基于FBG传感器的光伏电站箱变设备的温度监测

针对光伏电站箱变设备在运行过程中的产热问题,基于光纤布拉格光栅传感技术,设计了温度在线实时监测系统,实现了对箱变进线柜中变压器、输电线缆接头、箱体壳等11处关键点温度的在线实时监测.对监测所得结果,分析了24 h的温度数据,很好的反应了监测点的温度变化情况,所得温度数据,可用于进一步开发保护预警系统.与传统测量方法相比,光纤布拉格光栅传感技术具有绝缘、耐高压、抗电磁干扰能力强等优点,并可应用于不同电学环境的温度监测.     

光纤布拉格光栅水下钢筋腐蚀传感器

基于光纤布拉格光栅(fiber Bragg grating,FBG)的预应力释放和应变测量原理,提出了一种用于水下钢筋混凝土结构中钢筋腐蚀监测的FBG钢筋腐蚀传感器。传感器以两根FBG为核心元件,将FBG-1预拉后紧密缠绕、固定于精细加工过的钢筋件表面,用于监测腐蚀产物流失导致的预应力松弛;将FBG-2安装于钢筋件的轴向通孔中,作为温度补偿器用于消除FBG-1的温度交叉敏感效应。为了提高传感器的成活率,将传感器封装在砂浆中,并且推导了被测钢筋件的质量腐蚀率计算公式。通过电化学加速腐蚀实验研究了传感器的工作性能,通过监测FBG的波长变化来测量钢筋的腐蚀程度。实验结果表明,FBG钢筋腐蚀传感器可以监测水下钢筋混凝土结构中的钢筋腐蚀,并且具有较大的测量范围、较高的灵敏度和稳定性,适用于港口码头、桥墩、水坝、蓄水池等钢筋混凝土结构中的钢筋腐蚀监测。     

沥青路面用光纤光栅温度传感器校准方法研究

为了准确修正应用光纤光栅传感技术监测得到的沥青路面应变响应信息,并为沥青路面温度场实测提供有效的技术手段,针对光纤光栅温度传感器在沥青路面应用的标定方法及输出特征展开了研究.采用水浴方法对使用前传感器进行标定;通过对碾压成型后的复合车辙板试件内温度传感器的再次标定,分析了沥青路面碾压工艺对埋设光纤光栅温度传感器标定结果的影响;采用车辙试验仪对成型的复合车辙板进行碾压,模拟分析荷载对光纤光栅温度传感器输出结果的影响.结果表明：二次多项式拟合可满足温度误差不超过±0.5℃的标定合格标准,符合光纤光栅温度传感器的标定模型;复合车辙试件成型12h的温度传感器标定结果与水浴标定结果差距较大,但2d后的标定结果差距减小;荷载会对温度传感器的输出信息产生影响,但响应信息仍能保证精度.     

层状地基中PHC管桩的静压残余应力试验研究

静压桩贯入过程中,因桩顶卸荷残留于桩身的应力较为显著。通过成层土地基中5根桩身预埋准分布式FBG光纤传感器的静压桩足尺试验,对开口PHC管桩沉桩过程中施工残余应力性状、沉桩结束17 d内桩身残余应力的发展变化情况及其对后续静载荷试验影响进行了阐述。试验表明,开口PHC管桩桩身残余应力及桩侧平均残余摩阻力随贯入深度呈折线型分布,中性面深度与贯入桩长比值介于0.66～0.92之间,其大小与桩端持力层密实度及桩端残余应力呈正相关关系。土塞效应成为制约开口PHC管桩桩端残余应力不同于其他桩型的主要因素之一;休止期内桩身残余应力逐渐趋于稳定,中性面处桩身残余应力降低幅度介于3.2%～29.88%之间,桩端残余应力降低幅度介于10.78%～32.39%之间;静载荷试验过程中不考虑施工残余应力将高估中性面以上桩侧摩阻力约53.46%,低估中性面以下桩侧摩阻力及桩端阻力分别56.62%,10%。研究成果可为进一步研究开口PHC管桩施工残余应力性状提供依据。     

Assessment of hydraulic performance and fouling control caused by pulse flow in hollow fiber membrane module

To shed light on the effect of pulse flow on shear force and membrane fouling, the pulse frequency and flow velocity based on fiber Bragg grating (FBG) sensing technology were studied. The results show that there is a threshold for this synergy between the pulse frequency and flow velocity, which forms more easily at a high pulse frequency and low flow velocity. Moreover, the transition from pulse flow to continuous flow affects the shear force distribution with the membrane module height. Besides, at the same volumetric flow, Re gradually reaches a plateau as the pulse frequency increases from 1 to 5 Hz, and the membrane fouling control has a better flux recovery, which can reach a maximum of 28.89%. Finally, the results also show that the combined effect of high pulse frequency and low flow velocity would be higher than that of low pulse frequency and high flow velocity.     

Development of a monitoring and warning system based on optical fiber sensing technology for masonry retaining walls and trees

Hong Kong has a long history of applying masonry retaining walls to provide horizontal platforms and stabilize man-made slopes. Due to the sub-tropical climate, some masonry retaining walls are colonized by trees. Extreme weather, such as typhoons and heavy rains, may cause rupture or root failure of those trees, thus resulting in instability of the retaining walls. A monitoring and warning system for the movement of masonry retaining walls and sway of trees has been designed with the application of fiber Bragg grating (FBG) sensing technology. The monitoring system is also equipped with a solar power system and 4G data transmission devices. The key functions of the proposed monitoring system include remote sensing and data access, early warning, and real-time data visualization. The setups and working principles of the monitoring systems and related transducers are introduced. The feasibility, accuracy, serviceability and reliability of this monitoring system have been checked by in-site calibration tests and four-month monitoring. Besides, a two-level interface has been developed for data visualization. The monitoring results show that the monitored masonry retaining wall had a reversible movement up to 2.5 mm during the monitoring period. Besides, it is found that the locations of the maximum strain on trees depend on the crown spread of trees.     

基于FPGA的多通道高速光纤光栅解调系统

研发了一种基于波长扫描光源和嵌入式解调的多通道高速光纤布拉格光栅解调系统。该系统采用半导体光放大器(SOA)结合可调谐F-P滤波器产生频率为1 kHz的稳定波长扫描光。通过使用对称三角波技术和快速FPGA解调算法,系统最终能够同时实现16个通道以及2 kHz的解调速率,测量范围80 nm。     

A new method for resolving the influence of circular birefringence in FBG weak pressure sensor

Ideally, there is a linear relationship between the max of PDL and pressure in FBG weak pressure sensor. However, the linear relationship has been broken down because of the cross sensitivity about the circular birefringence and pressure. In this paper, the relative PDL was proposed to solve the cross sensitivity problem. For different circular birefringences, the experimental results show the same pressure sensitivity value of 2.29 dB/(N/nm). The theoretical analysis and experimental results prove that the proposed method can solve the cross-sensitivity problem in FBG weak pressure sensor. This research can provide useful information to practical application.     

Pullout performance of GFRP anti-floating anchor in weathered soil

Anchors are often used as anti-floating reinforcements in civil engineering structures. However, conventional steel bars present disadvantages concerning corrosion and poor adaptability to aggressive environments. Glass fiber-reinforced polymer (GFRP) components could provide a solution to these problems. In this paper the feasibility of GFRP anti-floating anchors is evaluated. Four full scale pullout tests were performed in moderately decomposed granite (MDG). Bare Fiber Bragg grating (FBG) sensors were embedded into the specimens during the pultrusion process to monitor the stress–strain distribution along their lengths. Based on the results the behavior of the anchors was assessed, including the relationships between the pullout force and the head displacement, the axial strain along anchors and the shear stress at the GFRP-grout interface. The stress distribution of anchors showing interlaminar shear failure was then analyzed based on a maximum shear stress criterion. It was proved that the load transfer mechanism of GFRP and steel anti-floating anchors differs significantly. GFRP anti-floating anchors reach failure due to interlaminar shear failure, while conventional steel anchors generally fail as a result of shear at the grout–soil interface. The test results also showed that the embedded FBG technique is reliable for monitoring the stress–strain state of an anisotropic material.     

Crack tip identification with long FBG sensors in mixed-mode delamination

The uncertainty of the crack tip position inside composite coupons during a delamination test under variable fracture mode conditions reduces the accuracy of the experimental results. In this work a method is presented where the crack tip position is located using long embedded Fibre Bragg Grating (FBG) sensors together with the Optical Low Coherence Reflectometry (OLCR) technique. With this technique the local Bragg wavelength is measured which then enables to calculate the axial strain profile within the grating. Carbon/epoxy samples are tested under different mode ratios through the standard Mixed-Mode Bending (MMB) test. Embedded long FBG sensors are used to measure the axial strain profile along the whole grating at different stages of the test. The crack tip can be precisely identified with the long embedded FBGs and then checked by means of a visual inspection after complete delamination of the sample. The data indicate that the long FBG sensor detects the crack tip inside the sample at least as precisely as the traditionally performed visual inspections carried out during the test by means of the lateral markings. Numerical simulations using cohesive elements are in good agreement with the experimental data.