Theoretical and numerical simulation study on jet formation and penetration of different liner structures driven by electromagnetic pressure

The use of a shaped liner driven by electromagnetic force is a new means of forming jets. To study the mechanism of jet formation driven by electromagnetic force, we considered the current skin effect and the characteristics of electromagnetic loading and established a coupling model of"Electric—Magnetic—Force"and the theoretical model of jet formation under electromagnetic force. The jet formation and penetration of conical and trumpet liners have been calculated. Then, a numerical simulation of liner collapse under electromagnetic force, jet generation, and the stretching motion were performed using an ANSYS multiphysics processor. The calculated jet velocity, jet shape, and depth of penetration were consistent with the experimental results, with a relative error of less than 10％. In addition, we calculated the jet formation of different curvature trumpet liners driven by the same loading condition and ob-tained the influence rule of the curvature of the liner on jet formation. Results show that the theoretical model and the ANSYS multiphysics numerical method can effectively calculate the jet formation of liners driven by electromagnetic force, and in a certain range, the greater the curvature of the liner is, the greater the jet velocity is.     

Numerical simulation study on penetration performance of depleted Uranium (DU) alloy fragments

Due to its high strength, high density, high hardness and good penetration capabilities, Depleted ura-nium alloys have already shined in armor-piercing projectiles. There should also be a lot of room for improvement in the application of fragment killing elements. Therefore, regarding the performance of the depleted uranium alloy to penetrate the target plate, further investigation is needed to analyze its advantages and disadvantages compared to tungsten alloy. To study the difference in penetration per-formance between depleted uranium alloy and tungsten alloy fragments,firstly, a theoretical analysis of the adiabatic shear sensitivity of DU and tungsten alloys was given from the perspective of material constitutive model. Then, taking the cylindrical fragment penetration target as the research object, the penetration process and velocity characteristics of the steel target plates penetrated by DU alloy frag-ment and tungsten alloy fragment were compared and analyzed, by using finite element software ANSYS/LS-DYNA and Lagrange algorithm. Lastly, the influence of different postures when impacting target and different fragment shapes on the penetration results is carried out in the research. The results show that in the penetration process of the DU and tungsten alloy fragments, the self-sharpening properties of the DU alloy can make the fragment head sharper and the penetrating ability enhance. Under the same conditions, the penetration capability of cylindrical fragment impacting target in vertical posture is better than that in horizontal posture, and the penetration capability of the spherical fragment is slightly better than that of cylindrical fragment.     

Investigation of the mechanical and ballistic properties of hybrid carbon/ aramid woven laminates

High-performance ballistic fibers, such as aramid fiber and ultra-high-molecular-weight polyethylene (UHMWPE), are commonly used in anti-ballistic structures due to their low density, high tensile strength and high specific modulus. However, their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure. In contrast, carbon fiber reinforced epoxy resin matrix composites (CFRP) have the characteristics of high modulus in the thickness direction and high shear resistance. However, carbon fibers are rarely used and applied for protection purposes. A hybridization with aramid fiber reinforced epoxy resin matrix composites (AFRP) and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites. The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated. Through conducting mechanical property tests and ballistic tests, two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software, respectively. The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced. The ballistic tests’ results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7% of AFRP. When CFRP was on the striking face, the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage. The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process. These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt% and 30 wt%.     

Experiment and simulation of launching process of a small-diameter steel cartridge case

In order to explore the rules of the deformation force during the launching of a small-diameter steel cartridge, the semi-closed bomb test method is used to test the greatest strains on chamber outer wall under the different chamber pressures. The pressure curves of cartridge chamber are measured in experiment, and the tensile test data of cartridge are loaded into the numerical calculation to compare with the experimental data. The conclusion was obtained that the calculated results match better with the experimental results by considering strain rate bilinear kinematic hardening material constitutive model. The forces on the various parts of the cartridge during launching and their deformation rules are achieved, in which the equivalent plastic strain decreases and the cylinder ring withstands the maximum equivalent stress when the cartridge case clings to the bore from the mouth to the bottom.     

直流TIG焊接电弧的数值分析

以直流钨极氢弧焊电弧为研究对象,考虑阴极几何形状,建立了轴对称电弧数值计算模型,在电流密度计算中包括了阴极区和弧柱区。采用ＳＩＭＰＬＥ算法求解磁流体动力学方程组。所得电弧弧柱温度分布与实验结果相吻合;电弧速度分布、电磁力分布、电流密度分布、压力分布等电弧参量的计算结果能较全面地反映电弧内部的作用机制。     

翼板型水压扫雷具水压场的数值模拟

采用有限基本解法,对单板、双板、三板及四板翼板型水压扫雷具的水压场进行了数值计算,给出了海底的压力系数的分布,并与实验结果作了比较。     

细长壳体水声辐射问题的有限元结合边界元解法

采用三角形面积元,提出了一种计算任意形状的细长壳体水声辐射问题的有限元结合边界元解法,推导了三角形面积坐标下的质量矩阵。在水动力方面,根据单层势的概念,提出了声场速度势的边界积分表示式,给出了三角形面积坐标下的附加质量矩阵和附加阻尼矩阵,从而得以建立流固耦合的有限元动力响应方程。本方法的进一步发展可用于计算具有加强肋骨的双层壳体结构的声辐射问题以及船体在随机激励下的远场声功率谱。     

舰船水压场畸变的数值模拟

用有限基本解法对舰船下方附加翼板后的水压场进行了数值模拟。分光体船、附加单翼板和附加双翼板三种情况,在不同的水深下分别进行计算,获得了相应的纵向通过特性曲线,并与实验结果进行了比较。在不同的翼板位置、攻角和离船底距离下对水压场进行计算,以优化得到最佳水压场畸变效果。     

On the production of victory: Empirical determinants of battlefield success in modern war

Using a data set of historical battles from 1600 to 1973, this paper analyzes the empirical determinants of tactical success in modern war. Based on a reduced form approach we consider key elements of military theory as production factors for combat success as an output of a military production function. The paper focuses on the relationship of material and non-material factors to battlefield success, and especially on the role of superior force strengths. Contrary to the emphasis on technology which can be found in the recent literature, our estimation results indicate that numerical superiority has retained its crucial role for battlefield performance throughout history. In general, human elements of warfare, like leadership, morale and surprise, have continued to be important determinants of battle outcome despite technological progress in weapons.     

内编队地球重力场测量性能数值分析

内编队系统通过实现内卫星纯引力轨道环境和内卫星精密定轨,完成高精度地球重力场测量,实现了不依赖于加速度计的重力卫星实施新途径。针对内编队重力场测量性能难以解析分析的情况,基于MATLAB并行程序设计进行了重力场测量数值模拟,获得了内编队重力场测量的有效阶数及其精度。在内编队轨道高度为300km、内卫星干扰力为1.0×10-10m/s2、外卫星定轨精度为3cm、内外卫星相对状态测量精度为1mm的条件下,计算得到内编队测量重力场的有效阶数为72,相应的大地水准面累积误差为44cm,重力异常累积误差为4.5mGal,由此可知内编队测量重力场的有效阶数主要分布在低阶部分。