Flame extension length of inclined hydrogen jet fire impinging on a water curtain

The use of a water curtain system to prevent fire spread has been extensively investigated, but the case of an inclined jet fire inhibited with a water curtain is not involved. A series of experiments were conducted on inclined hydrogen jet fires with various fuel flow rates, nozzle diameters and inclination angles under the influence of a vertical water curtain. This study aims to explore the burning behaviors of inclined jet flames at the impingement area, specifically the flame extension lengths. The experimental results show that an increase in fuel flow rates or nozzle diameter leads to a larger flame extension length. With the increase of flame inclination angle, the flame extension length decreases and the influence of nozzle diameter on the flame extension length is attenuated. A new dimensionless heat release rate is proposed to correlate with the dimensionless flame extension length by incorporating an air entrainment coefficient. The model built in this study can be used to predict the flame extension length of jet flames with different diameters, fuel flows and inclinations under the influence of a water curtain, and is validated by data in the previous study.     

基于微台阶法对连拱隧道稳定性的研究

为研究软弱围岩基于微台阶法连拱隧道合理的掌子面纵向间距、仰拱一次开挖长度和开挖进尺施工参数,确保隧道安全和高效施工,以云南省元蔓高速公路风口山隧道为研究对象,从力学机理上分析了施工参数对隧道稳定的影响,采用数值模拟方法,分析纵向间距对中隔墙水平位移和开挖面叠加效应的影响、仰拱一次开挖长度对拱腰水平位移和中隔墙受力的影响、开挖进尺对围岩变形特征和掌子面剪应力的影响,对连拱隧道微台阶法进行最优化设计。结果表明,掌子面纵向间距2D、仰拱一次开挖长度4 m、开挖进尺2m为宜,可为类似连拱隧道的施工提供指导。     

广东省台风暴潮灾害社会经济系统脆弱性分析——模糊数学方法

给出了台风暴潮灾害社会经济系统脆弱性的定义,应用模糊综合评价方法提供了计算台风暴潮灾害社会经济系统脆弱性的评估模式,进而探讨了脆弱性的空间分布状况,并将其应用于广东省台风暴潮灾害的脆弱性评估,所提方法可以较好地综合多种社会经济因素对台风暴潮灾害的影响.     

侧部点式排烟模式下烟气分层特性研究

引入烟气掺混影响长度的概念,针对侧部点式排烟模式下不同火灾热释放速率、排烟流量等变化条件,对烟气层厚度、烟气层温度及水平流动速度随烟气水平蔓延的变化情况进行了数值模拟研究。结果表明:烟气掺混影响长度与排烟流量成正比例增长关系;排烟流量较小时,烟气存在明显分层,随着排烟流量的增大,烟气层与冷空气层剧烈掺混,烟气层变得紊乱,看不到明显的分层现象;同一纵向条件下排烟口附近上层烟气层的流速值随排烟流量增加呈现先增大后减小的趋势,不同纵向条件下排烟口外侧烟层流速较低,距离排烟口越远时,侧向排烟对烟气蔓延的抑制作用越弱;排烟流量对于烟气层稳定性的抑制作用主要集中在排烟口处及排烟口与隧道端部区段。     

基于TruckSim的大型货物运输车辆安全运行纵坡最大长度研究*

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。     

长径比对管道油气爆炸特性与火焰传播规律影响研究*

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。     

Experimental investigation of bubbly flow and turbulence in hydraulic jumps

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.     

The importance of mangrove forest in tsunami disaster mitigation

Tsunamis and storm surges have killed more than one million people and some three billion people currently live with a high risk of these disasters, which are becoming more frequent and devastating worldwide. Effective mitigation of such disasters is possible via healthy coastal forests, which can reduce the energy of tsunamis. In recent years, these natural barriers have declined due to adverse human and natural activities. In the past 20 years, the world has lost almost 50 per cent of its mangrove forests, making them one of the most endangered landscapes. It is essential to recover them and to use them as a shield against a tsunami and as a resource to secure optimal socio-economic, ecological and environmental benefits. This paper examines the emerging scenario facing mangrove forests, discusses protection from tsunamis, and proposes a way to improve the current situation. We hope that practical tips will help communities and agencies to work collectively to achieve a common goal.     

The Role of Wetlands for Mitigating Economic Damage from Hurricanes

Coastal communities along the United States coast often experience significant economic damage resulting from the impacts of tropical storms and hurricanes. Research suggests that certain factors that affect economic damages are increasing the vulnerability of coastal communities. Population growth, which increases vulnerability by placing valuable lives and assets in the path of storms, is expected to increase. Climate change has the potential to cause more frequent and intense storms, and coastal wetland loss is contributing to the vulnerability of coastal populations. Wetlands conservation and restoration is often advocated for as a means of reducing the impacts of coastal storms. The relationship between wetlands and storm surge energy is understood relatively well in physical terms, but very little economic analysis has been conducted to estimate the degree to which wetlands reduce economic impacts. Using factor analysis, the relationships among coastal populations, wetlands, storm intensity, and economic damage are explored. The factor analysis suggests that wetland presence is associated with a reduction in economic damages from coastal storms. Factor score analysis suggests that the proportion of damage explained by wetland presence is smaller for more intense storms. These results are consistent with those found in the physical science literature and have potentially large consequences for how wetlands are used in risk reduction.     

中国沿海风暴潮灾害的历史变化及未来趋向

中国是全球少数几个同时受台风风暴潮和温带风暴潮危害的国家之一,风暴潮灾一年四季,从面到北均可发生,本文基于中国沿海近５０年风暴潮灾时间变化和空间分布特点的分析,着重探讨了近５００年全国及长江、黄河、珠江三角洲的历史记录和近５０年实测风暴潮灾发生频次的变化及其与气候波动的关系,并对未来全球变化背景下,中国沿海风暴潮灾的变化趋向进行了讨论。结果表明：近５００年来,中国沿海的风暴潮灾的气温较高的偏暖时段