低压配电网智能无功补偿系统软硬件设计

根据晶闸管投切并联电容器（TSC）的无功补偿原理,介绍了以16位工业级单片机80C196KC为核心的智能无功优化控制器。该控制器硬件由单片80C196KC、存储器与I／O接口、电量测量、温度检测、执行机构、键盘／液晶显示器、通信等模块组成。控制器软件采用模块化结构设计．使用KC196汇编语言编程,包括显示、模数转换、看门狗、键盘扫描、参数计算、投切电容、通信等模块。该智能无功优化控制器采用电压一无功综合补偿自适应控制方式．在满足电压合格的前提下使功率因数最优为目标函数,根据低压配电网的电压和无功功率变化,具备自动调整相关控制系统参数以实现控制目标的能力。实现电客先投先切的功能。并且可避免投切振荡和过补偿。该控制器装置挂网运行后．效果良好。     

基于模式识别的盲分离语音信号获取方法

在批处理音频信号盲分离过程中,要将分离出的语音信号帧拼接成连续的语音比较困难,这主要是由于盲信号分离存在分离信号排列顺序的不确定性。笔者根据语音信号短时平稳特性,利用基音周期为窗长,连续分割盲分离信号,将各个窗内数据的归一化自相关函数值取平均作为音频信号的模式特征,最后根据相似性阈值和最小距离原则进行信号聚类分析,从而克服提取盲分离语音信号中的信号顺序不确定性,获得连续语音信号。实验仿真证明了该方法的有效性。     

Good extrusion foaming performance of long-chain branched PET induced by its enhanced crystallization property

Poly(ethylene terephthalate) (PET) was modified by regulating different contents of branching agent epoxy-based multifunctional oligomer and chain extender pyromellitic dianhydride in reactive extrusion process. The modified PET with better long-chain branched (LCB) structure boosted its rheological properties, and its enhancement of melt viscoelasticity resulted in excellent foamability in molten-state foaming process using supercritical CO₂ as blowing agent. More importantly, the branched structures acted as crystal sites to accelerate the crystallization kinetic of LCB PET whether under atmospheric pressure or high-pressure CO₂. The shear and elongation flow inside die further quickly induced the crystallization of LCB PET. The rapidly generated fine crystals could both introduce heterogeneous cell nucleation and suppress CO₂ escape, so the cell morphology of LCB PET in continuous extrusion foaming process exhibited a three-fold increase in cell density and smaller uniform cell size with respect to those of other foam-grade PET with long-chain structure.     

轿车轮胎滚动阻力的研究

以215/50R17 91H轿车轮胎为研究对象,采用正交试验及单因素试验探讨各因素对轮胎滚动阻力的影响。结果表明,轮胎的充气压力对其滚动阻力影响最大,其次是轮辋规格和负荷,行驶速度对滚动阻力的影响很小。外轮廓、接地印痕和纵向滑移特性试验结果表明,使用7.5J×17轮辋、负荷率为53%、充气压力为220 kPa、行驶速度为80 km·h-1时,对轮胎滚动阻力、操纵性能、制动性能和耐久性能均比较有利。     

Effect of Grain Size on the Thermal Conductivity of Si3N4

Polycrystalline Si₃N₄ samples with different grain-size distributions and a nearly constant volume content of grain-boundary phase (6.3 vol%) were fabricated by hot-pressing at 1800°C and subsequent HIP sintering at 2400°C. The HIP treatment of hot-pressed Si₃N₄ resulted in the formation of a large amount of ß-Si₃N₄ grains ∼10 µm in diameter and ∼50 µm long, and the elimination of smaller matrix grains. The room-temperature thermal conductivities of the HIPed Si₃N₄ materials were 80 and 102 Wm⁻¹K⁻¹, respectively, in the directions parallel and perpendicular to the hot-pressing axis. These values are slightly higher than those obtained for hot-pressed samples (78 and 93 Wm⁻¹K⁻¹). The calculated phonon mean free path of sintered Si₃N₄ was ∼20 nm at room temperature, which is very small as compared to the grain size. Experimental observations and theoretical calculations showed that the thermal conductivity of Si₃N₄ at room temperature is independent of grain size, but is controlled by the internal defect structure of the grains such as point defects and dislocations.     

降低厚壁圆筒与接管连接处应力峰值的方法

本文介绍了一种降低厚壁圆筒与接管连接处应力峰值的方法。文中指出如果在厚壁圆筒上开长轴在环向上的椭圆孔,为了使开孔能与普通的圆形接管连接,其最佳的椭圆孔通道为：其长短半轴之比由容器内表面的变化到容器外表面的圆形。并以试验结果加以证实。     

垂直轴风力机三维效应的数值模拟研究

文章针对二维和三维垂直轴风力机的数值模拟的差异,提出了风力机的三维效应是造成模拟差异的主要原因。运用计算流体力学方法对某直线翼垂直轴风力机模型进行了二维和三维的数值模研究。通过比对实验得到的风力机功率系数,发现三维模拟结果与实验值吻合。观察尖速比为1.5时二维和三维垂直轴风力机的速度型分布曲线、流向速度云图和涡量云图,研究了阻塞效应、叶梢涡、支撑结构和塔架对数值模拟结果的影响。研究发现:在二维的数值模拟中,风力机没有受阻塞效应影响,功率系数被严重高估;三维的数值模拟能够模拟出全部的流畅细节,受叶梢涡和支撑结构的影响,风力机的功率系数明显降低。     

透平端壁湍流分离_再附边界层计算

本文根据Veldman的边界层与势流相互作用模型,提出了一种带有湍流分离气泡的端壁边界层的计算方法。本文给出的计算方法适用于由凸台、凹槽、后台阶、壁面扩张角较大及根部反动度为负等因素引起的带有湍流分离气泡的边界层的计算,并且具有计算时间短,节省计算机内存等特点。     

优化工艺下电磁搅拌对板坯冶金效果的影响

为了研究板坯辊式电磁搅拌器对板坯冶金效果的影响,采用现场试验的方法,经过调整电磁搅拌工艺参数及连铸工艺参数,揭示了优化工艺条件下电磁搅拌对板坯冶金效果的影响。研究表明,电源频率为7 Hz,电流分别为0、100、400 A时,电磁搅拌力依次增强,对板坯的冶金效果逐渐改善;当电磁搅拌辊的数量增加时,板坯非稳态下的低倍质量提高;当相同电磁搅拌参数应用于相同钢种时,只有在综合优化连铸工艺参数条件下才能得到好的冶金效果。参数条件为电源频率7 Hz、板坯拉速0.9 m/min、电流400 A。