电离层对短波测向系统的影响分析

目的研究电离层对短波测向系统的影响。方法从电离层传播介质入手,分析路径偏离效应和波干涉效应的形成机理及其对短波测向的影响。结果电离层系统倾斜引起的测向误差可借助电离层长期预测模型、短期预测算法或电离层实时探测数据对测向方位偏差进行补偿。行波扰动不可预测,只能依据行波扰动观测结果进行测向误差校正。波干涉误差可通过时间平滑进行抑制。结论提升现有短波测向系统测向性能的根本途径是为短波测向系统配备电离层探测设备,准确获取系统覆盖区内电离层状态信息,并进行传播效应补偿。     

Ignition of dust-air atmospheres by ultrasonic waves

This paper shows the results of our investigations on the ignition source ultrasound in dust-air atmospheres. Ultrasound is, on the one hand, considered to be an ignition source according to international safety standards (EN 1127–1 (2011)). On the other hand, though, ultrasound is used for various applications in gases and air, such as level and flow measurement, or in the process industry, but no explosion accidents have yet been reported. Our research now shows that it is indeed possible to ignite dust-air mixtures in ultrasound fields under certain conditions. We conducted our experiments in an ultrasound standing wave field and used maize starch, calcium stearate and sulfur dust. For ignitions, an absorbing target was needed to convert the acoustic energy into heat. From theoretical estimations and experiments critical conditions that provoke ultrasonically triggered explosions are identified.     

Flame acceleration in unconfined hydrogen/air deflagrations using infrared photography

Flame behavior and blast waves generated during unconfined hydrogen deflagrations were experimentally studied using infrared photography. Infrared photography enables expanding spherical flame behaviors to be measured and flame acceleration exponents to be evaluated. In the present experiments, hydrogen/air mixtures of various concentrations were filled in a plastic tent of thin vinyl sheet of 1 m³ and ignited by an electric spark. The onset of accelerative dynamics on the flame propagation was analyzed by the time histories of the flame radius and the stretched flame speed. The results demonstrated that the self-acceleration of the flame, which was caused by diffusional-thermal and hydrodynamic instabilities of the blast wave, was influenced by hydrogen deflagrations in unconfined areas. In particular, it was demonstrated that the overpressure rapidly increased with time. The burning velocity acceleration was greatly enhanced with spontaneous-turbulization.     

贵州井下煤层爆破地震波特征及其影响

贵州省煤层赋存条件差,煤矿地质条件复杂。由于煤矿井下爆破采掘适应性强、初期投资小等特点,适应于地质条件复杂、断层多的源赋存复杂条件的中小型煤矿,因此目前贵州煤矿井下煤层采掘多采用爆破作业方式。但井下煤层爆破作业易引发煤尘、瓦斯爆炸、煤与瓦斯突出等矿山灾害,因此研究煤矿井下爆破规律及其对煤矿各方面安全的影响是十分必要和迫切的。通过比较选用小波包分析方法,对现场实验的井下煤层爆破地震波信号进行分析,得出其能量、频率等特征,并分析了其对前方煤体瓦斯抽放量及瓦斯压力的影响规律。     

吸声系数的先进现场测试技术发展概述

首先介绍了最常用的测试吸声系数的驻波管法与混响室法并阐述了两种方法优缺点。驻波管法测试的是法向吸声系数,混响室法得到的是各个入射方向的平均吸声系数,两种方法测试时均与实际安装情况存在一定差异,难以完成现场复杂环境下吸声系数的准确测试。而很多情况下,需要测试得到的是实际工作环境中的吸声系数,于是总结了传递函数法、PU矢量法、参量阵扬声器法、脉冲响应法、倒频谱法、最长序列数法以及减法技术等吸声系数的现场测试方法的原理与研究进展,分析了各测试方法的优缺点。     

毫米波近场成像技术综述

介绍了用于探测人体隐蔽物体的毫米波焦面阵成像系统及毫米波全息成像系统;简述了利用合成孔径原理提高系统分辨率的毫米波全息成像系统的基本原理;着重分析了毫米波焦面阵成像系统的天线近场聚焦特性、空间分辨率计算、系统采样间隔选择、物体辐射特性等关键技术.该系统在探测人体隐蔽物体方面具有广阔的应用前景.     

射频连续电磁波对某数字电路的辐照效应研究

在GTEM室中用射频连续波对某导弹装备上的一块数字控制电路进行电磁辐照,在一定的场强下,引入的电磁干扰还未导致被监测的与非门产生错误反转时,产生控制信号的自激多谐振荡器却首先受到了电磁干扰,主要表现为产生的方波控制信号的占空比增大.分别研究了波源频率在245MHz和330MHz的情况下电路受干扰的情况,辐照实验分别对待测设备按水平横向放置、水平纵向放置和竖直放置3种放置方位分别进行了辐照.最后对水平横向放置的两个频点,将方波控制信号的占空比随场强的变化进行了相关性拟合,建立了数学模型.     

微波消解在测定环境样品中金属元素的应用

微波消解具有快速、简单、消耗试剂少和不易造成样品污染等特点,在环境样品中金属元素的测定方面得到了广泛的应用。本文介绍了微波消解的原理、常用试剂以及在各种环境样品中金属元素测定的应用进展,并对该技术的应用前景作了展望。     

A quantitative correlation of evaluating the flame speed for the BST method in vapor cloud explosions

In recent decades, vapor cloud explosions (VCEs) have occurred frequently and resulted in numerous personnel injuries and large property losses. As a main concern in the petrochemical industry, it is of great importance to assess the consequence of VCEs. Currently, the TNT equivalency method (TNT EM), the TNO multi-energy method (TNO MEM), and the Baker-Strehlow-Tang (BST) method are widely used to estimate the blast load from VCEs. The TNO MEM and BST method determine the blast load from blast curves based on the class number and the flame speed, respectively. To quantitatively evaluate the flame speed for the BST method, the experimental data is adopted to validate the confinement specific correlation (CSC) for the determination of the class number in the TNO MEM. As a bridge, a quantitative evaluation correlation (QEC) between CSC correlation and the flame speed is established and the blast wave shapes corresponding to different flame speeds are proposed. CFD software FLACS was used to verify the quantitative correlation with the numerical models of three geometrical scales. It is found that the calculated flame speeds by the QEC are in good agreement with the simulated ones. A petrochemical plant is selected as a realistic scenario to analyze the TNT EM, TNO MEM, BST method and FLACS simulations in terms of the positive-phase side-on overpressure and impulse at different distances. Compared with the flame speed table, the predicted overpressure from BST curves determined by the proposed QEC is closer to that from FLACS and more conservative. Furthermore, the predicted results of different methods are compared with each other. It is found that the estimated positive-phase side-on overpressure and impulse by the TNO MEM are the largest, and the estimated impulse by the TNT EM is the smallest. Moreover, the estimated overpressure and impulse are larger in the higher reactivity gas.     

球形障碍物对瓦斯爆燃火焰影响试验研究

为进一步开发煤矿井下瓦斯爆炸事故的隔抑爆技术装备,利用截面为0.2 m×0.2 m的方形管道、纹影仪和高速摄像机,开展无障碍物时和球形障碍物存在情况下的瓦斯爆燃传播试验。研究发现,无障碍物时,密闭管道内爆燃火焰的结构和传播速度受反射压力波的影响很大,湍流火焰、化学反应作用能力与反射压力波的相互作用是造成火焰传播速度变化的主要原因;球形障碍物存在时,火焰受扰动后被拉伸为前锋、中锋和尾锋,前锋速度最快,尾锋最慢;火焰前锋从经过障碍物开始整体呈加速趋势,与无障碍物相比,通过观察段的时间明显缩短。