架空及埋地天然气管道泄漏扩散数值研究

天然气在管道运输过程中,由于含硫等腐蚀性气体对管道内壁的腐蚀作用,在管内其他压力的作用下,会引起穿孔泄漏。泄漏后的天然气扩散后,可能会引发火灾、中毒或爆炸。因此,进行天然气管道泄漏扩散及数值模拟研究,对管道输送安全运营和保障人生财产安全意义重大。该文利用CFD软件对架空及埋地含硫天然气管道穿孔泄漏后的甲烷、硫化氢气体的扩散进行了数值模拟。结果表明,受土壤毛孔阻力的影响,埋地天然气管道泄漏爆炸范围比架空天然气管道泄漏要小,但其在地面的影响时间长,硫化氢的中毒范围比架空要低30m左右。为天然气的安全输送及环境保护提供了理论依据。     

超短半径径向水平井抽采煤层气渗流规律的数值模拟

为得到超短半径径向水平井开采煤层气过程中的气体渗流规律以及进行产量预测,在基本假设条件下,建立了径向水平井开采煤层气的固流耦合渗流数学模型;在一定的边界条件及初始条件下,利用Matlab软件进行编程计算后,得到直井和不同数目分支径向水平井开采煤层气1000天后的压力场、速度场和气产量变化规律.数值模拟结果表明,在一定的...     

2016年冬季寿县一次边界层低空急流对污染物扩散的影响

利用安徽寿县地区2016年12月16~17日的观测资料与模拟资料,分析了一次夜间边界层低空急流对PM_2.5扩散的影响.此过程中,急流分布范围广,强度大,最大风速可达10~12m/s,而且风向随高度有明显转向,高低层风向差可达90°.急流发展过程中,急流轴基本位于200m以下,急流的最小风速高度出现在400~800m之间.通过分析可知,对于不同高度,急流对污染物扩散的影响存在明显差异.地面至急流轴范围内,PM_2.5总体减少.急流的出现使湍流混合明显增强,在湍流作用下污染物向上混合,使该层PM_2.5显著减少,净质量通量的峰值可达-103×10^-3μg/(m²·s).急流的水平输送可带来上风方较为清洁气团,同样减少了该层的PM_2.5浓度.但与湍流作用相比其影响较小,净质量通量仅为-2.9×10^-3μg/(m²·s).急流存在时,还会加强向下的垂直风速,在垂直输送作用下,上层污染物向下输送,增加了该层PM_2.5浓度,净质量通量约为11×10^-3μg/(m²·s).急流轴至风向转变高度之间,PM_2.5总体增加.这是由于湍流作用将低层高浓度污染物输送至该层,使PM_2.5浓度增加,净质量通量约为23.9×10^-3μg/(m²·s);水平输送作用使该层PM_2.5浓度略有增加,净质量通量约为2.3×10^-3μg/(m²·s);而垂直输送作用带来了高处较为清洁的气团,减少了PM_2.5浓度,净质量通量约为-6.6×10^-3μg/(m²·s).风向转变高度至LLJ最小风速高度之间,PM_2.5总体增加.湍流作用仍占主导,净质量通量约为17.8×10^-3μg/(m²·s);垂直输送作用稍有贡献,净质量通量约为1.4×10^-3μg/(m²·s);而水平输送起减少作用,净质量通量约为-3.7×10^-3μg/(m²·s).     

Hemming process with counteraction force to prevent creepage

Creepage, a typical phenomenon in the hemming process, can be defined as undesired roll-in of the panel at the bending line. Creepage also reduces the final panel width and makes the hemming radius larger. In this study, experimental observations are reported, and a finite element model, based on the LS-DYNA^® two dimensional plane strain solid formulation, is utilized to study the mechanics of how the hem flange bends and folds during the hemming process. A novel hemming process incorporating a counteraction force is proposed in order to prevent the creepage phenomenon during the hemming process. An experimental hemming tool was designed according to this concept, and optimization of the tooling geometry was carried out utilizing the finite element model. An experimental study was conducted to confirm that the new hemming process can prevent creep be employed to help retain a sharp radius during flanging operation.     

基于响应曲面法的有效抽采半径多因素交互影响机制研究*

为探究钻孔有效抽采半径的关键影响因素及各因素间交互作用,构建应力应变-瓦斯吸附解吸耦合渗透率变化模型,采用COMSOL软件进行数值模拟,分析单一因素变化对钻孔有效抽采半径的影响,并通过Design-Expert软件设计响应曲面试验,分析多因素交互作用对钻孔有效抽采半径变化的影响机制,获得有效抽采半径对多因素交互影响的响应曲面模型。研究结果表明:不同因素对钻孔有效抽采半径影响的显著性顺序为:煤层初始渗透率、原始瓦斯压力、抽采时间,煤层初始渗透率和抽采时间与有效抽采半径呈正相关关系,原始瓦斯压力与有效抽采半径呈负相关。1个影响因素的变化会影响其他因素对有效抽采半径的影响,煤层初始渗透率能够放大其他因素对有效抽采半径的影响,而原始瓦斯压力则会降低其他因素对有效抽采半径的影响。     

Fluid Mechanics of Serpentine Flow Fields on a Porous Media

Laminar flows are investigated in single and double parallel serpentine channels mounted on a porous media and it is found that significant convective transport occurs in porous media for practical fuel cell conditions. This transport increases with increasing flow Reynolds number, with decreasing land width, and most significantly with increasing channel length.

Increasing the number of parallel channels significantly decreases the pressure drop across the fuel cell, but also significantly decreases the magnitude of convective transport in the porous media. Increased parasitic loads must be put in the context of the change in electrochemical performance.

This paper presents both data and a methodology for beginning to think about flow field design from a hydrodynamic perspective.     

Fuelling an Environmental Conflict through Information Diffusion Strategies

When an environmental conflict occurs, the information people have access to play a crucial role in how the conflict develops. Through a case study of an ongoing conflict related to a highly contested wind farm in Québec (Canada), this paper focuses on how the news of the project was announced by the developer and on how it was then diffused by different involved actors. It aims to answer the following questions: who is informed, when are these people informed, and how does it impact the unfolding conflict? Field observation and in-depth interviews with 93 individuals involved in the public hearing process were conducted. An important part of the analysis was made using social network analysis to reconstruct diffusion of the news of the project among the sample over a 5-year period. The main findings showed that the developer made strategic choices regarding information diffusion (confidentiality, exclusion of some actors—especially the citizens, rumors, etc.) that spurred on opposition in the latest stage of development of the project. The population's awareness was slow to grow, mainly because the news of the project was slow to spread in the community.     

Sustainable monitoring of concrete structures: strength and durability performance of polymer-modified self-sensing concrete

Concrete structures all over the world are reaching the end of their service life sooner than expected. This is due to the fact that ordinary Portland cement-based concrete deteriorates under environmental actions and also that structural inspections and conservation actions are expensive. Besides, as they consume energy and non-renewable resources, they have negative environmental impacts. Self-sensing concrete provides an alternative way of monitoring concrete-reinforced structures at a much lesser cost and with lesser environmental impact. Although the short-term mechanical properties of these materials are usually well documented, the long-term durability issues about carbon fibre concrete still deserve further investigations. This paper reports some investigation of the strength and durability characteristics of several concrete mixtures modified with different percentages of polymer and carbon fibre addition. The results show that the addition of carbon fibre decreases the strength and increases water penetration under pressure and also increases chloride diffusion, whereas polymer addition is responsible for a denser microstructure and higher concrete durability.     

非等压下考虑渗流和剪胀的圆巷围岩弹塑性统一解

对于富水地层中深埋圆形巷道,为研究多种因素影响下巷道围岩塑性区范围和洞周位移的变化规律,对巷道围岩进行了弹塑性理论分析。对围岩应力场和渗流场进行耦合分析,基于统一强度理论和非关联流动法则,推导出多种因素影响下深埋圆形巷道围岩应力、位移和塑性区半径的解析计算式。结合工程实例进行计算分析,结果表明:中间主应力参数、围岩侧压系数、初始孔隙水压和剪胀角对围岩塑性区径向位移和塑性区范围均有显著影响,但影响规律各不相同;考虑中间主应力作用时,其他各因素的影响效应减弱。综合考虑以上各因素对围岩稳定性的影响,计算结果更加接近工程实际情况。     

Greenhouse gas mitigation in developing countries through technology transfer?: a survey of empirical evidence

While greenhouse gas (GHG) emissions are projected to rise primarily in the developing countries, the potential for developing new GHG mitigation technologies exists primarily in the industrialized countries. It is thus important, not only for predictions about future emission paths but also for climate change mitigation policies, to understand how the international diffusion of such technologies takes place and how it affects the energy infrastructure and GHG emissions in developing countries. This paper provides an overview of the channels through which these technologies diffuse and focuses on the empirical evidence pertaining to the effects these technologies have on GHG emissions in developing countries.