Microwave Communication to Moving Parts Inside Machines

Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce standing-wave effects is also discussed.     

Multiphase flow measurements using coupled slotted orifice plate and swirl flow meter

Multiphase flow metering is a major focus for oil and gas industries. The performance of a modified version of a close coupled slotted orifice plate and swirl flow meter for multiphase flow was evaluated to provide further development of a new type of multiphase flow meter. The slotted orifice provides well homogenized flow for several pipe diameters downstream of the plate. This characteristic provides a homogeneous mixture at the inlet of the swirl meter for a wide range of gas volume fractions (GVF) and flow rates. In order to evaluate the performance of the designed flow-meter, its response was investigated for varying pressures and water flow rates. The proper correlations were established to provide high accurate two-phase flow measurements. The new proposed approach provides the GVF measurement with less than ±0.63% uncertainty for GVF range from 60% to 95%.     

一种新的RFID防碰撞算法设计

该文提出了一种基于码分多址思想的时隙ALOHA算法(CS-ALOHA),来解决射频识别(RFID)中的防碰撞问题。在建立该算法的数学模型的基础上,分析了其对系统吞吐量带来的好处,并推导出系统稳定的条件。理论与仿真实验表明,采用CS-ALOHA算法的系统稳定范围要大于时隙ALOHA系统,并且当选用的扩频码组阶数为N时,CS-ALOHA算法的最大吞吐量可达原时隙ALOHA的N倍。     

炮孔爆破中新的岩体断裂理论

本文提出了炮孔中非对称爆炸载荷(如极限偏心装药和特殊药卷)产生的“非对称效应”,分析了这种非对称载荷对无限岩体中炮孔周围裂隙的生成,扩展和最终分布的影响。研究得出:在偏心装药时,在装药与炮孔壁接触面上首先生成裂隙,预先生成的裂隙引起的稀疏波对孔壁上其它方向上的裂纹的生成与扩展有限制作用,这一制约遵循下列必要条件: 根据J一积分原理导出了计算裂隙产生所需时间的理论公式,计算结果与动光弹试验结果基本吻合。 最后,分析了切缝药包爆炸产生非对称载荷的机理,介绍了这项新技术在断裂控制中的应用效果。 本文所提出的关于炮孔爆破中新的岩体断裂理论以及所得出的初步结论对于爆破破岩机理的研究和指导工程实践都具有重要意义。     

A NEW ANALYZING APPROACH TO MODELING SLOTTED MULTIPLE ACCESS SYSTEMS

In this paper, the analyzing approaches proposed by Zhao Dongfeng, et al.(1997) have been extensively studied. The average cyclic times of the slotted multiple access systems are analyzed by using the average cycle method. Analytic formulae for mean values of a successful period and a colliding period and an idle period are derived. The upper bounds of the system throughput with capture effect and collision resolution are provided. Finally, the simulation results of the slotted multiple access channels are given.     

PSC型旋风管组合结构参数对分离性能的影响

通过导叶式旋风管不同组合结构分离性能的对比实验,研究了排尘结构、排气芯管结构以及分离空间高度等结构参数对旋风管分离性能的影响规律。通过大量实验数据分析,绘制出旋风管不同组合结构的分离性能曲线,总结出不同结构参数变化对旋风管分离性能相应的影响规律。     

Thin-walled structures with slotted connections stability problems

In this paper the linear and non-linear stability analyses of elastic structures with unilateral supports or connections are presented. Local and global buckling phenomena are analysed for a wide range of columns’ lengths to encounter coupled instability, which appears when local buckling occurs close to global one. Influence of clearances on buckling and post-critical response is examined. This phenomena is illustrated using simplified models, where the clearances are introduced as translation or rotation gaps. Main attention is focused on modelling the double sigma members, where the cross-sections are composed of two sigma members, connected in discrete points distributed along the webs. The influence of spacing and way of numerical modelling of connectors on buckling behaviour of beams is studied. Numerical examples illustrate the importance of proper modelling of the structures with slotted connections accounting for initial imperfections. The examples are solved using FEM.     

平板缝隙天线的计算机辅助设计

基于边值积分方程方法的小型平面缝隙阵的机助设计方法。这种计算方法是严格的。但即使对于小型阵，计算量也相当大。对小型阵提出缝列与耦合分支分别设计的方法，并给出模型实验结果。实验结果表明，对于一般指标的方阵，这种方法是可行的。对于低分瓣和超低旁瓣阵，尤其大型阵，还需以严格计算代替大量实验，去寻求简化计算的经验方法，建立一种半经验的机助设计方法。     

First Passage Time Analysis in Wireless Sensor Networks for SPR and MPR Systems

In this paper, we study the performance of Slotted ALOHA in an elementary process in wireless sensor networks, in which sensors are activated by rare events and transmit packets to a single sink node within single hop. The time cost of the process can be viewed as a first passage time and we give the expectation of time and energy cost which is dependent on both the size of active nodes and their transmission rate by a first passage time analysis. Meanwhile, given the size of active nodes n, we demonstrated that the optimal transmission rate λ_min(n) by which the first passage time attains its minimum, is nearly . Our result indicates that time cost of the process in which each node transmits packet with transmission rate λ_min(n) increases nearly linearly with n increasing. We present the maximum likelihood estimate (MLE) of the size of active nodes from the viewpoint of sink nodes so that activated nodes can adjust its transmission rate to improve the performance of the process. Energy dissipation and time cost of the procedure in the channel model of Multi Packet Reception (MPR) are considered also. Numerical results indicate that both time cost and energy consumption of the procedure in MPR channel is superior to that in Single Packet Reception (SPR) channel while the transmission rate near or less than the optimal values with which time costs attain their minimum. Otherwise the energy dissipation in MPR channel is more than that in SPR channel although comparison of time cost in the above two channels reveals the superiority of MPR channel.

A novel protection for powerformers in NIEPS

A new type of high-voltage generator which offers a direct connection to the power network without the need for a step-up transformer is called powerformer. The neutral of the most powerformers is unearthed which belongs to NIEPS. When a stator single phase-to-ground fault occurs in a powerformer, every generator that is connected in parallel with the faulty powerformer has the same voltage. Traditional protection schemes using zero sequence voltage and third-harmonic voltage signals cannot detect which powerformer is faulted. In order to solve this problem for powerformer protection, a novel stator single phase-to-ground fault protection based on the direction and magnitude of zero-sequence currents is proposed in this paper. Simulation results have shown that, under different fault conditions, the new scheme can distinguish reliably internal faults from external faults, and can detect stator single phase-to-ground fault occurred in which powerformer with resistance 1 kΩ. A 100% of the winding can be fully protected.