双药室喷管气流反推减后坐机理

为解决发射高初速榴弹的榴弹机枪系统后坐力大的问题,提出了一种双药室拉瓦尔喷管气流反推减后坐技术.设计了适用于高速榴弹机枪系统的双药室拉瓦尔喷管减后坐装置,利用一维非定常流理论推导了双药室喷管低后坐武器的内弹道阶段和后效期阶段的气体动力学方程;将试验测得的压力峰值、弹丸初速及后坐力与仿真数值进行对比,验证建立的双药室喷管气流反推减后坐计算模型的正确合理性;计算双药室喷管低后坐武器后药室、前药室、导气室及喷管气室的压力,并分析压力参数随时间变化规律;对比分析双药室喷管武器与普通武器的膛压曲线、弹丸速度曲线,重点分析双药室喷管内气流压力、温度、密度和速度随时间变化曲线及在喷管内分布状况;探讨了后药室装药量、喷管导气孔直径及喷管内经对武器喷管反推力、喷管减后坐效率、弹丸初速等武器发射性能的影响.研究结果表明,在保持弹丸初速不变的情况下,合理匹配双药室减后坐结构参数,采用双药室喷管气流减后坐技术可实现武器低后坐发射的目的.     

Electro-sorption of ammonium by a modified membrane capacitive deionization unit

A modified membrane capacitive deionization (MCDI) unit with additional flow channels in the anode and cathode chambers was used to study the performance of ammonium ion removal. The influences of operating parameters including initial ammonium concentration, flow rate and applied potential and the effect of flow in the anode and cathode chambers were investigated. Flow through the anode and cathode chambers significantly enhanced the electro-sorption efficiency. The electro-sorption of ammonium at 5 mL/min was about 65% greater than without flow.     

Combined effects of the filling ratio and the vapour space thickness on the performance of a flat plate heat pipe

An experimental study of a flat plate heat pipe (FPHP) is presented. Temperature fields in the FPHP are measured for different filling ratios, heat fluxes and vapour space thicknesses. The system is hermetically sealed with a transparent plate for meniscus curvature radius observations by confocal microscopy. Experimental results show that the liquid distribution in the FPHP - and thus its thermal performance - depends strongly on both the filling ratio and the vapour space thickness. A small vapour space thickness induces liquid retention and thus reduces the thermal resistance of the system. Nevertheless, the vapour space thickness influences the level of the meniscus curvature radii in the grooves and hence reduces the maximum capillary pressure. As a result, it has to be carefully optimised to improve the performance of the FPHP. In all the cases, the optimum filling is in the range one to two times the total volume of the grooves. A theoretical approach, in non-working conditions, has been developed to model the distribution of the liquid inside the FPHP in function of the filling ratio and the vapour space thickness.     

FDTD method for site attenuation analysis of compact anechoic chamber using large‐cell concept

In this paper, the FDTD method has been applied to analyze the site attenuation of an anechoic chamber at 100 MHz or less where the ray tracing method is not applicable. To calculate site attenuation by a personal computer, the dipole antenna and the EM absorber were modeled using a large cell which was larger than the diameter of the antenna element and the thickness of the EM absorber. The equivalent diameter of the antenna element was determined so that the calculated site attenuation in free space agreed with that by the method of moments, and the equivalent dielectric constant and permeability of the absorber were determined so that the reflection coefficient agreed with that by the transmission theory. The site attenuation of the compact anechoic chamber was calculated for frequencies from 30 MHz to 100 MHz and compared with the measured one to confirm the validity of the proposed modeling method. The results indicated that the deviation between the calculated values and the measured ones was within 2 dB. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 9–16, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20411     

A RANS flamelet-progress-variable method for computing reacting flows of real-gas mixtures

This paper provides an efficient numerical method for solving reacting flows of industrial interest in the presence of significant real-gas effects. The method combines a state-of-the-art solver of the Reynolds-averaged Navier-Stokes equations - equipped with the low-Reynolds number k-ω turbulence closure - with a combustion flamelet-progress-variable approach. A real-gas model as well as a detailed kinetic scheme are used to generate the flamelet library. The method is tested versus several applications chosen to demonstrate the importance of the real-gas effects and of the kinetic scheme for computing high-pressure combustion. The major contribution of the paper is to provide a single-phase approach which solves turbulent reacting real-gas flows at a computational cost comparable with that of the simulation of a non-reacting flow thanks to the use of the flamelet library.     

A hybrid scheme of signal process techniques to improve the measurement accuracy of antenna radiation patterns inside an anechoic chamber

Abstract

Antenna measurement inside an anechoic chamber can significantly suffer from measurement inaccuracy due to the scattering from the shielding walls and internal structures, if the space is not sufficiently large and the absorbers have not significantly reduced the multipath signals, which raises multipath interference. This paper develops a hybrid scheme that integrates the concepts of signal processing techniques including time gating, matrix pencil and multiple signal classification methods to reduce the multipath effects and improve the measurement accuracy. Characteristic comparison between individual method as well as the hybrid scheme will be performed based on experimental examinations.     

电波暗室综述

扼要地介绍了电波暗室的由来、应用、类型、性能指标、设计方法、建造、指定测试方法及现状与发展动向     

基于DOP值的暗室天线组合优选设计

基于卫星导航接收机抗干扰测试环境的建设在终端测试中有着至关重要的作用。通过分析建设抗干扰环境的需求,从系统总体和软硬件设计的角度介绍了一种基于导航信号定位精度因子(DOP)的暗室天线组合选择方案。在关键技术分析后给出了系统仿真方案与性能测试方法、结果分析和结论。该方法能够为微波暗室的多发射天线开孔改造以及空分抗干扰接收机测试环境的构建提供一种设计依据。     

微波暗室静区性能仿真预测方法

为了有效预测微波暗室的静区性能,使用FEKO软件进行任意入射角度条件下角锥吸波材料的前向反射率仿真,并以某矩形暗室结构为例,利用吸波材料反射率仿真结果,采用射线追踪法计算了发射天线位于天线阵面上典型位置时暗室静区内反射电平的分布情况.经比较,仿真结果与实际测量结果一致性较好,该方法为微波暗室性能预测提供了有效手段.     

仿真暗室归一化场地衰减理论值计算

国际电磁兼容标准给出了标准距离的归一化场地衰减(NSA)的理论值,但在实际应用中需要知道非标准距离的理论值。根据归一化场地衰减的定义,介绍了一种NSA理论值计算模型。对该模型进行了数学推导,得出了NSA的计算公式,并通过计算机编程进行了计算。计算结果表明:计算误差小于0.1dB,满足标准要求。该模型可以用于仿真暗室中不同测试距离、不同收发天线高度的NSA理论值计算。