共查询到20条相似文献,搜索用时 31 毫秒
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《Atmospheric Environment. Part A. General Topics》1992,26(17):3219-3238
A key aspect in modeling the fate of pollutants released into the atmosphere is the parameterization of sub-grid scale processes so as to quantify their effect on resolvable scale features. Averaging emissions of species over grid squares characteristic of present-day regional and global models generally results in underpredicting concentrations of these species. This also causes inaccurate predictions for secondary pollutant species derived through complex chemical mechanisms. An algorithm is developed to provide improved sub-grid representation of emissions. A two-dimensional finite element technique is used to discretize the horizontal domain. The three-dimensional transport equation is time-split into this two-dimensional component and a one-dimensional vertical component to represent the transport processes. Compared to the locally one-dimensional finite element method (LOD-FEM), this technique allows use of variable grid sizes in the discretization of the horizontal domain, thus providing for local mesh refinement and consequently improved sub-grid representation in the numerical solution. The advantages of the scheme are inherent: the computational burden in terms of storage requirements is not increased, and the need for developing the troublesome interface boundary condition of a nested-grid procedure is avoided. A simplified first-order chemistry module has been incorporated to test the scheme for both primary and secondary pollutant species. Several test cases are presented to verify the efficacy of the proposed algorithm. Results from test cases for a simplified scenario indicate that the procedure enables one to simulate a more realistic range of concentrations for both the reactant and product species. Furthermore, comparison with the analytical solutions indicates that the numerical scheme is capable of reproducing the analytical solution, both qualitatively as well as quantitatively, in a superior manner compared to a uniform mesh. 相似文献
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Parallel computations of turbulent diffusion in convective boundary layers on shared-memory machines
《Atmospheric Environment. Part A. General Topics》1992,26(13):2425-2435
Currently, time-splitting finite difference or finite element schemes are commonly used in air-pollution modeling. In light of the recent advances in parallel processing, it is crucial to evaluate the performance of these time-splitting schemes on different multiprocessors. In this paper, we use a K-theory diffusion model and a second-order closure model to simulate turbulent diffusion in convective boundary layers. The objective is to assess the “portability” of time-splitting finite element schemes for shared-memory multiprocessors, such as IBM 3090-600J, the Alliant FX/8, the Sequent Symmetry S81 and the Encore Multimax. It was found that significant speed-ups were obtained as a result of parallelization with small programming efforts. Furthermore, our two- and three-dimensional results also suggest that second-order closure models are now computationally affordable and feasible for realistic air pollution modeling. 相似文献
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《Atmospheric Environment. Part A. General Topics》1992,26(14):2523-2535
A simple Lagrangian puff trajectory model and its software implementation, STRALE, are described. Standard meteorological data are used as input for the simulation of the three-dimensional atmospheric transport and dispersion of a pollutant released by a point source. The schemes adopted to describe the vertical diffusion and the interaction with the mixing layer are discussed on the basis of the comparison between simulated and measured 137Cs activities for the Chernobyl nuclear accident. 相似文献
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一维平流输送问题的欧拉-泰勒-伽辽金算法及数值试验 总被引:1,自引:1,他引:0
介绍了一维常系数平流输送问题的Euler-Taylor-Galerkin(ETG)算法?为获得精确的时间导数,该算法采用了包括二阶和三阶时间导数的前向泰勒级数展开,这些导数值可从空间控制微分方程求出?由此产生一般的时间分离方程?该方程采用标准的Bubnov-Galerkin有限元方法在空间离散化?在使用线性元(帽子函数)和Euler时间差分格式时,可获得精确的Taylor-Galerkin算法?当采用2步显示步骤时,算法为计算效率很高的显式?数值实验结果显示,ETG算法的误差很小,而相误差更可忽略不计,结果令人满意 相似文献
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《Atmospheric Environment. Part A. General Topics》1992,26(8):1493-1512
A new photochemical oxidant model, CALGRID, has been developed for regulatory assessments of ozone control strategies. The model features: low numerical diffusion transport schemes that explicitly conserve mass on a terrain following mesh; modern boundary-layer representations converted to K-theory and applied to a variety of both fixed level and space-time variable vertical meshes; the ability to switch chemical schemes easily among the SAPRC hierarchy; a comprehensive resistance-based, dry deposition algorithm; and a highly-modular, streamlined FORTRAN 77 code that is highly vectorized and easily adapted to emerging parallel processor technology. The model is controlled by an easy to modify, self-documenting “control file” which also enables many consistency checks and serves to protect against a number of simple, yet common, simulation errors. The paper describes each of the model's principal technical modules in detail. 相似文献
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《Atmospheric Environment. Part A. General Topics》1991,25(10):2385-2394
Accurately describing the transport from urban to regional areas, and vice versa, is necessary for effective emission control strategies. However, this task is complicated by the need to use a fine spatial scale in cities to resolve the steep concentration gradients, and the desire to use a coarser scale in rural areas for computational efficiency. A multiscale transport scheme is developed for use in multiscale air quality models. This Petrov-Galerkin finite element scheme accommodates a fine-grid mesh within a coarse-grid mesh. Spurious waves are eliminated locally, without loss of high-order accuracy, by applying a mass-conservative smoothing filter. Some aliasing errors are observed due to the changes in the mesh size. Nevertheless, the scheme performs bettern than others used for following the transport of pollutants in regional models and has the added advantage of accurately describing the transition from urban to rural areas, and vice versa. 相似文献
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《Atmospheric Environment. Part A. General Topics》1992,26(4):681-692
A model for the dispersion of a passive puff near the ground is developed. The model is based on the Monin-Obukhov similarity theory for the atmospheric surface layer, which is used to specify eddy diffusivities and the wind speed profile. Starting from the diffusion equation in a puff-following coordinate-system, rate equations are derived for the standard deviations of the concentration distribution and for its skewness. Approximate solutions are obtained for the shape of the concentration distribution and for the puff velocity. 相似文献
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用特征有限无法预测大运河对某市潜水污染的影响 总被引:3,自引:0,他引:3
用特征有限元法预测了在井群开采条件下大运河对某市潜水污染的影响,计算了直到2020年的污染物相对浓度的分布。该方法数值弥散和数值振荡较小,有相当的实用价值。 相似文献
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用特征有限无法预测大运河对某市潜水污染的影响 总被引:1,自引:0,他引:1
用特征有限元法预测了在井群开采条件下大运河水对某市潜水污染的影响,计算了直到2020年的污染物相对浓度的分布.该方法数值弥散和数值振荡较小,有相当的实用价值. 相似文献
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A new approach to predicting the maximum temperature in dry drilling based on a finite element model
A new analysis approach is developed to predict the temperature in dry drilling. The working rake angle and the working relief angle which the effect of feed is considered at an arbitrary point in the leading cutting edge of a twist drill are developed for the equivalent model. Then finite element models are developed to predict the drilling temperature based on the equivalent model. Commercial finite element codes Abaqus, Deform 2D and Third Wave Systems AdvantEdge have been used. In simulations, different chip separation models and material models are applied in the three codes. And the effect of the laws of drilling velocities and feed rates on the temperature are investigated by the finite element method. Predicted results of the maximum temperatures by three codes are compared with experiments, respectively. Results indicate that the drilling temperature results of simulations have good agreement to the experimental ones, and the errors are all less than 15%. 相似文献
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以移动烟团积分模式为基础,采用数学模型分析法,从理论上导出了小风和静风状态下的TSP大气扩散模式。该模式描述了重力沉降和地面不完全反射对颗粒物大气扩散过程的影响;与现有的大气扩散模式体系完全相容,可以方便地应用于小风和静风状态下TSP地面浓度的预测计算 相似文献
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本文用控制容积离散化方法模拟计算环境中充体的运动和污染物迁移扩散过程。该方法通用性强、可适用于一维、二维甚至三维对流、扩散问题的模拟计算,另一方面能真实反映水体的运动规律,因而可确保的合理性和稳定性,本文所建立的方法具有较高的精度和很好的稳定性。 相似文献
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目的研究某核电厂换料水池底部密封结构中密封元件的性能。方法利用有限元分析软件ANSYS,采用超弹单元建立换料水池底部密封结构密封元件的二维轴对称模型,并运用接触单元模拟密封接触界面进行计算分析。结果经计算得到换料水池底部密封结构密封元件的预紧力-变形量曲线。结论计算结果为分析换料水池底部密封结构密封试验的泄漏原因提供了理论依据,同时也为工程中密封元件预紧力的确定提供了较有价值的参考。 相似文献
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从控制方程出发,以Galerkin有限元法为基础,结合有限元法的较新改进,推导、建立了一个适合于浅水湖泊TP浓度分布计算的二维迎风有限元的数值模型,并将其应用于太湖,研究了太湖水体中TP分布特征。 相似文献
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针对湖泊富营养化问题,对太原市迎泽湖进行资料收集和长期水体监测,综合水动力模型、水质模型,融合参与湖泊富营养化的各种生命活动过程,建立湖泊富营养化耦合模型,用实测水质数据进行参数率定与验证,选取总氮、总磷、叶绿素a及透明度4项因子进行模拟,得出迎泽湖营养物质输移扩散及时空分布规律.结合迎泽湖实际情况,从补水方式、补水频率以及改变湖泊柔性结构三方面,提出改变水动力条件的方案并进行数值模拟,研究了各方案水动力、物质输移扩散的改进效果,结果表明,作为富营养化程度表征的叶绿素a在空间和时间分布上均存在一定的规律性,其浓度变化范围在0.035~0.105mg/L之间;藻类等浮游植物迅速增殖导致水质恶化水华暴发,而采取加大湖水水力循环和改善入口水质的控制方案,可有效改善湖水水质. 相似文献