上喷式矿井排风热回收装置内液滴运动模型及其优化计算

为了减小常见下喷式装置风吹水损失大的问题,设计了上喷式矿井排风热回收装置.通过液滴受力及运动分析,将上喷式液滴的运动划分为2个阶段.根据牛顿第二定律,建立了简化的液滴动量方程;在该方程的基础上,结合运动阶段划分,得到临界条件下的力平衡关系式;利用该式,在10个不同相对速度下,得到了上喷式与下喷式的保证液滴不被吹飞的临界直径.应用变量替换,将液滴动量方程变换为液滴运动距离的微分式;继而,根据液滴及空气之间的雷诺数组合,导出了液滴最大上升高度的5个积分计算式.应用这些积分式,数值计算了不同迎面风速、液滴粒径及液滴初速度下,上喷式中液滴最大上升高度、下喷式中液滴最大下降高度.对比计算结果,相比下喷式,上喷式具有节水、液滴选择范围宽和低耗高效的优势.     

二氧化碳灭火系统扑灭风电机组舱内火灾试验研究

为有效遏制全国多地风力发电机组火灾事故的势头,基于灭火系统在风电机组防火设计中的重要性,提出采用二氧化碳灭火系统对风电机舱进行灭火保护的解决方案。在建造国内首台风电机组火灾模拟试验装置的基础上,通过试验研究二氧化碳灭火系统在常温状态和低温状态下对风电机组火灾的灭火能力。结果表明,该灭火系统能够对风力发电机组进行全淹没灭火保护,适用于空间狭小且结构复杂的风电机舱;在低温条件下,其喷放时间和灭火时间虽比常温状态下长,但灭火效能并未降低。     

Experimental study on fire suppression performance of the high pressure water mist in the engine room of an offshore platform

The total flooding application water mist system is a new type of environmentally-friendly fixed extinguishing system. The optimizing design can improve its fire extinguishing performance. At present, the water mist fire extinguishing system in the engine room of the offshore deepwater semi-submersible support platform has not attracted sufficient attention. In this paper, the water mist in the engine room of a deepwater semi-submersible support platform was studied. It contains the effect of water mist on the heat absorption and oxygen insulation of diesel pool fires. The applicable parameters of the water mist fire extinguishing system were also determined. Moreover, based on the shielding of the fire source in the engine room and the different requirements for water mist extinguishing parameters, a hierarchical multi-parameter combined high-pressure water mist fire extinguishing system was proposed. In the full-scale experimental engine room model, according to the fire extinguishing experiments for diesel pool fires with different areas, this kind of hierarchical multi-parameter water mist system is very effective on shielded and non-shielded fires. In addition, it is still effective even in a non-closed environment coupled with smoke exhausting.     

Experimental investigation of the performance of modified expanded graphite powder doped with zinc borate in extinguishing sodium fires

Sodium is the main cooling medium in the circuit of fourth-generation nuclear reactors, and its leakage constitutes a severe fire hazard because of its high chemical activity. In this study, expandable graphite (EG), which is a traditional sodium fire-extinguishing agent, was modified with zinc borate (ZB) as an intercalator, and the modified EG_ZB was characterized. Moreover, the effectiveness of the modified EG_ZB in extinguishing sodium fires was tested using a self-developed fire-extinguishing experimental device. This study's results indicated that EG, EG_ZB had a smaller particle size, higher thermal stability, higher fire-extinguishing speed, and lower powder mass consumption than EG. During the fire-extinguishing process, ZnO decomposed by ZB captured free radicals and inhibited the combustion reaction. Furthermore, B₂O₃ was adsorbed on the surface of the EG layer, which strengthened covering and asphyxiation. The findings of this study provide crucial information for effectively controlling fires caused by active metals and metallo-organic compounds.     

基于缓冲区重采样的LSTM林火预测模型*

为提高林火风险预测精度,挖掘地图上隐含的空间信息、时间序列上隐含的长期趋势和循环波动,提出1种基于缓冲区重采样的长短期记忆（LSTM）林火预测模型,选取15个与林火相关的影响因素,以方差膨胀因子为评价指标对其进行多重共线性检验,方差膨胀因子大于10的因素具有共线性,并采用信息增益率验证筛选结果的合理性。考虑到火灾的空间聚集特性,采用缓冲区分析与过采样相结合方法减少样本不均衡现象的影响,最终得到176 732条样本。对12个影响因素和研究时间段的火点建立LSTM预测模型,对森林火灾发生风险进行预测。研究结果表明:基于缓冲区重采样的LSTM林火预测模型有效考虑时空上隐含的信息,预测模型准确率为87.06%,特异性为97.99%,敏感度为76.12%,阳性预测率为97.43%,阴性预测率为80.41%,ROC曲线与AUC值均优于随机森林（RF）和支持向量机（SVM）这2种基准算法。维尔克松秩和检验发现,本文提出的模型与基准算法结果具有显著性差异。研究结果可为提高林火风险预测精度提供参考。     

Influences on stakeholder support for a wildfire early warning system in a UK protected area

Projected increases in wildfire risk and impacts to human populations in the UK have prompted the installation of expanded management approaches such as early warning systems (EWSs). Newer iterations of wildfire EWSs help mitigate risk through rapid detection, often using high-resolution monitoring technology and instantaneous information collection. While existing research suggests that local social context plays an important role in the effective application of EWSs, little is known about factors that contribute to stakeholder support for these technocratic systems and their successful implementation in protected areas. This study examines support for an EWS in Northumberland National Park, UK, using focus groups with a broad range of local stakeholders. We found that diverse stakeholder understandings of wildfire, different perceptions of wildfire risk, and varied identification of values at risk collectively help explain mixed support for the EWS. Mixed support also was an outgrowth of distrust between several stakeholder groups, indicating a need for improved communication regarding wildfire risk management across stakeholder groups. Results suggest that EWSs adopted in multi-use protected areas shared by a range of stakeholder are most likely to be successful when stakeholders have shared understandings of the hazard and opportunities for collective planning to address its risks. We conclude that EWSs are a viable approach to wildfire risk reduction, but there needs to be a critical consideration of pre-existing stakeholder dynamics for effective EWS implementation.     

It’s All in the Numbers: Acreage Tallies and Environmental Program Evaluation

Increasingly, performance measurement is being used to hold federal agencies accountable, represent environmental progress, and evaluate the effectiveness of environmental programs. The need to track measurable outputs has created a tendency to present programmatic progress solely by quantifiable data, despite the inherent complexity of natural resource management. Wetlands and fire management programs are two specific environmental arenas that have come to overemphasize the tracking of acreage numbers to validate existing policy direction. In both of these arenas, we find the definition and categorization of "countable" acres to be inconsistent and unreliable. We explore this systemic flaw for both wetlands and fire programs and describe its implications for environmental policy and natural resource management more broadly. We conclude with recommendations for improved performance measurement in these arenas.     

Flame Propagation Across Gelled Alkane-In-Water Emulsions

Flame propagation rates were measured for flames spreading across surfaces of gel-like alkane-in-water emulsions. A long, slender, water-cooled trough was used to contain the mixtures. Abrupt changes in the flame propagation velocities - of nearly two orders of magnitude - were observed to occur near ‘critical’ concentrations of certain alkane/water mixtures. Four alkanes were used - pentane, hexane, heptane, and octane - and fuel rich emulsions (in which water was the continuous phase) were employed. The ability of the aqueous phase of the emulsion to inhibit the release of fuel into the vapor phase plays an important role in the observed behavior. That is, the rate at which fuel can diffuse through both the emulsion and the thin liquid layers that reside on it, is an essential kinetic aspect of the phenomena which determine the flame propagation rate across gelled alkane-in-water emulsions.     

Forest Stand Dynamics and Livestock Grazing in Historical Context

Abstract:  Livestock grazing has been implicated as a cause of the unhealthy condition of ponderosa pine forest stands in the western United States. An evaluation of livestock grazing impacts on natural resources requires an understanding of the context in which grazing occurred. Context should include timing of grazing, duration of grazing, intensity of grazing, and species of grazing animal. Historical context, when and under what circumstances grazing occurred, is also an important consideration. Many of the dense ponderosa pine forests and less-than-desirable forest health conditions of today originated in the early 1900s. Contributing to that condition was a convergence of fire, climate, and grazing factors that were unique to that time. During that time period, substantially fewer low-intensity ground fires (those that thinned dense stands of younger trees) were the result of reduced fine fuels (grazing), a substantial reduction in fires initiated by Native Americans, and effective fire-suppression programs. Especially favorable climate years for tree reproduction occurred during the early 1900s. Exceptionally heavy, unregulated, unmanaged grazing by very large numbers of horses, cattle, and sheep during the late nineteenth and early twentieth centuries occurred in most of the U.S. West and beginning earlier in portions of the Southwest. Today, livestock numbers on public lands are substantially lower than they were during this time and grazing is generally managed. Grazing then and grazing now are not the same.     

浅海平台油气火灾事故模拟评估应用

全球海洋油气开发重特大火灾事故频发,油气生产安全面临严峻挑战,以我国浅海某中心平台组为研究对象,对可能发生的三相分离器喷射火火灾、管线交叉处喷射火火灾、生产平台池火火灾以及储罐平台池火火灾,采用FDS软件建立该平台组的火灾动力学模型,对油气泄漏后火灾的发展态势、火场温度、热辐射强度、设备温度以及不同火灾工况的对比分析,研究火灾发生后对人员伤害,以及平台上油气管线、分离器、油气储罐、平台栈桥等重要设备安全性的影响,并提出操作人员和重要设备的安全距离。针对火灾事故风险控制提出建议措施,对海上火灾风险分析未来研究方向进行阐述。