Statistical analysis of the occurrence rate of geomagnetic storms during solar cycles 20–24

This study examines the occurrences rate of geomagnetic storms during the solar cycles (SCs) 20–24. It also investigates the solar sources at SCs 23 and 24. The Disturbed storm time (Dst) and Sunspot Number (SSN) data were used in the study. The study establishes that the magnitude of the rate of occurrences of geomagnetic storms is higher (lower) at the descending phases (minimum phases) of solar cycle. It as well reveals that severe and extreme geomagnetic storms (Dst < -250 nT) seldom occur at low solar activity but at very high solar activity and are mostly associated with coronal mass ejections (CMEs) when occurred. Storms caused by CME + CH-HSSW are more prominent during the descending phase than any other phase of the solar cycle. Solar minimum features more CH-HSSW- associated storms than any other phase. It was also revealed that all high intensity geomagnetic storms (strong, severe and extreme) are mostly associated with CMEs. However, CH-HSSW can occasionally generate strong storms during solar minimum. The results have proven that CMEs are the leading cause of geomagnetic storms at the ascending, maximum and the descending phases of the cycles 23 and 24 followed by CME + CH-HSSW. The results from this study indicate that the rate of occurrence of geomagnetic storms could be predicted in SC phases.     

小型平板回路热管蒸发器内传热与流动的三维数值模拟

针对小型平板回路热管蒸发器内的流动与传热，建立了多区域耦合的数学物理模型，并应用FLUENT软件进行了三维数值模拟。结果表明:蒸发器传热特性在不同热负荷下呈现出较大的差异，其温度分布不仅取决于热负荷，更依赖于毛细芯表面发生的两种传热机制，即毛细蒸发和热传导。相比高热负荷(Q=120W)和低热负荷(Q=40W)，中等热负荷(Q=80W)下蒸发器各个部位的温度均较低。三种不同热负荷下，毛细芯反向导热均大于侧壁漏热，补偿腔内与毛细芯相邻处易出现高温区。冷凝回流液在补偿腔内的流动形成两个涡，这种流动特点有利于降低毛细芯的温度。当热负荷与系统冷凝能力匹配时，整个系统流动与传热特性最优。      

无人机地面控制站 应急电源逆变控制系统设计

为了给地面控制站提供安全可靠的应急电源,文章主要根据由DSP数字技术+脉宽调制SPWM驱动+IGBT+隔离滤波为一体化设计发展起来的一个新型UPS电源系统,并对逆变控制系统进行了硬件和软件设计。通过对控制系统的仿真验证,得出所需的稳定的三相交流电,说明该电源逆变控制系统可以为无人机地面控制站提供安全可靠的应急电源。     

Modelling and analysis of metal flowing behaviors in constraining ring rolling of tapered ring with thin wall and three high ribs

Tapered ring with thin wall and three high ribs(TRTWTHR), showing complicated geometry(wall thickness is less than 4 mm and rib height exceeds 20 mm), is extensively utilized to fabricate the critical structural parts of aerospace equipment such as spacecraft cabin, rocket body and fuel tank because of light weight and high carrying capacity. How to fabricate TRTWTHR with high performance is a critical problem that aerospace area needs to solve. In this work, constraining ring rolling(CRR) techn...