Come hybrid or high water: Making the case for a Green–Gray approach toward resilient urban stormwater management

120 years or more of unsustainable urban development has damaged the natural environment and disrupted essential ways to stabilize water body overflow and even mitigate pluvial flooding. In light of catastrophic flooding that has occurred globally, a renewed commitment to transforming built surfaces and incorporating more green infrastructures (GIs) has emerged. In fact, one could argue that an overcommitment to GI is being touted in the literature, but largely disconnected from more real-world possibilities, considering all things. In this commentary, we make the case that as cities transition from development patterns of the past and even considering climate-induced storm characteristics of the future, a hybridized solution (e.g., Green–Gray) should be considered. Smaller approaches to urban greening have been implemented in areas that need larger-scale restorations, thus proving to be insufficient. Likewise, the uncertainty surrounding rainfall and storm events has forced us to be more strategically balanced in our efforts to achieve resilience in our stormwater infrastructure. Hybridized solutions that include a diverse set of systems, anchored in local conditions, position us best for effective urban stormwater management. In the absence of such solutions, runoff volumes will continue to rise, flooding will prevail, and disenfranchised communities will remain disproportionately impacted by these impacts of urbanization.     

Explosions of gasoline–air mixture in the tunnels containing branch configuration

In order to investigate the effects of branch tunnels on explosion propagation, experiments were performed in five different configuration tunnels (straight configuration and configurations with 1 branch, 2 branches, 3 branches and 4 branches). Pressure and flame transducers were used to record the history of the pressure development and track the velocity of the flame front. It was shown that the branch tunnels had ability to enhance the maximum overpressure, rate of overpressure rise, and deflagration index (K_G) of the gasoline–air mixture explosion due to the turbulence induced by the branch tunnels. The overpressure rise rate and K_G of the explosion increased as a function of the number of branch tunnels. Experiments also showed that the maximum flame speed increased as the branch number increasing from 0 to 3 due to the enlargement of turbulence induced by the branch tunnels. However, an increase of branch number did not always lead to an enhancement of flame speed because the heat loss was intensified resulting from the increase of flame surface caused by the branch tunnels. When the number of branch tunnels exceeded 3, the maximum flame speed dropped.     

Assessment and improvement of integrated HSE and macro-ergonomics factors by fuzzy cognitive maps: The case of a large gas refinery

This study analyzes and assesses the integrated health, safety, environment (HSE) and ergonomics (HSEE) factors by fuzzy cognitive maps (FCM) approach. This is achieved through integrating ergonomic and macro-ergonomic as well as occupational health and safety arrangements in an integrated modeling for assessment of their multi-faceted impact on workers' productivity, injury rate and satisfaction. This paper uses FCM to assess the direct and indirect effects of HSEE factors on system performance indicators. The results of FCM are used to develop leading indicators useful for proactive management of productivity, injury rate, and job satisfaction. The result of a comprehensive survey of 37 experts in control rooms and maintenance activities in a large gas refinery is used to show the applicability and usefulness of FCM approach. Moreover, FCM results are used to determine the causal structure of HSEE factors and system performance indicators. It is concluded that macro-ergonomics factors such as instructions and education, familiarity with organization's rules, and proper communications most contribute to improve workers' safety, satisfaction, and productivity.     

Experimental investigation of gas explosion in single vessel and connected vessels

Gas explosion in connected vessels usually leads to high pressure and high rate of pressure increase which the vessels and pipes can not tolerate. Severe human casualties and property losses may occur due to the variation characteristics of gas explosion pressure in connected vessels. To determine gas explosion strength, an experimental testing system for methane and air mixture explosion in a single vessel, in a single vessel connected a pipe and in connected vessels has been set up. The experiment apparatus consisted of two spherical vessels of 350 mm and 600 mm in diameter, three connecting pipes of 89 mm in diameter and 6 m in length. First, the results of gas explosion pressure in a single vessel and connected vessels were compared and analyzed. And then the development of gas explosion, its changing characteristics and relevant influencing factors were analyzed. When gas explosion occurs in a single vessel, the maximum explosion pressure and pressure growth rate with ignition at the center of a spherical vessel are higher than those with ignition on the inner-wall of the vessel. In conclusion, besides ignition source on the inner wall, the ignition source at the center of the vessels must be avoided to reduce the damage level. When the gas mixture is ignited in the large vessel, the maximum explosion pressure and explosion pressure rising rate in the small vessel raise. And the maximum explosion pressure and pressure rising rate in connected vessels are higher than those in the single containment vessel. So whenever possible, some isolation techniques, such as fast-acting valves, rotary valves, etc., might be applied to reduce explosion strength in the integrated system. However, when the gas mixture is ignited in the small vessel, the maximum explosion pressures in the large vessel and in the small vessel both decrease. Moreover, the explosion pressure is lower than that in the single vessel. When gas explosion happens in a single vessel connected to a pipe, the maximum explosion pressure occurs at the end of the pipe if the gas mixture is ignited in the spherical vessel. Therefore, installing a pipe into the system can reduce the maximum explosion pressure, but it also causes the explosion pressure growth rate to increase.     

外源氮输入对不同土地利用排水沟底泥反硝化和N2O排放影响

农田排水沟通过底泥硝化-反硝过程可消纳部分农业面源氮.水稻、蔬菜和水果是太湖地区种植业的主要土地利用类型,各种植区排水河沟密布,且不同种植区沟道接受外源氮差异明显,直接影响沟道消纳氮能力.分别采集太湖地区果园、稻田和菜地种植区排水沟道沉积物,设计上覆水N0、N1、N2、N3和N4这5个外源NO-3-N输入梯度,净氮输入量分别为0、0.5、1.0、5.0和10 mg·L~(-1),开展室内培养试验,研究外源氮输入对不同土地利用区排水沟道底泥反硝化和N2O排放的影响.结果表明,外源氮输入激发了排水沟底泥反硝化作用,3条沟道底泥反硝化速率均随上覆水NO-3-N输入浓度增大显著增大(P0.05),底泥累积反硝化量与输入NO-3-N浓度呈显著线性正相关关系(R20.75);除菜地外,沟道底泥N2O排放速率和累积排放量随外源NO-3-N输入浓度增大均无显著增大趋势(P0.05).在无外源氮或低外源氮输入时(N0和N1),果园、菜地和稻田种植区3种沟道之间底泥反硝化和N2O排放累积损失氮量的差异不显著(P0.05).随NO-3-N输入浓度增大,特别是高外源氮输入(N3和N4)条件下,果园和稻田排水沟道底泥反硝化消纳氮量显著高于菜地沟道底泥反硝化损失氮量(P0.05),而菜地排水沟底泥N2O排放损失氮量显著高于其它2条沟道底泥的N2O排放损失氮量(P0.05).排水沟底泥有机碳矿化速率与反硝化损失速率成正相关关系(n=15),微生物矿化(CO2-C)作用促进了沟道底泥硝化反硝过程.     

高瓦斯孤岛工作面预抽钻孔封孔工艺优化研究

针对王坡煤矿高瓦斯孤岛工作面预抽钻孔封孔质量差、抽采效果不理想的问题,基于围岩裂隙演化钻孔封堵原理,采用数值模拟和现场指标测试相结合的方法对巷道围岩应力场分布进行分析,进而确定了3210孤岛工作面抽采钻孔的合理封孔段深度为距煤壁15 m,并考虑距煤壁3 m范围内煤体破碎严重的问题,将原“两堵一注”封孔工艺优化为“三堵一注”封孔工艺。针对两种封孔工艺开展了现场抽采钻孔封孔试验,在60 d的抽采监测期内,优化工艺试验钻孔的平均甲烷体积分数为47.19%,较原有封孔工艺的平均甲烷体积分数高15.90%。现场试验结果表明,数值模拟与钻屑指标测定法综合确定合理封孔深度是科学有效的,抽采钻孔的封孔质量得到明显改善,抽采效果显著提高。     

Effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm determined using computational fluid dynamics

Storage tank separation distance, which considerably affects forestalling and mitigating accident consequences, is principally determined by thermal radiation modeling and meeting industry safety requirements. However, little is known about the influence of separation distance on gas dispersion or gas explosion, which are the most destructive types of accidents in industrial settings. This study evaluated the effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm. Experiments were conducted using Flame Acceleration Simulator, an advanced computational fluid dynamics software program. Codes governing the design of separation distances in China and the United States were compared. A series of geometrical models of storage tanks with various separation distances were established. Overall, increasing separation distance led to a substantial reduction in vapor cloud volume and size in most cases. Notably, a 1.0 storage diameter separation distance appeared to be optimal. In terms of vapor cloud explosion, a greater separation distance had a marked effect on mitigating overpressure in gas explosions. Therefore, separation distance merited consideration in the design of storage tanks to prevent gas dispersion and explosion.     

Simplified multiple equations' inverse problem of vented vessels subjected to internal gas explosions

This paper analyses the experimental data reported by Höchst and Leuckel (1998) for combustion in partially confined vessels and uses the data from these experiments to establish the burning rate based on a simplified model for the combustion process in such vessels. The model establishes three fundamental parameters which are necessary in characterizing the combustion process. These are: i) the burning rate, ii) the fraction of vent area occupied by burnt gas (or discharge sub-model), and iii) the vent area model (if cover mechanisms with variable vent areas are utilized). A set of independent equations is derived to determine the burning rate according to conservation of mass and volume for each gas fraction separately along with a general equation based on general volume conservation. Using this method we are able to describe the combustion process and examine the effect of various discharge models. The advantages of the model presented here include rapid applicability and a valuable analysis to derive mass burn rate and other useful parameters using experimental data from vented explosions with reasonable residual reactant values. Based on these results, the correct interpretation of the obtained burning rate can be used in order to explain the correct prediction of flame velocity and position according to a reasonable discharge model. The paper also evaluates the suitability of several discharge models for phenomenological models of vented explosions. The most appropriate is a Heaviside step function which considers that only unburnt gas is initially expelled, with that component decreasing and the burnt gas component increasing until finally only burnt gas is expelled. The obtained results in this study can be used to predict the burning rate behavior and the combustion process of similar problems.     

Locating the gas leakage source in the atmosphere using the dispersion wave method

A new and simple method for locating emission source was proposed in this work based on gas dynamic dispersion information. The simulation of the unsteady state dispersion of leakage gas emission from the geosequestration project showed that the transportation process of emission gases in the atmosphere is similar to wave propagation, and the time parameter of the dispersion wave is linearly related to the downwind distance. Therefore, monitoring the dispersion wave at different downwind positions can be used to estimate the leakage source position. An estimation formula for locating emission sources was derived. First, an estimation formula for locating emission sources was derived under some initial assumptions. Then, the deviation of the location formula was investigated using a computational fluid dynamics (CFD) model and analytic solution to get the offset distance under different conditions. The results showed that the average distance is stable for a certain atmosphere and terrestrial conditions. This method needs no more than 3 sensors’ dynamic information to locate the emission source, and hence it is highly useful for conditions with limited sensors. A numerical test demonstrated that the absolute error of the source estimation is within the range of 1–30 m. Finally, experimental tests were conducted to verify the feasibility of the source location with dispersion waves. Therefore, the dispersion wave monitor is a potentially simple and feasible way to estimate the source location for gas emission event management with limited sensors in the process industries.