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971.
为制定合理、高效的应急状况下建筑物内人群疏散方案,考虑拥堵对人流速度的影响及疏散中不同人员特点,对建筑物内人群疏散动态实时分配问题进行研究。首先,采用元胞传输理论将建筑物内复杂的结构转化为元胞—连接桥路网模型,进而以最短疏散时间为目标函数、元胞流量守恒和流量传播为约束条件建立线性优化模型。通过对模型的求解可以得到不同优先级人员的网络清空时间、各路段实时人员数量及路径选择最优方案。案例分析结果表明,疏散过程中人员的优先级差异以及拥堵的发生均会影响不同人员的网络清空时间,因此,针对建筑物内人群疏散进行建模时,应考虑以上因素。 相似文献
972.
为了研究运输设备对巷道火灾中温度场及烟气流动的影响,本文采用火灾模拟软件FDS考察了两种通风速度情况下运输设备对水平巷道火灾中烟气流动的影响,并将结果进行分析比较。结果表明:与空旷巷道相比,障碍巷道内的烟气沉降较快,运输设备会使得烟流在水平方向上的迁移加快,当其位于火源右侧时;与高通风速度的巷道相比,低风速情况下运输设备对巷道温度分布影响更明显,高温区集中分布在火源与设备之间;另外运输设备会对巷道内的气流速度分布产生较大影响,巷道局部一段区域内气流速度呈现分布不均的现象。 相似文献
973.
974.
975.
淮北平原“四水”转化模型实验研究与应用 总被引:1,自引:0,他引:1
论文基于野外实验,采用五道沟实验站和杨楼实验区1965-2007年长系列资料,考虑土壤水垂向运动和再分布、冠层截留、蒸发、填洼、大孔隙、潜水排出补给地表水等要素,采用野外实验数据逐步细化和确定参数,提出淮北平原集总式“四水”转化模型,并提出一种新的冠层截留量年内分布确定方法。模型物理意义明确,对资料的要求较低,实用性较强。模型在杨楼流域应用结果表明,模拟流量过程线精度较高,在潜水位变动过线的拟合上效果较优,在径流过程和土壤含水量的拟合上表现较好。通过模型逐年计算统计,得出杨楼实验流域1991-2007年逐年及多年平均“四水”转化定量关系,为该区水文预报和作物水利用提供技术依据。 相似文献
976.
977.
于春季、秋季和冬季分别对北京市3类典型道路(开阔型、十字路口型、峡谷型)空气中CO污染进行了现场监测,对CO时空分布和影响因素进行分析。结果表明:十字路口CO平均浓度最高,为2.81mg/m3,CO日变化幅度较小,在中午上下班时间出现高峰,峡谷型道路次之,为2.55mg/m3,CO日变化呈单峰型,在中午前出现爬坡,下午有所降低,学院路CO污染最轻,CO平均浓度为2.39mg/m3,CO浓度日变化呈多峰型,早中晚高,其他时段较低;冬季CO污染最严重,平均浓度明显高于春季和秋季,分别为3.18mg/m3、2.49mg/m3,和2.45mg/m3;风向对CO的分布也有很大影响,背风面的CO浓度明显高于迎风面的CO浓度。 相似文献
978.
Turbulence characteristics within sparse and dense canopies 总被引:2,自引:0,他引:2
Laurence Pietri Alexandre Petroff Muriel Amielh Fabien Anselmet 《Environmental Fluid Mechanics》2009,9(3):297-320
Boundary layer interactions with canopies control various environmental processes. In the case of dense and homogeneous canopies,
the so-called mixing layer analogy is most generally used. When the canopy becomes sparser, a transition occurs between the
mixing layer and the boundary layer perturbed by interactions between element wakes. This transition has still to be fully
understood and characterized. The experimental work presented here deals with the effect of the canopy density on the flow
turbulence and involves an artificial canopy placed in a fully developed turbulent boundary layer. One and two-component velocity
measurements are performed, both within and above the canopy. The influence of the spacing between canopy elements is studied.
Longitudinal velocity statistical moments and Reynolds stresses are calculated and compared to literature data. For spacings
greater than the canopy height, evidences of this transition are found in the evolution of the skewness factor, shear length
scale and mixing length. 相似文献
979.
Gravity driven flows on inclines can be caused by cold, saline or turbid inflows into water bodies. Another example are cold
downslope winds, which are caused by cooling of the atmosphere at the lower boundary. In a well-known contribution, Ellison
and Turner (ET) investigated such flows by making use of earlier work on free shear flows by Morton, Taylor and Turner (MTT).
Their entrainment relation is compared here with a spread relation based on a diffusion model for jets by Prandtl. This diffusion
approach is suitable for forced plumes on an incline, but only when the channel topography is uniform, and the flow remains
supercritical. A second aspect considered here is that the structure of ET’s entrainment relation, and their shallow water
equations, agrees with the one for open channel flows, but their depth and velocity scales are those for free shear flows,
and derived from the velocity field. Conversely, the depth of an open channel flow is the vertical extent of the excess mass
of the liquid phase, and the average velocity is the (known) discharge divided by the depth. As an alternative to ET’s parameterization,
two sets of flow scales similar to those of open channel flows are outlined for gravity currents in unstratified environments.
The common feature of the two sets is that the velocity scale is derived by dividing the buoyancy flux by the excess pressure
at the bottom. The difference between them is the way the volume flux is accounted for, which—unlike in open channel flows—generally
increases in the streamwise direction. The relations between the three sets of scales are established here for gravity currents
by allowing for a constant co-flow in the upper layer. The actual ratios of the three width, velocity, and buoyancy scales
are evaluated from available experimental data on gravity currents, and from field data on katabatic winds. A corresponding
study for free shear flows is referred to. Finally, a comparison of mass-based scales with a number of other flow scales is
carried out for available data on a two-layer flow over an obstacle. Mass-based flow scales can also be used for other types
of flows, such as self-aerated flows on spillways, water jets in air, or bubble plumes. 相似文献
980.
Transient gas flow in relief line is computed to determine the effects of fluctuations of discharge capacity on flow field. Based on the theories of computational fluid dynamics and aerodynamics, the solution and the analysis were carried out using finite volume CFD solver FLUENT 13.0. Flow fields in seven working conditions were simulated in the numerical investigation and their results were compared. The results showed that the fluctuations of discharge capacity, including extent and period, exert obvious effects on transient gas flow field in relief line. The larger the fluctuation extent and the shorter the fluctuation period, the more significant is the effect. The application method of simulation results is provided to guide the laying and fixing of pipelines, which is verified by filed measurement. 相似文献