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131.
According to standard procedures, flammability and explosion parameters for dusts and dust mixtures are evaluated in 20 L and/or 1 m3 vessels, with equivalent results provided a correct ignition delay time (60 ms in the 20 L vessel; 600 ms in the 1 m3 vessel). In this work, CFD simulations of flow field and dust concentration distribution in the 1 m3 spherical vessel are performed, and the results compared to the data previously obtained for the 20 L. It has been found that in the 1 m3 vessel, the spatial distribution of the turbulent kinetic energy is lower and much more uniform. Concerning the dust distribution, as in the case of the 20 L, dust is mainly concentrated at the outer zones of the vortices generated inside the vessel. Furthermore, an incomplete feeding is attained, with most of the dust trapped in the perforated annular nozzle. Starting from the maps of dust concentration and turbulent kinetic energy, the deflagration index KSt is calculated in both vessels. In the conditions of the present work, the KSt is found to be 2.4 times higher in the 20 L than in the 1 m3 vessel. 相似文献
132.
Steel tanks are widely used in the storage of various chemical liquids, and the blast resistance of the tanks is very important because of the explosiveness of these liquids. To explore a feasible method to improve the blast resistance of steel tanks, the effect of polyurea coating on the blast resistance of steel storage tank is investigated in this paper. The responses of monolithic steel tanks and polyurea coated tanks under blast loads are studied by field blast experiments using TNT explosive, and the results shows that the polyurea layers are effective in reducing the maximum and residual displacements of the tank. Numerical simulations are performed and validated, and the deformation process and stress and strain distribution of the tanks are analyzed accordingly. The increase on the bending moment of the plastic hinge lines of the tanks and the increase of the area density of the cylindrical shell induced by the polyurea layers are believed to be the two main factors contributing to the displacement reduction effect of polyurea in this paper. The validated numerical model is used to study the influence of polyurea layer's thickness on the deflection of the tank, and a nearly inversely proportional relationship between the thickness and the maximum displacement is found. Three deformation modes of the tanks are identified when subjected to blast load with varying intensity and it is found that the displacement reduction effect of polyurea varies in different deformation modes. 相似文献
133.
Preventing the propagation of flames in a pipeline is an effective measure for avoiding gas explosion accidents and reducing losses. To evaluate the effect of wire mesh, acting as a porous media, experimental and simulation studies are conducted to determine the influence of the wire mesh on the dynamics of premixed methane/air flame propagation in a semi-closed pipe. Four different kinds of wire mesh with different numbers of layers are chosen in the experiments and simulation, and the mechanism of wire mesh quenching of the flame is investigated. The experimental and simulation results are consistent. Flames are quenched when 4 layers of 40-mesh or 3 layers of 60-mesh wire mesh are used; however, once the flame propagates through the wire mesh, the risk of methane combustion may increase. The wire mesh becomes the key factor causing flame folds and acceleration, and the greater the number of layers or the larger the mesh size is, the more obvious the folds after the flame passes through the wire mesh. Moreover, the combination of heat absorption and disruption of the continuous flame surface by the mesh causes flame quenching. Wire mesh can effectively attenuate the flame temperature during premixed flame propagation in a pipe, and the attenuated maximum rate reaches approximately 79% in the case of adding 3 layers of 60-mesh wire mesh. 相似文献
134.
The sensitivity of the United States Forest Health Monitoring network to outbreaks of defoliating insects was examined by means of a simulation study. A model constructed specifically for the study was used to generate a wide variety of defoliation patterns in forested landscapes. Forest configuration was that of Minnesota, USA, as expressed by the GAP land cover classification. Combinations of model parameters were based on a Latin Hypercube sample. The relationship between the average number of plots defoliated and outbreak characteristics was then examined via multiple regression. Both theoretical and model results pointed to a strong, linear relationship between the average number of plots defoliated and outbreak size. Model results provided additional insight, suggesting a significant relationship between the average number of plots defoliated and other outbreak characteristics after outbreak size was taken into account. 相似文献
135.
粉尘点污染扩散模型的可视化研究 总被引:1,自引:0,他引:1
在分析和总结了瞬时点尘源在静止流体、均匀紊流和湍流条件下扩散模型的数学表达式和浓度分布方程的基础上,运用Matlab软件进行可视化处理,生成一系列的三维图形,可从不同的角度进行观察和分析,使之能够直观、形象的了解粉尘扩散过程,并从中了解到粉尘扩散的一些特点,该项研究对粉尘防治工作与危害预测都有重要的理论与实践意义。 相似文献
136.
137.
138.
TUGAI: An Integrated Simulation Tool for Ecological Assessment of Alternative Water Management Strategies in a Degraded River Delta 总被引:1,自引:0,他引:1
Schlüter M Rüger N Savitsky AG Novikova NM Matthies M Lieth H 《Environmental management》2006,38(4):638-653
The development of ecologically sound water allocation strategies that account for the needs of riverine ecosystems is a pressing
issue, especially in semiarid river basins. In the Aral Sea Basin, a search for strategies to mitigate ecological and socioeconomic
deterioration has been in process since the early 1990s. The Geographic Information System–based simulation tool TUGAI has
been developed to support the policy determination process by providing a simple, problem-oriented method to assess ecological
effects of alternative water management strategies for the Amudarya River. It combines a multiobjective water allocation model
with simple, spatially explicit statistical and rule-based models of landscape dynamics. Changes in environmental conditions
are evaluated by a fuzzy habitat suitability index for Populus euphratica, which is the dominant species of the characteristic riverine Tugai forests. Water management scenarios can be developed
by altering spatiotemporal water distribution in the delta area or the amount of water inflow into the delta. Outcomes of
scenario analysis are qualitative comparisons of the ecological effects of different options for a time period of up to 28
years. The given approach utilizes different types of knowledge, from quantitative hydrological data to qualitative local
expert knowledge. The main purpose of the tool is to integrate the knowledge in a comprehensive way to make it available for
discussions on alternative policies in moderated workshops with stakeholders. In this article, the modules of the tool, their
integration, and three hypothetical scenarios are presented. Based on the experience gained when developing the TUGAI tool,
we propose that the general framework can be transferred to other areas where tradeoffs in water allocation between the environment
and other water users are of major concern. The potential for a simulation tool to structure and inform a complex resource
management situation by involving local experts and stakeholders in the development of possible future scenarios will become
increasingly valuable for transparent and participatory resource management. 相似文献
139.
River channel migration and cutoff events within large river riparian corridors create heterogeneous and biologically diverse
landscapes. However, channel stabilization (riprap and levees) impede the formation and maintenance of riparian areas. These
impacts can be mitigated by setting channel constraints away from the channel. Using a meander migration model to measure
land affected, we examined the relationship between setback distance and riparian and off-channel aquatic habitat formation
on a 28-km reach of the Sacramento River, California, USA. We simulated 100 years of channel migration and cutoff events
using 11 setback scenarios: 1 with existing riprap and 10 assuming setback constraints from about 0.5 to 4 bankfull channel
widths (bankfull width: 235 m) from the channel. The percentage of land reworked by the river in 100 years relative to current
(riprap) conditions ranged from 172% for the 100-m constraint setback scenario to 790% for the 800-m scenario. Three basic
patterns occur as the setback distance increases due to different migration and cutoff dynamics: complete restriction of cutoffs,
partial restriction of cutoffs, and no restriction of cutoffs. Complete cutoff restriction occurred at distances less than
about one bankfull channel width (235 m), and no cutoff restriction occurred at distances greater than about three bankfull
widths (∼700 m). Managing for point bars alone allows the setbacks to be narrower than managing for cutoffs and aquatic habitat.
Results suggest that site-specific “restriction of cutoff” thresholds can be identified to optimize habitat benefits versus
cost of acquired land along rivers affected by migration processes. 相似文献
140.
亚洲大陆2000~2002年春季大气沙尘时空特征的数值模拟 总被引:14,自引:0,他引:14
将矿物沙尘释放与沉降模式和全球大气化学传输模式相耦合,建立了一个能够完整描述沙尘的扬起、输送和沉降动态过程的模式系统,并利用实时气象资料强迫该模式,对2000、2001和2002年春季(3~5月)亚洲大气沙尘时空特征进行了数值模拟研究.结果表明,模拟的3年春季平均大气柱沙尘浓度分布与地面观测的3年春季平均沙尘暴频率分布范围基本吻合,模拟的沙尘气溶胶光学厚度与卫星观测的气溶胶指数具有显著的相关性,验证了该模式对亚洲沙尘的扬起、传输和沉降过程及大气沙尘载荷时空特征有较好的模拟能力,并基于模拟的沙尘释放通量与沙尘气溶胶光学厚度的相关分析,探讨了亚洲沙尘可能的传输路径. 相似文献