Precision manufacturing of turbine wheel slots by trim-offset approach of WEDM

The present study aims to precisely manufacture the turbine wheel slot using a novel trim-offset approach of wire-electrical-discharge-machining (WEDM) in order to overcome the challenges of a conventional broaching process. Two dimensional model of turbine wheel slot is prepared in ‘ELCAM’ software to generate the computer-numerical-control (CNC) code of fir-tree-profile geometry. The experimental plan based on a trim-offset approach is executed to minimize the thermal damage and to improve the surface fatigue strength, which is most desirable for a long operating life of the jet engine. An average cutting speed of ~1.5 mm/min is observed for rough-cut and ~5 mm/min for trim-cut operation. Six categories of wires are used to manufacture the turbine wheel slots without any wire breakage and gap-short issue. The fabricated profile slots have demonstrated an average roughness (Ra) of 0.65 μm, profile accuracy within ±5 μm, minimum hardness alteration (34.87 Hv), and negligible recast layer (<5 μm) using B-150 wire and fulfilled the essential requirements of the gas turbine industries. Compared to wire-electrochemical-machining (WECM), WEDM trim-offset approach is quite advantageous and should be beneficial for the researchers working in ‘Precision machining of aerospace materials’.     

城市景观中的缝与槽

缝与槽是线性艺术在城市景观中的表现方式,本文从线性艺术效果、虚实与光影、功能与建造三个方面进行研究与分析,使人们深入理解线性艺术在现代城市景观设计中的作用和效果。     

基于探测线圈法的双馈式发电机转子匝间短路槽的定位研究

双馈式感应发电机广泛应用于风力发电领域,发电机转子绕组匝间短路是目前国内外研究的热点之一。由于双馈风力发电机的特殊结构和工作特性,准确定位发生匝间短路故障的槽号存在一定难度。本文从有限元理论出发,利用Ansoft仿真分析正常和转子绕组匝间短路故障后的气隙磁密的变化特性。从磁特性角度出发,分析了故障槽定位的可行性;通过探测线圈和光电装置的结合,对比分析正常与故障下采集信号的差值,即可确定故障槽的位置。     

基于特征的曲面钣金零件三维参数化造型研究

为了保证典型曲面钣金特征的数据信息不会随着曲率的不同而发生改变,提出了一种由程序驱动的基于特征的曲面钣金零件三维参数化造型技术。分析了复杂曲面钣金零件的基础模型建模要求,并在总结造型方法整体框架的基础上,给出了实体建模与三维参数化设计的具体实现方法。通过对曲面加强槽的三维参数化造型,验证了该方法的准确性与通用性。     

随钻中子测井仪机械强度计算方法研究

鉴于随钻测井（LWD）对于随钻测井仪器的机械强度的要求,文章研究了随钻中子仪器的机械强度,利用SOLIDWORKS、ANSYS等软件建立并分析随钻中子仪器模型,通过改变几种不同参数中子源仓凹槽的深度、长度等,模拟计算出了中子仪器在受到拉力、压力、扭矩作用时的源仓凹槽部分的等效应力分布图以及受到的最大应力集中值．     

Reduced‐frame TDMA protocols for wireless sensor networks

Time‐division multiple‐access (TDMA) is a common medium access control paradigm in wireless sensor networks. However, in its traditional form, the TDMA‐based protocols suffer from low channel utilization and high message delay because of a long frame length needed to provide collision‐free transmissions, which is particularly damaging in dense wireless sensor networks. In this paper, we investigate the performance and the energy efficiency of a class of TDMA‐based protocols, called reduced‐frame TDMA, where every TDMA slot is augmented with a short time period dedicated for carrier sense multiple access‐based contention resolution mechanism. Because of their ability to dynamically resolve collisions caused by conflicting slot assignments, the reduced‐frame TDMA protocols can be configured with any frame length, independently of node density. In addition, we present a distributed heuristic slot assignment algorithm that minimizes interslot interference in the presence of limited number of slots per frame. The simulation results indicate that the reduced‐frame TDMA protocols significantly reduce the message delay and increase the maximum throughput without incurring significant penalty in energy efficiency compared with the traditional TDMA scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

北京电信网155 Mbit/s信号时隙编号统一规则

介绍了北京电信网155Mbit/s信号时隙编号统一问题产生的原因，探讨了北京电信网155Mbit/s信号时隙编号统一原则，并论述了北京电信传输网、交换网155Mbit/s信号时隙编号统一策略。     

基于动态优先级表的TDMA时隙分配

Ad Hoc网络组网效率提升的一个重要方面就是研究高效的时隙分配算法,动态TDMA时隙分配机制已经成为提高组网效率的一个热门研究点。这里基于动态优先级表提出一种新颖的动态时隙分配算法,该算法能在时间维上保证各节点对空闲时隙资源竞争使用的公平性。仿真结果表明基于动态优先级表的时隙分配算法能高效利用时隙资源,提高信道利用率。     

黑龙江省移动基站动力及环境集中监控系统

介绍了黑龙江省移动基站集中监控系统网络结构、系统功能、监控对象及供电方式，并探讨了黑龙江省移动基站动力及环境集中监控系统的传输方案。     

EPON中上行时隙的动态分配

根据以太网数据包具有变长性的特点,描述了在以太网无源光网络(Ethernet Passive Optical Network,EPON)系统中局端光线路终端(Optical Line Terminal,OLT)根据终端用户的实际需求,动态分配给各个光网络单元(Optical Network Unit,ONU)上行时隙。动态时隙的分配能充分利用上行信道,大大减少了因为变长数据包不能完全适合固定时隙而带来的带宽浪费。