Theoretical investigation of shock stand-off distance for non-equilibrium flows over spheres

We derived a theoretical solution of the shock stand-off distance for a non-equilibrium flow over spheres based on Wen and Hornung＇s solution and Olivier＇s solution. Compared with previous approaches, the main advantage of the present approach is allowing an analytic solution without involving any semi-empirical parameter for the whole non-equilibrium flow regimes. The effects of some important physical quantities therefore can be fully revealed via the analytic solution. By combining the current solution with Ideal Dissociating Gas（IDG） model, we investigate the effects of free stream kinetic energy and free stream dissociation level（which can be very different between different facilities） on the shock stand-off distance.

Safety Distance Determination for 500 kV AC Transmission Line’s Helicopter Inspection

As an efficient and advanced line inspection method, helicopter line patrol is gradually more and more used in transmission lines inspection, promoting the elaborate operation of transmission lines and reducing the management cost. However, as a 'floating-potential conductor' near to a high-voltage transmission line, the helicopter would be at a high electric field region;and bring security risk to equipment and operating personnel. In this paper, the electric field strength near the cabin at locations of different distance from transmission lines is investigated by calculation, and the field in the helicopter cabin is also calculated with finite element method (FEM). The result indicates that the potential difference becomes higher with the decrease of the distance between the helicopter and transmission line. Considering the discharge energy and the guarantee of the persons’ safety, the safety distance is determined as d≥15 m.

爆炸冲击波超压非均匀分布特性及最优测点数量

为掌握炸药爆炸冲击波超压的非均匀分布特性,根据非理想爆轰波特征及空气冲击波的形成机制,探讨了炸药爆炸冲击波超压峰值时空非均匀分布的原因和表现形式,得到了实验影像和测试数据的验证;开展了公斤级和百公斤级装药爆炸冲击波实验,分析了相同对比距离的多个超压峰值测试结果之间的偏离特性,结果表明炸药组分非理想程度越高、装药质量越大、距离装药越近,冲击波超压峰值非均匀特征越显著。在实验数据偏离分析基础上,提出了满足非均匀分布超压准确测试的最优测点数量,将爆炸场划分为对比距离小于1.5 m/kg^(1/3)、1.5~3.0 m/kg^(1/3)、3~5 m/kg^(1/3)和大于5 m/kg^(1/3)共4个区域,对应的最优测点数量分别为6个、5个、4个和2个。

重复体外冲击波碎石治疗上尿路结石患者疗效预测模型的建立与验证

目的分析重复体外冲击波碎石(ESWL)治疗上尿路结石(UUC)效果的独立影响因素,并根据独立影响因素构建重复ESWL治疗UUC疗效的列线图模型。方法回顾性收集2020年1月—2022年12月十堰市人民医院接受重复ESWL治疗的203例UUC患者的临床资料,按照治疗效果分为成功组(117例)和失败组(86例),比较两组患者的一般资料:年龄、性别;结石特征:结石体积(SV)、结石表面积(SA)、皮肤至结石距离(SSD)、结石最大CT值、平均结石密度(MSD)、结石异质性指数(SHI)等。采用logistic回归分析重复ESWL治疗UUC的独立预测因素,纳入有意义的变量(P<0.05)建立列线图。采用受试者工作特征(ROC)曲线和递减曲线分析(DCA)评价模型的效能,并进行内部验证。结果逐步回归显示,SV、SSD、MSD、SHI是重复ESWL治疗UUC的独立影响因素(P<0.05)。ROC曲线下面积(AUC)=0.793,95%CI:0.674~0.911;当最佳阈值为0.619时,其敏感度为77.1%,特异度为74.0%。DCA曲线在两条极端曲线之上。Hosmer-Lemeshow拟合优度检验显示,模型具有较好的校准度(χ^(2)=5.526,P=0.489),矫正C指数为0.746。结论SV、SSD、MSD、SHI是重复ESWL治疗UUC的独立预测因素,由上述指标建立的模型具有较好的预测效能。

Mitigation effects on the reflected overpressure of blast shock with water surrounding an explosive in a confined space

The mitigation of blast shock with water has broad application prospects. Understanding the mitigation effects on the reflected overpressure of the explosion shock with water surrounding an explosive in a confined space is of great significance for military explosives safety applications. To estimate the effects of the parameters on the reflected overpressure of blasted shock wave, a series of experiments were carried out in confined containers with spherical explosives immersed in a certain thickness of water,and numerical simulations were conducted to explore the corresponding mechanisms. The results reveal that the reflected overpressure is abnormally aggravated at a small scaled distance. This aggravation is due to the high impulse of the bulk accelerated water shell converted from the explosion. With increasing scaled distance, the energy will be gradually dissipated. The mitigation effects will appear with the dispersed water phase front impacting at a larger scaled distance, except in the case of a dense water phase state. A critical scaled distance range of 0.7-0.8 m/kg^(1/3) for effective mitigation was found. It is suggested that the scaled distance of space walls should be larger than the critical value for a certain water-to-explosive weight ratio range(5-20).

坑道内爆炸平面波形成位置的数值分析

为了研究爆炸位置和炸药质量对坑道内爆炸平面波形成位置的影响,开展了不同爆心位置和多种炸药质量下的TNT坑道内爆炸数值模拟,记录了不同距离处的冲击波压力曲线,得到了冲击波到达时间和峰值等参量。结果表明,爆炸位置与坑道端口距离在小于1/3倍坑道直径范围内变化时,坑道内超压峰值分布会有一定程度的波动,超过1/3倍坑道直径后,超压峰值分布几乎不发生变化;平面波形成位置与爆心的距离不受爆心到端口距离的影响;炸药在同一坑道、同一位置爆炸时,炸药质量越大,则平面波形成位置到爆心的比例距离越小。

等离子体合成射流激波-激波干扰控制数值模拟

为了减弱高超声速飞行器头激波和侧翼前缘激波的干扰,建立了等离子体合成射流对高超声速飞行器激波-激波干扰控制的仿真模型,分析了等离子体合成射流激波-激波干扰控制的流场特性,探究了等离子体合成射流进行高超声速飞行器激波-激波干扰控制的效果,开展了激励器安装位置以及激励器注入能量的参数影响研究。研究表明:等离子体合成射流产生的弓形激波能使头激波抬起一定角度,减小头激波和侧翼前缘激波干扰,达到控制激波-激波干扰区热流和压力的效果;随着出口距离的增大,对热流和压力的控制效果先增大后减小;在一定范围内,注入能量越高,控制效果越好。

浅埋爆炸空气冲击波峰值压力计算方法研究

为研究装药比例埋深和比例距离对浅埋爆炸空气冲击波峰值压力的影响,测试了3种比例埋深工况下,7种比例距离处浅埋爆炸空气冲击波的峰值压力,结合量纲分析对试验数据进行拟合,得到了浅埋爆炸空气冲击波峰值压力的经验公式。结果表明:空气冲击波峰值压力随着比例埋深和比例距离的增加而减小;随着比例距离增加,比例埋深对空气冲击波峰值压力的影响减弱;空气冲击波峰值压力ΔPD与装药量Q、爆心距R和埋深L有关,其经验公式为:■。

分子黏性对解析湍流壁面函数的影响

基于可压缩解析壁面函数(MAWF),考虑高超声速湍流边界层内温度、密度和分子黏性系数变化规律,使用黏性底层边缘处的密度和黏性系数重新定义无量纲壁面距离,并在黏性底层内构造抛物型和双曲型分子黏性系数分布,建立了新的可压缩解析壁面函数,即抛物型(para-MAWF)和双曲型(hyper-MAWF)解析壁面函数。通过高超声速激波边界层干扰算例对其进行验证,并与密网格低雷诺数Lauder-Sharma(LS)k-ε模型和MAWF数值结果进行对比。研究结果表明:所构造的解析壁面函数有效提高了MAWF黏性底层内分子黏性系数和温度分布的预测精度,相较于MAWF其预测的壁面热流结果更接近实验结果;所构造的两种壁面函数中双曲型解析壁面函数预测的壁面热流更接近于实验值,考虑到两种壁面函数数值结果差异较小,在5%之内,且双曲型壁面函数公式更为简单,对于高超声速算例更推荐使用双曲型分布的解析壁面函数。

基于PHAST的高压烃类注气管道安全防护距离研究

为了确定高压注气管道两侧安全防护距离,确保高压烃类注气管道及站场的本质安全,结合火灾爆炸事故伤害准则,以某伴生气驱试验高压注气管道为研究对象,基于PHAST软件模拟分析管道压力、管径、泄漏孔径及温度对气体泄漏的火灾热辐射距离、爆炸超压距离的影响。结果表明,不同因素对事故后果影响强弱顺序为:管径、温度、压力、泄漏孔径。建议在高压集输管道敷设过程中,应考虑发生泄漏时对周围环境的影响,明确影响范围,充分预留安全距离,初步建议DN25、DN50、DN80、DN100、DN150管道的安全防护距离应分别为35~40,65~75,100~110,127~135,200 m。

Stomatal movement in response to long distance-communicated signals initiated by heat shock in partial roots of Commelina communis L.

The systematic or long-distance signal transmission plays crucial roles inanimal lives. Compared with animals, however, much less is known about the roles of long-distancesignal communication in plant lives. Using the model plant Commelina communisL, we have probed theroot to shoot communication mediated by heat-shock signals. The results showed that a heat shock of5 min at 40°C in partial roots, i.e. half or even 1/4 root system, could lead to a significantdecrease in stomatal conductance. The regulation capability depends on both heat shock temperatureand the amount of root system, i.e. with higher temperature and more roots stressed, the leafconductance would decrease more significantly. Interestingly, the stomatal regulation by heat shocksignal is in a manner of oscillation: when stomata conductance decreased to the lowest level withinabout 30 min, it would increase rapidly and sometimes even exceed the initial level, and afterseveral cycles the stomata conductance would be finallystabilized at a lower level. Feeding xylemsap collected from heat-shocked plants could lead to a decrease in stomata conductance, suggestingthat the heat shock-initiated signal is basically a positive signal. Further studies showed thatheat shock wasnot able to affect ABA content in xylem sap, and also, not able to lead to a decreasein leaf water status, which suggested that the stomatal regulation was neither mediated by ABA norby a hydraulic signal. Heat shock could lead to an increase in xylemsap H_2O_2 content, andmoreover, the removal of H_2O_2 by catalase could partially recover the stomatal inhibition by xylemsap collected from heat-shocked plants, suggesting that H_2O_2 might be able to act as one of theroot signals to control the stomatal movement. Due to the fact that heat-shock and drought areusually two concomitant stresses, the stomatal regulation by heat-shock signal should be ofsignificance for plant response to stresses. The observation for the stomatal regulation in anoscillation manner by presently identified new signals should contribute to further understanding ofthe mystery for the pant systematic signaling in response to stresses.

爆炸冲击波对天然气管道变形影响规律的研究

采用LS-DYNA有限元软件对空爆条件下爆炸冲击波作用天然气管道破坏效果进行模拟仿真分析,得到了不同爆心距、不同管道壁厚、不同炸药质量等工况下冲击波对管道破坏的影响规律。基于冲击波传播理论,解释了爆心距、管道壁厚、炸药质量对管道破坏机理的影响规律,通过拟合仿真数据结果得到不同工况下管道变形曲线,研究结果可为裸露天然气管道防护提供理论依据。

An Investigation of Effect of Stand-Off Distance on the Material Removal Characteristics and Surface Generation in Fluid Jet Polishing

Fluid jet polishing(FJP)is a versatile polishing process that has many advantages compared to other polishing processes.Stand-off distance(SOD)is one of the key parameters in flu id jet polishi ng.However,relatively little research work has been carried out to investigate its effect of SOD on material removal characteristics and surface generation in FJP.In this paper,a systematic investigation of the effect of SOD on the tool influence function and surface topography in FJP was conducted.Experiments were designed for FJP two kinds of materials corresponding to ductile and brittle materials.They are nickel copper(NiCu)alloy and BK7 optical glass,respectively.In this study,the SOD was varied from 2 to 35 mm.Analysis and discussions were made on its effect on the shape of TIF,material removal rate,and surface topography.It is interesting to note that the TIF shape becomes a Gaussian-like shape with large SOD both on NiCu and BK7,which provides a novel way to optimize the TIF in FJP.The variation of the material removal rate and surface roughness versus SOD on NiCu and BK7 were also determined from the experimental results.Moreover,the surface topography of NiCu and BK7 were characterized from the results measured from the white light interferometer and scan electron microscope.The outcome of the study provides a better understanding of the material removal characteristics and surface generation mechanism in FJP.

制度距离对企业全球供应链战略选择的影响研究——基于供应链权力的中介效应

在制度环境不确定下,跨国企业会做出怎样的供应链战略选择?文章基于制度理论和资源依赖理论,结合来自拥有全球供应链企业的问卷调查数据,构建了制度距离与全球供应链战略选择相互作用关系的理论模型,进一步剖析了供应链权力、外部冲击分别在其中所起的中介效应和调节效应,研究结果表明:制度距离对供应链权力及本地化、近邻化、多元化三种全球供应链战略选择产生正向影响,供应链权力对全球供应链战略选择也产生正向影响;供应链权力在制度距离与全球供应链战略选择之间的作用关系起着部分中介的作用,但外部冲击在制度距离与全球供应链战略选择之间的调节效应并不显著。

覆土库标准外部距离差异性研究

为更好地理解和应用相关标准对覆土库外部距离的规定,采用对比法,就现行国家标准关于覆土库对居民点、企业、铁路、公路和高压线路的外部距离的差异性进行探讨,分析覆土库外部距离差异性形成的原因,对覆土库在设计、安全评价和安全管理中宜采用的标准提出建议,给出相应的研究结论。

伞形灯光秀构筑物群的配电及控制设计要点简析

以某工程的伞形灯光秀构筑物群为例,介绍其配电和控制设计的要点及解决措施:分析末端保护电气的类型及特性与最大供电距离的关系,解决末端保护电器的电击安全防护问题;校验供电半径和线缆截面积,以避免电压偏差对照明质量的影响;根据构筑单体钢结构特点及灯具设置特点,合理设计防雷与接地措施和系统接地型式;实时监测每条配电回路的电流、电压状态,保障电源供电;采用具有电源监测和灯光控制功能的总控管理平台实现灯具多彩、多情景、交互的照明效果。

TNT空中爆炸超压的相似律

利用高分辨率、高精度试压系统测定了静爆试验中不同装药量TNT的冲击波超压。依据试验数据,提出了描述冲击波超压峰值与比例距离关系的改良经验式,并与试验数据和文献值进行了对比分析。结果表明,系统的相对偏差小于5.3%,与文献数据相对偏差的平均值为5.61%,拟合的新公式可应用于战斗部爆炸威力评估和理论计算。

空气中TNT爆炸冲击波超压峰值的预测及数值模拟

通过对空气中TNT爆炸冲击波超压峰值的已有研究成果进行比较分析,发现不同学者对其预测结果存在一定差别,并据此拟合总结出能较好地描述冲击波超压峰值与比例距离关系的表达式。同时用LS-DYNA动力有限元软件模拟了2种不同装药量条件下空气中TNT炸药爆炸产生的冲击波的传播,模拟所得的超压峰值小于经验公式的结果,装药量大的模拟结果更接近经验公式预测值。有必要对爆炸冲击波的参数和经验公式进行进一步的研究。

常规弹药爆炸破片和冲击波作用规律理论研究

研究常规弹药爆炸后破片和冲击波的作用规律。通过对弹片和冲击波运动规律的分析认为,按照以往的模型进行计算时,存在TNT当量不守恒的问题。研究了TNT当量守恒条件下,冲击波和破片同时到达目标距离的问题,所得计算模型较以往的模型更为合理。对于mpmax,冲击波和破片同时到达的距离为4.26 m,以往模型为3.76 m;对于mp,冲击波和破片同时到达的距离为4.30 m,而以往模型为3.83 m,偏差约13%。另外,经过理论推导和计算认为,冲击波和破片同时到达目标的距离,与破片形状和破片质量关系不大。

前向空腔的弓形激波特性研究

在FD-14A激波风洞中Ma=10流场对前向空腔构型开展试验研究,应用高速阴影技术捕捉弓形激波的平均位置及振荡幅值,利用压力传感器测量空腔底部的脉动压力。在现有无空腔钝头体激波脱体距离预测方法的基础上发展了前向空腔构型的激波脱体距离预测方法,结合国外的试验测量结果与Organ-pipe理论,验证了这种方法的有效性和适用性,且该方法对激波脱体距离的预测结果与FD-14A风洞试验结果一致。此外,基于这种方法讨论了空腔振荡频率预测方法存在的争议。最后,研究了Ma=10流场下球锥体-前向空腔构型的脱体激波振荡幅值与平均速度的规律。