大容量电弧炉负荷对电网的影响及其防范措施

着重分析了大容量电弧炉冲击负荷的特点,为了保障电力系统自身的安全可靠运行,应根据电弧炉负荷的特点在进行相关的电气设备选型和运行管理中采取适宜的防范措施,尽量减小大容量电弧炉冲击负荷对电网的影响。     

航空用夹布橡胶薄膜高精度尺寸孔的优化加工方法

提出了利用预制底孔来减小橡胶零件冲制时自然收缩量波动范围的工艺方案.解析了夹布橡胶薄膜高精度尺寸孔的加工工艺参数设计方法.生产实践证明:采用预冲底孔的方法冲制夹布橡胶薄膜,尺寸波动小于0.02 mm,而用原工艺加工的尺寸孔的波动达到0.15 mm.     

工况变化对贯流式水轮机叶顶间隙流态的影响

贯流式水轮机是低水头水能资源开发的主力机型之一,而转轮叶片叶顶间隙流动特性是影响其空化、稳定性能的关键因素.基于数值模拟的方法,本文研究了工况变化引发转轮叶片叶顶间隙泄漏涡初生位置、形态变化的机理,分析了间隙泄漏涡形态改变对水轮机空化、稳定性的影响规律.主要结果表明:工况变化必然伴随导叶开度变化,导叶开度的改变使得转轮...     

高速铁路、劳动力流动与制造业就业波动 ——基于中介效应模型的分析

基于1999—2013年的制造业微观数据估计了中国271个城市的就业变动指标,进而基于劳动力流动的中介效应模型探讨了高速铁路对于城市就业波动的影响效应.研究发现,高速铁路虽然能够有效促进劳动力跨城市的流动,但显著降低了就业创造率和就业破坏率,即存在着"双抑制"现象,并且在两者的耦合作用下对就业净增长率造成负向冲击.在区...     

三电平逆变器中点电位波动的分析与控制

三电平逆变器的直流侧电压平衡问题直接影响着逆变器及其电机调速系统的可靠性。为此,分析了空间矢量对三电平逆变器中点电位波动的影响,并提出了一种抑制中点电位波动的实时控制方法。仿真结果验证了所提出的控制方法是有效的。     

Classification and identification of gas–liquid dispersion states in a jet bubbling reactor

Three gas–liquid dispersion states including flooding, loading, and complete dispersion are observed sequentially in a jet bubbling reactor with an increase of the liquid jet velocity at the nozzle outlet (u_j). The gas–liquid dispersion states are identified through the slope (k) of the curve of fluctuation distribution index (FI) versus u_j as follows: (a) under the flooding, k = 0; (b) under the loading, k > 0; (c) under the complete dispersion, k < 0. In particular, the u_j at the transition points from flooding to loading and from loading to complete dispersion are referred to flooding jet velocity (u_jf, the transition point between k = 0 and k > 0) and complete dispersion jet velocity (u_jcd, the transition point from k > 0 to k < 0), respectively. The average relative deviations of the u_j at the transition points obtained through the acoustic emission measurement and visual observation are less than 5%.     

变燃速发射药芯料体积流率波动值的数值模拟

利用POLYFLOW软件,对不同操作条件下变燃速发射药芯料在机筒内的流动情况进行三维数值模拟,对其体积流率波动因素进行研究。结果表明,芯料的体积流率与螺杆转速成正比,不同转速下芯料体积流率高频波动值在0.02%~0.03%之间,芯料的体积流率波动值与螺杆转速波动值成正比关系;芯料的体积流率与入口压力成正比,不同入口压力下体积流率高频波动值为0.024%~0.026%;入口压力波动较大时,芯料的体积流率波动随着入口压力的增大而较快增加。     

基于参数对比的凸轮转子伺服马达优化设计

针对目前用于连续回转伺服驱动的液压马达品种类型不多的特点,对一种新型的凸轮转子叶片马达进行了研究,提出了基于参数对比的伺服马达优化设计方法。通过对过渡曲线压力角、马达排量公式、马达瞬时流量脉动率以及凸轮正压力的解析式推导及分析,得出了压力角与凸轮大小半径、马达排量与凸轮轴向长度、流量脉动率与叶片厚度以及凸轮正压力与叶片径向长度之间的关系。通过仿真时的参数对比,得到了马达最关键的两个零件即凸轮转子和叶片的优化参数。基于该优化参数设计的液压凸轮转子叶片马达被成功地应用到连续回转电液伺服系统中,并得到了良好的伺服精度,从而证明了马达参数优化设计的可行性和有效性。     

Flow regime identification in horizontal pneumatic conveying by nonintrusive acoustic emission detection

This work investigated flow regimes identification in horizontal pneumatic conveying from the scope of particle motions based on acoustic emission detection. Results showed that the variation of acoustic energy and acoustic energy fraction could be used to identify the transition between suspension flow and stratified flow. Near the transition point, the acoustic energy was maximum, and the energy fraction of particle-wall collision mutated at high mass fluxes. Furthermore, the fluctuation distribution index (FI) was constructed learning from the concept of polymer molecular weight distribution index, and the “circumferential fluctuation difference (D)” was defined. Based on this, new identification criteria and flow regime diagram were established. In suspension flow, D >0. In stratified flow, D <0. While in slug flow, D ≈ 0. According to these criteria, flow regimes can be identified independently of changing trends of measurement parameters. The universality of above criteria was further verified under different operating conditions.     

固液两相流对离心泵压力脉动特性的影响

为了研究含沙水流下径向式导叶离心泵内的压力脉动变化规律,采用大涡模拟和Mixture多相流模型相结合的数值模拟方法,并结合SIMPLEC算法,对输送固液两相流介质的径向式导叶离心泵进行了全流道三维非定常数值计算,并在叶轮与导叶交接面及蜗壳出口段处,将固液两相介质与清水介质时的计算结果进行对比分析。数值计算结果表明,离旋转轴越远处压力脉动幅值越小;导叶与蜗壳内叶频是压力脉动主要频率,且在1倍叶频处最大;导叶内压力脉动幅值均大于蜗壳内,且随着颗粒粒径的增大,压力脉动幅值逐渐减小;蜗壳隔舌处的压力脉动幅值大于蜗壳其他部位;在叶轮与导叶交接面处,清水介质时压力脉动幅值大于固液两相介质时,固液两相介质时脉动波形滞后于清水介质时0.003 5 s;蜗壳出口段,固液两相时压力脉动幅值均大于清水时。