Directory of Open Access Journals (Sweden)
Daniel Martínez-Castro
2016-10-01
Full Text Available A sensitivity study about the performance of the RegCM-4.3 regional climate model, driven by ERA Interim reanalysis was conducted for a domain including the Caribbean, with horizontal resolution of 50 km from year 2000 to 2001. Sixteen configurations of the model, including variations in the parameters of the Tiedtke convective scheme were tested. The performance of the model using these configurations was compared with data and with simulations using Emanuel (EM and Grell over land-Emanuel over sea (GE convective parameterization schemes. Global datasets of temperature and precipitation and quality controlled data form the weather station networks of Cuba, Jamaica and the Dominican Republic were used as reference. After an analysis of the simulated precipitation fields, some of the configurations were discarded and four of them were chosen to evaluate the representation by the model of the main climatological features of the region. The chosen configurations simulate the general wind and precipitation patterns reasonably well, and at the same time, the seasonal diurnal cycles and the Caribbean low level jet, but they showed different skill in reproducing the particular features of the regional climate. For the rainy season GE shows the best performance, while EM and the default Tiedtke scheme (TI widely overestimate precipitation in the Pacific coast of Central America, whereas for the dry season, the Tiedtke scheme underestimates precipitation, but after tuning parameters biases were reduced. TI scheme showed the best representation of the precipitation seasonal cycle, while the diurnal circle was best reproduced by the GE scheme. Temperature fields were best simulated by Tiedtke configurations, as the area with negative bias was reduced.
A hybrid convection scheme for use in non-hydrostatic numerical weather prediction models
Directory of Open Access Journals (Sweden)
Volker Kuell
2008-12-01
Full Text Available The correct representation of convection in numerical weather prediction (NWP models is essential for quantitative precipitation forecasts. Due to its small horizontal scale convection usually has to be parameterized, e.g. by mass flux convection schemes. Classical schemes originally developed for use in coarse grid NWP models assume zero net convective mass flux, because the whole circulation of a convective cell is confined to the local grid column and all convective mass fluxes cancel out. However, in contemporary NWP models with grid sizes of a few kilometers this assumption becomes questionable, because here convection is partially resolved on the grid. To overcome this conceptual problem we propose a hybrid mass flux convection scheme (HYMACS in which only the convective updrafts and downdrafts are parameterized. The generation of the larger scale environmental subsidence, which may cover several grid columns, is transferred to the grid scale equations. This means that the convection scheme now has to generate a net convective mass flux exerting a direct dynamical forcing to the grid scale model via pressure gradient forces. The hybrid convection scheme implemented into the COSMO model of Deutscher Wetterdienst (DWD is tested in an idealized simulation of a sea breeze circulation initiating convection in a realistic manner. The results are compared with analogous simulations with the classical Tiedtke and Kain-Fritsch convection schemes.
Simulating deep convection with a shallow convection scheme
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C. Hohenegger
2011-10-01
Full Text Available Convective processes profoundly affect the global water and energy balance of our planet but remain a challenge for global climate modeling. Here we develop and investigate the suitability of a unified convection scheme, capable of handling both shallow and deep convection, to simulate cases of tropical oceanic convection, mid-latitude continental convection, and maritime shallow convection. To that aim, we employ large-eddy simulations (LES as a benchmark to test and refine a unified convection scheme implemented in the Single-column Community Atmosphere Model (SCAM. Our approach is motivated by previous cloud-resolving modeling studies, which have documented the gradual transition between shallow and deep convection and its possible importance for the simulated precipitation diurnal cycle.
Analysis of the LES reveals that differences between shallow and deep convection, regarding cloud-base properties as well as entrainment/detrainment rates, can be related to the evaporation of precipitation. Parameterizing such effects and accordingly modifying the University of Washington shallow convection scheme, it is found that the new unified scheme can represent both shallow and deep convection as well as tropical and mid-latitude continental convection. Compared to the default SCAM version, the new scheme especially improves relative humidity, cloud cover and mass flux profiles. The new unified scheme also removes the well-known too early onset and peak of convective precipitation over mid-latitude continental areas.
Ghosh, Sudipta; Dey, Sagnik; Das, Sushant; Venkataraman, Chandra; Patil, Nitin U.
2017-04-01
Black carbon (BC) aerosols absorb solar radiation, thereby causing a warming at the top-of-the-atmosphere (TOA) in contrast to most of the other aerosol species that scatter radiation causing a cooling at TOA. BC is considered to be an important contributor of global warming, second only to CO2 with a net radiative forcing of 1.1 w/m2. They have important regional climate effects, because of their spatially non-uniform heating and cooling. So it is very important to understand the spatio-temporal distribution of BC over India. In this study, we have used a regional climate model RegCM4.5 to simulate BC distribution over India with a focus on the BC estimation. The importance of incorporation of regional emission inventory has been shown and the sensitivity of BC distribution to various convective schemes in the model has been explored. The model output has been validated with in-situ observations. It is quite evident that regional inventory is capturing larger columnar burden of BC and OC than the global inventory. The difference in BC burden is clear at many places with the largest difference (in the order from 2 x 10-11 kg m-2 sec-1 in global inventory to 4 x 10-11 kg m-2 sec-1 in regional inventory) being observed over the Indo-Gangetic Basin. This difference is mainly attributed to the local sources like kerosene lamp burning, residential cooking on solid biomass fuel and agricultural residue burning etc., that are not considered in the global inventory. The difference is also noticeable for OC. Thus BC burden has increased with incorporation of regional emission inventory in the model, suggesting the importance of regional inventory in improved simulation and estimation of aerosols in this region. BC distribution is also sensitive to choice of scheme with Emanuel scheme capturing a comparatively smaller BC burden during the monsoon than Tiedtke scheme. Further long-term simulation with customized model is required to examine impact of BC. Keywords: Black
A continuous and prognostic convection scheme based on buoyancy, PCMT
Guérémy, Jean-François; Piriou, Jean-Marcel
2016-04-01
A new and consistent convection scheme (PCMT: Prognostic Condensates Microphysics and Transport), providing a continuous and prognostic treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is the buoyancy, key element of any vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form (CAPE) to determine the closure condition. The continuous treatment of convection, from dry thermals to deep precipitating convection, is achieved with the help of a continuous formulation of the entrainment-detrainment rates (depending on the convective vertical velocity) and of the CAPE relaxation time (depending on the convective over-turning time). The convective tendencies are directly expressed in terms of condensation and transport. Finally, the convective vertical velocity and condensates are fully prognostic, the latter being treated using the same microphysics scheme as for the resolved condensates but considering the convective environment. A Single Column Model (SCM) validation of this scheme is shown, allowing detailed comparisons with observed and explicitly simulated data. Four cases covering the convective spectrum are considered: over ocean, sensitivity to environmental moisture (S. Derbyshire) non precipitating shallow convection to deep precipitating convection, trade wind shallow convection (BOMEX) and strato-cumulus (FIRE), together with an entire continental diurnal cycle of convection (ARM). The emphasis is put on the characteristics of the scheme which enable a continuous treatment of convection. Then, a 3D LAM validation is presented considering an AMMA case with both observations and a CRM simulation using the same initial and lateral conditions as for the parameterized one. Finally, global
Shepherd, Tristan J.; Walsh, Kevin J.
2017-08-01
This study investigates the effect of the choice of convective parameterization (CP) scheme on the simulated tracks of three intense tropical cyclones (TCs), using the Weather Research and Forecasting (WRF) model. We focus on diagnosing the competing influences of large-scale steering flow, beta drift and convectively induced changes in track, as represented by four different CP schemes (Kain-Fritsch (KF), Betts-Miller-Janjic (BMJ), Grell-3D (G-3), and the Tiedtke (TD) scheme). The sensitivity of the results to initial conditions, model domain size and shallow convection is also tested. We employ a diagnostic technique by Chan et al. (J Atmos Sci 59:1317-1336, 2002) that separates the influence of the large-scale steering flow, beta drift and the modifications of the steering flow by the storm-scale convection. The combined effect of the steering flow and the beta drift causes TCs typically to move in the direction of the wavenumber-1 (WN-1) cyclonic potential vorticity tendency (PVT). In instances of asymmetrical TCs, the simulated TC motion does not necessarily match the motion expected from the WN-1 PVT due to changes in the convective pattern. In the present study, we test this concept in the WRF simulations and investigate whether if the diagnosed motion from the WN-1 PVT and the TC motion do not match, this can be related to the emerging evolution of changes in convective structure. Several systematic results are found across the three cyclone cases. The sensitivity of TC track to initial conditions (the initialisation time and model domain size) is less than the sensitivity of TC track to changing the CP scheme. The simulated track is not overly sensitive to shallow convection in the KF, BMJ, and TD schemes, compared to the track difference between CP schemes. The G3 scheme, however, is highly sensitive to shallow convection being used. Furthermore, while agreement between the simulated TC track direction and the WN-1 diagnostic is usually good, there are
Pilon, Romain; Zhang, Chidong; Dudhia, Jimy
2016-09-01
The November event of the Madden-Julian oscillation (MJO) during the Dynamics of North Atlantic Models (DYNAMO) field campaign was simulated using the global compressible nonhydrostatic Model for Prediction Across Scales with global coarse (60 and 15 km) and regional (the Indian Ocean) cloud-permitting (3 km) meshes. The purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in MJO simulations. Two cumulus schemes were used: Tiedtke and Grell-Freitas. The deep and shallow components of Tiedtke scheme can be turned on and off individually. The results reveal that microphysics alone (without cumulus parameterization) is able to produce strong signals of the MJO in precipitation with 3 km mesh and weak MJO signals with 15 km mesh. A shallow scheme (Tiedtke) along with microphysics strengthens the MJO signals but makes them less well organized on large scales. A deep cumulus scheme can either improve the large-scale organization of MJO precipitation produced by microphysics and shallow convection (Tiedtke) or impair them (Grell-Freitas). The deep scheme of Tiedtke cannot reproduce the MJO well without its shallow counterpart. The main role of shallow convection in the model is to transport moisture upward to the lower to middle troposphere. By doing so, it removes dry biases in the lower to middle troposphere, a distinct feature in simulations with weak or no MJO signals, and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes. Changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the MJO. All roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection. Results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving
Towards the ultimate variance-conserving convection scheme
International Nuclear Information System (INIS)
Os, J.J.A.M. van; Uittenbogaard, R.E.
2004-01-01
In the past various arguments have been used for applying kinetic energy-conserving advection schemes in numerical simulations of incompressible fluid flows. One argument is obeying the programmed dissipation by viscous stresses or by sub-grid stresses in Direct Numerical Simulation and Large Eddy Simulation, see e.g. [Phys. Fluids A 3 (7) (1991) 1766]. Another argument is that, according to e.g. [J. Comput. Phys. 6 (1970) 392; 1 (1966) 119], energy-conserving convection schemes are more stable i.e. by prohibiting a spurious blow-up of volume-integrated energy in a closed volume without external energy sources. In the above-mentioned references it is stated that nonlinear instability is due to spatial truncation rather than to time truncation and therefore these papers are mainly concerned with the spatial integration. In this paper we demonstrate that discretized temporal integration of a spatially variance-conserving convection scheme can induce non-energy conserving solutions. In this paper the conservation of the variance of a scalar property is taken as a simple model for the conservation of kinetic energy. In addition, the derivation and testing of a variance-conserving scheme allows for a clear definition of kinetic energy-conserving advection schemes for solving the Navier-Stokes equations. Consequently, we first derive and test a strictly variance-conserving space-time discretization for the convection term in the convection-diffusion equation. Our starting point is the variance-conserving spatial discretization of the convection operator presented by Piacsek and Williams [J. Comput. Phys. 6 (1970) 392]. In terms of its conservation properties, our variance-conserving scheme is compared to other spatially variance-conserving schemes as well as with the non-variance-conserving schemes applied in our shallow-water solver, see e.g. [Direct and Large-eddy Simulation Workshop IV, ERCOFTAC Series, Kluwer Academic Publishers, 2001, pp. 409-287
Kipling, Zak; Stier, Philip; Labbouz, Laurent; Wagner, Till
2017-01-01
The Convective Cloud Field Model (CCFM) attempts to address some of the shortcomings of both the commonly used bulk mass-flux parameterisations and those using a prescribed spectrum of clouds. By considering the cloud spectrum as a competitive system in which cloud types interact through their environment in competition for convective available potential energy (CAPE), the spectrum is able to respond dynamically to changes in the environment. An explicit Lagrangian entraining plume model for each cloud type allows for the representation of convective-cloud microphysics, paving the way for the study of aerosol-convection interactions at the global scale where their impact remains highly uncertain. In this paper, we introduce a new treatment of convective triggering, extending the entraining plume model below cloud base to explicitly represent the unsaturated thermals which initiate convection. This allows for a realistic vertical velocity to develop at cloud base, so that the cloud microphysics can begin with physically based activation of cloud condensation nuclei (CCN). We evaluate this new version of CCFM in the context of the global model ECHAM6-HAM, comparing its performance to the standard Tiedtke-Nordeng parameterisation used in that model. We find that the spatio-temporal distribution of precipitation is improved, both against a climatology from the Global Precipitation Climatology Project (GPCP) and also against diurnal cycles from the Tropical Rainfall Measurement Mission (TRMM) with a reduced tendency for precipitation to peak too early in the afternoon. Cloud cover is quite sensitive to the vertical level from which the dry convection is initiated, but when this is chosen appropriately the cloud cover compares well with that from Tiedtke-Nordeng. CCFM can thus perform as well as, or better than, the standard scheme while providing additional capabilities to represent convective-cloud microphysics and dynamic cloud morphology at the global scale.
Evaluation of the WRF Double-Moment 6-Class Microphysics Scheme for Precipitating Convection
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Song-You Hong
2010-01-01
Full Text Available This study demonstrates the characteristics of the Weather Research and Forecasting (WRF Double-Moment 6-Class (WDM6 Microphysics scheme for representing precipitating moist convection in 3D platforms, relative to the WSM6 scheme that has been widely used in the WRF community. For a case study of convective system over the Great Plains, the WDM6 scheme improves the evolutionary features such as the bow-type echo in the leading edge of the squall line. We also found that the WRF with WDM6 scheme removes spurious oceanic rainfall that is a systematic defect resulting from the use of the WSM6 scheme alone. The simulated summer monsoon rainfall in East Asia is improved by weakening (strengthening light (heavy precipitation activity. These changes can be explained by the fact that the WDM6 scheme has a wider range in cloud and rain number concentrations than does the WSM6 scheme.
Bony, Sandrine; Dufresne, Jean‐Louis; Roehrig, Romain
2016-01-01
Abstract Several studies have pointed out the dependence of low‐cloud feedbacks on the strength of the lower‐tropospheric convective mixing. By analyzing a series of single‐column model experiments run by a climate model using two different convective parametrizations, this study elucidates the physical mechanisms through which marine boundary‐layer clouds depend on this mixing in the present‐day climate and under surface warming. An increased lower‐tropospheric convective mixing leads to a reduction of low‐cloud fraction. However, the rate of decrease strongly depends on how the surface latent heat flux couples to the convective mixing and to boundary‐layer cloud radiative effects: (i) on the one hand, the latent heat flux is enhanced by the lower‐tropospheric drying induced by the convective mixing, which damps the reduction of the low‐cloud fraction, (ii) on the other hand, the latent heat flux is reduced as the lower troposphere stabilizes under the effect of reduced low‐cloud radiative cooling, which enhances the reduction of the low‐cloud fraction. The relative importance of these two different processes depends on the closure of the convective parameterization. The convective scheme that favors the coupling between latent heat flux and low‐cloud radiative cooling exhibits a stronger sensitivity of low‐clouds to convective mixing in the present‐day climate, and a stronger low‐cloud feedback in response to surface warming. In this model, the low‐cloud feedback is stronger when the present‐day convective mixing is weaker and when present‐day clouds are shallower and more radiatively active. The implications of these insights for constraining the strength of low‐cloud feedbacks observationally is discussed. PMID:28239438
Directory of Open Access Journals (Sweden)
Ku David N
2010-07-01
Full Text Available Abstract Background The finite volume solver Fluent (Lebanon, NH, USA is a computational fluid dynamics software employed to analyse biological mass-transport in the vasculature. A principal consideration for computational modelling of blood-side mass-transport is convection-diffusion discretisation scheme selection. Due to numerous discretisation schemes available when developing a mass-transport numerical model, the results obtained should either be validated against benchmark theoretical solutions or experimentally obtained results. Methods An idealised aneurysm model was selected for the experimental and computational mass-transport analysis of species concentration due to its well-defined recirculation region within the aneurysmal sac, allowing species concentration to vary slowly with time. The experimental results were obtained from fluid samples extracted from a glass aneurysm model, using the direct spectrophometric concentration measurement technique. The computational analysis was conducted using the four convection-diffusion discretisation schemes available to the Fluent user, including the First-Order Upwind, the Power Law, the Second-Order Upwind and the Quadratic Upstream Interpolation for Convective Kinetics (QUICK schemes. The fluid has a diffusivity of 3.125 × 10-10 m2/s in water, resulting in a Peclet number of 2,560,000, indicating strongly convection-dominated flow. Results The discretisation scheme applied to the solution of the convection-diffusion equation, for blood-side mass-transport within the vasculature, has a significant influence on the resultant species concentration field. The First-Order Upwind and the Power Law schemes produce similar results. The Second-Order Upwind and QUICK schemes also correlate well but differ considerably from the concentration contour plots of the First-Order Upwind and Power Law schemes. The computational results were then compared to the experimental findings. An average error of 140
Carroll, Gráinne T; Devereux, Paul D; Ku, David N; McGloughlin, Timothy M; Walsh, Michael T
2010-07-19
The finite volume solver Fluent (Lebanon, NH, USA) is a computational fluid dynamics software employed to analyse biological mass-transport in the vasculature. A principal consideration for computational modelling of blood-side mass-transport is convection-diffusion discretisation scheme selection. Due to numerous discretisation schemes available when developing a mass-transport numerical model, the results obtained should either be validated against benchmark theoretical solutions or experimentally obtained results. An idealised aneurysm model was selected for the experimental and computational mass-transport analysis of species concentration due to its well-defined recirculation region within the aneurysmal sac, allowing species concentration to vary slowly with time. The experimental results were obtained from fluid samples extracted from a glass aneurysm model, using the direct spectrophometric concentration measurement technique. The computational analysis was conducted using the four convection-diffusion discretisation schemes available to the Fluent user, including the First-Order Upwind, the Power Law, the Second-Order Upwind and the Quadratic Upstream Interpolation for Convective Kinetics (QUICK) schemes. The fluid has a diffusivity of 3.125 x 10-10 m2/s in water, resulting in a Peclet number of 2,560,000, indicating strongly convection-dominated flow. The discretisation scheme applied to the solution of the convection-diffusion equation, for blood-side mass-transport within the vasculature, has a significant influence on the resultant species concentration field. The First-Order Upwind and the Power Law schemes produce similar results. The Second-Order Upwind and QUICK schemes also correlate well but differ considerably from the concentration contour plots of the First-Order Upwind and Power Law schemes. The computational results were then compared to the experimental findings. An average error of 140% and 116% was demonstrated between the experimental
Computational evaluation of convection schemes in fluid dynamics problems
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Paulo Laerte Natti
2012-11-01
Full Text Available This article provides a computational evaluation of the popular high resolution upwind WACEB, CUBISTA and ADBQUICKEST schemes for solving non-linear fluid dynamics problems. By using the finite difference methodology, the schemes are analyzed and implemented in the context of normalized variables of Leonard. In order to access the performance of the schemes, Riemann problems for 1D Burgers, Euler and shallow water equations are considered. From the numerical results, the schemes are ranked according to their performance in solving these non-linear equations. The best scheme is then applied in the numerical simulation of tridimensional incompressible moving free surface flows.
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Hourdin, Frederic; Musat, Ionela; Bony, Sandrine; Codron, Francis; Dufresne, Jean-Louis; Fairhead, Laurent; Grandpeix, Jean-Yves; LeVan, Phu; Li, Zhao-Xin; Lott, Francois [CNRS/UPMC, Laboratoire de Meteorologie Dynamique (LMD/IPSL), Paris Cedex 05 (France); Braconnot, Pascale; Friedlingstein, Pierre [Laboratoire des Sciences du Climat et de l' Environnement (LSCE/IPSL), Saclay (France); Filiberti, Marie-Angele [Institut Pierre Simon Laplace (IPSL), Paris (France); Krinner, Gerhard [Laboratoire de Glaciologie et Geophysique de l' Environnement, Grenoble (France)
2006-12-15
The LMDZ4 general circulation model is the atmospheric component of the IPSL-CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley-Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke's convection scheme, used in previous versions, the Emanuel's scheme improves the representation of the Hadley-Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke's parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model. (orig.)
Madhulatha, A.; Rajeevan, M.
2018-02-01
Main objective of the present paper is to examine the role of various parameterization schemes in simulating the evolution of mesoscale convective system (MCS) occurred over south-east India. Using the Weather Research and Forecasting (WRF) model, numerical experiments are conducted by considering various planetary boundary layer, microphysics, and cumulus parameterization schemes. Performances of different schemes are evaluated by examining boundary layer, reflectivity, and precipitation features of MCS using ground-based and satellite observations. Among various physical parameterization schemes, Mellor-Yamada-Janjic (MYJ) boundary layer scheme is able to produce deep boundary layer height by simulating warm temperatures necessary for storm initiation; Thompson (THM) microphysics scheme is capable to simulate the reflectivity by reasonable distribution of different hydrometeors during various stages of system; Betts-Miller-Janjic (BMJ) cumulus scheme is able to capture the precipitation by proper representation of convective instability associated with MCS. Present analysis suggests that MYJ, a local turbulent kinetic energy boundary layer scheme, which accounts strong vertical mixing; THM, a six-class hybrid moment microphysics scheme, which considers number concentration along with mixing ratio of rain hydrometeors; and BMJ, a closure cumulus scheme, which adjusts thermodynamic profiles based on climatological profiles might have contributed for better performance of respective model simulations. Numerical simulation carried out using the above combination of schemes is able to capture storm initiation, propagation, surface variations, thermodynamic structure, and precipitation features reasonably well. This study clearly demonstrates that the simulation of MCS characteristics is highly sensitive to the choice of parameterization schemes.
Development of a moisture scheme for the explicit numerical simulation of moist convection
CSIR Research Space (South Africa)
Bopape, Mary-Jane M
2010-09-01
Full Text Available .kashan.co.za] Development of a moisture scheme for the explicit numerical simulation of moist convection M BOPAPE, F ENGELBRECHT, D RANDALL AND W LANDMAN CSIR Natural Resources and the Environment, PO Box 395, Pretoria, 0001, South Africa Email: mbopape... sigma coordinate model that incorporates moisture effects, so that it can simulate convective clouds and precipitation. moisture terms equivalent to those of the miller and pearce (1974) model are incorporated in the equation set used: ; (1) ; (2...
Armand J, K. M.
2017-12-01
In this study, version 4 of the regional climate model (RegCM4) is used to perform 6 years simulation including one year for spin-up (from January 2001 to December 2006) over Central Africa using four convective schemes: The Emmanuel scheme (MIT), the Grell scheme with Arakawa-Schulbert closure assumption (GAS), the Grell scheme with Fritsch-Chappell closure assumption (GFC) and the Anthes-Kuo scheme (Kuo). We have investigated the ability of the model to simulate precipitation, surface temperature, wind and aerosols optical depth. Emphasis in the model results were made in December-January-February (DJF) and July-August-September (JAS) periods. Two subregions have been identified for more specific analysis namely: zone 1 which corresponds to the sahel region mainly classified as desert and steppe and zone 2 which is a region spanning the tropical rain forest and is characterised by a bimodal rain regime. We found that regardless of periods or simulated parameters, MIT scheme generally has a tendency to overestimate. The GAS scheme is more suitable in simulating the aforementioned parameters, as well as the diurnal cycle of precipitations everywhere over the study domain irrespective of the season. In JAS, model results are similar in the representation of regional wind circulation. Apart from the MIT scheme, all the convective schemes give the same trends in aerosols optical depth simulations. Additional experiment reveals that the use of BATS instead of Zeng scheme to calculate ocean flux appears to improve the quality of the model simulations.
Arbitrary Dimension Convection-Diffusion Schemes for Space-Time Discretizations
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Bank, Randolph E. [Univ. of California, San Diego, CA (United States); Vassilevski, Panayot S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Zikatanov, Ludmil T. [Bulgarian Academy of Sciences, Sofia (Bulgaria)
2016-01-20
This note proposes embedding a time dependent PDE into a convection-diffusion type PDE (in one space dimension higher) with singularity, for which two discretization schemes, the classical streamline-diffusion and the EAFE (edge average finite element) one, are investigated in terms of stability and error analysis. The EAFE scheme, in particular, is extended to be arbitrary order which is of interest on its own. Numerical results, in combined space-time domain demonstrate the feasibility of the proposed approach.
B-express: A new bounded extremum-preserving strategy for convective schemes
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Darwish, M.; Moukalled, F.
2000-03-01
The indiscriminate application of the convective boundedness criterion (CBC) in all flow regions results in a new and subtle error that leads to a significant reduction in accuracy at locations where physical extrema (maxima or minima) with steep profiles are present. In this article, a new Bounded EXtremum-PREServing Strategy (B-EXPRESS) that addresses this issue is presented. The B-EXPRESS is a two-stage procedure in which an extremum recognition algorithm (ERA) is first applied to a solution converged to a set level to flag locations at which enforcing the CBC leads to extrema attenuation. Then, in the second stage, an unbounded scheme is used at the flagged locations, while a bounded scheme is used elsewhere. The new strategy is applied to the SMART (a third-order-bounded scheme) and BSEVENTH (a seventh-order-bounded scheme) schemes to yield two new schemes denoted by B-EXPRESS-3 and B-EXPRESS-7, respectively. These schemes are tested by solving four problems of pure convection in an oblique velocity field of sinusoidal, elliptic, triangular, and box profiles. Results obtained reveal that the B-EXPRESS-3 greatly reduces the rate of attenuation in the levels of the profiles and is as accurate as the BSEVENTH scheme, which, on average, requires 540% more CPU time than the B-EXPRESS-3 scheme. Moreover, the B-EXPRESS-7 scheme computations do not show any observable attenuation in the levels of the profiles while marginally increasing the CPU effort (3.43% on average) over the BSEVENTH scheme.
Decoupled Scheme for Time-Dependent Natural Convection Problem II: Time Semidiscreteness
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Tong Zhang
2014-01-01
stability and the corresponding optimal error estimates are presented. Furthermore, a decoupled numerical scheme is proposed by decoupling the nonlinear terms via temporal extrapolation; optimal error estimates are established. Finally, some numerical results are provided to verify the performances of the developed algorithms. Compared with the coupled numerical scheme, the decoupled algorithm not only keeps good accuracy but also saves a lot of computational cost. Both theoretical analysis and numerical experiments show the efficiency and effectiveness of the decoupled method for time-dependent natural convection problem.
Shishkin, G. I.
2015-11-01
An initial-boundary value problem is considered for a singularly perturbed parabolic convection-diffusion equation with a perturbation parameter ɛ (ɛ ∈ (0, 1]) multiplying the highest order derivative. The stability of a standard difference scheme based on monotone approximations of the problem on a uniform mesh is analyzed, and the behavior of discrete solutions in the presence of perturbations is examined. The scheme does not converge ɛ-uniformly in the maximum norm as the number of its grid nodes is increased. When the solution of the difference scheme converges, which occurs if N -1 ≪ ɛ and N -1 0 ≪ 1, where N and N 0 are the numbers of grid intervals in x and t, respectively, the scheme is not ɛ-uniformly well conditioned or stable to data perturbations in the grid problem and to computer perturbations. For the standard difference scheme in the presence of data perturbations in the grid problem and/or computer perturbations, conditions on the "parameters" of the difference scheme and of the computer (namely, on ɛ, N, N 0, admissible data perturbations in the grid problem, and admissible computer perturbations) are obtained that ensure the convergence of the perturbed solutions. Additionally, the conditions are obtained under which the perturbed numerical solution has the same order of convergence as the solution of the unperturbed standard difference scheme.
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Thang M. Luong
2018-01-01
Full Text Available A commonly noted problem in the simulation of warm season convection in the North American monsoon region has been the inability of atmospheric models at the meso-β scales (10 s to 100 s of kilometers to simulate organized convection, principally mesoscale convective systems. With the use of convective parameterization, high precipitation biases in model simulations are typically observed over the peaks of mountain ranges. To address this issue, the Kain–Fritsch (KF cumulus parameterization scheme has been modified with new diagnostic equations to compute the updraft velocity, the convective available potential energy closure assumption, and the convective trigger function. The scheme has been adapted for use in the Weather Research and Forecasting (WRF. A numerical weather prediction-type simulation is conducted for the North American Monsoon Experiment Intensive Observing Period 2 and a regional climate simulation is performed, by dynamically downscaling. In both of these applications, there are notable improvements in the WRF model-simulated precipitation due to the better representation of organized, propagating convection. The use of the modified KF scheme for atmospheric model simulations may provide a more computationally economical alternative to improve the representation of organized convection, as compared to convective-permitting simulations at the kilometer scale or a super-parameterization approach.
Luong, Thang
2018-01-22
A commonly noted problem in the simulation of warm season convection in the North American monsoon region has been the inability of atmospheric models at the meso-β scales (10 s to 100 s of kilometers) to simulate organized convection, principally mesoscale convective systems. With the use of convective parameterization, high precipitation biases in model simulations are typically observed over the peaks of mountain ranges. To address this issue, the Kain–Fritsch (KF) cumulus parameterization scheme has been modified with new diagnostic equations to compute the updraft velocity, the convective available potential energy closure assumption, and the convective trigger function. The scheme has been adapted for use in the Weather Research and Forecasting (WRF). A numerical weather prediction-type simulation is conducted for the North American Monsoon Experiment Intensive Observing Period 2 and a regional climate simulation is performed, by dynamically downscaling. In both of these applications, there are notable improvements in the WRF model-simulated precipitation due to the better representation of organized, propagating convection. The use of the modified KF scheme for atmospheric model simulations may provide a more computationally economical alternative to improve the representation of organized convection, as compared to convective-permitting simulations at the kilometer scale or a super-parameterization approach.
Energy Technology Data Exchange (ETDEWEB)
Moukalled, F.; Darwish, M. [American Univ. of Beirut (Lebanon)
1997-01-01
The bounded skew central difference scheme (NVF SCDS) is used to study numerically the combined effect of vertical ({epsilon}{sub y}) and horizontal ({epsilon}{sub x}) eccentricities on natural convection in an annulus between a heated horizontal cylinder and its square enclosure. Four Rayleigh numbers (Ra = 10{sup 3}, 10{sup 4}, 10{sup 5}, and 10{sup 6}), three aspect ratios (R/L = 0.1, 0.2, and 0.3), and eccentricity values ranging from {minus}0.3 to 0.3 are considered. At constant enclosure aspect ratio, the total heat transfer increases with increasing Rayleigh number. For constant Rayleigh-number values, convection contribution to total heat transfer decreases with increasing values of R/L. For conduction-dominated flows, heat transfer increases with increasing {vert_bar}{epsilon}{sub y}{vert_bar} and/or {vert_bar}{epsilon}{sub x}{vert_bar}. For convection-dominated flows, heat transfer increases with decreasing {epsilon}{sub y} for {epsilon}{sub y} < 0, decreases with increasing {epsilon}{sub y} for {epsilon}{sub y} > 0, and decreases with decreasing {epsilon}{sub x} for {epsilon}{sub x} < 0. For the case when conduction and convection are of equal importance, there is a critical {epsilon}{sub x} for which the total heat transfer is minimum.
Computer difference scheme for a singularly perturbed convection-diffusion equation
Shishkin, G. I.
2014-08-01
The Dirichlet problem for a singularly perturbed ordinary differential convection-diffusion equation with a perturbation parameter ɛ (that takes arbitrary values from the half-open interval (0, 1]) is considered. For this problem, an approach to the construction of a numerical method based on a standard difference scheme on uniform meshes is developed in the case when the data of the grid problem include perturbations and additional perturbations are introduced in the course of the computations on a computer. In the absence of perturbations, the standard difference scheme converges at an (δ st ) rate, where δ st = (ɛ + N -1)-1 N -1 and N + 1 is the number of grid nodes; the scheme is not ɛ-uniformly well conditioned or stable to perturbations of the data. Even if the convergence of the standard scheme is theoretically proved, the actual accuracy of the computed solution in the presence of perturbations degrades with decreasing ɛ down to its complete loss for small ɛ (namely, for ɛ = (δ-2max i, j |δ a {/i j }| + δ-1 max i, j |δ b {/i j }|), where δ = δ st and δ a {/i j }, δ b {/i j } are the perturbations in the coefficients multiplying the second and first derivatives). For the boundary value problem, we construct a computer difference scheme, i.e., a computing system that consists of a standard scheme on a uniform mesh in the presence of controlled perturbations in the grid problem data and a hypothetical computer with controlled computer perturbations. The conditions on admissible perturbations in the grid problem data and on admissible computer perturbations are obtained under which the computer difference scheme converges in the maximum norm for ɛ ∈ (0, 1] at the same rate as the standard scheme in the absence of perturbations.
Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods
Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard
2013-04-01
Thermal and chemical evolution of Earth's deep mantle can be studied by modeling vigorous convection in a chemically heterogeneous fluid. Numerical modeling of such a system poses several computational challenges. Dominance of heat advection over the diffusive heat transport, and a negligible amount of chemical diffusion results in sharp gradients of thermal and chemical fields. The exponential dependence of the viscosity of mantle materials on temperature also leads to high gradients of the velocity field. The accuracy of many numerical advection schemes degrades quickly with increasing gradient of the solution, while the computational effort, in terms of the scheme complexity and required resolution, grows. Additional numerical challenges arise due to a large range of length-scales characteristic of a thermochemical convection system with highly variable viscosity. To examplify, the thickness of the stem of a rising thermal plume may be a few percent of the mantle thickness. An even thinner filament of an anomalous material that is entrained by that plume may consitute less than a tenth of a percent of the mantle thickness. We have developed a two-dimensional FEM code to model thermochemical convection in a hollow cylinder domain, with a depth- and temperature-dependent viscosity representative of the mantle (Steinberger and Calderwood, 2006). We use marker-in-cell method for advection of chemical and thermal fields. The main advantage of perfoming advection using markers is absence of numerical diffusion during the advection step, as opposed to the more diffusive field-methods. However, in the common implementation of the marker-methods, the solution of the momentum and energy equations takes place on a computational grid, and nodes do not generally coincide with the positions of the markers. Transferring velocity-, temperature-, and chemistry- information between nodes and markers introduces errors inherent to inter- and extrapolation. In the numerical scheme
On the design of general-purpose flux limiters for finite element schemes. I. Scalar convection
Kuzmin, D.
2006-12-01
The algebraic flux correction (AFC) paradigm is extended to finite element discretizations with a consistent mass matrix. It is shown how to render an implicit Galerkin scheme positivity-preserving and remove excessive artificial diffusion in regions where the solution is sufficiently smooth. To this end, the original discrete operators are modified in a mass-conserving fashion so as to enforce the algebraic constraints to be satisfied by the numerical solution. A node-oriented limiting strategy is employed to control the raw antidiffusive fluxes which consist of a convective part and a contribution of the consistent mass matrix. The former offsets the artificial diffusion due to 'upwinding' of the spatial differential operator and lends itself to an upwind-biased flux limiting. The latter eliminates the error induced by mass lumping and calls for the use of a symmetric flux limiter. The concept of a target flux and a new definition of upper/lower bounds make it possible to combine the advantages of algebraic FCT and TVD schemes introduced previously by the author and his coworkers. Unlike other high-resolution schemes for unstructured meshes, the new algorithm reduces to a consistent (high-order) Galerkin scheme in smooth regions and is designed to provide an optimal treatment of both stationary and time-dependent problems. Its performance is illustrated by application to the linear advection equation for a number of 1D and 2D configurations.
Evaluating the Effect of Physics Schemes in WRF Simulations of Summer Rainfall in North West Iran
Directory of Open Access Journals (Sweden)
Sadegh Zeyaeyan
2017-07-01
Full Text Available The numerical weather forecast model Weather Research and Forecasting (WRF has a range of applications because it offers multiple physical options, enabling the users to optimizing WRF for specific scales, geographical locations and applications. Summer rainfall cannot be predicted well in North West of Iran (NWI. Most of them are convective. Sometimes rainfall is heavy, so that it causes flash flood. In this research, some configurations of WRF were tested with four summer rainfall events in NWI to find the best configuration. Five cumulus, four planetary boundary layers (PBL and two microphysical schemes were combined. Twenty-six different configurations (models were implemented at two resolutions of 5 and 15 km for duration of 48 h. Four events, with over 20 mm convective daily rainfall total, were selected at NWI during summer season between 2010 and 2015. These events were tested by developing 26 unique models. Results were verified using several methods. The aim was to find the best results during the first 24 h. Although no single configuration can be introduced for all times, thresholds, and atmospheric system to provide reliable and accurate forecast, the best configuration for WRF can be identified. Kain-Fritsch (new Eta, Betts-Miller-Janjic, Modified Kain-Fritsch, Multi-scale Kain-Fritsch and newer Tiedtke cumulus schemes and Mellor-Yamada-Janjic, Shin-Hong ‘scale-aware’, Medium Range Forecast (MRF and Yonsei University (YSU Planetary Boundary Layer schemes and Kessler, WRF Single Moment 3 class simple ice (WSM3 microphysics schemes were selected. The result show that Cumulus schemes are the most sensitive and Microphysics schemes are the less sensitive. The comparison of 15 km and 5 km resolution simulations do not show obvious advantages in downscaling the results. Configuration with newer Tiedtke cumulus, Mellor-Yamada-Janjic PBL, WSM3 and Kessler microphysics schemes give the best results for the 5 and 15 km resolutions. The
Sahu, L. K.; Sheel, Varun; Kajino, M.; Deushi, M.; Gunthe, Sachin S.; Sinha, P. R.; Yadav, Ravi; Pal, Devendra; Nedelec, P.; Thouret, Valérie; Smit, Herman G.
2017-07-01
This study is based on the analysis of the measurement of ozone and water vapor by airbus in-service aircraft (MOZAIC) data of vertical ozone (O3) and carbon monoxide (CO) over Hyderabad during November 2005-March 2009. Measurements in the upper troposphere show highest values of O3 (53-75 ppbv) and CO (80-110 ppbv) during the pre-monsoon and post-monsoon seasons, respectively. The episodes of strong wind shears (>20 ms-1) were frequent during the monsoon/post-monsoon months, while weak shear conditions (MOZART-4 shows rapid increase with OLR indicating large overestimation of convective transport. A modified Tiedtke convective scheme provides better representation compared to the Hack/Zhang-McFarlane schemes for both O3 and CO during the monsoon season. The difference between observation and simulations were particularly large during transition from El Niño to La Niña phases. The different convection scheme and horizontal resolution in the MOZART-4 and CCM2 seem to be the major causes of disagreement between these models. Vertical profiles of both O3 and CO during extreme events such a tropical cyclones (TCs) show strong influence of the convective-dynamics over Bay of Bengal (BOB).
Pradhan, P. K.; Liberato, Margarida L. R.; Ferreira, Juan A.; Dasamsetti, S.; Vijaya Bhaskara Rao, S.
2018-01-01
The role of the convective parameterization schemes (CPSs) in the ARW-WRF (WRF) mesoscale model is examined for extratropical cyclones (ETCs) over the North Atlantic Ocean. The simulation of very severe winter storms such as Xynthia (2010) and Gong (2013) are considered in this study. Most popular CPSs within WRF model, along with Yonsei University (YSU) planetary boundary layer (PBL) and WSM6 microphysical parameterization schemes are incorporated for the model experiments. For each storm, four numerical experiments were carried out using New Kain Fritsch (NKF), Betts-Miller-Janjic (BMJ), Grell 3D Ensemble (Gr3D) and no convection scheme (NCS) respectively. The prime objectives of these experiments were to recognize the best CPS that can forecast the intensity, track, and landfall over the Iberian Peninsula in advance of two days. The WRF model results such as central sea level pressure (CSLP), wind field, moisture flux convergence, geopotential height, jet stream, track and precipitation have shown sensitivity CPSs. The 48-hour lead simulations with BMJ schemes produce the best simulations both regarding ETCs intensity and track than Gr3D and NKF schemes. The average MAE and RMSE of intensities are least that (6.5 hPa in CSLP and 3.4 ms- 1 in the 10-m wind) found in BMJ scheme. The MAE and RMSE for and intensity and track error have revealed that NCS produces large errors than other CPSs experiments. However, for track simulation of these ETCs, at 72-, 48- and 24-hour means track errors were 440, 390 and 158 km respectively. In brevity, BMJ and Gr3D schemes can be used for short and medium range predictions of the ETCs over North Atlantic. For the evaluation of precipitation distributions using Gr3D scheme are good agreement with TRMM satellite than other CPSs.
Energy Technology Data Exchange (ETDEWEB)
Darwish, M.D.; Moukalled, F. [American Univ. of Beirut (Lebanon). Dept. of Mechanical Engineering
1996-09-01
This article deals with the development of a new method for accelerating the solution of flow problems discretized using high-resolution convective schemes. The technique is based on the normalized variable and space formulation (NVSF) methodology and is denoted here by the normalized weighting-factor (NWF) method. In contrast with the well-known deferred-correction (DC) procedure, the NWF method is fully implicit and is derived by directly replacing the control-volume face values by their functional relationships in the discretized equation. The direct substitution is performed by the introduction of a variable, NWF, that accounts for the multiplicity of interpolation profiles in HR schemes. The new method is compared with the widely used DC procedure and is shown to be, on average, four times faster.
Directory of Open Access Journals (Sweden)
Yandy G. Mayor
2015-01-01
Full Text Available This paper evaluates the sensitivity to cumulus and microphysics schemes, as represented in numerical simulations of the Weather Research and Forecasting model, in characterizing a deep convection event over the Cuban island on 1 May 2012. To this end, 30 experiments combining five cumulus and six microphysics schemes, in addition to two experiments in which the cumulus parameterization was turned off, are tested in order to choose the combination that represents the event precipitation more accurately. ERA Interim is used as lateral boundary condition data for the downscaling procedure. Results show that convective schemes are more important than microphysics schemes for determining the precipitation areas within a high-resolution domain simulation. Also, while one cumulus scheme captures the overall spatial convective structure of the event more accurately than others, it fails to capture the precipitation intensity. This apparent discrepancy leads to sensitivity related to the verification method used to rank the scheme combinations. This sensitivity is also observed in a comparison between parameterized and explicit cumulus formation when the Kain-Fritsch scheme was used. A loss of added value is also found when the Grell-Freitas cumulus scheme was activated at 1 km grid spacing.
Modified exponential based differential quadrature scheme to solve convection diffusion equation
Arora, Geeta; Kataria, Pooja
2017-07-01
This paper proffers differential quadrature scheme to obtain approximate solution of one dimensional advection diffusion equation with Dirichlet's boundary conditions. The scheme uses modified exponential cubic spline basis functions to obtain the numerical results. The method uses less computational effort and produces more accurate results. In the numerical problems, L∞ and L2 errors show the relative performance of the method for different time levels. The results shown by the method are in good approximation with the exact solution.
Development of a moisture scheme for the explicit numerical simulation of moist convection
CSIR Research Space (South Africa)
Bopape, Mary-Jane M
2010-09-01
Full Text Available . The aim of this study is to add a moisture scheme to the NSM. As a first step a simple model that is equivalent to the first pressure-coordinate nonhydrostatic model used to simulate cumulonimbus clouds in 1974 is developed. The equation set that includes...
International Nuclear Information System (INIS)
Ren, Xiu-Hong; Hu, Jiang-Tao; Liu, Di; Zhao, Fu-Yun; Li, Xiao-Hong; Wang, Han-Qing
2016-01-01
Highlights: • Combined convective heat and airborne transports under different flow schemes. • Natural and forced convection dominated regimes were identified with transition. • Dual solution branches were sustained for the transitional mixing flow scheme. • Rest solutions evolving from motionless flows coincided with other solution branch. • Heat and species lines were presented to delineate heat and mass transport structures. - Abstract: This paper reports a numerical study of mixed convection on a heated and polluted strip within a slot ventilated enclosure in which the displacement and mixing flow schemes are considered. Contours of streamfunction, heatfunction, and massfunction are presented to clearly scrutinize the mechanism of heat and airborne pollutant transports. For the displacement flow scheme, thermal Nusselt and pollutant Sherwood numbers under different Reynolds numbers remain almost constant as the value of Gr/Re 2 decreases down to the regime of forced convection dominated. However, as Ar increases up to the regime of natural convection dominated, both Nu and Sh increase sharply with Ar (Gr/Re 2 ). Similar trends could be observed for the situation of mixing ventilated flow scheme. In the mixing scheme, non unique steady flow solutions could be observed for the range of transitional flow regime. Upward solutions, downward solutions and rest solutions have been exemplified with varying Gr/Re 2 . Dual solution branches could be sustained at the range of 39.0 ≤ Gr/Re 2 ≤ 6.0 × 10 3 , while the rest solutions obtained from rest states were completely coinciding with former continuous solutions. The present work could be significant for the natural optimization and passive control of heat and pollutant removals from the electronic boxes or building enclosures.
International Nuclear Information System (INIS)
Li, R.
2012-01-01
The aim of this research dissertation is at studying natural and mixed convections of fluid flows, and to develop and validate numerical schemes for interface tracking in order to treat incompressible and immiscible fluid flows, later. In a first step, an original numerical method, based on Finite Volume discretizations, is developed for modeling low Mach number flows with large temperature gaps. Three physical applications on air flowing through vertical heated parallel plates were investigated. We showed that the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal parallel plates cooled by mixed convection is smaller than those for natural or forced convections when the pressure drop at the outlet keeps constant. We also proved that mixed convection flows resulting from an imposed flow rate may exhibit unexpected physical solutions; alternative model based on prescribed total pressure at inlet and fixed pressure at outlet sections gives more realistic results. For channels heated by heat flux on one wall only, surface radiation tends to suppress the onset of re-circulations at the outlet and to unify the walls temperature. In a second step, the mathematical model coupling the incompressible Navier-Stokes equations and the Level-Set method for interface tracking is derived. Improvements in fluid volume conservation by using high order discretization (ENO-WENO) schemes for the transport equation and variants of the signed distance equation are discussed. (author)
Fuentes-Franco, Ramón; Giorgi, Filippo; Coppola, Erika; Zimmermann, Klaus
2017-07-01
The sensitivity of simulated tropical cyclones (TCs) to resolution, convection scheme and ocean surface flux parameterization is investigated with a regional climate model (RegCM4) over the CORDEX Central America domain, including the Tropical North Atlantic (TNA) and Eastern Tropical Pacific (ETP) basins. Simulations for the TC seasons of the ten-year period (1989-1998) driven by ERA-Interim reanalysis fields are completed using 50 and 25 km grid spacing, two convection schemes (Emanuel, Em; and Kain-Fritsch, KF) and two ocean surface flux representations, a Monin-Obukhov scheme available in the BATS land surface package (Dickinson et al. 1993), and the scheme of Zeng et al. (J Clim 11(10):2628-2644, 1998). The model performance is assessed against observed TC characteristics for the simulation period. In general, different sensitivities are found over the two basins investigated. The simulations using the KF scheme show higher TC density, longer TC duration (up to 15 days) and stronger peak winds (>50 ms-1) than those using Em (<40 ms-1). All simulations show a better spatial representation of simulated TC density and interannual variability over the TNA than over the ETP. The 25 km resolution simulations show greater TC density, duration and intensity compared to the 50 km resolution ones, especially over the ETP basin, and generally more in line with observations. Simulated TCs show a strong sensitivity to ocean fluxes, especially over the TNA basin, with the Monin-Obukhov scheme leading to an overestimate of the TC number, and the Zeng scheme being closer to observations. All simulations capture the density of cyclones during active TC seasons over the TNA, however, without data assimilation, the tracks of individual events do not match closely the corresponding observed ones. Overall, the best model performance is obtained when using the KF and Zeng schemes at 25 km grid spacing.
Maity, S.; Satyanarayana, A. N. V.; Mandal, M.; Nayak, S.
2017-11-01
In this study, an attempt has been made to investigate the sensitivity of land surface models (LSM) and cumulus convection schemes (CCS) using a regional climate model, RegCM Version-4.1 in simulating the Indian Summer Monsoon (ISM). Numerical experiments were conducted in seasonal scale (May-September) for three consecutive years: 2007, 2008, 2009 with two LSMs (Biosphere Atmosphere Transfer Scheme (BATS), Community Land Model (CLM 3.5) and five CCSs (MIT, KUO, GRELL, GRELL over land and MIT over ocean (GL_MO), GRELL over ocean and MIT over land (GO_ML)). Important synoptic features are validated using various reanalysis datasets and satellite derived products from TRMM and CRU data. Seasonally averaged surface temperature is reasonably well simulated by the model using both the LSMs along with CCSs namely, MIT, GO_ML and GL_MO schemes. Model simulations reveal slight warm bias using these schemes whereas significant cold bias is seen with KUO and GRELL schemes during all three years. It is noticed that the simulated Somali Jet (SJ) is weak in all simulations except MIT scheme in the simulations with (both BATS and CLM) in which the strength of SJ reasonably well captured. Although the model is able to simulate the Tropical Easterly Jet (TEJ) and Sub-Tropical Westerly Jet (STWJ) with all the CCSs in terms of their location and strength, the performance of MIT scheme seems to be better than the rest of the CCSs. Seasonal rainfall is not well simulated by the model. Significant underestimation of Indian Summer Monsoon Rainfall (ISMR) is observed over Central and North West India. Spatial distribution of seasonal ISMR is comparatively better simulated by the model with MIT followed by GO_ML scheme in combination with CLM although it overestimates rainfall over heavy precipitation zones. On overall statistical analysis, it is noticed that RegCM4 shows better skill in simulating ISM with MIT scheme using CLM.
Sarkadi, N.; Geresdi, I.; Thompson, G.
2016-11-01
In this study, results of bulk and bin microphysical schemes are compared in the case of idealized simulations of pre-frontal orographic clouds with enhanced embedded convection. The description graupel formation by intensive riming of snowflakes was improved compared to prior versions of each scheme. Two methods of graupel melting coincident with collisions with water drops were considered: (1) all simulated melting and collected water drops increase the amount of melted water on the surface of graupel particles with no shedding permitted; (2) also no shedding permitted due to melting, but the collision with the water drops can induce shedding from the surface of the graupel particles. The results of the numerical experiments show: (i) The bin schemes generate graupel particles more efficiently by riming than the bulk scheme does; the intense riming of snowflakes was the most dominant process for the graupel formation. (ii) The collision-induced shedding significantly affects the evolution of the size distribution of graupel particles and water drops below the melting level. (iii) The three microphysical schemes gave similar values for the domain integrated surface precipitation, but the patterns reveal meaningful differences. (iv) Sensitivity tests using the bulk scheme show that the depth of the melting layer is sensitive to the description of the terminal velocity of the melting snow. (v) Comparisons against Convair-580 flight measurements suggest that the bin schemes simulate well the evolution of the pristine ice particles and liquid drops, while some inaccuracy can occur in the description of snowflakes riming. (vi) The bin scheme with collision-induced shedding reproduced well the quantitative characteristics of the observed bright band.
Yang, Ben; Zhou, Yang; Zhang, Yaocun; Huang, Anning; Qian, Yun; Zhang, Lujun
2018-03-01
Closure assumption in convection parameterization is critical for reasonably modeling the precipitation diurnal variation in climate models. This study evaluates the precipitation diurnal cycles over East Asia during the summer of 2008 simulated with three convective available potential energy (CAPE) based closure assumptions, i.e. CAPE-relaxing (CR), quasi-equilibrium (QE), and free-troposphere QE (FTQE) and investigates the impacts of planetary boundary layer (PBL) mixing, advection, and radiation on the simulation by using the weather research and forecasting model. The sensitivity of precipitation diurnal cycle to PBL vertical resolution is also examined. Results show that the precipitation diurnal cycles simulated with different closures all exhibit large biases over land and the simulation with FTQE closure agrees best with observation. In the simulation with QE closure, the intensified PBL mixing after sunrise is responsible for the late-morning peak of convective precipitation, while in the simulation with FTQE closure, convective precipitation is mainly controlled by advection cooling. The relative contributions of different processes to precipitation formation are functions of rainfall intensity. In the simulation with CR closure, the dynamical equilibrium in the free troposphere still can be reached, implying the complex cause-effect relationship between atmospheric motion and convection. For simulations in which total CAPE is consumed for the closures, daytime precipitation decreases with increased PBL resolution because thinner model layer produces lower convection starting layer, leading to stronger downdraft cooling and CAPE consumption. The sensitivity of the diurnal peak time of precipitation to closure assumption can also be modulated by changes in PBL vertical resolution. The results of this study help us better understand the impacts of various processes on the precipitation diurnal cycle simulation.
Fuentes-Franco, Ramon; Giorgi, Filippo; Coppola, Erika; Zimmermann, Klaus
2016-04-01
The sensitivity of simulated tropical cyclones (TC) to resolution and convection scheme parameterization is investigated over the CORDEX Central America domain. The performance of the simulations, performed for a ten-year period (1989-1998) using ERA-Interim reanalysis as boundary and initial conditions, is assessed considering 50 km and 25 km resolution, and the use of two different convection schemes: Emanuel (Em) and Kain-Fritsch (KF). Two ocean surface fluxes are also compared as well: the Monin-Obukhov scheme, and the one proposed by Zeng et al. (1998). By comparing with observations, for the whole period we assess the spatial representation of the TC, and their intensity. At interannual scale we assess the representation of their variability and at daily scale we compare observed and simulated tracks in order to establish a measure of how similar to observed are the simulated tracks. In general the simulations using KF convection scheme show higher TC density, as well as longer-duration TC (up to 15 days) with stronger winds (> 50ms-1) than those using Em (<40ms-1). Similar results were found for simulations using 25 km respect to 50 km resolution. All simulations show a better spatial representation of simulated TC density and its interannual variability over the Tropical North Atlantic Ocean (TNA) than over the Eastern Tropical Pacific Ocean (ETP). The 25 km resolution simulations show an overestimation of TC density compared to observations over ETP off the coast of Mexico. The duration of the TC in simulations using 25km resolution is similar to the observations, while is underestimated by the 50km resolution. The Monin-Obukhov ocean flux overestimates the number of TCs, while Zeng parameterization give a number similar to observations in both oceans. At daily scale, in general all simulations capture the density of cyclones during highly active TC seasons over the TNA, however the tracks generally are not coincident with observations, except for highly
Llagostera, Jorge; Figueiredo, José R.
2000-01-01
Mixed convection on the flow past a heated length and past a porous cavity located in a horizontal wall bounding a saturated porous medium is numerically simulated. The cavity is heated from below. The steady-state regime is studied for several intensities of the buoyancy effects due to temperature variations. The influences of Péclet and Rayleigh numbers on the flow pattern and the temperature distributions are examined. Local and global Nusselt numbers are reported for the heated surface. T...
Devanand, Anjana; Ghosh, Subimal; Paul, Supantha; Karmakar, Subhankar; Niyogi, Dev
2017-08-01
Regional simulations of the seasonal Indian summer monsoon rainfall (ISMR) require an understanding of the model sensitivities to physics and resolution, and its effect on the model uncertainties. It is also important to quantify the added value in the simulated sub-regional precipitation characteristics by a regional climate model (RCM), when compared to coarse resolution rainfall products. This study presents regional model simulations of ISMR at seasonal scale using the Weather Research and Forecasting (WRF) model with the synoptic scale forcing from ERA-interim reanalysis, for three contrasting monsoon seasons, 1994 (excess), 2002 (deficit) and 2010 (normal). Impact of four cumulus schemes, viz., Kain-Fritsch (KF), Betts-Janjić-Miller, Grell 3D and modified Kain-Fritsch (KFm), and two micro physical parameterization schemes, viz., WRF Single Moment Class 5 scheme and Lin et al. scheme (LIN), with eight different possible combinations are analyzed. The impact of spectral nudging on model sensitivity is also studied. In WRF simulations using spectral nudging, improvement in model rainfall appears to be consistent in regions with topographic variability such as Central Northeast and Konkan Western Ghat sub-regions. However the results are also dependent on choice of cumulus scheme used, with KF and KFm providing relatively good performance and the eight member ensemble mean showing better results for these sub-regions. There is no consistent improvement noted in Northeast and Peninsular Indian monsoon regions. Results indicate that the regional simulations using nested domains can provide some improvements on ISMR simulations. Spectral nudging is found to improve upon the model simulations in terms of reducing the intra ensemble spread and hence the uncertainty in the model simulated precipitation. The results provide important insights regarding the need for further improvements in the regional climate simulations of ISMR for various sub-regions and contribute
Directory of Open Access Journals (Sweden)
V. S. Galligani
2017-10-01
Full Text Available In the present study, three meteorological events of extreme deep moist convection, characteristic of south-eastern South America, are considered to conduct a systematic evaluation of the microphysical parameterizations available in the Weather Research and Forecasting (WRF model by undertaking a direct comparison between satellite-based simulated and observed microwave radiances. A research radiative transfer model, the Atmospheric Radiative Transfer Simulator (ARTS, is coupled with the WRF model under three different microphysical parameterizations (WSM6, WDM6 and Thompson schemes. Microwave radiometry has shown a promising ability in the characterization of frozen hydrometeors. At high microwave frequencies, however, frozen hydrometeors significantly scatter radiation, and the relationship between radiation and hydrometeor populations becomes very complex. The main difficulty in microwave remote sensing of frozen hydrometeor characterization is correctly characterizing this scattering signal due to the complex and variable nature of the size, composition and shape of frozen hydrometeors. The present study further aims at improving the understanding of frozen hydrometeor optical properties characteristic of deep moist convection events in south-eastern South America. In the present study, bulk optical properties are computed by integrating the single-scattering properties of the Liu(2008 discrete dipole approximation (DDA single-scattering database across the particle size distributions parameterized by the different WRF schemes in a consistent manner, introducing the equal mass approach. The equal mass approach consists of describing the optical properties of the WRF snow and graupel hydrometeors with the optical properties of habits in the DDA database whose dimensions might be different (Dmax′ but whose mass is conserved. The performance of the radiative transfer simulations is evaluated by comparing the simulations with the available
Sol Galligani, Victoria; Wang, Die; Alvarez Imaz, Milagros; Salio, Paola; Prigent, Catherine
2017-10-01
In the present study, three meteorological events of extreme deep moist convection, characteristic of south-eastern South America, are considered to conduct a systematic evaluation of the microphysical parameterizations available in the Weather Research and Forecasting (WRF) model by undertaking a direct comparison between satellite-based simulated and observed microwave radiances. A research radiative transfer model, the Atmospheric Radiative Transfer Simulator (ARTS), is coupled with the WRF model under three different microphysical parameterizations (WSM6, WDM6 and Thompson schemes). Microwave radiometry has shown a promising ability in the characterization of frozen hydrometeors. At high microwave frequencies, however, frozen hydrometeors significantly scatter radiation, and the relationship between radiation and hydrometeor populations becomes very complex. The main difficulty in microwave remote sensing of frozen hydrometeor characterization is correctly characterizing this scattering signal due to the complex and variable nature of the size, composition and shape of frozen hydrometeors. The present study further aims at improving the understanding of frozen hydrometeor optical properties characteristic of deep moist convection events in south-eastern South America. In the present study, bulk optical properties are computed by integrating the single-scattering properties of the Liu(2008) discrete dipole approximation (DDA) single-scattering database across the particle size distributions parameterized by the different WRF schemes in a consistent manner, introducing the equal mass approach. The equal mass approach consists of describing the optical properties of the WRF snow and graupel hydrometeors with the optical properties of habits in the DDA database whose dimensions might be different (Dmax') but whose mass is conserved. The performance of the radiative transfer simulations is evaluated by comparing the simulations with the available coincident
Almazroui, Mansour; Islam, Md. Nazrul; Al-Khalaf, A. K.; Saeed, Fahad
2016-05-01
A suitable convective parameterization scheme within Regional Climate Model version 4.3.4 (RegCM4) developed by the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy, is investigated through 12 sensitivity runs for the period 2000-2010. RegCM4 is driven with European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim 6-hourly boundary condition fields for the CORDEX-MENA/Arab domain. Besides ERA-Interim lateral boundary conditions data, the Climatic Research Unit (CRU) data is also used to assess the performance of RegCM4. Different statistical measures are taken into consideration in assessing model performance for 11 sub-domains throughout the analysis domain, out of which 7 (4) sub-domains give drier (wetter) conditions for the area of interest. There is no common best option for the simulation of both rainfall and temperature (with lowest bias); however, one option each for temperature and rainfall has been found to be superior among the 12 options investigated in this study. These best options for the two variables vary from region to region as well. Overall, RegCM4 simulates large pressure and water vapor values along with lower wind speeds compared to the driving fields, which are the key sources of bias in simulating rainfall and temperature. Based on the climatic characteristics of most of the Arab countries located within the study domain, the drier sub-domains are given priority in the selection of a suitable convective scheme, albeit with a compromise for both rainfall and temperature simulations. The most suitable option Grell over Land and Emanuel over Ocean in wet (GLEO wet) delivers a rainfall wet bias of 2.96 % and a temperature cold bias of 0.26 °C, compared to CRU data. An ensemble derived from all 12 runs provides unsatisfactory results for rainfall (28.92 %) and temperature (-0.54 °C) bias in the drier region because some options highly overestimate rainfall (reaching up to 200 %) and underestimate
Singh, K. S.; Bhaskaran, Prasad K.
2017-12-01
This study evaluates the performance of the Advanced Research Weather Research and Forecasting (WRF-ARW) model for prediction of land-falling Bay of Bengal (BoB) tropical cyclones (TCs). Model integration was performed using two-way interactive double nested domains at 27 and 9 km resolutions. The present study comprises two major components. Firstly, the study explores the impact of five different planetary boundary layer (PBL) and six cumulus convection (CC) schemes on seven land-falling BoB TCs. A total of 85 numerical simulations were studied in detail, and the results signify that the model simulated better both the track and intensity by using a combination of Yonsei University (YSU) PBL and the old simplified Arakawa-Schubert CC scheme. Secondly, the study also investigated the model performance based on the best possible combinations of model physics on the real-time forecasts of four BoB cyclones (Phailin, Helen, Lehar, and Madi) that made landfall during 2013 based on another 15 numerical simulations. The predicted mean track error during 2013 was about 71 km, 114 km, 133 km, 148 km, and 130 km respectively from day-1 to day-5. The Root Mean Square Error (RMSE) for Minimum Central Pressure (MCP) was about 6 hPa and the same noticed for Maximum Surface Wind (MSW) was about 4.5 m s-1 noticed during the entire simulation period. In addition the study also reveals that the predicted track errors during 2013 cyclones improved respectively by 43%, 44%, and 52% from day-1 to day-3 as compared to cyclones simulated during the period 2006-2011. The improvements noticed can be attributed due to relatively better quality data that was specified for the initial mean position error (about 48 km) during 2013. Overall the study signifies that the track and intensity forecast for 2013 cyclones using the specified combinations listed in the first part of this study performed relatively better than the other NWP (Numerical Weather Prediction) models, and thereby finds
Directory of Open Access Journals (Sweden)
Luciano Ponzi Pezzi
2008-06-01
Full Text Available The sensitivity of cumulus convection parameterizations is investigated using the CPTEC/COLA Atmospheric General Circulation Model (AGCM with T62L28 resolution. This model has been used at CPTEC/INPE since 1995 with the Kuo convective scheme for weather and seasonal climate forecasts. In this study, two sets of integrations are performed using climatological Sea Surface Temperature (SST of the Southern Hemisphere summer season (December, January and February as bottom boundary conditions. Five integrations with different initial conditions are applied for each ensemble. The study was divided in two groups, one using the adjusted Relaxed Arakawa-Schubert convection scheme considering modifications in the convection physics (ARAS and the other one using the Kuo convection scheme (KUO. The atmospheric circulation and precipitation model results are compared with NCEP/NCAR reanalysis data and CMAP precipitation data. The results are analyzed mainly over South America and also for the Southern Hemisphere to verify the model response compared to observed data when different convection scheme is applied. The adjusted scheme for RAS suggested in this study, reduced errors in several areas of South America, when comparing with the previous version. Over most of South America areas KUO gives smaller errors than ARAS. Over tropical Pacific Ocean, Southeastern Brazil and south of northeast Brazil, ARAS scheme shows better results.A sensibilidade da parametrização de convecção tipo cumulus é investigada com o uso do modelo de circulação geral da atmosfera (MCGA CPTEC/COLA. Este modelo tem sido usado no CPTEC/INPE desde 1995 com o esquema Kuo de convecção para previsões de tempo e sazonal climática. Neste estudo, dois conjuntos de integrações são realizados usando-se temperatura da superfície do mar (TSM climatológica como condição inferior de contorno, do verão do Hemisfério Sul (Dezembro, Janeiro e Fevereiro. Cinco integrações partindo
International Nuclear Information System (INIS)
Guenther, C.
1988-08-01
This report describes numerical tests with various difference schemes to solve the convection-diffusion equation. Starting point of this investigation has been a scheme proposed by the author, the so-called 'LECUSSO-scheme', which is of order O(Δx 2 ) and avoids unphysical spatial oscillations meaning that this scheme does not suffer from any mesh-Reynolds-number-restriction. To test this scheme a previously described example introduced by Beier et al. with known analytical solution was adoptd and numerically solved using a variety of difference schemes. This is done for a wide range of Reynolds-numbers (20 ≤ Re' ≤ 5000) and equidistant meshes of different size, the comparison being done with respect to the space-dependent error and to the maximum spatial error of the numerical solution. The results of the numerical tests may be summarized as follows: Flows with boundary layers, as the most interesting case are very favourably calculated using upwind methods of second or higher order in conservation form with respect to the absolute value of the maximum spatial error. The amount of this error is near 1/3 of the error obtained with standard schemes unless these schemes not yet produced obsolete results since a mesh-Reynolds-number condition had been violated. As to the increased amount of work (additional 5th point, two different additional types of modified difference approximations with fewer points near the boundary), LSUDS-C (in conservation form) is not better than LECUSSO-C and QUICK-PLUS. The reduced errors of the upwind methods of higher order enable us to proceed to the numerical calculation of flows with higher Reynolds-numbers than before. (orig./GL [de
Weis, P.; Driesner, T.; Coumou, D.; Geiger, S.
2014-01-01
Thermohaline convection of subsurface fluids strongly influences heat and mass fluxes within the Earth's crust. The most effective hydrothermal systems develop in the vicinity of magmatic activity and can be important for geothermal energy production and ore formation. As most parts of these systems
Annan, Kodwo
2012-01-01
The efficiency of a high-flux dialyzer in terms of buffering and toxic solute removal largely depends on the ability to use convection-diffusion mechanism inside the membrane. A two-dimensional transient convection-diffusion model coupled with acid-base correction term was developed. A finite volume technique was used to discretize the model and to numerically simulate it using MATLAB software tool. We observed that small solute concentration gradients peaked and were large enough to activate solute diffusion process in the membrane. While CO(2) concentration gradients diminished from their maxima and shifted toward the end of the membrane, HCO(3)(-) concentration gradients peaked at the same position. Also, CO(2) concentration decreased rapidly within the first 47 minutes while optimal HCO(3)(-) concentration was achieved within 30 minutes of the therapy. Abnormally high diffusion fluxes were observed near the blood-membrane interface that increased diffusion driving force and enhanced the overall diffusive process. While convective flux dominated total flux during the dialysis session, there was a continuous interference between convection and diffusion fluxes that call for the need to seek minimal interference between these two mechanisms. This is critical for the effective design and operation of high-flux dialyzers.
Directory of Open Access Journals (Sweden)
Kodwo Annan
2012-01-01
Full Text Available The efficiency of a high-flux dialyzer in terms of buffering and toxic solute removal largely depends on the ability to use convection-diffusion mechanism inside the membrane. A two-dimensional transient convection-diffusion model coupled with acid-base correction term was developed. A finite volume technique was used to discretize the model and to numerically simulate it using MATLAB software tool. We observed that small solute concentration gradients peaked and were large enough to activate solute diffusion process in the membrane. While CO2 concentration gradients diminished from their maxima and shifted toward the end of the membrane, concentration gradients peaked at the same position. Also, CO2 concentration decreased rapidly within the first 47 minutes while optimal concentration was achieved within 30 minutes of the therapy. Abnormally high diffusion fluxes were observed near the blood-membrane interface that increased diffusion driving force and enhanced the overall diffusive process. While convective flux dominated total flux during the dialysis session, there was a continuous interference between convection and diffusion fluxes that call for the need to seek minimal interference between these two mechanisms. This is critical for the effective design and operation of high-flux dialyzers.
Convective Propagation Characteristics Using a Simple Representation of Convective Organization
Neale, R. B.; Mapes, B. E.
2016-12-01
Observed equatorial wave propagation is intimately linked to convective organization and it's coupling to features of the larger-scale flow. In this talk we a use simple 4 level model to accommodate vertical modes of a mass flux convection scheme (shallow, mid-level and deep). Two paradigms of convection are used to represent convective processes. One that has only both random (unorganized) diagnosed fluctuations of convective properties and one with organized fluctuations of convective properties that are amplified by previously existing convection and has an explicit moistening impact on the local convecting environment We show a series of model simulations in single-column, 2D and 3D configurations, where the role of convective organization in wave propagation is shown to be fundamental. For the optimal choice of parameters linking organization to local atmospheric state, a broad array of convective wave propagation emerges. Interestingly the key characteristics of propagating modes are the low-level moistening followed by deep convection followed by mature 'large-scale' heating. This organization structure appears to hold firm across timescales from 5-day wave disturbances to MJO-like wave propagation.
El-Amin, Mohamed
2011-05-14
In this paper, a finite difference scheme is developed to solve the unsteady problem of combined heat and mass transfer from an isothermal curved surface to a porous medium saturated by a non-Newtonian fluid. The curved surface is kept at constant temperature and the power-law model is used to model the non-Newtonian fluid. The explicit finite difference method is used to solve simultaneously the equations of momentum, energy and concentration. The consistency of the explicit scheme is examined and the stability conditions are determined for each equation. Boundary layer and Boussinesq approximations have been incorporated. Numerical calculations are carried out for the various parameters entering into the problem. Velocity, temperature and concentration profiles are shown graphically. It is found that as time approaches infinity, the values of wall shear, heat transfer coefficient and concentration gradient at the wall, which are entered in tables, approach the steady state values.
Energy Technology Data Exchange (ETDEWEB)
Jiji, L.M. [City Univ. of New York, NY (United States). Dept. of Mechanical Engineering
2006-07-01
Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the following ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters. (orig.)
Jiji, Latif M.
Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the follow ing ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters.
Convective Replica-Exchange in Ergodic Regimes.
Signorini, Giorgio F; Giovannelli, Edoardo; Spill, Yannick G; Nilges, Michael; Chelli, Riccardo
2014-03-11
In a recent article (J. Comput. Chem. 2013, 34, 132-140), convective replica-exchange (convective-RE) has been presented as an alternative to the standard even-odd transition scheme. Computations on systems of various complexity have shown that convective-RE may increase the number of replica round-trips in temperature space with respect to the standard exchange scheme, leading to a more effective sampling of energy basins. Moreover, it has been shown that the method may prevent the formation of bottlenecks in the diffusive walk of replicas through the space of temperature states. By using an ideal temperature-RE model and a classical harmonic-oscillator RE scheme, we study the performances of convective-RE when ergodicity is not broken and convergence of acceptance probabilities is attained. In this dynamic regime, the round-trip ratio between convective and standard-RE is at maximum ∼ 1.5, a value much smaller than that observed in nonergodic simulations. For large acceptance probabilities, the standard-RE outperforms convective-RE. Our observations suggest that convective-RE can safely be used in either ergodic or non-ergodic regimes; however, convective-RE is advantageous only when bottlenecks occur in the state-space diffusion of replicas, or when acceptance probabilities are globally low. We also show that decoupling of the state-space dynamics of the stick replica from the dynamics of the remaining replicas improves the efficiency of convective-RE at low acceptance probability regimes.
National Convective Weather Diagnostic
National Oceanic and Atmospheric Administration, Department of Commerce — Current convective hazards identified by the National Convective Weather Detection algorithm. The National Convective Weather Diagnostic (NCWD) is an automatically...
Thorogood, Robert M.
1983-01-01
A convective heater for heating fluids such as a coal slurry is constructed of a tube circuit arrangement which obtains an optimum temperature distribution to give a relatively constant slurry film temperature. The heater is constructed to divide the heating gas flow into two equal paths and the tube circuit for the slurry is arranged to provide a mixed flow configuration whereby the slurry passes through the two heating gas paths in successive co-current, counter-current and co-current flow relative to the heating gas flow. This arrangement permits the utilization of minimum surface area for a given maximum film temperature of the slurry consistent with the prevention of coke formation.
CONVECTION IN CONDENSIBLE-RICH ATMOSPHERES
Energy Technology Data Exchange (ETDEWEB)
Ding, F. [Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637 (United States); Pierrehumbert, R. T., E-mail: fding@uchicago.edu [Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom)
2016-05-01
Condensible substances are nearly ubiquitous in planetary atmospheres. For the most familiar case—water vapor in Earth’s present climate—the condensible gas is dilute, in the sense that its concentration is everywhere small relative to the noncondensible background gases. A wide variety of important planetary climate problems involve nondilute condensible substances. These include planets near or undergoing a water vapor runaway and planets near the outer edge of the conventional habitable zone, for which CO{sub 2} is the condensible. Standard representations of convection in climate models rely on several approximations appropriate only to the dilute limit, while nondilute convection differs in fundamental ways from dilute convection. In this paper, a simple parameterization of convection valid in the nondilute as well as dilute limits is derived and used to discuss the basic character of nondilute convection. The energy conservation properties of the scheme are discussed in detail and are verified in radiative-convective simulations. As a further illustration of the behavior of the scheme, results for a runaway greenhouse atmosphere for both steady instellation and seasonally varying instellation corresponding to a highly eccentric orbit are presented. The latter case illustrates that the high thermal inertia associated with latent heat in nondilute atmospheres can damp out the effects of even extreme seasonal forcing.
Added value of convection-permitting reanalyses
Wahl, S.; Keller, J. D.; Ohlwein, C.; Hense, A.; Friederichs, P.; Crewell, S.
2016-12-01
Atmospheric reanalyses are a state-of-the-art tool to generate consistent and realistic state estimates of the atmospheric system. They are used for validation of meteorological and hydrological models, climate monitoring, and renewable energy applications, amongst others. Current reanalyses are mainly global, while regional reanalyses are emerging for North America, the polar region, and most recently for Europe. Due to the horizontal resolution used, deep convection is still parameterized even in the regional reanalyses. However, convective parameterization is a major source of errors and uncertainties in atmospheric models. Therefore, it is expected that convection permitting reanalysis systems are able to adequately simulate the mechanisms leading to high-impact weather, notably heavy precipitation and winds related to deep moist convection. A novel convective-scale regional reanalysis system for Central Europe (COSMO-REA2) has been developed by the Hans-Ertel Center for Weather Research - Climate Monitoring Branch. The system is based on the COSMO model and uses a nudging scheme for the assimilation of observational data. In addition, radar-derived rain rates are assimilated through a latent heat nudging scheme. With a horizontal grid-spacing of 2 km, the model parameterization for deep moist convective processes is turned off. As we expect the largest benefit of the convection-permitting system for precipitation, the evaluation focuses on this essential climate variable (ECV). Furthermore, precipitation is crucial for climate monitoring purposes, e.g., in the form of extreme precipitation which is an major cause of severe damages and societal costs in Europe. This study illustrates the added value of the convective-scale reanalysis compared to coarser gridded regional European and global reanalyses.
Convective transfers; Transferts convectifs
Energy Technology Data Exchange (ETDEWEB)
Accary, G.; Raspo, I.; Bontoux, P. [Aix-Marseille-3 Univ. Paul Cezanne, CNRS, Lab. MSNM-GP UMR 6181, 13 - Marseille (France); Zappoli, B. [Centre National d' Etudes Spatiales (CNES), 31 - Toulouse (France); Polidori, G.; Fohanno, S. [Laboratoire de Thermomecanique, 51 - Reims (France); Hirata, S.C.; Goyeau, B.; Gobin, D. [Paris-6 et Paris-11 Univ., FAST-UMR CNRS 7608, 91 - Orsay (France); Cotta, R.M. [UFRJ/LTTC/PEM/EE/COPPE, Rio de Janeiro (Brazil); Perrin, L.; Reulet, P.; Micheli, F.; Millan, P. [Office National d' Etudes et de Recherches Aerospatiales (ONERA), 31 - Toulouse (France); Menard, V. [France Telecom R and D, 22 - Lannion (France); Benkhelifa, A.; Penot, F. [Ecole Nationale Superieure de Mecanique et d' Aerotechnique (ENSMA), Lab. d' Etudes Thermiques, UMR CNRS 6608, 86 - Poitiers (France); Ng Wing Tin, M.; Haquet, J.F.; Journeau, C. [CEA Cadarache (DEN/DTN/STRI/LMA), Lab. d' Essais pour la Maitrise des Accidents Graves, 13 - Saint-Paul-lez-Durance (France); Naffouti, T.; Hammani, M.; Ben Maad, R. [Faculte des Sciences de Tunis, Lab. d' Energetique et des Transferts Thermique et Massique, Dept. de Physique, Tunis (Tunisia); Zinoubi, J. [Institut Preparatoire aux Etudes d' Ingenieurs de Nabeul (Tunisia); Menard, V.; Le Masson, S.; Nortershauser, D. [France Telecom R and D, 22 - Lannion (France); Stitou, A.; Perrin, L.; Millan, P. [ONERA, 31 - Toulouse (France)
2005-07-01
This session about convective transfers gathers 31 articles dealing with: numerical study of the hydrodynamic stability of a bottom heated supercritical fluid layer; establishment of laminar-turbulent transition criteria of free convection dynamic and thermal boundary layers; heat transfer changes in free convection by mechanical and thermal disturbances; natural convection stability in partially porous horizontal layers; experimental characterization of the dynamic and thermal aspects of a natural convection flow inside a confined space; determination of transitions towards non-stationary natural convection inside a differentially heated inclined cavity; interface temperatures for the convection of fluids with variable viscosity; influence of the height of a vertical cylinder on the flow resulting from a plume-thermosyphon interaction; simultaneous measurement of dynamic and thermal fields by thermo-chromic liquid crystals in natural convection; numerical simulation of turbulent natural convection flows inside a heated room; numerical and experimental study of mixed convection heat transfer inside an axisymmetrical network; analysis of laminar flow instabilities in assisted mixed convection; entropy generation in mixed convection; thermal and mass convection in non-stationary regime inside a ventilated cavity; study of a low Reynolds number mixed convection flow; numerical study of a convective flow inside a rotating annular cavity; study of the dynamical behaviour of a transient mixed convection flow inside a thick vertical duct; internal laminar convection: selection criteria for the identification of natural, mixed or forced regimes; turbulent flow and convection heat transfer inside a channel with corrugated walls; study of the impact of an axisymmetrical jet on a concave wall; modeling of volume irreversibilities of turbulent forced convection; numerical study of forced convection irreversibilities around a network of cylindrical tubes; estimation of the
National Convective Weather Forecast
National Oceanic and Atmospheric Administration, Department of Commerce — The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated signficant current convection. It is a supplement to, but does NOT...
Toward a Unified Representation of Atmospheric Convection in Variable-Resolution Climate Models
Energy Technology Data Exchange (ETDEWEB)
Walko, Robert [Univ. of Miami, Coral Gables, FL (United States)
2016-11-07
The purpose of this project was to improve the representation of convection in atmospheric weather and climate models that employ computational grids with spatially-variable resolution. Specifically, our work targeted models whose grids are fine enough over selected regions that convection is resolved explicitly, while over other regions the grid is coarser and convection is represented as a subgrid-scale process. The working criterion for a successful scheme for representing convection over this range of grid resolution was that identical convective environments must produce very similar convective responses (i.e., the same precipitation amount, rate, and timing, and the same modification of the atmospheric profile) regardless of grid scale. The need for such a convective scheme has increased in recent years as more global weather and climate models have adopted variable resolution meshes that are often extended into the range of resolving convection in selected locations.
Directory of Open Access Journals (Sweden)
Antonio Vicente Pereira Neto
2011-12-01
Full Text Available Foram realizadas mudanças no esquema de parametrização convectiva de Kain-Fritsch (KF2, para melhor representar a precipitação na região do Centro de Lançamento de Alcântara (CLA em simulações com o modelo regional MM5. Simulações de 24 h em um domínio aproximadamente centrado no CLA, com espaçamento de grade de 30 km foram realizadas para o período de 2005-2006 (calibração e 2008 (validação. O KF2 foi modificado sob a seguinte configuração: passo de tempo de 60 s, uso do esquema de convecção explícita warm rain e uso conjunto dos esquemas de convecção rasa de Grell e do KF2. As mudanças no KF2 foram: aumento da profundidade de nuvem necessária para disparar a convecção profunda e ajuste de alguns parâmetros da função disparo da convecção dependentes da velocidade vertical ascendente na coluna atmosférica. Com as modificações, houve expressiva melhoria na representação do total de precipitação e da fração dos dias do mês com chuva na escala mensal. O padrão espacial de erros no domínio, no entanto, não sofreu muitas alterações sobre o continente (em geral, a precipitação foi melhor representada sobre o continente do que sobre o oceano. Todas as etapas de mudanças e ajustes realizadas no trabalho poderão ser empregadas para melhorar a representação da precipitação em outras regiões específicas.Changes in the Kain-Fritsch convective parameterization scheme (KF2 were included to better represent the precipitation in simulations using the MM5 regional model for the Alcântara Launch Center (CLA region. Daily (24 h integrations for a 30 km grid spacing domain centered in CLA were performed for 2005-2006 (calibration and 2008 (validation. KF2 scheme was modified under the following simulation settings: time step of 60 s, use of warm rain scheme and joint use of Grell and KF2 shallow convection schemes. Changes in KF2 were: increase of minimum cloud depth to initiate deep convection and
Energy Technology Data Exchange (ETDEWEB)
Fan, Jiwen [Pacific Northwest National Laboratory, Richland Washington USA; Liu, Yi-Chin [Pacific Northwest National Laboratory, Richland Washington USA; Air Resources Board, Sacramento California USA; Xu, Kuan-Man [NASA Langley Research Center, Hampton Virginia USA; North, Kirk [Department of Atmospheric and Oceanic Sciences, McGill University, Montréal Québec Canada; Collis, Scott [Environmental Science Division, Argonne National Laboratory, Argonne Illinois USA; Dong, Xiquan [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Zhang, Guang J. [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Chen, Qian [Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing China; Kollias, Pavlos [Pacific Northwest National Laboratory, Richland Washington USA; Ghan, Steven J. [Pacific Northwest National Laboratory, Richland Washington USA
2015-04-27
The ultimate goal of this study is to improve the representation of convective transport by cumulus parameterization for mesoscale and climate models. As Part 1 of the study, we perform extensive evaluations of cloud-resolving simulations of a squall line and mesoscale convective complexes in midlatitude continent and tropical regions using the Weather Research and Forecasting model with spectral bin microphysics (SBM) and with two double-moment bulk microphysics schemes: a modified Morrison (MOR) and Milbrandt and Yau (MY2). Compared to observations, in general, SBM gives better simulations of precipitation and vertical velocity of convective cores than MOR and MY2 and therefore will be used for analysis of scale dependence of eddy transport in Part 2. The common features of the simulations for all convective systems are (1) themodel tends to overestimate convection intensity in the middle and upper troposphere, but SBM can alleviate much of the overestimation and reproduce the observed convection intensity well; (2) the model greatly overestimates Ze in convective cores, especially for the weak updraft velocity; and (3) the model performs better for midlatitude convective systems than the tropical system. The modeled mass fluxes of the midlatitude systems are not sensitive to microphysics schemes but are very sensitive for the tropical case indicating strong microphysics modification to convection. Cloud microphysical measurements of rain, snow, and graupel in convective cores will be critically important to further elucidate issues within cloud microphysics schemes
DEFF Research Database (Denmark)
van Leeuwen, Theo
2013-01-01
This chapter presents a framework for analysing colour schemes based on a parametric approach that includes not only hue, value and saturation, but also purity, transparency, luminosity, luminescence, lustre, modulation and differentiation.......This chapter presents a framework for analysing colour schemes based on a parametric approach that includes not only hue, value and saturation, but also purity, transparency, luminosity, luminescence, lustre, modulation and differentiation....
Description and Application of the CE-SE Scheme
Directory of Open Access Journals (Sweden)
Martin KOSÍK
2010-12-01
Full Text Available The CE-SE scheme is new numerical methodology for conservation laws. It was developed by Dr.Chang of NASA Glenn Research Center and his collaborators. The 1D and 2D variant of CE-SE scheme for scalar convection and for Euler equations for incompressible flows is described. The CESE scheme is compared with classical schemes in 1D. The solution to inviscid incompressible flow in GAMM channel in 2D is presented.
Cheng, W. Y.; Kim, D.; Rowe, A.; Park, S.
2017-12-01
Despite the impact of mesoscale convective organization on the properties of convection (e.g., mixing between updrafts and environment), parameterizing the degree of convective organization has only recently been attempted in cumulus parameterization schemes (e.g., Unified Convection Scheme UNICON). Additionally, challenges remain in determining the degree of convective organization from observations and in comparing directly with the organization metrics in model simulations. This study addresses the need to objectively quantify the degree of mesoscale convective organization using high quality S-PolKa radar data from the DYNAMO field campaign. One of the most noticeable aspects of mesoscale convective organization in radar data is the degree of convective clustering, which can be characterized by the number and size distribution of convective echoes and the distance between them. We propose a method of defining contiguous convective echoes (CCEs) using precipitating convective echoes identified by a rain type classification algorithm. Two classification algorithms, Steiner et al. (1995) and Powell et al. (2016), are tested and evaluated against high-resolution WRF simulations to determine which method better represents the degree of convective clustering. Our results suggest that the CCEs based on Powell et al.'s algorithm better represent the dynamical properties of the convective updrafts and thus provide the basis of a metric for convective organization. Furthermore, through a comparison with the observational data, the WRF simulations driven by the DYNAMO large-scale forcing, similarly applied to UNICON Single Column Model simulations, will allow us to evaluate the ability of both WRF and UNICON to simulate convective clustering. This evaluation is based on the physical processes that are explicitly represented in WRF and UNICON, including the mechanisms leading to convective clustering, and the feedback to the convective properties.
Belikov, D.A.; Maksyutov, S.; Krol, M.C.; Fraser, A.; Rigby, M.; Bian, H.; Agusti-Panareda, A.; Bergmann, D.; Bousquet, P.; Cameron-Smith, P.; Chipperfield, M.P.; Fortems-Cheiney, A.; Gloor, E.; Haynes, K.; Hess, P.; Houweling, S.; Kawa, S.R.; Law, R.M.; Loh, Z.; Meng, L.; Palmer, P.I.; Patra, P.K.; Prinn, R.G.; Saito, R.; Wilson, C.
2013-01-01
A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical
J.K. Hoogland (Jiri); C.D.D. Neumann
2000-01-01
textabstractIn this article we present a new approach to the numerical valuation of derivative securities. The method is based on our previous work where we formulated the theory of pricing in terms of tradables. The basic idea is to fit a finite difference scheme to exact solutions of the pricing
Directory of Open Access Journals (Sweden)
Nordlund Åke
2009-04-01
Full Text Available We review the properties of solar convection that are directly observable at the solar surface, and discuss the relevant underlying physics, concentrating mostly on a range of depths from the temperature minimum down to about 20 Mm below the visible solar surface.The properties of convection at the main energy carrying (granular scales are tightly constrained by observations, in particular by the detailed shapes of photospheric spectral lines and the topology (time- and length-scales, flow velocities, etc. of the up- and downflows. Current supercomputer models match these constraints very closely, which lends credence to the models, and allows robust conclusions to be drawn from analysis of the model properties.At larger scales the properties of the convective velocity field at the solar surface are strongly influenced by constraints from mass conservation, with amplitudes of larger scale horizontal motions decreasing roughly in inverse proportion to the scale of the motion. To a large extent, the apparent presence of distinct (meso- and supergranulation scales is a result of the folding of this spectrum with the effective “filters” corresponding to various observational techniques. Convective motions on successively larger scales advect patterns created by convection on smaller scales; this includes patterns of magnetic field, which thus have an approximately self-similar structure at scales larger than granulation.Radiative-hydrodynamical simulations of solar surface convection can be used as 2D/3D time-dependent models of the solar atmosphere to predict the emergent spectrum. In general, the resulting detailed spectral line profiles agree spectacularly well with observations without invoking any micro- and macroturbulence parameters due to the presence of convective velocities and atmosphere inhomogeneities. One of the most noteworthy results has been a significant reduction in recent years in the derived solar C, N, and O abundances with
Observing Convective Aggregation
Holloway, Christopher E.; Wing, Allison A.; Bony, Sandrine; Muller, Caroline; Masunaga, Hirohiko; L'Ecuyer, Tristan S.; Turner, David D.; Zuidema, Paquita
2017-11-01
Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.
Stein, Robert F
2012-07-13
Convection is the transport of energy by bulk mass motions. Magnetic fields alter convection via the Lorentz force, while convection moves the fields via the curl(v×B) term in the induction equation. Recent ground-based and satellite telescopes have increased our knowledge of the solar magnetic fields on a wide range of spatial and temporal scales. Magneto-convection modelling has also greatly improved recently as computers become more powerful. Three-dimensional simulations with radiative transfer and non-ideal equations of state are being performed. Flux emergence from the convection zone through the visible surface (and into the chromosphere and corona) has been modelled. Local, convectively driven dynamo action has been studied. The alteration in the appearance of granules and the formation of pores and sunspots has been investigated. Magneto-convection calculations have improved our ability to interpret solar observations, especially the inversion of Stokes spectra to obtain the magnetic field and the use of helioseismology to determine the subsurface structure of the Sun.
Transition to finger convection in double-diffusive convection
Kellner, M.; Tilgner, A.
2014-01-01
Finger convection is observed experimentally in an electrodeposition cell in which a destabilizing gradient of copper ions is maintained against a stabilizing temperature gradient. This double-diffusive system shows finger convection even if the total density stratification is unstable. Finger convection is replaced by an ordinary convection roll if convection is fast enough to prevent sufficient heat diffusion between neighboring fingers, or if the thermal buoyancy force is less than 1/30 of...
Kakac, Sadik; Pramuanjaroenkij, Anchasa
2014-01-01
Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....
A shallow convection parameterization for the non-hydrostatic MM5 mesoscale model
Energy Technology Data Exchange (ETDEWEB)
Seaman, N.L.; Kain, J.S.; Deng, A. [Pennsylvania State Univ., University Park, PA (United States)
1996-04-01
A shallow convection parameterization suitable for the Pennsylvannia State University (PSU)/National Center for Atmospheric Research nonhydrostatic mesoscale model (MM5) is being developed at PSU. The parameterization is based on parcel perturbation theory developed in conjunction with a 1-D Mellor Yamada 1.5-order planetary boundary layer scheme and the Kain-Fritsch deep convection model.
Energy Technology Data Exchange (ETDEWEB)
Ghadimi, Mohammad; Ghadamian, Hossein [Islamic Azad Univ., Tehran (Iran, Islamic Republic of). Dept. of Energy Engineering, Science and Research Branch; Hamidi, Aliasghar A. [Tehran Univ. (Iran, Islamic Republic of). Dept. of Chemical Engineering; Fazelpour, Farivar [Islamic Azad Univ. of South Tehran Branch, Tehran (Iran, Islamic Republic of). Dept. of Energy System Engineering; Behghadam, Mehdi [Islamic Azad Univ. of Roudehen Branch, Tehran (Iran, Islamic Republic of). Dept. of Mechanical Engineering
2012-11-01
The present paper describes a two-dimensional finite volume numerical simulation of flow and heat transfer in airflow windows by free and forced convection techniques. The governing equations are the fully elliptic, Reynolds-averaged Navier-Stokes equations. The simple algorithm is employed to correct the pressure term. The second-order upwind scheme is used to discretize the convection terms. The (k-{epsilon}/RNG) turbulence model is applied for the flow simulation. The mesh used is the body-fitted, multi-plane grid system. Results on the variations of velocity and temperature profiles with geometrical parameters, at different temperature and velocity, for heat transfer by free and forced convection techniques are presented. Comparisons of the present results on temperature distribution for forced convection and for free convection with the available experimental forced convection data indicate that the airflow-influenced forced convection methods are considerably enhanced. (orig.)
Is Convection Sensitive to Model Vertical Resolution and Why?
Xie, S.; Lin, W.; Zhang, G. J.
2017-12-01
Model sensitivity to horizontal resolutions has been studied extensively, whereas model sensitivity to vertical resolution is much less explored. In this study, we use the US Department of Energy (DOE)'s Accelerated Climate Modeling for Energy (ACME) atmosphere model to examine the sensitivity of clouds and precipitation to the increase of vertical resolution of the model. We attempt to understand what results in the behavior change (if any) of convective processes represented by the unified shallow and turbulent scheme named CLUBB (Cloud Layers Unified by Binormals) and the Zhang-McFarlane deep convection scheme in ACME. A short-term hindcast approach is used to isolate parameterization issues from the large-scale circulation. The analysis emphasizes on how the change of vertical resolution could affect precipitation partitioning between convective- and grid-scale as well as the vertical profiles of convection-related quantities such as temperature, humidity, clouds, convective heating and drying, and entrainment and detrainment. The goal is to provide physical insight into potential issues with model convective processes associated with the increase of model vertical resolution. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Numerical schemes for explosion hazards
International Nuclear Information System (INIS)
Therme, Nicolas
2015-01-01
In nuclear facilities, internal or external explosions can cause confinement breaches and radioactive materials release in the environment. Hence, modeling such phenomena is crucial for safety matters. Blast waves resulting from explosions are modeled by the system of Euler equations for compressible flows, whereas Navier-Stokes equations with reactive source terms and level set techniques are used to simulate the propagation of flame front during the deflagration phase. The purpose of this thesis is to contribute to the creation of efficient numerical schemes to solve these complex models. The work presented here focuses on two major aspects: first, the development of consistent schemes for the Euler equations, then the buildup of reliable schemes for the front propagation. In both cases, explicit in time schemes are used, but we also introduce a pressure correction scheme for the Euler equations. Staggered discretization is used in space. It is based on the internal energy formulation of the Euler system, which insures its positivity and avoids tedious discretization of the total energy over staggered grids. A discrete kinetic energy balance is derived from the scheme and a source term is added in the discrete internal energy balance equation to preserve the exact total energy balance at the limit. High order methods of MUSCL type are used in the discrete convective operators, based solely on material velocity. They lead to positivity of density and internal energy under CFL conditions. This ensures that the total energy cannot grow and we can furthermore derive a discrete entropy inequality. Under stability assumptions of the discrete L8 and BV norms of the scheme's solutions one can prove that a sequence of converging discrete solutions necessarily converges towards the weak solution of the Euler system. Besides it satisfies a weak entropy inequality at the limit. Concerning the front propagation, we transform the flame front evolution equation (the so
Mode-to-mode energy transfers in convective patterns
Indian Academy of Sciences (India)
Abstract. We investigate the energy transfer between various Fourier modes in a low- dimensional model for thermal convection. We have used the formalism of mode-to-mode energy transfer rate in our calculation. The evolution equations derived using this scheme is the same as those derived using the hydrodynamical ...
Peters, Karsten; Jakob, Christian; Möbis, Benjamin
2015-04-01
An adequate representation of convective processes in numerical models of the atmospheric circulation (general circulation models, GCMs) remains one of the grand challenges in atmospheric science. In particular, the models struggle with correctly representing the spatial distribution and high variability of tropical convection. It is thought that this model deficiency partly results from formulating current convection parameterisation schemes in a purely deterministic manner. Here, we use observations of tropical convection to inform the design of a novel convection parameterisation with stochastic elements. The novel scheme is built around the Stochastic MultiCloud Model (SMCM, Khouider et al 2010). We present the progress made in utilising SMCM-based estimates of updraft area fractions at cloud base as part of the deep convection scheme of a GCM. The updraft area fractions are used to yield one part of the cloud base mass-flux used in the closure assumption of convective mass-flux schemes. The closure thus receives a stochastic component, potentially improving modeled convective variability and coherence. For initial investigations, we apply the above methodology to the operational convective parameterisation of the ECHAM6 GCM. We perform 5-year AMIP simulations, i.e. with prescribed observed SSTs. We find that with the SMCM, convection is weaker and more coherent and continuous from timestep to timestep compared to the standard model. Total global precipitation is reduced in the SMCM run, but this reduces i) the overall error compared to observed global precipitation (GPCP) and ii) middle tropical tropospheric temperature biases compared to ERA-Interim. Hovmoeller diagrams indicate a slightly higher degree of convective organisation compared to the base case and Wheeler-Kiladis frequency wavenumber diagrams indicate slightly more spectral power in the MJO range.
Analysis of explicit multirate and partitioned Runge-Kutta schemes for conservation laws
W. Hundsdorfer (Willem); A. Mozartova (Anna); V. Savcenco (Valeriu)
2007-01-01
textabstractMultirate schemes for conservation laws or convection-dominated problems seem to come in two flavors: schemes that are locally inconsistent, and schemes that lack mass-conservation. In this paper these two defects are discussed for one-dimensional conservation laws. Particular attention
Mathematical models of convection
Andreev, Victor K; Goncharova, Olga N; Pukhnachev, Vladislav V
2012-01-01
Phenomena of convection are abundant in nature as well as in industry. This volume addresses the subject of convection from the point of view of both, theory and application. While the first three chapters provide a refresher on fluid dynamics and heat transfer theory, the rest of the book describes the modern developments in theory. Thus it brings the reader to the ""front"" of the modern research. This monograph provides the theoretical foundation on a topic relevant to metallurgy, ecology, meteorology, geo-and astrophysics, aerospace industry, chemistry, crystal physics, and many other fiel
Scheme Program Documentation Tools
DEFF Research Database (Denmark)
Nørmark, Kurt
2004-01-01
This paper describes and discusses two different Scheme documentation tools. The first is SchemeDoc, which is intended for documentation of the interfaces of Scheme libraries (APIs). The second is the Scheme Elucidator, which is for internal documentation of Scheme programs. Although the tools...... as named functions in Scheme. Finally, the Scheme Elucidator is able to integrate SchemeDoc resources as part of an internal documentation resource....
CDM Convective Forecast Planning guidance
National Oceanic and Atmospheric Administration, Department of Commerce — The CDM Convective Forecast Planning (CCFP) guidance product provides a foreast of en-route aviation convective hazards. The forecasts are updated every 2 hours and...
Additive operator-difference schemes splitting schemes
Vabishchevich, Petr N
2013-01-01
Applied mathematical modeling isconcerned with solving unsteady problems. This bookshows how toconstruct additive difference schemes to solve approximately unsteady multi-dimensional problems for PDEs. Two classes of schemes are highlighted: methods of splitting with respect to spatial variables (alternating direction methods) and schemes of splitting into physical processes. Also regionally additive schemes (domain decomposition methods)and unconditionally stable additive schemes of multi-component splitting are considered for evolutionary equations of first and second order as well as for sy
Convective overshooting in stars
Andrássy, R.
2015-01-01
Numerous observations provide evidence that the standard picture, in which convective mixing is limited to the unstable layers of a star, is incomplete. The mixing layers in real stars are significantly more extended than what the standard models predict. Some of the observations require changing
Stochasticc convection parameterization
Dorrestijn, J.
2016-01-01
Clouds are chaotic, difficult to predict, but above all, magnificent natural phenomena. There are different types of clouds: stratus, a layer of clouds that may produce drizzle, cirrus, clouds in the higher parts of the atmosphere, and cumulus, clouds that arise in convective updrafts. Thermals,
Lui, Yuk Sing; Tam, Chi Yung Francis; Au-Yeung, Yee Man
2017-04-01
This study examines the sensitivity of precipitation simulations over the CORDEX-Southeast Asia (SEA) domain to the cumulus convection scheme used in the Regional Climate Model version 4 (RegCM4). With the ERA-interim reanalysis as lateral boundary conditions, model integrations using the MIT-Emanuel cumulus parameterization scheme, and those using a "mixed convection scheme" (namely with the MIT-Emanuel scheme over ocean and the Grell scheme with Arakawa Schubert-type closure over land), have been carried out for the 2001-2010 period. On the seasonal average, the use of the mixed convection scheme, in comparison to MIT-Emanuel scheme everywhere, improves rainfall simulations over the South China Sea (SCS) by reducing the summer-time wet bias there. On the other hand, runs with the mixed convection scheme under(over)-estimate rainfall over land in Southeastern China (western coastlines of Indochina and the Philippines). For the diurnal variation of precipitation, it is found that the RegCM4 can reproduce well the characteristics of the diurnal cycle (DC) in SEA. Compared with the mixed convection scheme, the MIT-Emanual scheme performs better in reproducing the amplitude and phase of DC over the landside coastal area of Indochina during summer. Empirical Orthogonal Function (EOF) analysis indicates that switching from the MIT-Emanuel scheme to the mixed convection scheme leads to a reduction in importance of the second EOF mode, which corresponds to rainfall peaked in the afternoon (local time). Further analyses reveal that such underestimation is related to increased cloud cover in RegCM4 using the mixed convection scheme; enhanced cloudiness in turn leads to reduced surface air temperature over land and thus reduced convective instability at 1200 and 1500 local time in the model simulations.
Convective heat transfer on Mars
International Nuclear Information System (INIS)
Arx, A.V. von; Delgado, A. Jr.
1991-01-01
An examination was made into the feasibility of using convective heat transfer on Mars to reject the waste heat from a Closed Brayton Cycle. Forced and natural convection were compared to thermal radiation. For the three radiator configurations studied, it was concluded that thermal radiation will yield the minimum mass and forced convection will result in the minimum area radiator. Other issues such as reliability of a fan motor were not addressed. Convective heat transfer on Mars warrants further investigation. However, the low density of the Martian atmosphere makes it difficult to utilize convective heat transfer without incurring a weight penalty
New bounded skew central difference scheme. Part 1: Formulation and testing
Energy Technology Data Exchange (ETDEWEB)
Moukalled, F.; Darwish, M. [American Univ. of Beirut (Lebanon)
1997-01-01
The skew central difference scheme is combined with the normalized variable formulation to yield a new bounded skew central difference scheme. The newly developed scheme is tested and compared with the upwind scheme, the bounded skew upwind scheme, and the high-resolution SMART scheme by solving four problems: (1) pure convection of a step profile in an oblique velocity field; (2) sudden expansion of an oblique flow field in a rectangular cavity; (3) driven flow in a skew cavity; and (4) gradual expansion in an axisymmetric, nonorthogonal channel. Results generated reveal the new scheme to be bounded and to be the most accurate among those investigated.
Convection and stellar oscillations
DEFF Research Database (Denmark)
Aarslev, Magnus Johan
2017-01-01
energy exchange between convection and pulsations, i.e. the modal part of the surface effect. Studying excitation and damping mechanisms requires a non-adiabatic treatment. A major part of my research has been modelling damping rates of red giant stars observed by {\\Kp}. The basis for the non...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them....... However, the effects are barely prominent enough to be distinguishable with today's observational precision. But it does provide means of determining the mixing-length and enables consistent patching. The previously mentioned investigations are based on adiabatic frequency calculations, which neglect...
Bejan, Adrian
2013-01-01
Written by an internationally recognized authority on heat transfer and thermodynamics, this second edition of Convection Heat Transfer contains new and updated problems and examples reflecting real-world research and applications, including heat exchanger design. Teaching not only structure but also technique, the book begins with the simplest problem solving method (scale analysis), and moves on to progressively more advanced and exact methods (integral method, self similarity, asymptotic behavior). A solutions manual is available for all problems and exercises.
Isotta, Francesco; Spichtinger, Peter; Lohmann, Ulrike; von Salzen, Knut
2010-05-01
Convection is a crucial component of weather and climate. Its parameterization in General Circulation Models (GCMs) is one of the largest sources of uncertainty. Convection redistributes moisture and heat, affects the radiation budget and transports tracers from the PBL to higher levels. Shallow convection is very common over the globe, in particular over the oceans in the trade wind regions. A recently developed shallow convection scheme by von Salzen and McFarlane (2002) is implemented in the ECHAM5-HAM GCM instead of the standard convection scheme by Tiedtke (1989). The scheme of von Salzen and McFarlane (2002) is a bulk parameterization for an ensemble of transient shallow cumuli. A life cycle is considered, as well as inhomogeneities in the horizontal distribution of in-cloud properties due to mixing. The shallow convection scheme is further developed to take the ice phase and precipitation in form of rain and snow into account. The double moment microphysics scheme for cloud droplets and ice crystals implemented is consistent with the stratiform scheme and with the other types of convective clouds. The ice phase permits to alter the criterion to distinguish between shallow convection and the other two types of convection, namely deep and mid-level, which are still calculated by the Tiedtke (1989) scheme. The lunching layer of the test parcel in the shallow convection scheme is chosen as the one with maximum moist static energy in the three lowest levels. The latter is modified to the ``frozen moist static energy'' to account for the ice phase. Moreover, tracers (e.g. aerosols) are transported in the updraft and scavenged in and below clouds. As a first test of the performance of the new scheme and the interaction with the rest of the model, the Barbados Oceanographic and Meteorological EXperiment (BOMEX) and the Rain In Cumulus over the Ocean experiment (RICO) case are simulated with the single column model (SCM) and the results are compared with large eddy
Theoretical basis for convective invigoration due to increased aerosol concentration
Directory of Open Access Journals (Sweden)
Z. J. Lebo
2011-06-01
Full Text Available The potential effects of increased aerosol loading on the development of deep convective clouds and resulting precipitation amounts are studied by employing the Weather Research and Forecasting (WRF model as a detailed high-resolution cloud resolving model (CRM with both detailed bulk and bin microphysics schemes. Both models include a physically-based activation scheme that incorporates a size-resolved aerosol population. We demonstrate that the aerosol-induced effect is controlled by the balance between latent heating and the increase in condensed water aloft, each having opposing effects on buoyancy. It is also shown that under polluted conditions, increases in the CCN number concentration reduce the cumulative precipitation due to the competition between the sedimentation and evaporation/sublimation timescales. The effect of an increase in the IN number concentration on the dynamics of deep convective clouds is small and the resulting decrease in domain-averaged cumulative precipitation is shown not to be statistically significant, but may act to suppress precipitation. It is also shown that even in the presence of a decrease in the domain-averaged cumulative precipitation, an increase in the precipitation variance, or in other words, andincrease in rainfall intensity, may be expected in more polluted environments, especially in moist environments.
A significant difference exists between the predictions based on the bin and bulk microphysics schemes of precipitation and the influence of aerosol perturbations on updraft velocity within the convective core. The bulk microphysics scheme shows little change in the latent heating rates due to an increase in the CCN number concentration, while the bin microphysics scheme demonstrates significant increases in the latent heating aloft with increasing CCN number concentration. This suggests that even a detailed two-bulk microphysics scheme, coupled to a detailed activation scheme, may not be
Wu, Longtao; Wong, Sun; Wang, Tao; Huffman, George J.
2018-01-01
Simulation of moist convective processes is critical for accurately representing the interaction among tropical wave activities, atmospheric water vapor transport, and clouds associated with the Indian monsoon Intraseasonal Oscillation (ISO). In this study, we apply the Weather Research and Forecasting (WRF) model to simulate Indian monsoon ISO with three different treatments of moist convective processes: (1) the Betts-Miller-Janjić (BMJ) adjustment cumulus scheme without explicit simulation of moist convective processes; (2) the New Simplified Arakawa-Schubert (NSAS) mass-flux scheme with simplified moist convective processes; and (3) explicit simulation of moist convective processes at convection permitting scale (Nest). Results show that the BMJ experiment is unable to properly reproduce the equatorial Rossby wave activities and the corresponding phase relationship between moisture advection and dynamical convergence during the ISO. These features associated with the ISO are approximately captured in the NSAS experiment. The simulation with resolved moist convective processes significantly improves the representation of the ISO evolution, and has good agreements with the observations. This study features the first attempt to investigate the Indian monsoon at convection permitting scale.
A stochastic parameterization for deep convection using cellular automata
Bengtsson, L.; Steinheimer, M.; Bechtold, P.; Geleyn, J.
2012-12-01
Cumulus parameterizations used in most operational weather and climate models today are based on the mass-flux concept which took form in the early 1970's. In such schemes it is assumed that a unique relationship exists between the ensemble-average of the sub-grid convection, and the instantaneous state of the atmosphere in a vertical grid box column. However, such a relationship is unlikely to be described by a simple deterministic function (Palmer, 2011). Thus, because of the statistical nature of the parameterization challenge, it has been recognized by the community that it is important to introduce stochastic elements to the parameterizations (for instance: Plant and Craig, 2008, Khouider et al. 2010, Frenkel et al. 2011, Bentsson et al. 2011, but the list is far from exhaustive). There are undoubtedly many ways in which stochastisity can enter new developments. In this study we use a two-way interacting cellular automata (CA), as its intrinsic nature possesses many qualities interesting for deep convection parameterization. In the one-dimensional entraining plume approach, there is no parameterization of horizontal transport of heat, moisture or momentum due to cumulus convection. In reality, mass transport due to gravity waves that propagate in the horizontal can trigger new convection, important for the organization of deep convection (Huang, 1988). The self-organizational characteristics of the CA allows for lateral communication between adjacent NWP model grid-boxes, and temporal memory. Thus the CA scheme used in this study contain three interesting components for representation of cumulus convection, which are not present in the traditional one-dimensional bulk entraining plume method: horizontal communication, memory and stochastisity. The scheme is implemented in the high resolution regional NWP model ALARO, and simulations show enhanced organization of convective activity along squall-lines. Probabilistic evaluation demonstrate an enhanced spread in
Midlatitude Continental Convective Clouds Experiment (MC3E)
Energy Technology Data Exchange (ETDEWEB)
Jensen, MP; Petersen, WA; Del Genio, AD; Giangrande, SE; Heymsfield, A; Heymsfield, G; Hou, AY; Kollias, P; Orr, B; Rutledge, SA; Schwaller, MR; Zipser, E
2010-04-01
Convective processes play a critical role in the Earth’s energy balance through the redistribution of heat and moisture in the atmosphere and subsequent impacts on the hydrologic cycle. Global observation and accurate representation of these processes in numerical models is vital to improving our current understanding and future simulations of Earth’s climate system. Despite improvements in computing power, current operational weather and global climate models are unable to resolve the natural temporal and spatial scales that are associated with convective and stratiform precipitation processes; therefore, they must turn to parameterization schemes to represent these processes. In turn, the physical basis for these parameterization schemes needs to be evaluated for general application under a variety of atmospheric conditions. Analogously, space-based remote sensing algorithms designed to retrieve related cloud and precipitation information for use in hydrological, climate, and numerical weather prediction applications often rely on physical “parameterizations” that reliably translate indirectly related instrument measurements to the physical quantity of interest (e.g., precipitation rate). Importantly, both spaceborne retrieval algorithms and model convective parameterization schemes traditionally rely on field campaign data sets as a basis for evaluating and improving the physics of their respective approaches. The Midlatitude Continental Convective Clouds Experiment (MC3E) will take place in central Oklahoma during the April–May 2011 period. The experiment is a collaborative effort between the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility and the National Aeronautics and Space Administration’s (NASA) Global Precipitation Measurement (GPM) mission Ground Validation (GV) program. The field campaign leverages the unprecedented observing infrastructure currently available in the central United States
Belikov, D. A.; Maksyutov, S.; Krol, M.; Fraser, A.; Rigby, M.; Bian, H.; Agusti-Panareda, A.; Bergmann, D.; Bousquet, P.; Cameron-Smith, P.; Chipperfield, M. P.; Fortems-Cheiney, A.; Gloor, E.; Haynes, K.; Hess, P.; Houweling, S.; Kawa, S. R.; Law, R. M.; Loh, Z.; Meng, L.; Palmer, P. I.; Patra, P. K.; Prinn, R. G.; Saito, R.; Wilson, C.
2013-02-01
A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES) global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer 222Rn is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of 222Rn are evaluated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH4 Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme in general is consistent with observed and modeled results.
Directory of Open Access Journals (Sweden)
D. A. Belikov
2013-02-01
Full Text Available A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer ^{222}Rn is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of ^{222}Rn are evaluated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH_{4} Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme in general is consistent with observed and modeled results.
Modelling of stellar convection
Kupka, Friedrich; Muthsam, Herbert J.
2017-07-01
The review considers the modelling process for stellar convection rather than specific astrophysical results. For achieving reasonable depth and length we deal with hydrodynamics only, omitting MHD. A historically oriented introduction offers first glimpses on the physics of stellar convection. Examination of its basic properties shows that two very different kinds of modelling keep being needed: low dimensional models (mixing length, Reynolds stress, etc.) and "full" 3D simulations. A list of affordable and not affordable tasks for the latter is given. Various low dimensional modelling approaches are put in a hierarchy and basic principles which they should respect are formulated. In 3D simulations of low Mach number convection the inclusion of then unimportant sound waves with their rapid time variation is numerically impossible. We describe a number of approaches where the Navier-Stokes equations are modified for their elimination (anelastic approximation, etc.). We then turn to working with the full Navier-Stokes equations and deal with numerical principles for faithful and efficient numerics. Spatial differentiation as well as time marching aspects are considered. A list of codes allows assessing the state of the art. An important recent development is the treatment of even the low Mach number problem without prior modification of the basic equation (obviating side effects) by specifically designed numerical methods. Finally, we review a number of important trends such as how to further develop low-dimensional models, how to use 3D models for that purpose, what effect recent hardware developments may have on 3D modelling, and others.
Bidispersive-inclined convection
Mulone, Giuseppe; Straughan, Brian
2016-01-01
A model is presented for thermal convection in an inclined layer of porous material when the medium has a bidispersive structure. Thus, there are the usual macropores which are full of a fluid, but there are also a system of micropores full of the same fluid. The model we employ is a modification of the one proposed by Nield & Kuznetsov (2006 Int. J. Heat Mass Transf. 49, 3068–3074. (doi:10.1016/j.ijheatmasstransfer.2006.02.008)), although we consider a single temperature field only. PMID:27616934
Directory of Open Access Journals (Sweden)
Michael Keller
2016-05-01
Full Text Available Diurnal moist convection is an important element of summer precipitation over Central Europe and the Alps. It is poorly represented in models using parameterized convection. In this study, we investigate the diurnal cycle of convection during 11 days in June 2007 using the COSMO model. The numerical simulations are compared with satellite measurements of GERB and SEVIRI, AVHRR satellite-based cloud properties and ground-based precipitation and temperature measurements. The simulations use horizontal resolutions of 12 km (convection-parameterizing model, CPM and 2 km (convection-resolving model, CRM and either a one-moment microphysics scheme (1M or a two-moment microphysics scheme (2M.They are conducted for a computational domain that covers an extended Alpine area from Northern Italy to Northern Germany. The CPM with 1M exhibits a significant overestimation of high cloud cover. This results in a compensation effect in the top of the atmosphere energy budget due to an underestimation of outgoing longwave radiation (OLR and an overestimation of reflected solar radiation (RSR. The CRM reduces high cloud cover and improves the OLR bias from a domain mean of −20.1 to −2.6 W/m2. When using 2M with ice sedimentation in the CRM, high cloud cover is further reduced. The stronger diurnal cycle of high cloud cover and associated convection over the Alps, compared to less mountainous regions, is well represented by the CRM but underestimated by the CPM. Despite substantial differences in high cloud cover, the use of a 2M has no significant impact on the diurnal cycle of precipitation. Furthermore, a negative mid-level cloud bias is found for all simulations.
Kenfack Jiotsa, Aurélien; Politi, Antonio; Torcini, Alessandro
2013-06-01
We generalize the concept of the convective (or velocity-dependent) Lyapunov exponent from the maximum rate Λ(v) to an entire spectrum Λ(v, n). Our results are derived by following two distinct computational protocols: (i) Legendre transform within the chronotopic approach (Lepri et al 1996 J. Stat. Phys. 82 1429); (ii) by letting evolve an ensemble of initially localized perturbations. The two approaches turn out to be mutually consistent. Moreover, we find the existence of a phase transition: above a critical value n = nc of the integrated density of exponents, the zero-velocity convective exponent is strictly smaller than the corresponding Lyapunov exponent. This phenomenon is traced back to a change of concavity of the so-called temporal Lyapunov spectrum for n > nc, which, therefore, turns out to be a dynamically invariant quantity. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Lyapunov analysis: from dynamical systems theory to applications’.
A satellite infrared technique to estimate tropical convective and stratiform rainfall
Adler, Robert F.; Negri, Andrew J.
1988-01-01
A new method of estimating both convective and stratiform precipitation from satellite infrared data is described. This technique defines convective cores and assigns rain rate and rain area to these features based on the infrared brightness temperature and the cloud model approach of Adler and Mack (1984). The method was tested for four south Florida cases during the second Florida Area Cumulus Experiment, and the results are presented and compared with three other satellite rain estimation schemes.
Improving microphysics in a convective parameterization: possibilities and limitations
Labbouz, Laurent; Heikenfeld, Max; Stier, Philip; Morrison, Hugh; Milbrandt, Jason; Protat, Alain; Kipling, Zak
2017-04-01
The convective cloud field model (CCFM) is a convective parameterization implemented in the climate model ECHAM6.1-HAM2.2. It represents a population of clouds within each ECHAM-HAM model column, simulating up to 10 different convective cloud types with individual radius, vertical velocities and microphysical properties. Comparisons between CCFM and radar data at Darwin, Australia, show that in order to reproduce both the convective cloud top height distribution and the vertical velocity profile, the effect of aerodynamic drag on the rising parcel has to be considered, along with a reduced entrainment parameter. A new double-moment microphysics (the Predicted Particle Properties scheme, P3) has been implemented in the latest version of CCFM and is compared to the standard single-moment microphysics and the radar retrievals at Darwin. The microphysical process rates (autoconversion, accretion, deposition, freezing, …) and their response to changes in CDNC are investigated and compared to high resolution CRM WRF simulations over the Amazon region. The results shed light on the possibilities and limitations of microphysics improvements in the framework of CCFM and in convective parameterizations in general.
Approximation and stability of three-dimensional natural convection flows in a porous medium
International Nuclear Information System (INIS)
Janotto, Marie-Laurence
1991-01-01
The equations of the three-dimensional natural convection in a porous medium within a differentially heated horizontal walls cavity are solved by a pseudo-spectral method. First we will present the evolution of the two main modes according to two models of convection. A few asymptotic properties connected to the small and large eddies are set up and numerically validated. A new approximate inertial manifold is then proposed. The numerical scheme used is an exponential fitting algorithm the convergence of which is proved. We will present the physical mechanism at the origin of the un-stationary three-dimensional convection at high Rayleigh numbers. (author) [fr
Eliseev, A. V.; Coumou, D.; Chernokulsky, A. V.; Petoukhov, V.; Petri, S.
2013-01-01
In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for Earth system models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single-column convective clouds. It distinguishes between ice and
Nield, Donald A
1992-01-01
This book provides a user-friendly introduction to the topic of convection in porous media The authors as- sume that the reader is familiar with the basic elements of fluid mechanics and heat transfer, but otherwise the book is self-contained The book will be useful both as a review (for reference) and as a tutorial work, suitable as a textbook in a graduate course or seminar The book brings into perspective the voluminous research that has been performed during the last two decades The field has recently exploded because of worldwide concern with issues such as energy self-sufficiency and pollution of the environment Areas of application include the insulation of buildings and equipment, energy storage and recovery, geothermal reservoirs, nuclear waste disposal, chemical reactor engineering, and the storage of heat-generating materials such as grain and coal Geophysical applications range from the flow of groundwater around hot intrusions to the stability of snow against avalanches
Nield, Donald A
2013-01-01
Convection in Porous Media, 4th Edition, provides a user-friendly introduction to the subject, covering a wide range of topics, such as fibrous insulation, geological strata, and catalytic reactors. The presentation is self-contained, requiring only routine mathematics and the basic elements of fluid mechanics and heat transfer. The book will be of use not only to researchers and practicing engineers as a review and reference, but also to graduate students and others entering the field. The new edition features approximately 1,750 new references and covers current research in nanofluids, cellular porous materials, strong heterogeneity, pulsating flow, and more. Recognized as the standard reference in the field Includes a comprehensive, 250-page reference list Cited over 2300 times to date in its various editions Serves as an introduction for those entering the field and as a comprehensive reference for experienced researchers Features new sections on nanofluids, carbon dioxide sequestration, and applications...
Internal Wave Generation by Convection
Lecoanet, Daniel Michael
In nature, it is not unusual to find stably stratified fluid adjacent to convectively unstable fluid. This can occur in the Earth's atmosphere, where the troposphere is convective and the stratosphere is stably stratified; in lakes, where surface solar heating can drive convection above stably stratified fresh water; in the oceans, where geothermal heating can drive convection near the ocean floor, but the water above is stably stratified due to salinity gradients; possible in the Earth's liquid core, where gradients in thermal conductivity and composition diffusivities maybe lead to different layers of stable or unstable liquid metal; and, in stars, as most stars contain at least one convective and at least one radiative (stably stratified) zone. Internal waves propagate in stably stratified fluids. The characterization of the internal waves generated by convection is an open problem in geophysical and astrophysical fluid dynamics. Internal waves can play a dynamically important role via nonlocal transport. Momentum transport by convectively excited internal waves is thought to generate the quasi-biennial oscillation of zonal wind in the equatorial stratosphere, an important physical phenomenon used to calibrate global climate models. Angular momentum transport by convectively excited internal waves may play a crucial role in setting the initial rotation rates of neutron stars. In the last year of life of a massive star, convectively excited internal waves may transport even energy to the surface layers to unbind them, launching a wind. In each of these cases, internal waves are able to transport some quantity--momentum, angular momentum, energy--across large, stable buoyancy gradients. Thus, internal waves represent an important, if unusual, transport mechanism. This thesis advances our understanding of internal wave generation by convection. Chapter 2 provides an underlying theoretical framework to study this problem. It describes a detailed calculation of the
Dynamic downscaling over western Himalayas: Impact of cloud microphysics schemes
Tiwari, Sarita; Kar, Sarat C.; Bhatla, R.
2018-03-01
Due to lack of observation data in the region of inhomogeneous terrain of the Himalayas, detailed climate of Himalayas is still unknown. Global reanalysis data are too coarse to represent the hydroclimate over the region with sharp orography gradient in the western Himalayas. In the present study, dynamic downscaling of the European Centre for Medium-Range Weather Forecast (ECMWF) Reanalysis-Interim (ERA-I) dataset over the western Himalayas using high-resolution Weather Research and Forecast (WRF) model has been carried out. Sensitivity studies have also been carried out using convection and microphysics parameterization schemes. The WRF model simulations have been compared against ERA-I and available station observations. Analysis of the results suggests that the WRF model has simulated the hydroclimate of the region well. It is found that in the simulations that the impact of convection scheme is more during summer months than in winter. Examination of simulated results using various microphysics schemes reveal that the WRF single-moment class-6 (WSM6) scheme simulates more precipitation on the upwind region of the high mountain than that in the Morrison and Thompson schemes during the winter period. Vertical distribution of various hydrometeors shows that there are large differences in mixing ratios of ice, snow and graupel in the simulations with different microphysics schemes. The ice mixing ratio in Morrison scheme is more than WSM6 above 400 hPa. The Thompson scheme favors formation of more snow than WSM6 or Morrison schemes while the Morrison scheme has more graupel formation than other schemes.
The convection patterns in microemulsions
International Nuclear Information System (INIS)
Korneta, W.; Lopez Quintela, M.A.; Fernandez Novoa, A.
1991-07-01
The Rayleigh-Benard convection in the microemulsion consisting of water (7.5%), cyclohexan (oil-61.7%) and diethylenglycolmonobutylether (surfactant-30.8%) is studied from the onset of convection to the phase separation. The five classes of convection patterns are observed and recorded on the video: localized travelling waves, travelling waves, travelling waves and localized steady rolls, steady rolls and steady polygons. The Fourier transforms and histograms of these patterns are presented. The origin of any pattern is discussed. The intermittent behaviour close to the phase separation was observed. Possible applications of the obtained results are suggested. (author). 6 refs, 4 figs
Convection-enhanced water evaporation
Directory of Open Access Journals (Sweden)
B. M. Weon
2011-03-01
Full Text Available Water vapor is lighter than air; this can enhance water evaporation by triggering vapor convection but there is little evidence. We directly visualize evaporation of nanoliter (2 to 700 nL water droplets resting on silicon wafer in calm air using a high-resolution dual X-ray imaging method. Temporal evolutions of contact radius and contact angle reveal that evaporation rate linearly changes with surface area, indicating convective (instead of diffusive evaporation in nanoliter water droplets. This suggests that convection of water vapor would enhance water evaporation at nanoliter scales, for instance, on microdroplets or inside nanochannels.
National Research Council Canada - National Science Library
McWilliams, James
1999-01-01
... mechanism of water mass transformation. The resultant newly mixed deep water masses form a component of the thermohaline circulation, and hence it is essential to understand the deep convection process if the variability of the meridional...
Dunn, James C.; Hardee, Harry C.; Striker, Richard P.
1985-01-01
A convective heat flow probe device is provided which measures heat flow and fluid flow magnitude in the formation surrounding a borehole. The probe comprises an elongate housing adapted to be lowered down into the borehole; a plurality of heaters extending along the probe for heating the formation surrounding the borehole; a plurality of temperature sensors arranged around the periphery of the probe for measuring the temperature of the surrounding formation after heating thereof by the heater elements. The temperature sensors and heater elements are mounted in a plurality of separate heater pads which are supported by the housing and which are adapted to be radially expanded into firm engagement with the walls of the borehole. The heat supplied by the heater elements and the temperatures measured by the temperature sensors are monitored and used in providing the desired measurements. The outer peripheral surfaces of the heater pads are configured as segments of a cylinder and form a full cylinder when taken together. A plurality of temperature sensors are located on each pad so as to extend along the length and across the width thereof, with a heating element being located in each pad beneath the temperature sensors. An expansion mechanism driven by a clamping motor provides expansion and retraction of the heater pads and expandable packer-type seals are provided along the probe above and below the heater pads.
Convection-enhanced water evaporation
B. M. Weon; J. H. Je; C. Poulard
2011-01-01
Water vapor is lighter than air; this can enhance water evaporation by triggering vapor convection but there is little evidence. We directly visualize evaporation of nanoliter (2 to 700 nL) water droplets resting on silicon wafer in calm air using a high-resolution dual X-ray imaging method. Temporal evolutions of contact radius and contact angle reveal that evaporation rate linearly changes with surface area, indicating convective (instead of diffusive) evaporation in nanoliter water droplet...
Monotonicity Conditions for Multirate and Partitioned Explicit Runge-Kutta Schemes
Hundsdorfer, Willem
2013-01-01
Multirate schemes for conservation laws or convection-dominated problems seem to come in two flavors: schemes that are locally inconsistent, and schemes that lack mass-conservation. In this paper these two defects are discussed for one-dimensional conservation laws. Particular attention will be given to monotonicity properties of the multirate schemes, such as maximum principles and the total variation diminishing (TVD) property. The study of these properties will be done within the framework of partitioned Runge-Kutta methods. It will also be seen that the incompatibility of consistency and mass-conservation holds for ‘genuine’ multirate schemes, but not for general partitioned methods.
Wang, Yong; Zhang, Guang J.; He, Yu-Jun
2017-12-01
With the incorporation of the Plant-Craig stochastic deep convection scheme into the Zhang-McFarlane deterministic parameterization in the Community Atmospheric Model version 5 (CAM5), its impact on extreme precipitation at different resolutions (2°, 1°, and 0.5°) is investigated. CAM5 with the stochastic deep convection scheme (experiment (EXP)) simulates the precipitation extreme indices better than the standard version (control). At 2° and 1° resolutions, EXP increases high percentile (>99th) daily precipitation over the United States, Europe, and China, resulting in a better agreement with observations. However, at 0.5° resolution, due to enhanced grid-scale precipitation with increasing resolution, EXP overestimates extreme precipitation over southeastern U.S. and eastern Europe. The reduced biases in EXP at each resolution benefit from a broader probability distribution function of convective precipitation intensity simulated. Among EXP simulations at different resolutions, if the spatial averaging area over which input quantities used in convective closure are spatially averaged in the stochastic convection scheme is comparable, the modeled convective precipitation intensity decreases with increasing resolution, when gridded to the same resolution, while the total precipitation is not sensitive to model resolution, exhibiting some degree of scale-awareness. Sensitivity tests show that for the same resolution, increasing the size of spatial averaging area decreases convective precipitation but increases the grid-scale precipitation.
Heat convection in a set of three vertical cylinders
International Nuclear Information System (INIS)
Serrano Ramirez, M.L. de.
1993-01-01
Experimental results on temperature and heat flow in a set of three vertical cylinders with internal generation of heat, water submerged and in free convection are presented in this work . Temperature distribution, Nusselt number and convective coefficient (h) for each rod, developed for the distance between the axis of cylinders in vertical position, as a consequence of the application of power in its outside, are analyzed. Experimental information about heat transfer by free convection in vertical cylinders and surfaces is analyzed. Information of the several author who have carried out studies about the heat transfer on vertical cylinders was compiled, and the proposed equations with the experimental data obtained in the thermo fluids laboratory of National Institute of Nuclear Research (ININ) were tested. The way in which separation distance, s, distribution temperature array, Nusselt number, and convective coefficient calculated for the proposed channel with the Keyhani, Dutton and experimental equations are tabulated and they are plotted for each power value and for each separation between rods. The scheme of the used equipment and the experimentation description as well as the observations of tests and graphical results are included. (Author)
Fan, J.; Han, B.; Varble, A.; Morrison, H.; North, K.; Kollias, P.; Chen, B.; Dong, X.; Giangrande, S. E.; Khain, A.; Lin, Y.; Mansell, E.; Milbrandt, J.; Stenz, R.; Thompson, G.; Wang, Y.
2016-12-01
The large spread in CRM model simulations of deep convection and aerosol effects on deep convective clouds (DCCs) makes it difficult to (1) further our understanding of deep convection and (2) define "benchmarks" and then limit their use in parameterization developments. A constrained model intercomparsion study on a mid-latitude mesoscale squall line is performed using the Weather Research & Forecasting (WRF) model at 1-km horizontal grid spacing with eight cloud microphysics schemes to understand specific processes that lead to the large spreads of simulated convection and precipitation. Various observational data are employed to evaluate the baseline simulations. All simulations tend to produce a wider convective area but a much narrower stratiform area. The magnitudes of virtual potential temperature drop, pressure rise, and wind speed peak associated with the passage of the gust front are significantly smaller compared with the observations, suggesting simulated cool pools are weaker. Simulations generally overestimate the vertical velocity and radar reflectivity in convective cores compared with the retrievals. The modeled updraft velocity and precipitation have a significant spread across eight schemes. The spread of updraft velocity is the combination of both low-level pressure perturbation gradient (PPG) and buoyancy. Both PPG and thermal buoyancy are small for simulations of weak convection but both are large for those of strong convection. Ice-related parameterizations contribute majorly to the spread of updraft velocity, while they are not the reason for the large spread of precipitation. The understandings gained in this study can help to focus future observations and parameterization development.
Evaluation of cloud convection and tracer transport in a three-dimensional chemical transport model
Directory of Open Access Journals (Sweden)
W. Feng
2011-06-01
Full Text Available We investigate the performance of cloud convection and tracer transport in a global off-line 3-D chemical transport model. Various model simulations are performed using different meteorological (reanalyses (ERA-40, ECMWF operational and ECMWF Interim to diagnose the updraft mass flux, convective precipitation and cloud top height.
The diagnosed upward mass flux distribution from TOMCAT agrees quite well with the ECMWF reanalysis data (ERA-40 and ERA-Interim below 200 hPa. Inclusion of midlevel convection improves the agreement at mid-high latitudes. However, the reanalyses show strong convective transport up to 100 hPa, well into the tropical tropopause layer (TTL, which is not captured by TOMCAT. Similarly, the model captures the spatial and seasonal variation of convective cloud top height although the mean modelled value is about 2 km lower than observed.
The ERA-Interim reanalyses have smaller archived upward convective mass fluxes than ERA-40, and smaller convective precipitation, which is in better agreement with satellite-based data. TOMCAT captures these relative differences when diagnosing convection from the large-scale fields. The model also shows differences in diagnosed convection with the version of the operational analyses used, which cautions against using results of the model from one specific time period as a general evaluation.
We have tested the effect of resolution on the diagnosed modelled convection with simulations ranging from 5.6° × 5.6° to 1° × 1°. Overall, in the off-line model, the higher model resolution gives stronger vertical tracer transport, however, it does not make a large change to the diagnosed convective updraft mass flux (i.e., the model results using the convection scheme fail to capture the strong convection transport up to 100 hPa as seen in the archived convective mass fluxes. Similarly, the resolution of the forcing winds in the higher resolution CTM does not make a
Tan, Z.; Shaw, T.
2017-12-01
State-of-the-art climate models exhibit a large spread in the magnitude of projected poleward jet shift and Hadley cell expansion in response to warming. Interestingly, some idealized gray radiation models with simplified convective schemes produce an equatorward jet shift in response to warming. In order to understand the impact of radiation and convection on the circulation response and resolve the discrepancies across the model hierarchy, we introduce a new model radiation-convection hierarchy. The hierarchy spans idealized (gray) through sophisticated (RRTMG) radiation, and idealized (Betts-Miller) through sophisticated (eddy-diffusivity mass-flux scheme) convection schemes in the same general circulation model. It is used to systematically explore the impact of radiation and convection on the extratropical circulation response to climate change independent of mean surface temperature and meridional temperature gradient responses. With a gray radiation scheme, the jet stream shift depends on the prescribed stratospheric optical depth, which controls the climatological jet regime. A large optical depth leads to a split jet and an equatorward shift. A small optical depth leads to a poleward shift. The different shifts are connected to the vertical extent of tropical long wave cooling that impacts the subtropical jet and Hadley circulation. In spite of these sensitivities, the storm track position, defined by the meridonal eddy heat flux and moist static energy flux maxima, shifts robustly poleward. In contrast to gray radiation, with a comprehensive radiation scheme, the jet and storm track shift robustly poleward irrespective of radiative assumptions (clear sky versus cloudy sky, ozone versus no ozone). This response is reproduced by adding more spectral bands and including the water vapor feedback in the gray scheme. Dynamical sensitivities to convective assumption are also explored. Overall the new hierarchy highlights the importance of radiative and
Tropical deep convective cloud morphology
Igel, Matthew R.
A cloud-object partitioning algorithm is developed. It takes contiguous CloudSat cloudy regions and identifies various length scales of deep convective clouds from a tropical, oceanic subset of data. The methodology identifies a level above which anvil characteristics become important by analyzing the cloud object shape. Below this level in what is termed the pedestal region, convective cores are identified based on reflectivity maxima. Identifying these regions allows for the assessment of length scales of the anvil and pedestal of the deep convective clouds. Cloud objects are also appended with certain environmental quantities from the ECMWF reanalysis. Simple geospatial and temporal assessments show that the cloud object technique agrees with standard observations of local frequency of deep-convective cloudiness. Additionally, the nature of cloud volume scale populations is investigated. Deep convection is seen to exhibit power-law scaling. It is suggested that this scaling has implications for the continuous, scale invariant, and random nature of the physics controlling tropical deep convection and therefore on the potentially unphysical nature of contemporary convective parameterizations. Deep-convective clouds over tropical oceans play important roles in Earth's climate system. The response of tropical, deep convective clouds to sea surface temperatures (SSTs) is investigated using this new data set. Several previously proposed feedbacks are examined: the FAT hypothesis, the Iris hypothesis, and the Thermostat hypothesis. When the data are analyzed per cloud object, each hypothesis is broadly found to correctly predict cloud behavior in nature, although it appears that the FAT hypothesis needs a slight modification to allow for cooling cloud top temperatures with increasing SSTs. A new response that shows that the base temperature of deep convective anvils remains approximately constant with increasing SSTs is introduced. These cloud-climate feedbacks are
Directory of Open Access Journals (Sweden)
H. Tost
2010-02-01
Full Text Available Moist convection in global modelling contributes significantly to the transport of energy, momentum, water and trace gases and aerosols within the troposphere. Since convective clouds are on a scale too small to be resolved in a global model their effects have to be parameterised. However, the whole process of moist convection and especially its parameterisations are associated with uncertainties. In contrast to previous studies on the impact of convection on trace gases, which had commonly neglected the convective transport for some or all compounds, we investigate this issue by examining simulations with five different convection schemes. This permits an uncertainty analysis due to the process formulation, without the inconsistencies inherent in entirely neglecting deep convection or convective tracer transport for one or more tracers.
Both the simulated mass fluxes and tracer distributions are analysed. Investigating the distributions of compounds with different characteristics, e.g., lifetime, chemical reactivity, solubility and source distributions, some differences can be attributed directly to the transport of these compounds, whereas others are more related to indirect effects, such as the transport of precursors, chemical reactivity in certain regions, and sink processes.
The model simulation data are compared with the average regional profiles of several measurement campaigns, and in detail with two campaigns in fall and winter 2005 in Suriname and Australia, respectively.
The shorter-lived a compound is, the larger the differences and consequently the uncertainty due to the convection parameterisation are, as long as it is not completely controlled by local production that is independent of convection and its impacts (e.g. water vapour changes. Whereas for long-lived compounds like CO or O_{3} the mean differences between the simulations are less than 25%, differences for short-lived compounds reach
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
Energy Technology Data Exchange (ETDEWEB)
Eikelder, M.F.P. ten, E-mail: m.f.p.teneikelder@tudelft.nl [EDF R& D, AMA, 7 boulevard Gaspard Monge, 91120 Palaiseau (France); Eindhoven University of Technology, Department of Mathematics and Computer Science, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Daude, F. [EDF R& D, AMA, 7 boulevard Gaspard Monge, 91120 Palaiseau (France); IMSIA, UMR EDF-CNRS-CEA-ENSTA 9219, Université Paris Saclay, 828 Boulevard des Maréchaux, 91762 Palaiseau (France); Koren, B.; Tijsseling, A.S. [Eindhoven University of Technology, Department of Mathematics and Computer Science, P.O. Box 513, 5600 MB Eindhoven (Netherlands)
2017-02-15
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
de Bont, Chris
2018-01-01
This booklet was written to share research results with farmers and practitioners in Tanzania. It gives a summary of the empirical material collected during three months of field work in the Mawala irrigation scheme (Kilimanjaro Region), and includes maps, tables and photos. It describes the history of the irrigation scheme, as well current irrigation and farming practices. It especially focuses on the different kinds of infrastructural improvement in the scheme (by farmers and the government...
Multigrid solution of the convection-diffusion equation with high-Reynolds number
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jun [George Washington Univ., Washington, DC (United States)
1996-12-31
A fourth-order compact finite difference scheme is employed with the multigrid technique to solve the variable coefficient convection-diffusion equation with high-Reynolds number. Scaled inter-grid transfer operators and potential on vectorization and parallelization are discussed. The high-order multigrid method is unconditionally stable and produces solution of 4th-order accuracy. Numerical experiments are included.
Effect of perturbation of convective energy transport on the luminosity and radius of the sun
International Nuclear Information System (INIS)
Endal, A.S.; Twigg, L.W.
1982-01-01
The response of solar models to perturbations of the efficiency of convective energy transport is studied for a number of cases. Such perturbations primarily affect the shallow superadiabatic layer of the convective envelope (at depths 3 km below the photosphere). Independent of the details of the perturbation scheme, the resulting change in the solar radius (ΔR/R) is always very small compared to the change in luminosity (ΔL/L). This appears to be true for any physical mechanism of solar variability which operates in the outer layers of the convection zone. Changes of the solar radius have been inferred by Dunham et al. from historical observations of solar eclipses in 1715 and 1925. Considering the constraints on concurrent luminosity changes, this type of solar variability must be indicative of changes in the solar structure at substantial depths below the superadiabatic layer of the convective envelope
Martínez-Castro, Daniel; Vichot-Llano, Alejandro; Bezanilla-Morlot, Arnoldo; Centella-Artola, Abel; Campbell, Jayaka; Giorgi, Filippo; Viloria-Holguin, Cecilia C.
2017-09-01
A sensitivity study of the performance of the RegCM4 regional climate model driven by the ERA Interim reanalysis is conducted for the Central America and Caribbean region. A set of numerical experiments are completed using four configurations of the model, with a horizontal grid spacing of 25 km for a period of 6 years (1998-2003), using three of the convective parameterization schemes implemented in the model, the Emanuel scheme, the Grell over land-Emanuel over ocean scheme and two configurations of the Tiedtke scheme. The objective of the study is to investigate the ability of each configuration to reproduce different characteristics of the temperature, circulation and precipitation fields for the dry and rainy seasons. All schemes simulate the general temperature and precipitation patterns over land reasonably well, with relatively high correlations compared to observation datasets, though in specific regions there are positive or negative biases, greater in the rainy season. We also focus on some circulation features relevant for the region, such as the Caribbean low level jet and sea breeze circulations over islands, which are simulated by the model with varied performance across the different configurations. We find that no model configuration assessed is best performing for all the analysis criteria selected, but the Tiedtke configurations, which include the capability of tuning in particular the exchanges between cloud and environment air, provide the most balanced range of biases across variables, with no outstanding systematic bias emerging.
Pu, Zhaoxia; Lin, Chao; Dong, Xiquan; Krueger, Steven K.
2018-01-01
Mesoscale convective systems (MCSs) and their associated cloud properties are the important factors that influence the aviation activities, yet they present a forecasting challenge in numerical weather prediction. In this study, the sensitivity of numerical simulations of an MCS over the US Southern Great Plains to ice hydrometeors in bulk microphysics (MP) schemes has been investigated using the Weather Research and Forecasting (WRF) model. It is found that the simulated structure, life cycle, cloud coverage, and precipitation of the convective system as well as its associated cold pools are sensitive to three selected MP schemes, namely, the WRF single-moment 6-class (WSM6), WRF double-moment 6-class (WDM6, with the double-moment treatment of warm-rain only), and Morrison double-moment (MORR, with the double-moment representation of both warm-rain and ice) schemes. Compared with observations, the WRF simulation with WSM6 only produces a less organized convection structure with a short lifetime, while WDM6 can produce the structure and length of the MCS very well. Both simulations heavily underestimate the precipitation amount, the height of the radar echo top, and stratiform cloud fractions. With MORR, the model performs well in predicting the lifetime, cloud coverage, echo top, and precipitation amount of the convection. Overall results demonstrate the importance of including double-moment representation of ice hydrometeors along with warm-rain. Additional experiments are performed to further examine the role of ice hydrometeors in numerical simulations of the MCS. Results indicate that replacing graupel with hail in the MORR scheme improves the prediction of the convective structure, especially in the convective core region.
Energy Technology Data Exchange (ETDEWEB)
Dean, Caryn L. [Pennsylvania State Univ., University Park, PA (United States)
1993-05-01
This report details a radiative-convective model, combining previously developed cumulus, stable cloud and radiation parameterizations with a boundary layer scheme, which was developed in the current study. The cloud model was modified to incorporate the effects of both small and large clouds. The boundary layer model was adapted from a mixed layer model was only slightly modified to couple it with the more sophisticated cloud model. The model was tested for a variety of imposed divergence profiles, which simulate the regions of the tropical ocean from approximately the intertropical Convergence Zone (ITCZ) to the subtropical high region. The sounding used to initialize the model for most of the runs is from the trade wind region of ATEX. For each experiment, the model was run with a timestep of 300 seconds for a period of 7 days.
Zhang, G. J.; Song, X.
2017-12-01
The double ITCZ bias has been a long-standing problem in coupled atmosphere-ocean models. A previous study indicates that uncertainty in the projection of global warming due to doubling of CO2 is closely related to the double ITCZ biases in global climate models. Thus, reducing the double ITCZ biases is not only important to getting the current climate features right, but also important to narrowing the uncertainty in future climate projection. In this work, we will first review the possible factors contributing to the ITCZ problem. Then, we will focus on atmospheric convection, presenting recent progress in alleviating the double ITCZ problem and its sensitivity to details of convective parameterization, including trigger conditions for convection onset, convective memory, entrainment rate, updraft model and closure in the NCAR CESM1. These changes together can result in dramatic improvements in the simulation of ITCZ. Results based on both atmospheric only and coupled simulations with incremental changes of convection scheme will be shown to demonstrate the roles of convection parameterization and coupled interaction between convection, atmospheric circulation and ocean circulation in the simulation of ITCZ.
Directory of Open Access Journals (Sweden)
Oluwole Daniel Makinde
2011-01-01
Full Text Available Steady laminar natural convection flow over a semi-infinite moving vertical plate in the presence of internal heat generation and a convective surface boundary condition is examined in this paper. It is assumed that the left surface of the plate is in contact with a hot fluid while the cold fluid on the right surface of the plate contains a heat source that decays exponentially with the classical similarity variable. The governing non-linear partial differential equations have been transformed by a similarity transformation into a system of ordinary differential equations, which are solved numerically by applying shooting iteration technique together with fourth order Runge-Kutta integration scheme. The effects of physical parameters on the dimensionless velocity and temperature profiles are depicted graphically and analyzed in detail. Finally, numerical values of physical quantities, such as the local skin-friction coefficient and the local Nusselt number are presented in tabular form.
Merk, D.; Zinner, T.
2013-01-01
In this paper a new detection scheme for convective initiation (CI) under day and night conditions is presented. The new algorithm combines the strengths of two existing methods for detecting CI with geostationary satellite data. It uses the channels of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat Second Generation (MSG). For the new algorithm five infrared (IR) criteria from the Satellite Convection Analysis and Tracking algorithm (SATCAST) and one high-resolut...
DEFF Research Database (Denmark)
Juhl, Hans Jørn; Stacey, Julia
2001-01-01
to carry out a campaign targeted at this segment. The awareness percentage is already 92 % and 67% of the respondents believe they know the meaning of the scheme. But it stands to reason to study whether the respondents actually know what the labelling scheme stands for or if they just think they do...
Constructing space difference schemes which satisfy a cell entropy inequality
Merriam, Marshal L.
1989-01-01
A numerical methodology for solving convection problems is presented, using finite difference schemes which satisfy the second law of thermodynamics on a cell-by-cell basis in addition to the usual conservation laws. It is shown that satisfaction of a cell entropy inequality is sufficient, in some cases, to guarantee nonlinear stability. Some details are given for several one-dimensional problems, including the quasi-one-dimensional Euler equations applied to flow in a nozzle.
Directory of Open Access Journals (Sweden)
R. Sitharthan
2016-09-01
Full Text Available This paper aims at modelling an electronically coupled distributed energy resource with an adaptive protection scheme. The electronically coupled distributed energy resource is a microgrid framework formed by coupling the renewable energy source electronically. Further, the proposed adaptive protection scheme provides a suitable protection to the microgrid for various fault conditions irrespective of the operating mode of the microgrid: namely, grid connected mode and islanded mode. The outstanding aspect of the developed adaptive protection scheme is that it monitors the microgrid and instantly updates relay fault current according to the variations that occur in the system. The proposed adaptive protection scheme also employs auto reclosures, through which the proposed adaptive protection scheme recovers faster from the fault and thereby increases the consistency of the microgrid. The effectiveness of the proposed adaptive protection is studied through the time domain simulations carried out in the PSCAD⧹EMTDC software environment.
ENVIRONMENTAL ASPECTS OF THE INTENSIFICATION CONVECTIVE DRYING
Directory of Open Access Journals (Sweden)
A. M. Gavrilenkov
2012-01-01
Full Text Available Identified and analyzed the relationship of the intensity convective drying and air pollution emissions of heat. The ways to reduce the thermal pollution of the atmosphere at convective drying.
Solar Surface Magneto-Convection
Directory of Open Access Journals (Sweden)
Robert F. Stein
2012-07-01
Full Text Available We review the properties of solar magneto-convection in the top half of the convection zones scale heights (from 20 Mm below the visible surface to the surface, and then through the photosphere to the temperature minimum. Convection is a highly non-linear and non-local process, so it is best studied by numerical simulations. We focus on simulations that include sufficient detailed physics so that their results can be quantitatively compared with observations. The solar surface is covered with magnetic features with spatial sizes ranging from unobservably small to hundreds of megameters. Three orders of magnitude more magnetic flux emerges in the quiet Sun than emerges in active regions. In this review we focus mainly on the properties of the quiet Sun magnetic field. The Sun’s magnetic field is produced by dynamo action throughout the convection zone, primarily by stretching and twisting in the turbulent downflows. Diverging convective upflows and magnetic buoyancy carry magnetic flux toward the surface and sweep the field into the surrounding downflow lanes where the field is dragged downward. The result is a hierarchy of undulating magnetic Ω- and U-loops of different sizes. New magnetic flux first appears at the surface in a mixed polarity random pattern and then collects into isolated unipolar regions due to underlying larger scale magnetic structures. Rising magnetic structures are not coherent, but develop a filamentary structure. Emerging magnetic flux alters the convection properties, producing larger, darker granules. Strong field concentrations inhibit transverse plasma motions and, as a result, reduce convective heat transport toward the surface which cools. Being cooler, these magnetic field concentrations have a shorter scale height and become evacuated. The field becomes further compressed and can reach strengths in balance with the surrounding gas pressure. Because of their small internal density, photons escape from deeper in
Stationary thermal convection in a viscoelastic ferrofluid
Energy Technology Data Exchange (ETDEWEB)
Laroze, D., E-mail: david.laroze@gmail.co [Max Planck Institute for Polymer Research, D 55021 Mainz (Germany); Instituto de Alta Investigacion, Universidad de Tarapaca, Casilla 7D, Arica (Chile); Martinez-Mardones, J. [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Perez, L.M. [Departamento de Ingenieria Metalurgica, Universidad de Santiago de Chile, Av. Bernardo OHiggins 3363, Santiago (Chile); Rojas, R.G. [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile)
2010-11-15
We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. We focus in the stationary convection for idealized boundary conditions. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system. Close to bifurcation, the coefficients of the corresponding amplitude equation are determined analytically. Finally, the secondary instabilities are performed.
Threshold Signature Schemes Application
Directory of Open Access Journals (Sweden)
Anastasiya Victorovna Beresneva
2015-10-01
Full Text Available This work is devoted to an investigation of threshold signature schemes. The systematization of the threshold signature schemes was done, cryptographic constructions based on interpolation Lagrange polynomial, elliptic curves and bilinear pairings were examined. Different methods of generation and verification of threshold signatures were explored, the availability of practical usage of threshold schemes in mobile agents, Internet banking and e-currency was shown. The topics of further investigation were given and it could reduce a level of counterfeit electronic documents signed by a group of users.
Energy Technology Data Exchange (ETDEWEB)
Cotton, W.R.
1997-08-12
This research has focused on the development of a parameterization scheme for mesoscale convective systems (MCSs), to be used in numerical weather prediction models with grid spacing too coarse to explicitly simulate such systems. This is an extension to cumulus parameterization schemes, which have long been used to account for the unresolved effects of convection in numerical models. Although MCSs generally require an extended sequence of numerous deep convective cells in order to develop into their characteristic sizes and to persist for their typical durations, their effects on the large scale environment are significantly different than that due to the collective effects of numerous ordinary deep convective cells. These differences are largely due to a large stratiform cloud that develops fairly early in the MCS life-cycle, where mesoscale circulations and dynamics interact with the environment in ways that call for a distinct MCS parameterization. Comparing an MCS and a collection of deep convection that ingests the same amount of boundary layer air and moisture over an extended several hour period, the MCS will generally generates more stratiform rainfall, produce longer-lasting and optically thicker cirrus, and result in different vertical distributions of large-scale tendencies due to latent heating and moistening, momentum transfers, and radiational heating.
True polar wander on convecting planets
Rose, Ian Robert
the characteristic size of moment of inertia anomalies decreases with higher Ra, but that the characteristic response time for TPW also decreases. These two effects approximately cancel. However, the orientation of the principal axes of the moment of inertia becomes less stable to perturbations at high Ra, thereby increasing the rate of TPW. Overall, I find that a more vigorously convecting planet is more likely to experience large TPW events. If early Earth had more vigorous convection, it may have experienced more TPW than present-day Earth. Flow induced by density anomalies in the mantle deflects free surfaces at the surface and the CMB, and the mass anomalies due to these deflections contribute to the moment of inertia. A full accounting of the moment of inertia anomalies must include these surface effects. Numerical models of mantle convection with a free surface have suffered from numerical sloshing instabilities. I analyze the sloshing instability by constructing a generalized eigenvalue problem for the relaxation time spectrum. The minimum relaxation time of the spectrum sets the maximum stable timestep. This analysis gives the first quantitative explanation for why existing techniques for stabilizing geodynamic simulations with a free surface work. I also use this perspective to construct an alternative stabilization scheme based on nonstandard finite differences. This scheme has a single parameter, given by an estimate of the minimum relaxation time, and allows for still larger timesteps. Finally, I develop a new method for analyzing apparent polar wander (APW) paths described by sequences of paleomagnetic poles. Existing techniques, such as spline fits and running means, do not fully account for the uncertainties in the position and timing of paleomagnetic pole paths. Furthermore, they impose regularization on the solution, and the resulting uncertainties are difficult to interpret. Our technique is an extension of paleomagnetic Euler pole (PEP) analysis. I
Energy Technology Data Exchange (ETDEWEB)
Willcock, J J; Lumsdaine, A; Quinlan, D J
2008-08-19
Tabled execution is a generalization of memorization developed by the logic programming community. It not only saves results from tabled predicates, but also stores the set of currently active calls to them; tabled execution can thus provide meaningful semantics for programs that seemingly contain infinite recursions with the same arguments. In logic programming, tabled execution is used for many purposes, both for improving the efficiency of programs, and making tasks simpler and more direct to express than with normal logic programs. However, tabled execution is only infrequently applied in mainstream functional languages such as Scheme. We demonstrate an elegant implementation of tabled execution in Scheme, using a mix of continuation-passing style and mutable data. We also show the use of tabled execution in Scheme for a problem in formal language and automata theory, demonstrating that tabled execution can be a valuable tool for Scheme users.
Recent advances in computational-analytical integral transforms for convection-diffusion problems
Cotta, R. M.; Naveira-Cotta, C. P.; Knupp, D. C.; Zotin, J. L. Z.; Pontes, P. C.; Almeida, A. P.
2017-10-01
An unifying overview of the Generalized Integral Transform Technique (GITT) as a computational-analytical approach for solving convection-diffusion problems is presented. This work is aimed at bringing together some of the most recent developments on both accuracy and convergence improvements on this well-established hybrid numerical-analytical methodology for partial differential equations. Special emphasis is given to novel algorithm implementations, all directly connected to enhancing the eigenfunction expansion basis, such as a single domain reformulation strategy for handling complex geometries, an integral balance scheme in dealing with multiscale problems, the adoption of convective eigenvalue problems in formulations with significant convection effects, and the direct integral transformation of nonlinear convection-diffusion problems based on nonlinear eigenvalue problems. Then, selected examples are presented that illustrate the improvement achieved in each class of extension, in terms of convergence acceleration and accuracy gain, which are related to conjugated heat transfer in complex or multiscale microchannel-substrate geometries, multidimensional Burgers equation model, and diffusive metal extraction through polymeric hollow fiber membranes. Numerical results are reported for each application and, where appropriate, critically compared against the traditional GITT scheme without convergence enhancement schemes and commercial or dedicated purely numerical approaches.
International Nuclear Information System (INIS)
2002-04-01
This scheme defines the objectives relative to the renewable energies and the rational use of the energy in the framework of the national energy policy. It evaluates the needs and the potentialities of the regions and preconizes the actions between the government and the territorial organizations. The document is presented in four parts: the situation, the stakes and forecasts; the possible actions for new measures; the scheme management and the regional contributions analysis. (A.L.B.)
A transilient matrix for moist convection
Energy Technology Data Exchange (ETDEWEB)
Romps, D.; Kuang, Z.
2011-08-15
A method is introduced for diagnosing a transilient matrix for moist convection. This transilient matrix quantifies the nonlocal transport of air by convective eddies: for every height z, it gives the distribution of starting heights z{prime} for the eddies that arrive at z. In a cloud-resolving simulation of deep convection, the transilient matrix shows that two-thirds of the subcloud air convecting into the free troposphere originates from within 100 m of the surface. This finding clarifies which initial height to use when calculating convective available potential energy from soundings of the tropical troposphere.
Seismic Constraints on Interior Solar Convection
Hanasoge, Shravan M.; Duvall, Thomas L.; DeRosa, Marc L.
2010-01-01
We constrain the velocity spectral distribution of global-scale solar convective cells at depth using techniques of local helioseismology. We calibrate the sensitivity of helioseismic waves to large-scale convective cells in the interior by analyzing simulations of waves propagating through a velocity snapshot of global solar convection via methods of time-distance helioseismology. Applying identical analysis techniques to observations of the Sun, we are able to bound from above the magnitudes of solar convective cells as a function of spatial convective scale. We find that convection at a depth of r/R(solar) = 0.95 with spatial extent l < 30, where l is the spherical harmonic degree, comprise weak flow systems, on the order of 15 m/s or less. Convective features deeper than r/R(solar) = 0.95 are more difficult to image due to the rapidly decreasing sensitivity of helioseismic waves.
Statistical evaluation of the simulated convective activity over Central Greece
Kartsios, Stergios; Kotsopoulos, Stylianos; Karacostas, Theodore S.; Tegoulias, Ioannis; Pytharoulis, Ioannis; Bampzelis, Dimitrios
2015-04-01
In the framework of the project DAPHNE (www.daphne-meteo.gr), the non-hydrostatic Weather Research and Forecasting model with the Advanced Research dynamic solver (WRF-ARW, version 3.5.1) is used to produce very high spatiotemporal resolution simulations of the convective activity over Thessaly plain and hence, enhancing our knowledge on the impact of high resolution elevation and land use data in the moist convection. The expecting results act as a precursor for the potential applicability of a planned precipitation enhancement program. The three model domains, covering Europe, the Mediterranean Sea and northern Africa (d01), the wider area of Greece (d02) and Thessaly region-central Greece (d03), are used at horizontal grid-spacings of 15km, 5km and 1km respectively. ECMWF operational analyses at 6-hourly intervals (0.25ox0.25o lat.-long.) are imported as initial and boundary conditions of the coarse domain, while in the vertical, 39 sigma levels (up to 50 hPa) are used, with increased resolution in the boundary layer. Microphysical processes are represented by WSM6 scheme, sub-grid scale convection by Kain-Fritsch scheme, longwave and shortwave radiation by RRTMG scheme, surface layer by Monin-Obukhov (MM5), boundary layer by Yonsei University and soil physics by NOAH Unified model. Six representative days with different upper-air synoptic circulation types are selected, while high resolution (3'') elevation data from the Shuttle Radar Topography Mission (SRTM - version 4) are inserted in the innermost domain (d03), along with the Corine Land Cover 2000 raster data (3''x3''). The aforementioned data sets are used in different configurations, in order to evaluate the impact of each one on the simulated convective activity in the vicinity of Thessaly region, using a grid of available meteorological stations in the area. For each selected day, four (4) sensitivity simulations are performed, setting a total number of 24 runs. Finally, the best configuration provides
Convective aggregation in realistic convective-scale simulations
Holloway, Christopher E.
2017-06-01
To investigate the real-world relevance of idealized-model convective self-aggregation, five 15 day cases of real organized convection in the tropics are simulated. These include multiple simulations of each case to test sensitivities of the convective organization and mean states to interactive radiation, interactive surface fluxes, and evaporation of rain. These simulations are compared to self-aggregation seen in the same model configured to run in idealized radiative-convective equilibrium. Analysis of the budget of the spatial variance of column-integrated frozen moist static energy shows that control runs have significant positive contributions to organization from radiation and negative contributions from surface fluxes and transport, similar to idealized runs once they become aggregated. Despite identical lateral boundary conditions for all experiments in each case, systematic differences in mean column water vapor (CWV), CWV distribution shape, and CWV autocorrelation length scale are found between the different sensitivity runs, particularly for those without interactive radiation, showing that there are at least some similarities in sensitivities to these feedbacks in both idealized and realistic simulations (although the organization of precipitation shows less sensitivity to interactive radiation). The magnitudes and signs of these systematic differences are consistent with a rough equilibrium between (1) equalization due to advection from the lateral boundaries and (2) disaggregation due to the absence of interactive radiation, implying disaggregation rates comparable to those in idealized runs with aggregated initial conditions and noninteractive radiation. This points to a plausible similarity in the way that radiation feedbacks maintain aggregated convection in both idealized simulations and the real world.Plain Language SummaryUnderstanding the processes that lead to the organization of tropical rainstorms is an important challenge for weather
Uncertainty associated with convective wet removal of entrained aerosols in a global climate model
Directory of Open Access Journals (Sweden)
B. Croft
2012-11-01
Full Text Available The uncertainties associated with the wet removal of aerosols entrained above convective cloud bases are investigated in a global aerosol-climate model (ECHAM5-HAM under a set of limiting assumptions for the wet removal of the entrained aerosols. The limiting assumptions for the wet removal of entrained aerosols are negligible scavenging and vigorous scavenging (either through activation, with size-dependent impaction scavenging, or with the prescribed fractions of the standard model. To facilitate this process-based study, an explicit representation of cloud-droplet-borne and ice-crystal-borne aerosol mass and number, for the purpose of wet removal, is introduced into the ECHAM5-HAM model. This replaces and is compared with the prescribed cloud-droplet-borne and ice-crystal-borne aerosol fraction scavenging scheme of the standard model.
A 20% to 35% uncertainty in simulated global, annual mean aerosol mass burdens and optical depth (AOD is attributed to different assumptions for the wet removal of aerosols entrained above convective cloud bases. Assumptions about the removal of aerosols entrained above convective cloud bases control modeled upper tropospheric aerosol concentrations by as much as one order of magnitude.
Simulated aerosols entrained above convective cloud bases contribute 20% to 50% of modeled global, annual mean aerosol mass convective wet deposition (about 5% to 10% of the total dry and wet deposition, depending on the aerosol species, when including wet scavenging of those entrained aerosols (either by activation, size-dependent impaction, or with the prescribed fraction scheme. Among the simulations, the prescribed fraction and size-dependent impaction schemes yield the largest global, annual mean aerosol mass convective wet deposition (by about two-fold. However, the prescribed fraction scheme has more vigorous convective mixed-phase wet removal (by two to five-fold relative to the size-dependent impaction
CRUCIB: an axisymmetric convection code
International Nuclear Information System (INIS)
Bertram, L.A.
1975-03-01
The CRUCIB code was written in support of an experimental program aimed at measurement of thermal diffusivities of refractory liquids. Precise values of diffusivity are necessary to realistic analysis of reactor safety problems, nuclear waste disposal procedures, and fundamental metal forming processes. The code calculates the axisymmetric transient convective motions produced in a right circular cylindrical crucible, which is surface heated by an annular heat pulse. Emphasis of this report is placed on the input-output options of the CRUCIB code, which are tailored to assess the importance of the convective heat transfer in determining the surface temperature distribution. Use is limited to Prandtl numbers less than unity; larger values can be accommodated by replacement of a single block of the code, if desired. (U.S.)
Cryogenic helium gas convection research
International Nuclear Information System (INIS)
Donnelly, R.J.
1994-10-01
This is a report prepared by a group interested in doing research in thermal convection using the large scale refrigeration facilities available at the SSC Laboratories (SSCL). The group preparing this report consists of Michael McAshan at SSCL, Robert Behringer at Duke University, Katepalli Sreenivasan at Yale University, Xiao-Zhong Wu at Northern Illinois University and Russell Donnelly at the University of Oregon, who served as Editor for this report. This study reports the research and development opportunities in such a project, the technical requirements and feasibility of its construction and operation, and the costs associated with the needed facilities and support activities. The facility will be a unique national resource for studies of high-Reynolds-number and high-Rayleigh-number and high Rayleigh number turbulence phenomena, and is one of the six items determined as suitable for potential funding through a screening of Expressions of Interest. The proposed facility is possible only because of the advanced cryogenic technology available at the SSCL. Typical scientific issues to be addressed in the facility will be discussed. It devolved during our study, that while the main experiment is still considered to be the thermal convection experiment discussed in our original Expression of Interest, there are now a very substantial set of other, important and fundamental experiments which can be done with the large cryostat proposed for the convection experiment. We believe the facility could provide several decades of front-line research in turbulence, and shall describe why this is so
The Continental Drift Convection Cell
Whitehead, J. A.; Behn, M. D.
2014-12-01
Continents on Earth periodically assemble to form supercontinents, and then break up again into smaller continental blocks (the Wilson Cycle). Highly developed but realistic numerical models cannot resolve if continents respond passively to mantle convection or whether they modulate flow. Our simplified numerical model addresses this problem: A thermally insulating continent floats on a stress-free surface for infinite Prandtl number cellular convection with constant material properties in a chamber 8 times longer than its depth. The continent moves back and forth across the chamber driven by a "continental drift convection cell" of a form not previously described. Subduction exists at the upstream end with cold slabs dipping at an angle beneath the moving continent. Fluid moves with the continent in the upper region of this cell with return flow near the bottom. Many continent/subduction regions on Earth have these features. The drifting cell enhances vertical heat transport by approximately 30% compared to a fixed continent, especially at the core-mantle boundary, and significantly decreases lateral mantle temperature differences. However, continent drift or fixity has smaller effects on profiles of horizontally averaged temperature. Although calculations are done at Rayleigh numbers lower than expected for Earth's mantle (2x105 and 106), the drift speed extrapolates to reasonable Wilson Cycle speeds for larger Ra.
Neelin, J. D.; Kuo, Y. H.; Schiro, K. A.; Langenbrunner, B.; Mechoso, C. R.; Sahany, S.; Bernstein, D. N.
2015-12-01
Previous work by various authors has pointed to the role of humidity in the lower free troposphere in affecting the onset of deep convection in the tropics. Empirical relations between column water vapor and the onset of precipitation have been inferred to be related to this. Evidence includes deep-convective conditional instability calculations for entraining plumes, in which the lower free-tropospheric environment affects the onset of deep convection due to the impact on buoyancy of turbulent entrainment of dry versus moist air. Tropical Western Pacific in situ observations, and tropical ocean basin satellite retrievals in comparison to climate model diagnostics each indicate that substantial entrainment is required to explain the observed relationship. In situ observations from the GoAmazon field campaign confirm that the basic relationship holds over tropical land much as it does over tropical ocean (although with greater additional sensitivity to boundary layer variations and to freezing processes). The relationship between deep convection and water vapor is, however, a two-way street, with convection moistening the free troposphere. One might thus argue that there has not yet been a smoking gun in terms of establishing the causality of the precipitation-water vapor relationship. Parameter perturbation experiments in the coupled Community Earth System Model show that when the deep convective scheme has low values of entrainment, the set of statistics associated with the transition to deep convection are radically altered, and the observed pickup of precipitation with column water vapor is no longer seen. In addition to cementing the dominant direction of causality in the fast timescale precipitation-column water vapor relationship, the results point to impacts of this mechanism on the climatology. Because at low entrainment the convection can fire before the lower troposphere is moistened, the climatology of water vapor remains lower than observed. These
Energy Technology Data Exchange (ETDEWEB)
Placidi, M.; Jung, J. -Y.; Ratti, A.; Sun, C.
2014-07-25
This paper describes beam distribution schemes adopting a novel implementation based on low amplitude vertical deflections combined with horizontal ones generated by Lambertson-type septum magnets. This scheme offers substantial compactness in the longitudinal layouts of the beam lines and increased flexibility for beam delivery of multiple beam lines on a shot-to-shot basis. Fast kickers (FK) or transverse electric field RF Deflectors (RFD) provide the low amplitude deflections. Initially proposed at the Stanford Linear Accelerator Center (SLAC) as tools for beam diagnostics and more recently adopted for multiline beam pattern schemes, RFDs offer repetition capabilities and a likely better amplitude reproducibility when compared to FKs, which, in turn, offer more modest financial involvements both in construction and operation. Both solutions represent an ideal approach for the design of compact beam distribution systems resulting in space and cost savings while preserving flexibility and beam quality.
Energy Technology Data Exchange (ETDEWEB)
Placidi, M.; Jung, J.-Y.; Ratti, A.; Sun, C., E-mail: csun@lbl.gov
2014-12-21
This paper describes beam distribution schemes adopting a novel implementation based on low amplitude vertical deflections combined with horizontal ones generated by Lambertson-type septum magnets. This scheme offers substantial compactness in the longitudinal layouts of the beam lines and increased flexibility for beam delivery of multiple beam lines on a shot-to-shot basis. Fast kickers (FK) or transverse electric field RF Deflectors (RFD) provide the low amplitude deflections. Initially proposed at the Stanford Linear Accelerator Center (SLAC) as tools for beam diagnostics and more recently adopted for multiline beam pattern schemes, RFDs offer repetition capabilities and a likely better amplitude reproducibility when compared to FKs, which, in turn, offer more modest financial involvements both in construction and operation. Both solutions represent an ideal approach for the design of compact beam distribution systems resulting in space and cost savings while preserving flexibility and beam quality.
A robust WENO scheme for nonlinear waves in a moving reference frame
DEFF Research Database (Denmark)
Kontos, Stavros; Bingham, Harry B.; Lindberg, Ole
2016-01-01
For robust nonlinear wave simulation in a moving reference frame, we recast the free surface problem in Hamilton-Jacobi form and propose a Weighted Essentially Non-Oscillatory (WENO) scheme to automatically handle the upwinding of the convective term. A new automatic procedure for deriving the li...
The convection electric field in auroral substorms
DEFF Research Database (Denmark)
Gjerløv, Jesper Wittendorff; Hoffman, R.A.
2001-01-01
Dynamics Explorer 2 (DE 2) electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge-type auroral substorms. Thirty-one individual DE 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained...... this database enabled us to compile a model of the ionospheric convection electric field. The characteristics of the premidnight convection reversal show a pronounced local time dependency. Far west of the surge it is a fairly well defined point reversal or convection shear. Approaching the surge and within...... the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields. Therefore we adopt the term Harang region rather than the Harang discontinuity for the premidnight convection reversal. A relatively narrow convection...
Numerical study of double-diffusive convection in a vertical annular enclosure with a baffle
Pushpa, B. V.; Prasanna, B. M. R.; Younghae, Do; Sankar, M.
2017-10-01
This paper numerically examines the influence of a circular thin baffle on thermosolutal convection in a vertical annular enclosure. The inner and outer cylindrical walls, and the baffle are retained with different temperatures and concentrations, while the upper and lower boundaries are kept at adiabatic and impermeable. The model equations are solved using an implicit finite difference scheme consisting of ADI and SLOR methods. Numerical simulations are performed to understand the size and position effects of the baffle on the thermosolutal convection and are successfully captured through our results. It has been observed that the baffle size and location has very important role in controlling the thermosolutal convective flow and the corresponding heat and mass transport characteristics. Further, our results are in good agreement with the available benchmark results for limiting cases.
Mixed convection in a lid-driven square cavity with partial slip
International Nuclear Information System (INIS)
Ismael, Muneer A.; Pop, Ioan; Chamkha, Ali J.
2014-01-01
Steady laminar mixed convection inside a lid-driven square cavity filled with water is studied numerically. The lid is due to the movement of the isothermal top and bottom walls which are maintained at T c and T h , respectively, with T h is higher than T c . A partial slip condition was imposed in these two moving walls. The vertical walls of the cavity are kept adiabatic. The appliance of the numerical analysis was USR finite difference method with upwind scheme treatments of the convective terms included in the momentum and energy equations. The studied relevant parameters were: the partial slip parameter S (0-∞); Richardson number Ri (0.01-100) and the direction of the moving walls (λ t = 1, λ b = ±1). The results have showed that there are critical values for the partial slip parameter at which the convection is declined. (authors)
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 2. Electronic Commerce - Payment Schemes. V Rajaraman. Series Article Volume 6 Issue 2 February 2001 pp 6-13. Fulltext. Click here to view fulltext PDF. Permanent link: https://www.ias.ac.in/article/fulltext/reso/006/02/0006-0013 ...
Link Monotonic Allocation Schemes
Slikker, M.
1999-01-01
A network is a graph where the nodes represent players and the links represent bilateral interaction between the players. A reward game assigns a value to every network on a fixed set of players. An allocation scheme specifies how to distribute the worth of every network among the players. This
Alternative health insurance schemes
DEFF Research Database (Denmark)
Keiding, Hans; Hansen, Bodil O.
2002-01-01
In this paper, we present a simple model of health insurance with asymmetric information, where we compare two alternative ways of organizing the insurance market. Either as a competitive insurance market, where some risks remain uninsured, or as a compulsory scheme, where however, the level...... competitive insurance; this situation turns out to be at least as good as either of the alternatives...
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 2. Electronic Commerce - Payment Schemes. V Rajaraman. Series Article Volume 6 Issue 2 February 2001 pp 6-13 ... Author Affiliations. V Rajaraman1. IBM Professor of Information Technology JNCASR Bangalore 560 064, India.
DEFF Research Database (Denmark)
Pötz, Katharina Anna; Haas, Rainer; Balzarova, Michaela
2013-01-01
of schemes that can be categorized on focus areas, scales, mechanisms, origins, types and commitment levels. Research limitations/implications – The findings contribute to conceptual and empirical research on existing models to compare and analyse CSR standards. Sampling technique and depth of analysis limit...
Simple monotonic interpolation scheme
International Nuclear Information System (INIS)
Greene, N.M.
1980-01-01
A procedure for presenting tabular data, such as are contained in the ENDF/B files, that is simpler, more general, and potentially much more compact than the present schemes used with ENDF/B is presented. The method has been successfully used for Bondarenko interpolation in a module of the AMPX system. 1 figure, 1 table
Transitions Between Convective Patterns in Chemical Fronts
Wu, Y.; Vasquez, D. A.; Edwards, Boyd F.; Wilder, J. W.
1995-01-01
We present a theory for the transition from nonaxisymmetric to axisymmetric convection in iodate-arsenous acid reaction fronts propagating in a vertical slab. The transition takes place away from the onset of convection, where a convectionless flat front becomes unstable to a nonaxisymmetric convective front. The transition is studied by numerically solving a reaction-diffusion equation coupled with nonlinear hydrodynamics in a two-dimensional slab.
Natural convection with combined driving forces
Ostrach, S.
1980-01-01
The problem of free and natural convection with combined driving forces is considered in general and all possible configurations are identified. Dimensionless parameters are discussed in order to help categorize the various problems, and existing work is critically evaluated. Four distinct cases are considered for conventional convection and for the situation when the body force and the density gradient are parallel but opposed. Considerable emphasis is given to unstable convection in horizontal layers.
Convection of Moist Saturated Air: Analytical Study
Robert Zakinyan; Arthur Zakinyan; Roman Ryzhkov; Kristina Avanesyan
2016-01-01
In the present work, the steady-state stationary thermal convection of moist saturated air in a lower atmosphere has been studied theoretically. Thermal convection was considered without accounting for the Coriolis force, and with only the vertical temperature gradient. The analytical solution of geophysical fluid dynamics equations, which generalizes the formulation of the moist convection problem, is obtained in the two-dimensional case. The stream function is derived in the Boussinesq appr...
New patterns of centrifugally driven thermal convection
Jaletzky, M.; Busse, F. H.
2000-01-01
An experimental study is described of convection driven by thermal buoyancy in the annular gap between two corotating coaxial cylinders, heated from the outside and cooled from the inside. Steady convection patterns of the hexaroll and of the knot type are observed in the case of high Prandtl number fluids, for which the Coriolis force is sufficiently small. Oblique rolls and phase turbulence in the form of irregular patterns of convection can also be observed in wide regions of the parameter...
Chen, Huangxin
2017-09-01
In this paper we consider the energy stability estimates for some fully discrete schemes which both consider time and spatial discretizations for the incompressible Navier–Stokes equations. We focus on three kinds of fully discrete schemes, i.e., the linear implicit scheme for time discretization with the finite difference method (FDM) on staggered grids for spatial discretization, pressure-correction schemes for time discretization with the FDM on staggered grids for the solutions of the decoupled velocity and pressure equations, and pressure-stabilization schemes for time discretization with the FDM on staggered grids for the solutions of the decoupled velocity and pressure equations. The energy stability estimates are obtained for the above each fully discrete scheme. The upwind scheme is used in the discretization of the convection term which plays an important role in the design of unconditionally stable discrete schemes. Numerical results are given to verify the theoretical analysis.
Directory of Open Access Journals (Sweden)
Shahnam Javadi
2013-07-01
Full Text Available In this paper, the $(G'/G$-expansion method is applied to solve a biological reaction-convection-diffusion model arising in mathematical biology. Exact traveling wave solutions are obtained by this method. This scheme can be applied to a wide class of nonlinear partial differential equations.
Kamata, Shunichi
2018-01-01
Solid-state thermal convection plays a major role in the thermal evolution of solid planetary bodies. Solving the equation system for thermal evolution considering convection requires 2-D or 3-D modeling, resulting in large calculation costs. A 1-D calculation scheme based on mixing length theory (MLT) requires a much lower calculation cost and is suitable for parameter studies. A major concern for the MLT scheme is its accuracy due to a lack of detailed comparisons with higher dimensional schemes. In this study, I quantify its accuracy via comparisons of thermal profiles obtained by 1-D MLT and 3-D numerical schemes. To improve the accuracy, I propose a new definition of the mixing length (l), which is a parameter controlling the efficiency of heat transportation due to convection, for a bottom-heated convective layer. Adopting this new definition of l, I investigate the thermal evolution of Saturnian icy satellites, Dione and Enceladus, under a wide variety of parameter conditions. Calculation results indicate that each satellite requires several tens of GW of heat to possess a thick global subsurface ocean suggested from geophysical analyses. Dynamical tides may be able to account for such an amount of heat, though the reference viscosity of Dione's ice and the ammonia content of Dione's ocean need to be very high. Otherwise, a thick global ocean in Dione cannot be maintained, implying that its shell is not in a minimum stress state.
Titan Balloon Convection Model, Phase I
National Aeronautics and Space Administration — This innovative research effort is directed at determining, quantitatively, the convective heat transfer coefficients applicable to a Montgolfiere balloon operating...
REVERSALS IN THE 6-CELLS CONVECTION DRIVEN
Directory of Open Access Journals (Sweden)
G.M. Vodinchar
2015-12-01
Full Text Available We describe the large-scale model geodynamo, which based on indirect data of inhomogeneities in the density of the Earth’s core. Convection structure is associated with spherical harmonic Y24 , which defines the basic poloidal component of velocity. Coriolis drift of this mode determines the toroidal component of velocity. Thus, 6 convective cells are formed. The model takes into account the feedback effect of the magnetic field on convection. It was ascertained that the model contains stable regimes of field generation. The velocity of convection and the dipole component of the magnetic field are close to the observed ones.
Scale analysis of convective clouds
Directory of Open Access Journals (Sweden)
Micha Gryschka
2008-12-01
Full Text Available The size distribution of cumulus clouds due to shallow and deep convection is analyzed using satellite pictures, LES model results and data from the German rain radar network. The size distributions found can be described by simple power laws as has also been proposed for other cloud data in the literature. As the observed precipitation at ground stations is finally determined by cloud numbers in an area and individual sizes and rain rates of single clouds, the cloud size distributions might be used for developing empirical precipitation forecasts or for validating results from cloud resolving models being introduced to routine weather forecasts.
Characterizing Convection in Stellar Atmospheres
International Nuclear Information System (INIS)
Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank
2011-01-01
We perform 3D radiative hydrodynamic simulations to study the properties of convection in the superadiabatic layer of stars. The simulations show differences in both the stratification and turbulent quantities for different types of stars. We extract turbulent pressure and eddy sizes, as well as the T-τ relation for different stars and find that they are sensitive to the energy flux and gravity. We also show that contrary to what is usually assumed in the field of stellar atmospheres, the structure and gas dynamics of simulations of turbulent atmospheres cannot be parameterized with T eff and log(g) alone.
Kramer, J.; Jecl, R.; Škerget, L.
2008-09-01
In the present work, a Boundary Domain Integral Method, which has been already established for the solution of viscous incompressible fluid flow through porous media, is extended to capture compressible fluid flow in porous media. The presented numerical scheme was used for solving the problem of double diffusive natural convection in a square porous cavity heated from a side, while the horizontal walls are maintained at different concentrations. The Brinkman extension of Darcy equation is used to model the flow through porous medium. The velocity-vorticity formulation is employed enabeling the computation scheme to be partitioned into kinematic and kinetic parts. The results of double diffusive natural convection in porous cavity are presented in terms of velocity, temperature and concentration redistributions.
A ubiquitous ice size bias in simulations of tropical deep convection
Directory of Open Access Journals (Sweden)
M. W. Stanford
2017-08-01
Full Text Available The High Altitude Ice Crystals – High Ice Water Content (HAIC-HIWC joint field campaign produced aircraft retrievals of total condensed water content (TWC, hydrometeor particle size distributions (PSDs, and vertical velocity (w in high ice water content regions of mature and decaying tropical mesoscale convective systems (MCSs. The resulting dataset is used here to explore causes of the commonly documented high bias in radar reflectivity within cloud-resolving simulations of deep convection. This bias has been linked to overly strong simulated convective updrafts lofting excessive condensate mass but is also modulated by parameterizations of hydrometeor size distributions, single particle properties, species separation, and microphysical processes. Observations are compared with three Weather Research and Forecasting model simulations of an observed MCS using different microphysics parameterizations while controlling for w, TWC, and temperature. Two popular bulk microphysics schemes (Thompson and Morrison and one bin microphysics scheme (fast spectral bin microphysics are compared. For temperatures between −10 and −40 °C and TWC > 1 g m−3, all microphysics schemes produce median mass diameters (MMDs that are generally larger than observed, and the precipitating ice species that controls this size bias varies by scheme, temperature, and w. Despite a much greater number of samples, all simulations fail to reproduce observed high-TWC conditions ( > 2 g m−3 between −20 and −40 °C in which only a small fraction of condensate mass is found in relatively large particle sizes greater than 1 mm in diameter. Although more mass is distributed to large particle sizes relative to those observed across all schemes when controlling for temperature, w, and TWC, differences with observations are significantly variable between the schemes tested. As a result, this bias is hypothesized to partly result from
On Converting Secret Sharing Scheme to Visual Secret Sharing Scheme
Directory of Open Access Journals (Sweden)
Wang Daoshun
2010-01-01
Full Text Available Abstract Traditional Secret Sharing (SS schemes reconstruct secret exactly the same as the original one but involve complex computation. Visual Secret Sharing (VSS schemes decode the secret without computation, but each share is m times as big as the original and the quality of the reconstructed secret image is reduced. Probabilistic visual secret sharing (Prob.VSS schemes for a binary image use only one subpixel to share the secret image; however the probability of white pixels in a white area is higher than that in a black area in the reconstructed secret image. SS schemes, VSS schemes, and Prob. VSS schemes have various construction methods and advantages. This paper first presents an approach to convert (transform a -SS scheme to a -VSS scheme for greyscale images. The generation of the shadow images (shares is based on Boolean XOR operation. The secret image can be reconstructed directly by performing Boolean OR operation, as in most conventional VSS schemes. Its pixel expansion is significantly smaller than that of VSS schemes. The quality of the reconstructed images, measured by average contrast, is the same as VSS schemes. Then a novel matrix-concatenation approach is used to extend the greyscale -SS scheme to a more general case of greyscale -VSS scheme.
Tests of a Convective Cloud Model with Soundings During the TCM-90 Field Experiment
1992-03-01
Meteorology Robert L. Haney, Chai an Department of Meteorology ii ABSTRACT A new proposed scheme for representing cumulus convection in a large-scale...towers and the total heating at lower levels ( Houze 1989). In particular, its propensity to mix with the environment and sink as a result of evaporative...observations. Technical Report NPS MR-91-006, Naval Postgraduate School, Monterey, CA 93943. 66 Houze , R. A., Jr., 1989: Observed structure of
Energy Technology Data Exchange (ETDEWEB)
Elliott, C.J.; Fisher, H.; Pepin, J. [Los Alamos National Lab., NM (United States); Gillmann, R. [Federal Highway Administration, Washington, DC (United States)
1996-07-01
Traffic classification techniques were evaluated using data from a 1993 investigation of the traffic flow patterns on I-20 in Georgia. First we improved the data by sifting through the data base, checking against the original video for questionable events and removing and/or repairing questionable events. We used this data base to critique the performance quantitatively of a classification method known as Scheme F. As a context for improving the approach, we show in this paper that scheme F can be represented as a McCullogh-Pitts neural network, oar as an equivalent decomposition of the plane. We found that Scheme F, among other things, severely misrepresents the number of vehicles in Class 3 by labeling them as Class 2. After discussing the basic classification problem in terms of what is measured, and what is the desired prediction goal, we set forth desirable characteristics of the classification scheme and describe a recurrent neural network system that partitions the high dimensional space up into bins for each axle separation. the collection of bin numbers, one for each of the axle separations, specifies a region in the axle space called a hyper-bin. All the vehicles counted that have the same set of in numbers are in the same hyper-bin. The probability of the occurrence of a particular class in that hyper- bin is the relative frequency with which that class occurs in that set of bin numbers. This type of algorithm produces classification results that are much more balanced and uniform with respect to Classes 2 and 3 and Class 10. In particular, the cancellation of errors of classification that occurs is for many applications the ideal classification scenario. The neural network results are presented in the form of a primary classification network and a reclassification network, the performance matrices for which are presented.
Scalable Nonlinear Compact Schemes
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Debojyoti [Argonne National Lab. (ANL), Argonne, IL (United States); Constantinescu, Emil M. [Univ. of Chicago, IL (United States); Brown, Jed [Univ. of Colorado, Boulder, CO (United States)
2014-04-01
In this work, we focus on compact schemes resulting in tridiagonal systems of equations, specifically the fifth-order CRWENO scheme. We propose a scalable implementation of the nonlinear compact schemes by implementing a parallel tridiagonal solver based on the partitioning/substructuring approach. We use an iterative solver for the reduced system of equations; however, we solve this system to machine zero accuracy to ensure that no parallelization errors are introduced. It is possible to achieve machine-zero convergence with few iterations because of the diagonal dominance of the system. The number of iterations is specified a priori instead of a norm-based exit criterion, and collective communications are avoided. The overall algorithm thus involves only point-to-point communication between neighboring processors. Our implementation of the tridiagonal solver differs from and avoids the drawbacks of past efforts in the following ways: it introduces no parallelization-related approximations (multiprocessor solutions are exactly identical to uniprocessor ones), it involves minimal communication, the mathematical complexity is similar to that of the Thomas algorithm on a single processor, and it does not require any communication and computation scheduling.
A Test of Sensitivity to Convective Transport in a Global Atmospheric CO2 Simulation
Bian, H.; Kawa, S. R.; Chin, M.; Pawson, S.; Zhu, Z.; Rasch, P.; Wu, S.
2006-01-01
Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO2 distributions. GlobalCO2 in the year 2000 is simulated using theCTM driven by assimilated meteorological fields from the NASA s Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO2 by adopting the same CO2 emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection. Replacing Conv1 by Conv2 results in an overestimate of CO2 over biospheric sink regions. The largest discrepancies result in a CO2 difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO2 seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO2 sink. It is shown that the overestimated CO2 driven by Conv2 can be offset by introducing these supplemental emissions.
Sensitivity of CO2 Simulation in a GCM to the Convective Transport Algorithms
Zhu, Z.; Pawson, S.; Collatz, G. J.; Gregg, W. W.; Kawa, S. R.; Baker, D.; Ott, L.
2014-01-01
Convection plays an important role in the transport of heat, moisture and trace gases. In this study, we simulated CO2 concentrations with an atmospheric general circulation model (GCM). Three different convective transport algorithms were used. One is a modified Arakawa-Shubert scheme that was native to the GCM; two others used in two off-line chemical transport models (CTMs) were added to the GCM here for comparison purposes. Advanced CO2 surfaced fluxes were used for the simulations. The results were compared to a large quantity of CO2 observation data. We find that the simulation results are sensitive to the convective transport algorithms. Overall, the three simulations are quite realistic and similar to each other in the remote marine regions, but are significantly different in some land regions with strong fluxes such as Amazon and Siberia during the convection seasons. Large biases against CO2 measurements are found in these regions in the control run, which uses the original GCM. The simulation with the simple diffusive algorithm is better. The difference of the two simulations is related to the very different convective transport speed.
Quantum identification schemes with entanglements
International Nuclear Information System (INIS)
Mihara, Takashi
2002-01-01
We need secure identification schemes because many situations exist in which a person must be identified. In this paper, we propose three quantum identification schemes with entanglements. First, we propose a quantum one-time pad password scheme. In this scheme, entanglements play the role of a one-time pad password. Next, we propose a quantum identification scheme that requires a trusted authority. Finally, we propose a quantum message authentication scheme that is constructed by combining a different quantum cryptosystem with an ordinary authentication tag
Convective mixing and accretion in white dwarfs
International Nuclear Information System (INIS)
Koester, D.
1976-01-01
The evolution of convection zones in cooling white dwarfs with helium envelopes and outer hydrogen layers is calculated with a complete stellar evolution code. It is shown that white dwarfs of spectral type DB cannot be formed from DA stars by convective mixing. However, for cooler temperatures (Tsub(e) [de
Directory of Open Access Journals (Sweden)
G. V. Kalashnikov
2014-01-01
Full Text Available The estimation of thermodynamic perfection of separate technological processes is executed at heat-moisture of handling of fruit and a line of manufacture of fruit apple chips and dried fruits. The technological scheme of a line of processing of fruits and manufactures of fruit chips on the basis of convection and the microwave-dryings suggested resource-saving. The technique is made and results of calculation of thermal expenses for various schemes of manufacture of apple chips are resulted. For the offered scheme material, thermal and power streams on the basis of balance parities of technological processes are certain. The comparative thermal production efficiency of apple chips for a base foreign variant and the offered technological scheme with the closed cycle of use of the heat-carrier and the combined convection-microwave-drying is shown. In this paper we define the thermal and energy flows for the processes of convective drying, pre-microwave drying, hydrothermal treatment and final microwave drying plant material, which are one of the main stages of the production of all kinds of fruit and vegetable concentrates, including fruit apple chips. Resource-saving ways moisture-heat of handling (hydration, blanching, drying, etc. produce raw materials in the production of food concentrates suggested a reduced water flow with a high degree of use of its potential power and microwave sources. To assess the thermal efficiency of the various processes and production schemes used as indicators of thermal efficiency and proposed value of specific heat (kJ / kg given mass productivity per unit of feedstock and translational moisture. The values of the mass fraction of the heat of material flows for the base and the proposed resource-saving production scheme fruit chips, for example, apple, based on a combination of convection-microwave drying each control surface.
Convective penetration in a young sun
Pratt, Jane; Baraffe, Isabelle; Goffrey, Tom; MUSIC developers group
2018-01-01
To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. This model provides a scenario that can explain the observed lithium abundance in the sun and in solar-like stars at a range of ages.
Convection of Moist Saturated Air: Analytical Study
Directory of Open Access Journals (Sweden)
Robert Zakinyan
2016-01-01
Full Text Available In the present work, the steady-state stationary thermal convection of moist saturated air in a lower atmosphere has been studied theoretically. Thermal convection was considered without accounting for the Coriolis force, and with only the vertical temperature gradient. The analytical solution of geophysical fluid dynamics equations, which generalizes the formulation of the moist convection problem, is obtained in the two-dimensional case. The stream function is derived in the Boussinesq approximation with velocity divergence taken as zero. It has been shown that the stream function is asymmetrical in vertical direction contrary to the dry and moist unsaturated air convection. It has been demonstrated that the convection in moist atmosphere strongly depends on the vapor mass fraction gradient.
Energy Technology Data Exchange (ETDEWEB)
Kinyanjui, M.; Kwanza, J.K.; Uppal, S.M. [Jomo Kenyatta University of Agriculture and Technology, Nairobi (Cayman Islands). Dept. of Mathematics and Statistics
2001-05-01
Simultaneous heat and mass transfer in unsteady free convection flow with radiation absorption past an impulsively started infinite vertical porous plate subjected to a strong magnetic field is presented. The governing equations for the problem are solved by a finite difference scheme. The influence of the various parameters on the convectively cooled or convectively heated plate in the laminar boundary layer are considered. An analysis of the effects of the parameters on the concentration, velocity and temperature profiles, as well as skin friction and the rates of mass and heat transfer, is done with the aid of graphs and tables. (author)
Axisymmetric Marangoni convection in microencapsulation
Subramanian, Pravin; Zebib, Abdelfattah; McQuillan, Barry
2005-07-01
Spherical shells used as laser targets in inertial confinement fusion (ICF) experiments are made by microencapsulation. In one phase of manufacturing, the spherical shells contain a solvent (fluorobenzene (FB)) and a solute (polystyrene (PAMS)) in a water-FB environment. Evaporation of the FB results in the desired hardened plastic hollow spherical shells, 1-2 mm in diameter. Perfect sphericity is demanded for efficient fusion ignition and the observed surface roughness maybe driven by Marangoni instabilities due to surface tension dependence on the FB concentration (buoyant forces are negligible in this micro-scale problem). Here we model this drying process and compute nonlinear, time-dependent, axisymmetric, variable viscosity, infinite Schmidt number solutocapillary convection in the shells. Comparison with results from linear theory and available experiments are made.
Convective evaporation of vertical films.
Boulogne, François; Dollet, Benjamin
2018-02-28
Motivated by the evaporation of soap films, which has a significant effect on their lifetime, we performed an experimental study on the evaporation of vertical surfaces with model systems based on hydrogels. From the analogy between heat and mass transfer, we adopt a model describing the natural convection in the gas phase due to a density contrast between dry and saturated air. Our measurements show a good agreement with this model, both in terms of scaling law with the Grashof number and in terms of order of magnitude. We discuss the corrections to take into account, notably the contribution of edge effects, which have a small but visible contribution when lateral and bottom surface areas are not negligible compared to the main evaporating surface area.
Actively convected liquid metal divertor
International Nuclear Information System (INIS)
Shimada, Michiya; Hirooka, Yoshi
2014-01-01
The use of actively convected liquid metals with j × B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j × B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v × B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem. (letter)
Actively convected liquid metal divertor
Shimada, Michiya; Hirooka, Yoshi
2014-12-01
The use of actively convected liquid metals with j × B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j × B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v × B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem.
Yasas, F M
1977-01-01
In response to a United Nations resolution, the Mobile Training Scheme (MTS) was set up to provide training to the trainers of national cadres engaged in frontline and supervisory tasks in social welfare and rural development. The training is innovative in its being based on an analysis of field realities. The MTS team consisted of a leader, an expert on teaching methods and materials, and an expert on action research and evaluation. The country's trainers from different departments were sent to villages to work for a short period and to report their problems in fulfilling their roles. From these grass roots experiences, they made an analysis of the job, determining what knowledge, attitude and skills it required. Analysis of daily incidents and problems were used to produce indigenous teaching materials drawn from actual field practice. How to consider the problems encountered through government structures for policy making and decisions was also learned. Tasks of the students were to identify the skills needed for role performance by job analysis, daily diaries and project histories; to analyze the particular community by village profiles; to produce indigenous teaching materials; and to practice the role skills by actual role performance. The MTS scheme was tried in Nepal in 1974-75; 3 training programs trained 25 trainers and 51 frontline workers; indigenous teaching materials were created; technical papers written; and consultations were provided. In Afghanistan the scheme was used in 1975-76; 45 participants completed the training; seminars were held; and an ongoing Council was created. It is hoped that the training program will be expanded to other countries.
Bonus Schemes and Trading Activity
Pikulina, E.S.; Renneboog, L.D.R.; Ter Horst, J.R.; Tobler, P.N.
2013-01-01
Abstract: Little is known about how different bonus schemes affect traders’ propensity to trade and which bonus schemes improve traders’ performance. We study the effects of linear versus threshold (convex) bonus schemes on traders’ behavior. Traders purchase and sell shares in an experimental stock
International Nuclear Information System (INIS)
Grashilin, V.A.; Karyshev, Yu.Ya.
1982-01-01
A 6-cycle scheme of step motor is described. The block-diagram and the basic circuit of the step motor control are presented. The step motor control comprises a pulse shaper, electronic commutator and power amplifiers. The step motor supply from 6-cycle electronic commutator provides for higher reliability and accuracy than from 3-cycle commutator. The control of step motor work is realised by the program given by the external source of control signals. Time-dependent diagrams for step motor control are presented. The specifications of the step-motor is given
The Mechanism of First Raindrops Formation in Deep Convective Clouds
Energy Technology Data Exchange (ETDEWEB)
Khain, Alexander; Prabha, Thara; Benmoshe, Nir; Pandithurai, G.; Ovchinnikov, Mikhail
2013-08-22
The formation of first raindrops in deep convective clouds is investigated. A combination of observational data analysis and 2-D and 3-D numerical bin microphysical simulations of deep convective clouds suggests that the first raindrops form at the top of undiluted or slightly diluted cores. It is shown that droplet size distributions in these regions are wider and contain more large droplets than in diluted volumes. The results of the study indicate that the initial raindrop formation is determined by the basic microphysical processes within ascending adiabatic volumes. It allows one to predict the height of the formation of first raindrops considering the processes of nucleation, diffusion growth and collisions. The results obtained in the study explain observational results reported by Freud and Rosenfeld (2012) according to which the height of first raindrop formation depends linearly on the droplet number concentration at cloud base. The results also explain why a simple adiabatic parcel model can reproduce this dependence. The present study provides a physical basis for retrieval algorithms of cloud microphysical properties and aerosol properties using satellites proposed by Rosenfeld et al. ( 2012). The study indicates that the role of mixing and entrainment in the formation of the first raindrops is not of crucial importance. It is also shown that low variability of effective and mean volume radii along horizontal traverses, as regularly observed by in situ measurements, can be simulated by high-resolution cloud models, in which mixing is parameterized by a traditional 1.5 order turbulence closure scheme.
Rayleigh-Taylor convection in confined porous media
Zonta, Francesco; de Paoli, Marco; Soldati, Alfredo
2017-11-01
Motivated by the dissolution phenomena occurring during carbon sequestration processes, we analyze Rayleigh-Taylor convection in isotropic porous media. In the Rayleigh-Taylor configuration, a layer of dense fluid (CO2+brine) lyes on top of a layer of light fluid (brine). The velocity field is computed with the Darcy law, whereas the concentration field is determined by the advection-diffusion equation. We used a pseudospectral scheme (Fourier discretization in periodic direction and Chebyshev polynomial in wall-normal direction) to run Direct Numerical Simulations (DNS) of the present system. We focused in particular on the behavior of the mixing length h (the tip-to-rear finger distance), a fundamental quantity to characterize all the transfer phenomena (solute, convection and energy) occurring in the analyzed case. In particular, we observed that the time behavior of h is twofold: during the initial transient evolution, h has a self similar universal behavior; later, due to the presence of boundaries, the behavior becomes more complex and hard to predict. Physical implications of the present results on dissolution modeling approaches will be also addressed.
Packet reversed packet combining scheme
International Nuclear Information System (INIS)
Bhunia, C.T.
2006-07-01
The packet combining scheme is a well defined simple error correction scheme with erroneous copies at the receiver. It offers higher throughput combined with ARQ protocols in networks than that of basic ARQ protocols. But packet combining scheme fails to correct errors when the errors occur in the same bit locations of two erroneous copies. In the present work, we propose a scheme that will correct error if the errors occur at the same bit location of the erroneous copies. The proposed scheme when combined with ARQ protocol will offer higher throughput. (author)
Zhang, Guang J.; Wu, Xiaoqing; Zeng, Xiping; Mitovski, Toni
2016-10-01
The fractional entrainment rate in convective clouds is an important parameter in current convective parameterization schemes of climate models. In this paper, it is estimated using a 1-km-resolution cloud-resolving model (CRM) simulation of convective clouds from TWP-ICE (the Tropical Warm Pool-International Cloud Experiment). The clouds are divided into different types, characterized by cloud-top heights. The entrainment rates and moist static energy that is entrained or detrained are determined by analyzing the budget of moist static energy for each cloud type. Results show that the entrained air is a mixture of approximately equal amount of cloud air and environmental air, and the detrained air is a mixture of ~80 % of cloud air and 20 % of the air with saturation moist static energy at the environmental temperature. After taking into account the difference in moist static energy between the entrained air and the mean environment, the estimated fractional entrainment rate is much larger than those used in current convective parameterization schemes. High-resolution (100 m) large-eddy simulation of TWP-ICE convection was also analyzed to support the CRM results. It is shown that the characteristics of entrainment rates estimated using both the high-resolution data and CRM-resolution coarse-grained data are similar. For each cloud category, the entrainment rate is high near cloud base and top, but low in the middle of clouds. The entrainment rates are best fitted to the inverse of in-cloud vertical velocity by a second order polynomial.
Granular convection driven by shearing inertial forces.
Rodríguez-Liñán, G M; Nahmad-Molinari, Y
2006-01-01
Convection velocity measurements in vertically vibrated granular materials are presented. The convection velocity close to the walls grows quadratically with the difference between the maximum and critical, or excess, amplitude (proposed as a dynamic parameter to describe related problems) and it is shown numerically that the average bed-bottom relative velocity during the distancing between them, grows linearly with the squared as well. This is interpreted as the signature of an inertial shearing force or momentum transfer proportional to the bed-container relative velocity, acting mainly during the bed-plate distancing part of each cycle which leads to the formation of the convective flux.
Transient Mixed Convection Validation for NGNP
International Nuclear Information System (INIS)
Smith, Barton; Schultz, Richard
2015-01-01
The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.
Measuring Convective Mass Fluxes Over Tropical Oceans
Raymond, David
2017-04-01
Deep convection forms the upward branches of all large-scale circulations in the tropics. Understanding what controls the form and intensity of vertical convective mass fluxes is thus key to understanding tropical weather and climate. These mass fluxes and the corresponding conditions supporting them have been measured by recent field programs (TPARC/TCS08, PREDICT, HS3) in tropical disturbances considered to be possible tropical storm precursors. In reality, this encompasses most strong convection in the tropics. The measurements were made with arrays of dropsondes deployed from high altitude. In some cases Doppler radar provided additional measurements. The results are in some ways surprising. Three factors were found to control the mass flux profiles, the strength of total surface heat fluxes, the column-integrated relative humidity, and the low to mid-tropospheric moist convective instability. The first two act as expected, with larger heat fluxes and higher humidity producing more precipitation and stronger lower tropospheric mass fluxes. However, unexpectedly, smaller (but still positive) convective instability produces more precipitation as well as more bottom-heavy convective mass flux profiles. Furthermore, the column humidity and the convective instability are anti-correlated, at least in the presence of strong convection. On spatial scales of a few hundred kilometers, the virtual temperature structure appears to be in dynamic balance with the pattern of potential vorticity. Since potential vorticity typically evolves on longer time scales than convection, the potential vorticity pattern plus the surface heat fluxes then become the immediate controlling factors for average convective properties. All measurements so far have taken place in regions with relatively flat sea surface temperature (SST) distributions. We are currently seeking funding for a measurement program in the tropical east Pacific, a region that exhibits strong SST gradients and
Transient Mixed Convection Validation for NGNP
Energy Technology Data Exchange (ETDEWEB)
Smith, Barton [Utah State Univ., Logan, UT (United States); Schultz, Richard [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2015-10-19
The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.
A multisensor evaluation of the asymmetric convective model, version 2, in southeast Texas.
Kolling, Jenna S; Pleim, Jonathan E; Jeffries, Harvey E; Vizuete, William
2013-01-01
There currently exist a number of planetary boundary layer (PBL) schemes that can represent the effects of turbulence in daytime convective conditions, although these schemes remain a large source of uncertainty in meteorology and air quality model simulations. This study evaluates a recently developed combined local and nonlocal closure PBL scheme, the Asymmetric Convective Model, version 2 (ACM2), against PBL observations taken from radar wind profilers, a ground-based lidar, and multiple daytime radiosonde balloon launches. These observations were compared against predictions of PBLs from the Weather Research and Forecasting (WRF) model version 3.1 with the ACM2 PBL scheme option, and the Fifth-Generation Meteorological Model (MM5) version 3.7.3 with the Eta PBL scheme option that is currently being used to develop ozone control strategies in southeast Texas. MM5 and WRF predictions during the regulatory modeling episode were evaluated on their ability to predict the rise and fall of the PBL during daytime convective conditions across southeastern Texas. The MM5 predicted PBLs consistently underpredicted observations, and were also less than the WRF PBL predictions. The analysis reveals that the MM5 predicted a slower rising and shallower PBL not representative of the daytime urban boundary layer. Alternatively, the WRF model predicted a more accurate PBL evolution improving the root mean square error (RMSE), both temporally and spatially. The WRF model also more accurately predicted vertical profiles of temperature and moisture in the lowest 3 km of the atmosphere. Inspection of median surface temperature and moisture time-series plots revealed higher predicted surface temperatures in WRF and more surface moisture in MM5. These could not be attributed to surface heat fluxes, and thus the differences in performance of the WRF and MM5 models are likely due to the PBL schemes. An accurate depiction of the diurnal evolution of the planetary boundary layer (PBL) is
Convection in complex shaped vessel; Convection dans des enceintes de forme complexe
Energy Technology Data Exchange (ETDEWEB)
NONE
2000-07-01
The 8 november 2000, the SFT (Societe Francaise de Thermique) organized a technical day on the convection in complex shaped vessels. Nine papers have been presented in the domains of the heat transfers, the natural convection, the fluid distribution, the thermosyphon effect, the steam flow in a sterilization cycle and the transformers cooling. Eight papers are analyzed in ETDE and one paper dealing with the natural convection in spent fuels depository is analyzed in INIS. (A.L.B.)
Convective Radio Occultations Final Campaign Summary
Energy Technology Data Exchange (ETDEWEB)
Biondi, R. [Atmospheric Radiation Measurement, Washington, DC (United States)
2016-03-01
Deep convective systems are destructive weather phenomena that annually cause many deaths and injuries as well as much damage, thereby accounting for major economic losses in several countries. The number and intensity of such phenomena have increased over the last decades in some areas of the globe. Damage is mostly caused by strong winds and heavy rain parameters that are strongly connected to the structure of the particular storm. Convection over land is usually stronger and deeper than over the ocean and some convective systems, known as supercells, also develop tornadoes through processes that remain mostly unclear. The intensity forecast and monitoring of convective systems is one of the major challenges for meteorology because in situ measurements during extreme events are too sparse or unreliable and most ongoing satellite missions do not provide suitable time/space coverage.
Dynamics of acoustic-convective drying of sunflower cake
Zhilin, A. A.
2017-10-01
The dynamics of drying sunflower cake by a new acoustic-convective method has been studied. Unlike the conventional (thermal-convective) method, the proposed method allows moisture to be extracted from porous materials without applying heat to the sample to be dried. Kinetic curves of drying by the thermal-convective and acoustic-convective methods were obtained and analyzed. The advantages of the acoustic-convective extraction of moisture over the thermal-convective method are discussed. The relaxation times of drying were determined for both drying methods. An intermittent drying mode which improves the efficiency of acoustic-convective extraction of moisture is considered.
Natural convection type BWR reactor
International Nuclear Information System (INIS)
Tobimatsu, Toshimi.
1990-01-01
In a natural convection type BWR reactor, a mixed stream of steams and water undergo a great flow resistance. In particular, pressure loss upon passing from an upper plenum to a stand pipe and pressure loss upon passing through rotational blades are great. Then, a steam dryer comprising laminated dome-like perforated plates and a drain pipe for flowing down separated water to a downcomer are disposed above a riser. The coolants heated in the reactor core are boiled, uprise in the riser as a gas-liquid two phase flow containing voids, release steams containing droplets from the surface of the gas-liquid two phase, flow into the steam dryer comprising the perforated plates and are separated into a gas and a liquid. The dried steams flow to a turbine passing through a main steam pipe and the condensated droplets flow down through the drain pipe and the downcomer to the lower portion of the reactor core. In this way, the conventional gas-liquid separator can be saved without lowering the quality of steam drying to reduce the pressure loss and to improve the operation performance. (N.H.)
Controlling arbitrary humidity without convection.
Wasnik, Priyanka S; N'guessan, Hartmann E; Tadmor, Rafael
2015-10-01
In this paper we show a way that allows for the first time to induce arbitrary humidity of desired value for systems without convective flow. To enable this novelty we utilize a semi-closed environment in which evaporation is not completely suppressed. In this case, the evaporation rate is determined both by the outer (open) humidity and by the inner (semi-closed) geometry including the size/shape of the evaporating medium and the size/shape of the semi-closure. We show how such systems can be used to induce desired humidity conditions. We consider water droplet placed on a solid surface and study its evaporation when it is surrounded by other drops, hereon "satellite" drops and covered by a semi-closed hemisphere. The main drop's evaporation rate is proportional to its height, in agreement with theory. Surprisingly, however, the influence of the satellite drops on the main drop's evaporation suppression is not proportional to the sum of heights of the satellite drops. Instead, it shows proportionality close to the satellite drops' total surface area. The resultant humidity conditions in the semi-closed system can be effectively and accurately induced using different satellite drops combinations. Copyright © 2015 Elsevier Inc. All rights reserved.
Combined convective heat transfer from short cylinders
International Nuclear Information System (INIS)
Oosthuizen, P.H.; Paul, J.T.
1985-01-01
Considerable experimental evidence has been produced recently showing that the free convective heat transfer rate from horizontal circular cylinders becomes influenced by the length to diameter ratio L/D. The major aim of the present study was to determine the influence of the L/D ratio on the conditions under which buoyancy forces cause the heat transfer rate to start to deviate significantly from that existing in purely forced convection
Numerical Study of a Convective Turbulence Encounter
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The specific case was encountered during one of NASA's flight tests and was characterized by severe turbulence. The event was associated with overshooting convective turrets that contained low to moderate radar reflectivity. Model comparisons with observations are quite favorable. Turbulence hazard metrics are proposed and applied to the numerical data set. Issues such as adequate grid size are examined.
Driving forces: Slab subduction and mantle convection
Hager, Bradford H.
1988-01-01
Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.
Transmission usage cost allocation schemes
International Nuclear Information System (INIS)
Abou El Ela, A.A.; El-Sehiemy, R.A.
2009-01-01
This paper presents different suggested transmission usage cost allocation (TCA) schemes to the system individuals. Different independent system operator (ISO) visions are presented using the proportional rata and flow-based TCA methods. There are two proposed flow-based TCA schemes (FTCA). The first FTCA scheme generalizes the equivalent bilateral exchanges (EBE) concepts for lossy networks through two-stage procedure. The second FTCA scheme is based on the modified sensitivity factors (MSF). These factors are developed from the actual measurements of power flows in transmission lines and the power injections at different buses. The proposed schemes exhibit desirable apportioning properties and are easy to implement and understand. Case studies for different loading conditions are carried out to show the capability of the proposed schemes for solving the TCA problem. (author)
Miller, Timothy L.; Robertson, Franklin R.; Cohen, Charles; Mackaro, Jessica
2009-01-01
The Goddard Earth Observing System Model, Version 5 (GEOS-5) is a system of models that have been developed at Goddard Space Flight Center to support NASA's earth science research in data analysis, observing system modeling and design, climate and weather prediction, and basic research. The work presented used GEOS-5 with 0.25o horizontal resolution and 72 vertical levels (up to 0.01 hP) resolving both the troposphere and stratosphere, with closer packing of the levels close to the surface. The model includes explicit (grid-scale) moist physics, as well as convective parameterization schemes. Results will be presented that will demonstrate strong dependence in the results of modeling of a strong hurricane on the type of convective parameterization scheme used. The previous standard (default) option in the model was the Relaxed Arakawa-Schubert (RAS) scheme, which uses a quasi-equilibrium closure. In the cases shown, this scheme does not permit the efficient development of a strong storm in comparison with observations. When this scheme is replaced by a modified version of the Kain-Fritsch scheme, which was originally developed for use on grids with intervals of order 25 km such as the present one, the storm is able to develop to a much greater extent, closer to that of reality. Details of the two cases will be shown in order to elucidate the differences in the two modeled storms.
Patrick Honohan
1987-01-01
A Ponzi scheme is an arrangement whereby a promoter offers an investment opportunity with attractive dividends, but where the only basis for the dividends is the future receipts from new investors. The first of these two notes explores some of the analytical properties of a Ponzi scheme, addressing in particular the question whether it is possible for a Ponzi scheme to exist if all the participants are rational. The second note briefly examines the collapse of the PMPA insurance company whos...
Numerical turbulent convective heat transfer and fluid flow in complex channels
Energy Technology Data Exchange (ETDEWEB)
Rokni, M.
1996-04-01
This investigation concerns numerical turbulent heat transfer and fluid flow in complex channels for fully developed periodic state. Numerical application of different turbulence models for forced convective heat transfer in three dimensional channels are presented. It also concerns prediction of secondary motions and temperature distribution in straight and corrugated ducts with different cross section area. The standard linear k-e and Speziale`s non-linear k-e models with wall functions are applied to calculate the turbulent shear stresses. SED, GGDH and WET models are used to predict the turbulent heat fluxes. The overall thermal-hydraulic performance is presented in terms of friction factor and Nu-number. Some formulas are also presented to estimate the Nu-number in various wavy channels. The numerical approach is based on the finite volume technique with non-staggered grid arrangement. Rhie-Chow interpolation with SIMPLEC-algorithm is used. The convective terms are treated by hybrid, MUSCL, van Leer and QUICK schemes while the diffusive terms are treated by central difference scheme. The fully developed turbulent state is achieved by imposing periodic conditions in the main flow direction. In general, a numerical method for calculation of turbulent convective heat transfer in complex channels is presented. 4 refs, 3 figs
Entropy conservative finite element schemes
Tadmor, E.
1986-01-01
The question of entropy stability for discrete approximations to hyperbolic systems of conservation laws is studied. The amount of numerical viscosity present in such schemes is quantified and related to their entropy stability by means of comparison. To this end, two main ingredients are used: entropy variables and the construction of certain entropy conservative schemes in terms of piecewise-linear finite element approximations. It is then shown that conservative schemes are entropy stable, if and (for three-point schemes) only if, they contain more numerical viscosity than the abovementioned entropy conservation ones.
DEFF Research Database (Denmark)
Rotbart, Noy Galil
in a distributed fashion increases. Second, attempting to answer queries on vertices of a graph stored in a distributed fashion can be significantly more complicated. In order to lay theoretical foundations to the first penalty mentioned a large body of work concentrated on labeling schemes. A labeling scheme...... evaluation of fully dynamic labeling schemes. Due to a connection between adjacency labeling schemes and the graph theoretical study of induced universal graphs, we study these in depth and show novel results for bounded degree graphs and power-law graphs. We also survey and make progress on the related...
Topology optimization of natural convection: Flow in a differentially heated cavity
Saglietti, Clio; Schlatter, Philipp; Berggren, Martin; Henningson, Dan
2017-11-01
The goal of the present work is to develop methods for optimization of the design of natural convection cooled heat sinks, using resolved simulation of both fluid flow and heat transfer. We rely on mathematical programming techniques combined with direct numerical simulations in order to iteratively update the topology of a solid structure towards optimality, i.e. until the design yielding the best performance is found, while satisfying a specific set of constraints. The investigated test case is a two-dimensional differentially heated cavity, in which the two vertical walls are held at different temperatures. The buoyancy force induces a swirling convective flow around a solid structure, whose topology is optimized to maximize the heat flux through the cavity. We rely on the spectral-element code Nek5000 to compute a high-order accurate solution of the natural convection flow arising from the conjugate heat transfer in the cavity. The laminar, steady-state solution of the problem is evaluated with a time-marching scheme that has an increased convergence rate; the actual iterative optimization is obtained using a steepest-decent algorithm, and the gradients are conveniently computed using the continuous adjoint equations for convective heat transfer.
Natural Convection Heat Transfer in Concentric Horizontal Annuli Containing a Saturated Porous Medi
Directory of Open Access Journals (Sweden)
Ahmed F. Alfahaid, R.Y. Sakr
2012-10-01
Full Text Available Natural convection in horizontal annular porous media has become a subject receiving increasing attention due to its practical importance in the problem of insulators, such as ducting system in high temperature gas-cooled reactors, heating systems, thermal energy storage systems, under ground cable systems, etc. This paper presents a numerical study for steady state thermal convection in a fully saturated porous media bounded by two horizontal concentric cylinders, the cylinders are impermeable to fluid motion and maintained at different, uniform temperatures. The solution scheme is based on two-dimensional model, which is governed by Darcy-Oberbeck-Boussinesq equations. The finite element method using Galerkin technique is developed and employed to solve the present problem. A numerical simulation is carried out to examine the parametric effects of Rayleigh number and radius ratio on the role played by natural convection heat transfer in the porous annuli. The numerical results obtained from the present model were compared with the available published results and good agreement is observed. The average Nusselt number at the heating surface of the inner cylinder is correlated to Rayleigh number and radius ratio.Keywords: Natural convection, numerical investigation, saturated porous media, finite element method, concentric horizontal annuli.
hybrid modulation scheme fo rid modulation scheme fo dulation ...
African Journals Online (AJOL)
eobe
This work proposes a switching technique for ca proposes a switching technique for ca. (SCSPWM) scheme is employed in the generation circulation schemes are presented for this concepts, it is now possible to generate equal ave pts, it is now possible to generate equal ave semiconductor switches. This results in equal ...
Entropy Production in Convective Hydrothermal Systems
Boersing, Nele; Wellmann, Florian; Niederau, Jan
2016-04-01
Exploring hydrothermal reservoirs requires reliable estimates of subsurface temperatures to delineate favorable locations of boreholes. It is therefore of fundamental and practical importance to understand the thermodynamic behavior of the system in order to predict its performance with numerical studies. To this end, the thermodynamic measure of entropy production is considered as a useful abstraction tool to characterize the convective state of a system since it accounts for dissipative heat processes and gives insight into the system's average behavior in a statistical sense. Solving the underlying conservation principles of a convective hydrothermal system is sensitive to initial conditions and boundary conditions which in turn are prone to uncertain knowledge in subsurface parameters. There exist multiple numerical solutions to the mathematical description of a convective system and the prediction becomes even more challenging as the vigor of convection increases. Thus, the variety of possible modes contained in such highly non-linear problems needs to be quantified. A synthetic study is carried out to simulate fluid flow and heat transfer in a finite porous layer heated from below. Various two-dimensional models are created such that their corresponding Rayleigh numbers lie in a range from the sub-critical linear to the supercritical non-linear regime, that is purely conductive to convection-dominated systems. Entropy production is found to describe the transient evolution of convective processes fairly well and can be used to identify thermodynamic equilibrium. Additionally, varying the aspect ratio for each Rayleigh number shows that the variety of realized convection modes increases with both larger aspect ratio and higher Rayleigh number. This phenomenon is also reflected by an enlarged spread of entropy production for the realized modes. Consequently, the Rayleigh number can be correlated to the magnitude of entropy production. In cases of moderate
Sman, van der R.G.M.
1999-01-01
Packaging is crucial for the control of quality of fresh agricultural products. How to optimise the packaging design for a particular product and distribution chain, is still not fully understood. Various empirical studies have shown that existing packaging designs can still be improved
Impacts of convection schemes on simulating tropical-temperate troughs over southern Africa
CSIR Research Space (South Africa)
Tozuka, T
2013-03-01
Full Text Available of TTTs. Rather, it is related to excessive upper level convergence and associated subsidence over southern Africa. Furthermore, the model versions are shown to be successful in capturing the observed drier (wetter) conditions over the southern African...
Convection and exchangers in variable regime; Convection et echangeurs en regime variable
Energy Technology Data Exchange (ETDEWEB)
Bagui, F.; Abdelghani-Idrissi, M.A. [Rouen Univ. IUT, Centre de Developpement Durable, 76 - Mont Saint Aignan (France); Bagui, F. [Ecole d' Ingenieurs CESI, 76 - Mont Saint Aignan (France); Desmet, B.; Lalot, S.; Harmand, S. [Valenciennes et du Hainaut-Cambresis Univ., Lab. de Mecanique et Energetique, 59 - Valenciennes (France); Maillet, D. [Institut National Polytechnique, INPL-UHP Nancy-1, LEMTA-CNRS UMR 7563, 54 - Vandoeuvre les Nancy (France)
2005-07-01
This session about convection and exchangers in variable regime gathers three articles dealing with: the transient regimes of tubular heat exchangers; heat exchangers and convection in non-permanent regime; and the limitations of the H coefficient: two short-time and short-scale examples. (J.S.)
Directory of Open Access Journals (Sweden)
Imad Khan
Full Text Available This article concerns with mixed convection, heat and mass transfer characteristics of Eyring-Powell nanofluid over a cone and plate with chemical reactive species. The nonlinear partial differential equations (PDEâS are normalized by means of appropriate transformations. Governing equations are solved computationally by using shooting technique with fifth order Runge-Kutta scheme. A comparison for the cone and plate is given in each graph and table. The effects of emerging physical parameters such as porosity parameter, Lewis number, Prandtl number, Brownian moment, magnetic field parameter, thermophoresis parameter and mixed convection parameter on the momentum, temperature and concentration profiles are examined through graphs and tables. Keywords: Mixed convection flow, Eyring-Powell nanofluid, Chemical reaction, Cone and plate
Kumar, Vikash; Rani, Abha; Singh, Ajay Kumar
2017-12-01
The problem of conjugate free convection from a vertical fin embedded in a fluid-saturated porous medium is investigated. The governing nonlinear equations are solved iteratively by a highly implicit finite difference scheme. In this paper, the results based on four models, viz the Darcy model, the Brinkman model, the non-Darcian model with nonlinear inertia and viscous terms, and also the non-Darcian model with viscous, nonlinear inertia and velocity square terms, are compared. It is seen that fin cooling is more effective at higher Grashof or Darcy numbers due to stronger convection effects. The local Nusselt number is observed to increase with the Grashof or Darcy numbers and decrease slightly with the conduction-convection parameter. The limitation of the Darcy's law is observed at higher values of permeability when the non-Darcian models are more relevant.
CANONICAL BACKWARD DIFFERENTIATION SCHEMES FOR ...
African Journals Online (AJOL)
The schemes are based on rational interpolation obtained from canonical polynomials. They are A-stable. The test problems show that they give better results than Euler backward method and trapezoidal method near a singular point. KEY WORDS: backward differentiation scheme, collocation, initial value problems.
Directory of Open Access Journals (Sweden)
Kalidas Das
2016-10-01
Full Text Available The present work is concerned with heat and mass transfer of an electrically conducting second grade MHD fluid past a semi-infinite stretching sheet with convective surface heat flux. The analysis accounts for thermophoresis and thermal radiation. A similarity transformations is used to reduce the governing equations into a dimensionless form. The local similarity equations are derived and solved using Nachtsheim-Swigert shooting iteration technique together with Runge–Kutta sixth order integration scheme. Results for various flow characteristics are presented through graphs and tables delineating the effect of various parameters characterizing the flow. Our analysis explores that the rate of heat transfer enhances with increasing the values of the surface convection parameter. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of thermal radiation parameter.
Density maximum effect on Soret-induced natural convection in a square porous cavity
Alloui, Z.; Robillard, L.; Vasseur, P.
2010-10-01
This paper reports a numerical study on the effect of density maximum on Soret-induced convection in a square porous cavity. Dirichlet boundary conditions for temperature are applied to the vertical walls of the enclosure, while the two horizontal ones are assumed impermeable and insulated. The non-dimensional equations for momentum, energy and concentration are solved by a finite volume method with power-law scheme for convection and diffusion. A parametric study is undertaken as a function of the main dimensionless group characterizing the problem, namely the thermal Rayleigh number, RT, the solutal Rayleigh number, RS, the Lewis number Le and an extremum parameter γ, which quantifies the effect of the nonlinear equation of state. The results are presented in the form of streamlines, isotherms and isoconcentration lines for various values of the governing parameters. Comprehensive Nusselt number data are presented as functions of the governing parameters mentioned above.
Numerical study of convection in phase change material based on Lattice-Boltzmann method
Zhang, Tianyu; Feng, Ying; Zhao, Zhening
2017-06-01
In this paper, the lattice Boltzmann method was studied for the phase change process with convective heat transfer in phase change energy storage materials. Firstly, the macroscopic heat transfer equations for the phase change process with convective heat transfer was given, by which we built the lattice Boltzmann equations for solving the problems. In the model, the speed model of D2Q9 was selected, and the boundary conditions including of non-equilibrium extrapolation and bounce back scheme were selected. Then, the effects of different Rayleigh number on the temperature field and velocity field were analyzed. Further research in a square cavity heat transfer processes with high temperature object and low temperature object were studied, in order to observe the effects of different temperature objects in the phase change process using the changes of phase field.
Simultaneous Heat and Mass Transfer Model for Convective Drying of Building Material
Upadhyay, Ashwani; Chandramohan, V. P.
2018-04-01
A mathematical model of simultaneous heat and moisture transfer is developed for convective drying of building material. A rectangular brick is considered for sample object. Finite-difference method with semi-implicit scheme is used for solving the transient governing heat and mass transfer equation. Convective boundary condition is used, as the product is exposed in hot air. The heat and mass transfer equations are coupled through diffusion coefficient which is assumed as the function of temperature of the product. Set of algebraic equations are generated through space and time discretization. The discretized algebraic equations are solved by Gauss-Siedel method via iteration. Grid and time independent studies are performed for finding the optimum number of nodal points and time steps respectively. A MATLAB computer code is developed to solve the heat and mass transfer equations simultaneously. Transient heat and mass transfer simulations are performed to find the temperature and moisture distribution inside the brick.
Properties of convective motions in facular regions
Kostik, R.; Khomenko, E. V.
2012-09-01
Aims: We study the properties of solar granulation in a facular region from the photosphere up to the lower chromosphere. Our aim is to investigate the dependence of granular structure on magnetic field strength. Methods: We used observations obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife) using two different instruments: the Triple Etalon SOlar Spectrometer (TESOS) to measure velocity and intensity variations along the photosphere in the Ba ii 4554 Å line; and, simultaneously, the Tenerife Infrared Polarimeter (TIP-II) to the measure Stokes parameters and the magnetic field strength at the lower photosphere in the Fe i 1.56 μm lines. Results: We find that the convective velocities of granules in the facular area decrease with magnetic field while the convective velocities of intergranular lanes increase with the field strength. Similar to the quiet areas, there is a contrast and velocity sign reversal taking place in the middle photosphere. The reversal heights depend on the magnetic field strength and are, on average, about 100 km higher than in the quiet regions. The correlation between convective velocity and intensity decreases with magnetic field at the bottom photosphere, but increases in the upper photosphere. The contrast of intergranular lanes observed close to the disk center is almost independent of the magnetic field strength. Conclusions: The strong magnetic field of the facular area seems to stabilize the convection and to promote more effective energy transfer in the upper layers of the solar atmosphere, since the convective elements reach greater heights.
Convective transport resistance in the vitreous humor
Penkova, Anita; Sadhal, Satwindar; Ratanakijsuntorn, Komsan; Moats, Rex; Tang, Yang; Hughes, Patrick; Robinson, Michael; Lee, Susan
2012-11-01
It has been established by MRI visualization experiments that the convection of nanoparticles and large molecules with high rate of water flow in the vitreous humor will experience resistance, depending on the respective permeabilities of the injected solute. A set of experiments conducted with Gd-DTPA (Magnevist, Bayer AG, Leverkusen, Germany) and 30 nm gadolinium-based particles (Gado CELLTrackTM, Biopal, Worcester, MA) as MRI contrast agents showed that the degree of convective transport in this Darcy-type porous medium varies between the two solutes. These experiments consisted of injecting a mixture of the two (a 30 μl solution of 2% Magnevist and 1% nanoparticles) at the middle of the vitreous of an ex vivo whole bovine eye and subjecting the vitreous to water flow rate of 100 μl/min. The water (0.9% saline solution) was injected at the top of the eye, and was allowed to drain through small slits cut at the bottom of the eyeball. After 50 minutes of pumping, MRI images showed that the water flow carried the Gd-DTPA farther than the nanoparticles, even though the two solutes, being mixed, were subjected to the same convective flow conditions. We find that the convected solute lags the water flow, depending on the solute permeability. The usual convection term needs to be adjusted to allow for the filtration effect on the larger particles in the form (1- σ) u . ∇ c with important implications for the modeling of such systems.
Topology Optimisation for Coupled Convection Problems
DEFF Research Database (Denmark)
Alexandersen, Joe
This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport in a sur......This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite element formulation is implemented in an object-oriented parallel finite element framework programmed in the C++ programming language, developed by the Top-Opt research group of the Department of Mechanical Engineering at The Technical University of Denmark. The presented work is seen...
An extended Finite Variable Difference Method with application to QUICK scheme. Optimized QUICK
International Nuclear Information System (INIS)
Sakai, Katsuhiro
1996-01-01
A Finite Variable Difference Method (FVDM) proposed previously by the author for locally exact numerical schemes is extended so as to be applicable to polynomial expansion schemes. This extended FVDM is applied to the QUICK scheme. The optimum differencing points are analytically derived in terms of mesh Reynolds numbers so that the variance of the numerical solution is minimized under the condition that roots of the resulting characteristic equation are nonnegative to insure the numerical stability. This optimized scheme coincides with the original QUICK scheme at Rm=8/3, which is the critical value of its stability, and complements a stable scheme for Rm greater than 8/3. This optimization improves the numerical solution for the steady and unsteady convection-diffusion equations without numerical oscillations. In the same manner as the previous result for the locally exact numerical schemes, it has been made clear based on the extended FVDM that optimum differencing points from the view point of numerical stability and accuracy exist for the polynomial expansion schemes. (author)
Energy Technology Data Exchange (ETDEWEB)
Bettaibi, Soufiene, E-mail: Bettaibisoufiene@gmail.com [UR: Rayonnement Thermique, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia); Kuznik, Frédéric [INSA-Lyon, CETHIL, F-69621 Villeurbanne (France); Université de Lyon, CNRS, UMR5008, F-69622 Villeurbanne (France); Sediki, Ezeddine [UR: Rayonnement Thermique, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia)
2014-06-27
Highlights: • Mixed convection heat transfer in 2D lid-driven cavity is studied numerically. • Hybrid scheme with multiple relaxation time lattice Boltzmann method is used to obtain the velocity field. • Finite difference method is used to compute the temperature. • Effect of both Richardson and Reynolds numbers for mixed convection is studied. - Abstract: Mixed convection heat transfer in two-dimensional lid-driven rectangular cavity filled with air (Pr=0.71) is studied numerically. A hybrid scheme with multiple relaxation time lattice Boltzmann method (MRT-LBM) is used to obtain the velocity field while the temperature field is deduced from energy balance equation by using the finite difference method (FDM). The main objective of this work is to investigate the model effectiveness for mixed convection flow simulation. Results are presented in terms of streamlines, isotherms and Nusselt numbers. Excellent agreement is obtained between our results and previous works. The different comparisons demonstrate the robustness and the accuracy of our proposed approach.
Topology of convection beneath the solar surface
International Nuclear Information System (INIS)
Stein, R.F.; Nordlund, A.
1989-01-01
It is shown that the topology of convection beneath the solar surface is dominated by effects of stratification. Convection in a strongly stratified medium has: (1) gentle expanding structureless warm upflows and (2) strong converging filamentary cool downdrafts. The horizontal flow topology is cellular, with a hierarchy of cell sizes. The small density scale height in the surface layers forces the formation of the solar granulation, which is a shallow surface phenomenon. Deeper layers support successively larger cells. The downflows of small cells close to the surface merge into filamentary downdrafts of larger cells at greater depths, and this process is likely to continue through most of the convection zone. Radiative cooling at the surface provides the entropy-deficient material which drives the circulation. 13 refs
Boundary layer control of rotating convection systems.
King, Eric M; Stellmach, Stephan; Noir, Jerome; Hansen, Ulrich; Aurnou, Jonathan M
2009-01-15
Turbulent rotating convection controls many observed features of stars and planets, such as magnetic fields, atmospheric jets and emitted heat flux patterns. It has long been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force. Here, however, we present results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. We formulate a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers. This transition scaling theory unifies the disparate results of an extensive array of previous experiments, and is broadly applicable to natural convection systems.
Convective mixing in helium white dwarfs
International Nuclear Information System (INIS)
Vauclair, G.; Fontaine, G.
1979-01-01
The conditions under which convective mixing episodes take place between the helium envelopes and the underlying carbon layers in helium-rich white dwarfs are investigated. It is found that, for essentially any value of the initial helium content less than the maximum mass a helium convection zone can have, mixing does occur, and leads, in the vast majority of cases, to an almost pure carbon superficial composition. Mixing products that show only traces of carbon while retaining helium-dominated envelopes are possible only if the initial helium content is quite close to the maximum possible mass of the helium convection zone. In the presence of turbulence, this restriction could be relaxed, however, and the helium-rich lambda4670 stars may possibly be explained in this fashion
Das, S.; Banu, A.S.; Jana, R.N.; Makinde, O.D.
2015-01-01
This paper is concerned with the entropy generation in a magnetohydrodynamic (MHD) pseudo-plastic nanofluid flow through a porous channel with convective heating. Three different types of nanoparticles, namely copper, aluminum oxide and titanium dioxide are considered with pseudo-plastic carboxymethyl cellulose (CMC)–water used as base fluids. The governing equations are solved numerically by shooting technique coupled with Runge–Kutta scheme. The effects of the pertinent parameters on the fl...
Organization of tropical convection in low vertical wind shears: Role of updraft entrainment
Tompkins, Adrian M.; Semie, Addisu G.
2017-06-01
Radiative-convective equilibrium simulations with a 2 km horizontal resolution are conducted to investigate the impact on convective organization of different parameterizations for horizontal and vertical subgrid turbulence mixing. Three standard approaches for representing horizontal diffusion produce starkly differing mixing rates, particularly for the entrainment mixing into updrafts, which differ by more than an order of magnitude between the schemes. The simulations demonstrate that the horizontal subgrid mixing of water vapor is key, with high mixing rates a necessary condition for organization of convection to occur, since entrainment of dry air into updrafts suppresses convection. It is argued that diabatic budgets, while demonstrating the role of spatially heterogeneous radiative heating rates in driving organization, can overlook the role of physical processes such as updraft entrainment. These results may partially explain previous studies that showed that organization is more likely to occur at coarser resolutions, when entrainment is solely represented by subgrid-scale turbulence schemes, highlighting the need for benchmark simulations of higher horizontal resolution. The recommendation is for the use of larger ensembles to ensure robustness of conclusions to subgrid-scale parameterization assumptions when numerically investigating convective organization, possibly through a coordinated community model intercomparison effort.Plain Language SummaryThunderstorms dry out the atmosphere since they produce rainfall. However, their efficiency at drying the atmosphere depends on how they are arranged; take a set of thunderstorms and sprinkle them randomly over the tropics and the troposphere will remain quite moist, but take that same number of thunderstorms and place them all close together in a "cluster" and the atmosphere will be much drier. Previous work has indicated that thunderstorms might start to cluster more as temperatures increase, thus drying the
Nowotarski, Christopher J.
Nearly all previous numerical simulations of supercell thunderstorms have neglected surface uxes of heat, moisture, and momentum as well as horizontal inhomogeneities in the near-storm environment from resulting dry boundary layer convection. This investigation uses coupled radiation and land-surface schemes within an idealized cloud model to identify the effects of organized boundary layer convection in the form of horizontal convective rolls (HCRs) on the strength, structure, and evolution of simulated supercell thunderstorms. The in uence of HCRs and the importance of their orientation relative to storm motion is tested by comparing simulations with a convective boundary layer (CBL) against those with a horizontally homogeneous base state having the same mean environment. The impact of anvil shading on the CBL is tested by comparing simulations with and without the effects of clouds in the radiative transfer scheme. The results of these simulations indicate that HCRs provide a potentially important source of environmental vertical vorticity in the sheared, near-storm boundary layer. These vorticity perturbations are amplified both beneath the main supercell updraft and along the trailing out ow boundary, leading to the formation of occasionally intense misovortices. HCRs perpendicular to storm motion are found to have a detrimental effect on the strength and persistence of the lowlevel mesocyclone, particularly during its initial development. Though the mean environment is less supportive of low-level rotation with a wind profile conducive to HCRs oriented parallel to storm motion, such HCRs are found to often enhance the low-level mesocyclone circulation. When anvil shading is included, stabilization results in generally weaker low-level mesocyclone circulation, regardless of HCR orientation. Moreover, HCRs diminish in the near-storm environment such that the effects of HCRs on the supercell are mitigated. HCRs are also shown to be a necessary condition for the
Sensitivity of Tropical Cyclones to Parameterized Convection in the NASA GEOS5 Model
Lim, Young-Kwon; Schubert, Siegfried D.; Reale, Oreste; Lee, Myong-In; Molod, Andrea M.; Suarez, Max J.
2014-01-01
The sensitivity of tropical cyclones (TCs) to changes in parameterized convection is investigated to improve the simulation of TCs in the North Atlantic. Specifically, the impact of reducing the influence of the Relaxed Arakawa-Schubert (RAS) scheme-based parameterized convection is explored using the Goddard Earth Observing System version5 (GEOS5) model at 0.25 horizontal resolution. The years 2005 and 2006 characterized by very active and inactive hurricane seasons, respectively, are selected for simulation. A reduction in parameterized deep convection results in an increase in TC activity (e.g., TC number and longer life cycle) to more realistic levels compared to the baseline control configuration. The vertical and horizontal structure of the strongest simulated hurricane shows the maximum lower-level (850-950hPa) wind speed greater than 60 ms and the minimum sea level pressure reaching 940mb, corresponding to a category 4 hurricane - a category never achieved by the control configuration. The radius of the maximum wind of 50km, the location of the warm core exceeding 10 C, and the horizontal compactness of the hurricane center are all quite realistic without any negatively affecting the atmospheric mean state. This study reveals that an increase in the threshold of minimum entrainment suppresses parameterized deep convection by entraining more dry air into the typical plume. This leads to cooling and drying at the mid- to upper-troposphere, along with the positive latent heat flux and moistening in the lower-troposphere. The resulting increase in conditional instability provides an environment that is more conducive to TC vortex development and upward moisture flux convergence by dynamically resolved moist convection, thereby increasing TC activity.
A test of sensitivity to convective transport in a global atmospheric CO{sub 2} simulation
Energy Technology Data Exchange (ETDEWEB)
Bian, H. [NASA Goddard Space Flight Center, Greenbelt, MD (United States). UMBC Goddard Earth Science and Technology Center; Kawa, S.R.; Chin, M.; Pawson, S.; Zhu, Z. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Rasch, P. [National Center for Atmospheric Research, Boulder, CO (United States); Wu, S. [Harvard Univ., Cambridge, MA (United States)
2006-11-15
Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO{sub 2} distributions. Global CO{sub 2} in the year 2000 is simulated using the CTM driven by assimilated meteorological fields from the NASA's Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO{sub 2} by adopting the same CO{sub 2} emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection.Replacing Conv1 by Conv2 results in an overestimate of CO{sub 2} over biospheric sink regions. The largest discrepancies result in a CO{sub 2} difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO{sub 2} seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO{sub 2} sink. It is shown that the overestimated CO{sub 2} driven by Conv2 can be offset by introducing these supplemental emissions.
Evaluation of a Mesoscale Convective System in Variable-Resolution CESM
Payne, A. E.; Jablonowski, C.
2017-12-01
Warm season precipitation over the Southern Great Plains (SGP) follows a well observed diurnal pattern of variability, peaking at night-time, due to the eastward propagation of mesoscale convection systems that develop over the eastern slopes of the Rockies in the late afternoon. While most climate models are unable to adequately capture the organization of convection and characteristic pattern of precipitation over this region, models with high enough resolution to explicitly resolve convection show improvement. However, high resolution simulations are computationally expensive and, in the case of regional climate models, are subject to boundary conditions. Newly developed variable resolution global climate models strike a balance between the benefits of high-resolution regional climate models and the large-scale dynamics of global climate models and low computational cost. Recently developed parameterizations that are insensitive to the model grid scale provide a way to improve model performance. Here, we present an evaluation of the newly available Cloud Layers Unified by Binormals (CLUBB) parameterization scheme in a suite of variable-resolution CESM simulations with resolutions ranging from 110 km to 7 km within a regionally refined region centered over the SGP Atmospheric Radiation Measurement (ARM) site. Simulations utilize the hindcast approach developed by the Department of Energy's Cloud-Associated Parameterizations Testbed (CAPT) for the assessment of climate models. We limit our evaluation to a single mesoscale convective system that passed over the region on May 24, 2008. The effects of grid-resolution on the timing and intensity of precipitation, as well as, on the transition from shallow to deep convection are assessed against ground-based observations from the SGP ARM site, satellite observations and ERA-Interim reanalysis.
Final results of the CONDORS convective diffusion experiment
Briggs, Gary A.
1993-01-01
The Convective Diffusion Observed by Remote Sensors (CONDORS) field experiment conducted at the Boulder Atmospheric Observatory used innovative techniques to obtain three-dimensional mappings of plume concentration fields, χ/ Q, of oil fog detected by lidar and “chaff” detected by Doppler radar. It included extensive meteorological measurements and, in 1983, tracer gases measured at a single sampling arc. Final results from ten hours of elevated and surface release data are summarized here. Many intercomparisons were made. Oil fog χ/ Q measured 40m above the arc are mostly in good agreement with SF 6 values, except in a few instances with large spacial inhomogeneities over short distances. After a correction scheme was applied to compensate for the effect of its settling speed, chaff ∫χ dy/Q agreed well with those of oil except in two cases of oil fog “hot spots”. Mass or frequency distribution vs. azimuth or elevation angle comparisons were made for chaff, oil, and wind, with mostly good agreements. Spacial standard deviations, σy and σz, of chaff and oil agree overall and are consistent at short range with velocity standard deviations σvand σw ≈ 0.6w* (the convective scale velocity), as measured at z>100m. Surface release σy is enhanced up to 60% at small x, consistent with the Prairie Grass measurements and with larger σv and reduced wind speed measured near the surface. Decreased σy at small dimensionless average times is also noted. Finally, convectively scaled ∫χ dy, C y, were plotted versus dimensionless x and z for oil, chaff, and corrected chaff for each 30 60 min period. Aggregated CONDORS C y fields compare well with laboratory tank and LES numerical simulations; surface-released oil fog compares expecially well with the tank experiments. However, large deviations from the norm occurred in individual averaging periods; these deviations correlated strongly with anomalies in measured ω distributions.
Spectral scheme for spacetime physics
International Nuclear Information System (INIS)
Seriu, Masafumi
2002-01-01
Based on the spectral representation of spatial geometry, we construct an analysis scheme for spacetime physics and cosmology, which enables us to compare two or more universes with each other. In this scheme the spectral distance plays a central role, which is the measure of closeness between two geometries defined in terms of the spectra. We apply this scheme for analyzing the averaging problem in cosmology; we explicitly investigate the time evolution of the spectra, distance between two nearby spatial geometries, simulating the relation between the real Universe and its model. We then formulate the criteria for a model to be a suitable one
Coordinated renewable energy support schemes
DEFF Research Database (Denmark)
Morthorst, P.E.; Jensen, S.G.
2006-01-01
This paper illustrates the effect that can be observed when support schemes for renewable energy are regionalised. Two theoretical examples are used to explain interactive effects on, e.g., the price of power, conditions for conventional power producers, and changes in import and export of power...... RES-E support schemes already has a common liberalised power market. In this case the introduction of a common support scheme for renewable technologies will lead to more efficient sitings of renewable plants, improving economic and environmental performance of the total power system...
Might electrical earthing affect convection of light
International Nuclear Information System (INIS)
Budrikis, Z.L.
1982-01-01
Partial convection of light by moving media was predicted by Fresnel and verified by Fizeau, Zeeman and others. It is accepted as an important argument in favour of the Special Theory of Relativity. The suggestion is made here that the convection is partial only when the propagating medium is moved with respect to its electrically earthed surroundings and that it would be total if an earthed shield was co-moving with the medium. This is based on a reinterpretation of Maxwell's equations wherein they are seen as macroscopic relationships that are in each case valid only in respect of a particular inertial frame of reference, the local electrical earth frame. (Auth.)
The driving force for magnetospheric convection
Johnson, F. S.
1978-01-01
Viscously driven magnetospheric models, as well as a model involving interconnection between the geomagnetic field and the magnetic field in the solar wind, have been proposed to describe the driving force for magnetospheric convection. Lack of a satisfactory theory for the interconnection in the latter model and, in the case of the viscous interaction models, inadequacies in predicting the quantity of the driving force, make these two classes of models less than successful. Accordingly, a mechanically driven magnetospheric model is proposed: solar wind plasma enters the magnetosphere around the neutral points, covers the inner surface of the magnetopause and subsequently expands, driving convection as it escapes from the open tail.
Basic theory behind parameterizing atmospheric convection
Plant, R. S.; Fuchs, Z.; Yano, J. I.
2014-01-01
Last fall, a network of the European Cooperation in Science and Technology (COST), called “Basic Concepts for Convection Parameterization in Weather Forecast and Climate Models” (COST Action ES0905; see http://w3.cost.esf.org/index.php?id=205&action_number=ES0905), organized a 10-day training course on atmospheric convection and its parameterization. The aim of the workshop, held on the island of Brac, Croatia, was to help young scientists develop an in-depth understanding of the core theory ...
Topology Optimisation for Coupled Convection Problems
DEFF Research Database (Denmark)
Alexandersen, Joe; Andreasen, Casper Schousboe; Aage, Niels
stabilised finite elements implemented in a parallel multiphysics analysis and optimisation framework DFEM [1], developed and maintained in house. Focus is put on control of the temperature field within the solid structure and the problems can therefore be seen as conjugate heat transfer problems, where heat...... conduction governs in the solid parts of the design domain and couples to convection-dominated heat transfer to a surrounding fluid. Both loosely coupled and tightly coupled problems are considered. The loosely coupled problems are convection-diffusion problems, based on an advective velocity field from...
Relaxation schemes for Chebyshev spectral multigrid methods
Kang, Yimin; Fulton, Scott R.
1993-01-01
Two relaxation schemes for Chebyshev spectral multigrid methods are presented for elliptic equations with Dirichlet boundary conditions. The first scheme is a pointwise-preconditioned Richardson relaxation scheme and the second is a line relaxation scheme. The line relaxation scheme provides an efficient and relatively simple approach for solving two-dimensional spectral equations. Numerical examples and comparisons with other methods are given.
Good governance for pension schemes
Thornton, Paul
2011-01-01
Regulatory and market developments have transformed the way in which UK private sector pension schemes operate. This has increased demands on trustees and advisors and the trusteeship governance model must evolve in order to remain fit for purpose. This volume brings together leading practitioners to provide an overview of what today constitutes good governance for pension schemes, from both a legal and a practical perspective. It provides the reader with an appreciation of the distinctive characteristics of UK occupational pension schemes, how they sit within the capital markets and their social and fiduciary responsibilities. Providing a holistic analysis of pension risk, both from the trustee and the corporate perspective, the essays cover the crucial role of the employer covenant, financing and investment risk, developments in longevity risk hedging and insurance de-risking, and best practice scheme administration.
A Novel Iris Segmentation Scheme
Directory of Open Access Journals (Sweden)
Chen-Chung Liu
2014-01-01
Full Text Available One of the key steps in the iris recognition system is the accurate iris segmentation from its surrounding noises including pupil, sclera, eyelashes, and eyebrows of a captured eye-image. This paper presents a novel iris segmentation scheme which utilizes the orientation matching transform to outline the outer and inner iris boundaries initially. It then employs Delogne-Kåsa circle fitting (instead of the traditional Hough transform to further eliminate the outlier points to extract a more precise iris area from an eye-image. In the extracted iris region, the proposed scheme further utilizes the differences in the intensity and positional characteristics of the iris, eyelid, and eyelashes to detect and delete these noises. The scheme is then applied on iris image database, UBIRIS.v1. The experimental results show that the presented scheme provides a more effective and efficient iris segmentation than other conventional methods.
High Ra, high Pr convection with viscosity gradients
Indian Academy of Sciences (India)
First page Back Continue Last page Overview Graphics. High Ra, high Pr convection with viscosity gradients. Weak upward flow through mesh. Top fluid more viscous. Unstable layer Instability Convection.
Breeding schemes in reindeer husbandry
Directory of Open Access Journals (Sweden)
Lars Rönnegård
2003-04-01
Full Text Available The objective of the paper was to investigate annual genetic gain from selection (G, and the influence of selection on the inbreeding effective population size (Ne, for different possible breeding schemes within a reindeer herding district. The breeding schemes were analysed for different proportions of the population within a herding district included in the selection programme. Two different breeding schemes were analysed: an open nucleus scheme where males mix and mate between owner flocks, and a closed nucleus scheme where the males in non-selected owner flocks are culled to maximise G in the whole population. The theory of expected long-term genetic contributions was used and maternal effects were included in the analyses. Realistic parameter values were used for the population, modelled with 5000 reindeer in the population and a sex ratio of 14 adult females per male. The standard deviation of calf weights was 4.1 kg. Four different situations were explored and the results showed: 1. When the population was randomly culled, Ne equalled 2400. 2. When the whole population was selected on calf weights, Ne equalled 1700 and the total annual genetic gain (direct + maternal in calf weight was 0.42 kg. 3. For the open nucleus scheme, G increased monotonically from 0 to 0.42 kg as the proportion of the population included in the selection programme increased from 0 to 1.0, and Ne decreased correspondingly from 2400 to 1700. 4. In the closed nucleus scheme the lowest value of Ne was 1300. For a given proportion of the population included in the selection programme, the difference in G between a closed nucleus scheme and an open one was up to 0.13 kg. We conclude that for mass selection based on calf weights in herding districts with 2000 animals or more, there are no risks of inbreeding effects caused by selection.
Small-scale classification schemes
DEFF Research Database (Denmark)
Hertzum, Morten
2004-01-01
. While coordination mechanisms focus on how classification schemes enable cooperation among people pursuing a common goal, boundary objects embrace the implicit consequences of classification schemes in situations involving conflicting goals. Moreover, the requirements specification focused on functional...... requirements and provided little information about why these requirements were considered relevant. This stands in contrast to the discussions at the project meetings where the software engineers made frequent use of both abstract goal descriptions and concrete examples to make sense of the requirements...
Energy Technology Data Exchange (ETDEWEB)
Fan, Jiwen [Pacific Northwest National Laboratory, Richland Washington USA; Han, Bin [Pacific Northwest National Laboratory, Richland Washington USA; School of Atmospheric Sciences, Nanjing University, Nanjing China; Varble, Adam [Department of Atmospheric Sciences, University of Utah, Salt Lake City Utah USA; Morrison, Hugh [National Center for Atmospheric Research, Boulder Colorado USA; North, Kirk [Department of Atmospheric and Oceanic Sciences, McGill University, Montreal Quebec USA; Kollias, Pavlos [Department of Atmospheric and Oceanic Sciences, McGill University, Montreal Quebec USA; School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook New York USA; Chen, Baojun [School of Atmospheric Sciences, Nanjing University, Nanjing China; Dong, Xiquan [Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson Arizona USA; Giangrande, Scott E. [Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton New York USA; Khain, Alexander [The Institute of the Earth Science, The Hebrew University of Jerusalem, Jerusalem Israel; Lin, Yun [Department of Atmospheric Sciences, Texas A& M University, College Station Texas USA; Mansell, Edward [NOAA/OAR/National Severe Storms Laboratory, Norman Oklahoma USA; Milbrandt, Jason A. [Meteorological Research Division, Environment and Climate Change Canada, Dorval Canada; Stenz, Ronald [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Thompson, Gregory [National Center for Atmospheric Research, Boulder Colorado USA; Wang, Yuan [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena California USA
2017-09-06
A constrained model intercomparison study of a mid-latitude mesoscale squall line is performed using the Weather Research & Forecasting (WRF) model at 1-km horizontal grid spacing with eight cloud microphysics schemes, to understand specific processes that lead to the large spread of simulated cloud and precipitation at cloud-resolving scales, with a focus of this paper on convective cores. Various observational data are employed to evaluate the baseline simulations. All simulations tend to produce a wider convective area than observed, but a much narrower stratiform area, with most bulk schemes overpredicting radar reflectivity. The magnitudes of the virtual potential temperature drop, pressure rise, and the peak wind speed associated with the passage of the gust front are significantly smaller compared with the observations, suggesting simulated cool pools are weaker. Simulations also overestimate the vertical velocity and Ze in convective cores as compared with observational retrievals. The modeled updraft velocity and precipitation have a significant spread across the eight schemes even in this strongly dynamically-driven system. The spread of updraft velocity is attributed to the combined effects of the low-level perturbation pressure gradient determined by cold pool intensity and buoyancy that is not necessarily well correlated to differences in latent heating among the simulations. Variability of updraft velocity between schemes is also related to differences in ice-related parameterizations, whereas precipitation variability increases in no-ice simulations because of scheme differences in collision-coalescence parameterizations.
McCaul, Eugene W., Jr.; Case, Jonathan L.; Zavodsky, Bradley; Srikishen, Jayanthi; Medlin, Jeffrey; Wood, Lance
2014-01-01
Convection-allowing numerical weather simula- tions have often been shown to produce convective storms that have significant sensitivity to choices of model physical parameterizations. Among the most important of these sensitivities are those related to cloud microphysics, but planetary boundary layer parameterizations also have a significant impact on the evolution of the convection. Aspects of the simulated convection that display sensitivity to these physics schemes include updraft size and intensity, simulated radar reflectivity, timing and placement of storm initi- ation and decay, total storm rainfall, and other storm features derived from storm structure and hydrometeor fields, such as predicted lightning flash rates. In addition to the basic parameters listed above, the simulated storms may also exhibit sensitivity to im- posed initial conditions, such as the fields of soil temper- ature and moisture, vegetation cover and health, and sea and lake water surface temperatures. Some of these sensitivities may rival those of the basic physics sensi- tivities mentioned earlier. These sensitivities have the potential to disrupt the accuracy of short-term forecast simulations of convective storms, and thereby pose sig- nificant difficulties for weather forecasters. To make a systematic study of the quantitative impacts of each of these sensitivities, a matrix of simulations has been performed using all combinations of eight separate microphysics schemes, three boundary layer schemes, and two sets of initial conditions. The first version of initial conditions consists of the default data from large-scale operational model fields, while the second features specialized higher- resolution soil conditions, vegetation conditions and water surface temperatures derived from datasets created at NASA's Short-term Prediction and Operational Research Tran- sition (SPoRT) Center at the National Space Science and Technology Center (NSSTC) in Huntsville, AL. Simulations as
Modeling Diffusion and Buoyancy-Driven Convection with Application to Geological CO2 Storage
Allen, Rebecca
2015-04-01
CO2 storage modeling. Our model contains the multiple- relaxation-time scheme and moment-based boundary conditions to avoid the numer- ical slip error that is associated with standard bounce-back. The model’s accuracy and robustness is demonstrated by an excellent agreement between our results and benchmark data for thermal flows ranging from Ra = 103 to 108. Our thermal model captures analogous flow behavior to that of CO2 through fluid-filled porous media, including the transition from diffusive transport to initiation and development of convective fingering.
Thermal convection driven by acoustic field under microgravity
Tanabe, Mitsuaki; 田辺 光昭
2007-01-01
Natural convection is suppressed in space environment due to the weightlessness. Only centrifugal force is utilized currently to drive gas-phase thermal convection in space. This paper presents an alternative way to drive thermal convection. From the investigation of combustion oscillation in rocket motors, a new thermal convection had been found in stationary acoustic fields. Analyzing the phenomena, acoustic radiation force is found to be the candidate driving force. With a simplified syste...
Prédiction des structures convectives terrestres
Bello , Léa
2015-01-01
Since its formation, the Earth is slowly cooling. The heat produced by the core and the radioactive decay in the mantle is evacuated toward the surface by convection. The evolving convective structures thereby created control a diversity of surface phenomena such as vertical motion of continents or sea level variation. The study presented here attempts to determine which convective structures can be predicted, to what extent and over what timescale. Because of the chaotic nature of convection...
Natural convection flow between moving boundaries | Chepkwony ...
African Journals Online (AJOL)
The laminar steady natural convection flow of viscous, incompressible fluid between two moving vertical plates is considered. It is assumed that the plates are moving in opposite direction with equal velocity. The two-point boundary value problem governing the flow is characterized by a non-dimensional parameter K. It is ...
Oscillatory Convection in Rotating Liquid Metals
Bertin, Vincent; Grannan, Alex; Aurnou, Jonathan
2016-11-01
We have performed laboratory experiments in a aspect ratio Γ = 2 cylinder using liquid gallium (Pr = 0 . 023) as the working fluid. The Ekman number varies from E = 4 ×10-5 to 4 ×10-6 and the Rayleigh number varies from Ra = 3 ×105 to 2 ×107 . Using heat transfer and temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes develop, coexisting with the inertial oscillatory modes in the bulk. When the strength of the buoyancy increases further, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr = 1 planetary and stellar dynamo models, but in the form of oscillatory motions. Therefore, convection driven dynamo action in low Pr fluids can differ substantively than that occurring in typical Pr = 1 numerical models. Our results also suggest that low wavenumber, wall modes may be dynamically and observationally important in liquid metal dynamo systems. We thank the NSF Geophysics Program for support of this project.
An Observational Investigation of Penetrative Convection
DEFF Research Database (Denmark)
Jensen, Niels Otto; Lenschow, D. H.
1978-01-01
Data taken during the Air Mass Transformation Experiment (AMTEX) by the NCAR Electra aircraft have proven useful for investigating the structure of thermals penetrating into the turbulent inversion layer which caps the convective mixed layer. Variances, covariances, spectra and cospectra of poten...
Salinity transfer in bounded double diffusive convection
Yang, Yantao; van der Poel, Erwin; Ostilla Monico, Rodolfo; Sun, Chao; Verzicco, Roberto; Grossmann, Siegfried; Lohse, Detlef
2015-01-01
The double diffusive convection between two parallel plates is numerically studied for a series of parameters. The flow is driven by the salinity difference and stabilised by the thermal field. Our simulations are directly compared with experiments by Hage & Tilgner (Phys. Fluids, vol. 22, 2010,
Mixed convection in a baffled grooved channel
Indian Academy of Sciences (India)
A remarkable enhancement of heat transfer is observed in presence of baffle. The study has also pointed out that for optimal performance, the position and height of the baffle need to be adjusted depending on the direction of external flow. Keywords. Heat transfer; grooved channel; mixed convection; Richardson number;.
Radiative-convective equilibrium model intercomparison project
Wing, Allison A.; Reed, Kevin A.; Satoh, Masaki; Stevens, Bjorn; Bony, Sandrine; Ohno, Tomoki
2018-03-01
RCEMIP, an intercomparison of multiple types of models configured in radiative-convective equilibrium (RCE), is proposed. RCE is an idealization of the climate system in which there is a balance between radiative cooling of the atmosphere and heating by convection. The scientific objectives of RCEMIP are three-fold. First, clouds and climate sensitivity will be investigated in the RCE setting. This includes determining how cloud fraction changes with warming and the role of self-aggregation of convection in climate sensitivity. Second, RCEMIP will quantify the dependence of the degree of convective aggregation and tropical circulation regimes on temperature. Finally, by providing a common baseline, RCEMIP will allow the robustness of the RCE state across the spectrum of models to be assessed, which is essential for interpreting the results found regarding clouds, climate sensitivity, and aggregation, and more generally, determining which features of tropical climate a RCE framework is useful for. A novel aspect and major advantage of RCEMIP is the accessibility of the RCE framework to a variety of models, including cloud-resolving models, general circulation models, global cloud-resolving models, single-column models, and large-eddy simulation models.
Free convection film flows and heat transfer
Shang, Deyi
2010-01-01
Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.
MARANGONI CONVECTION IN V-SHAPED CONTAINERS
HOOGSTRATEN, HW; HOEFSLOOT, HCJ; JANSSEN, LPBM
This paper presents a numerical study of the time evolution of Marangoni convection in two V-shaped containers involved in the microgravity experiments reported in Hoefsloot et al.[7]. First the case of the triangular container with a plane gas/liquid interface is considered, next the container
Terminal project heat convection in thin cylinders
International Nuclear Information System (INIS)
Morales Corona, J.
1992-01-01
Heat convection in thin cylinders and analysis about natural convection for straight vertical plates, and straight vertical cylinders submersed in a fluid are presented some works carry out by different authors in the field of heat transfer. In the part of conduction, deduction of the equation of heat conduction in cylindrical coordinates by means of energy balance in a control volume is presented. Enthalpy and internal energy are used for the outlining of the equation and finally the equation in its vectorial form is obtained. In the convection part development to calculate the Nusselt number for a straight vertical plate by a forces analysis, an energy balance and mass conservation over a control volume is outlined. Several empiric correlations to calculate the Nusselt number and its relations with other dimensionless numbers are presented. In the experimental part the way in which a prototype rode is assembled is presented measurements of temperatures attained in steady state and in free convection for working fluids as air and water are showed in tables. Also graphs of Nusselt numbers obtained in the experimental way through some empiric correlations are showed (Author)
Turbulent Convection and Pulsation Stability of Stars
Xiong, Da-run
2017-10-01
The controversies about the excitation mechanism for low-temperature variables are reviewed: (1) Most people believe that γ Doradus variables are excited by the so-called convective blocking mechanism. Our researches show that the excitation of γ Doradus has no substantial difference from that of δ Scuti. They are two subgroups of a broader type of δ Stuti-γ Doradus stars: δ Scuti is the p-mode subgroup, while γ Doradus is the g-mode subgroup. (2) Most people believe that the solar and stellar solar-like oscillations are damped by convection, and they are driven by the so-called turbulent random excitation mechanism. Our researches show that convection is not solely a damping mechanism for stellar oscillations, otherwise it is unable to explain the Mira and Mira-like variables. By using our non-local and time-dependent theory of convection, we can reproduce not only the pulsationally unstable strip of δ Scuti and γ Doradus variables, but also the solar-like oscillation features of low-luminosity red giants and the Mira-like oscillation features of high-luminosity red giants.
Theories for convection in stellar atmospheres
International Nuclear Information System (INIS)
Nordlund, Aa.
1976-02-01
A discussion of the fundamental differences between laboratory convection in a stellar atmosphere is presented. The shortcomings of laterally homogeneous model atmospheres are analysed, and the extent to which these shortcoming are avoided in the two-component representation is discussed. Finally a qualitative discussion on the scaling properties of stellar granulation is presented. (Auth.)
Natural convection in horizontal fluid layers
International Nuclear Information System (INIS)
Suo-Antilla, A.J.
1977-02-01
The experimental work includes developing and using a thermal convection cell to obtain measurements of the heat flux and turbulent core temperature of a horizontal layer of fluid heated internally and subject to both stabilizing and destabilizing temperature differences. The ranges of Rayleigh numbers tested were 10 7 equal to or less than R/sub I/ equal to or less than 10 13 and -10 10 equal to or less than R/sub E/ equal to or less than 10 10 . Power integral methods were found to be adequate for interpolating and extrapolating the data. The theoretical work consists of the derivation, solution and use of the mean field equations for study of thermally driven convection in horizontal layers of infinite extent. The equations were derived by a separation of variables technique where the horizontal directions were described by periodic structures and the vertical being some function of z. The derivation resulted in a coupled set of momentum and energy equations. The equations were simplified by using the infinite Prandtl number limit and neglecting direct intermodal interaction. Solutions to these equations are used to predict the existence of multi-wavenumber flows at all supercritical Rayleigh numbers. Subsequent inspection of existing experimental photographs of convecting fluids confirms their existence. The onset of time dependence is found to coincide with the onset of the second convective mode. Each mode is found to consist of two wavenumbers and typically the velocity and temperature fields of the right modal branch are found to be out of phase
Vortex convection in nonuniform compressible flow
Szumowski, A. P.; Meier, G. E. A.
1988-03-01
Vortex convection in longitudinally nonuniform transonic flow fields was studied. Vortices moving in moderately accelerated flow are distinct in the subsonic and supersonic range. Due to the acceleration, the vortices of the Karman street separate continuously one from another. They form a series of periodically shedding individual vortices. The density distribution of the accelerated vortices stays circular. Vortices in subsonic stream (behind the shock wave in the divergent part of the Laval nozzle) impinging on an obstacle (in this case on the regulating valve) cause shock fronts which move upstream. In a subsonic stream flowing out from the convergent nozzle, the primary vortices inside the stream significantly perturb its boundaries and induce secondary vortices (at the boundaries). Flow patterns in a duct with a sudden enlargement of cross section are influenced by the vortices convected in the flow too. However, the observed perturbations of these patterns are relatively weak. The unsteady behaviour of the free stream is not only the effect of the vortex convection but also of the unsteady interactions with the boundaries, i.e., the adjusting valve and the test-section walls. However, the effect of the vortex convection is the stronger.
Presentation on Tropical Mesoscale convective Systems and ...
Indian Academy of Sciences (India)
IAS Admin
Microphysics of deep convection. Fountain. (Water Vapor). Intrusion. (Ozone). Circulation. Mass and Energy. Budget. Thermal, Radiation and. Chemistry. Hydrological Cycle. Global ... 厂 Represented as time of overpass. 厂 Shallow: Short lived ... NEW Definition of WET & DRY Spell Introduced. Wind Shear. Temperature ...
Crystal-Growing Crucible To Suppress Convection
Richter, R.
1986-01-01
Platform under growth region stabilizes melt for more uniform crystal growth. In new crucible, platform just below growth interface so melt is too shallow to support convection. Critical depth for onset of pertinent instability calculated from heat flux through surface of melt, volume coefficient of thermal expansion, thermal conductivity, thermal diffusivity, and kinematic viscosity.
Natural convection inside an irregular porous cavity
International Nuclear Information System (INIS)
Beltran, Jorge I. LLagostera; Trevisan, Osvair Vidal
1990-01-01
Natural convection flow induced by heating from below in a irregular porous cavity is investigated numerically. The influence of the modified Rayleigh number and geometric ratios on heat transfer and fluid flow is studied. Global and local Nusselt for Rayleigh numbers covering the range 0 - 1600 and for several geometric ratios. The fluid flow and the temperature field are illustrated by contour maps. (author)
Determination of the convective heat transfer coefficient
Spierings, D.; Bosman, F.; Peters, T.; Plasschaert, F.
The value of the convective heat transfer coefficient (htc) is determined under different loading conditions by using a computer aided method. The thermal load has been applied mathematically as well as experimentally to the coronal surface of an axisymmetric tooth model. To verify the assumptions
Energy Technology Data Exchange (ETDEWEB)
Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Siddiq, M.K. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Abbasi, F.M. [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Meraj, M.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Ashraf, M. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan)
2016-10-15
The present work deals with the steady laminar three-dimensional mixed convective magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluid over a bidirectional stretching surface. A uniform magnetic field is applied normal to the flow direction. Similarity variables are implemented to convert the non-linear partial differential equations into ordinary ones. Convective boundary conditions are utilized at surface of the sheet. A numerical technique of Runge–Kutta–Fehlberg (RFK45) is used to obtain the results of velocity, temperature and concentration fields. The physical dimensionless parameters are discussed through tables and graphs. - Highlights: • Mixed convective boundary layer flow of Casson nanofluid is taken into account. • Impact of magnetic field is examined. • Convective heat and mass conditions are imposed. • Numerical solutions are presented and discussed.
Testing particle filters on convective scale dynamics
Haslehner, Mylene; Craig, George. C.; Janjic, Tijana
2014-05-01
Particle filters have been developed in recent years to deal with highly nonlinear dynamics and non Gaussian error statistics that also characterize data assimilation on convective scales. In this work we explore the use of the efficient particle filter (P.v. Leeuwen, 2011) for convective scale data assimilation application. The method is tested in idealized setting, on two stochastic models. The models were designed to reproduce some of the properties of convection, for example the rapid development and decay of convective clouds. The first model is a simple one-dimensional, discrete state birth-death model of clouds (Craig and Würsch, 2012). For this model, the efficient particle filter that includes nudging the variables shows significant improvement compared to Ensemble Kalman Filter and Sequential Importance Resampling (SIR) particle filter. The success of the combination of nudging and resampling, measured as RMS error with respect to the 'true state', is proportional to the nudging intensity. Significantly, even a very weak nudging intensity brings notable improvement over SIR. The second model is a modified version of a stochastic shallow water model (Würsch and Craig 2013), which contains more realistic dynamical characteristics of convective scale phenomena. Using the efficient particle filter and different combination of observations of the three field variables (wind, water 'height' and rain) allows the particle filter to be evaluated in comparison to a regime where only nudging is used. Sensitivity to the properties of the model error covariance is also considered. Finally, criteria are identified under which the efficient particle filter outperforms nudging alone. References: Craig, G. C. and M. Würsch, 2012: The impact of localization and observation averaging for convective-scale data assimilation in a simple stochastic model. Q. J. R. Meteorol. Soc.,139, 515-523. Van Leeuwen, P. J., 2011: Efficient non-linear data assimilation in geophysical
International symposium on transient convective heat transfer: book of abstracts
International Nuclear Information System (INIS)
1996-01-01
The international symposium on convective heat transfer was held on 19-23 August 1996, in Cesme, Izmir, Turkey. The spesialists discussed forced convection, heat exchangers, free convection and multiphase media and phase change at the meeting. Almost 53 papers were presented in the meeting
Probing the transition from shallow to deep convection
Energy Technology Data Exchange (ETDEWEB)
Kuang, Zhiming [Harvard Univ., Cambridge, MA (United States); Gentine, Pierre [Columbia Univ., New York, NY (United States)
2016-05-01
In this funded project we highlighted the components necessary for the transition from shallow to deep convection. In particular we defined a prototype of shallow to deep convection, which is currently being implemented in the NASA GISS model. We also tried to highlight differences between land and oceanic convection.
Physical balances in subseafloor hydrothermal convection cells
Jupp, Tim E.; Schultz, Adam
2004-05-01
We use a simplified model of convection in a porous medium to investigate the balances of mass and energy within a subseafloor hydrothermal convection cell. These balances control the steady state structure of the system and allow scalings for the height, permeability, and residence time of the "reaction zone" at the base of the cell to be calculated. The scalings are presented as functions of (1) the temperature TD of the heat source driving the convection and (2) the total power output ΦU. The model is then used to illustrate how the nonlinear thermodynamic properties of water may impose the observed upper limit of ˜400°C on vent temperatures. The properties of water at hydrothermal conditions are contrasted with those of a hypothetical "Boussinesq fluid" for which temperature variations in fluid properties are either linearized or ignored. At hydrothermal pressures, water transports a maximum amount of energy by buoyancy-driven advection at ˜400°C. This maximum is a consequence of the nonlinear thermodynamic properties of water and does not arise for a simple Boussinesq fluid. Inspired by the "Malkus hypothesis" and by recent work on dissipative systems, we speculate that convection cells in porous media attain a steady state in which the upwelling temperature TU maximizes the total power output of the cell. If true, this principle would explain our observation (in previous numerical simulations) that water in hydrothermal convection cells upwells at TU ˜ 400°C when driven by a heat source above ˜500°C.
Convective mass transfer around a dissolving bubble
Duplat, Jerome; Grandemange, Mathieu; Poulain, Cedric
2017-11-01
Heat or mass transfer around an evaporating drop or condensing vapor bubble is a complex issue due to the interplay between the substrate properties, diffusion- and convection-driven mass transfer, and Marangoni effects, to mention but a few. In order to disentangle these mechanisms, we focus here mainly on the convective mass transfer contribution in an isothermal mass transfer problem. For this, we study the case of a millimetric carbon dioxide bubble which is suspended under a substrate and dissolved into pure liquid water. The high solubility of CO2 in water makes the liquid denser and promotes a buoyant-driven flow at a high (solutal) Rayleigh number (Ra˜104 ). The alteration of p H allows the concentration field in the liquid to be imaged by laser fluorescence enabling us to measure both the global mass flux (bubble volume, contact angle) and local mass flux around the bubble along time. After a short period of mass diffusion, where the boundary layer thickens like the square root of time, convection starts and the CO2 is carried by a plume falling at constant velocity. The boundary layer thickness then reaches a plateau which depends on the bubble cross section. Meanwhile the plume velocity scales like (dV /d t )1 /2 with V being the volume of the bubble. As for the rate of volume loss, we recover a constant mass flux in the diffusion-driven regime followed by a decrease in the volume V like V2 /3 after convection has started. We present a model which agrees well with the bubble dynamics and discuss our results in the context of droplet evaporation, as well as high Rayleigh convection.
Energy Technology Data Exchange (ETDEWEB)
Hinojosa, J.F. [Universidad de Sonora, Departamento de Ingenieria Quimica y Metalurgia, Hermosillo, Sonora (Mexico); Cervantes-de Gortari, J. [Universidad Nacional Autonoma de Mexico, Departamento de Termofluidos, Facultad de Ingenieria, Mexico, D.F. (Mexico)
2010-06-15
In this work the numeric results, of the steady-state and transient heat transfer by natural convection in a horizontal isothermal open cubic cavity are presented. The most important assumptions in the mathematical formulation are two, the flow is laminar and the Boussinesq approximation is valid. The conservation equations in primitive variables are solved using the finite volume method and the SIMPLEC algorithm. The advective terms are approximated by the SMART scheme and the diffusive terms are approximated using the central differencing scheme. The results are obtained for a Rayleigh number range from 10{sup 4} to 10{sup 7}.The numerical model predicted flow instabilities and Nusselt number oscillations for high Rayleigh numbers. (orig.)
Two nonlinear control schemes contrasted on a hydrodynamiclike model
Keefe, Laurence R.
1993-01-01
The principles of two flow control strategies, those of Huebler (Luescher and Huebler, 1989) and of Ott et al. (1990) are discussed, and the two schemes are compared for their ability to control shear flow, using fully developed and transitional solutions of the Ginzburg-Landau equation as models for such flows. It was found that the effectiveness of both methods in obtaining control of fully developed flows depended strongly on the 'distance' in state space between the uncontrolled flow and goal dynamics. There were conceptual difficulties in applying the Ott et al. method to transitional convectively unstable flows. On the other hand, the Huebler method worked well, within certain limitations, although at a large cost in energy terms.
Computational scheme for transient temperature distribution in PWR vessel wall
International Nuclear Information System (INIS)
Dedovic, S.; Ristic, P.
1980-01-01
Computer code TEMPNES is a part of joint effort made in Gosa Industries in achieving the technique for structural analysis of heavy pressure vessels. Transient heat conduction problems analysis is based on finite element discretization of structures non-linear transient matrix formulation and time integration scheme as developed by Wilson (step-by-step procedure). Convection boundary conditions and the effect of heat generation due to radioactive radiation are both considered. The computation of transient temperature distributions in reactor vessel wall when the water temperature suddenly drops as a consequence of reactor cooling pump failure is presented. The vessel is treated as as axisymmetric body of revolution. The program has two finite time element options a) fixed predetermined increment and; b) an automatically optimized time increment for each step dependent on the rate of change of the nodal temperatures. (author)
Second-order accurate kinetic schemes for the ultra-relativistic Euler equations
International Nuclear Information System (INIS)
Kunik, Matthias; Qamar, Shamsul; Warnecke, Gerald
2003-01-01
A second-order accurate kinetic scheme for the numerical solution of the relativistic Euler equations is presented. These equations describe the flow of a perfect fluid in terms of the particle density n, the spatial part of the four-velocity u and the pressure p. The kinetic scheme, is based on the well-known fact that the relativistic Euler equations are the moments of the relativistic Boltzmann equation of the kinetic theory of gases when the distribution function is a relativistic Maxwellian. The kinetic scheme consists of two phases, the convection phase (free-flight) and collision phase. The velocity distribution function at the end of the free-flight is the solution of the collisionless transport equation. The collision phase instantaneously relaxes the distribution to the local Maxwellian distribution. The fluid dynamic variables of density, velocity, and internal energy are obtained as moments of the velocity distribution function at the end of the free-flight phase. The scheme presented here is an explicit method and unconditionally stable. The conservation laws of mass, momentum and energy as well as the entropy inequality are everywhere exactly satisfied by the solution of the kinetic scheme. The scheme also satisfies positivity and L 1 -stability. The scheme can be easily made into a total variation diminishing method for the distribution function through a suitable choice of the interpolation strategy. In the numerical case studies the results obtained from the first- and second-order kinetic schemes are compared with the first- and second-order upwind and central schemes. We also calculate the experimental order of convergence and numerical L 1 -stability of the scheme for smooth initial data
Multiuser switched diversity scheduling schemes
Shaqfeh, Mohammad
2012-09-01
Multiuser switched-diversity scheduling schemes were recently proposed in order to overcome the heavy feedback requirements of conventional opportunistic scheduling schemes by applying a threshold-based, distributed, and ordered scheduling mechanism. The main idea behind these schemes is that slight reduction in the prospected multiuser diversity gains is an acceptable trade-off for great savings in terms of required channel-state-information feedback messages. In this work, we characterize the achievable rate region of multiuser switched diversity systems and compare it with the rate region of full feedback multiuser diversity systems. We propose also a novel proportional fair multiuser switched-based scheduling scheme and we demonstrate that it can be optimized using a practical and distributed method to obtain the feedback thresholds. We finally demonstrate by numerical examples that switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the ultimate network capacity of full feedback systems in Rayleigh fading conditions. © 2012 IEEE.
Directory of Open Access Journals (Sweden)
W. A. Gallus Jr.
2008-04-01
Full Text Available Simulations of a squall line system which occurred on 12 August 2004 near Munich, Germany are performed using a fine grid version of the Weather Research and Forecasting (WRF model with five different microphysical schemes. Synthetic dual polarization observations are created from the model output and compared with detailed observations gathered by the DLR polarimetric radar POLDIRAD located near Munich. Synthetic polarimetric radar scans are derived from the model forecasts employing the polarimetric radar forward operator SynPolRad. Evaluations of the microphysical parameterization schemes are carried out comparing Plan Position Indicator (PPI and Range Height Indicator (RHI scans of reflectivity and the spatial distribution of hydrometeor types. The hydrometeor types are derived applying a hydrometeor classification scheme to the observed and simulated polarimetric radar quantities. Furthermore, the Ebert-McBride contiguous rain area method of verification is tested in a variety of ways on the reflectivity output from the simulations. It is found that all five schemes overestimate reflectivity in the domain, particularly in the stratiform region of the convective system. All four schemes including graupel as a hydrometeor type produce too much of it. Differences are seen among the schemes in their depiction of reflectivity in the convective line and their representation of radar bright bands.
Zhou, Bowen; Xue, Ming; Zhu, Kefeng
2017-04-01
Compared to the representation of vertical turbulent mixing through various PBL schemes, the treatment of horizontal turbulence mixing in the boundary layer within mesoscale models, with O(10) km horizontal grid spacing, has received much less attention. In mesoscale models, subgrid-scale horizontal fluxes most often adopt the gradient-diffusion assumption. The horizontal mixing coefficients are usually set to a constant, or through the 2D Smagorinsky formulation, or in some cases based on the 1.5-order turbulence kinetic energy (TKE) closure. In this work, horizontal turbulent mixing parameterizations using physically based characteristic velocity and length scales are proposed for the convective boundary layer based on analysis of a well-resolved, wide-domain large-eddy simulation (LES). The proposed schemes involve different levels of sophistication. The first two schemes can be used together with first-order PBL schemes, while the third uses TKE to define its characteristic velocity scale and can be used together with TKE-based higher-order PBL schemes. The current horizontal mixing formulations are also assessed a priori through the filtered LES results to illustrate their limitations. The proposed parameterizations are tested a posteriori in idealized simulations of turbulent dispersion of a passive scalar. Comparisons show improved horizontal dispersion by the proposed schemes, and further demonstrate the weakness of the current schemes.
Numerical simulation of double-diffusive finger convection
Hughes, J.D.; Sanford, W.E.; Vacher, H.L.
2005-01-01
A hybrid finite element, integrated finite difference numerical model is developed for the simulation of double-diffusive and multicomponent flow in two and three dimensions. The model is based on a multidimensional, density-dependent, saturated-unsaturated transport model (SUTRA), which uses one governing equation for fluid flow and another for solute transport. The solute-transport equation is applied sequentially to each simulated species. Density coupling of the flow and solute-transport equations is accounted for and handled using a sequential implicit Picard iterative scheme. High-resolution data from a double-diffusive Hele-Shaw experiment, initially in a density-stable configuration, is used to verify the numerical model. The temporal and spatial evolution of simulated double-diffusive convection is in good agreement with experimental results. Numerical results are very sensitive to discretization and correspond closest to experimental results when element sizes adequately define the spatial resolution of observed fingering. Numerical results also indicate that differences in the molecular diffusivity of sodium chloride and the dye used to visualize experimental sodium chloride concentrations are significant and cause inaccurate mapping of sodium chloride concentrations by the dye, especially at late times. As a result of reduced diffusion, simulated dye fingers are better defined than simulated sodium chloride fingers and exhibit more vertical mass transfer. Copyright 2005 by the American Geophysical Union.
Galerkin method for feedback controlled Rayleigh Bénard convection
Münch, A.; Wagner, B.
2008-11-01
The problem of feedback controlled Rayleigh-Bénard convection is considered. For this problem with the simple flow structure in the vertical direction, a Galerkin method that uses only a few basis functions in this direction is presented. This approximation yields considerable simplification of the problem, explicitly incorporates the non-classical boundary conditions at the horizontal boundaries of the fluid layer resulting from feedback control and reduces the dimension of the original problem by one. This method is in spirit very similar to lubrication theory, where the simple laminar flow in the vertical direction is integrated out across the height of the fluid layer. Using a minimal set of appropriate basis functions to capture the nonlinear behaviour of the flow, we investigate the effects of feedback control on amplitude, wavelength and selection of patterns via weakly nonlinear analysis and numerical simulations of the resulting dimension-reduced problems in two and three dimensions. In the second part of this study we discuss the derivation of the appropriate basis functions and prove convergence of the Galerkin scheme. This paper is published as part of a collection in honour of Todd Dupont's 65th birthday.
Explicit simulation of a midlatitude Mesoscale Convective System
Energy Technology Data Exchange (ETDEWEB)
Alexander, G.D.; Cotton, W.R. [Colorado State Univ., Fort Collins, CO (United States)
1996-04-01
We have explicitly simulated the mesoscale convective system (MCS) observed on 23-24 June 1985 during PRE-STORM, the Preliminary Regional Experiment for the Stormscale Operational and Research and Meterology Program. Stensrud and Maddox (1988), Johnson and Bartels (1992), and Bernstein and Johnson (1994) are among the researchers who have investigated various aspects of this MCS event. We have performed this MCS simulation (and a similar one of a tropical MCS; Alexander and Cotton 1994) in the spirit of the Global Energy and Water Cycle Experiment Cloud Systems Study (GCSS), in which cloud-resolving models are used to assist in the formulation and testing of cloud parameterization schemes for larger-scale models. In this paper, we describe (1) the nature of our 23-24 June MCS dimulation and (2) our efforts to date in using our explicit MCS simulations to assist in the development of a GCM parameterization for mesoscale flow branches. The paper is organized as follows. First, we discuss the synoptic situation surrounding the 23-24 June PRE-STORM MCS followed by a discussion of the model setup and results of our simulation. We then discuss the use of our MCS simulation. We then discuss the use of our MCS simulations in developing a GCM parameterization for mesoscale flow branches and summarize our results.
Using Jupiter's gravitational field to probe the Jovian convective dynamo.
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-03-23
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.
Gregarious convection and radiative feedbacks in idealized worlds
Mapes, B. E.
2016-06-01
What role does convection play in cloud feedbacks? What role does convective aggregation play in climate? A flurry of recent studies explores "self-aggregation" of moist convection in diverse simulations using explicit convection and interactive radiation. The implications involve upper level dry areas acting as infrared windows—the climate system's "radiator fins." A positive feedback maintains these: dry columns undergo radiative cooling which drives descent and further drying. If the resulting clumpiness of vapor and cloud fields depends systematically on global temperature, then convective organization could be a climate system feedback. How reconcilable and how relevant are these interesting but idealized studies?
Prein, Andreas F; Langhans, Wolfgang; Fosser, Giorgia; Ferrone, Andrew; Ban, Nikolina; Goergen, Klaus; Keller, Michael; Tölle, Merja; Gutjahr, Oliver; Feser, Frauke; Brisson, Erwan; Kollet, Stefan; Schmidli, Juerg; van Lipzig, Nicole P M; Leung, Ruby
2015-06-01
Regional climate modeling using convection-permitting models (CPMs; horizontal grid spacing climate information on regional to local scales compared to traditionally used large-scale models (LSMs; horizontal grid spacing >10 km). CPMs no longer rely on convection parameterization schemes, which had been identified as a major source of errors and uncertainties in LSMs. Moreover, CPMs allow for a more accurate representation of surface and orography fields. The drawback of CPMs is the high demand on computational resources. For this reason, first CPM climate simulations only appeared a decade ago. In this study, we aim to provide a common basis for CPM climate simulations by giving a holistic review of the topic. The most important components in CPMs such as physical parameterizations and dynamical formulations are discussed critically. An overview of weaknesses and an outlook on required future developments is provided. Most importantly, this review presents the consolidated outcome of studies that addressed the added value of CPM climate simulations compared to LSMs. Improvements are evident mostly for climate statistics related to deep convection, mountainous regions, or extreme events. The climate change signals of CPM simulations suggest an increase in flash floods, changes in hail storm characteristics, and reductions in the snowpack over mountains. In conclusion, CPMs are a very promising tool for future climate research. However, coordinated modeling programs are crucially needed to advance parameterizations of unresolved physics and to assess the full potential of CPMs.
Time evolution simulation of heat removal in a small water tank by natural convection
International Nuclear Information System (INIS)
Freitas, Carlos Alberto de; Jachic, Joao; Moreira, Maria de Lourdes
2013-01-01
One of the cooling modes for any source of heat such as in a shutdown nuclear core is the natural convection. The design specifications of any cooling pool can only be done when the removal heat rate and the corresponding mass flow rate is reasonably established. In our simulation scheme, we assumed that the body forces acting in the cubic water cell are: the weight, the drag force and the integrated pressure forces on the horizontal surfaces, the viscosity shear forces on the vertical surfaces and also a special viscosity drag force due to the mass dislocation along a Bernoulli type current tube outside the motive region. For a suitable time step, the uprising convection velocity is determined by an implicit and also by an explicit solution algorithm. The resulting differential equation depends on updating specific mass, dynamic viscosity and constant pressure heat coefficient with the last known temperature in the cell that absorbed heat. Numerical calculation software was performed using MATLAB’s technical computing language and then applied for a heat generation plate simulating a spent fuel assembler from a shutdown nuclear core. The results show time evolution of convection, terminal velocity and water temperature distribution. Pool dimension as well as pool level decrement are also determined for various air exhausting system conditions and heat rate of the spent fuel plate being cooled. (author)
Li, Chunggang; Tsubokura, Makoto; Wang, Weihsiang
2017-11-01
The automatic dissipation adjustment (ADA) model based on truncated Navier-Stokes equations is utilized to investigate the feasibility of using implicit large eddy simulation (ILES) with ADA model on the transition in natural convection. Due to the high Rayleigh number coming from the larger temperature difference (300K), Roe scheme modified for low Mach numbers coordinating ADA model is used to resolve the complicated flow field. Based on the qualitative agreement of the comparisons with DNS and experimental results and the capability of numerically predicating a -3 decay law for the temporal power spectrum of the temperature fluctuation, this study thus validates the feasibility of ILES with ADA model on turbulent natural convection. With the advantages of ease of implementation because no explicit modeling terms are needed and nearly free of tuning parameters, ADA model offers to become a promising tool for turbulent thermal convection. Part of the results is obtained using the K computer at the RIKEN Advanced Institute for Computational Science (Proposal number hp160232).
A review of the theoretical basis for bulk mass flux convective parameterization
Directory of Open Access Journals (Sweden)
R. S. Plant
2010-04-01
Full Text Available Most parameterizations for precipitating convection in use today are bulk schemes, in which an ensemble of cumulus elements with different properties is modelled as a single, representative entraining-detraining plume. We review the underpinning mathematical model for such parameterizations, in particular by comparing it with spectral models in which elements are not combined into the representative plume. The chief merit of a bulk model is that the representative plume can be described by an equation set with the same structure as that which describes each element in a spectral model. The equivalence relies on an ansatz for detrained condensate introduced by Yanai et al. (1973 and on a simplified microphysics. There are also conceptual differences in the closure of bulk and spectral parameterizations. In particular, we show that the convective quasi-equilibrium closure of Arakawa and Schubert (1974 for spectral parameterizations cannot be carried over to a bulk parameterization in a straightforward way. Quasi-equilibrium of the cloud work function assumes a timescale separation between a slow forcing process and a rapid convective response. But, for the natural bulk analogue to the cloud-work function, the relevant forcing is characterised by a different timescale, and so its quasi-equilibrium entails a different physical constraint. Closures of bulk parameterizations that use a parcel value of CAPE do not suffer from this timescale issue. However, the Yanai et al. (1973 ansatz must be invoked as a necessary ingredient of those closures.
Magnetic Control of Convection during Protein Crystallization
Ramachandran, N.; Leslie, F. W.
2004-01-01
An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular Crystals for diffraction analyses has been the central focus for bio-chemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and Sedimentation as is achieved in "microgravity", we have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, f o d o n of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. We postulate that limited convection in a magnetic field will provide the environment for the growth of high quality crystals. The approach exploits the variation of fluid magnetic susceptibility with counteracts on for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility
An intelligent robotics control scheme
Orlando, N. E.
1984-01-01
The problem of robot control is viewed at the level of communicating high-level commands produced by intelligent algorithms to the actuator/sensor controllers. Four topics are considered in the design of an integrated control and communications scheme for an intelligent robotic system: the use of abstraction spaces, hierarchical versus heterarchical control, distributed processing, and the interleaving of the steps of plan creation and plan execution. A scheme is presented for an n-level distributed hierarchical/heterarchical control system that effectively interleaves intelligent planning, execution, and sensory feedback. A three-level version of this scheme has been successfully implemented in the Intelligent Systems Research Lab at NASA Langley Research Center. This implementation forms the control structure for DAISIE (Distributed Artificially Intelligent System for Interacting with the Environment), a testbed system integrating AI software with robotics hardware.
One-qubit fingerprinting schemes
International Nuclear Information System (INIS)
Beaudrap, J. Niel de
2004-01-01
Fingerprinting is a technique in communication complexity in which two parties (Alice and Bob) with large data sets send short messages to a third party (a referee), who attempts to compute some function of the larger data sets. For the equality function, the referee attempts to determine whether Alice's data and Bob's data are the same. In this paper, we consider the extreme scenario of performing fingerprinting where Alice and Bob both send either one bit (classically) or one qubit (in the quantum regime) messages to the referee for the equality problem. Restrictive bounds are demonstrated for the error probability of one-bit fingerprinting schemes, and show that it is easy to construct one-qubit fingerprinting schemes which can outperform any one-bit fingerprinting scheme. The author hopes that this analysis will provide results useful for performing physical experiments, which may help to advance implementations for more general quantum communication protocols
Modulation Schemes for Wireless Access
Directory of Open Access Journals (Sweden)
F. Vejrazka
2000-12-01
Full Text Available Four modulation schemes, namely minimum shift keying (MSK, Gaussianminimum shift keying (GMSK, multiamplitude minimum shift keying(MAMSK and ÃÂ€/4 differential quadrature phase shift keying (ÃÂ€/4-QPSKare described and their applicability to wireless access is discussedin the paper. Low complexity receiver structures based on differentialdetection are analysed to estimate the performance of the modulationschemes in the additive Gaussian noise and the Rayleigh and Riceenvelope fast fading channel. The bandwidth efficiency is calculated toevaluate the modulation schemes. The results show that the MAMSK schemegives the greatest bandwidth efficiency, but its performance in theRayleigh channel is rather poor. In contrast, the MSK scheme is lessbandwidth efficient, but it is more resistant to Rayleigh fading. Theperformance of ÃÂ€/4-QPSK signal is considerably improved by appropriateprefiltering.
Electrical injection schemes for nanolasers
DEFF Research Database (Denmark)
Lupi, Alexandra; Chung, Il-Sug; Yvind, Kresten
2013-01-01
injection schemes have been compared: vertical pi- n junction through a current post structure as in1 and lateral p-i-n junction with either uniform material as in2 or with a buried heterostructure (BH) as in3. To allow a direct comparison of the three schemes the same active material composition consisting......The performance of injection schemes among recently demonstrated electrically pumped photonic crystal nanolasers has been investigated numerically. The computation has been carried out at room temperature using a commercial semiconductor simulation software. For the simulations two electrical...... threshold current has been achieved with the lateral electrical injection through the BH; while the lowest resistance has been obtained from the current post structure even though this model shows a higher current threshold because of the lack of carrier confinement. Final scope of the simulations...
Simple scheme for gauge mediation
International Nuclear Information System (INIS)
Murayama, Hitoshi; Nomura, Yasunori
2007-01-01
We present a simple scheme for constructing models that achieve successful gauge mediation of supersymmetry breaking. In addition to our previous work [H. Murayama and Y. Nomura, Phys. Rev. Lett. 98, 151803 (2007)] that proposed drastically simplified models using metastable vacua of supersymmetry breaking in vectorlike theories, we show there are many other successful models using various types of supersymmetry-breaking mechanisms that rely on enhanced low-energy U(1) R symmetries. In models where supersymmetry is broken by elementary singlets, one needs to assume U(1) R violating effects are accidentally small, while in models where composite fields break supersymmetry, emergence of approximate low-energy U(1) R symmetries can be understood simply on dimensional grounds. Even though the scheme still requires somewhat small parameters to sufficiently suppress gravity mediation, we discuss their possible origins due to dimensional transmutation. The scheme accommodates a wide range of the gravitino mass to avoid cosmological problems
Mathematical modeling of convective mixing in porous media for geological carbon dioxide storage
Hassanzadeh, Hassan
As concern about the adverse consequences of anthropogenic climate change has grown, so too has research into methods to reduce the emissions of greenhouse gases that will drive future climatic change. Carbon dioxide emissions arising from use of fossil-fuels are likely to be the dominant drivers of climate change over the coming century. The use of carbon dioxide and geologic storage (or sequestration) offers the possibility of maintaining access to fossil energy while reducing emissions of carbon dioxide to the atmosphere. One of the essential concerns in geologic storage is the risk of leakage of CO 2 from the injection sites. Carbon dioxide injected into saline aquifers, dissolves in the resident brines, increasing their density potentially leading to convective mixing. Convective mixing increases the rate of dissolution, and therefore decreases the time-scale over which leakage is possible. Understanding the factors that drive convective mixing and accurate estimation of the rate of dissolution in saline aquifers is important for assessing geological CO 2 storage sites. This dissertation has three components, which includes linear stability analysis, prediction of CO2-brine PVT, and numerical modeling. A hydrodynamic stability analysis is performed for non-linear, transient concentration fields in a saturated, homogenous and isotropic porous medium under various initial and boundary conditions. The role of the natural flow of aquifers and associated dispersion on the onset of convection in the saline aquifers is also investigated. A fugacity and an activity models are combined to develop an accurate thermodynamic module appropriate for geological CO2 storage application. A three-dimensional, two-phase and two-component numerical model for simulation of CO2 storage in saline aquifers is also developed. The numerical model employs higher order and total-variation-diminishing schemes, capillary pressure, relative permeability hysteresis, and full dispersion
Convective equilibrium and mixing-length theory for stellarator reactors
Energy Technology Data Exchange (ETDEWEB)
Ho, D.D.M.; Kulsrud, R.M.
1985-09-01
In high ..beta.. stellarator and tokamak reactors, the plasma pressure gradient in some regions of the plasma may exceed the critical pressure gradient set by ballooning instabilities. In these regions, convective cells break out to enhance the transport. As a result, the pressure gradient can rise only slightly above the critical gradient and the plasma is in another state of equilibrium - ''convective equilibrium'' - in these regions. Although the convective transport cannot be calculated precisely, it is shown that the density and temperature profiles in the convective region can still be estimated. A simple mixing-length theory, similar to that used for convection in stellar interiors, is introduced in this paper to provide a qualitative description of the convective cells and to show that the convective transport is highly efficient. A numerical example for obtaining the density and temperature profiles in a stellarator reactor is given.
Behaviors and transitions along the path to magnetostrophic convection
Grannan, A. M.; Vogt, T.; Horn, S.; Hawkins, E. K.; Aggarwal, A.; Aurnou, J. M.
2017-12-01
The generation of magnetic fields in planetary and stellar interiors are believed to be controlled primarily by turbulent convection constrained by Coriolis and Lorentz forces in their electrically conducting fluid layers. Yet relatively few laboratory experiments are capable of investigating the different regimes of turbulent magnetohydrodynamic convection. In this work, we perform one laboratory experiment in a cylinder at a fixed heat flux using the liquid metal gallium in order to investigate, sequentially: Rayleigh-Bènard convection without any imposed constraints, magnetoconvection with a Lorentz constraint imposed by vertical magnetic field, rotating convection with a Coriolis constraint imposed by rotation, and finally the magnetostrophic convective regime where both Coriolis and Lorentz are imposed and equal. Using an array of internal and external temperature probes, we show that each regime along the path to magnetostrophic convection is unique. The behaviors and transitions in the dominant modes of convection as well as their fundamental frequencies and wavenumbers are investigated.
Convective equilibrium and mixing-length theory for stellarator reactors
International Nuclear Information System (INIS)
Ho, D.D.M.; Kulsrud, R.M.
1985-09-01
In high β stellarator and tokamak reactors, the plasma pressure gradient in some regions of the plasma may exceed the critical pressure gradient set by ballooning instabilities. In these regions, convective cells break out to enhance the transport. As a result, the pressure gradient can rise only slightly above the critical gradient and the plasma is in another state of equilibrium - ''convective equilibrium'' - in these regions. Although the convective transport cannot be calculated precisely, it is shown that the density and temperature profiles in the convective region can still be estimated. A simple mixing-length theory, similar to that used for convection in stellar interiors, is introduced in this paper to provide a qualitative description of the convective cells and to show that the convective transport is highly efficient. A numerical example for obtaining the density and temperature profiles in a stellarator reactor is given
Stelten, Sean; Gallus, William
2017-04-01
was then simulated with four different configurations of a 4 km horizontal grid spacing WRF model. These WRF runs showed similar location errors and problems with initiating convection at a lower altitude than observed as was found from the simulations performed during PECAN. Three of the four PBL schemes behaved similarly, but one, the ACM2, was often an outlier, failing to indicate the convective initiation.
Electrical Injection Schemes for Nanolasers
DEFF Research Database (Denmark)
Lupi, Alexandra; Chung, Il-Sug; Yvind, Kresten
2014-01-01
Three electrical injection schemes based on recently demonstrated electrically pumped photonic crystal nanolasers have been numerically investigated: 1) a vertical p-i-n junction through a post structure; 2) a lateral p-i-n junction with a homostructure; and 3) a lateral p-i-n junction....... For this analysis, the properties of different schemes, i.e., electrical resistance, threshold voltage, threshold current, and internal efficiency as energy requirements for optical interconnects are compared and the physics behind the differences is discussed....
High-resolution weather forecasting is affected by many aspects, i.e. model initial conditions, subgrid-scale cumulus convection and cloud microphysics schemes. Recent 12km grid studies using the Weather Research and Forecasting (WRF) model have identified the importance of inco...
A block-iterative nodal integral method for forced convection problems
International Nuclear Information System (INIS)
Decker, W.J.; Dorning, J.J.
1992-01-01
A new efficient iterative nodal integral method for the time-dependent two- and three-dimensional incompressible Navier-Stokes equations has been developed. Using the approach introduced by Azmy and Droning to develop nodal mehtods with high accuracy on coarse spatial grids for two-dimensional steady-state problems and extended to coarse two-dimensional space-time grids by Wilson et al. for thermal convection problems, we have developed a new iterative nodal integral method for the time-dependent Navier-Stokes equations for mechanically forced convection. A new, extremely efficient block iterative scheme is employed to invert the Jacobian within each of the Newton-Raphson iterations used to solve the final nonlinear discrete-variable equations. By taking advantage of the special structure of the Jacobian, this scheme greatly reduces memory requirements. The accuracy of the overall method is illustrated by appliying it to the time-dependent version of the classic two-dimensional driven cavity problem of computational fluid dynamics
Convective Flow in an Aquifer Layer
Directory of Open Access Journals (Sweden)
Dambaru Bhatta
2017-10-01
Full Text Available Here, we investigate weakly nonlinear hydrothermal two-dimensional convective flow in a horizontal aquifer layer with horizontal isothermal and rigid boundaries. We treat such a layer as a porous medium, where Darcy’s law holds, subjected to the conditions that the porous layer’s permeability and the thermal conductivity are variable in the vertical direction. This analysis is restricted to the case that the subsequent hydraulic resistivity and diffusivity have a small rate of change with respect to the vertical variable. Applying the weakly nonlinear approach, we derive various order systems and express their solutions. The solutions for convective flow quantities such as vertical velocity and the temperature that arise as the Rayleigh number exceeds its critical value are computed and presented in graphical form.
Numerical Simulation of a Convective Turbulence Encounter
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.
Equilibrium Transport in Double-Diffusive Convection
2011-06-01
convection changes in other environments. External planetary systems, such as the atmospheric makeup of planets within our solar system, are...21) where ( fx ,fy) are the Floquet factors in x and y. Substituting Equation (21) in the linearized governing equations and collecting...the individual Fourier components reduces the stability problem to matrix form Equation (13). Maximizing the growth rates with respect to ( fx ,fy,m
Natural convection cooling of spent fuels depository
International Nuclear Information System (INIS)
Menant, B.
2000-01-01
The operating CASCAD Facility was commissioned at Cadarache since 1990. Spent fuels are being storage for a 50 years period. The heat giving by the wastes is evacuated essentially by natural convection. The Trio U software is applied to the thermohydraulic operating of the system. The results allow to illustrate the installation and show system instabilities effects which appear at many scales. (A.L.B.)
An experimental study of mixed convection
International Nuclear Information System (INIS)
Saez, Manuel
1998-01-01
The aim of our study is to establish a reliable data base for improving thermal-hydraulic codes, in the field of turbulent flows with buoyancy forces. The flow considered is mixed convection in the Reynolds and Richardson number range: Re=10 3 to 6*10 4 and Ri=10 -4 to 1. Experiments are carried out in an upward turbulent flow between vertical parallel plates at different wall temperatures. Part 1 gives a detailed data base of turbulent mixed flow of free and forced convection. Part II presents the installation and the calibration system intended for probes calibration. Part III describes the measurement technique (constant-temperature probe and cold-wire probe) and the method for measuring the position of the hot-wire anemometer from the wall surface. The measurement accuracy is within 0.001 mm in the present system. Part IV relates the development of a method for near wall measurements. This correction procedure for hot-wire anemometer close to wall has been derived on the basis of a two-dimensional numerical study. The method permits to obtain a quantitative correction of the wall influence on hot-wires and takes into account the velocity profile and the effects the wall material has on the heat loss. Part V presents the experimental data obtained in the channel in forced and mixed convection. Results obtained in the forced convection regime serve as a verification of the measurement technique close to the wall and give the conditions at the entrance of the test section. The effects of the buoyancy force on the mean velocity and temperature profiles are confirmed. The buoyancy strongly affects the flow structure and deforms the distribution of mean velocity. The velocity profiles are asymmetric. The second section of part V gives an approach of analytical wall functions with buoyancy forces, on the basis of the experimental data obtained in the test section. (author) [fr
Simulating North American mesoscale convective systems with a convection-permitting climate model
Prein, Andreas F.; Liu, Changhai; Ikeda, Kyoko; Bullock, Randy; Rasmussen, Roy M.; Holland, Greg J.; Clark, Martyn
2017-10-01
Deep convection is a key process in the climate system and the main source of precipitation in the tropics, subtropics, and mid-latitudes during summer. Furthermore, it is related to high impact weather causing floods, hail, tornadoes, landslides, and other hazards. State-of-the-art climate models have to parameterize deep convection due to their coarse grid spacing. These parameterizations are a major source of uncertainty and long-standing model biases. We present a North American scale convection-permitting climate simulation that is able to explicitly simulate deep convection due to its 4-km grid spacing. We apply a feature-tracking algorithm to detect hourly precipitation from Mesoscale Convective Systems (MCSs) in the model and compare it with radar-based precipitation estimates east of the US Continental Divide. The simulation is able to capture the main characteristics of the observed MCSs such as their size, precipitation rate, propagation speed, and lifetime within observational uncertainties. In particular, the model is able to produce realistically propagating MCSs, which was a long-standing challenge in climate modeling. However, the MCS frequency is significantly underestimated in the central US during late summer. We discuss the origin of this frequency biases and suggest strategies for model improvements.
Energy Technology Data Exchange (ETDEWEB)
Ghalambaz, M.; Noghrehabadi, A.; Ghanbarzadeh, A., E-mail: m.ghalambaz@gmail.com, E-mail: ghanbarzadeh.a@scu.ac.ir [Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)
2014-04-15
In this paper, the natural convective flow of nanofluids over a convectively heated vertical plate in a saturated Darcy porous medium is studied numerically. The governing equations are transformed into a set of ordinary differential equations by using appropriate similarity variables, and they are numerically solved using the fourth-order Runge-Kutta method associated with the Gauss-Newton method. The effects of parametric variation of the Brownian motion parameter (Nb), thermophoresis parameter (Nt) and the convective heating parameter (Nc) on the boundary layer profiles are investigated. Furthermore, the variation of the reduced Nusselt number and reduced Sherwood number, as important parameters of heat and mass transfer, as a function of the Brownian motion, thermophoresis and convective heating parameters is discussed in detail. The results show that the thickness of the concentration profiles is much lower than the temperature and velocity profiles. For low values of the convective heating parameter (Nc), as the Brownian motion parameter increases, the non-dimensional wall temperature increases. However, for high values of Nc, the effect of the Brownian motion parameter on the non-dimensional wall temperature is not significant. As the Brownian motion parameter increases, the reduced Sherwood number increases and the reduced Nusselt number decreases. (author)
Stein, Thorwald; Hogan, Robin; Hanley, Kirsty; Clark, Peter; Halliwell, Carol; Lean, Humphrey; Nicol, John; Plant, Robert
2016-04-01
National weather services increasingly use convection-permitting simulations to assist in their operational forecasts. The skill in forecasting rainfall from convection is much improved in such simulations compared to global models that rely on parameterisation schemes, but it is less obvious if and how increased model resolution or more advanced mixing and microphysics schemes improve the physical representation of convective storms. Here, we present a novel statistical approach using high-resolution radar data to evaluate the morphology, dynamics, and evolution of convective storms over southern England. In the DYMECS project (Dynamical and Microphysical Evolution of Convective Storms) we have used an innovative track-and-scan approach to target individual storms with the Chilbolton radar, which measures cloud and precipitation at scales less than 300m out to 100km. These radar observations provide three-dimensional storm volumes and estimates of updraft core strength and sizes at adequate scales to test high-resolution models. For two days of interest, we have run the Met Office forecast model at its operational configuration (1.5km grid length) and at grid lengths of 500m, 200m, and 100m. Radar reflectivity and Doppler winds were simulated from the model cloud and wind output for a like-with-like comparison against the radar observations. Our results show that although the 1.5km simulation produces similar domain-averaged rainfall as the other simulations, the majority of rainfall is produced from storms that are a factor 1.5-2 larger than observed as well as longer lived, while the updrafts of these storms are an order of magnitude greater than estimated from observations. We generally find improvements as model resolution increases, although our results depend strongly on the mixing-length parameter in the model turbulence scheme. Our findings highlight the promising role of high-resolution radar data and observational strategies targeting individual storms
Efficient adaptive fuzzy control scheme
Papp, Z.; Driessen, B.J.F.
1995-01-01
The paper presents an adaptive nonlinear (state-) feedback control structure, where the nonlinearities are implemented as smooth fuzzy mappings defined as rule sets. The fine tuning and adaption of the controller is realized by an indirect adaptive scheme, which modifies the parameters of the fuzzy
New practicable Siberian Snake schemes
International Nuclear Information System (INIS)
Steffen, K.
1983-07-01
Siberian Snake schemes can be inserted in ring accelerators for making the spin tune almost independent of energy. Two such schemes are here suggested which lend particularly well to practical application over a wide energy range. Being composed of horizontal and vertical bending magnets, the proposed snakes are designed to have a small maximum beam excursion in one plane. By applying in this plane a bending correction that varies with energy, they can be operated at fixed geometry in the other plane where most of the bending occurs, thus avoiding complicated magnet motion or excessively large magnet apertures that would otherwise be needed for large energy variations. The first of the proposed schemes employs a pair of standard-type Siberian Snakes, i.e. of the usual 1st and 2nd kind which rotate the spin about the longitudinal and the transverse horizontal axis, respectively. The second scheme employs a pair of novel-type snakes which rotate the spin about either one of the horizontal axes that are at 45 0 to the beam direction. In obvious reference to these axes, they are called left-pointed and right-pointed snakes. (orig.)
Homogenization scheme for acoustic metamaterials
Yang, Min
2014-02-26
We present a homogenization scheme for acoustic metamaterials that is based on reproducing the lowest orders of scattering amplitudes from a finite volume of metamaterials. This approach is noted to differ significantly from that of coherent potential approximation, which is based on adjusting the effective-medium parameters to minimize scatterings in the long-wavelength limit. With the aid of metamaterials’ eigenstates, the effective parameters, such as mass density and elastic modulus can be obtained by matching the surface responses of a metamaterial\\'s structural unit cell with a piece of homogenized material. From the Green\\'s theorem applied to the exterior domain problem, matching the surface responses is noted to be the same as reproducing the scattering amplitudes. We verify our scheme by applying it to three different examples: a layered lattice, a two-dimensional hexagonal lattice, and a decorated-membrane system. It is shown that the predicted characteristics and wave fields agree almost exactly with numerical simulations and experiments and the scheme\\'s validity is constrained by the number of dominant surface multipoles instead of the usual long-wavelength assumption. In particular, the validity extends to the full band in one dimension and to regimes near the boundaries of the Brillouin zone in two dimensions.
Planche, Céline; Marsham, John; Carslaw, Ken; Mann, Graham; Wilkinson, Jonathan; Field, Paul
2013-04-01
The interaction of aerosols with clouds is known to significantly affect cloud dynamics and the patterns and intensity of precipitation. However, aerosol-cloud interactions are very poorly handled in low resolution climate and operational NWP models. For example, in the global operational NWP Met Office Unified Model (UM), simple land-sea contrasts in cloud droplet concentrations are specified. In reality, changes in cloud condensation nuclei affect warm rain production, which goes on to affect the ice production in mixed-phase convective clouds. It is important to establish the value of including such interactions in these models. In the framework of the ASCI (AeroSol Cloud Interactions) project, in which we are developing a coupled version of the UM with multi-moment bulk cloud and aerosol schemes, we consider the sensitivities of two UK case studies of mixed-phase convection to warm-rain production. A suite of (one way) nested models was used with grid lengths of 12, 4, 1, 0.333 and 0.1 km. This configuration allows us to evaluate the impacts of changing warm-rain production by autoconversion at very high resolution and evaluate the uncertainties in this impact according to the grid resolution. The two case studies were observed during the Convective Storm Initiation Project (CSIP) field campaign in southern England in 2005 and have contrasting characteristics. The first case is characterised by moderately intense convective showers forming throughout the day in a north-westerly airstream below an upper-level PV anomaly, with a shallow boundary layer and low freezing level. The second case is warmer with a deeper boundary layer with weaker winds and less shear, and is characterised by isolate convective cells, with one persistent stronger storm. The less organised convection in the second case requires a smaller grid-spacing than the more organised showers in the first case. The first case is almost insensitive to even very large changes in autoconversion, while
An explicit method for convection problems involving a change of phase
International Nuclear Information System (INIS)
Morgan, K.
1981-01-01
The numerical analysis of problems of heat transfer in materials which undergo a liquid/solid change of phase has attracted much interest as such problems are of practical importance in the steel and nuclear industries. It is normally assumed that transfer of heat by conduction is the dominant mechanism whereas it is known from experimental evidence that convection plays a dominant role in many phase change problems of practical interest. In this paper an attempt has been made to include the effect of convection in two-dimensional heat transfer problems involving a change of phase. The finite element method is used to solve the heat conduction equation in the solid and to solve the full Navier-Stokes equations and the convective-diffusion in the fluid. The explicit fractional step method is used to solve the momentum and continuity equations and the phase change is modelled by means of the enthalpy method. The velocity and temperature fields are represented by the use of four noded bilinear elements with a discontinuous, elementwise constant, representation adopted for the pressure field. With the explicit time stepping scheme, the representation for the temperature field is shown to be capable of modelling accurately the phase change process by comparing numerical results with the analytical solution for a one-dimensional problem involving conduction only. Results are presented for the problem of freezing in a plane thermal cavity when the temperature of one of the vertical walls is suddenly reduced and the effect of convection on the freezing process is illustrated. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Yun, Yuxing [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA; State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing China; Fan, Jiwen [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA; Xiao, Heng [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA; Zhang, Guang J. [Scripps Institution of Oceanography, University of California, San Diego CA USA; Ghan, Steven J. [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA; Xu, Kuan-Man [NASA Langley Research Center, Hampton VA USA; Ma, Po-Lun [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA; Gustafson, William I. [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland WA USA
2017-11-01
Realistic modeling of cumulus convection at fine model resolutions (a few to a few tens of km) is problematic since it requires the cumulus scheme to adapt to higher resolution than they were originally designed for (~100 km). To solve this problem, we implement the spatial averaging method proposed in Xiao et al. (2015) and also propose a temporal averaging method for the large-scale convective available potential energy (CAPE) tendency in the Zhang-McFarlane (ZM) cumulus parameterization. The resolution adaptability of the original ZM scheme, the scheme with spatial averaging, and the scheme with both spatial and temporal averaging at 4-32 km resolution is assessed using the Weather Research and Forecasting (WRF) model, by comparing with Cloud Resolving Model (CRM) results. We find that the original ZM scheme has very poor resolution adaptability, with sub-grid convective transport and precipitation increasing significantly as the resolution increases. The spatial averaging method improves the resolution adaptability of the ZM scheme and better conserves the total transport of moist static energy and total precipitation. With the temporal averaging method, the resolution adaptability of the scheme is further improved, with sub-grid convective precipitation becoming smaller than resolved precipitation for resolution higher than 8 km, which is consistent with the results from the CRM simulation. Both the spatial distribution and time series of precipitation are improved with the spatial and temporal averaging methods. The results may be helpful for developing resolution adaptability for other cumulus parameterizations that are based on quasi-equilibrium assumption.
Impact of WRF model PBL schemes on air quality simulations over Catalonia, Spain.
Banks, R F; Baldasano, J M
2016-12-01
Here we analyze the impact of four planetary boundary-layer (PBL) parametrization schemes from the Weather Research and Forecasting (WRF) numerical weather prediction model on simulations of meteorological variables and predicted pollutant concentrations from an air quality forecast system (AQFS). The current setup of the Spanish operational AQFS, CALIOPE, is composed of the WRF-ARW V3.5.1 meteorological model tied to the Yonsei University (YSU) PBL scheme, HERMES v2 emissions model, CMAQ V5.0.2 chemical transport model, and dust outputs from BSC-DREAM8bv2. We test the performance of the YSU scheme against the Assymetric Convective Model Version 2 (ACM2), Mellor-Yamada-Janjic (MYJ), and Bougeault-Lacarrère (BouLac) schemes. The one-day diagnostic case study is selected to represent the most frequent synoptic condition in the northeast Iberian Peninsula during spring 2015; regional recirculations. It is shown that the ACM2 PBL scheme performs well with daytime PBL height, as validated against estimates retrieved using a micro-pulse lidar system (mean bias=-0.11km). In turn, the BouLac scheme showed WRF-simulated air and dew point temperature closer to METAR surface meteorological observations. Results are more ambiguous when simulated pollutant concentrations from CMAQ are validated against network urban, suburban, and rural background stations. The ACM2 scheme showed the lowest mean bias (-0.96μgm -3 ) with respect to surface ozone at urban stations, while the YSU scheme performed best with simulated nitrogen dioxide (-6.48μgm -3 ). The poorest results were with simulated particulate matter, with similar results found with all schemes tested. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Savonije, G.J.; Takens, R.J.
1976-01-01
A generalization of the Henyey-scheme is given that introduces the mass of the convective core and the density at the outer edge of the convective core boundary as unknowns which have to be solved simultaneously with the other unknowns. As a result, this boundary is determined in a physically self-consistent way for expanding as well as contracting cores, i.e. during the Henyey iterative cycle; its position becomes consistent with the overall physical structure of the star, including the run of the chemical abundances throughout the star. Using this scheme, the evolution of helium stars was followed up to carbon ignition for a number of stellar masses. As compared with some earlier investigations, the calculations show a rather large increase in mass of the convective cores during core helium burning. Evolutionary calculations for a 2M(sun) helium star show that the critical mass for which a helium star ignites carbon non-degenerately lies near 2M(sun). (orig.) [de
Wang, Haoliang; Liu, Yubao; Cheng, William Y. Y.; Zhao, Tianliang; Xu, Mei; Liu, Yuewei; Shen, Si; Calhoun, Kristin M.; Fierro, Alexandre O.
2017-11-01
In this study, a lightning data assimilation (LDA) scheme was developed and implemented in the National Center for Atmospheric Research Weather Research and Forecasting-Real-Time Four-Dimensional Data Assimilation system. In this LDA method, graupel mixing ratio (qg) is retrieved from observed total lightning. To retrieve qg on model grid boxes, column-integrated graupel mass is first calculated using an observation-based linear formula between graupel mass and total lightning rate. Then the graupel mass is distributed vertically according to the empirical qg vertical profiles constructed from model simulations. Finally, a horizontal spread method is utilized to consider the existence of graupel in the adjacent regions of the lightning initiation locations. Based on the retrieved qg fields, latent heat is adjusted to account for the latent heat releases associated with the formation of the retrieved graupel and to promote convection at the observed lightning locations, which is conceptually similar to the method developed by Fierro et al. Three severe convection cases were studied to evaluate the LDA scheme for short-term (0-6 h) lightning and precipitation forecasts. The simulation results demonstrated that the LDA was effective in improving the short-term lightning and precipitation forecasts by improving the model simulation of the qg fields, updrafts, cold pool, and front locations. The improvements were most notable in the first 2 h, indicating a highly desired benefit of the LDA in lightning and convective precipitation nowcasting (0-2 h) applications.
Convective Weather Avoidance with Uncertain Weather Forecasts
Karahan, Sinan; Windhorst, Robert D.
2009-01-01
Convective weather events have a disruptive impact on air traffic both in terminal area and in en-route airspaces. In order to make sure that the national air transportation system is safe and efficient, it is essential to respond to convective weather events effectively. Traffic flow control initiatives in response to convective weather include ground delay, airborne delay, miles-in-trail restrictions as well as tactical and strategic rerouting. The rerouting initiatives can potentially increase traffic density and complexity in regions neighboring the convective weather activity. There is a need to perform rerouting in an intelligent and efficient way such that the disruptive effects of rerouting are minimized. An important area of research is to study the interaction of in-flight rerouting with traffic congestion or complexity and developing methods that quantitatively measure this interaction. Furthermore, it is necessary to find rerouting solutions that account for uncertainties in weather forecasts. These are important steps toward managing complexity during rerouting operations, and the paper is motivated by these research questions. An automated system is developed for rerouting air traffic in order to avoid convective weather regions during the 20- minute - 2-hour time horizon. Such a system is envisioned to work in concert with separation assurance (0 - 20-minute time horizon), and longer term air traffic management (2-hours and beyond) to provide a more comprehensive solution to complexity and safety management. In this study, weather is dynamic and uncertain; it is represented as regions of airspace that pilots are likely to avoid. Algorithms are implemented in an air traffic simulation environment to support the research study. The algorithms used are deterministic but periodically revise reroutes to account for weather forecast updates. In contrast to previous studies, in this study convective weather is represented as regions of airspace that pilots
International Nuclear Information System (INIS)
Kim, Hyeon Il
2010-02-01
convection regime, and (4) recently conducted experiments in a deteriorated turbulent heat transfer regime. The validation proved that the Launder-Sharma model can supply improved solutions and much better knowledge about not only the wall temperature but also the heat transfer phenomena in turbulent mixed convection regime, the DTHT, compared to that offered by a single-dimensional empirical correlation. A set of modules to provide Computational Fluid Dynamics (CFD) capability being able to handle multi-dimensional heat transfer is incorporated into a system code for GCRs, GAMMA+, by adopting the Launder-Sharma model of turbulence. We implemented the model into the original system code based on the same schemes, that is, the Implicit Continuous fluid Eulerian (ICE) scheme in a staggered mesh layout, and Newton linearization as constructed in the original code in such a way that the model did not interfere with the numerical stability. The extended code, GAMMA T , was successfully verified and validated in that the model was well formulated with a firmly established numerical foundation through comparisons with an available set of data covering turbulent forced convection regime. The GAMMA T code showed strong potential for future use as a robust integrated system code with the capability of multi-scale analysis in it
Project financing renewable energy schemes
International Nuclear Information System (INIS)
Brandler, A.
1993-01-01
The viability of many Renewable Energy projects is critically dependent upon the ability of these projects to secure the necessary financing on acceptable terms. The principal objective of the study was to provide an overview to project developers of project financing techniques and the conditions under which project finance for Renewable Energy schemes could be raised, focussing on the potential sources of finance, the typical project financing structures that could be utilised for Renewable Energy schemes and the risk/return and security requirements of lenders, investors and other potential sources of financing. A second objective is to describe the appropriate strategy and tactics for developers to adopt in approaching the financing markets for such projects. (author)
Finite volume schemes for Vlasov
Directory of Open Access Journals (Sweden)
Crouseilles Nicolas
2013-01-01
Full Text Available We present finite volume schemes for the numerical approximation of the one-dimensional Vlasov-Poisson equation (FOV CEMRACS 2011 project. Stability analysis is performed for the linear advection and links with semi-Lagrangian schemes are made. Finally, numerical results enable to compare the different methods using classical plasma test cases. Des schémas de type volumes finis sont étudiés ici pour l’approximation de l’équation de Vlasov-Poisson (projet FOV, CEMRACS 2011. Une analyse de stabilité est effectuée dans le cas de l’advection linéaire et plusieurs liens sont faits entre les méthodes volumes finis et semi-Lagrangiennes. Enfin, les méthodes sont comparées sur des cas tests académiques de la physique des plasmas.
Distance labeling schemes for trees
DEFF Research Database (Denmark)
Alstrup, Stephen; Gørtz, Inge Li; Bistrup Halvorsen, Esben
2016-01-01
We consider distance labeling schemes for trees: given a tree with n nodes, label the nodes with binary strings such that, given the labels of any two nodes, one can determine, by looking only at the labels, the distance in the tree between the two nodes. A lower bound by Gavoille et al. [Gavoille...... variants such as, for example, small distances in trees [Alstrup et al., SODA, 2003]. We improve the known upper and lower bounds of exact distance labeling by showing that 1/4 log2(n) bits are needed and that 1/2 log2(n) bits are sufficient. We also give (1 + ε)-stretch labeling schemes using Theta...
Archimedean Proof of the Physical Impossibility of Earth Mantle Convection
Herndon, J. Marvin
2010-01-01
Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all ma...
Strategic Repositioning for Convection Business Case Study: AR Vendor
Anindita, Pratisara Satwika; Toha, Mohamad
2013-01-01
The study aims to determine suitable position and strategy in order to reach superiority in convection business based on the company strengths and weaknesses. A study conducted in late 2012 at AR Vendor, a home-based convection company which focus on the t-shirt screen printing service. In response to the issue of the below average profit margin, the company has to rethink their position and strategy in handling the convection business environment. While AR Vendor business may growth in accor...
Forced convection in nanoparticles doped nematics without reorientation
International Nuclear Information System (INIS)
Hakobyan, M.R.; Hakobyan, R.S.
2016-01-01
The problem of forced convection in the cell of nanoparticles doped nematic liquid crystal with both boundaries being free, plane and isotherm is discussed. These boundary conditions (offered by Rayleigh) allow to get simple and exact solution for boundary-value problem, from which its most important peculiarities can be clearly seen. Particularly, there appears a possibility to induce convection without reorientation of liquid crystal director. It was shown that nanoparticles could have significant influence on the convection
Primary Issues of Mixed Convection Heat Transfer Phenomena
International Nuclear Information System (INIS)
Chae, Myeong-Seon; Chung, Bum-Jin
2015-01-01
The computer code analyzing the system operating and transient behavior must distinguish flow conditions involved with convective heat transfer flow regimes. And the proper correlations must be supplied to those flow regimes. However the existing safety analysis codes are focused on the Light Water Reactor and they are skeptical to be applied to the GCRs (Gas Cooled Reactors). One of the technical issues raise by the development of the VHTR is the mixed convection, which occur when the driving forces of both forced and natural convection are of comparable magnitudes. It can be encountered as in channel of the stacked with fuel elements and a decay heat removal system and in VHTR. The mixed convection is not intermediate phenomena with natural convection and forced convection but independent complicated phenomena. Therefore, many researchers have been studied and some primary issues were propounded for phenomena mixed convection. This paper is to discuss some problems identified through reviewing the papers for mixed convection phenomena. And primary issues of mixed convection heat transfer were proposed respect to thermal hydraulic problems for VHTR. The VHTR thermal hydraulic study requires an indepth study of the mixed convection phenomena. In this study we reviewed the classical flow regime map of Metais and Eckert and derived further issues to be considered. The following issues were raised: (1) Buoyancy aided an opposed flows were not differentiated and plotted in a map. (2) Experimental results for UWT and UHF condition were also plotted in the same map without differentiation. (3) The buoyancy coefficient was not generalized for correlating with buoyancy coefficient. (4) The phenomenon analysis for laminarization and returbulization as buoyancy effects in turbulent mixed convection was not established. (5) The defining to transition in mixed convection regime was difficult
Forced and free convection turbulent boundary layers in gas lasers
International Nuclear Information System (INIS)
Woodroffe, J.A.
1975-01-01
Approximate expressions for the effect on optical path length through a turbulent vertical boundary layer caused by the combined presence of forced and free convection were obtained to first order in the asymptotic cases of dominant forced convection and dominant free convection. The effect in both cases is a reduction of the boundary-layer thickness. Characteristic scaling lengths are presented which aid in the optical analysis of the flowfield
New schemes for particle accelerators
International Nuclear Information System (INIS)
Nishida, Y.
1985-01-01
In the present paper, the authors propose new schemes for realizing the v/sub p/xB accelerator, by using no plasma system for producing the strong longitudinal waves. The first method is to use a grating for obtaining extended interaction of an electron beam moving along the grating surface with light beam incident also along the surface. Here, the light beam propagates obliquely to the grating grooves for producing strong electric field, and the electron beam propagates in parallel to the light beam. The static magnetic field is applied perpendicularly to the grating surface. In the present system, the beam interacts synchronously with the p-polarized wave which has the electric field be parallel to the grating surface. Another conventional scheme is to use a delay circuit. Here, the light beam propagates obliquely between a pair of array of conductor fins or slots. The phase velocity of the spatial harmonics in the y-direction (right angle to the array of slots) is slower than the speed of light. With the aid of powerful laser light or microwave source, it should be possible to miniaturise linacs by using the v/sub p/xB effect and schemes proposed here
An Arbitrated Quantum Signature Scheme without Entanglement"*
International Nuclear Information System (INIS)
Li Hui-Ran; Luo Ming-Xing; Peng Dai-Yuan; Wang Xiao-Jun
2017-01-01
Several quantum signature schemes are recently proposed to realize secure signatures of quantum or classical messages. Arbitrated quantum signature as one nontrivial scheme has attracted great interests because of its usefulness and efficiency. Unfortunately, previous schemes cannot against Trojan horse attack and DoS attack and lack of the unforgeability and the non-repudiation. In this paper, we propose an improved arbitrated quantum signature to address these secure issues with the honesty arbitrator. Our scheme takes use of qubit states not entanglements. More importantly, the qubit scheme can achieve the unforgeability and the non-repudiation. Our scheme is also secure for other known quantum attacks . (paper)
An Arbitrated Quantum Signature Scheme without Entanglement*
Li, Hui-Ran; Luo, Ming-Xing; Peng, Dai-Yuan; Wang, Xiao-Jun
2017-09-01
Several quantum signature schemes are recently proposed to realize secure signatures of quantum or classical messages. Arbitrated quantum signature as one nontrivial scheme has attracted great interests because of its usefulness and efficiency. Unfortunately, previous schemes cannot against Trojan horse attack and DoS attack and lack of the unforgeability and the non-repudiation. In this paper, we propose an improved arbitrated quantum signature to address these secure issues with the honesty arbitrator. Our scheme takes use of qubit states not entanglements. More importantly, the qubit scheme can achieve the unforgeability and the non-repudiation. Our scheme is also secure for other known quantum attacks.
Analogical Argument Schemes and Complex Argument Structure
Directory of Open Access Journals (Sweden)
Andre Juthe
2015-09-01
Full Text Available This paper addresses several issues in argumentation theory. The over-arching goal is to discuss how a theory of analogical argument schemes fits the pragma-dialectical theory of argument schemes and argument structures, and how one should properly reconstruct both single and complex argumentation by analogy. I also propose a unified model that explains how formal valid deductive argumentation relates to argument schemes in general and to analogical argument schemes in particular. The model suggests “scheme-specific-validity” i.e. that there are contrasting species of validity for each type of argument scheme that derive from one generic conception of validity.
Using Intel Xeon Phi to accelerate the WRF TEMF planetary boundary layer scheme
Mielikainen, Jarno; Huang, Bormin; Huang, Allen
2014-05-01
The Weather Research and Forecasting (WRF) model is designed for numerical weather prediction and atmospheric research. The WRF software infrastructure consists of several components such as dynamic solvers and physics schemes. Numerical models are used to resolve the large-scale flow. However, subgrid-scale parameterizations are for an estimation of small-scale properties (e.g., boundary layer turbulence and convection, clouds, radiation). Those have a significant influence on the resolved scale due to the complex nonlinear nature of the atmosphere. For the cloudy planetary boundary layer (PBL), it is fundamental to parameterize vertical turbulent fluxes and subgrid-scale condensation in a realistic manner. A parameterization based on the Total Energy - Mass Flux (TEMF) that unifies turbulence and moist convection components produces a better result that the other PBL schemes. For that reason, the TEMF scheme is chosen as the PBL scheme we optimized for Intel Many Integrated Core (MIC), which ushers in a new era of supercomputing speed, performance, and compatibility. It allows the developers to run code at trillions of calculations per second using the familiar programming model. In this paper, we present our optimization results for TEMF planetary boundary layer scheme. The optimizations that were performed were quite generic in nature. Those optimizations included vectorization of the code to utilize vector units inside each CPU. Furthermore, memory access was improved by scalarizing some of the intermediate arrays. The results show that the optimization improved MIC performance by 14.8x. Furthermore, the optimizations increased CPU performance by 2.6x compared to the original multi-threaded code on quad core Intel Xeon E5-2603 running at 1.8 GHz. Compared to the optimized code running on a single CPU socket the optimized MIC code is 6.2x faster.
Directory of Open Access Journals (Sweden)
Tasawar Hayat
Full Text Available The present article has been arranged to study the Hall current and Joule heating effects on peristaltic flow of viscous fluid in a channel with flexible walls. Both fluid and channel are in a state of solid body rotation. Convective conditions for heat transfer in the formulation are adopted. Viscous dissipation in energy expression is taken into account. Resulting differential systems after invoking small Reynolds number and long wavelength considerations are numerically solved. Runge-Kutta scheme of order four is implemented for the results of axial and secondary velocities, temperature and heat transfer coefficient. Comparison with previous limiting studies is shown. Outcome of new parameters of interest is analyzed. Keywords: Rotating frame, Hall current, Joule heating, Convective conditions, Wall properties
International Nuclear Information System (INIS)
Laval, H.; Giuliani, S.
1985-01-01
This paper describes an explicit finite element solution to transient conductive-convective heat transfer problems with phase change within an electrically heated region. The basic governing equations include the incompressible Navier-Stokes equations and the thermal energy equation. The phase change is modelled by a variant of the enthalpy method. Heat is generated by Joule effect due to the passage of an electric current for which a steady situation is assumed. An explicit scheme is used for the time integration, based on a fractional step method. A second-order Taylor-Galerkin method is introduced in the convection phase. The equations are discretized successively in space using the standard Galerkin finite element method. A reduced integration has been introduced as an option. In addition, a group representation is used for the non-linear velocity terms. To illustrate the proposed methodology, an application related to experimental tests is described. (orig.)
International Nuclear Information System (INIS)
Navarro, J. A.; Madariaga, J. A.; Santamaria, C. M.; Saviron, J. M.
1980-01-01
10 refs. Flow pattern calculations in natural convection between two vertical coaxial cylinders are reported. It is assumed trough the paper. that fluid properties, viscosity, thermal conductivity and density, depend no-linearly on temperature and that the aspects (height/radius) ratio of the cylinders is high. Velocity profiles are calculated trough a perturbative scheme and analytic results for the three first perturbation orders are presented. We outline also an iterative method to estimate the perturbations on the flow patterns which arise when a radial composition gradient is established by external forces in a two-component fluid. This procedure, based on semiempirical basis, is applied to gaseous convection. The influence of the molecules gas properties on tho flow is also discussed. (Author) 10 refs
Numerical simulation of two-dimensional Rayleigh-Benard convection
Grigoriev, Vasiliy V.; Zakharov, Petr E.
2017-11-01
This paper considered Rayleigh-Benard convection (natural convection). This is a flow, which is formed in a viscous medium when heated from below and cooled from above. As a result, are formed vortices (convective cells). This process is described by a system of nonlinear differential equations in Oberbeck-Boussinesq approximation. As the governing parameters characterizing convection states Rayleigh number, Prandtl number are picked. The problem is solved by using finite element method with computational package FEniCS. Numerical results for different Rayleigh numbers are obtained. Studied integral characteristic (Nusselt number) depending on the Rayleigh number.
Cumulus convection and the terrestrial water-vapor distribution
Donner, Leo J.
1988-01-01
Cumulus convection plays a significant role in determining the structure of the terrestrial water vapor field. Cumulus convection acts directly on the moisture field by condensing and precipitating water vapor and by redistributing water vapor through cumulus induced eddy circulations. The mechanisms by which cumulus convection influences the terrestrial water vapor distribution is outlined. Calculations using a theory due to Kuo is used to illustrate the mechanisms by which cumulus convection works. Understanding of these processes greatly aids the ability of researchers to interpret the seasonal and spatial distribution of atmospheric water vapor by providing information on the nature of sources and sinks and the global circulation.
Urban Influences on Convection and Lightning Over Houston
National Research Council Canada - National Science Library
Gauthier, Michael L
2006-01-01
The research presented in this dissertation addresses a fundamental question regarding urban, ultimately anthropogenic, influences on convection as it relates to lightning production and precipitation structure...
Fourth Convection and Moisture Experiment ER2 MODIS Airborne Simulator
National Aeronautics and Space Administration — The Convection And Moisture EXperiment (CAMEX) 4 focused on the study of tropical cyclone (hurricane) development, tracking, intensification, and landfalling impacts...
Natural convection in superposed fluid-porous layers
Bagchi, Aniruddha
2013-01-01
Natural Convection in Composite Fluid-Porous Domains provides a timely overview of the current state of understanding on the phenomenon of convection in composite fluid-porous layers. Natural convection in horizontal fluid-porous layers has received renewed attention because of engineering problems such as post-accident cooling of nuclear reactors, contaminant transport in groundwater, and convection in fibrous insulation systems. Because applications of the problem span many scientific domains, the book serves as a valuable resource for a wide audience.
Thermal convection thresholds in a Oldroyd magnetic fluid
Energy Technology Data Exchange (ETDEWEB)
Perez, L.M. [Departamento de Ingenieria Metalurgica, Universidad de Santiago de Chile, Av. Bernardo OHiggins 3363, Santiago (Chile); Bragard, J. [Departamento de Fisica y Matematica Aplicada, Universidad de Navarra, 31080 Pamplona (Spain); Laroze, D., E-mail: david.laroze@gmail.co [Max Planck Institute for Polymer Research, D 55021 Mainz (Germany); Instituto de Alta Investigacion, Universidad de Tarapaca, Casilla 7D, Arica (Chile); Martinez-Mardones, J. [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Pleiner, H. [Max Planck Institute for Polymer Research, D 55021 Mainz (Germany)
2011-03-15
We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. The viscoelastic properties is given by the Oldroyd model. We obtain explicit expressions for the convective thresholds in terms of the parameters of the system in the case of idealized boundary conditions. We also calculate numerically the convective thresholds for the case of realistic boundary conditions. The effect of the Kelvin force and of the rheology on instability thresholds for a diluted suspensions are emphasized. - Research highlights: > We study the linear analysis of the convection in magnetic fluids. > The Rheological properties are given by the Oldroyd model. > The numerical results are performed by the Spectral method.
Inside the supernova: A powerful convective engine
Herant, Marc; Benz, Willy; Hix, W. Raphael; Fryer, Chris L.; Colgate, Stirling A.
1994-01-01
We present an extensive study of the inception of supernova explosions by following the evolution of the cores of two massive stars (15 and 25 Solar mass) in multidimension. Our calculations begin at the onset of core collapse and stop several hundred milliseconds after the bounce, at which time successful explosions of the appropriate magnitude have been obtained. Similar to the classical delayed explosion mechanism of Wilson, the explosion is powered by the heating of the envelope due to neutrinos emitted by the protoneutron star as it radiates the gravitational energy liberated by the collapse. However, as was shown by Herant, Benz, & Colgate, this heating generates strong convection outside the neutrinosphere, which we demonstrate to be critical to the explosion. By breaking a purely stratified hydrostatic equilibrium, convection moves the nascent supernova away from a delicate radiative equilibrium between neutrino emission and absorption, Thus, unlike what has been observed in one-dimensional calculations, explosions are rendered quite insensitive to the details of the physical input parameters such as neutrino cross sections or nuclear equation of state parameters. As a confirmation, our comparative one-dimensional calculations with identical microphysics, but in which convection cannot occur, lead to dramatic failures. Guided by our numerical results, we have developed a paradigm for the supernova explosion mechanism. We view a supernova as an open cycle thermodynamic engine in which a reservoir of low-entropy matter (the envelope) is thermally coupled and physically connected to a hot bath (the protoneutron star) by a neutrino flux, and by hydrodynamic instabilities. This paradigm does not invoke new or modified physics over previous treatments, but relies on compellingly straightforward thermodynamic arguments. It provides a robust and self-regulated explosion mechanism to power supernovae that is effective under a wide range of physical parameters.
Effect of rotation on ferro thermohaline convection
Sekar, R; Ramanathan, A
2000-01-01
The ferro thermohaline convection in a rotating medium heated from below and salted from above has been analysed. The solute is magnetic oxide, which modifies the magnetic field established as a perturbation. The effect of salinity has been included in magnetisation and in the density of the ferrofluid. The conditions for both stationary and oscillatory modes have been obtained using linear stability analysis and it has been found that stationary mode is favoured in comparison with oscillatory mode. The numerical and graphical results are presented. It has been observed that rotation stabilises the system.
Measurement of natural convection by speckle photography
International Nuclear Information System (INIS)
Wernekinck, U.; Merzkirch, W.
1986-01-01
The principle of speckle photography can be applied to the measurement of density variations in fluids. A modification of existing experimental arrangements allows for the measurement of large values of the light deflection angles as they may occur in heat and mass transfer situations. The method is demonstrated for the case of a helium jet exhausting into still air and the natural convective flow along a heated plate. The obtained data are compared with results measured with classical optical interferometers, and good agreement is found. The advantages of the new technique over the classical optical methods are briefly discussed. 11 references
Coupled Michigan MHD - Rice Convection Model Results
de Zeeuw, D.; Sazykin, S.; Wolf, D.; Gombosi, T.; Powell, K.
2002-12-01
A new high performance Rice Convection Model (RCM) has been coupled to the adaptive-grid Michigan MHD model (BATSRUS). This fully coupled code allows us to self-consistently simulate the physics in the inner and middle magnetosphere. A study will be presented of the basic characteristics of the inner and middle magnetosphere in the context of a single coupled-code run for idealized storm inputs. The analysis will include region-2 currents, shielding of the inner magnetosphere, partial ring currents, pressure distribution, magnetic field inflation, and distribution of pV^gamma.
Natural convection between two concentric spheres
International Nuclear Information System (INIS)
Blondel-Roux, Marie
1983-01-01
After an overview of researches on natural convection in a confined or semi-confined environment, this research thesis reports the use of the Caltagirone and Mojtabi numerical model and the study of its validity for different values of the Rayleigh and Prandtl numbers. Results obtained with this model are compared with experimental ones. Thermal transfer curves are presented and discussed, as well as the different temperature fields numerically obtained, flow function fields, velocities in the fluid layer, and temperature profiles with respect to the Rayleigh number [fr
Mixing in heterogeneous internally-heated convection
Limare, A.; Kaminski, E. C.; Jaupart, C. P.; Farnetani, C. G.; Fourel, L.; Froment, M.
2017-12-01
Past laboratory experiments of thermo chemical convection have dealt with systems involving fluids with different intrinsic densities and viscosities in a Rayleigh-Bénard setup. Although these experiments have greatly improved our understanding of the Earth's mantle dynamics, they neglect a fundamental component of planetary convection: internal heat sources. We have developed a microwave-based method in order to study convection and mixing in systems involving two layers of fluid with different densities, viscosities, and internal heat production rates. Our innovative laboratory experiments are appropriate for the early Earth, when the lowermost mantle was likely enriched in incompatible and heat producing elements and when the heat flux from the core probably accounted for a small fraction of the mantle heat budget. They are also relevant to the present-day mantle if one considers that radioactive decay and secular cooling contribute both to internal heating. Our goal is to quantify how two fluid layers mix, which is still very difficult to resolve accurately in 3-D numerical calculations. Viscosities and microwave absorptions are tuned to achieve high values of the Rayleigh-Roberts and Prandtl numbers relevant for planetary convection. We start from a stably stratified system where the lower layer has higher internal heat production and density than the upper layer. Due to mixing, the amount of enriched material gradually decreases to zero over a finite time called the lifetime. Based on more than 30 experiments, we have derived a scaling law that relates the lifetime of an enriched reservoir to the layer thickness ratio, a, to the density and viscosity contrasts between the two layers, and to their two different internal heating rates in the form of an enrichment factor beta=1+2*a*H1/H, where H1 is the heating rate of the lower fluid and H is the average heating rate. We find that the lifetime of the lower enriched reservoir varies as beta**(-7/3) in the low
Hamiltonian Description of Convective-cell Generation
International Nuclear Information System (INIS)
Krommes, J.A.; Kolesnikov, R.A.
2004-01-01
The nonlinear statistical growth rate eq for convective cells driven by drift-wave (DW) interactions is studied with the aid of a covariant Hamiltonian formalism for the gyrofluid nonlinearities. A statistical energy theorem is proven that relates eq to a second functional tensor derivative of the DW energy. This generalizes to a wide class of systems of coupled partial differential equations a previous result for scalar dynamics. Applications to (i) electrostatic ion-temperature-gradient-driven modes at small ion temperature, and (ii) weakly electromagnetic collisional DW's are noted
Hayat, Tasawar; Ashraf, Muhammad Bilal; Alsulami, Hamed H; Alhuthali, Muhammad Shahab
2014-01-01
The objective of present research is to examine the thermal radiation effect in three-dimensional mixed convection flow of viscoelastic fluid. The boundary layer analysis has been discussed for flow by an exponentially stretching surface with convective conditions. The resulting partial differential equations are reduced into a system of nonlinear ordinary differential equations using appropriate transformations. The series solutions are developed through a modern technique known as the homotopy analysis method. The convergent expressions of velocity components and temperature are derived. The solutions obtained are dependent on seven sundry parameters including the viscoelastic parameter, mixed convection parameter, ratio parameter, temperature exponent, Prandtl number, Biot number and radiation parameter. A systematic study is performed to analyze the impacts of these influential parameters on the velocity and temperature, the skin friction coefficients and the local Nusselt number. It is observed that mixed convection parameter in momentum and thermal boundary layers has opposite role. Thermal boundary layer is found to decrease when ratio parameter, Prandtl number and temperature exponent are increased. Local Nusselt number is increasing function of viscoelastic parameter and Biot number. Radiation parameter on the Nusselt number has opposite effects when compared with viscoelastic parameter.
Directory of Open Access Journals (Sweden)
MD. FAISAL KADER
2012-10-01
Full Text Available In the present paper, the effect of solar radiation on automobiles has been studied by both experimentally and numerically. The numerical solution is done by an operation friendly and fast CFD code – SC/Tetra with a full scale model of a SM3 car and turbulence is modeled by the standard k-ε equation. Numerical analysis of the three-dimensional model predicts a detailed description of fluid flow and temperature distribution in the passenger compartment during both the natural convection due to the incoming solar radiation and mixed convection due to the flow from defrost nozzle and radiation. It can be seen that solar radiation is an important parameter to raise the compartment temperature above the ambient temperature during summer. During natural convection, the rate of heat transfer is fast at the initial period. In the mixed convection analyses, it is found that the temperature drops down to a comfortable range almost linearly at the initial stage. Experimental investigations are performed to determine the temperature contour on the windshield and the local temperature at a particular point for further validation of the numerical results.
Choudhury, Devanil; Das, Someshwar
2017-06-01
The Advanced Research WRF (ARW) model is used to simulate Very Severe Cyclonic Storms (VSCS) Hudhud (7-13 October, 2014), Phailin (8-14 October, 2013) and Lehar (24-29 November, 2013) to investigate the sensitivity to microphysical schemes on the skill of forecasting track and intensity of the tropical cyclones for high-resolution (9 and 3 km) 120-hr model integration. For cloud resolving grid scale (CONTROL forecast. This study is aimed to investigate the sensitivity to microphysics on the track and intensity with explicitly resolved convection scheme. It shows that the Goddard one-moment bulk liquid-ice microphysical scheme provided the highest skill on the track whereas for intensity both Thompson and Goddard microphysical schemes perform better. The Thompson scheme indicates the highest skill in intensity at 48, 96 and 120 hr, whereas at 24 and 72 hr, the Goddard scheme provides the highest skill in intensity. It is known that higher resolution domain produces better intensity and structure of the cyclones and it is desirable to resolve the convection with sufficiently high resolution and with the use of explicit cloud physics. This study suggests that the Goddard cumulus ensemble microphysical scheme is suitable for high resolution ARW simulation for TC's track and intensity over the BoB. Although the present study is based on only three cyclones, it could be useful for planning real-time predictions using ARW modelling system.
Energy Technology Data Exchange (ETDEWEB)
Xue, Lulin [National Center for Atmospheric Research, Boulder, Colorado; Fan, Jiwen [Pacific Northwest National Laboratory, Richland, Washington; Lebo, Zachary J. [University of Wyoming, Laramie, Wyoming; Wu, Wei [National Center for Atmospheric Research, Boulder, Colorado; University of Illinois at Urbana–Champaign, Urbana, Illinois; Morrison, Hugh [National Center for Atmospheric Research, Boulder, Colorado; Grabowski, Wojciech W. [National Center for Atmospheric Research, Boulder, Colorado; Chu, Xia [University of Wyoming, Laramie, Wyoming; Geresdi, István [University of Pécs, Pécs, Hungary; North, Kirk [McGill University, Montréal, Québec, Canada; Stenz, Ronald [University of North Dakota, Grand Forks, North Dakota; Gao, Yang [Pacific Northwest National Laboratory, Richland, Washington; Lou, Xiaofeng [Chinese Academy of Meteorological Sciences, Beijing, China; Bansemer, Aaron [National Center for Atmospheric Research, Boulder, Colorado; Heymsfield, Andrew J. [National Center for Atmospheric Research, Boulder, Colorado; McFarquhar, Greg M. [National Center for Atmospheric Research, Boulder, Colorado; University of Illinois at Urbana–Champaign, Urbana, Illinois; Rasmussen, Roy M. [National Center for Atmospheric Research, Boulder, Colorado
2017-12-01
The squall line event on May 20, 2011, during the Midlatitude Continental Convective Clouds (MC3E) field campaign has been simulated by three bin (spectral) microphysics schemes coupled into the Weather Research and Forecasting (WRF) model. Semi-idealized three-dimensional simulations driven by temperature and moisture profiles acquired by a radiosonde released in the pre-convection environment at 1200 UTC in Morris, Oklahoma show that each scheme produced a squall line with features broadly consistent with the observed storm characteristics. However, substantial differences in the details of the simulated dynamic and thermodynamic structure are evident. These differences are attributed to different algorithms and numerical representations of microphysical processes, assumptions of the hydrometeor processes and properties, especially ice particle mass, density, and terminal velocity relationships with size, and the resulting interactions between the microphysics, cold pool, and dynamics. This study shows that different bin microphysics schemes, designed to be conceptually more realistic and thus arguably more accurate than bulk microphysics schemes, still simulate a wide spread of microphysical, thermodynamic, and dynamic characteristics of a squall line, qualitatively similar to the spread of squall line characteristics using various bulk schemes. Future work may focus on improving the representation of ice particle properties in bin schemes to reduce this uncertainty and using the similar assumptions for all schemes to isolate the impact of physics from numerics.
Rasmussen, K. L.; Prein, A. F.; Rasmussen, R. M.; Ikeda, K.; Liu, C.
2017-11-01
Novel high-resolution convection-permitting regional climate simulations over the US employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two continuous 13-year simulations were conducted using (1) ERA-Interim reanalysis and (2) ERA-Interim reanalysis plus a climate perturbation for the RCP8.5 scenario. The simulations adequately reproduce the observed precipitation diurnal cycle, indicating that they capture organized and propagating convection that most climate models cannot adequately represent. This study shows that weak to moderate convection will decrease and strong convection will increase in frequency in a future climate. Analysis of the thermodynamic environments supporting convection shows that both convective available potential energy (CAPE) and convective inhibition (CIN) increase downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a warming climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and provides an environment where CAPE can build to extreme levels that may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5 °C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting water and energy budgets on Earth.
Lang, S. E.; Tao, W. K.; Wu, D.
2016-12-01
The Goddard Convective-Stratiform Heating (or CSH) algorithm is used to retrieve estimates of cloud heating over the global Tropics using TRMM rainfall data and a set of look-up-tables (LUTs) derived from a series of multi-week cloud-resolving model (CRM) simulations using the Goddard Cumulus Ensemble model (or GCE). These simulations link satellite observables (i.e., surface rainfall and stratiform fraction) with cloud heating profiles, which are not directly observable. The strength of the algorithm relies in part on the representativeness of the simulations; more realistic simulations provide a stronger link between the observables and simulated heating profiles. The current "TRMM" version of the CSH algorithm relies on 2D GCE simulations using an improved version of the Goddard 3-class ice scheme (3ICE), a moderate-sized domain, and 1-km horizontal resolution. Updating the LUTs, which are suitable for tropical and continental summertime environments requires new, more realistic GCE simulations. New simulations are performed using a new, improved 4-class ice scheme, which has been shown to outperform the 3ICE scheme, especially for intense convection. Additional grid configurations are also tested and evaluated to find the best overall setup to for re-deriving and updating the CSH tropical/summertime LUTs.
Stratiform/convective rain delineation for TRMM microwave imager
Islam, Tanvir; Srivastava, Prashant K.; Dai, Qiang; Gupta, Manika; Wan Jaafar, Wan Zurina
2015-10-01
This article investigates the potential for using machine learning algorithms to delineate stratiform/convective (S/C) rain regimes for passive microwave imager taking calibrated brightness temperatures as only spectral parameters. The algorithms have been implemented for the Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI), and calibrated as well as validated taking the Precipitation Radar (PR) S/C information as the target class variables. Two different algorithms are particularly explored for the delineation. The first one is metaheuristic adaptive boosting algorithm that includes the real, gentle, and modest versions of the AdaBoost. The second one is the classical linear discriminant analysis that includes the Fisher's and penalized versions of the linear discriminant analysis. Furthermore, prior to the development of the delineation algorithms, a feature selection analysis has been conducted for a total of 85 features, which contains the combinations of brightness temperatures from 10 GHz to 85 GHz and some derived indexes, such as scattering index, polarization corrected temperature, and polarization difference with the help of mutual information aided minimal redundancy maximal relevance criterion (mRMR). It has been found that the polarization corrected temperature at 85 GHz and the features derived from the "addition" operator associated with the 85 GHz channels have good statistical dependency to the S/C target class variables. Further, it has been shown how the mRMR feature selection technique helps to reduce the number of features without deteriorating the results when applying through the machine learning algorithms. The proposed scheme is able to delineate the S/C rain regimes with reasonable accuracy. Based on the statistical validation experience from the validation period, the Matthews correlation coefficients are in the range of 0.60-0.70. Since, the proposed method does not rely on any a priori information, this makes it very
DYNAMICS OF TURBULENT CONVECTION AND CONVECTIVE OVERSHOOT IN A MODERATE-MASS STAR
Energy Technology Data Exchange (ETDEWEB)
Kitiashvili, I. N.; Mansour, N. N.; Wray, A. A. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Kosovichev, A. G., E-mail: irina.n.kitiashvili@nasa.gov [New Jersey Institute of Technology, Newark, NJ 07102 (United States)
2016-04-10
We present results of realistic three-dimensional (3D) radiative hydrodynamic simulations of the outer layers of a moderate-mass star (1.47 M {sub ⊙}), including the full convection zone, the overshoot region, and the top layers of the radiative zone. The simulation results show that the surface granulation has a broad range of scales, from 2 to 12 Mm, and that large granules are organized in well-defined clusters, consisting of several granules. Comparison of the mean structure profiles from 3D simulations with the corresponding one-dimensional (1D) standard stellar model shows an increase of the stellar radius by ∼800 km, as well as significant changes in the thermodynamic structure and turbulent properties of the ionization zones. Convective downdrafts in the intergranular lanes between granulation clusters reach speeds of more than 20 km s{sup −1}, penetrate through the whole convection zone, hit the radiative zone, and form an 8 Mm thick overshoot layer. Contrary to semi-empirical overshooting models, our results show that the 3D dynamic overshoot region consists of two layers: a nearly adiabatic extension of the convection zone and a deeper layer of enhanced subadiabatic stratification. This layer is formed because of heating caused by the braking of the overshooting convective plumes. This effect has to be taken into account in stellar modeling and the interpretation of asteroseismology data. In particular, we demonstrate that the deviations of the mean structure of the 3D model from the 1D standard model of the same mass and composition are qualitatively similar to the deviations for the Sun found by helioseismology.
Decoupling schemes for the SSC Collider
International Nuclear Information System (INIS)
Cai, Y.; Bourianoff, G.; Cole, B.; Meinke, R.; Peterson, J.; Pilat, F.; Stampke, S.; Syphers, M.; Talman, R.
1993-05-01
A decoupling system is designed for the SSC Collider. This system can accommodate three decoupling schemes by using 44 skew quadrupoles in the different configurations. Several decoupling schemes are studied and compared in this paper
Decoupling schemes for the SCC Collider
International Nuclear Information System (INIS)
Cai, Y.; Bourianoff, G.; Cole, B.; Meinke, R.; Peterson, J.; Pilat, F.; Stampke, S.; Syphers, M.; Talman, R.
1993-01-01
A decoupling system is designed for the SSC Collider. This system can accommodate three decoupling schemes by using 44 skew quadrupoles in the different configurations. Several decoupling schemes are studied and compared in this paper
TVD schemes for open channel flow
Delis, A. I.; Skeels, C. P.
1998-04-01
The Saint Venant equations for modelling flow in open channels are solved in this paper, using a variety of total variation diminishing (TVD) schemes. The performance of second- and third-order-accurate TVD schemes is investigated for the computation of free-surface flows, in predicting dam-breaks and extreme flow conditions created by the river bed topography. Convergence of the schemes is quantified by comparing error norms between subsequent iterations. Automatically calculated time steps and entropy corrections allow high CFL numbers and smooth transition between different conditions. In order to compare different approaches with TVD schemes, the most accurate of each type was chosen. All four schemes chosen proved acceptably accurate. However, there are important differences between the schemes in the occurrence of clipping, overshooting and oscillating behaviour and in the highest CFL numbers allowed by a scheme. These variations in behaviour stem from the different orders and inherent properties of the four schemes.
Algebraic K-theory of generalized schemes
DEFF Research Database (Denmark)
Anevski, Stella Victoria Desiree
Nikolai Durov has developed a generalization of conventional scheme theory in which commutative algebraic monads replace commutative unital rings as the basic algebraic objects. The resulting geometry is expressive enough to encompass conventional scheme theory, tropical algebraic geometry and ge...
Algebraic K-theory of generalized schemes
DEFF Research Database (Denmark)
Anevski, Stella Victoria Desiree
Nikolai Durov has developed a generalization of conventional scheme theory in which commutative algebraic monads replace commutative unital rings as the basic algebraic objects. The resulting geometry is expressive enough to encompass conventional scheme theory, tropical algebraic geometry...
A high-order solver for aerodynamic flow simulations and comparison of different numerical schemes
Mikhaylov, Sergey; Morozov, Alexander; Podaruev, Vladimir; Troshin, Alexey
2017-11-01
An implementation of high order of accuracy Discontinuous Galerkin method is presented. Reconstruction is done for the conservative variables. Gradients are calculated using the BR2 method. Coordinate transformations are done by serendipity elements. In computations with schemes of order higher than 2, curvature of the mesh lines is taken into account. A comparison with finite volume methods is performed, including WENO method with linear weights and single quadrature point on a cell side. The results of the following classical tests are presented: subsonic flow around a circular cylinder in an ideal gas, convection of two-dimensional isentropic vortex, and decay of the Taylor-Green vortex.
Positivity-preserving high-resolution schemes for systems of conservation laws
Parent, Bernard
2012-01-01
A new class of flux-limited schemes for systems of conservation laws is presented that is both high-resolution and positivity-preserving. The schemes are obtained by extending the Steger-Warming method to second-order accuracy through the use of component-wise TVD flux limiters while ensuring that the coefficients of the discretization equation are positive. A coefficient is considered positive if it has all-positive eigenvalues and has the same eigenvectors as those of the convective flux Jacobian evaluated at the corresponding node. For certain systems of conservation laws, such as the Euler equations for instance, this condition is sufficient to guarantee positivity-preservation. The method proposed is advantaged over previous positivity-preserving flux-limited schemes by being capable to capture with high resolution all wave types (including contact discontinuities, shocks, and expansion fans). Several test cases are considered in which the Euler equations in generalized curvilinear coordinates are solved in 1D, 2D, and 3D. The test cases confirm that the proposed schemes are positivity-preserving while not being significantly more dissipative than the conventional TVD methods. The schemes are written in general matrix form and can be used to solve other systems of conservation laws, as long as they are homogeneous of degree one.
Mechanisms initiating deep convection over complex terrain during COPS
Directory of Open Access Journals (Sweden)
Christoph Kottmeier
2008-12-01
Full Text Available Precipitating convection in a mountain region of moderate topography is investigated, with particular emphasis on its initiation in response to boundary-layer and mid- and upper-tropospheric forcing mechanisms. The data used in the study are from COPS (Convective and Orographically-induced Precipitation Study that took place in southwestern Germany and eastern France in the summer of 2007. It is found that the initiation of precipitating convection can be roughly classified as being due to either: (i surface heating and low-level flow convergence; (ii surface heating and moisture supply overcoming convective inhibition during latent and/or potential instability; or (iii mid-tropospheric dynamical processes due to mesoscale convergence lines and forced mean vertical motion. These phenomena have to be adequately represented in models in order to improve quantitative precipitation forecast. Selected COPS cases are analysed and classified into these initiation categories. Although only a subset of COPS data (mainly radiosondes, surface weather stations, radar and satellite data are used here, it is shown that convective systems are captured in considerable detail by sensor synergy. Convergence lines were observed by Doppler radar in the location where deep convection is triggered several hours later. The results suggest that in many situations, observations of the location and timing of convergence lines will facilitate the nowcasting of convection. Further on, forecasting of the initiation of convection is significantly complicated if advection of potentially convective air masses over changing terrain features plays a major role. The passage of a frontal structure over the Vosges - Rhine valley - Black Forest orography was accompanied by an intermediate suppression of convection over the wide Rhine valley. Further downstream, an intensification of convection was observed over the Black Forest due to differential surface heating, a convergence line
Convective initiation in the vicinity of the subtropical Andes
Rasmussen, K. L.; Houze, R.
2014-12-01
Extreme convection tends to form in the vicinity of mountain ranges, and the Andes in subtropical South America help spawn some of the most intense convection in the world. An investigation of the most intense storms for 11 years of TRMM Precipitation Radar (PR) data shows a tendency for squall lines to initiate and develop in this region with the canonical leading convective line/trailing stratiform structure. The synoptic environment and structures of the extreme convection and MCSs in subtropical South America are similar to those found in other regions of the world, especially the United States. In subtropical South America, however, the topographical influence on the convective initiation and maintenance of the MCSs is unique. A capping inversion in the lee of the Andes is important in preventing premature triggering. The Andes and other mountainous terrain of Argentina focus deep convective initiation in a narrow region. Subsequent to initiation, the convection often evolves into propagating mesoscale convective systems similar to those seen over the Great Plains of the U. S. and produces damaging tornadoes, hail, and floods across a wide agricultural region. Numerical simulations conducted with the NCAR Weather Research and Forecasting (WRF) Model extend the observational analysis and provide an objective evaluation of storm initiation, terrain effects, and development mechanisms. The simulated mesoscale systems closely resemble the storm structures seen by the TRMM Precipitation Radar as well as the overall shape and character of the storms shown in GOES satellite data. A sensitivity experiment with different configurations of topography, including both decreasing and increasing the height of the Andes Mountains, provides insight into the significant influence of orography in focusing convective initiation in this region. Lee cyclogenesis and a strong low-level jet are modulated by the height of the Andes Mountains and directly affect the character
MIRD radionuclide data and decay schemes
Eckerman, Keith F
2007-01-01
For all physicians, scientists, and physicists working in the nuclear medicine field, the MIRD: Radionuclide Data and Decay Schemes updated edition is an essential sourcebook for radiation dosimetry and understanding the properties of radionuclides. Includes CD Table of Contents Decay schemes listed by atomic number Radioactive decay processes Serial decay schemes Decay schemes and decay tables This essential reference for nuclear medicine physicians, scientists and physicists also includes a CD with tabulations of the radionuclide data necessary for dosimetry calculations.
Secret Sharing Schemes and Advanced Encryption Standard
2015-09-01
Secret Sharing Scheme, they have only been better under certain parameters; there is always a trade -off with some parameter of the scheme. xiv...NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS SECRET SHARING SCHEMES AND ADVANCED ENCRYPTION STANDARD by Bing Yong Lim September 2015 Thesis...AND SUBTITLE SECRET SHARING SCHEMES AND ADVANCED ENCRYPTION STANDARD 5. FUNDING NUMBERS 6. AUTHOR(S) Lim, Bin Yong 7. PERFORMING ORGANIZATION NAME(S
Tightly Secure Signatures From Lossy Identification Schemes
Abdalla , Michel; Fouque , Pierre-Alain; Lyubashevsky , Vadim; Tibouchi , Mehdi
2015-01-01
International audience; In this paper, we present three digital signature schemes with tight security reductions in the random oracle model. Our first signature scheme is a particularly efficient version of the short exponent discrete log-based scheme of Girault et al. (J Cryptol 19(4):463–487, 2006). Our scheme has a tight reduction to the decisional short discrete logarithm problem, while still maintaining the non-tight reduction to the computational version of the problem upon which the or...
Venusian Applications of 3D Convection Modeling
Bonaccorso, Timary Annie
2011-01-01
This study models mantle convection on Venus using the 'cubed sphere' code OEDIPUS, which models one-sixth of the planet in spherical geometry. We are attempting to balance internal heating, bottom mantle viscosity, and temperature difference across Venus' mantle, in order to create a realistic model that matches with current planetary observations. We also have begun to run both lower and upper mantle simulations to determine whether layered (as opposed to whole-mantle) convection might produce more efficient heat transfer, as well as to model coronae formation in the upper mantle. Upper mantle simulations are completed using OEDIPUS' Cartesian counterpart, JOCASTA. This summer's central question has been how to define a mantle plume. Traditionally, we have defined a hot plume the region with temperature at or above 40% of the difference between the maximum and horizontally averaged temperature, and a cold plume as the region with 40% of the difference between the minimum and average temperature. For less viscous cases (1020 Pa?s), the plumes generated by that definition lacked vigor, displaying buoyancies 1/100th of those found in previous, higher viscosity simulations (1021 Pa?s). As the mantle plumes with large buoyancy flux are most likely to produce topographic uplift and volcanism, the low viscosity cases' plumes may not produce observable deformation. In an effort to eliminate the smallest plumes, we experimented with different lower bound parameters and temperature percentages.
Forced convection heat transfer in He II
International Nuclear Information System (INIS)
Kashani, A.
1986-01-01
An investigation of forced convection heat transfer in He II is conducted. The study includes both experimental and theoretical treatments of the problem. The experiment consists of a hydraulic pump and a copper flow tube, 3 mm in ID and 2m long. The system allows measurements of one-dimensional heat and mass transfer in He II. The heat transfer experiments are performed by applying heat at the midpoint along the length of the flow tube. Two modes of heat input are employed, i.e., step function heat input and square pulse heat input. The heat transfer results are discussed in terms of temperature distribution in the tube. The experimental temperature profiles are compared with numerical solutions of an analytical model developed from the He II energy equation. The bath temperature is set at three different values of 1.65, 1.80, and 1.95 K. The He II flow velocity is varied up to 90 cm/s. Pressure is monitored at each end of the flow tube, and the He II pressure drop is obtained for different flow velocities. Results indicate that He II heat transfer by forced convention is considerably higher than that by internal convection. The theoretical model is in close agreement with the experiment. He II pressure drop and friction factor are very similar to those of an ordinary fluid
Convective diffusion in protein crystal growth
Baird, J. K.; Meehan, E. J.; Xidis, A. L.; Howard, S. B.
1986-08-01
We considered a protein crystal in the form of a flat plate suspended in its parent solution so that the normal to the largest face was perpendicular to the acceleration due to gravity. For simplicity, the protein concentration in the solution adjacent to the plate was taken to be the equilibrium solubility. The bulk of the solution was supersaturated, however, which gave rise to a horizontal concentration gradient driving fluid toward the plate. We also took into account the diffusion of the dissolved protein with respect to the moving fluid. In the boundary layer next to the plate, we solved the Navier-Stokes equation and the equation for convective diffusion to determine the flow velocity and the protein mass flux. We found that, because of the convection, the local rate of growth of the plate varied strongly with depth. The variation was diminished by a factor of 1/30 when the local gravity was reduced from g to 10 -6g as occurs aboard the Space Shuttle in earth orbit. For an aqueous solution of lysozyme at a concentration of 40 mg/ml, the boundary layer at the top of a 1 mm high crystal has a thickness of 80 μm in earths gravity and 2570 μm in 10 -6g. We examined the optical transmission of the boundary layer and compared it with the "haloes" observed by Feher et al. about growing hemispherical crystals of lysozyme.
Thermal Convection on an Ablating Target
Mehmedagic, Igbal; Thangam, Siva
2015-11-01
Modeling and analysis of thermal convection of a metallic targets subject to radiative flux is of relevance to various manufacturing processes as well as for the development of protective shields. The present work involves the computational modeling of metallic targets subject to high heat fluxes that are both steady and pulsed. Modeling of the ablation and associated fluid dynamics when metallic surfaces are exposed to high intensity pulsed laser fluence at normal atmospheric conditions is considered. The incident energy from the laser is partly absorbed and partly reflected by the surface during ablation and subsequent vaporization of the convecting melt also participates in the radiative exchange. The energy distribution during the process between the bulk and vapor phase strongly depends on optical and thermodynamic properties of the irradiated material, radiation wavelength, and laser pulse intensity and duration. Computational findings based on effective representation and prediction of the heat transfer, melting and vaporization of the targeting material as well as plume formation and expansion are presented and discussed in the context of various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. Funded in part by U. S. Army ARDEC, Picatinny Arsenal, NJ.
Directory of Open Access Journals (Sweden)
Sabrina Wahl
2017-10-01
Full Text Available Atmospheric reanalyses are a state-of-the-art tool to generate consistent and realistic state estimates of the atmospheric system. They provide a synthesis of various heterogeneous observational systems and model simulations using a physical model together with a data assimilation scheme. Current reanalyses are mainly global, while regional reanalyses are emerging for North America, the polar region, and most recently for Europe. However, deep convection is still parameterized even in the regional reanalyses. A novel convective-scale regional reanalysis system for Central Europe (COSMO-REA2 has been developed by the Hans-Ertel Center for Weather Research – Climate Monitoring Branch. The system is based on the COSMO model and uses observational nudging for regional data assimilation. In addition to conventional observations, radar-derived rain rates are assimilated using latent heat nudging. With a horizontal grid-spacing of 2 km, the model runs without parameterization of deep moist convection. COSMO-REA2 produces horizontal wind fields that represent a realistic energy spectrum for horizontal scales above 14 km. COSMO-REA2 is currently available for seven years from 2007 to 2013.This study illustrates the improved representation of local precipitation over Germany by the convective-scale reanalysis COSMO-REA2 compared to coarser gridded European and global reanalyses. A systematic verification using rain gauge data reveals the added value of high-resolution regional atmospheric reanalyses on different time scales. On monthly to annual time scales, regional reanalyses yield better estimates of the spatial variability of precipitation patterns which can not be provided by coarser gridded global models. On hourly to daily time scales, the convective-scale reanalysis substantially improves the representation of local precipitation in two ways. On the one hand, COSMO-REA2 shows an enhanced representation of observed frequencies of local
Simulation of Deep Convective Clouds with the Dynamic Reconstruction Turbulence Closure
Shi, X.; Chow, F. K.; Street, R. L.; Bryan, G. H.
2017-12-01
The terra incognita (TI), or gray zone, in simulations is a range of grid spacing comparable to the most energetic eddy diameter. Spacing in mesoscale and simulations is much larger than the eddies, and turbulence is parameterized with one-dimensional vertical-mixing. Large eddy simulations (LES) have grid spacing much smaller than the energetic eddies, and use three-dimensional models of turbulence. Studies of convective weather use convection-permitting resolutions, which are in the TI. Neither mesoscale-turbulence nor LES models are designed for the TI, so TI turbulence parameterization needs to be discussed. Here, the effects of sub-filter scale (SFS) closure schemes on the simulation of deep tropical convection are evaluated by comparing three closures, i.e. Smagorinsky model, Deardorff-type TKE model and the dynamic reconstruction model (DRM), which partitions SFS turbulence into resolvable sub-filter scales (RSFS) and unresolved sub-grid scales (SGS). The RSFS are reconstructed, and the SGS are modeled with a dynamic eddy viscosity/diffusivity model. The RSFS stresses/fluxes allow backscatter of energy/variance via counter-gradient stresses/fluxes. In high-resolution (100m) simulations of tropical convection use of these turbulence models did not lead to significant differences in cloud water/ice distribution, precipitation flux, or vertical fluxes of momentum and heat. When model resolutions are coarsened, the Smagorinsky and TKE models overestimate cloud ice and produces large-amplitude downward heat flux in the middle troposphere (not found in the high-resolution simulations). This error is a result of unrealistically large eddy diffusivities, i.e., the eddy diffusivity of the DRM is on the order of 1 for the coarse resolution simulations, the eddy diffusivity of the Smagorinsky and TKE model is on the order of 100. Splitting the eddy viscosity/diffusivity scalars into vertical and horizontal components by using different length scales and strain rate
A study of aerosol indirect effects and feedbacks on convective precipitation
Da Silva, Nicolas; Mailler, Sylvain; Drobinski, Philippe
2017-04-01
Atmospheric aerosols from natural and anthropogenic origin are present in the troposphere of the Mediterranean basin and continental Europe, occasionnally reaching very high concentrations in air masses with a strong content of aerosols related to mineral dust emissions, wildfires, or anthropogenic contamination [1]. On the other hand precipitations in the Mediterranean basin need to be understood precisely since drought and extreme precipitation events are a part of Mediterranean climate which can strongly affect the people and the economic activity in the Mediterranean basin [2]. The present study is a contribution to the investigations on the effects of aerosols on precipitation in the Mediterranean basin and continental Europe. For that purpose, we used the Weather Research and Forecasting Model (WRF) parameterized with the Thompson aerosol-aware microphysics schemes, performing two sensitivity simulations forced with two different aerosol climatologies during six months covering an entire summer season on a domain, covering the Mediterranean basin and continental Europe at 50 km resolution. Aerosols may affect atmospheric dynamics through their direct and semidirect radiative effects as well as through their indirect effects (through the changes of cloud microphysics). While it is difficult to disentangle these differents effects in reality, numerical modelling with the WRF model make it possible to isolate indirect effects by modifying them without affecting the direct or semidirect effects of aerosols in an attempt to examine the effect of aerosols on precipitations through microphysical effects only. Our first results have shown two opposite responses depending whether the precipitation are convective or large-scale. Since convective precipitations seem to be clearly inhibited by increased concentrations of cloud-condensation nuclei, we attempted to understand which processes and feedbacks are involved in this reduction of parameterized convective
THROUGHPUT ANALYSIS OF EXTENDED ARQ SCHEMES
African Journals Online (AJOL)
PUBLICATIONS1
and Wait (SW), Selective Repeat (SR), Stutter. (ST) and Go-Back-N (GBN) (Lin and Costello,. 2003). Combinations of these schemes lead to mixed mode schemes which include the SR-. GBN, SR-ST1 and SR-ST2. In the mixed mode schemes, when a prescribed number of failures occur in the SR mode, the GBN or ST ...
Dodson, J. B.; Taylor, P. C.
2017-12-01
The number and varieties of both satellite cloud observations and cloud simulations are increasing rapidly. This create a challenge in identifying the best methods for quantifying the physical processes associated with deep convection, and then comparing convective observations with simulations. The use of satellite simulators in conjunction with model output is an increasingly popular method of comparison studies. However, the complexity of deep convective systems renders simplistic comparison metrics hazardous, possibly resulting is misleading or even contradicting conclusions. To investigate this, CloudSat observations of Amazonian deep convective cores (DCCs) and associated anvils are compared and contrasted with output from cloud resolving models in a manner that both highlights microphysical proprties of observed convection, and displays the effects of microphysical parameterizations on allowing robust comparisons. First, contoured frequency by altitude diagrams (CFAD) are calculated from the reflectivity fields of DCCs observed by CloudSat. This reveals two distinct modes of hydrometeor variability in the high level cloud region, with one dominated by snow and aggregates, and the other by large graupel and hail. Second, output from the superparameterized Community Atmospheric Model (SP-CAM) data are processed with the Quickbeam radar simulator to produce CFADs which can be compared with the observed CFADs. Two versions of SP-CAM are used, with one (version 4) having single-moment microphysics which excludes graupel/hail, and the other (version 5) a double-moment scheme with graupel. The change from version 4 to 5 improves the reflectivity CFAD, even without corresponding changes to non-hydrometeor fields such as vertical velocity. However, it does not produce a realistic double hydrometeor mode. Finally, the influences of microphysics are further tested in the System for Atmospheric Modeling (SAM), which allows for higher control over model parameters than
The Original Management Incentive Schemes
Richard T. Holden
2005-01-01
During the 1990s, the structure of pay for top corporate executives shifted markedly as the use of stock options greatly expanded. By the early 2000s, as the dot-com boom ended and the Nasdaq stock index melted down, these modern executive incentive schemes were being sharply questioned on many grounds—for encouraging excessive risk-taking and a short-run orientation, for being an overly costly and inefficient method of providing incentives, and even for tempting managers of firms like Enron,...
The mathematics of Ponzi schemes
Artzrouni, Marc
2009-01-01
A first order linear differential equation is used to describe the dynamics of an investment fund that promises more than it can deliver, also known as a Ponzi scheme. The model is based on a promised, unrealistic interest rate; on the actual, realized nominal interest rate; on the rate at which new deposits are accumulated and on the withdrawal rate. Conditions on these parameters are given for the fund to be solvent or to collapse. The model is fitted to data available on Charles...
Adaptive Optics Metrics & QC Scheme
Girard, Julien H.
2017-09-01
"There are many Adaptive Optics (AO) fed instruments on Paranal and more to come. To monitor their performances and assess the quality of the scientific data, we have developed a scheme and a set of tools and metrics adapted to each flavour of AO and each data product. Our decisions to repeat observations or not depends heavily on this immediate quality control "zero" (QC0). Atmospheric parameters monitoring can also help predict performances . At the end of the chain, the user must be able to find the data that correspond to his/her needs. In Particular, we address the special case of SPHERE."
Network Regulation and Support Schemes
DEFF Research Database (Denmark)
Ropenus, Stephanie; Schröder, Sascha Thorsten; Jacobsen, Henrik
2009-01-01
At present, there exists no explicit European policy framework on distributed generation. Various Directives encompass distributed generation; inherently, their implementation is to the discretion of the Member States. The latter have adopted different kinds of support schemes, ranging from feed-in...... tariffs to market-based quota systems, and network regulation approaches, comprising rate-of-return and incentive regulation. National regulation and the vertical structure of the electricity sector shape the incentives of market agents, notably of distributed generators and network operators...
Boiler startup under conditions of convective heating of the highly reactive coal dust
Zhuikov, A. V.; Kulagin, V. A.; Baranova, M. P.; Glushkov, D. O.
2016-12-01
Experimental research of conditions and characteristics of ignition of the pulverized coal (with a particle size of approximately 80 μm) of different-type brown coals (1B, 2B, and 3B) during convective heating by a heated airflow (at a temperature of 425-600°C and velocity of 1-5 m/s) is carried out. The use of low-inertia thermocouples, a high-speed video camera, and dedicated software has made it possible to determine the minimum oxidizer parameters needed for coal dust ignition, and the approximation dependences of a main characteristic of the process under study―ignition delay time―on the air temperature. Results of experimental studies provide a basis for developing an optimal scheme of the boiler startup without heavy oil, which differs from the known schemes by the relatively low energy consumption for fuel-burning initiation. By example of the BKZ 75-39FB boiler, the economic usefulness of applying the boiler startup without heavy oil is shown. This scheme can be implemented using the proposed ignition burner that functions as a part of the direct system of pulverized-fuel preparation.
Directory of Open Access Journals (Sweden)
Elizaveta V. Kolesnik
2017-10-01
Full Text Available Several schemes of the second-order approximation worked out in the literature for unstructured-grid-based computations of gasdynamic flows are described. The convective fluxes on the control-volume's faces are evaluated using Roe's approximate Riemann solver. The MUSCL approach with the use of various quasi-one-dimensional schemes of reconstruction of gasdynamic variables and limiters making the solution monotonic is applied in order to improve the approximation accuracy. Comparative analysis of the working capacity of the schemes under consideration has been carried out through solving two problems of inviscid gas flow. Namely, the transonic NACA-0012 airfoil flow and the superpersonic flow in a duct with a central ramp were computed. The smoothness of solution, obtained with different schemes, dissipativity features of the schemes and computational process stability were evaluated.
Solar wind effects on ionospheric convection: a review
DEFF Research Database (Denmark)
Lu, G.; Cowley, S.W.H.; Milan, S.E.
2002-01-01
), and travelling convection vortices (TCVs). Furthermore, the large-scale ionospheric convection configuration has also demonstrated a strong correspondence to variations in the interplanetary medium and substorm activity. This report briefly discusses the progress made over the past decade in studies...
Modelling of convection during solidification of metal and alloys
Indian Academy of Sciences (India)
The role of convection during solidification is studied with the help of a mathematical model. The effect of various mush models on convection and consequent macrosegregation is examined with the help of numerical simulations. The predicted macrosegregation profiles are compared with published experimental data.
Plains Elevated Convection at Night (PECAN) Experiment Science Plan
Energy Technology Data Exchange (ETDEWEB)
Turner, D [National Oceanic and Atmospheric Administration; Parsons, D [NCAR; Geerts, B [Department of Atmospheric Science, University of Wyoming
2015-03-01
The Plains Elevated Convection at Night (PECAN) experiment is a large field campaign that is being supported by the National Science Foundation (NSF) with contributions from the National Oceanic and Atmospheric Administration (NOAA), the National Atmospheric and Space Administration (NASA), and the U.S. Department of Energy (DOE). The overarching goal of the PECAN experiment is to improve the understanding and simulation of the processes that initiate and maintain convection and convective precipitation at night over the central portion of the Great Plains region of the United States (Parsons et al. 2013). These goals are important because (1) a large fraction of the yearly precipitation in the Great Plains comes from nocturnal convection, (2) nocturnal convection in the Great Plains is most often decoupled from the ground and, thus, is forced by other phenomena aloft (e.g., propagating bores, frontal boundaries, low-level jets [LLJ], etc.), (3) there is a relative lack of understanding how these disturbances initiate and maintain nocturnal convection, and (4) this lack of understanding greatly hampers the ability of numerical weather and climate models to simulate nocturnal convection well. This leads to significant uncertainties in predicting the onset, location, frequency, and intensity of convective cloud systems and associated weather hazards over the Great Plains.
Transition to geostrophic convection: the role of the boundary conditions
Kunnen, R.P.J.; Ostilla-Monico, Rodolfo; van der Poel, Erwin; Verzicco, Roberto; Lohse, Detlef
2016-01-01
Rotating Rayleigh–Bénard convection, the flow in a rotating fluid layer heated from below and cooled from above, is used to analyse the transition to the geostrophic regime of thermal convection. In the geostrophic regime, which is of direct relevance to most geo- and astrophysical flows, the system
Using naive Bayes classifier for classification of convective rainfall ...
Indian Academy of Sciences (India)
convective clouds using SEVIRI data. 1. Introduction ... needed to sup- port convective rain generation with the so-called ... Data and methods. 2.1 Satellite and radar data. The dataset used in this study is MSG/SEVIRI data and corresponding ground-based radar data. Aiming to achieve comparability of these types of data ...
Temperature-dependent viscosity effects on free convection flow ...
African Journals Online (AJOL)
Temperature-dependent viscosity effects on free convection flow over a vertical moving cylinder with constant axial velocity under consideration of radial ... Prandtl number, viscosity-variation parameter, thermal conductivity-variation parameter and magnetic parameter on free convection flow and heat transfer is discussed.
Free Convective Flow of a Reacting Fluid between Vertical Porous ...
African Journals Online (AJOL)
Free Convective Flow of a Reacting Fluid between Vertical Porous Plates. ... written in dimensionless forms. The resulting second order equations are solved to obtain expressions for the velocity, temperature, mass transfer skin friction, and rate of heat transfer. Keywords: Convective flow, reacting fluid, vertical porous plates ...
Link between convection and meridional gradient of sea surface ...
Indian Academy of Sciences (India)
A sensitivity analysis showed that the corresponding threshold for was 29°C. We hypothesise that the excess heating (∼1° C above the threshold for deep convection)required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.
Dielectrophoretic Rayleigh-Bénard convection under microgravity conditions.
Yoshikawa, H N; Tadie Fogaing, M; Crumeyrolle, O; Mutabazi, I
2013-04-01
Thermal convection in a dielectric fluid layer between two parallel plates subjected to an alternating electric field and a temperature gradient is investigated under microgravity conditions. A thermoelectric coupling resulting from the thermal variation of the electric permittivity of the fluid produces the dielectrophoretic (DEP) body force, which can be regarded as thermal buoyancy due to an effective gravity. This electric gravity can destabilize a stationary conductive state of the fluid to develop convection. The similarity of the DEP thermal convection with the Rayleigh-Bénard (RB) convection is examined by considering its behavior in detail by a linear stability theory and a two-dimensional direct numerical simulation. The results are analyzed from an energetic viewpoint and in the framework of the Ginzburg-Landau (GL) equation. The stabilizing effects of a thermoelectric feedback make the critical parameters different from those in the RB instability. The nonuniformity of the electric gravity arising from the finite variation of permittivity also affects the critical parameters. The characteristic constants of the GL equation are comparable with those for the RB convection. The heat transfer in the DEP convection is weaker than in the RB convection as a consequence of the feedback that impedes the convection.
Heat removal by natural convection in a RPR reactor
International Nuclear Information System (INIS)
Sampaio, P.A.B. de
1987-01-01
In this paper natural convection in RPR reactor is analysed. The effect of natural convection valves size on cladding temperature is studied. The reactor channel heat transfer problem is solved using finite elements in a two-dimensional analysis. Results show that two valves with Φ = 0.16 m are suited to keep coolant and cladding temperatures below 73 0 C. (author) [pt
Convection diagnosis and nowcasting for oceanic aviation applications
Kessinger, Cathy; Donovan, Michael; Bankert, Richard; Williams, Earle; Hawkins, Jeffrey; Cai, Huaqing; Rehak, Nancy; Megenhardt, Daniel; Steiner, Matthias
2008-08-01
An oceanic convection diagnosis and nowcasting system is described whose domain of interest is the region between the southern continental United States and the northern extent of South America. In this system, geostationary satellite imagery are used to define the locations of deep convective clouds through the weighted combination of three independent algorithms. The resultant output, called the Convective Diagnosis Oceanic (CDO) product, is independently validated against space-borne radar and lighting products from the Tropical Rainfall Measuring Mission (TRMM) satellite to ascertain the ability of the CDO to discriminate hazardous convection. The CDO performed well in this preliminary investigation with some limitations noted. Short-term, 1-hr and 2-hr nowcasts of convection location are performed within the Convective Nowcasting Oceanic (CNO) system using a storm tracker. The CNO was found to have good statistical performance at extrapolating existing storm positions. Current work includes the development and implementation of additional atmospheric features for nowcasting convection initiation and to improve nowcasting of mature convection evolution.
Efficiency of Heat Transfer in Turbulent Rayleigh-Benard Convection
Czech Academy of Sciences Publication Activity Database
Urban, Pavel; Musilová, Věra; Skrbek, L.
2011-01-01
Roč. 107, č. 1 (2011), 014302:1-4 ISSN 0031-9007 R&D Projects: GA AV ČR KJB200650902 Institutional research plan: CEZ:AV0Z20650511 Keywords : natural convection * thermal convection Subject RIV: BK - Fluid Dynamics Impact factor: 7.370, year: 2011
REMINDER: Saved Leave Scheme (SLS)
2003-01-01
Transfer of leave to saved leave accounts Under the provisions of the voluntary saved leave scheme (SLS), a maximum total of 10 days'* annual and compensatory leave (excluding saved leave accumulated in accordance with the provisions of Administrative Circular No 22B) can be transferred to the saved leave account at the end of the leave year (30 September). We remind you that unused leave of all those taking part in the saved leave scheme at the closure of the leave year accounts is transferred automatically to the saved leave account on that date. Therefore, staff members have no administrative steps to take. In addition, the transfer, which eliminates the risk of omitting to request leave transfers and rules out calculation errors in transfer requests, will be clearly shown in the list of leave transactions that can be consulted in EDH from October 2003 onwards. Furthermore, this automatic leave transfer optimizes staff members' chances of benefiting from a saved leave bonus provided that they ar...
Stratiform Precipitation in Regions of Convection: A Meteorological Paradox?.
Houze, Robert A., Jr.
1997-10-01
It was once generally thought that stratiform precipitation was something occurring primarily, if not exclusively, in middle latitudes-in baroclinic cyclones and fronts. Early radar observations in the Tropics, however, showed large radar echoes composed of convective rain alongside stratiform precipitation, with the stratiform echoes covering great areas and accounting for a large portion of the tropical rainfall. These observations seemed paradoxical, since stratiform precipitation should not have been occurring in the Tropics, where baroclinic cyclones do not occur. Instead it was falling from convection-generated clouds, generally thought to be too violent to be compatible with the layered, gently settling behavior of stratiform precipitation.In meteorology, convection is a dynamic concept; specifically, it is the rapid, efficient, vigorous overturning of the atmosphere required to neutralize an unstable vertical distribution of moist static energy. Most clouds in the Tropics are convection-generated cumulonimbus. These cumulonimbus clouds contain an evolving pattern of newer and older precipitation. The young portions of the cumulonimbus are too violent to produce stratiform precipitation. In young, vigorous convective regions of the cumulonimbus, precipitation particles increase their mass by collection of cloud water, and the particles fall out in heavy showers, which appear on radar as vertically oriented convective "cells." In regions of older convection, however, the vertical air motions are generally weaker, and the precipitation particles drift downward, with the particles increasing their mass by vapor diffusion. In these regions the radar echoes are stratiform, and typically these echoes occur adjacent to regions of younger convective showers. Thus, the stratiform and convective precipitation both occur within the same complex of convection-generated cumulonimbus cloud.The feedbacks of the apparent heat source and moisture sink of tropical
Arbitrated quantum signature scheme using Bell states
International Nuclear Information System (INIS)
Li Qin; Chan, W. H.; Long Dongyang
2009-01-01
In an arbitrated quantum signature scheme, the signatory signs the message and the receiver verifies the signature's validity with the assistance of the arbitrator. We present an arbitrated quantum signature scheme using two-particle entangled Bell states similar to the previous scheme using three-particle entangled Greenberger-Horne-Zeilinger states [G. H. Zeng and C. H. Keitel, Phys. Rev. A 65, 042312 (2002)]. The proposed scheme can preserve the merits in the original scheme while providing a higher efficiency in transmission and reducing the complexity of implementation.
Heat transfer of laminar mixed convection of liquid
Shang, De-Yi
2016-01-01
This book presents a new algorithm to calculate fluid flow and heat transfer of laminar mixed convection. It provides step-by-step tutorial help to learn quickly how to set up the theoretical and numerical models of laminar mixed convection, to consider the variable physical properties of fluids, to obtain the system of numerical solutions, to create a series of formalization equations for the convection heat transfer by using a curve-fitting approach combined with theoretical analysis and derivation. It presents the governing ordinary differential equations of laminar mixed convection, equivalently transformed by an innovative similarity transformation with the description of the related transformation process. A system of numerical calculations of the governing ordinary differential equations is presented for the water laminar mixed convection. A polynomial model is induced for convenient and reliable treatment of variable physical properties of liquids. The developed formalization equations of mixed convec...
Estimating Bulk Entrainment With Unaggregated and Aggregated Convection
Becker, Tobias; Bretherton, Christopher S.; Hohenegger, Cathy; Stevens, Bjorn
2018-01-01
To investigate how entrainment is influenced by convective organization, we use the ICON (ICOsahedral Nonhydrostatic) model in a radiative-convective equilibrium framework, with a 1 km spatial grid mesh covering a 600 by 520 km2 domain. We analyze two simulations, with unaggregated and aggregated convection, and find that, in the lower free troposphere, the bulk entrainment rate increases when convection aggregates. The increase of entrainment rate with aggregation is caused by a strong increase of turbulence in the close environment of updrafts, masking other effects like the increase of updraft size and of static stability with aggregation. Even though entrainment rate increases with aggregation, updraft buoyancy reduction through entrainment decreases because aggregated updrafts are protected by a moist shell. Parameterizations that wish to represent mesoscale convective organization would need to model this moist shell.
Neutral beam injection and plasma convection in a magnetic field
International Nuclear Information System (INIS)
Okuda, H.; Hiroe, S.
1988-06-01
Injection of a neutral beam into a plasma in a magnetic field has been studied by means of numerical plasma simulations. It is found that, in the absence of a rotational transform, the convection electric field arising from the polarization charges at the edges of the beam is dissipated by turbulent plasma convection, leading to anomalous plasma diffusion across the magnetic field. The convection electric field increases with the beam density and beam energy. In the presence of a rotational transform, polarization charges can be neutralized by the electron motion along the magnetic field. Even in the presence of a rotational transform, a steady-state convection electric field and, hence, anomalous plasma diffusion can develop when a neutral beam is constantly injected into a plasma. Theoretical investigations on the convection electric field are described for a plasma in the presence of rotational transform. 11 refs., 19 figs
The influence of convective current generator on the global current
Directory of Open Access Journals (Sweden)
V. N. Morozov
2006-01-01
Full Text Available The mathematical generalization of classical model of the global circuit with taking into account the convective current generator, working in the planetary boundary layer was considered. Convective current generator may be interpreted as generator, in which the electromotive force is generated by processes, of the turbulent transport of electrical charge. It is shown that the average potential of ionosphere is defined not only by the thunderstorm current generators, working at the present moment, but by the convective current generator also. The influence of the convective processes in the boundary layer on the electrical parameters of the atmosphere is not only local, but has global character as well. The numerical estimations, made for the case of the convective-unstable boundary layer demonstrate that the increase of the average potential of ionosphere may be of the order of 10% to 40%.
Convection and segregation in a flat rotating sandbox
Rietz, Frank; Stannarius, Ralf
2012-01-01
A flat box, almost completely filled with a mixture of granulate, is rotated slowly about its horizontal central axis. In this experiment, a regular vortex flow of the granular material is observed in the cell plane. These vortex structures have a superficial analogy to convection rolls in dissipative structures of ordinary liquids. Whereas in the latter, the origin of the convection can often be attributed to gradients e.g. of densities or surface tensions, there is no trivial explanation at present for the convection of the granulate in the rotating container. Despite the simplicity of the experiment, the underlying mechanisms for convection and segregation are difficult to extract. Here, we present a comprehensive experimental study of the patterns under various experimental conditions and propose a mechanism for the convection.
Patterns of granular convection and separation in narrow vibration bed
Liu, Chuanping; Wu, Ping; Wang, Li; Tong, Lige; Yin, Shaowu
2017-06-01
Granular convection/separation of single and binary component particles are studied in a narrow vibration bed, respectively. With filling the single light particles (molecular sieve beads), the bed exhibits five different states successively by increasing the vibration frequency f from 15Hz to 70 Hz (vibration strength Γ>3), as the global convection, symmetrical heap, unsymmetrical heap, local convection and pseudo solid. Comparatively, the granular bed of the single heavy particles (steel beads) is only in pseudo solid state at the above vibration condition. By filling binary component particles (molecular sieve and same size steel beads) instead of the single component, the bed shows similar convection state with that of the single molecular sieve beads, and the heavy steel beads are aggregated in the centre of convention roll as a core. Varying the initial distribution of binary component particles, the final convection and separation are not influenced, although the aggregation process of steel beads changes.
Dynamics of mixed convective-stably-stratified fluids
Couston, L.-A.; Lecoanet, D.; Favier, B.; Le Bars, M.
2017-09-01
We study the dynamical regimes of a density-stratified fluid confined between isothermal no-slip top and bottom boundaries (at temperatures Tt and Tb) via direct numerical simulation. The thermal expansion coefficient of the fluid is temperature dependent and chosen such that the fluid density is maximum at the inversion temperature Tb>Ti>Tt . Thus, the lower layer of the fluid is convectively unstable while the upper layer is stably stratified. We show that the characteristics of the convection change significantly depending on the degree of stratification of the stable layer. For strong stable stratification, the convection zone coincides with the fraction of the fluid that is convectively unstable (i.e., where T >Ti ), and convective motions consist of rising and sinking plumes of large density anomaly, as is the case in canonical Rayleigh-Bénard convection; internal gravity waves are generated by turbulent fluctuations in the convective layer and propagate in the upper layer. For weak stable stratification, we demonstrate that a large fraction of the stable fluid (i.e., with temperature T phenomenological description of the transition between the regimes of plume-dominated and entrainment-dominated convection through analysis of the differences in the heat transfer mechanisms, kinetic energy density spectra, and probability density functions for different stratification strengths. Importantly, we find that the effect of the stable layer on the convection decreases only weakly with increasing stratification strength, meaning that the dynamics of the stable layer and convection should be studied self-consistently in a wide range of applications.
Directory of Open Access Journals (Sweden)
Tasawar Hayat
Full Text Available Main objective of present study is to analyze the mixed convective peristaltic transport of water based nanofluids using five different nanoparticles i.e. (Al2O3, CuO, Cu, Ag and TiO2. Two thermal conductivity models namely the Maxwell's and Hamilton-Crosser's are used in this study. Hall and Joule heating effects are also given consideration. Convection boundary conditions are employed. Furthermore, viscous dissipation and heat generation/absorption are used to model the energy equation. Problem is simplified by employing lubrication approach. System of equations are solved numerically. Influence of pertinent parameters on the velocity and temperature are discussed. Also the heat transfer rate at the wall is observed for considered five nanofluids using the two phase models via graphs.
MHD Natural Convection with Convective Surface Boundary Condition over a Flat Plate
Directory of Open Access Journals (Sweden)
Mohammad M. Rashidi
2014-01-01
Full Text Available We apply the one parameter continuous group method to investigate similarity solutions of magnetohydrodynamic (MHD heat and mass transfer flow of a steady viscous incompressible fluid over a flat plate. By using the one parameter group method, similarity transformations and corresponding similarity representations are presented. A convective boundary condition is applied instead of the usual boundary conditions of constant surface temperature or constant heat flux. In addition it is assumed that viscosity, thermal conductivity, and concentration diffusivity vary linearly. Our study indicates that a similarity solution is possible if the convective heat transfer related to the hot fluid on the lower surface of the plate is directly proportional to (x--1/2 where x- is the distance from the leading edge of the solid surface. Numerical solutions of the ordinary differential equations are obtained by the Keller Box method for different values of the controlling parameters associated with the problem.
High resolution finite volume scheme for the quantum hydrodynamic equations
Lin, Chin-Tien; Yeh, Jia-Yi; Chen, Jiun-Yeu
2009-03-01
The theory of quantum fluid dynamics (QFD) helps nanotechnology engineers to understand the physical effect of quantum forces. Although the governing equations of quantum fluid dynamics and classical fluid mechanics have the same form, there are two numerical simulation problems must be solved in QFD. The first is that the quantum potential term becomes singular and causes a divergence in the numerical simulation when the probability density is very small and close to zero. The second is that the unitarity in the time evolution of the quantum wave packet is significant. Accurate numerical evaluations are critical to the simulations of the flow fields that are generated by various quantum fluid systems. A finite volume scheme is developed herein to solve the quantum hydrodynamic equations of motion, which significantly improve the accuracy and stability of this method. The QFD equation is numerically implemented within the Eulerian method. A third-order modified Osher-Chakravarthy (MOC) upwind-centered finite volume scheme was constructed for conservation law to evaluate the convective terms, and a second-order central finite volume scheme was used to map the quantum potential field. An explicit Runge-Kutta method is used to perform the time integration to achieve fast convergence of the proposed scheme. In order to meet the numerical result can conform to the physical phenomenon and avoid numerical divergence happening due to extremely low probability density, the minimum value setting of probability density must exceed zero and smaller than certain value. The optimal value was found in the proposed numerical approach to maintain a converging numerical simulation when the minimum probability density is 10 -5 to 10 -12. The normalization of the wave packet remains close to unity through a long numerical simulation and the deviations from 1.0 is about 10 -4. To check the QFD finite difference numerical computations, one- and two-dimensional particle motions were
High resolution finite volume scheme for the quantum hydrodynamic equations
International Nuclear Information System (INIS)
Lin, C.-T.; Yeh, J.-Y.; Chen, J.-Y.
2009-01-01
The theory of quantum fluid dynamics (QFD) helps nanotechnology engineers to understand the physical effect of quantum forces. Although the governing equations of quantum fluid dynamics and classical fluid mechanics have the same form, there are two numerical simulation problems must be solved in QFD. The first is that the quantum potential term becomes singular and causes a divergence in the numerical simulation when the probability density is very small and close to zero. The second is that the unitarity in the time evolution of the quantum wave packet is significant. Accurate numerical evaluations are critical to the simulations of the flow fields that are generated by various quantum fluid systems. A finite volume scheme is developed herein to solve the quantum hydrodynamic equations of motion, which significantly improve the accuracy and stability of this method. The QFD equation is numerically implemented within the Eulerian method. A third-order modified Osher-Chakravarthy (MOC) upwind-centered finite volume scheme was constructed for conservation law to evaluate the convective terms, and a second-order central finite volume scheme was used to map the quantum potential field. An explicit Runge-Kutta method is used to perform the time integration to achieve fast convergence of the proposed scheme. In order to meet the numerical result can conform to the physical phenomenon and avoid numerical divergence happening due to extremely low probability density, the minimum value setting of probability density must exceed zero and smaller than certain value. The optimal value was found in the proposed numerical approach to maintain a converging numerical simulation when the minimum probability density is 10 -5 to 10 -12 . The normalization of the wave packet remains close to unity through a long numerical simulation and the deviations from 1.0 is about 10 -4 . To check the QFD finite difference numerical computations, one- and two-dimensional particle motions were
Langenbrunner, B.; Neelin, J. D.
2016-12-01
Despite increasing complexity and process representation in global climate models (GCMs), accurate climate simulation is limited by uncertainties in sub-grid scale model physics, where cloud processes and precipitation occur, and the interaction with large-scale dynamics. Identifying highly sensitive parameters and constraining them against observations is therefore a valuable step in narrowing uncertainty. However, changes in parameterizations often improve some variables or aspects of the simulation while degrading others. This analysis addresses means of improving GCM simulation of present-day tropical Pacific climate in the face of these tradeoffs. Focusing on the deep convection scheme in the fully coupled Community Earth System Model (CESM) version 1, four parameters were systematically sampled, and a metamodel or model emulator was used to reconstruct the parameter space of this perturbed physics ensemble. Using this metamodel, a Pareto front is constructed to visualize multiobjective tradeoffs in model performance, and results highlight the most important aspects of model physics as well as the most sensitive parameter ranges. For example, parameter tradeoffs arise in the tropical Pacific where precipitation cannot improve without sea surface temperature getting worse. Tropical precipitation sensitivity is found to be highly nonlinear for low values of entrainment in convecting plumes, though it is fairly insensitive at the high end of the plausible range. Increasing the adjustment timescale for convective closure causes the centroid of tropical precipitation to vary as much as two degrees latitude, highlighting the effect these physics can have on large-scale features of the hydrological cycle. The optimization procedure suggests that simultaneously increasing the maximum downdraft mass flux fraction and the adjustment timescale can yield improvements to surface temperature and column water vapor without degrading the simulation of precipitation. These
Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport
Directory of Open Access Journals (Sweden)
C. R. Hoyle
2011-08-01
Full Text Available The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP, chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF. The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.
Convective towers detection using GPS radio occultations
DEFF Research Database (Denmark)
Biondi, Riccardo; Neubert, Torsten; Syndergaard, S.
an important role since they lead to deep convective activity. With this work we want to investigate if severe storms leave a significant signature in radio occultation profiles in the tropical tropopause layer. The GPS radio occultation (RO) technique is useful for studying severe weather phenomena because...... the GPS signals penetrate through clouds and allow measurements of atmospheric profiles related to temperature, pressure, and water vapour with high vertical resolution. Using tropical cyclone best track database and data from different GPS RO missions (COSMIC, GRACE, CHAMP, SACC and GPSMET), we selected...... 1194 profiles in a time window of 3 hours and a space window of 300 km from the eye of the cyclone. We show that the bending angle anomaly of a GPS RO signal is typically larger than the climatology above the tropopause. Comparisons with co-located radiosondes, climatology of tropopause altitudes...
Imaging convection and magnetism in the sun
Hanasoge, Shravan
2015-01-01
This book reviews the field of helioseismology and its outstanding challenges and also offers a detailed discussion of the latest computational methodologies. The focus is on the development and implementation of techniques to create 3-D images of convection and magnetism in the solar interior and to introduce the latest computational and theoretical methods to the interested reader. With the increasing availability of computational resources, demand for greater accuracy in the interpretation of helioseismic measurements and the advent of billion-dollar instruments taking high-quality observations, computational methods of helioseismology that enable probing the 3-D structure of the Sun have increasingly become central. This book will benefit students and researchers with proficiency in basic numerical methods, differential equations and linear algebra who are interested in helioseismology.
Convection patterns in a spherical fluid shell
Feudel, F.; Bergemann, K.; Tuckerman, L. S.; Egbers, C.; Futterer, B.; Gellert, M.; Hollerbach, R.
2011-04-01
Symmetry-breaking bifurcations have been studied for convection in a nonrotating spherical shell whose outer radius is twice the inner radius, under the influence of an externally applied central force field with a radial dependence proportional to 1/r5. This work is motivated by the GeoFlow experiment, which is performed under microgravity condition at the International Space Station where this particular central force can be generated. In order to predict the observable patterns, simulations together with path-following techniques and stability computations have been applied. Branches of axisymmetric, octahedral, and seven-cell solutions have been traced. The bifurcations producing them have been identified and their stability ranges determined. At higher Rayleigh numbers, time-periodic states with a complex spatiotemporal symmetry are found, which we call breathing patterns.
Design Aspects of the Rayleigh Convection Code
Featherstone, N. A.
2017-12-01
Understanding the long-term generation of planetary or stellar magnetic field requires complementary knowledge of the large-scale fluid dynamics pervading large fractions of the object's interior. Such large-scale motions are sensitive to the system's geometry which, in planets and stars, is spherical to a good approximation. As a result, computational models designed to study such systems often solve the MHD equations in spherical geometry, frequently employing a spectral approach involving spherical harmonics. We present computational and user-interface design aspects of one such modeling tool, the Rayleigh convection code, which is suitable for deployment on desktop and petascale-hpc architectures alike. In this poster, we will present an overview of this code's parallel design and its built-in diagnostics-output package. Rayleigh has been developed with NSF support through the Computational Infrastructure for Geodynamics and is expected to be released as open-source software in winter 2017/2018.
Convection naturelle dans un milieu poreux multicouche
Ould-Amer, Yacine; Slama, Saoussène
2007-01-01
International audience; Dans la présente étude, nous nous sommes intéressés à la convection naturelle dans une cavité carrée poreuse multicouche. Chaque couche de milieu poreux (trois dans la présente étude) est considérée homogène, isotrope et saturée par un seul fluide. Cette enceinte est supposée être chauffée à des températures différentes le long des parois latérales, les deux autres sont isolés. Dans le but de généraliser les résultats, les équations gouvernantes sont mises sous forme a...
Mixed convection in fluid superposed porous layers
Dixon, John M
2017-01-01
This Brief describes and analyzes flow and heat transport over a liquid-saturated porous bed. The porous bed is saturated by a liquid layer and heating takes place from a section of the bottom. The effect on flow patterns of heating from the bottom is shown by calculation, and when the heating is sufficiently strong, the flow is affected through the porous and upper liquid layers. Measurements of the heat transfer rate from the heated section confirm calculations. General heat transfer laws are developed for varying porous bed depths for applications to process industry needs, environmental sciences, and materials processing. Addressing a topic of considerable interest to the research community, the brief features an up-to-date literature review of mixed convection energy transport in fluid superposed porous layers.
Prediction of flow instability during natural convection
International Nuclear Information System (INIS)
Farhadi, Kazem
2005-01-01
The occurrence of flow excursion instability during passive heat removal for Tehran Research Reactor (TRR) has been analyzed at low-pressure and low-mass rate of flow conditions without boiling taking place. Pressure drop-flow rate characteristics in the general case are determined upon a developed code for this purpose. The code takes into account variations of different pressure drop components caused by different powers as well as different core inlet temperatures. The analysis revealed the fact that the instability can actually occur in the natural convection mode for a range of powers per fuel plates at a predetermined inlet temperature with fixed geometry of the core. Low mass rate of flow and high sub-cooling are the two important conditions for the occurrence of static instability in the TRR. The calculated results are compared with the existing data in the literature. (author)
Modes of convection in the magnetotail
International Nuclear Information System (INIS)
Baumjohann, Wolfgang
2002-01-01
The flow of plasma in the Earth's magnetotail cannot reach a steady state, since adiabatic convection would lead to exceedingly high pressure of the associated magnetic flux tubes closer to the Earth, the so-called pressure catastrophe. The natural way to avoid the pressure catastrophe is to significantly reduce the flux tube volume by reconnection, and observations show a near-Earth reconnection line typically around 20-25 Earth radii down tail. Earthward flows from this reconnection line are rather bursty and typically seen outside of 10 Earth radii. At this point they are strongly braked by the here dominant dipolar magnetic field. The pressure gradients piled up by the flow lead to the substorm current wedge, and possibly other substorm phenomena observed in the Earth's ionosphere. When more and more flux tubes are piled up, the dipolarization front moves tailward and finally shuts off near-Earth reconnection
Holloway, C. E.; Woolnough, S. J.
2016-03-01
Idealized explicit convection simulations of the Met Office Unified Model exhibit spontaneous self-aggregation in radiative-convective equilibrium, as seen in other models in previous studies. This self-aggregation is linked to feedbacks between radiation, surface fluxes, and convection, and the organization is intimately related to the evolution of the column water vapor field. Analysis of the budget of the spatial variance of column-integrated frozen moist static energy (MSE), following Wing and Emanuel (2014), reveals that the direct radiative feedback (including significant cloud longwave effects) is dominant in both the initial development of self-aggregation and the maintenance of an aggregated state. A low-level circulation at intermediate stages of aggregation does appear to transport MSE from drier to moister regions, but this circulation is mostly balanced by other advective effects of opposite sign and is forced by horizontal anomalies of convective heating (not radiation). Sensitivity studies with either fixed prescribed radiative cooling, fixed prescribed surface fluxes, or both do not show full self-aggregation from homogeneous initial conditions, though fixed surface fluxes do not disaggregate an initialized aggregated state. A sensitivity study in which rain evaporation is turned off shows more rapid self-aggregation, while a run with this change plus fixed radiative cooling still shows strong self-aggregation, supporting a "moisture-memory" effect found in Muller and Bony (2015). Interestingly, self-aggregation occurs even in simulations with sea surface temperatures (SSTs) of 295 and 290 K, with direct radiative feedbacks dominating the budget of MSE variance, in contrast to results in some previous studies.
Engineering photochemical smog through convection towers
Energy Technology Data Exchange (ETDEWEB)
Elliott, S.; Prueitt, M.L.; Bossert, J.E.; Mroz, E.J.; Krakowski, R.A.; Miller, R.L. [Los Alamos National Lab., NM (United States); Jacobson, M.Z.; Turco, R.P. [Los Alamos National Lab., NM (United States)]|[Univ. of California, Los Angeles, CA (United States). Atmospheric Sciences Dept.
1995-02-01
Reverse convection towers have attracted attention as a medium for cleansing modern cities. Evaporation of an aqueous mist injected at the tower opening could generate electrical power by creating descent, and simultaneously scavenge unsightly and unhealthful particulates. The study offered here assesses the influence to tower water droplets on the photochemical component of Los Angeles type smog. The primary radical chain initiator OH is likely removed into aqueous phases well within the residence time of air in the tower, and then reacts away rapidly. Organics do not dissolve, but nighttime hydrolysis of N{sub 2}O{sub 5} depletes the nitrogen oxides. A lack of HOx would slow hydrocarbon oxidation and so also ozone production. Lowering of NOx would also alter ozone production rates, but the direction is uncertain. SO{sub 2} is available in sufficient quantities in some urban areas to react with stable oxidants, and if seawater were the source of the mist, the high pH would lead to fast sulfur oxidation kinetics. With an accommodation coefficient of 10{sup {minus}3}, however, ozone may not enter the aqueous phase efficiently. Even if ozone is destroyed or its production suppressed, photochemical recovery times are on the order of hours, so that tower processing must be centered on a narrow midday time window. The cost of building the number of structures necessary for this brief turnover could be prohibitive. The increase in humidity accompanying mist evaporation could be controlled with condensers, but might otherwise counteract visibility enhancements by recreating aqueous aerosols. Quantification of the divergent forcings convection towers must exert upon the cityscape would call for coupled three dimensional modeling of transport, microphysics, and photochemistry. 112 refs.
Facilitating atmosphere oxidation through mantle convection
Lee, K. K. M.; Gu, T.; Creasy, N.; Li, M.; McCammon, C. A.; Girard, J.
2017-12-01
Earth's mantle connects the surface with the deep interior through convection, and the evolution of its redox state will affect the distribution of siderophile elements, recycling of refractory isotopes, and the oxidation state of the atmosphere through volcanic outgassing. While the rise of oxygen in the atmosphere, i.e., the Great Oxidation Event (GOE) occurred 2.4 billion years ago (Ga), multiple lines of evidence point to oxygen production in the atmosphere well before 2.4 Ga. In contrast to the fluctuations of atmospheric oxygen, vanadium in Archean mantle lithosphere suggests that the mantle redox state has been constant for 3.5 Ga. Indeed, the connection between the redox state of the deep Earth and the atmosphere is enigmatic as is the effect of redox state on mantle dynamics. Here we show a redox-induced density contrast affects mantle convection and may potentially cause the oxidation of the upper mantle. We compressed two synthetic enstatite chondritic samples with identical bulk compositions but formed under different oxygen fugacities (fO2) to lower mantle pressures and temperatures and find Al2O3 forms its own phase separate from the dominant bridgmanite phase in the more reduced composition, in contrast to a more Al-rich, bridgmanite-dominated assemblage for a more oxidized starting composition. As a result, the reduced material is 1-1.5% denser than the oxidized material. Subsequent experiments on other plausible mantle compositions, which differ only in redox state of the starting glass materials, show similar results: distinct mineral assemblages and density contrasts up to 4%. Our geodynamic simulations suggest that such a density contrast causes a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. The resulting heterogeneous redox conditions in Earth's interior may have contributed to the large low-shear velocity provinces in the lower mantle and the
Directory of Open Access Journals (Sweden)
Imad Khan
Full Text Available Current work highlights the computational aspects of MHD Carreau nanofluid flow over an inclined stretching cylinder with convective boundary conditions and Joule heating. The mathematical modeling of physical problem yields nonlinear set of partial differential equations. A suitable scaling group of variables is employed on modeled equations to convert them into non-dimensional form. The integration scheme Runge-Kutta-Fehlberg on the behalf of shooting technique is utilized to solve attained set of equations. The interesting aspects of physical problem (linear momentum, energy and nanoparticles concentration are elaborated under the different parametric conditions through graphical and tabular manners. Additionally, the quantities (local skin friction coefficient, local Nusselt number and local Sherwood number which are responsible to dig out the physical phenomena in the vicinity of stretched surface are computed and delineated by varying controlling flow parameters. Keywords: MHD, Carreau nanofluid, Inclined stretching cylinder, Joule heating, Shooting technique
Unsteady three-dimensional behavior of natural convection in horizontal annulus
International Nuclear Information System (INIS)
Ohya, Toshizo; Miki, Yasutomi; Morita, Kouji; Fukuda, Kenji; Hasegawa, Shu
1988-01-01
An numerical analysis has been performed on unsteady three-dimensional natural convection in a concentric horizontal annulus filled with air. The explicit leap-frog scheme is used for integrating three-dimensional time-dependent equations and the fast Fourier transform (FFT) for solving the Poisson equations for pressure. An oscillatory flow is found to occur at high Rayleigh numbers, which agree qualitatively with the experimental observation made by Bishop et al. An experiment is also conducted to measure temperature fluctuations; a comparison between periods of fluctuations obtained numerically and experimentally shows a good agreement. Numerical calculations yield various statistical parameters of turbulence at higher Rayleigh numbers, which wait experimental verificaions, however. (author)
International Nuclear Information System (INIS)
Yener, Y.; Shahidi-Zandi, B.; Ozisik, M.N.; North Carolina State Univ., Raleigh)
1984-01-01
The interaction of radiation and forced convection in a thermally developing steady turbulent flow of an absorbing, emitting, isotropically scattering gray fluid in a parallel-plate channel is investigated. The plates are assumed to be gray, opaque, diffusely emitting and diffusely reflecting. A formal solution to the energy equation is developed in terms of turbulent Graetz eigenfunctions for a step-change in the temperature of the plates, while the radiation part of the problem is analyzed by the Galerkin method. An iterative scheme is employed to evaluate the resulting equations numerically. The effects of the conduction-radiation parameter, optical thickness, single-scattering albedo and the surface emissivity on the temperature distribution and the local Nusselt number in the thermal entrance region are investigated for severalvalues of the Reynolds number and the Prandtl number. The results are presented in graphical forms. 25 references
Laminar forced convective heat transfer in a two-dimensional branching tee junction
International Nuclear Information System (INIS)
Khodadadi, J.M.; Nguyen, T.M.; Vlachos, N.S.
1985-01-01
Laminar forced convective heat transfer in a two-dimensional ninety degree branching tee junction is studied numerically. The governing elliptic equations are solved by a finite-difference numerical scheme utilizing primitive dependent variables. A wide range of Reynolds numbers and dividing flowrates is studied while the working fluid is air with constant properties which is heated via the constant temperature walls of the bifurcation. The location of the separation and reattachment points corresponding to the two recirculation zones which form near the bifurcation are quantified as a function of the Reynolds number and dividing flowrate. The variation of the local Nusselt number along the walls of the bifurcation is discussed in light of the direct effects of the highly perturbed flowfield
Directory of Open Access Journals (Sweden)
Habibi Matin Meisam
2014-01-01
Full Text Available Forced convection boundary layer magneto-hydrodynamic (MHD flow of a nanofluid over a permeable stretching plate is studied in this paper. The effects of suction-injection and viscous dissi1pation are taken into account. The nanofluid model includes Brownian motion and thermophoresis effects. The governing momentum, energy and nanofluid solid volume fraction equations are solved numerically using an implicit finite difference scheme known as Keller-box method and the results are compared with available numerical data. The results for the dimensionless velocity, dimensionless temperature, dimensionless nanofluid solid volume fraction, reduced Nusselt and reduced Sherwood numbers are presented illustrating the effects of magnetic parameter, suction-injection parameter, Brownian motion parameter, thermophoresis parameter, Prandtl number, Eckert number and Lewis number.
Natural convection - radiation interaction in boundary layer flow over horizontal surfaces
International Nuclear Information System (INIS)
Ali, M.M.; Chen, T.S.; Armaly, B.F.
1982-01-01
A numerical model is developed for natural convection-radiation interaction in the boundary layer over a semi-infinite horizontal flat plate with one hot and one cold surface. The fluid is assumed to be gray, to emit, absorb, be nonscattering, and constant with a density variation in the vertical direction, which induces a buoyancy force. Two-dimensional, boundary-layer equations are defined, and the radiative heat flux is simplified using a Rosseland approximation. Conservation equations are transformed into a system of nonlinear ordinary differential equations which can be solved simultaneously with a Runge-Kutta integration scheme, along with the Newton-Raphson shooting technique. The thermal radiation is found to enhance the wall shear stress and the surface heat transfer rate on both the hot and cold sides
Characteristics of Extreme Summer Convection over equatorial America and Africa
Zuluaga, M. D.; Houze, R.
2013-12-01
Fourteen years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) version 7 data for June-August show the temporal and spatial characteristics of extreme convection over equatorial regions of the American and African continents. We identify three types of extreme systems: storms with deep convective cores (contiguous convective 40 dBZ echoes extending ≥10 km in height), storms with wide convective cores (contiguous convective 40 dBZ echoes with areas >1,000 km2) and storms with broad stratiform regions (stratiform echo >50,000 km2). European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis is used to describe the environmental conditions around these forms of extreme convection. Storms with deep convective cores occur mainly over land: in the equatorial Americas, maximum occurrence is in western Mexico, Northern Colombia and Venezuela; in Africa, the region of maximum occurrence is a broad zone enclosing the central and west Sudanian Savanna, south of the Sahel region. Storms with wide convective radar echoes occur in these same general locations. In the American sector, storms with broad stratiform precipitation regions (typifying robust mesoscale convective systems) occur mainly over the eastern tropical Pacific Ocean and the Colombia-Panama bight. In the African sector, storms with broad stratiform precipitation areas occur primarily over the eastern tropical Atlantic Ocean near the coast of West Africa. ECMWF reanalyses show how the regions of extreme deep convection associated with both continents are located mainly in regions affected by diurnal heating and influenced by atmospheric jets in regions with strong humidity gradients. Composite analysis of the synoptic conditions leading to the three forms of extreme convection provides insights into the forcing mechanisms in which these systems occur. These analyses show how the monsoonal flow directed towards the Andes slopes is mainly what concentrates the occurrence of extreme
Enhanced object-based tracking algorithm for convective rain storms and cells
Muñoz, Carlos; Wang, Li-Pen; Willems, Patrick
2018-03-01
This paper proposes a new object-based storm tracking algorithm, based upon TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting). TITAN is a widely-used convective storm tracking algorithm but has limitations in handling small-scale yet high-intensity storm entities due to its single-threshold identification approach. It also has difficulties to effectively track fast-moving storms because of the employed matching approach that largely relies on the overlapping areas between successive storm entities. To address these deficiencies, a number of modifications are proposed and tested in this paper. These include a two-stage multi-threshold storm identification, a new formulation for characterizing storm's physical features, and an enhanced matching technique in synergy with an optical-flow storm field tracker, as well as, according to these modifications, a more complex merging and splitting scheme. High-resolution (5-min and 529-m) radar reflectivity data for 18 storm events over Belgium are used to calibrate and evaluate the algorithm. The performance of the proposed algorithm is compared with that of the original TITAN. The results suggest that the proposed algorithm can better isolate and match convective rainfall entities, as well as to provide more reliable and detailed motion estimates. Furthermore, the improvement is found to be more significant for higher rainfall intensities. The new algorithm has the potential to serve as a basis for further applications, such as storm nowcasting and long-term stochastic spatial and temporal rainfall generation.
Convective heat transfer from a heated elliptic cylinder at uniform wall temperature
Energy Technology Data Exchange (ETDEWEB)
Kaprawi, S.; Santoso, Dyos [Mechanical Department of Sriwijaya University, Jl. Raya Palembang-Prabumulih Km. 32 Inderalaya 50062 Ogan Ilir (Indonesia)
2013-07-01
This study is carried out to analyse the convective heat transfer from a circular and an elliptic cylinders to air. Both circular and elliptic cylinders have the same cross section. The aspect ratio of cylinders range 0-1 are studied. The implicit scheme of the finite difference is applied to obtain the discretized equations of hydrodynamic and thermal problem. The Choleski method is used to solve the discretized hydrodynamic equation and the iteration method is applied to solve the discretized thermal equation. The circular cylinder has the aspect ratio equal to unity while the elliptical cylinder has the aspect ratio less than unity by reducing the minor axis and increasing the major axis to obtain the same cross section as circular cylinder. The results of the calculations show that the skin friction change significantly, but in contrast with the elliptical cylinders have greater convection heat transfer than that of circular cylinder. Some results of calculations are compared to the analytical solutions given by the previous authors.
Unsteady free convection from a sphere in a porous medium with variable surface temperature
International Nuclear Information System (INIS)
Rahimi, Asghar Baradaran
2011-01-01
All works on natural convection around a sphere in porous media, except the transient work of Nakayama and Koyama and Nguyen and Paik which are for body of arbitrary geometric configuration, have been conducted only for constant temperature or constant heat flux on its surface. In this paper a transient free convection flow around a sphere with variable surface temperature and embedded in a porous medium has been considered. The temperature of the sphere is suddenly raised and subsequently maintained at values that vary with position on surface. This situation is specially encountered when nuclear wastes, for example, are buried in earth. The method of asymptotic expansions is applied for small Rayleigh numbers up to the second-order of approximation and then a finite-difference scheme is used to solve the problem numerically for finite values of Rayleigh numbers. Transient and steady-state flow and temperature patterns around the sphere are discussed in details and a comparison between numerical and analytical results has been presented. (author)
Scheme of thinking quantum systems
International Nuclear Information System (INIS)
Yukalov, V I; Sornette, D
2009-01-01
A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans. The algebra of probability operators, associated with the possible options available to the decision maker, plays the role of the algebra of observables in quantum theory of measurements. A scheme is advanced for a practical realization of decision procedures by thinking quantum systems. Such thinking quantum systems can be realized by using spin lattices, systems of magnetic molecules, cold atoms trapped in optical lattices, ensembles of quantum dots, or multilevel atomic systems interacting with electromagnetic field
Support Schemes and Ownership Structures
DEFF Research Database (Denmark)
Ropenus, Stephanie; Schröder, Sascha Thorsten; Costa, Ana
of the ongoing fuel cell based micro‐combined heat and power (mCHP) demonstration projects by addressing the socio‐economic and systems analyses perspectives of a large‐scale promotion scheme of fuel cells. This document constitutes the deliverable of Work Package 1 of the FC4Home project and provides......In recent years, fuel cell based micro‐combined heat and power has received increasing attention due to its potential contribution to energy savings, efficiency gains, customer proximity and flexibility in operation and capacity size. The FC4Home project assesses technical and economic aspects...... previous findings and provides a short “preview” of the quantitative analyses in subsequent Work Packages by giving some food for thought on the way....
Goldstein, A. S.; Juarez, T. M.; Helmke, C. D.; Gustin, M. C.; Mikos, A. G.; McIntire, L. V. (Principal Investigator)
2001-01-01
Culture of seeded osteoblastic cells in three-dimensional osteoconductive scaffolds in vitro is a promising approach to produce an osteoinductive material for repair of bone defects. However, culture of cells in scaffolds sufficiently large to bridge critical-sized defects is a challenge for tissue engineers. Diffusion may not be sufficient to supply nutrients into large scaffolds and consequently cells may grow preferentially at the periphery under static culture conditions. Three alternative culturing schemes that convect media were considered: a spinner flask, a rotary vessel, and a perfusion flow system. Poly(DL-lactic-co-glycolic acid) (PLGA) foam discs (12.7 mm diameter, 6.0 mm thick, 78.8% porous) were seeded with osteoblastic marrow stromal cells and cultured in the presence of dexamethasone and L-ascorbic acid for 7 and 14 days. Cell numbers per foam were found to be similar with all culturing schemes indicating that cell growth could not be enhanced by convection, but histological analysis indicated that the rotary vessel and flow system produced a more uniform distribution of cells throughout the foams. Alkaline phosphatase (ALP) activity per cell was higher with culture in the flow system and spinner flask after 7 days, while no differences in osteocalcin (OC) activity per cell were observed among culturing methods after 14 days in culture. Based on the higher ALP activity and better cell uniformity throughout the cultured foams, the flow system appears to be the superior culturing method, although equally important is the fact that in none of the tests did any of the alternative culturing techniques underperform the static controls. Thus, this study demonstrates that culturing techniques that utilize fluid flow, and in particular the flow perfusion system, improve the properties of the seeded cells over those maintained in static culture.
Nocturnal offshore convection near the island of Corsica
Barthlott, Christian; Adler, Bianca; Kalthoff, Norbert; Handwerker, Jan; Kohler, Martin; Wieser, Andreas
2014-05-01
In the region of Corsica, located in the western Mediterranean Sea, the mean daily lightning activity for late summer and autumn as an indicator for deep convection shows a distinct maximum in mid-afternoon and a secondary maximum in the night. During the night, most of the lightning activity is located offshore and near the island's coastline. Currently there are no observational data which could be used to explain this nocturnal offshore convection but understanding its formation mechanism is crucial for accurately forecasting the regional weather. In this work, we explore two possible mechanisms initiating nocturnal offshore convection: (i) convergence with subsequent lifting due to the interaction between drainage winds and the synoptic flow over the sea and (ii) dynamically induced lee-side convergence due to the island barrier effect. To this end, we perform numerical simulations with the Consortium for Small-scale Modeling (COSMO) model at a convection-resolving horizontal grid spacing of 2.8 km. The analysis of two cases with different low-level wind directions reveals that the role of the island's drainage flow can either favour or hinder the development of deep convection. Furthermore, convective initiation is very sensitive to terrain elevation and model initialisation time and small changes of these features can decide whether deep convection occurs or not.
Thermodynamic Environments Supporting Extreme Convection in Subtropical South America
Rasmussen, K. L.; Trier, S. B.
2015-12-01
Extreme convection tends to form in the vicinity of mountain ranges, and the Andes in subtropical South America help spawn some of the most intense convection in the world. Subsequent to initiation, the convection often evolves into propagating mesoscale convective systems (MCSs) similar to those seen over the U.S. Great Plains and produces damaging tornadoes, hail, and floods across a wide agricultural region. In recent years, studies on the nature of convection in subtropical South America using spaceborne radar data have elucidated key processes responsible for their extreme characteristics, including a strong relationship between the Andes topography and convective initiation. Building on previous work, an investigation of the thermodynamic environment supporting some of the deepest convection in the world will be presented. In particular, an analysis of the thermodynamic destabilization in subtropical South America, which considers the parcel buoyancy minimum for conditionally unstable air parcels, will be presented. Additional comparisons between the nocturnal nature and related diurnal cycle of MCSs in subtropical South America the U.S. Great Plains will provide insights into the processes controlling MCS initiation and upscale growth.
Convective effects in a regulatory and proposed fire model
International Nuclear Information System (INIS)
Wix, S.D.; Hohnstreiter, G.F.
1995-01-01
Radiation is the dominant mode of heat transfer in large fires. However, convection can be as much as 10 to 20 percent of the total heat transfer to an object in a large fire. The current radioactive material transportation packaging regulations include convection as a mode of heat transfer in the accident condition scenario. The current International Atomic Energy Agency Safety Series 6 packaging regulation states ''the convection coefficient shall be that value which the designer can justify if the package were exposed to the specified fire''. The current Title 10, Code of Federal Regulations, Part 71 (10CFR71) packaging regulation states ''when significant, convection heat input must be included on the basis of still, ambient air at 800 degrees C (1475 degrees F)''. Two questions that can arise in an analysts mind from an examination of the packaging regulations is whether convection is significant and whether convection should be included in the design analysis of a radioactive materials transportation container. The objective of this study is to examine the convective effects on an actual radioactive materials transportation package using a regulatory and a proposed thermal boundary condition
Improved nowcasting of precipitation based on convective analysis fields
Directory of Open Access Journals (Sweden)
T. Haiden
2007-04-01
Full Text Available The high-resolution analysis and nowcasting system INCA (Integrated Nowcasting through Comprehensive Analysis developed at the Austrian national weather service provides three-dimensional fields of temperature, humidity, and wind on an hourly basis, and two-dimensional fields of precipitation rate in 15 min intervals. The system operates on a horizontal resolution of 1 km and a vertical resolution of 100–200 m. It combines surface station data, remote sensing data (radar, satellite, forecast fields of the numerical weather prediction model ALADIN, and high-resolution topographic data. An important application of the INCA system is nowcasting of convective precipitation. Based on fine-scale temperature, humidity, and wind analyses a number of convective analysis fields are routinely generated. These fields include convective boundary layer (CBL flow convergence and specific humidity, lifted condensation level (LCL, convective available potential energy (CAPE, convective inhibition (CIN, and various convective stability indices. Based on the verification of areal precipitation nowcasts it is shown that the pure translational forecast of convective cells can be improved by using a decision algorithm which is based on a subset of the above fields, combined with satellite products.
Consistent second-order boundary implementations for convection-diffusion lattice Boltzmann method
Zhang, Liangqi; Yang, Shiliang; Zeng, Zhong; Chew, Jia Wei
2018-02-01
In this study, an alternative second-order boundary scheme is proposed under the framework of the convection-diffusion lattice Boltzmann (LB) method for both straight and curved geometries. With the proposed scheme, boundary implementations are developed for the Dirichlet, Neumann and linear Robin conditions in a consistent way. The Chapman-Enskog analysis and the Hermite polynomial expansion technique are first applied to derive the explicit expression for the general distribution function with second-order accuracy. Then, the macroscopic variables involved in the expression for the distribution function is determined by the prescribed macroscopic constraints and the known distribution functions after streaming [see the paragraph after Eq. (29) for the discussions of the "streaming step" in LB method]. After that, the unknown distribution functions are obtained from the derived macroscopic information at the boundary nodes. For straight boundaries, boundary nodes are directly placed at the physical boundary surface, and the present scheme is applied directly. When extending the present scheme to curved geometries, a local curvilinear coordinate system and first-order Taylor expansion are introduced to relate the macroscopic variables at the boundary nodes to the physical constraints at the curved boundary surface. In essence, the unknown distribution functions at the boundary node are derived from the known distribution functions at the same node in accordance with the macroscopic boundary conditions at the surface. Therefore, the advantages of the present boundary implementations are (i) the locality, i.e., no information from neighboring fluid nodes is required; (ii) the consistency, i.e., the physical boundary constraints are directly applied when determining the macroscopic variables at the boundary nodes, thus the three kinds of conditions are realized in a consistent way. It should be noted that the present focus is on two-dimensional cases, and theoretical
On Optimal Designs of Some Censoring Schemes
Directory of Open Access Journals (Sweden)
Dr. Adnan Mohammad Awad
2016-03-01
Full Text Available The main objective of this paper is to explore suitability of some entropy-information measures for introducing a new optimality censoring criterion and to apply it to some censoring schemes from some underlying life-time models. In addition, the paper investigates four related issues namely; the effect of the parameter of parent distribution on optimal scheme, equivalence of schemes based on Shannon and Awad sup-entropy measures, the conjecture that the optimal scheme is one stage scheme, and a conjecture by Cramer and Bagh (2011 about Shannon minimum and maximum schemes when parent distribution is reflected power. Guidelines for designing an optimal censoring plane are reported together with theoretical and numerical results and illustrations.
Tissue engineering scheming by artificial intelligence.
Xu, J; Ge, H; Zhou, X; Yang, D
2005-01-01
Tissue engineers are often confused when seeking the most effective, economical and secure scheme for tissue engineering. The aim of this study is to generate tissue engineering schemes with artificial intelligence instead of human intelligence. The experimental data of tissue engineered cartilage were integrated and standardized with a centralized database, and a scheme engine was developed using artificial intelligent methods (artificial neural networks and decision trees). The scheme engine was trained with existing cases in the database, and then was used to generate tissue engineering schemes for new experimental animals. Following the schemes generated by the artificial intelligent system, we cured 18 of the 20 experimental animals. In conclusion, artificial intelligence is a powerful method for decision making in the tissue engineering realm.
How can conceptual schemes change teaching?
Wickman, Per-Olof
2012-03-01
Lundqvist, Almqvist and Östman describe a teacher's manner of teaching and the possible consequences it may have for students' meaning making. In doing this the article examines a teacher's classroom practice by systematizing the teacher's transactions with the students in terms of certain conceptual schemes, namely the epistemological moves, educational philosophies and the selective traditions of this practice. In connection to their study one may ask how conceptual schemes could change teaching. This article examines how the relationship of the conceptual schemes produced by educational researchers to educational praxis has developed from the middle of the last century to today. The relationship is described as having been transformed in three steps: (1) teacher deficit and social engineering, where conceptual schemes are little acknowledged, (2) reflecting practitioners, where conceptual schemes are mangled through teacher practice to aid the choices of already knowledgeable teachers, and (3) the mangling of the conceptual schemes by researchers through practice with the purpose of revising theory.
Single-mode theory of diffusive layers in thermohaline convection
Gough, D. O.; Toomre, J.
1982-01-01
A two-layer configuration of thermohaline convection is studied, with the principal aim of explaining the observed independence of the buoyancy-flux ratio on the stability parameter when the latter is large. Temperature is destabilizing and salinity is stabilizing, so diffusive interfaces separate the convecting layers. The convection is treated in the single-mode approximation, with a prescribed horizontal planform and wavenumber. Surveys of numerical solutions are presented for a selection of Rayleigh numbers R, stability parameters lambda and horizontal wavenumbers. The solutions yield a buoyancy flux ratio chi that is insensitive to lambda, in accord with laboratory experiments. However chi increases with increasing R, in contradiction to laboratory observations.
Analysis of forced convection heat transfer to supercritical carbon dioxide
International Nuclear Information System (INIS)
Ko, H.S.; Sakurai, Katsumi; Okamoto, Koji; Madarame, Haruki
2000-01-01
The supercritical carbon dioxide flow has been visualized under forced convection by a Mach-Zehnder interferometry system. The forced convection heat transfer has been examined by an one-sided wall heater in the vertical rectangular test section. Temperature and density distributions of the heated carbon dioxide inside the test section have been calculated from the measured interferometry projections for the visible interferograms conditions. The relationship of the temperature distributions with the physical conditions has been analyzed to inspect the forced convection heat transfer of the supercritical carbon dioxide flow. (author)
Confinement and dynamical regulation in two-dimensional convective turbulence
DEFF Research Database (Denmark)
Bian, N.H.; Garcia, O.E.
2003-01-01
In this work the nature of confinement improvement implied by the self-consistent generation of mean flows in two-dimensional convective turbulence is studied. The confinement variations are linked to two distinct regulation mechanisms which are also shown to be at the origin of low......-frequency bursting in the fluctuation level and the convective heat flux integral, both resulting in a state of large-scale intermittency. The first one involves the control of convective transport by sheared mean flows. This regulation relies on the conservative transfer of kinetic energy from tilted fluctuations...
Convection with local thermal non-equilibrium and microfluidic effects
Straughan, Brian
2015-01-01
This book is one of the first devoted to an account of theories of thermal convection which involve local thermal non-equilibrium effects, including a concentration on microfluidic effects. The text introduces convection with local thermal non-equilibrium effects in extraordinary detail, making it easy for readers newer to the subject area to understand. This book is unique in the fact that it addresses a large number of convection theories and provides many new results which are not available elsewhere. This book will be useful to researchers from engineering, fluid mechanics, and applied mathematics, particularly those interested in microfluidics and porous media.
Resonance ionization scheme development for europium
Chrysalidis, K; Fedosseev, V N; Marsh, B A; Naubereit, P; Rothe, S; Seiffert, C; Kron, T; Wendt, K
2017-01-01
Odd-parity autoionizing states of europium have been investigated by resonance ionization spectroscopy via two-step, two-resonance excitations. The aim of this work was to establish ionization schemes specifically suited for europium ion beam production using the ISOLDE Resonance Ionization Laser Ion Source (RILIS). 13 new RILIS-compatible ionization schemes are proposed. The scheme development was the first application of the Photo Ionization Spectroscopy Apparatus (PISA) which has recently been integrated into the RILIS setup.
Alternative schemes for the inertial fusion energy
Energy Technology Data Exchange (ETDEWEB)
Tikhonchuk, V.T. [Centre Lasers Intenses et Applications, University Bordeaux 1-CNRS-CEA, 33405, Talence (France); Mima, K., E-mail: tikhonchuk@celia.u-bordeaux1.fr [Institute of Laser Engineering, Osaka University, Osaka (Japan)
2011-10-15
The advanced target designs are requiring a lower laser energy for ignition and promising higher energy gains. Two approaches are under development within the European inertial fusion energy project HiPER: the fast ignition scheme with energetic electrons and the shock ignition scheme. The fundamental physical issues and major experimental works related to the alternative ignition schemes as well as the reactor designs are discussed.
Resonance ionization scheme development for europium
Energy Technology Data Exchange (ETDEWEB)
Chrysalidis, K., E-mail: katerina.chrysalidis@cern.ch; Goodacre, T. Day; Fedosseev, V. N.; Marsh, B. A. [CERN (Switzerland); Naubereit, P. [Johannes Gutenberg-Universität, Institiut für Physik (Germany); Rothe, S.; Seiffert, C. [CERN (Switzerland); Kron, T.; Wendt, K. [Johannes Gutenberg-Universität, Institiut für Physik (Germany)
2017-11-15
Odd-parity autoionizing states of europium have been investigated by resonance ionization spectroscopy via two-step, two-resonance excitations. The aim of this work was to establish ionization schemes specifically suited for europium ion beam production using the ISOLDE Resonance Ionization Laser Ion Source (RILIS). 13 new RILIS-compatible ionization schemes are proposed. The scheme development was the first application of the Photo Ionization Spectroscopy Apparatus (PISA) which has recently been integrated into the RILIS setup.
Data mining for detecting Bitcoin Ponzi schemes
Bartoletti, Massimo; Pes, Barbara; Serusi, Sergio
2018-01-01
Soon after its introduction in 2009, Bitcoin has been adopted by cyber-criminals, which rely on its pseudonymity to implement virtually untraceable scams. One of the typical scams that operate on Bitcoin are the so-called Ponzi schemes. These are fraudulent investments which repay users with the funds invested by new users that join the scheme, and implode when it is no longer possible to find new investments. Despite being illegal in many countries, Ponzi schemes are now proliferating on Bit...
Comparing Security Notions of Secret Sharing Schemes
Directory of Open Access Journals (Sweden)
Songsong Dai
2015-03-01
Full Text Available Different security notions of secret sharing schemes have been proposed by different information measures. Entropies, such as Shannon entropy and min entropy, are frequently used in the setting security notions for secret sharing schemes. Different to the entropies, Kolmogorov complexity was also defined and used in study the security of individual instances for secret sharing schemes. This paper is concerned with these security notions for secret sharing schemes defined by the variational measures, including Shannon entropy, guessing probability, min entropy and Kolmogorov complexity.
Quantum signature scheme for known quantum messages
International Nuclear Information System (INIS)
Kim, Taewan; Lee, Hyang-Sook
2015-01-01
When we want to sign a quantum message that we create, we can use arbitrated quantum signature schemes which are possible to sign for not only known quantum messages but also unknown quantum messages. However, since the arbitrated quantum signature schemes need the help of a trusted arbitrator in each verification of the signature, it is known that the schemes are not convenient in practical use. If we consider only known quantum messages such as the above situation, there can exist a quantum signature scheme with more efficient structure. In this paper, we present a new quantum signature scheme for known quantum messages without the help of an arbitrator. Differing from arbitrated quantum signature schemes based on the quantum one-time pad with the symmetric key, since our scheme is based on quantum public-key cryptosystems, the validity of the signature can be verified by a receiver without the help of an arbitrator. Moreover, we show that our scheme provides the functions of quantum message integrity, user authentication and non-repudiation of the origin as in digital signature schemes. (paper)
A Spatial Domain Quantum Watermarking Scheme
International Nuclear Information System (INIS)
Wei Zhan-Hong; Chen Xiu-Bo; Niu Xin-Xin; Yang Yi-Xian; Xu Shu-Jiang
2016-01-01
This paper presents a spatial domain quantum watermarking scheme. For a quantum watermarking scheme, a feasible quantum circuit is a key to achieve it. This paper gives a feasible quantum circuit for the presented scheme. In order to give the quantum circuit, a new quantum multi-control rotation gate, which can be achieved with quantum basic gates, is designed. With this quantum circuit, our scheme can arbitrarily control the embedding position of watermark images on carrier images with the aid of auxiliary qubits. Besides reversely acting the given quantum circuit, the paper gives another watermark extracting algorithm based on quantum measurements. Moreover, this paper also gives a new quantum image scrambling method and its quantum circuit. Differ from other quantum watermarking schemes, all given quantum circuits can be implemented with basic quantum gates. Moreover, the scheme is a spatial domain watermarking scheme, and is not based on any transform algorithm on quantum images. Meanwhile, it can make sure the watermark be secure even though the watermark has been found. With the given quantum circuit, this paper implements simulation experiments for the presented scheme. The experimental result shows that the scheme does well in the visual quality and the embedding capacity. (paper)
Improved Load Shedding Scheme considering Distributed Generation
DEFF Research Database (Denmark)
Das, Kaushik; Nitsas, Antonios; Altin, Müfit
2017-01-01
. These schemes utilize directional relays, power flow through feeders, wind and PV measurements to optimally select the feeders to be disconnected during load shedding such that DG disconnection is minimized while disconnecting required amount of consumption. These different UFLS schemes are compared in terms......With high penetration of distributed generation (DG), the conventional under-frequency load shedding (UFLS) face many challenges and may not perform as expected. This article proposes new UFLS schemes, which are designed to overcome the shortcomings of traditional load shedding scheme...... of frequency response, amount of consumption and DG disconnected during load shedding....
Tectonic predictions with mantle convection models
Coltice, Nicolas; Shephard, Grace E.
2018-04-01
Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough
Singh, K. S.; Bonthu, Subbareddy; Purvaja, R.; Robin, R. S.; Kannan, B. A. M.; Ramesh, R.
2018-04-01
This study attempts to investigate the real-time prediction of a heavy rainfall event over the Chennai Metropolitan City, Tamil Nadu, India that occurred on 01 December 2015 using Advanced Research Weather Research and Forecasting (WRF-ARW) model. The study evaluates the impact of six microphysical (Lin, WSM6, Goddard, Thompson, Morrison and WDM6) parameterization schemes of the model on prediction of heavy rainfall event. In addition, model sensitivity has also been evaluated with six Planetary Boundary Layer (PBL) and two Land Surface Model (LSM) schemes. Model forecast was carried out using nested domain and the impact of model horizontal grid resolutions were assessed at 9 km, 6 km and 3 km. Analysis of the synoptic features using National Center for Environmental Prediction Global Forecast System (NCEP-GFS) analysis data revealed strong upper-level divergence and high moisture content at lower level were favorable for the occurrence of heavy rainfall event over the northeast coast of Tamil Nadu. The study signified that forecasted rainfall was more sensitive to the microphysics and PBL schemes compared to the LSM schemes. The model provided better forecast of the heavy rainfall event using the logical combination of Goddard microphysics, YSU PBL and Noah LSM schemes, and it was mostly attributed to timely initiation and development of the convective system. The forecast with different horizontal resolutions using cumulus parameterization indicated that the rainfall prediction was not well represented at 9 km and 6 km. The forecast with 3 km horizontal resolution provided better prediction in terms of timely initiation and development of the event. The study highlights that forecast of heavy rainfall events using a high-resolution mesoscale model with suitable representations of physical parameterization schemes are useful for disaster management and planning to minimize the potential loss of life and property.
A new framework for the analysis of continental-scale convection-resolving climate simulations
Leutwyler, D.; Charpilloz, C.; Arteaga, A.; Ban, N.; Di Girolamo, S.; Fuhrer, O.; Hoefler, T.; Schulthess, T. C.; Christoph, S.
2017-12-01
High-resolution climate simulations at horizontal resolution of O(1-4 km) allow explicit treatment of deep convection (thunderstorms and rain showers). Explicitly treating convection by the governing equations reduces uncertainties associated with parametrization schemes and allows a model formulation closer to physical first principles [1,2]. But kilometer-scale climate simulations with long integration periods and large computational domains are expensive and data storage becomes unbearably voluminous. Hence new approaches to perform analysis are required. In the crCLIM project we propose a new climate modeling framework that allows scientists to conduct analysis at high spatial and temporal resolution. We tackle the computational cost by using the largest available supercomputers such as hybrid CPU-GPU architectures. For this the COSMO model has been adapted to run on such architectures [2]. We then alleviate the I/O-bottleneck by employing a simulation data-virtualizer (SDaVi) that allows to trade-off storage (space) for computational effort (time). This is achieved by caching the simulation outputs and efficiently launching re-simulations in case of cache misses. All this is done transparently from the analysis applications [3]. For the re-runs this approach requires a bit-reproducible version of COSMO. That is to say a model that produces identical results on different architectures to ensure coherent recomputation of the requested data [4]. In this contribution we present a version of SDaVi, a first performance model, and a strategy to obtain bit-reproducibility across hardware architectures.[1] N. Ban, J. Schmidli, C. Schär. Evaluation of the convection-resolving regional climate modeling approach in decade-long simulations. J. Geophys. Res. Atmos., 7889-7907, 2014.[2] D. Leutwyler, O. Fuhrer, X. Lapillonne, D. Lüthi, C. Schär. Towards European-scale convection-resolving climate simulations with GPUs: a study with COSMO 4.19. Geosci. Model Dev, 3393
On the determination of the neutral drag coefficient in the convective boundary layer
DEFF Research Database (Denmark)
Grachev, A.A.; Fairall, C.W.; Larsen, Søren Ejling
1998-01-01
Based on the idea that free convection can be considered as a particular case of forced convection, where the gusts driven by the large-scale eddies are scaled with the Deardorff convective velocity scale, a new formulation for the neutral drag coefficient, C-Dn, in the convective boundary layer ...
Energy Technology Data Exchange (ETDEWEB)
Varble, A. C.; Zipser, Edward J.; Fridlind, Ann; Zhu, Ping; Ackerman, Andrew; Chaboureau, Jean-Pierre; Collis, Scott M.; Fan, Jiwen; Hill, Adrian; Shipway, Ben
2014-12-27
Ten 3D cloud-resolving model (CRM) simulations and four 3D limited area model (LAM) simulations of an intense mesoscale convective system observed on January 23-24, 2006 during the Tropical Warm Pool – International Cloud Experiment (TWP-ICE) are compared with each other and with observed radar reflectivity fields and dual-Doppler retrievals of vertical wind speeds in an attempt to explain published results showing a high bias in simulated convective radar reflectivity aloft. This high bias results from ice water content being large, which is a product of large, strong convective updrafts, although hydrometeor size distribution assumptions modulate the size of this bias. Snow reflectivity can exceed 40 dBZ in a two-moment scheme when a constant bulk density of 100 kg m-3 is used. Making snow mass more realistically proportional to area rather than volume should somewhat alleviate this problem. Graupel, unlike snow, produces high biased reflectivity in all simulations. This is associated with large amounts of liquid water above the freezing level in updraft cores. Peak vertical velocities in deep convective updrafts are greater than dual-Doppler retrieved values, especially in the upper troposphere. Freezing of large rainwater contents lofted above the freezing level in simulated updraft cores greatly contributes to these excessive upper tropospheric vertical velocities. Strong simulated updraft cores are nearly undiluted, with some showing supercell characteristics. Decreasing horizontal grid spacing from 900 meters to 100 meters weakens strong updrafts, but not enough to match observational retrievals. Therefore, overly intense simulated updrafts may partly be a product of interactions between convective dynamics, parameterized microphysics, and large-scale environmental biases that promote different convective modes and strengths than observed.
Phoenix, Daniel B.; Homeyer, Cameron R.; Barth, Mary C.
2017-08-01
Tropopause-penetrating convection is capable of rapidly transporting air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS), where it can have important impacts on chemistry, the radiative budget, and climate. However, obtaining in situ measurements of convection and convective transport is difficult and such observations are historically rare. Modeling studies, on the other hand, offer the advantage of providing output related to the physical, dynamical, and chemical characteristics of storms and their environments at fine spatial and temporal scales. Since these characteristics of simulated convection depend on the chosen model design, we examine the sensitivity of simulated convective transport to the choice of physical (bulk microphysics or BMP and planetary boundary layer or PBL) and chemical parameterizations in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). In particular, we simulate multiple cases where in situ observations are available from the recent (2012) Deep Convective Clouds and Chemistry (DC3) experiment. Model output is evaluated using ground-based radar observations of each storm and in situ trace gas observations from two aircraft operated during the DC3 experiment. Model results show measurable sensitivity of the physical characteristics of a storm and the transport of water vapor and additional trace gases into the UTLS to the choice of BMP. The physical characteristics of the storm and transport of insoluble trace gases are largely insensitive to the choice of PBL scheme and chemical mechanism, though several soluble trace gases (e.g., SO2, CH2O, and HNO3) exhibit some measurable sensitivity.
Convectively driven flow past an infinite moving vertical cylinder with ...
Indian Academy of Sciences (India)
, free convective flow over an infinite moving vertical cylinder under combined buoyancy effects of heat and mass transfer with thermal and mass stratifications. Laplace transform technique is adopted for finding solutions for velocity, ...
Turbulent convection in liquid metal with and without rotation.
King, Eric M; Aurnou, Jonathan M
2013-04-23
The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, Pr rotating Rayleigh-Bénard convection experiments in the liquid metal gallium (Pr = 0.025) over a range of nondimensional buoyancy forcing (Ra) and rotation periods (E). Our primary diagnostic is the efficiency of convective heat transfer (Nu). In general, we find that the convective behavior of liquid metal differs substantially from that of moderate Pr fluids, such as water. In particular, a transition between rotationally constrained and weakly rotating turbulent states is identified, and this transition differs substantially from that observed in moderate Pr fluids. This difference, we hypothesize, may explain the different classes of magnetic fields observed on the Gas and Ice Giant planets, whose dynamo regions consist of Pr 1 fluids, respectively.
Convective heat and mass transfer in rotating disk systems
Shevchuk, Igor V
2009-01-01
The book describes results of investigations of a series of convective heat and mass transfer problems in rotating-disk systems. Methodology used included integral methods, self-similar and approximate analytical solutions, as well as CFD.
effect of chemical reaction on unsteady mhd free convective two ...
African Journals Online (AJOL)
Joseph et al.
coefficient of skin friction, Nusselt number and Sherwood number are also tabulated and discussed appropriately. It was observed that the increase in chemical reaction coefficient/parameter suppresses both velocity and concentration profiles. Keywords: Chemical Reaction, MHD, Convective, Immiscible,. Unsteady.
Simultaneous effects of Hall and convective conditions on peristaltic ...
Indian Academy of Sciences (India)
stress fluid in an inclined asymmetric channel with convective conditions. Soret and Dufour and Hall effects are taken into account. Analysis has been carried out in a wave frame of reference. Expressions for velocity, pressure gradient, temperature ...
Mixing properties of thermal convection in the earth's mantle
Schmalzl, J.T.
1996-01-01
The structure of mantle convection will greatly influence the generation and the survival of compositional heterogeneities. Conversely, geochemical observations can be used to obtain information about heterogeneities in the mantle and then, with certain model assumptions, information about the
VARIATION OF STELLAR ENVELOPE CONVECTION AND OVERSHOOT WITH METALLICITY
International Nuclear Information System (INIS)
Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
2013-01-01
We examine how metallicity affects convection and overshoot in the superadiabatic layer of main sequence stars. We present results from a grid of three-dimensional radiation hydrodynamic simulations with four metallicities (Z = 0.040, 0.020, 0.010, 0.001), and spanning a range in effective temperature (4950 eff < 6230). We show that changing the metallicity alters properties of the convective gas dynamics, and the structure of the superadiabatic layer and atmosphere. Our grid of simulations shows that the amount of superadiabaticity, which tracks the transition from efficient to inefficient convection, is sensitive to changes in metallicity. We find that increasing the metallicity forces the location of the transition region to lower densities and pressures, and results in larger mean and turbulent velocities throughout the superadiabatic region. We also quantify the degree of convective overshoot in the atmosphere, and show that it increases with metallicity as well.
Radiation and chemical reaction effects on convective Rivlin ...
African Journals Online (AJOL)
dimensional, laminar, boundary-layer free convective Rivlin-Ericksen flow of incompressible and electrically conducting fluids past a porous vertical plate with a periodic suction are discussed. The dimensionless governing equations of the flow ...
Energy Transformation and Rearrangement Caused by Cumulus Convection,
understanding of how clouds interact with and modify their environment, the goal being to aid in the formulation of realistic parameterization of cumulus convection in large-scale atmospheric models .
Lattice Boltzmann model for melting with natural convection
International Nuclear Information System (INIS)
Huber, Christian; Parmigiani, Andrea; Chopard, Bastien; Manga, Michael; Bachmann, Olivier
2008-01-01
We develop a lattice Boltzmann method to couple thermal convection and pure-substance melting. The transition from conduction-dominated heat transfer to fully-developed convection is analyzed and scaling laws and previous numerical results are reproduced by our numerical method. We also investigate the limit in which thermal inertia (high Stefan number) cannot be neglected. We use our results to extend the scaling relations obtained at low Stefan number and establish the correlation between the melting front propagation and the Stefan number for fully-developed convection. We conclude by showing that the model presented here is particularly well-suited to study convection melting in geometrically complex media with many applications in geosciences
Test of a new theory for stellar convection using helioseismology
Paterno, L.; Ventura, R.; Canuto, V. M.; Mazzitelli, I.
1993-01-01
Two evolutionary models of the sun have been tested using helioseismological data. The two models use the same input microphysics (nuclear reaction rates, opacity, equation of state) and the same numerical evolutionary code, but differ in the treatment of turbulent convection. The first model employs the standard mixing - length theory of convection, while the second one employs a new turbulent convection model which overcomes some basic inconsistencies of the standard theory of convection. The test rests on the calculation of p-mode eigenfrequencies and on the comparison with the helioseismological data. The comparison shows an overall improvement of the eigenfrequencies calculated with the new model with respect to those calculated with the standard model, although it appears that both models still suffer from inaccuracies especially in the treatment of the surface layers.
Performance of a convective, infrared and combined infrared- convective heated conveyor-belt dryer.
El-Mesery, Hany S; Mwithiga, Gikuru
2015-05-01
A conveyor-belt dryer was developed using a combined infrared and hot air heating system that can be used in the drying of fruits and vegetables. The drying system having two chambers was fitted with infrared radiation heaters and through-flow hot air was provided from a convective heating system. The system was designed to operate under either infrared radiation and cold air (IR-CA) settings of 2000 W/m(2) with forced ambient air at 30 °C and air flow of 0.6 m/s or combined infrared and hot air convection (IR-HA) dryer setting with infrared intensity set at 2000 W/m(2) and hot at 60 °C being blown through the dryer at a velocity of 0.6 m/s or hot air convection (HA) at an air temperature of 60 °C and air flow velocity 0.6 m/s but without infrared heating. Apple slices dried under the different dryer settings were evaluated for quality and energy requirements. It was found that drying of apple (Golden Delicious) slices took place in the falling rate drying period and no constant rate period of drying was observed under any of the test conditions. The IR-HA setting was 57.5 and 39.1 % faster than IR-CA and HA setting, respectively. Specific energy consumption was lower and thermal efficiency was higher for the IR-HA setting when compared to both IR-CA and HA settings. The rehydration ratio, shrinkage and colour properties of apples dried under IR-HA conditions were better than for either IR-CA or HA.
Wing, A. A.; Camargo, S. J.; Sobel, A. H.
2015-12-01
"Self-aggregation" is a mode of convective organization found in idealized numerical simulations, in which there is a spontaneous transition from randomly distributed to organized convection despite homogeneous boundary conditions. Self-aggregation has primarily been studied in a non-rotating framework, but it has been hypothesized to be important to tropical cyclogenesis. In numerical simulations of tropical cyclones, a broad vortex or saturated column is often used to initialize the circulation. Here, we instead allow a circulation to develop spontaneously from a homogeneous environment in 3-d cloud-resolving simulations of radiative-convective equilibrium in a rotating framework, with interactive radiation and surface fluxes and fixed sea surface temperature. The goals of this study are two-fold: to study tropical cyclogenesis in an unperturbed environment free from the influence of a prescribed initial vortex or external disturbances, and to compare cyclogenesis to non-rotating self-aggregation. We quantify the feedbacks leading to tropical cyclogenesis using a variance budget equation for the vertically integrated frozen moist static energy. In the initial development of a broad circulation, the feedback processes are similar to the initial phase of non-rotating aggregation. Sensitivity tests in which the degree of interactive radiation is modified are also performed to determine the extent to which the radiative feedbacks that are essential to non-rotating self-aggregation are important for tropical cyclogenesis. Finally, we examine the evolution of the rotational and divergent flow, to determine the point at which rotation becomes important and the cyclogenesis process begins to differ from non-rotating aggregation.
Energy Technology Data Exchange (ETDEWEB)
Flaounas, Emmanouil; Bastin, Sophie [UPMC, CNRS/INSU, LATMOS/IPSL, Paris cedex 05 (France); Janicot, Serge [UPMC, IRD, LOCEAN-IPSL, Paris (France)
2011-03-15
Regional climate model (RCM) is a valuable scientific tool to address the mechanisms of regional atmospheric systems such as the West African monsoon (WAM). This study aims to improve our understanding of the impact of some physical schemes of RCM on the WAM representation. The weather research and forecasting model has been used by performing six simulations of the 2006 summer WAM season. These simulations use all combinations of three convective parameterization schemes (CPSs) and two planetary boundary layer schemes (PBLSs). By comparing the simulations to a large set of observations and analysis products, we have evaluated the ability of these RCM parameterizations to reproduce different aspects of the regional atmospheric circulation of the WAM. This study focuses in particular on the WAM onset and the rainfall variability simulated over this domain. According to the different parameterizations tested, the PBLSs seem to have the strongest effect on temperature, humidity vertical distribution and rainfall amount. On the other hand, dynamics and precipitation variability are strongly influenced by CPSs. In particular, the Mellor-Yamada-Janjic PBLS attributes more realistic values of humidity and temperature. Combined with the Kain-Fritsch CPS, the WAM onset is well represented. The different schemes combination tested also reveal the role of different regional climate features on WAM dynamics, namely the low level circulation, the land-atmosphere interactions and the meridional temperature gradient between the Guinean coast and the Sahel. (orig.)
Free convective condensation in a vertical enclosure
Energy Technology Data Exchange (ETDEWEB)
Fox, R.J.; Peterson, P.F. [Univ. of California, Berkeley, CA (United States); Corradini, M.L.; Pernsteiner, A.P. [Univ. of Wisconsin, Madison, WI (United States)
1995-09-01
Free convective condensation in a vertical enclosure was studied numerically and the results were compared with experiments. In both the numerical and experimental investigations, mist formation was observed to occur near the cooling wall, with significant droplet concentrations in the bulk. Large recirculation cells near the end of the condensing section were generated as the heavy noncondensing gas collecting near the cooling wall was accelerated downward. Near the top of the enclosure the recirculation cells became weaker and smaller than those below, ultimately disappearing near the top of the condenser. In the experiment the mist density was seen to be highest near the wall and at the bottom of the condensing section, whereas the numerical model predicted a much more uniform distribution. The model used to describe the formation of mist was based on a Modified Critical Saturation Model (MCSM), which allows mist to be generated once the vapor pressure exceeds a critical value. Equilibrium, nonequilibrium, and MCSM calculations were preformed, showing the experimental results to lie somewhere in between the equilibrium and nonequilibrium predictions of the numerical model. A single adjustable constant (indicating the degree to which equilibrium is achieved) is used in the model in order to match the experimental results.