Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.     

HP nonlinear guidance law design based on smooth sliding mode control

To eliminate the perturbation of interceptor detection induced by aerodynamic heating,the head pursuit (HP) guidance law for three-dimensional interception was presented. The guidance law positioned the interceptor ahead of the target on its flight trajectory,and the speed of interceptor was required to be lower than that of the target. On the basis of a novel head pursuit three-dimensional guidance model,a nonlinear guidance law was developed based on smooth sliding mode control theory. At the same time,a special observer was designed to estimate the target acceleration,and a numerical example on maneuvering ballistic target interception verified the effectiveness of the presented guidance law.     

Synchronization and channel estimation for MIMO OFDM wireless LAN systems

A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset (CFO) estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramér-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error (MMSE).     

新型燃煤烟气汞吸附剂的评价研究

利用汞蒸气发生器产生的单质汞,与压缩空气组成模拟烟气,在吸附剂评价实验台上进行吸附剂脱汞实验,研究不同吸附剂对单质汞的脱除效率．实验结果表明,活性炭对汞的吸附效率在60％左右,未改性的燃煤飞灰吸附效率在10％～20％,改性后的燃煤飞灰比表面积有很大程度的提高,吸附效率可以达到25％,与活性炭吸附效率相比仍有不小的差距．     

非线性部分最小二乘方法的研究与应用

该文将部分最小二乘算法与径向基函数神经网络相结合,给出了一种非线性部分最小二乘建模方法,可以更加有效地处理过程非线性和数据共线性等复杂特性,提高模型的精度和推广能力。该方法在确定径向基函数神经网络的隐节点时,采用了一种改进型的k-均值聚类算法来自动确定最优的聚类区数。对煤气化炉合成气组分浓度软测量建模的应用结果表明,采用该方法建立的软测量模型在模型精度和推广能力等方面明显优于二次型多项式部分最小二乘方法建立的模型,并且计算精度满足工业生产的实际要求。     

3D Simulation Research on Urea-SCR DeNO<em>x Catalyst for Diesel Engine

In order to reduce oxides of nitrogen (NOx) emanated from a diesel eng ine, a comprehensive urea selective catalyst reduction (SCR) DeNOx catalys t was modeled in which numerical simulations were used as a complementary tool f or the experimental investigations to make the design decisions, and hence short en the development process. In this approach, relevant conversion reactions were studied in 1D model, and the parameters obtained in this way were transferred t o 3D simulations. According to the results ...     

诱导风机智能控制系统的设计

文章详细介绍了智能诱导风机排风系统的设计,该系统能及时稀释CO气体浓度,并且系统更加节能降耗。智能诱导风机排风系统由集中控制器、诱导风机控制器和诱导风机组成。文中介绍了系统的硬件设计,给出了集中系统控制器和诱导风机控制器的软件流程图,描述了系统的工作状态和过程。     

自修复混凝土中玻璃纤维管最佳掺量的确定

在混凝土中埋入含有修复剂的中空玻璃纤维管,形成自愈合系统。纤维管的掺量直接影响到修复效果,掺加量太少不能把产生的裂缝完全修复,太多则会影响到混凝土材料的宏观性能。通过在混凝土中掺入不同体积率的中空玻璃纤维管和空白混凝土对比试验,观察对混凝土试件抗压强度、劈裂抗拉强度所造成的影响,确定出中空玻璃纤维管在混凝土中的最佳掺量。     

简支梁横向振动固有频率的误差分析

采用欧拉-伯努利梁理论求解等直梁的固有频率存在一定的误差,而考虑剪切变形及转动惯量影响的铁摩辛柯梁理论求解的固有频率较为精确.结合工程实际,在常用设计参数范围内,以矩形、圆形、薄壁圆管、工字形和箱形等工程常用典型截面的简支混凝土梁或钢梁为研究对象,计算分析了欧拉-伯努利梁理论求解横向振动固有频率的误差.计算结果表明:矩形、圆形截面混凝土梁的第1阶频率误差均在5%以内,可满足工程需要;工字形、箱形、圆管截面钢梁的第1阶频率误差,只有在高跨比较小时方可满足5%的限值;而对于第2阶及更高阶频率,误差通常远远超过5%,即该理论不再适用.     

磷渣粉在复合胶凝材料中的水化特性

用扫描电镜、X射线衍射和水化热测定等方法研究了磷渣粉在复合胶凝材料体系中的水化特性,并与Ⅱ级粉煤灰进行对比.结果表明:磷渣粉具有很强的缓凝特性,其缓凝性导致复合胶凝材料体系早期水化慢、强度低,但后期强度高,超过了对比粉煤灰,并存在强度最大时的最佳掺量.早期时磷渣粉可以延缓C3A的水化,AFt的生成明显减少,磷渣粉颗粒表面出现腐蚀痕迹;后期(180d)已找不到磷渣粉颗粒存在,磷渣粉颗粒几乎都全部水化,水化产物非常致密.