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121.
为研究适用于典型大型货物运输车辆的道路纵坡及最大坡长参数,构建大型货物运输车辆动力学仿真模型,并考虑车辆冲坡行为及公路线形设计习惯,建立包含直线提速蓄能路段、以最小长度控制的竖曲线路段以及不同坡度纵坡路段组成的试验道路,对比分析设计速度120 km/h、纵坡坡度1.0%~3.0%,设计速度100 km/h、纵坡坡度1.0%~4.0%以及设计速度80 km/h、纵坡坡度1.0%~5.0%3种不同道路条件下,大型货物运输车辆在试验路段的运行速度变化规律。依据速度一致性原则,以大型货物运输车辆的运行速度衰减度作为控制指标,得到各设计速度道路不同纵坡路段对应的最大纵坡长度。结果表明:在保证纵坡路段满足最小长度要求的条件下,通过减小纵坡路段长度,增大竖曲线长度,可提高大型货物运输车辆纵坡路段通过性。 相似文献
122.
为了探究长径比对油气爆炸传播特性与火焰传播规律的影响,为复杂管道受限空间油气爆炸防控提供理论参考,结合油气爆炸与爆炸抑制工程实际需要,构建不同长径比管道油气爆炸模拟实验系统,在此基础上开展不同初始浓度的预混油气-空气混合气爆炸实验。研究结果表明:管道内部的预混油气爆炸超压信号呈先上升后下降的趋势,由于耗散以及憋压效应导致超压下降平稳后仍大于初始压力;同时长径比增加会导致达到最大爆炸超压的油气浓度增加,油气爆炸超压峰值随着长径比的增加呈现上升→下降→上升的规律,小长径比管道的油气爆炸超压峰值高于大长径比管道,但同为小长径比管道或大长径比管道工况的实验结果对比显示爆炸超压峰值随着长径比增加而提升;而超压上升速率则会随着长径比的增加而上升;长径比的增加同时也会促进火焰的加速传播并减小火焰持续时间。 相似文献
123.
Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or
diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion
constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and
air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated
with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion
and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge
concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well
as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic
jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes.
Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented.
New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence
level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses
show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble
chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements
showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as
well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary
conditions on the turbulence structure. 相似文献
124.
Matthieu Guillemain Johan Elmberg Michel Gauthier-Clerc Grégoire Massez Richard Hearn Jocelyn Champagnon Géraldine Simon 《Ambio》2010,39(2):170-180
Animal populations are exposed to large-scale anthropogenic impact from e.g. climate change, habitat alteration and supplemental
stocking. All of these may affect body condition in wintering dabbling ducks, which in turn may affect an individual’s survival
and reproductive success. The aim of this study was to assess whether there have been morphometric changes in Mallard (Anas platyrhynchos) and Teal (Anas crecca) over the last 30 years at a major wintering site. Body mass and condition increased from the 1950s–1960s to the 2000s in
both species. The increase in body mass amounted to as much as 11.7%, with no corresponding change in body size. Improved
body condition was maintained from early to mid-winter, but then converged with historical values for late winter. Our interpretation
is that increasingly benign ambient winter conditions permit ducks to maintain better energetic “safety margins” throughout
winter, and that converging spring departure values may be related to evolutionary flight energetic optima. The observed changes
are consistent with large-scale climate amelioration and local/regional habitat improvement (both anthropogenic). 相似文献
125.
为研究不同因素对半横向排烟模式下公路隧道火灾烟气逆流长度的影响规律,采用理论分析推导火灾烟气逆流长度与火源功率、排烟速度、排烟口面积和排烟口间距4个因素的无量纲关系式,运用数值模拟研究不同因素下火灾烟气的运动规律,最后拟合得到烟气逆流长度的无量纲关系式.结果表明:在半横向排烟模式下,烟气逆流长度随火源功率的增大而增大,... 相似文献
126.
城市交通方式和道路系统的布局对城市的规模和空间结构具有重大影响。以芜湖市为例,通过对不同历史时期的比较,提出了城市在水运时期的单侧带状布局、陆路时期的放射布局和综合高速交通时期的都市区三种空间布局形式。此外,借用长度-半径维数模型与关联维数模型对交通方式与城市空间形态之间的关系进行了论证和探讨。 相似文献
127.
128.
为深入探索可获得光资源量(light availability)与水华鱼腥藻(Anabaena flos-aquae)浮沉关键因子——细胞比重、藻丝长度,以及水华鱼腥藻沉降损失的关系,开展了纯培养试验.在温度(25±1)℃,光照度分别为100,500,1000,3000,5000lx的条件下,培养时间35d,结果显示:在1~10d内鱼腥藻细胞比重随光照度增大而增大,在10d左右达到最大值,随后各光照组下鱼腥藻细胞比重较稳定且相差不大;光照越强,水华鱼腥藻的藻丝越短,其变化趋势是先增大到最大值再减小;光照越强,水华鱼腥藻的藻丝长度越快增大到最大值;实验结束时高光照度下水华鱼腥藻沉降损失比率较小,均低于10%,低光照下水华鱼腥藻沉降性能较好,最高可达到57.3%.实验结果表明:可获得光资源量下降直接影响鱼腥藻比重和藻丝长度并进一步导致鱼腥藻的沉降损失比率增大,这为持续型垂直混合导致蓝藻消亡的原因提供了新解释. 相似文献
129.
Molecular characterization of bacterial community in aerobic granular sludge
stressed by pentachlorophenol 总被引:2,自引:0,他引:2
To characterize the effects of pentachlorophenol (PCP) on the performance and microbial community of aerobic granular sludge in sequencing batch reactor (SBR), the web-based terminal restriction fragment length polymorphism (T-RFLP) and real-time PCR (RT- PCR) techniques were used to explore the bacterial community structure. When PCP increased from 0 to 50 mg/L, the COD removal rate changed little, while the ammonia removal rate dropped from 100% to 64.9%. The results of molecular characterization showed t... 相似文献
130.