基于分形理论的飞机雷击初始附着点的数值模拟

飞机雷击附着点的确定能够为飞机防雷设计提供依据,是飞机雷击区域划分和飞机各部件进行雷电试验鉴定的先决条件.本文提出了一种基于分形理论的飞机雷击初始附着点数值模拟的新方法.该方法首先依据标准SAE-ARP5416中有关飞机雷击附着点试验的规定,确定放电间隙、雷电起始坐标、飞机姿态和放电次数等参数,然后根据分形理论,使用电介质击穿模型模拟符合自然界雷电物理机理和几何特征的雷电先导分形发展过程,同时考虑飞机自身触发双向先导的情况,最终得到飞机的雷击附着点分布.通过本文方法仿真模拟得到飞机F-4雷击附着点的分布概率,并分别与该飞机飞行实验和实验室高压放电实验测试得到的真实雷击附着点的概率分布情况比较,结果基本吻合,验证了该方法的有效性.研究结果为飞机雷击附着点仿真模拟提供了一个有潜力的方法,可作为飞机防雷设计和今后开展相关研究工作的基础.     

一次人工触发闪电通道光谱结构分析

用无狭缝光谱仪获得了广东地区一次人工触发闪电首次回击过程的发射光谱,同时测量了回击电流峰值为18.3kA,回击持续时间为4.5ms。发现导线部分通道的发射谱线中存在407.5,419.0,425.3和517.9nm等激发能比较高的谱线,具有强闪电通道发射光谱的谱线结构,空气部分则具有弱闪电通道的谱线结构;导线部分与空气部分的基本谱线的相对强度差别较小,强闪电特征谱线相对强度相差非常大。通过对导线部分与空气部分谱线激发能等参数的分析,发现回击开始时,导线部分先导通道还未完全消失,回击脉冲电流对先导闪电通道等离子体进行了进一步激发,增加了等离子体的温度和密度,使得导线部分具有较高激发能的谱线被完全激发,相对于空气部分407.5,419.0,425.3和517.9nm等谱线的强度有较大程度的增加,造成导线部分通道与空气通道两种不同的光谱结构。通过光谱分析,获得了闪电通道不同部分的温度、电子密度等参数,发现导线部分通道的辐射特性不同于空气通道是导线部分通道发光亮度与电流相关性较差的原因。     

Identification of lightning vulnerability points on complex grounded structures

The identification of the most vulnerable points on a given structure to be struck by lightning is an important issue on the design of a reliable lightning protection system. Traditionally, these lightning strike points are identified using the rolling sphere method, through an empirical correlation with the prospective peak return stroke current. However, field observations in Kuala Lumpur and Singapore have shown that the points where lightning flashes strike buildings also depend on the height and geometry of the structure. Since a lightning strike point is believed to be the place on a grounded structure where a propagating upward leader is first initiated, a physical leader inception model is used here to estimate the background electric field required to initiate a stable upward leader from the corners of some complex buildings. The computed location of the points from where leaders are incepted are compared with the damaged points on buildings struck by lightning. The observed lightning strike points coincide rather well with the corners of the buildings which are characterized by lower leader inception electric fields. Furthermore, it is found that the geometry of the buildings significantly influences the conditions necessary to initiate upward leaders and, therefore, the location of the most likely strike points.     

A New Radioactive Lightning Protection

The protective zone of conventional lightning rod (Franklin's rod) is very small. In order to enlarge it, a greater number of such lightning rods can be set up or the Faraday cage employed. In the case of high objects or those covering large areas, this kind of protection is not economical. The use of radioactive sources for air ionization around the lightning rods enlarges the protective zone considerably. A comparison is given of the radioactive lightning rod, which use alpha emitters and are widely employed in some countries of western Europe and Africa, and the proposed radioactive lightning which uses a gamma radiation source.     

Statistical model of the lightning leader attraction to ground objects

A statistical model of the lightning channel attraction to ground objects is proposed based on the analysis of the available experimental data on the breakdown of long air gaps and the propagation of the lightning leader channel. The model allows one to estimate the probability of lightning interception by a lightning rod and of lightning damage of the protected object. Examples of calculating the probabilities of lightning strike to the lightning rod and neighboring areas are presented.     

闪电物理

闪电物理研究的重点是地闪的研究，地闪的物理过程包括云中起闪过程，闪电传播过程及接地过程，在较大范围的云中强电场区内，两雨滴掠过碰撞形成的细丝顶端产生的电晕或冰类痧汽凝结物表面的电晕可能触发闪电；闪电在空气中的传输过程就是先导从电晕向电弧的转化过程；闪电落地过程的核心是上迎先导的形成及与下行先导的连接，闪电物理研究的重点在闪电落地过程，并应与雷电防护研究结合起来进行。     

一次空中触发闪电通道光谱分析

利用无狭缝光谱仪获得了一次空中触发闪电过程中400～660 nm的发射光谱,对空中触发闪电小回击和上行正先导通道的发射光谱进行了分析,讨论了人工触发闪电导线通道与空气通道光谱的差异,发现导线段通道光谱持续了约140 ms,而空气段通道仅持续了0.167 ms;结合Fe,N,O等元素的电离能、激发能,给出了导线通道亮度强、持续时间长的原因。在电流强度相同的情况下,人工触发闪电通道的导线段有更多的粒子被激发,能产生更多的光谱辐射,导线段通道的亮度远强于空气段,导线段通道的光谱强度也远强于空气段;在随后的等离子体通道消散阶段导线段闪电通道的复合反应持续时间也更长。通过对小回击以及上行正先导导线通道上部、下部空气段光谱结构以及通道温度等参数与广东地区自然闪电特征谱线及温度等参数的比较,发现小回击通道光谱主要由NⅡ离子低激发态之间的跃迁组成,具有NⅡ 444.7 nm,NⅡ 517.9 nm,NⅡ 616.8 nm等广东地区一般强度自然闪电的特征谱线。上行正先导下部空气段通道具有高激发能的谱线开始消失,出现了H_α,H_β,OⅠ 615.8 nm等激发能较低的谱线,具有闪电回击后期的光谱结构。小回击通道以及上行正先导通道下部空气段温度分别为21 000和20 000 K,通道温度低于自然闪电温度。     

Physical nature of Ball lightning

Physical effects responsible for existence of Ball lightning are considered. It is shown that Ball lightning can be a pure optical phenomenon where only an intense light and compressed air interact. An anomalous great light intensity and light lifetime within Ball lightning are analyzed.     

基于先导放电理论的直升机初始雷击附着位置北大核心CSCD

提出了一种基于流注-先导放电理论的数值模拟方法来快速判断直升机初始雷击附着点。首先,根据标准SAE-ARP 5416A中规定的相关试验方法,确定平板电极大小、直升机离边界距离等参数。然后,利用Becerra-Cooray正极性先导起始和发展判据对UH-60"黑鹰"直升机的主旋翼翼尖、尾旋翼翼尖、水平尾翼以及机头部位进行分析比较。最后,通过不断改变平板电极电势的方法,找到各个关键位置产生稳定正极性先导所需的最小背景电场值,以此为依据来对其初始雷击附着位置进行分析。结果表明,主旋翼翼尖最易成为初始雷击附着位置,而机头则较难成为初始雷击附着位置。     

The properties and the nature of ball lightning

The observed properties of ball lightning are given. A model of mean ball lightning taking average iarameters is based on observed data. By comparing the observed data with contemporary information on the processes occuring in activated air, different aspects of the ball lightning phenomenon are analysed. Among these are the ways of energy storage in ball lightning, the mechanisms of thermal processes, the form and structure of ball lightning, and the electrical phenomena and luminous processes in ball lightning. The separate problems are investigated on the basis of model experiments. Numerical analysis of various aspects of the phenomenon allows us to construct a phenomenological model of ball lightning. This model conforms well with the observed data and up-to-date information on the different physical processes. The experimental modelling of ball lightning is analysed. Analogues of ball lightning are considered. A general phenomenological scheme of ball lightning is given.     

光谱法研究闪电通道的导电特性

依据无狭缝光栅摄谱仪在青海获得的云对地闪电回击光谱信息,结合空气等离子体传输理论,用四种不同方法计算了同一闪电放电通道的电导率。结果表明：各种方法所得闪电核心通道的电导率数量级均为104 S·m-1;且同一通道内的电导率随通道高度的增加有减小的趋势;通道内电子与一次、二次电离离子的碰撞以及它们各自的碰撞对通道电导率的贡献不可忽略;用碰撞积分的方法计算闪电核心通道的电导率结果更为合理。在通道电导率的基础上估算了回击通道的放电电流,与辐射峰值电场实验资料所得的相应峰值电流相比,其结果在合理的范围内, 并进一步探讨了温度与电流放电特性的相关性, 为研究闪电放电电流提供了一条可行的途径。     

Electric charge of a lightning ball

The electric charge of a lightning ball is found by comparing the electrohydrodynamic stabilities of a charged drop in an electrostatic suspension and a lightning ball floating in a superposition of the gravitational field and the surface electric field. It has been assumed that the electric field strength at the surface is limited by a breakdown value. For a lightning ball radius of 15 cm, its charge is estimated as several microcoulombs. Accordingly, the density of electrostatic energy accumulated in the lightning ball is on the order of one-hundredth of a joule per square centimeter. The density of the material that constitutes the lightning ball has been estimated for the case when the electric field strength at the site of its origination is several times higher than that in fine weather. The density of the lightning ball turns out to differ from that of air by only a few percents.     

An experimental study of the damage degrees to ancient building timber caused by lightning strikes

Lightning strikes are one of the main natural causes of damages to ancient buildings, and have attracted a great deal of attention to the problem of lightning strike disasters. In this study, the lightning strike damage mechanism of ancient building timber and the related damage degrees are investigated, based on the representative timber materials. A lightning-strike simulation device with a 10/350 μs lightning current waveform was adopted for the experiments. The experimental results showed that the lightning strike damages to ancient building timber mainly included timber heating caused by lightning arc heat and current, as well as the air shock wave effects of the lightning, which led to various effect modes under different conditions. The correlations between the damage degree of timber and the water content of timber, timber thickness, as well as the lightning current intensity, are obtained. The current peaks of lightning and the timber water content are the main external and internal causes which influence the damage degrees of ancient timber.     

Shielding failure rate calculation by means of downward and upward lightning leader movement models: Effect of environmental conditions

In this paper the effects of environmental conditions on shielding failure rate (SFR) of transmission lines are investigated. The study utilizes a previously published work in which leader progression model for lightning upward and downward leaders are used to calculate the SFR. Taking into account the effects of reduced air density and humidity on the parameters of upward leader model and wind pressure on the movement of lightning leaders and wires, SFR and maximum lightning stroke current causing shielding failure are computed. The electric field in all simulations is calculated by means of charge simulation method. The results of simulation show that the effects of relative air density and height of installation are quite higher than that of the wind pressure and humidity while the humidity has the lowest impact on the SFR of investigated transmission line.     

基于先导发展模型的舰艇避雷防护评估仿真

基于先导发展模型实现了海域上地闪先导2维数值放电模拟,完成了海域上地闪先导放电通道过程的图样采集。通过建立二维舰船模型,并根据相关标准对舰船模型进行避雷针的数量、高度、位置设定,对此模型进行雷电先导放电数值试验。经大量试验统计分析,舰船采用单根避雷针设计方案时,避雷针的高度较高,使得接闪概率明显增大,但在避雷针周围取得了较理想的防护效果;与单根设计方案相比,双根避雷针设计使得舰船整体结构高度降低,总的接闪次数有所减少,防护效果更佳。该评估方法可与长间隙放电试验和雷电观测互为补充,进一步完善了水面舰艇避雷系统防护评估检验技术,为舰艇的雷电防护提供理论基础。     

Electron band structure detection by high-order optical harmonic generation in solids

As the threshold field strength for the breakdown in air significantly exceeds the maximum measured thundercloud strength 3 kV/cm/atm, the problem of lightning initiation remains unclear. According to the popular idea, lightning can be initiated from streamer discharges developed in the enhanced electric field in a vicinity of hydrometeors. To test the idea, we carry out numerical simulations of positive streamer development around charged water drops at air pressure typical at thundercloud altitudes and at different background fields, drop sizes and charges. With real drop sizes and charges, the electric field required for the streamer formation is stronger than the measured fields; therefore, second mechanism is required to amplify the local field.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000 K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000 K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

On the interception of lightning flashes by power transmission lines

The design of the lightning protection system LPS of transmission lines is based on the well known electro-geometrical model. The electro-geometrical model assumes that the first point on a power transmission line that will come within striking distance of the tip of a down-coming stepped leader channel is the strike point of the lightning flash. The model neglects almost all of the physics associated with the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numerical methods, it is feasible to apply the physics of the discharge process to the study of lightning attachment. Such models take into account the movement of the downward and the resulting upward leaders from different points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachment phenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with the predictions of the electro-geometrical method.     

中央空调末端设备温度控制与分户计量系统研究

根据现代智能大厦物业管理的实际要求,对中央空调末端设备温度控制与分户计量系统进行研究,重点阐述了一种基于PIC单片微控制器为控制核心,应用电力线载波通信技术的空调冷量计费管理系统,详细介绍了该系统硬件及软件设计方案和关键技术。