来流湍流度对斜拉索风雨激振影响的理论研究

斜拉索风雨激振严重地影响斜拉桥的安全运营,而来流湍流度是影响风雨激振的一个重要因素。采用理论分析方法,研究来流湍流对斜拉索风雨激振响应的影响。引入2种类型的风场,首先,假设来流为简谐脉动风场,然后,采用谐波合成方法,将Kaimal风谱作为目标谱,模拟来流随机脉动风场。采用上述2种来流风场,在已建立的两质量三自由度理论模型的基础上,研究各种湍流度下拉索和水线的风雨激振振动规律。计算结果表明,当湍流度达到15%时,水线不能在拉索表面稳定地存在,风雨激振能得到有效的抑制;水线运动的脉动成分主要受来流风脉动成分的影响,拉索运动对水线运动有一定的影响,但影响较小;随着紊流度的增加,起振风速也增大。     

Vibration characteristics identification of ultra-long cables of a cable-stayed bridge in normal operation based on half-year monitoring data

Abstract

The Sutong Bridge with a span of 1088?m is supported by 272 cables, whose lengths range from 152.85?m to 576.77?m (the longest in the world). The half-year vibration acceleration data of two cables from structural health monitoring system (SHMS) is analysed, in conjunction with the wind field data, weather data and vehicle data to explore and three types of cable vibrations. The large-scale cable vibration is mainly rain-wind-induced vibrations (RWIV) when the wind direction lies in an angular range of 40°–80° relative to the cable axis, and the bridge-deck wind velocity is 4–20?m/s. The ultra-long cable also experiences in-plane vibrations, which satisfy many characteristics of vortex-induced vibrations (VIVs). Cable VIV occurs only when the bridge-deck wind velocity 4–8?m/s, with the frequency ranging from 9.5?Hz to 10?Hz. The daily small-amplitude vibration of the cables and steel girder is mainly induced by the passage of heavy trucks. There exists a positive correlation between the number of heavy trucks and the vibration level. Based on the characteristics and occurrence probabilities of these three types of cable vibrations, corresponding measures are suggested for the maintenance of ultra-long cables.     

基于双层排线探头的轧辊表面微裂纹检测方法

针对冷轧轧辊的表面微细裂纹检测问题,提出了一种双层排线磁化的交流漏磁检测方法,利用双层柔性排线对轧辊工 作表面进行仿形磁化,采用高精度隧穿磁阻(TMR)阵列作为检测元件,使其具备大曲率表面微米级裂纹的检测能力;并通过调 控双层排线的激励电流抵消切向背景磁场,进一步提高激励电流的同时,避免 TMR 超量程饱和问题;将磁场的切向分量用以表 征缺陷,使其能在单一扫查方向下表征多向裂纹。 基于以上分析,建立了双层排线与轧辊的三维有限元仿真模型,通过仿真研 究轧辊半径、缺陷角度和深度对交流漏磁信号的影响。 最后搭建了相应验证实验平台,实验结果表明该探头能有效磁化大曲率 表面并可检出与区分多向裂纹,可检测出 15 μm 深的微细裂纹。     

国内外电缆及光缆燃烧性能分级体系探讨

对国际电工委员会(IEC)、美国、欧盟及中国的电缆及光缆燃烧性能分级体系进行分析、比较和综述。通过研究发现:IEC仅发布了考核电缆的火焰蔓延距离、烟密度和无卤特性等单一的试验方法标准;美国主要针对电缆的火焰蔓延、产烟等特性分为4个级别;欧盟于2014年颁布了新的燃烧性分级体系,该分级体系主要从电缆的火焰蔓延和热释放等特性分为7个级别,同时针对不同场所又从电缆的产烟、燃烧滴落物和酸度进行了附加分级;我国新发布的电缆及光缆燃烧性能分级体系与欧盟类似。     

Fully automatic AI-based leak detection system

This paper presents a fully automatic system intended to detect leaks of dielectric fluid in underground high-pressure, fluid-filled (HPFF) cables. The system combines a number of artificial intelligence (AI) and data processing techniques to achieve high detection capabilities for various rates of leaks, including leaks as small as 15 l per hour. The system achieves this level of precision mainly thanks to a novel auto-tuning procedure, enabling learning of the Bayesian network – the decision-making component of the system – using simulated leaks of various rates. Significant new developments extending the capabilities of the original leak detection system described in [1] and [2] form the basis of this paper. Tests conducted on the real-life HPFF cable system in New York City are also discussed.     

稳定索加强的张拉膜结构设计与分析

以台州大学风雨操场屋盖为例 ,简要介绍了在跨度大、支承结构较柔的实际情况下 ,采用面内稳定索辅助脊索、谷索共同承力的张拉膜结构的设计过程。并结合风洞试验结果 ,对三种找形方案 ,即不采用稳定索、采用交叉稳定索、采用斜稳定索的结构形式在不同工况下的受力性能进行了比较分析。     

重庆奉节长江大桥斜拉索施工技术

重庆奉节长江大桥为主跨460m的双塔双索面斜拉桥。斜拉索施工采用了软硬牵引结合的方法,介绍了该桥斜拉索的挂设方法和施工工艺。     

2D thermal analysis for heat transfer from casing to winding pack in JT-60SA TF coils

In the framework of the Broader Approach Agreement, Europe is involved in the design activities for the Japanese Tokamak JT-60SA, investigating, among several issues, the operation of the superconducting TF magnets and their subsystems, aimed at the reactor conceptual design definition. In particular, one of the main critical aspects to study is the heating of the conductor due to both direct component of energy deposited by neutrons and by secondary gamma generated during plasma operation, and heat generated by the radiation on casing and transferred to the winding pack. Indeed, the operating temperature and the relevant temperature margin (i.e. the operating safety margin) of the magnet will depend strongly on the heat loads and on the capability of the coolant to remove it. Furthermore, the heat power to the conductor will depend on several aspects, namely the thickness of insulating material, the mass flow rate of helium flowing in the conductors and its thermodynamic properties at operating conditions, and the layout of the superconductors constituting the winding. Moreover, a crucial aspect in the final design will be the presence and position of the casing cooling channels. In this paper a 2D sensitivity analysis of heat transfer from casing to winding pack with respect to cooling channels number and position is presented, based on the reference layout of the magnet. As a result, we evaluated the optimum number and positioning of cooling channels needed, as a trade-off between magnet operating limits and available cryogenic power and if, at limit, they could be even neglected in normal operation, keeping dwell-time within reasonable values.     

用数码相机测量斜拉桥拉索模型的变形

结合数字近景摄影测量技术的优点及斜拉桥拉索变形的特点,利用普通数码相机对斜拉桥拉索模型的变形进行非接触式测量。考虑到相机光学畸变的直接线性变换,在确定变形平面的基础上,利用单张相片求解目标点物方三维坐标。介绍了实验的整个过程,包括控制点布设、相片拍摄、参数求解、变形平面确定、拉索上目标点变形值计算等。通过对已知点检验证明了用本文方法得到的变形测量精度能满足对桥梁模型进行分析研究的要求。     

数字通信对称电缆生产工艺及设备探讨

主要介绍了数字通信对称电缆主要生产工艺流程、各工序主要工艺控制点,比较了国内外常用数字通信电缆生产设备性能以及设备主要技术参数。