收发分离偏馈单反射面紧缩场静区评估方法

根据Lorentz互易定理,提出了一种对收发分离偏馈单反射面紧缩场静区评估的方法.两个馈源与反射面分别构成独立的、互为测量关系的天线系统,在相同静区位置构成各自的天线口面.对这两个等效天线系统在该平面产生的电磁场进行测试,得到收发系统在静区位置各自的电磁特性.根据收发天线各自的电磁场分布,按照天线接收原理可以得到双站合成的等效静区.双站等效静区呈对称分布,但相对于单站静区分布,双站等效静区范围变小,波动更小,边缘下降更平缓.采用物理光学法对上述等效静区进行了仿真,并进一步通过实验测试对此静区评估方法的有效性进行了验证.     

掠弯叶片前缘曲线同流场结构的关联

在全三维反问题还不成熟的条件下,由二维反问题和三维正问题组成的准三维设计体系中,叶片的前缘是由给定的积迭轴和基元叶型特征决定,具有任意性,难于对其加以控制。因此本文试图把掠弯叶片的前缘空间曲线作为设计自由度,增加到设计体系中,实现设计中前缘空间曲线同流场结构的关联,利用前缘形状控制流场中的激波结构和二次流的迁移,改善流场结构。并以一个高负荷跨音单级风扇的气动设计为例,对这一改进进行了验证。      

超声速自引射装置的工作过程研究

应用湍流κ-ε双方程模型,分析了液体火箭发动机自引射工作过程所用的超声速自引射装置(简称引射器,包括圆柱型和二次喉道型引射器)在相同二次流入口面积时的流场分布,依据流场分析值确定了激波在引射器内的位置,结果表明喷管内的气流达到满流状态,并根据有关参数计算了引射系数.对比引射器真空舱内压力仿真值和试车测量值,两者基本一致.      

基于SFEM的结构元件疲劳可靠性分析

将结构元件的弹性模量、泊松比、几何尺寸定义为随机场,并将随机场离散成随机变量,将抗拉强度定义为随机变量,采用Monte Carlo随机有限元法(MCSFEM),给出了元件危险点应力的随机分布。由危险点应力分布、材料的p-S-N曲线和Miner理论给出了概率名义应力法,计算常幅载荷下元件的寿命分布,并利用剩余寿命模型计算元件的可靠度。给出了两个算例,结果表明:计算结果与试验结果吻合良好。     

A numerical study of noontime bite-outs in F2-region electron density

Noontime bite-outs in ionospheric F₂-region electron density in the geomagnetic equatorial, low, and middle latitudes have been reproduced in this study using the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). The different driving mechanisms of F₂-region noontime bite-outs at different latitudes were further verified by modeling simulation. In the geomagnetic equator, the upward ExB plasma drifts are the main process to produce the noontime bite-outs in ionospheric electron density. In the geomagnetic low latitudes, both the electrical fields and poleward meridional winds play a crucial role in forming the noontime bite-outs. In contrast to the case at the geomagnetic equator, a weaker fountain effect might be an favorable condition for the noontime bite-outs to occur at low latitudes. For geomagnetic middle latitudes, an upward plasma flux and poleward meridional winds are the dominated drivers in producing the noontime bite-outs. Modeling results show that a large upward plasma flux and poleward meridional winds make the noontime bite-outs to occur and observable over middle latitudes.     

A hybrid chemical modification strategy for monocrystalline silicon micro-grinding: Experimental investigation and synergistic mechanism

For high performance manufacturing of micro parts and features, a hybrid chemical modification strategy is proposed to decrease critical energy barrier of mechanical removal of hard and brittle crystal material by refining localized machining condition. The strategy, namely UV-light and IR-laser hybrid chemical modification (UVIR-CM) strategy, includes two steps, an ultraviolet light (UV-light) catalytic advanced oxidation and an infrared laser (IR-laser) assisted selective modification based on Fenton liquid–solid reaction for monocrystalline silicon. The modification effects of UVIR-CM strategy were investigated by surface morphology micro-observation, cross-section transmission electron microscopy (TEM) observation, Raman spectroscopy analysis and nanoindentation test. Experimental results demonstrated that varied degrees of laser texturing appeared on different strategy samples’ IR-laser scanned area. And the IR-laser thermal damage has been successfully inhibited due to the refraction and reflection of energy by bubbles in liquid medium. But for the UVIR-CM strategy, a uniform and amorphous silicate layer is detected in a certain boundary. The UV-light promotes oxidation cycle ability of the chemical solution and ensures sufficient oxide modified layer for subsequent step. Attributing to synergism of photochemical, photothermal and kinetic effects induced by IR-laser, the modified layer displays layered structure with about 600 nm thickness, (2.7 ± 0.60) GPa nanohardness, and (93.7 ± 22.9) GPa indentation modulus. And the layered structure is amorphous layer, nanocrystal and micro-twins layer from the surface to the interior of sample. Consequently, it reveals that the subsequent mechanical removal will become easy due to decreasing energy barrier of monocrystalline silicon in selective area. Meanwhile, its original excellent mechanical properties also are maintained under a certain depth. The results contribute to develop a novel combined micro-machining technology to achieve collaborative manufacturing of structure shape and surface integrity for micro parts and feature.