Flame acceleration in tube explosions with up to three flat-bar obstacles with variable obstacle separation distance

The effect of obstacle separation distance on the severity of gas explosions has received little methodical study. It was the aim of this work to investigate the influence of obstacle spacing of up to three flat-bar obstacles. The tests were performed using methane-air (10% by vol.), in an elongated vented cylindrical vessel 162 mm internal diameter with an overall length-to-diameter, L/D, of 27.7. The obstacles had either 2 or 4 flat-bars and presenting 20% blockage ratio to the flow path. The different number of flat-bars for the same blockage achieved a change of the obstacle scale which was also part of this investigation. The first two obstacles were kept at the established optimum spacing and only the spacing between the second and third obstacles was varied. The profiles of maximum flame speed and overpressure with separation distance were shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced at 80 to 100 obstacle scales about 4 times further downstream than the position of maximum turbulence determined in the cold flow studies. Similar trends were observed for the flames speeds. In both cases the optimum spacing between the second and third obstacles corresponded to the same optimum spacing found for the first two obstacles demonstrating that the optimum separation distance does not change with number of obstacles. In planning the layout of new installations, the worst case separation distance needs to be avoided but incorporated when assessing the risk to existing set-ups. The results clearly demonstrate that high congestion in a given layout does not necessarily imply higher explosion severity as traditionally assumed. Less congested but optimally separated obstructions can lead to higher overpressures.     

通道中障碍物布局对行人运动影响的多格子模型研究

传统行人疏散运动模型对障碍物环境下的个体运动行为关注不足,而且未较好地讨论不同障碍物布局下的行人运动特性。通过改进多格子模型建立了考虑障碍物布局影响的行人运动模型,并与实验结果对比验证了该模型的有效性。利用该模型对不同障碍物布局下的单、双行人流进行模拟,探究不同障碍物布局对行人运动的影响。模拟结果表明,合理的障碍物布局有助于提高行人流的运动速度。丰富了传统多格子模型在障碍物环境下的运动规则,能够为行人交通设施设计及科学管理提供理论与技术支持。     

The effect of orifice plates with different shapes on explosion propagation of premixed methane–air in a semi-confined pipeline

The effect of internal shape of obstacles on the deflagration of premixed methane–air (concentration of 10%) was experimentally investigated in a semi-confined steel pipeline (with a square cross section size of 80 mm × 80 mm and 4 m long). The obstacles used in this study were circular, square, triangular and gear-shaped (4-teeth, 6-teeth and 8-teeth) orifice plates with a blockage ratio of 75%, and the perimeter of the orifice was regarded as a criterion for determining the sharpness of the orifice plate. The overpressure history, flame intensity histories, flame front propagation speed, maximum flame intensity and peak explosion overpressure were analyzed. The explosion in the pipeline can be divided into two stages: initial explosion and secondary explosion. The secondary explosion is caused by recoiled flame. The perimeter is positively related to the intensity of the recoiled flame and the ability of orifice plate to suppress the explosion propagation. In addition, the increase in the perimeter will cause the acceleration of the flame passing through the orifice plate, while after the perimeter of the orifice reaches a certain value, the effect of the increase in perimeter on explosion excitation becomes no obvious. The overpressure (static pressure) downstream of the orifice plate is the result of the combined effect of explosion intensity and turbulence. The increase in perimeter leads to the increase in turbulence downstream of the orifice plate which in turn causes more explosion pressure to be converted into dynamic pressure.     

RETRACTED ARTICLE: Evaluation for sustainable land use in mountain areas of Northwestern Yunnan Province, China

As an important component of sustainable development in mountain areas, evaluation for sustainable land use is always one of the hotpots of researches on sustainable development. Traditional evaluation for sustainable land use mainly focuses on the sustainability of land use model and biological production on temporal scale, and overlooks the effects of land use patterns on the sustainability, while landscape ecology can be a good help to realize the spatial analysis of sustainable land use. In this study, a synthetic evaluation indexes system for sustainable land use was constructed through the application of landscape metrics. Taking Yongsheng County of Yunnan Province, China as a case study, a series of quantitative evaluation were conducted in 1996, 1999 and 2001, to monitor the temporal dynamics of regional land use sustainability. Two indicators, contributing amount of indexes, and obstacle amount of indexes, were also set up to ascertain the significance of all the evaluation indexes to the evaluation results. The results showed that, in the study phases, the land use sustainability of the whole county had been low with a stable but great spatial difference, and great changes took place in regional land use system in 1999 with the deviation from the aim of sustainable land use. It also showed that, the most important indexes contributing for the land use sustainability in the study period, were the indexes of population density and land use degree, followed by the index of landscape diversity and cropping index. And the most important indexes counteracting the land use sustainability were the indexes of per unit area total production value of industry and agriculture, per unit area yield of cereal crops, landscape fragmentation, followed by the indexes of per unit area yield of economic crops and fertilizer consume per unit area.     

太湖流域水生态环境功能分区管理指标达成效率评估和预警研究

太湖流域严峻的水生态环境形势备受关注,而水生态环境功能分区管理体系实施现状和效果无法被准确把握。以太湖流域水生态环境功能分区为研究对象,基于四象限法则和二维向量结构指标体系等方法论,综合障碍因子分析与目标可达性分析,对太湖流域水生态环境功能分区管理绩效评估目标达成效率进行评估和预警,为水生态环境功能分区管控提供技术指导。结果表明,江苏省太湖流域目标达成效率情况较好,"高效"、"一般"、"低效"的比例依次下降,高预警级别的区域较少;环境效率指标中单位面积污染物减排管控效率较高,环境质量指标整体表现良好,须谨防向"低效"转变。