Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters (i.e. wheel speed, workpiece speed and depth of cut) on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride (CBN) abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardness and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 °C is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm³. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the burn-free and crack-free ground surface.     

PCB电源地层腔模辐射快速算法

电路板电源总线的分析非常复杂,虽然传统腔模方法是分析电路板电源总线的一种非常有效的方法,但是该方法具有收敛速度慢,计算时间长和不能分析电源总线辐射发射的缺点.在该算法的基础上,改进二重级数和形式的电源总线辐射发射方法并提出了单一级数和形式的电源总线辐射发射表达式.在此基础上指出了单一级数腔模理论解的适用条件,并对该快速算法的收敛性进行了分析.分析表明,该方法减少了传统二重级数求和的计算工作量,提高了收敛效率并节省了计算时间,而且能够有效逼近双级数腔模辐射算法的计算结果.通过对电路板的辐射发射数值仿真验证了该算法的有效性和正确性.     

SIMULATION OF TEMPERATURE FIELD IN ULTRA-HIGH FREQUENCY INDUCTION HEATING AND VERIFICATION

An experimental and numerical study on the temperature field induced in the ultra-high frequency induction heating is carried out.With an aim of predicting the thermal history of the workpiece,the influence factors of temperature field,such as the induction frequency,the dimension of coil and the gap between coil and workpiece,are investigated considering temperature-dependent material properties by using FLUX 2Dsoftware.The temperature field characteristic in ultra-high induction heating is obtained and discussed.The numerical values are compared with the experimental results.A good agreement between them is observed with 7.9% errors.     

基于模糊控制的纳卫星热控系统仿真

建立了球状纳卫星温度系统动态特性方程组,确定系统稳态温度值后搭建温度系统模型;设计合理的模糊逻辑控制器,与温度系统模型部分相结合,完成整个热控系统模型;分别采用±50%的阶跃信号模拟纳卫星温度系统在空间运行时受舱内仪器热源改变和外壳、辐射器所接受的太阳辐射加热量改变的影响,执行热控系统仿真,绘制仿真曲线与不加控制前的结果相比较.仿真结果表明,将模糊控制系统运用于纳卫星热控系统中能够准确、快速地对其系统温度进行合理控制,具有鲁棒性好、对参数变换不敏感、适应性强以及过渡过程时间短等优点.      

火控雷达在有源干扰环境中的作用距离评估

火控雷达在有源干扰环境中的作用距离直接关系到武器系统在电磁干扰环境中的实战效能和生存能力,因此提高火控雷达在有源干扰环境中的探测距离是雷达技术发展的最主要内容。文中分析了干扰环境里火控雷达的接收特性,探讨了火控雷达在有源噪声干扰环境中的作用距离模型,并根据模型绘制出了在自卫干扰和支援干扰情况下的火控雷达作用距离曲线,最后得出改进雷达抗干扰参数的几点结论。     

Effects of solar activity variations on the low latitude topside nighttime ionosphere

We have studied the topside nighttime ionosphere of the low latitude region using data obtained from DMSP F15, ROCSAT-1, KOMPSAT-1, and GUVI on the TIMED satellite for the period of 2000–2004, during which solar activity decreased from its maximum. As these satellites operated at different altitudes, we were able to discriminate altitude dependence of several key ionospheric parameters on the level of solar activity. For example, with intensifying solar activity, electron density was seen to increase more rapidly at higher altitudes than at lower altitudes, implying that the corresponding scale height also increased. The density increased without saturation at all observed altitudes when plotted against solar EUV flux instead of F10.7. The results of the present study, as compared with those of previous studies for lower altitudes, indicate that topside vertical scale height increases with altitude and that, when solar activity increases, topside vertical scale height increases more rapidly at higher altitudes than at lower altitudes. Temperature also increased more rapidly at higher altitudes than at lower altitudes as solar activity increased. In addition, the height of the F2 peak was seen to increase with increasing solar activity, along with the oxygen ion fraction measured above the F2 peak. These results confirm that the topside ionosphere rises and expands with increasing solar activity.     

自由分子流微电热推力器(FMMR)流动模拟与喷嘴型面分析

FMMR是一种工作在自由分子流状态下的微电热推力器。考虑稀薄效应对FMMR喷嘴型面设计和分析的影响,采用直接蒙特卡罗(DSMC)方法模拟等截面、扩张型面、收缩-扩张型面3种不同喷嘴内的气体流动,分析了各种喷嘴型面对推力器性能的影响规律。结果表明,FMMR采用扩张喷嘴相对于等截面喷嘴,有较大的性能提升,推力最大可增加38%,比冲最大可增加23%;采用收缩-扩张喷嘴较扩张喷嘴能进一步使推力增加21%,但对比冲无明显改善。     

对称面圆周角对轴对称降落伞流场特性的影响

根据降落伞的特点,通过3点假设(伞衣薄膜、伞的轴对称和流场定常),将三维复杂流动问题转化成二维轴对称问题,以节约计算时间.定义对称面圆周角,保持伞衣幅底部直径和顶孔直径不变,选取对称面圆周角在80°~140°范围内变化,建立一系列轴对称降落伞的计算模型.利用数值模拟手段,求解RNG (Renormalization Group)k-epsilon湍流模型下的N-S方程组,获得与有关单位试验相吻合的计算结果.分析发现对称面圆周角和伞衣幅高度对降落伞阻力影响很小.算例中阻力随对称面圆周角的变化在±0.28%以内.对称面圆周角的变化对轴对称降落伞尾流区流场的拓扑结构没有影响.对称轴上存在2个鞍点,随着对称面圆周角的增大,第1个鞍点的位置几乎不变,第2个鞍点的位置向尾流方向推移.      

太阳X-EUV成像望远镜波长选择装置

太阳X射线-极紫外射线(X-EUV,X rays-Extreme Ultraviolet)成像望远镜是我国专门服务于空间天气预报研究的太阳短波成像监测仪器,望远镜工作在0.4~10 nm的X射线波段和19.5 nm的极紫外谱段,能够提供全日面、高分辨率的成像观测.波长选择装置是该望远镜的一个重要子系统,可以增强望远镜动态响应范围,有助于获取更多的反演日冕等离子体参数,这些参数可用来诊断日冕活动.该装置的运动控制具有低功耗的特点,能够满足空间应用环境的特殊要求.其中,步进电机精位置控制是设计的重点,有2种光电编码矩阵可以用于位置检测,从工程可实现角度优选出其中一种,并且从工程可靠性角度分析了该光电编码矩阵的故障模式,提出了在轨故障处理的预案.