摘要 :
An introductory treatment of the fundamentals of diffusion theory is presented, starting with molecular diffusion and leading up to the statistical methods of turbulent diffusion. A multilayer diffusion model, designed to permit c...
展开
An introductory treatment of the fundamentals of diffusion theory is presented, starting with molecular diffusion and leading up to the statistical methods of turbulent diffusion. A multilayer diffusion model, designed to permit concentration and dosage calculations downwind of toxic clouds from rocket vehicles, is described. The concepts and equations of diffusion are developed on an elementary level, with emphasis on atmospheric applications.
收起
摘要 :
The 8th ERCOFTAC/IAHR/COST workshop on Refined Turbulence Modelling was held on211 17 and 18 June 1999 at Helsinki University of Technology in Espoo, Finland. The 211 main purpose of this series of workshops is to collect informat...
展开
The 8th ERCOFTAC/IAHR/COST workshop on Refined Turbulence Modelling was held on211 17 and 18 June 1999 at Helsinki University of Technology in Espoo, Finland. The 211 main purpose of this series of workshops is to collect information and knowledge 211 about the predictive capabilities of various turbulence models in different types 211 of flows. This is done by comparing model-predicted CFD results with experimental 211 or direct numerical simulation data in a broad range of well-defined test-case 211 flows.
收起
摘要 :
A review is presented on laboratory modeling of diffusion downwind of a continuous point source within a boundary layer of well defined height with turbulence driven by buoyant convection. Results of using mixed-layer scaling are ...
展开
A review is presented on laboratory modeling of diffusion downwind of a continuous point source within a boundary layer of well defined height with turbulence driven by buoyant convection. Results of using mixed-layer scaling are summarized and comparisons with atmospheric field measurements discussed. Concentration probability distributions from the laboratory as a function of dimensionless downwind distance are presented in a manner which discloses the differences from a lognormal distribution.
收起
摘要 :
Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Pr...
展开
Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefully their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL), diffusion in the stable boundary layer (SBL), and model uncertainty. Progress has been made in all areas, but it is most significant and ready for application to practical models in the case of the CBL. This has resulted from a clear understanding of the vertical structure and diffusion in the CBL, as demonstrated by laboratory experiments, numerical simulations, and field observations. Understanding of turbulence structure and diffusion in the SBL is less complete and not yet ready for general use in applications.
收起
摘要 :
We have employed spectral methods as well as direct simulations of the advection-diffusion equation to calculate the effective diffusivity for model flows. By calculating the eigenvalues and eigenvectors of a random matrix dependi...
展开
We have employed spectral methods as well as direct simulations of the advection-diffusion equation to calculate the effective diffusivity for model flows. By calculating the eigenvalues and eigenvectors of a random matrix depending only on the fluid velocity field, we obtain the spectral measures used in Stieltjes integral representations for the effective diffusivity. The enhancement of thermal transport through sea ice by brine advection was also modeled using the advection-diffusion equation. Moreover, an inverse problem was formulated to study this enhancement of sea ice thermal conductivity and better understand temperature data collected during a 2007 Antarctic expedition.
收起
摘要 :
This paper is devoted to a performance study of algorithms developed for solving211 global atmospheric transport-chemistry problems. The algorithms are applied 211 within two different operator splittings and are vectorized and pa...
展开
This paper is devoted to a performance study of algorithms developed for solving211 global atmospheric transport-chemistry problems. The algorithms are applied 211 within two different operator splittings and are vectorized and parallelized on a 211 Cray C09. For the performance study, we use a constructed, three-space 211 dimensional model problem, containing advection, vertical turbulent diffusion, 211 and chemical reactions. This numerical model problem is presented as a benchmark 211 on which other algorithms and implementations can be tested. In the context of 211 operator splitting, particular attention is paid to the issue of solving 211 chemistry and vertical turbulent diffusion, coupled or uncoupled.
收起
摘要 :
This paper compares calculations of vertical and surface dosage distributions, obtained from a finite difference numerical solution of the classical line source diffusion equation, to calculations obtained from an analytical solut...
展开
This paper compares calculations of vertical and surface dosage distributions, obtained from a finite difference numerical solution of the classical line source diffusion equation, to calculations obtained from an analytical solution and to observed distributions obtained from several line source releases. The analytical solution uses constant values of vertical turbulence and wind speed averaged with height. This solution then approximates the effects on surface dosages of increasing stability aloft by using reflection from the top of the mixing layer. The finite difference numerical solutions considers the change of eddy diffusivity and wind speed with height in such a way as to produce vertical dosage profile closer to the observed. Turbulence values for use in the numerical model are obtained from calculations of vertical diffusivity based on statistical theory. The numerical solution predicts the vertical dosage profile more accurately than the analytical solution. Both solutions predict surface dosages equally well. Verification of the numerical solution on other data appears desirable.
收起
摘要 :
Air pollution modeling, and problem areas in air pollution dispersion modeling were surveyed. Emission source inventory, meteorological data, and turbulent diffusion are discussed in terms of developing a dispersion model. Existin...
展开
Air pollution modeling, and problem areas in air pollution dispersion modeling were surveyed. Emission source inventory, meteorological data, and turbulent diffusion are discussed in terms of developing a dispersion model. Existing mathematical models of urban air pollution, and highway and airport models are discussed along with their limitations. Recommendations for improving modeling capabilities are included.
收起
