降低液压系统压力脉动方法

通过对液压系统中产生压力脉动的机理分析,介绍被动滤波和主动滤波两种降低压力脉动的方法。通过对比,提出主动滤波是降低压力脉动的一种行之有效的方法。     

全光3R中的窄条AlGaAs激光器自脉动研究

分析了利用窄条AlGaAs激光器的自持脉动来进行3R时钟恢复的原理,着重阐述F—P腔半导体激光器自持脉动产生的机理和条件,同时研究窄条AlGaAs激光器的结构参数对自持脉动的影响．在此基础上讨论了改变自脉动频率和提高输出光脉冲功率的方法．最后提出了通过采用一种不规则窄条结构来提高激光器的输出光脉冲频率的方法,并使用仿真程序进行了仿真实验．结果表明,采用该结构可以比在同样条件下采用规则窄条结构获得更高频率的输出光脉冲．     

大型混流可逆式机组“S”形特性的现场测试

“S”形特性影响到混流可逆式机组的空载并网、调相以及紧急停机等操作,对机组的安全、稳定运行非常重要.通过现场测试对宝泉抽水蓄能电站1号机组的“S”形特性进行了研究,获得了机组进入不稳定“S”区后的三导(上导、下导、水导)摆度、上下机架振动以及内部测点压力脉动的幅值及频谱特性,为深入认识混流可逆式机组的“S”形特性提供了依据.     

非定常流弯肘型尾水管不规则压力脉动预测

尾水管内螺旋状涡带引起的压力脉动是造成混流式水轮机机组振动的主要原因之一,直接威胁机组的安全运行。为此,提出一种基于CFD数值计算的水轮机尾水管压力脉动数字化预测法,并利用此法对一大型混流式水轮机偏工况下尾水管内水流流动进行了长时间非定常流计算,讨论该工况下尾水管内死水域与涡带的运动规律,预测了尾水管的不规则压力脉动,压力脉动分析结果表明,其波形、频率、相位与实际基本一致。     

Estimating teat canal cross-sectional area to determine the effects of teat-end and mouthpiece chamber vacuum on teat congestion

The primary objective of this experiment was to assess the effect of mouthpiece chamber vacuum on teat-end congestion. The secondary objective was to assess the interactive effects of mouthpiece chamber vacuum with teat-end vacuum and pulsation setting on teat-end congestion. The influence of system vacuum, pulsation settings, mouthpiece chamber vacuum, and teat-end vacuum on teat-end congestion were tested in a 2 × 2 factorial design. The low-risk conditions for teat-end congestion (TEL) were 40 kPa system vacuum (Vs) and 400-ms pulsation b-phase. The high-risk conditions for teat-end congestion (TEH) were 49 kPa Vs and 700-ms b-phase. The low-risk condition for teat-barrel congestion (TBL) was created by venting the liner mouthpiece chamber to atmosphere. In the high-risk condition for teat-barrel congestion (TBH) the mouthpiece chamber was connected to short milk tube vacuum. Eight cows (32 quarters) were used in the experiment conducted during 0400 h milkings. All cows received all treatments over the entire experimental period. Teatcups were removed after 150 s for all treatments to standardize the exposure period. Calculated teat canal cross-sectional area (CA) was used to assess congestion of teat tissue. The main effect of the teat-end treatment was a reduction in CA of 9.9% between TEL and TEH conditions, for both levels of teat-barrel congestion risk. The main effect of the teat-barrel treatment was remarkably similar, with a decrease of 9.7% in CA between TBL and TBH conditions for both levels of teat-end congestion risk. No interaction between treatments was detected, hence the main effects are additive. The most aggressive of the 4 treatment combinations (TEH plus TBH) had a CA estimate 20% smaller than for the most gentle treatment combination (TEL plus TBL). The conditions designed to impair circulation in the teat barrel also had a deleterious effect on circulation at the teat end. This experiment highlights the importance of elevated mouthpiece chamber vacuum on teat-end congestion and resultant decreases in CA.     

某大型水电站异常振动和出力不足问题研究

以我国自主研发的600 MW级混流式水轮发电机组投运后的运行状态为例展开研究分析。针对该大型水电站高负荷区出现的异常振动和最大出力不达标的严重问题,从问题的产生机理分析和故障诊断入手,先对引起异常振动的原因展开分析,然后通过对现场稳定性和出力测试结果进行评估,提出了对机组实施改进的方案,即沿着水轮发电机组转轮叶片的出水边进行切割修型,并同时对泄水锥进行改进,再结合数值和同步模型试验的模拟结果进行比较分析,成功地解决了该水电站的高负荷区域异常振动和出力不足问题,并由此提炼出一套较为完整的针对这一类型问题的分析和处理通用方法。     

基于PIC16F877A单片机软件环分的步进电机控制系统

本文介绍基于PIC16F877A单片机软件环分的数控步进电机控制系统。其控制电路新颖、简洁、组合方便。可以使系统简化,工作可靠,而且可以获得较高的控制精度。     

小波包特征熵神经网络在尾水管故障诊断中的应用

为精确诊断水轮机尾水管涡带，该文提出一种基于小波包特征熵的神经网络故障诊断新方法。对采集到的尾水管压力脉动信号进行三层小波包分解，提取小波包特征熵，然后构造信号的小波包特征熵向量，并以此向量作为故障样本对三层BP神经网络进行训练，实现智能化故障诊断。试验结果表明训练成功的BP网络能够很好地诊断机组尾水管是否发生涡带以及涡带的严重程度，为水轮机故障诊断开辟新的途径。     

水泵水轮机的"S"形特性及对机组性能的影响

针对水轮机全特性图上的“S”形特性,从理论上分析了其产生的原因及对抽水蓄能电站运行的影响,并结合实际剖析了“S”形特性对抽水蓄能电站日常运行的影响和常用的解决方法。     

电站锅炉燃气脉冲除灰过程研究

中国电站锅炉燃用大量的未经洗选的劣质煤,导致严重的锅炉积灰。积灰不仅使锅炉热效率下降,而且堵塞烟气通道,影响了锅炉的正常运行。燃气脉冲除灰技术是中国科学院力学研究所燃烧实验室开发的,并在30多台大型电站锅炉应用,取得了很好的效果。本文工作研究了该项技术中燃烧室结构和燃料对火焰传播和压力脉冲的影响;用压力传感器测量燃气脉冲在出口外流场中的压力分布,观察燃气脉冲的作用强度和作用范围;用振动传感器测量积灰板的振动,以及在不同空间位置振动加速度的变化情况,由此推论了除灰作用的机理。