Automatic measurement and warning of tension force reduction in a PT tendon using eddy current sensing

Post-tensioning (PT) using a bundle of pre-stressed strands is a critical process for assembling pre-fabricated and modularized bridge members. However, the tension force gradually diminishes over time due to such factors as corrosion, creep, and steel relaxation. Such changes compromise the overall safety of such structures. In this study, an eddy-current-based tension-force-loss warning (EC-TFLW) technique is proposed to detect and warn automatically of excessive loss of tension force in a PT tendon. A ring-type eddy-current sensor (ECS) is mounted on the outer surface of a wedge holding a tendon, and the level of eddy current measured by the ECS is related to the tension force of the tendon. The advantages of the proposed technique include: (1) low power consumption, (2) low cost, (3) simple installation, and (4) automated warning. The performance of the proposed EC-TFLW technique was validated experimentally in a full-scale lab test of a 3.3-m long, 15.2-mm diameter, mono-strand tendon that was tensioned using a universal testing machine (from 20 to 180 kN). Statistical hypothesis testing using the chi-square distribution was applied to the measured eddy current signals, and if the decline in tension exceeded a certain level, a warning was sent out automatically.     

High sensitivity rotating alternating current field measurement for arbitrary-angle underwater cracks

Alternating current field measurement (ACFM) technology has been used for sizing underwater structure cracks. However, conventional ACFM is more sensitive to cracks perpendicular to the induced current than cracks with other angles. In this paper, a rotating alternating current field measurement (RACFM) method and underwater test system are present for the detection of arbitrary-angle cracks with high sensitivity. The RACFM is proved by simulations and experiments. Arbitrary-angle cracks detection results obtained from ACFM and RACFM have shown that the RACFM method overcomes the limitation of directional detection of ACFM and effectively achieves high detection sensitivity for arbitrary-angle cracks on underwater structures.     

Effect of alternating current on corrosion and effectiveness of cathodic protection of pipelines

Abstract

In the present work, the alternating current (AC) induced corrosion of a cathodically protected X65 pipeline steel was studied in a neutral, extracted soil solution and a high pH, carbonate/bicarbonate solution by electrochemical and weight loss measurements, and surface characterisation. It was found that AC corrosion causes the alkalisation of the soil environment in the vicinity of pipeline no matter what the cathodic protection (CP) condition is. The degree of alkalisation depends on the AC current density. In the absence of AC interference or at a low AC current density, i.e. 20 A m^?2, a CP potential of ?950 mV versus Cu/CuSO₄ electrode provides a full protection over the steel. When the AC current density is >20 A m^?2, a new CP standard is recommended to avoid AC corrosion of pipelines.

Dans le présent travail, on a étudié la corrosion induite par le courant alternatif (AC) d’un acier X65 pour pipeline avec protection cathodique, dans une solution neutre d’extrait de sol et dans une solution de carbonate/bicarbonate à pH élevé, au moyen de mesures électrochimiques et de perte de poids ainsi que de la caractérisation de la surface. On a trouvé que la corrosion AC avait pour résultat l’alcalisation de l’environnement du sol au voisinage du pipeline, peu importe la condition de protection cathodique (CP). Le degré d’alcalisation dépend de la densité de courant AC. En l’absence d’interférence AC ou à une faible densité de courant AC, soit 20 A/m², un potentiel de CP de 2950 mV par rapport à l’électrode Cu/CuSO₄ protège complètement l’acier. Lorsque la densité de courant AC est plus élevée que 20 A/m², on recommande une nouvelle norme de CP pour éviter la corrosion AC des pipelines.     

长距离输电线路潜供电弧弧根跳跃与弧长剧变的物理机制与仿真

建立了长距离输电线路潜供电弧物理模拟实验平台,使用高速摄像仪拍摄潜供电弧的运动发展过程。实验发现,潜供电弧阳极弧根存在明显的跳跃现象,且潜供电弧运动过程中电弧长度经常出现暂时变短的现象,在电弧熄灭前的瞬间,电弧长度会急剧上升。为明晰引起上述现象的内在作用机制,建立了链式电弧模型,对长距离输电线路潜供电弧进行仿真分析,结果表明弧根跳跃与热浮力和电极结构密切相关,电极结构水平时潜供电弧弧根跳跃次数明显减少,更有利于电弧的疏导与熄灭。电弧长度暂时变短是由弧柱间短路引起的,而熄灭前潜供电流突然增大引起弧长的剧变。进一步研究了潜供电弧燃弧时间与风力之间的关系,风速较大时,风载荷在电弧受力中占主导作用,燃弧时间分散性较小。仿真还发现导线互相垂直时潜供电弧运动更为剧烈复杂,电弧更容易熄灭。     

基于非线性GA算法的MFF透射模型的参数辨识与优化

基于磁性流体(MF)磁链理论,建立了磁流体薄膜(MFF)传感模型,并通过Monte Carlo法分析了MF透射特性,建立了MFF透射模型。采用非线性遗传算法(GA)对MFF透射模型进行了参数辨识,分析了种群规模、进化代数、交叉率、变异率等参数选值对算法运行结果的影响,并选取了最佳参数组合,搭建了MFF电流传感器实验平台,分析了MFF厚度和粒子浓度对MFF透射性的影响,运用MFF透射模型对MFF电流传感器进行了仿真预测。实验及仿真结果表明该模型具有较好的预测性,预测误差在2.29%以内,所设计的MFF电流传感器的测量灵敏度达到11μW/A。     

一起220kV电容式电流互感器爆炸事故的分析

介绍了爆炸事故的简要经过和设备概况,为分析事故的原因对互感器进行了解体检查,结合解体检查结果,分析互感器设计制造工艺中存在的问题,分析事故原因和事故发展过程,并提出几点建议和预控措施。     

Modeling law of a meandering channel

Abstract

The sedimentary processes in river curves are difficult to reproduce in a model because of the distinctly 3‐D nature of the flow pattern. It is virtually impossible to build a model that can satisfy all criteria associated with the scaling of a 3‐D flow. Most sediment‐transport related models in use today are “1‐D model”, for which established scaling techniques are available. These models are built to provide similarity of the cross‐sectional average velocity and resistance coefficient; and they are “straight‐channel model”. This study shows how a set of 1‐D scaling criteria which can be expanded to allow for modeling of secondary currents and lateral variations in depth in river curves. This expansion is based upon theories which relate the strength of the centrifugally induced secondary velocity component to flow depth, channel planform curvature, and depth averaged mean velocity.     

A Five‐Element Multiplex Resonant Full‐Bridge DC‐DC Converter with a Variable Inductive Reactance

A five‐element multiplex resonant (LLCLC) full‐bridge DC‐DC converter controlled by pulse frequency modulation (PFM) is proposed in this paper. The high frequency (HF)‐link resonant DC‐DC converter proposed herein can perform wide‐range output power and voltage regulation with a narrow frequency range due to an antiresonant tank that works effectively as a wide‐range variable inductor. The advantageous characteristics of the antiresonant tank provide overcurrent protection in the case of the short‐circuited load condition as well as in the startup interval. Thus, the technical challenges of a conventional LLC DC‐DC converter can be overcome, and the reliability of the relevant switch‐mode power supplies can be improved. The operating principle of the LLCLC DC‐DC converter is described, after which its performance is evaluated in an experimental setup based on the 2.5 kW prototype. Finally, the feasibility of the proposed DC‐DC converter is discussed from a practical point of view.     

Development of an experimentally validated semi-empirical fully-coupled performance model of a PEM electrolysis cell with a 3-D structured porous transport layer

A semi-empirical non-isothermal model incorporating coupled momentum, heat and mass transport phenomena for predicting the performance of a proton exchange membrane (PEM) water electrolysis cell operating without flow channels is presented. Model input parameters such as electro-kinetics properties and mean pore size of the porous transport layer (PTL) were determined by rotating disc electrode and capillary flow porometry, respectively. This is the first report of a semi-empirical fully coupled model which allows one to quantify and investigate the effect of the gas phase and bubble coverage on PEM cell performance up to very high current densities of about 5 A/cm². The mass transport effects are discussed in terms of the operating conditions, design parameters and the microstructure of the PTL. The results show that, the operating temperature and pressure, and the inlet water flowrate and thickness of the PTL are the critical parameters for mitigating mass transport limitation at high current densities. The model presented here can serve as a tool for further development and scale-up effort in the area of PEM water electrolysis, and provide insight during the design stage.     

Subsurface cracks in AGR graphite bricks

Sub-surface cracks present difficulties for eddy current methods as the skin effect causes currents to flow preferentially near the surface. This work examines graphite as a case study for the qualitative assessment of sub-surface cracks and employs multi-frequency eddy current techniques. The research has particular relevance to Advanced Gas-Cooled Reactors (AGR׳s) as during their operation there is the potential for cracks to develop within moderator bricks. This work reports that subsurface slots of 18% brick thickness can be detected. This work confirms these results with a parametric 3D finite element study.