Unmanned aerial vehicle strike on a flat plate: Tests and numerical simulations

The incursion of Unmanned Aerial Vehicles (UAVs) into airports often occurs due to the popularity of drones, which may lead to a threat to aircraft flight safety. Therefore, estimating the dynamic impact load caused by drone strikes is essential. This paper proposes a test method with high precision and low cost involving launching of a UAV to impact a flat plate specimen by using an air gun. The test results of UAVs impacting flat plates at different impact velocities, such as the UAV damage deformation captured by a high-speed camera and strain vs time dynamic response curves of plates, were obtained and analysed. At the same time, a corresponding numerical simulation was carried out by using the explicit finite element software LS-DYNA. The predicted damage to the UAV and strain on the flat plate during the strike process were compared with the test results. The overall trend of the simulation results is in good agreement with the test results, at least for the first three milliseconds of the event. This shows that the numerical simulation model established in this paper is reasonable. The UAV numerical method established in the present paper can be used to carry out numerical simulations and evaluations of the collision safety of UAVs against large aircraft and high-value ground targets. The results show that the local deformation of the impacted target is uneven due to the distribution of concentrated mass components such as motors, battery, and camera. As the impact velocity of the UAV increases, all parts of the UAV are seriously damaged and basically in a fragmented state, and the battery is greatly deformed. The interaction between the UAV and the flat plate specimen is approximately 2.7 ms, and the UAV numerical simulation model established in this paper can well simulate the real UAV impact process.     

四元数在弹射座椅性能仿真中的应用

针对弹射座椅性能仿真中欧拉角速率方程在大幅度姿态运动时存在奇异性,以及四元数法由于姿态角的有界性而出现跳跃、难以实现全姿态角的问题,提出了四元数与欧拉角相结合的方法.阐述了四元数的定义、几何意义及四元数表示的运动学方程.通过四元数到欧拉角的转换,给出了仿真中四元数的积分初值计算公式;分析了弹射仿真中姿态角的跳跃和间断问题.以某型号座椅为例进行了仿真计算,通过对比仿真结果和试验数据,确认了仿真的有效性;与采用单一四元数法的仿真结果进行对比表明,该方法充分结合了四元数与欧拉角速率方程的优点,有效解决了欧拉角速率方程的奇异性和弹射仿真中全姿态角的实现.      

Solar filament eruptions and their physical role in triggering coronal mass ejections

Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80% of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built up by reconnection of a sheared arcade from the beginning of the eruption.     

高空模拟试车台主被动引射方案数值研究

采用二维轴对称雷诺平均方程和Spalart-Allmaras湍流模型,对一大面积比火箭发动机高空模拟试车台在不同引射方案下发动机启动至稳定运行过程中不同室压下的流场结构进行了数值模拟.空间上采用二阶迎风格式进行耦合求解,时间上采用显式Runge-Kutta方法进行迭代推进.结果表明,采用启动段主动引射、主级段被动引射的...     

高速冲击下块体金属玻璃动力学响应的实验研究

块体金属玻璃具有极高的力学强度,存在潜在的军事应用价值,实现其应用的关键在于认识材料在高应变率下的动力学行为特性。为此,利用飞片驱动速度可达3．5km／s的电炮加载装置,对一种新制备的锆基块体金属玻璃的动力学响应进行了实验研究。实验中,基于高精度DPS激光干涉仪测得的样品／窗口界面粒子速度波剖面,获得了新材料在应变率约为10^5／s下的冲击响应特性参数。在加载压力15～25GPa范围下,确定的Hugoniot弹性极限约为2．4GPa,线性拟合得到的冲击Hugoniot关系为Ds=（4．4±0．1）＋（0．58±0．08）up。     

聚能爆破切割清理弹射通道技术

 考虑到飞机隐身等因素,飞机驾驶舱顶部为金属结构而不是传统的座舱盖结构,在弹射救生过程中,采用聚能爆破切割技术,切割金属结构形成"座舱盖"并抛放以清理弹射通道,且已在B-1B、B2飞机上采用。利用座舱顶部金属结构平板件,对聚能切割器装药量、切割厚度,切割过程冲击噪声对飞行员的影响、爆破飞溅物对飞行员的损伤防护等进行了分析和试验研究,并将冲击噪声对飞行员的影响与国军标的要求进行了对比。通过本次研究,将为以后的工程应用提供基础性依据。     

基于 C-AHP的舰炮装备保障性指标体系

在指标体系构建过程中,应用一种云模型（CloudModel）与层次分析法（AHP）相结合的云层次分析法（C—AHP）,构建舰炮装备保障性指标体系的层次结构,针对指标体系中定性定量指标的特性,依据指标的相对重要性筛选各层次指标。实例证明,该方法可有效解决舰炮装备保障性指标体系构建中指标分类不明确,以及由于各类定性定量指标繁杂导致的指标筛选困难等问题。     

Characteristics of solar particle events at Mars relative to Earth

While not specifically designed to detect solar energetic particle radiation, the Electron Reflectometer onboard Mars Global Surveyor (MGS/ER) collected such data from January 1999 through October 2006. Energetic protons (?25 MeV) and other ions penetrated the MGS/ER shielding and registered counts within the instrument’s electronics. During solar particle events (SPE’s), prolonged enhancements in the particle background were observed at Mars with time intensity profiles similar to Earth based SPE observations. Throughout the lifespan of MGS/ER, 85 distinct SPE’s were observed. Basic characteristics of Mars based SPE observations and the frequency of SPE occurrences at Mars are compared to corresponding Earth based observations. Approximately 22% of SPE’s that occurred during MGS/ER operation were observed at Earth but not Mars. Similarly, 19% of SPE’s were observed at Mars but not Earth. Time intensity profiles at Earth and Mars match predictions provided in the literature, based on the physical location of the detector with respect to the motion of the interplanetary shock wave. Note: The work described herein was largely conducted as part of a doctoral dissertation produced by the author.     

Advance of interplanetary physics study in China: 2008—2010

Interplanetary physics study is an important ingredient in space weather research. Considerable progress this aspect has been achieved by the space physics community of China in recent years. This brief report summarizes the latest advances of the interplanetary physics research in China during the period of 2008--2010. This report includes solar corona and solar wind, interplanetary transients, energetic particles, MHD simulation, space plasma, and prediction methods for physical phenomena originating from both solar corona and interplanetary space.      

Actors of the main activity in large complex centres during the 23 solar cycle maximum

During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = −457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared.