by the surface structure modification while the net evaporation flux can be doubled compared to a flat film configuration.
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Rea, Ulzie, Tom McKrell, Lin-Wen Hu, and Jacopo Buongiorno. "Experimental Study of Laminar Convective Heat Transfer and Viscous Pressure Loss of Alumina-Water Nanofluid." In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52263.
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Laminar convective heat transfer and viscous pressure loss were investigated for alumina-water nanofluid in a flow loop with a vertical heated tube. The experimental results are in good agreement with traditional model predictions for laminar flow, if the loading- and temperature-dependent thermophysical properties are utilized. No abnormal heat transfer enhancement was observed. The heat transfer coefficients in the entrance region and in the fully-developed region are estimated to increase by 17% and 27%, respectively, for alumina nanofluid at 6 vol%. Measured pressure loss of the nanofluid is within 20% of theory. It is concluded that the nanofluid laminar convective heat transfer and viscous pressure loss behavior can be predicted by existing models as long as the correct mixture properties are used. This finding is consistent with our previous observation for alumina nanofluid tested in the fully-developed turbulent flow regime.
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Bons, Jeffrey P., James E. Wammack, Jared Crosby, Daniel Fletcher, and Thomas H. Fletcher. "Evolution of Surface Deposits on a High Pressure Turbine Blade: Part II — Convective Heat Transfer." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-91257.
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A TBC-coated turbine blade coupon was exposed to successive deposition in an accelerated deposition facility simulating flow conditions at the inlet to a first stage high pressure turbine (T = 1150°C, M = 0.31). The combustor exit flow was seeded with dust particulate that would typically be ingested by a large utility power plant. The turbine coupon was subjected to four successive 2 hour deposition tests. The particulate loading was scaled to simulate 0.02 ppmw (parts per million weight) of particulate over three months of continuous gas turbine operation for each 2 hour laboratory simulation (for a cumulative one year of operation). Three-dimensional maps of the deposit-roughened surfaces were created between each test, representing a total of four measurements evenly spaced through the lifecycle of a turbine blade surface. From these measurements, scaled models were produced for testing in a low-speed wind tunnel with a turbulent, zero pressure gradient boundary layer at Re = 750,000. The average surface heat transfer coefficient was measured using a transient surface temperature measurement technique. Stanton number increases initially with deposition but then levels off as the surface becomes less peaked. Subsequent deposition exposure then produces a second increase in St. Surface maps of St highlight the local influence of deposit peaks with regard to heat transfer.
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Wheeler, Robert, Judy Santa-Cruz, Darren Hartl, and Dimitris Lagoudas. "Effect of Processing and Loading on Equiatomic NiTi Fatigue Life and Localized Failure Mechanisms." In ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/smasis2013-3163.
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Shape Memory Alloys (SMAs) have many promising applications in the aerospace, automotive, and energy industries. However, due to a lack of understanding of their actuation fatigue, applications are sometimes limited to non-structural or non-critical components. This paper addresses the actuation fatigue characteristics of a specific SMA, equiatomic Nickel-Titanium (NiTi), with varying heat treatments, as well as different methods for assessing actuation fatigue response, including improved testing procedures and distributed extension measurement methods. Heat treatments ranged from 350°C to 400°C for one to three hours. Dogbone specimens processed from heat treated NiTi sheets were mechanically loaded on test frames which provided resistive heating and forced convective cooling with dry air via vortex tubes. Two mechanical loading schemes were utilized: constant uniaxial load (initial stress of 200MPa) and a linear or spring load centered at 200MPa (and ranging from approximately 150MPa to 250MPa). Linear loading schemes were introduced in order to better simulate actuation in an aerospace application, such as the morphing of semi-rigid surfaces. Specimens were thermally cycled to full actuation with a time-based control scheme developed in LabVIEW. Fatigue responses varied widely as a result of different heat treatments and loading schemes. Due to the main failure mechanism being high localized extension (necking) for the constant loading schemes, additional hardware and software were developed to visually capture extension distribution over specimen length. By analyzing actuation characteristics (e.g. transformation strain) and fatigue mechanisms, the ideal post-processing for actuator applications was determined. Utilizing the local extension distribution evolution over the fatigue life of NiTi specimens as well as postmortem analysis of the failure surfaces allowed for the failure modes to be determined for each heat treatment.
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Iqbal, O., S. Jonnalagedda, K. Arora, L. Zhong, and S. Gaikwad. "Comparison of 1-D vs 3-D Combustion Boundary Conditions for SI Engine Thermal Load Prediction." In ASME 2013 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/icef2013-19227.
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The thermal field generated in an engine block and cylinder head as a result of combustion loading is of paramount significance for structural durability. Computational fluid dynamics and heat transfer modeling provide strong tools; perhaps the best and most precise available for predicting thermal fields within cylinder head and engine block. However, an enduring challenge has been the temperature prediction on metal wall as a response to the time dependent fluctuations in the fluids. Fluid (coolant) flow in an engine is steady for a given engine speed and load, but combustion dynamics are inherently transient. In this study, an effective set of convective boundary condition data (as combustion load) is generated using two different approaches in a stand-alone simulation and mapped onto a decoupled Conjugate Heat Transfer (CHT) model to predict the temperature distribution in the engine. In the first approach, a predictive combustion model, tuned to dyno test data, is solved in a 1-D simulation code. This provides the cycle-averaged convective boundary condition that can be used for a CHT model as a uniform heat source. In the second, more detailed approach, in-cylinder combustion simulations involving transient piston and valve motion with flame propagation modeling are carried out using a 3-D simulation code. The 3-D methodology gives a detailed distribution of convective boundary conditions on the walls touching the combustion gases. In order to predict the gradients in heat transfer coefficient with high accuracy, the resulting temperature distribution from the CHT simulation is fed back into the combustion model to regenerate the set of convective boundary conditions. This process is repeated until a converged set of convective boundary conditions are obtained. In this paper engine temperature predictions obtained using combustion loads from both 1-D and 3-D approaches will be compared with the thermocouple data from engine dyno test.
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Qian, Shaoxiang, and Naoto Kasahara. "LES Analysis of Temperature Fluctuations at T-Junctions for Prediction of Thermal Loading." In ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57292.
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T-junctions are widely used for fluid mixing in nuclear power and chemical and refinery plants. Temperature fluctuations generated by the mixing of hot and cold fluids at a T-junction can cause high cycle thermal fatigue (HCTF) failure. Japan Society of Mechanical Engineers (JSME) published ‘Guideline for Evaluation of High Cycle Thermal Fatigue of a Pipe (JSME S017, 2003)’ which results in a very conservative evaluation. CFD/FEM coupling analysis is considered as a useful tool for the more rational evaluation of HCTF. The present paper aims at the validation of CFD simulations to establish a more rational method of evaluating thermal loading, prior to performing CFD/FEM coupling analysis. It is very important to choose the proper turbulence model for the analysis of unsteady phenomena such as the highly fluctuating flow and temperature fields at a T-junction. Here, large eddy simulation (LES) turbulence models suitable for the simulation of the unsteady phenomena were investigated. LES sub-grid scale (SGS) models used include standard Smagorinsky model (SM) and dynamic Smagorinsky model (DSM). The effects of numerical schemes for the calculation of the convective term in the energy equation on the simulation results were also investigated. LES analyses of the flow and temperature fields at a T-junction were carried out using the above SGS turbulence models. For the sake of comparison, the simulation conditions are the same as those of the WATLON experiments conducted at Japan Atomic Energy Agency (JAEA) in the literature. All of the simulation results show the flow pattern of the wall jet with the strong flow and temperature fluctuations, which is the same as that observed in the experiment. The simulation results indicate the numerical schemes have great effect on the temperature distribution and the temperature fluctuation intensity (TFI). The 1st-order upwind differencing (1UD) significantly underestimates the TFI for each LES model, although it exhibits a good numerical stability. On the other hand, the hybrid scheme, which is mainly the 2nd-order central differencing (2CD) blended with a small fraction of 1UD, can better predict the TFI for each LES model. Furthermore, the DSM model gives a prediction closer to the experimental results than the SM model while using the same numerical scheme. In this study, an important finding is that a combination of the DSM model and the hybrid scheme with a large blending factor can provide a prediction agreeing very well with the experimental results.
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Liu, Zhe, Lukas Benjamin Inhestern, James Braun, and Guillermo Paniagua. "Unsteady Heat Transfer Assessment of Supersonic Turbines Downstream of a Rotating Detonation Combustor." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91460.
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Abstract The supersonic outlet conditions from a rotating detonation combustor exhibit fluctuations in temperature and pressure that exceed 200% of their mean level. Such unsteady conditions will induce a large convective heat loading onto a downstream supersonic turbine. Hence, the precise evaluation of the thermal load to the vane and rotor is essential to the design of adequate cooling strategies. In this paper, a numerical framework is proposed to compute the convective heat transfer on two types of supersonic turbines: axial and radial outflow. The fluctuations imposed at the turbine inlet were obtained from a nozzle coupled to a rotating detonation combustor. Both radial and axial turbines were designed and subsequently analyzed with full stage unsteady simulations using an Unsteady Reynolds Averaged Navier–Stokes solver. The inlet boundary conditions to the turbine are based on CFD results from a rotating detonation combustor. The unsteady adiabatic convective heat transfer coefficient was obtained from two simulations performed at a fixed homogeneous wall temperature. The heat flux variation in span-wise and stream-wise direction is analyzed in detail. Budgeting of the unsteady heat flux mechanism was performed to identify the driving contributor of the heat transfer within the turbine and finally both designs are compared.
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Nemtsev, M. Yu, I. V. Semenov, B. S. Ermolaev, and V. E. Khrapovsky. "SIMULATION OF FILTRATION AND CONVECTIVE BURNING IN BLOCK CHARGES OF POWDER GRAINS INHIBITED BY POLYVINYL BUTYRAL AT CONSTANT VOLUME." In 8TH INTERNATIONAL SYMPOSIUM ON NONEQUILIBRIUM PROCESSES, PLASMA, COMBUSTION, AND ATMOSPHERIC PHENOMENA. TORUS PRESS, 2020. http://dx.doi.org/10.30826/nepcap2018-2-34.
Full textAbstract:
Increase of loading density could be considered as one of the ways of increasing muzzle velocity in guns. At the same time, reduction of maximum pressure requires increase in burning progressivity of the powder charge, which can be reached at the expense of coating of powder grains with polymer film and further compression to high density into block charge. Multidimensional numerical simulation of ignition and combustion of such charges is a relevant issue. Two-dimensional axisymmetric generalization of one-dimensional semianalytical model of convective burning of block charges is introduced. The gas-powder mixture is modeled by a two-phase nonequilibrium heterogeneous medium consisting of a multicomponent gas phase of the combustion products and a polydisperse condensed phase of the charge elements. Mathematical model and computational algorithm were validated through numerical simulation of the following problems: powder gas filtration in the dense charge, combustion of bulk and dense charges, consisting of 7-perforated grains, covered with film, in a closed vessel. Comparison of obtained results with experimental data demonstrates satisfactory predictive qualities of the model.