火箭弹防静电作用研究

针对电发火弹药静电放电问题,以某型130 mm火箭弹为例,采用真实静电感度测试系统测试了电火工品在有、无绝缘层时50%的静电点火能量,并在试验程序及数据处理中使用真实静电感度数据处理方法统计了50%静电发火能量的估计值。通过比较发现二者的差值在误差范围内,这表明静电放电研究中可以将弹体所接受的能量视作全部作用于火工品上,绝缘层不吸收静电放电的能量。在电发火弹药的防护中,必须采用静电防护措施杜绝电发火弹药的意外发火。     

飞行器MDO中灵敏度计算的自动微分方法

自动微分方法(ADM)是灵敏度计算的一种新方法,是处理飞行器多学科设计优化中灵敏度分析问题的有力工具。将ADM与估算灵敏度最常用的有限差分方法(FDM)以及与ADM同时期发展起来的另外一种灵敏度计算方法—复变量方法(CVM),从原理上进行了比较,研究了ADM前向模式在Visual C 6.0环境中的实现方法,结合多学科环境中的飞行器设计优化计算实例分析了该模式的优缺点。ADM在科学计算、工程计算等方面有很大的发展空间。     

A comprehensive review on material selection for polymer matrix composites subjected to impact load

Polymer matrix composites (PMC) are extensively been used in many engineering applications. Various natural fibers have emerged as potential replacements to synthetic fibers as reinforcing materials composites owing to their fairly better mechanical properties, low cost, environment friendliness and biodegradability. Selection of appropriate constituents of composites for a particular application is a tedious task for a designer/engineer. Impact loading has emerged as the serious threat for the composites used in structural or secondary structural application and demands the usage of appropriate fiber and matrix combination to enhance the energy absorption and mitigate the failure. The objective of the present review is to explore the composite with various fiber and matrix combination used for impact applications, identify the gap in the literature and suggest the potential naturally available fiber and matrix combination of composites for future work in the field of impact loading. The novelty of the present study lies in exploring the combination of naturally available fiber and matrix combination which can help in better energy absorption and mitigate the failure when subjected to impact loading. In addition, the application of multi attributes decision making (MADM) tools is demonstrated for selection of fiber and matrix materials which can serve as a benchmark study for the researchers in future.     

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets.However,the mechanism of impact flash remains unclear.A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun.The impact flash spectra for 6061 aluminum at 1.3-3.2 km/s collision speeds were recorded with a high-speed camera,a photoelectric sensor,and a time-resolved spectrometer.The intensity of the impact flash exhibited a pulse charac-teristic with time.The intensity(I)increased with impact velocity(V0)according to I∝Vn0,where n = 4.41 for V0 ＞ 2 km/s.However,for V0 ＜ 2 km/s,n = 2.21,and the intense flash duration is an order of magnitude less than that of higher V0.When V0 ＞ 2 km/s,a continuous spectrum(thermal radiation background)was observed and increased in intensity with V0.However,for V0 ＜ 2 km/s,only atomic line spectra were detected.There was no aluminum spectral lines for V0 ＜ 2 km/s,which indicated that it had not been vaporized.The initial intense flash was emission from excited and ionized ambient gases near the impact surface,and had little relationship with shock temperature rise,indicating a new mechanism of impact flash.     

An experiment evaluating how the tiny mass eccentricities in spin-stabilized projectiles affect the position of impact points

This study investigates and quantifies some possible sources affecting the position of impact points of small caliber spin-stabilized projectiles (such as 12.7 mm bullets). A comparative experiment utilizing the control variable method was designed to figure out the influence of tiny eccentric centroids on the projectiles. The study critically analyzes data obtained from characteristic parameter measurements and precision trials. It also combines Sobol's algorithm with an artificial intelligence algorithm—Adaptive Neuro-Fuzzy Inference Systems (ANFIS)—in order to conduct global sensitivity analysis and determine which parameters were most influential. The results indicate that the impact points of projectiles with an entry angle of 0° deflected to the left to that of projectiles with an entry angle of 90°. The difference of the mean coordinates of impact points was about 12.61 cm at a target range of 200 m. Variance analysis indicated that the entry angle — i.e. the initial position of mass eccentricity — had a notable influence. After global sensitivity analysis, the significance of the effect of mass eccentricity was confirmed again and the most influential factors were determined to be the axial moment and transverse moment of inertia (Izz Iyy), the mass of a projectile (m), the distance between nose and center of mass along the symmetry axis for a projectile (Lm), and the eccentric distance of the centroid (Lr). The results imply that the control scheme by means of modifying mass center (moving mass or mass eccentricity) is promising for designing small-caliber spin-stabilized projectiles.     

Preparation and characterization of HMX/EVA/hBNNSs micro-composites with improved thermal stability and reduced sensitivity

Hexagonal boron nitride nanosheets(HBNNSs)have huge potential in the field of coating materials owing to their remarkable chemical stability,mechanical strength and thermal conductivity.Thin-layer hBNNSs were obtained by a liquid-phase exfoliation of h-BN powders and incorporated into EVA coatings for improving the safety performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).HBNNSs and ethylene-vinyl acetate copolymer(EVA)were introduced to HMX by a solvent-slurry process.For com-parison,the HMX/EVA and HMX/EVA/graphene(HMX/EVA/G)composites were also prepared by a similar process.The morphology,crystal form,surface element distribution,thermal decomposition property and impact sensitivity of HMX/EVA/hBNNSs composites were contrastively investigated.Results showed that as prepared HMX/EVA/hBNNSs composites were well coated with hBNNSs and EVA,and exhibited better thermal stability and lower impact sensitivity than that of HMX/EVA and HMX/EVA/G composites,suggesting superior performance of desensitization of hBNNSs in explosives.     

潜艇自航模水下长波遥控系统

提出了利用无线长波对水下潜艇自航模进行长波遥控的通信技术,阐述了长波遥控的发射、接收及天线系统的硬件组成和系统设计。对发射天线的现场测试结果进行了分析,提出了实际电路的阻抗匹配实现方法;对接收信号的噪声和灵敏度等有关问题进行了分析,采用天线的方向性自适应控制技术解决了潜艇水下接收,在实际应用中取得较好的效果。     

谈英语教学的语用观

语用知识对学生理解和使用语言有着非常重要的作用。只有具备了一定的语用知识,学生才能准确地使用语言,才能真正学会一门语言。这就要求英语教师在讲解语言知识的同时一定要注重语用知识的传授。     

非线性评估中权重的敏感性分析

分析了非线性评估中权重的敏感性问题,给出了分析的思路和计算方法,并得出判断权重敏感的方法,定义了多维权重的敏感度,并由算例说明评价值的敏感性和权重的关系.     

寿命周期费用估算中的敏感度分析

针对寿命周期费用估算和分析时存在的费用不确定性,需要对关键参数进行敏感度分析,否则会影响到结果的正确性.通过分析引起费用不确定性的因素,阐述了敏感度分析的内涵和分析步聚.为了验证该方法,举出示例加以说明.认为:敏感度分析的费用估算与分析中的运用,将对合理决策产生重要作用.