高压管汇磁致伸缩导波缺陷检测模拟研究

针对高压管汇导波缺陷检测问题,基于磁致伸缩效应,借助COMSOL有限元仿真软件,建立高压管汇直管段的导波缺陷检测模型,探究导波的激励条件及缺陷检测效果,分析不同参数对缺陷附近磁感应强度分布的影响。研究结果表明:在频率为10 kHz的正弦电流信号激励下,可产生沿管道轴向传播的T（0,1）模态导波,并能辨别缺陷处的回波信号。改变缺陷的尺寸参数时,缺陷附近的磁感应强度随着缺陷深度增加呈增大趋势,随轴向宽度增加呈减小趋势,不同形状的缺陷对应的磁感应强度存在一定的差异;改变激励条件,磁感应强度均随激励电流、激励频率的增加呈不断增加趋势。     

Numerical and experimental study on the generation and propagation of negative wave in high-pressure gas pipeline leakage

Negative-wave-based leakage detection and localization technology has been widely used in the pipeline system to diminish leak loss and enhance environmental protection from hazardous leak events. However, the fluid mechanics behind the negative wave method has yet been disclosed. The objective of this paper is to investigate the generation and propagation of negative wave in high-pressure pipeline leakage. A three-dimensional computational fluid dynamic (CFD) study on the negative wave was carried out with large eddy simulation (LES) method. Experimentally validated simulation presented the transient wave generation at the leak onset and the comprehensive wave evolution afterwards. Negative wave was proven to be a kind of rarefaction acoustic waves induced by transient mass loss at the onset of leakage. Diffusion due to the density difference at wave fronts drives the negative wave propagation. Propagation of negative wave can be categorized into three states – semi-spherical wave, wave superposition and plane wave, based on different wave forms. The wave characteristics at different states were elucidated and the attenuation effects were discussed respectively. Finally, a non-dimensional correlation was proposed to predict the negative wave amplitude based on pipeline pressure and leak diameter.     

Inhibiting effects of gas–particle mixtures containing CO2, Mg(OH)2 particles,and NH4H2PO4 particles on methane explosion in a 20-L closed vessel

The main risk factors from methane explosion are the associated shock waves, flames, and harmful gases. Inert gases and inhibiting powders are commonly used to prevent and mitigate the damage caused by an explosion. In this study, three inhibitors (inert gas with 8.0 vol% CO₂, 0.25 g/L Mg(OH)₂ particles, and 0.25 g/L NH₄H₂PO₄ particles) were prepared. Their inhibiting effects on methane explosions with various concentrations of methane were tested in a nearly spherical 20-L explosion vessel. Both single-component inhibitors and gas–particle mixtures can substantially suppress methane explosions with varying degrees of success. However, various inhibitors exhibited distinct reaction mechanisms for methane gas, which indicated that their inhibiting effects for methane explosion varied. To alleviate amplitude, the ranking of single-component inhibitors for both explosion pressure (P_ex) and the rate of explosion pressure rise [(dP/dt)_ex] was as follows: CO₂, NH₄H₂PO₄ particles, and Mg(OH)₂ particles. In order of decreasing amplitude, the ranking of gas‒particle mixtures for both P_ex and (dP/dt)_ex was as follows: CO₂–NH₄H₂PO₄ mixture, CO₂‒Mg(OH)₂ mixture, and pure CO₂. Overall, the optimal suppression effect was observed in the system with the CO₂–NH₄H₂PO₄ mixture, which exhibited an eminent synergistic effect on methane explosions. The amplitudes of P_ex with methane concentrations of 7.0, 9.5, and 11.0 vol% decreased by 37.1%, 42.5%, and 98.6%, respectively, when using the CO₂–NH₄H₂PO₄ mixture. In addition, an antagonistic effect was observed with CO₂‒Mg(OH)₂ mixtures because MgO, which was generated by the thermal decomposition of Mg(OH)₂, can chemically react with water vapor and CO₂ to produce basic magnesium carbonate (xMgCO₃·yMg(OH)₂·zH₂O), thereby reducing the CO₂ concentration in a reaction system. This research revealed the inhibiting effects of gas‒particle mixtures (including CO₂, Mg(OH)₂ particles, and NH₄H₂PO₄ particles) on methane explosions and provided primary experimental data.     

瓦斯积聚量及爆炸距离对风机和防爆门的影响研究*

为揭示瓦斯积聚量及瓦斯爆炸距离对风机和防爆门的影响机制,利用Fluent模拟软件,结合宁煤集团羊场湾矿的实际情况,在构建三维数学物理模型的基础上,开展不同瓦斯积聚量（56.52,113.04,169.56,226.08 m3）和不同爆炸距离（20,30,50,70 m）条件下的模拟研究。研究结果表明:风机和防爆门处超压峰值随瓦斯积聚量增加而增加,均呈线性关系,瓦斯积聚量为56.52 m3时风机处超压峰值为0.260 MPa,小于风机破坏荷载0.306 MPa;考虑安全系数前提下,当瓦斯积聚量超过56.52 m3时防爆门应开启保护风机;在确定瓦斯积聚量为56.52 m3基础上,分析不同爆炸距离对风机和防爆门影响,由模拟结果可知,风机和防爆门处超压峰值随爆炸距离增加而降低,均呈幂函数关系。研究成果可为瓦斯爆炸对风机和防爆门的影响研究提供指导。     

Describing and Mapping Human-Induced Vegetation Change in the Australian Landscape

Australian reporting requirements for native vegetation require improved spatial and temporal information on the anthropogenic effects on vegetation. This includes better linkage of information on vegetation type (e.g., native vegetation association), extent and change, vegetation condition, or modification. The Vegetation Assets, States and Transitions (VAST) framework is presented as a means for ordering vegetation by degree of anthropogenic modification as a series of condition states, from a residual or base-line condition through to total removal. The VAST framework facilitates mapping and accounting for change and trends in the status and condition of vegetation. The framework makes clear the links between land management and vegetation condition states, provides a mechanism for describing the consequences of land management practices on vegetation condition, and contributes to an understanding of resilience. VAST is a simple communication and reporting tool designed to assist in describing and accounting for anthropogenic modification of vegetation. A benchmark is identified for each vegetation association. Benchmarks are based on structure, composition, and current regenerative capacity. This article describes the application of the VAST framework as a consistent national framework to translate and compile existing mapped information on the modification of native vegetation. We discuss the correspondence between these compiled VAST datasets at national and regional scales and describe their relevance for natural resource policy and planning.     

燃烧、爆炸过程复杂性行为的非线性动力学(Ⅰ)

从非线性动力学观点,总结了燃烧和爆炸系统的多种复杂现象。指出了其非线性现象之间的对应关系。提出了从非线性即从“系统”、“全局或大范围”、“演化”及“统一”地观点认识燃烧和爆炸现象的观点。     

一致激励条件下非线性工程场地地震动相干函数分析

在地震动过程中,土介质中的剪切波速往往出现显著的降低现象,体现出强烈的非线性性质。本文将随机振动的虚拟激励原理、土非线性分析的等效线性化方法与工程波动理论散射问题的求解方法相结合,建立了开放系统中一致激励条件下考虑岩土介质非线性的工程场地地震动随机场数值模拟方法。该方法将随机输入下的波动分析问题转换为虚拟激励下的确定性波动分析问题,非线性土体峰值剪应变的统计特征可通过剪应变均方差和峰值因子获得。结合具体算例及M on te—C arlo模拟方法对所提出方法的合理性进行了验证,在此基础上应用该方法对一致激励下实际工程场地的地震动相干性进行分析,结果表明场地的局部条件对地震动相干性有重要影响。     

Framework for integrating indigenous and scientific knowledge for disaster risk reduction

A growing awareness of the value of indigenous knowledge has prompted calls for its use within disaster risk reduction. The use of indigenous knowledge alongside scientific knowledge is increasingly advocated but there is as yet no clearly developed framework demonstrating how the two may be integrated to reduce community vulnerability to environmental hazards. This paper presents such a framework, using a participatory approach in which relevant indigenous and scientific knowledge may be integrated to reduce a community's vulnerability to environmental hazards. Focusing on small island developing states it presents an analysis of the need for such a framework alongside the difficulties of incorporating indigenous knowledge. This is followed by an explanation of the various processes within the framework, drawing on research completed in Papua New Guinea. This framework is an important first step in identifying how indigenous and scientific knowledge may be integrated to reduce community vulnerability to environmental hazards.     

多能场协同紫外光催化降解甲基橙的实验研究

以甲基橙为模拟废水,负载型纳米TiO2为光催化剂,在自制的多能场组合反应器中,初步研究了电场和超声场协同紫外光催化降解水中甲基橙的特点和规律。结果表明,在偏置电场电压为20 v,超声场声频为21.33 kHz、声强为0.375 W/cm2,紫外光波长为366 nm,功耗为O.25 W/mL,TiO2催化降解负荷为1.25 mL/cm2的条件下,对浓度为4 mg/L的甲基橙溶液分别处理30 min和90 min,脱色率分别可达91.67％和95.36％;比单一紫外光催化降解脱色率分别提高86.59％和86.79％。     

声波吹灰器在锅炉吹灰中的应用

扬子热电厂7#锅炉通过对吹灰器正确地选型以及因地制宜地安装改造,解决了吹灰系统长期不能投用的问题并发挥了较好的吹灰效果。吹灰器改造后的运行统计数据,验证了投用声波吹灰器对提高锅炉效率和锅炉安全性能有明显作用,具有推广意义。