The computed characteristics of turbulent flow and convection in concentric circular annuli. Part IV: Generalizations

This is the concluding portion of a four-part numerical investigation. The first was limited to the prediction of the velocity field, a prerequisite for the prediction of convection. The second concerned the prediction of the Nusselt number for uniform heating on the inner wall only, and the third the prediction of the Nusselt numbers for most of the other thermal boundary conditions that occur in practice. Herein, generalized predictive equations are presented for all of these conditions. The number of such equations and coefficients is minimized by the use of superposition and generalized expressions for the dependence on Re and Pr, and to some extent on the aspect ratio.     

三维流场数值模拟在柴油机喷油嘴中的应用

由于喷油嘴内的流动状态以及燃油喷射情况在很大程度上影响柴油机的排放和经济性能,对喷油嘴进行流场分析就显得越来越重要了。鉴于试验和测量受种种条件限制,可以采用CFD模型来预测柴油机喷油嘴内的流场状态,并与试验相结合,提高喷油嘴的选配和设计水平。采用Fluent软件进行模拟计算。主要研究喷油嘴的压力室、喷孔以及针阀的前端结构,并考虑燃油的可压缩性及黏度随压力、温度的变化。通过研究可以预测喷油嘴内流场的分布,分析喷油嘴设计的合理性,指出改进方向。     

大型机电设备故障信号实时采集方法研究仿真

大型机电设备工作环境复杂,故障频发,需要对故障信号进行实时采集和有效检测。传统方法采用时频分析的统计信号处理进行故障信号采集,对低信噪比的故障信号检测性能不好。提出一种基于非线性时间序列分析和相空间重构的大型机电设备故障信号实时采集方法,实现故障的检测和诊断。构建大型机电设备的故障数据检测模型,基于相空间重构分析的故障诊断方法,通过经验模态分解方法提取故障信号的特征信息,以此为数据基础建立智能专家系统,实现大型机电设备的故障诊断。在大型机电设备3种工况模式下测试大型机电设备的性能,得到信号采集时域波形,并进行相空间重构分析,实现故障分类诊断仿真,仿真实验表明,采用该方法进行故障信号的实时采集和故障诊断,故障分类性好,故障检测和诊断的效率较高。     

基于8PSK的新型高速正交光标记交换技术

提出了一种以八相移键控(8PSK)为净荷、ASK为标记的新型高谱效率高速正交光标记交换技术,首次实现了100 Gbit/s的高速正交光标记信号的80 km传输.分析了光信噪比(OSNR)、窄带滤波效应、信道中的非线性效应对标记与净荷性能的影响,并采用平衡相关探测和多符号相位估计(MSPE)技术实现了净荷8PSK信号的接收.与传统接收方式相比,8PSK净荷在相同误码率条件下,OSNR容限提升了约3 dB.经过80 km传输,ASK标记在BER=10~(-9),时OSNR为22.8 dB,8PSK相应的OSNR为20.3 dB.     

RFID防碰撞算法分析与研究

在RFID系统中碰撞是一个很常见的问题,如何有效地解决这一问题对于RFID系统来说至关重要,文中对解决防碰撞的常用方法Aloha算法和二进制树算法做了详细的研究,比较其优缺点,并提出了一种改进的RFID防碰撞算法.     

Low power clock recovery circuit for passive HF RFID tag

A low power clock recovery circuit for passive HF RFID tag is presented. The proposed clock recovery circuit, based on the architecture of Phase Locked Loop (PLL), is used to generate a stable system clock when communication occurs from interrogator to tag with 100% ASK modulation. An envelope detector is designed to detect the incident power from interrogator and control the operating state of the proposed clock recovery circuit. Loop bandwidth of PLL circuits is minimized to reduce the frequency deviation when operating in frequency maintaining state. Furthermore, an initialization circuit for loop filter is also used to speed up locking during initial system power-on-reset. Prototype chips have been fabricated in 0.35 μm 2P4M CMOS technology. A total current consumption of 3 μA has been achieved in the frequency maintaining state. Measurement results show that, when communication occurs from interrogator to tag with 100% ASK modulation, clock recovery circuit generates a stable and consecutive system clock and has an inevitable frequency derivation of 7.5% when operating in frequency maintaining state.     

游泳池触摸板计时系统的设计与实现

本课题根据游泳池计时系统的实际需求出发,设计了一套游泳池触摸板计时系统。该系统主要由以下部分组成：以嵌入式ARM系统为核心的部件,具有实时信息处理功能;512位的CPLD控制终端,具有集成数据和数据统计的功能;内置高精度晶体数字钟的计时器,具有计时功能。     

A Novel Terahertz Rat-Race Hybrid Coupler Based on PPDW

A novel rat-race hybrid coupler based on parallel-plate dielectric waveguide (PPDW) is proposed. PPDW has been proposed as a basic terahertz transmission line for its remarkable simple structure and comparatively low attenuation at terahertz frequency band. It can be applied to design many terahertz components. In this paper, a (3 N + 3/2) × lambda circumference PPDW rat-race hybrid coupler operating at quasi-TE₁₀ mode is studied. The investigation results show that, at 0.34 THz, the transmission losses of the two split output ports are both equals −3.2 dB; the return loss at its input port is below −20 dB; the insertion loss at each split transmission port is less than 0.2 dB; and the two isolated ports show good isolation of above 20 dB. Therefore, it will have wide potential applications at terahertz frequency band.     

基于AT89S52的程控滤波器的研究与设计

设计了一种新型程控滤波器,实现-3dB截止频率fc在1kHZ---20kHZ范围内可调,详细介绍了系统的硬件电路以及软件框图,测试实验表明测试结果与理论设计基本吻合,达到了设计的要求.     

基于五维混沌系统的信号加密研究

随着计算机技术、信息技术和通讯技术等高科技技术在近年来的迅猛发展,信息加密越来越受到人们的重视。提出了基于五维混沌系统用来实现通信加密的方法,该方法利用五维混沌源信号,对原始方波信号实现掩盖加密,利用迭代次数和混沌信号的加减手段设置密码,为信息加密提供了一种新方法。