Fractal model of lightning channel for simulating lightning strikes to transmission lines

How to accurately evaluate the direct-strike lightning protection is one of the key issues in the design of transmission lines. In this paper, three important issues in applying the fractal simulation to the lightning protection of transmission lines were discussed, including the criteria and implementation of upward leader inception, the connection with the magnitude of lightning current, and the calculation and control of fractal dimensions. Then we conducted the simulation iterately, leading to statistical results, which indicate that even if the transmission line satisfies the perfect shielding condition, shielding failure fault remains possible. Furthermore, we calculated the shielding failure fault rates of an EHV line with different ground obliquities and distribution of strike points over the interval between two neighboring towers along a UHV-DC line to find out the weak point of transmission-line lightning protection. This work provides a promising approach for improving the lightning protection property of transmission lines by optimizing the configuration of shielding wires and phase or pole conductors.     

多用途下肢康复外骨骼结构设计与实验

为有效解决由于脊柱损伤、脑损伤、脑血管疾病及骨关节手术所导致的人体下肢运动功能障碍,提出了一种多用途可拆卸下肢康复外骨骼设计方案,设计了基于扭矩传感器的力感知高集成助力关节,在腿部泛型尺寸结构设计的基础上,提出了一种基于螺纹传动的双向同步快调机构,实现了单手徒手快速调节外骨骼腿部长度的功能.基于外骨骼运动平衡安全性及广泛适用性等问题的考虑,将下肢康复外骨骼与可升降移动护架有机结合,提出了下肢康复外骨骼整体结构及可升降移动护架结构,既保证了外骨骼运动过程中的平衡安全性,又同时适用于轻度、中度、重度等不同程度的下肢运动功能障碍患者.为合理规划下肢康复外骨骼运动步态,进行了平地、上坡、下坡、上楼梯、下楼梯等步态数据的采集及处理,搭建了控制系统.为了验证理论研究成果,加工了实验样机,并进行了相关实验验证.实验结果表明:扭矩传感器具有较高的实时性及准确性,外骨骼具有广泛适应性,结合移动护架可为患者提供有效的减重环境,外骨骼可实现起立、坐下、平地行走、上下斜坡及上下楼梯等功能.     

一种模拟电路故障字典的改进方法

鉴于传统的故障字典法诊断准确度低、诊断速度慢等缺点,本文将概率论及数理统计原理引入传统的故障字典法中对其进行改进.提取电路各待测节点电压作为电路特征,基于概率论选取测试节点,应用极大极小准则使模糊域划分更为合理.以稳压电源电路为实例,对改进后方法与传统方法进行实验对比,结果表明,本文所述方法故障诊断准确度更高、测试节点数目更少,更为合理有效.     

Self-healing anti-icing coatings prepared from PDMS polyurea

With the help of double hydrogen bonds between urea groups, a self-healing anti-icing coating was prepared from polydimethylsiloxane (PDMS)-based polyurea (PDMSPU) that was synthesized from bis(3-aminopropyl)-terminated PDMS and 2,4-toluene diisocyanate. Furthermore, by incorporating a lubricant of inert silicone oil and the cross-linking agent of 1,3,5-tris-(4-aminophenoxy)benzene (TAPOB), the anti-icing coatings exhibited elastic, slippery and durable properties. The wettability, ice shear strength, abrasion-resistance, mechanical and self-healing properties of the prepared anti-icing coatings were systematically investigated. Results showed that the ice shear strength of the PDMSPU anti-icing coating with 150 wt% silicone oil was 7.9±2.9 kPa, significantly lower than that of pristine PDMSPU (74.7±7.2 kPa). The additional introduction of 2 wt% TAPOB could effectively counteract the adverse effect of the lubricant so that the tensile strength (∼1 MPa) of the coating could be comparable to pristine PDMSPU (855±96 kPa). The PDMSPU coating containing 150 wt% silicone oil and 2 wt% TAPOB could maintain the ice shear strength below 50 kPa against 10 icing/deicing cycles and at 12.0±3.3 kPa after 5000 abrasion cycles, and exhibit self-healing properties after treating at 60°C for 10 or 15 h. The slippery self-healing PDMSPU anti-icing coatings could be suitable for anti-icing surfaces in low temperature environments.

     

智能电能表自动化检定流水线的温度参比条件影响分析

文中建立智能电能表结构化模型,分析确定智能电能表受温度影响产生误差的主要因素,即AD转换器基准电压受温度影响的变化。采用机理建模的方法,建立了CMOS带隙基准源和AD转换器受温度影响的数学模型,采用普遍应用的点积和电能测量算法,研究分析基准电压随温度的变化对智能电能表误差的影响及关系;并通过试验,给出智能电能表误差变化随温度与时间变化的关系曲线。根据被试电能表的等级,给出大规模智能电能表自动化检定流水线的温度参比条件的建议。