Application of improved equivalent edge currents in synthetic aperture radar imaging

Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar (SAR) imaging simulation. According to the difficult problems that normal methods cannot calculate the scattering function of electrically large object under the condition to wideband, an effective method of improved equivalent edge currents is presented and applied to SAR imaging simulation for the first time. This method improves calculating velocity and has relatively high precision. The concrete steps of applying the method are given. By way of the simulation experiment, the effectiveness of the method is verified.     

调整法解装配尺寸链的完整计算

提出了利用建立空位与当量装配尺寸链的概念并论述调整原理，全面推导出调整件分别为增减环时的调整件组尺寸计算式．系统地叙述了解算步骤并列举试例．使调整法解算装配尺寸链获得全面完整的解算过程     

y+值对翼型气动参数计算精度的影响研究

基于RAE 2822翼型,为了研究粘性底层无量纲参数y+对翼型气动参数计算精度的影响,采用ANSYS ICEM剖分的计算域网格和三维N-S控制方程的有限体积法离散格式,选取SST湍流模型,在不同的y+值下借助ANSYS CFX模块数值计算了该翼型的气动参数,分析了相对误差,绘制了压力系数分布云图。结果表明:过大的y+值导致误差增大;在y+的理论值11.63附近,计算精度变化较小;较小的y+可使精度进一步提高,但过小的y+并不能得到过高的计算精度。y+值对翼型边界不同区域的计算精度影响有所不同,翼型气动参数数值计算时推荐y+取2-4。     

由指数寿命型不同元件组成的K/N(G)系统可靠性的置信限

本文对由寿命型不同元件组成的K/N(G)系统,提出了可靠性评定的经典和信赖(Fiducial)方法,并将R.G.Easterling 方法加以推广。此方法对电子设备和遥测系统的可靠性设计与分析尤为适用。     

在整环中利用等价关系构造一个除环

对著名代数学家Ｏｒｅ提出的一个等价关系问题给出一个较为巧妙的证法，并构造了一个除环．     

宽浅型明渠非定常流的数值模拟

本文根据不可压缩三维非定常流的动量方程和连续方程,求解了宽浅型明渠中三维流速分布和水位随时间的变化规律.采用单方程湍流模式确定涡粘性系数,沿垂向引入无尺度坐标,使计算网格能拟合自由面及床面.对控制方程采用有限差分离散、剖开算子法求解.通过引用欠松驰技术,提高了计算稳定性.计算表明,本文中提出的计算方法具有时间步长大、存储量小和机时省的优点.最后,用其求解长江口南港河段的潮流运动,计算结果与现场实测结果十分一致.     

膜式机械通风横流冷却塔节能研讨

横流塔由于气水对数平均焓差较小。故在同参数下冷却数较逆流塔大,通常设计中电耗约高46％左右。本文从分析气流在填料中流态出发,探讨填料的相对凸起、风速与传质强度、能耗及投资间关系。由于在一定冷却数下,填料体积与传质强度成反比,前者与塔投资有关,后者当填料间距远小于其长度及高度时,可近似认为仅与填料形状及风速有关,即与能耗有关,故按投资回收期来选择填料形式并决定经济风速才是合理有效的节能方法。样塔提供较原塔节能65.7％的实例。本文亦可供膜式逆流塔参考。     

Book reviews

Summary

Five early ontogenic stages of Scomberomorus lineolatus (C. &; V.) ranging in standard length from 18·4 mm to 99·5 mm are described.

Direct comparison of these early stages with those of S. commerson (Lac.) showed differences in the number of gill rakers, the length of preopercular spines and the position of the anal fin in relation to the second dorsal fin. In the case of S. guttatus (Bl. &; Schn.) the gill rakers are of the same number as in S. lineolatus but the preopercular spines decrease in size from above with the upper two subequal in size and none projects beyond the operculum.

In the earlier stages, S. lineolatus could be easily distinguished from S. guttatus by the absence of the bluish green coloration characteristic of S. guttatus. In later stages when the coloration has developed in both the species the only marked difference between the two is in the nature of the bent portion of the lateral line which is wavy in S. lineolatus and straight in S. guttatus.

The number of vertebrae is 46 in S. lineolatus; 42–45 with 43·9 as mean in S. commerson and 47–52 with 49·7 as mean in S. guttatus.     

模拟熔喷纤网的孔径分布及其对过滤性能的影响

首先根据纤维过滤介质的理论假设,对分布密度不同的熔喷纤网进行计算机模拟,然后利用图像分析方法,计算了其孔径大小及其分布并与实际情况对比;在模拟纤网基础上又从理论上计算了占全部孔数10％的大孔对过滤性能产生的影响,并发现经过这10％大孔的流量比例与当量孔径标准差成线性增加的关系。     

Modeling of Busbars in High Power Neutral Point Clamped Three-Level Inverters

The busbars in high power neutral point clamped three-level inverters are modeled using the Maxwell Q3D Extractor software, which is based on the partial element equivalent circuits method. The equivalent circuits of the busbars and devices model are simulated in the electric simulator PSlM to analyze the effects of the parasitic inductance on the switching characteristics of the integrated gate commutated thyristor （IGCT） in different topology positions. The simulation results agree well with the measured impedance analyzer results and the IGCT test results, which proves the effectiveness of the modeling method for the large, complex busbars.