光纤光栅传感技术及其在石油工业中的应用

阐述了光纤光栅温度和应变传感的响应机理．对光纤光栅多参量区分测量技术和光纤光栅传感网络复用与解调技术进行了综合评述．结合光纤光栅传感技术的本质突出优势和石油工业特点,讨论了其在油气生产中温度和压力测量、测井技术、地震波检测、长距离石油管道监测等方面的应用．     

分布式光纤管道泄漏检测及预警技术灵敏度分析

针对管道安全存在的问题,提出了一种基于Mach-Zehnder光纤干涉仪原理的分布式光纤管道泄漏检测及预警技术,利用与管道同沟敷设的光缆中的3条单模光纤构成分布式光纤微振动传感器检测管道沿线的振动信号,可以有效地检测管道沿线所发生泄漏和异常事件．分析和研究了检测系统的测试灵敏度影响因素,并采用不同光缆结构和埋设方式对检测系统的检测灵敏度进行测试．实验结果表明,该检测技术可以检测到1m范围内的人工挖掘信号,在气体管道压力不小于0．2MPa的条件下,可以检测到0．4m^3／min的气体管道泄漏．     

光纤光栅声发射检测新技术用于轴承状态监测的研究

轴承的健康状况对旋转机械的工作状况有极大的影响。航空器中的故障轴承会间接造成事故,给飞行安全带来灾难性的后果,需要进行早期故障的有效检测判别或状态监测。与振动等传统的检测手段相比,声发射可有效检测到故障的早期状态,准确判断故障类别和严重程度。介绍了滚动轴承故障声发射检测原理以及光纤光栅声发射检测新技术。以预制外圈缺陷的轴承为例,进行了压电式声发射传感系统和光纤光栅声发射传感系统检测的对比实验,实验和分析结果表明光纤光栅声发射方法检测到的信号谱底噪声小,谱线清晰、干净,更容易分辨故障频率和分析故障的严重程度,优于振动和压电式声发射传感方法。最后介绍该技术在直升机维修保障中的应用情况。     

基于光纤Bragg光栅传感的轴向柱塞泵非介入式振动测量方法

振动信号是机械设备故障诊断的重要信息来源。为克服传统检测方法需对系统进行拆卸的问题,创新性地利用光纤光栅传感方法对液压泵进行非介入式振动测量,充分发挥光纤传感的抗电磁干扰能力强、耐腐蚀、稳定性好、测量敏感度高等优点。对光纤光栅振动传感原作了分析,设计、仿真分析了双等强度悬臂梁式光纤Bragg光栅(Fiber Bragg Grating,FBG)振动传感器,在此基础上利用光纤光栅解调系统和振动试验台对传感器的性能进行实验验证,得到该传感器灵敏度为0.024 nm/(m·s~(-2)),固有频率为185 Hz,并且线性度较好;对轴向柱塞泵模态分析,优化布置传感采样点,实际测量泵的振动信号。研究结果可为液压泵非介入式状态监测和故障诊断提供可靠数据支持。     

混合干涉型分布式光纤天然气管道泄漏检测及定位方法研究

介绍了一种基于马赫-曾德尔和萨格纳克混合干涉仪原理的分布式光纤天然气管道泄漏检测系统.阐述了检测系统的检测原理及泄漏定位方法,在泄漏点距法拉第旋转镜为6 032m处进行了气体管道泄漏检测实验并重复做了20次试验,测试了传感光纤与泄漏点不同夹角对检测系统性能的影响.实验结果表明,该系统可以检测出管道内气体压力为0.3MPa、泄漏孔径为2.5mm的微小泄漏信号并进行定位,平均相对定位误差为1.29%.在40mm的管道外径下,传感光纤与泄漏点夹角在0～180°范围内,检测系统均能检测出泄漏信号并进行定位.     

光纤光栅振动传感系统仿真研究与分析

由于光纤光栅传感器具有灵敏度高、动态范围宽、不受电磁干扰、成本低、体积小等优点,使其在传感领域具有很好的应用前景.光纤光栅传感技术已成为现代传感领域的一个重要研究方向,其在振动传感领域的应用也取得了一定的成就.本文针对悬臂梁式光纤光栅振动传感,将光纤光栅振动传感元件近似为惯性式振动系统,以其数学模型为基础,利用Matl...     

基于光纤光栅传感器的飞机油箱表面复合材料板振动研究

飞机机翼油箱在飞行时容易受到各种振源影响,而油箱结构中的复合材料较容易受低频振动影响。试验利用布拉格光纤光栅传感器受到激励后光栅中心波长随应力变化这一特性,在恒温下用布拉格光纤光栅传感器对飞机油箱表面变截面碳纤维层合板受到的振动信号进行研究,并对通过光纤光栅解调仪采集下来的振动动态信号进行频谱分析。在计算出动态信号的频谱峰值后,分析得出变截面碳纤维层合板的振动信号受到截面厚度、激励点位置的共同影响。结果表明利用光纤Bragg光栅传感网络对飞机油箱表面变截面碳纤维层合板受到的振动影响进行监测。     

基于光纤传感的管道和容器压力测量方法研究

为解决飞机、舰船、火箭、车辆、石油及天然气领域所涉及的管道和压力容器的压力测量问题,对涉及的管道、容器的压力泄露进行监测、泄露分析和预警,避免传统介入式测量方法弊端.应用一种基于光纤传感的管道和容器的压力测量方法,通过对光纤光栅波长和标准压力值的标定,拟合波长-压力直线的关系,以光纤光栅波长的变化表征管路压力变化.该方...     

光纤光栅传感技术在桥梁试桩中的应用

基于对光纤布拉格光栅(FBG)传感特性的理论分析,研制了可用于桥梁试桩应变监测的光纤光栅钢筋应变计,并进行了标定试验;研究了光纤光栅传感器的布设工艺,在某特大跨海大桥试桩项目中的钻孔灌注桩里成功地埋入了52支光纤光栅钢筋应变计,进行了荷载试验.研究结果表明,在桥梁试桩项目中利用光纤光栅传感技术可以方便有效地对试桩的应变进行多点实时监测,为桥梁桩基础的优化设计提供了可靠的依据.     

基于F-P滤波器的光纤光栅振动传感解调系统的研究

光纤光栅传感技术较其它传感技术有其独特的优点,在振动传感中有很大的发展前景。文章提出了一种利用法布里-玻罗腔作为滤波器,将FBG传感振动信号产生的Bragg波长的漂移转化为F-P滤波器透过光强度的变化来传感解调的方法,通过实验验证,可知该方法能克服相位型光纤振动传感器和匹配光纤光栅振动传感器的一些缺点,性能稳定,价格低廉,精确度高,具有较高的实用价值,有望在实际应用中推广。     

光纤布喇格光栅的炸药熔铸温度监测研究

为了实现对炸药熔铸过程的温度监测,利用多通道解调仪对炸药熔铸过程温度场进行监测,在炸药熔铸测温的过程中采用了经过特殊封装处理过的光栅传感器。简单介绍了光栅的传感原理、布喇格光栅数据解调仪的原理、实验所用光纤布喇格光栅的封装工艺。将获取的温度数据经Matlab和Origin处理并绘制时间―温度曲线,发现炸药熔铸相变发生的瞬间,温度曲线发生较大的变化。研究结果表明:炸药在熔铸过程中会释放出潜热,在释放潜热时炸药的温度会从88℃上升到90℃,特殊封装后的光纤布喇格光栅传感器能很好地对炸药熔铸过程进行温度测量。     

一种用于低频测量的光纤光栅振动传感器

利用光纤光栅敏感技术,设计了一种用于低频测量的光纤光栅振动传感器.该传感器采用了等强度悬臂梁作为振动传感元件,并在等强度悬臂梁的上下双面优化布置性能匹配的两个光纤光栅,一个为振动敏感测量光栅,另一个为信号匹配滤波解调光栅.该结构设计可以补偿温度的不利影响,同时也提高了传感器信号检测的灵敏度.实测结果表明,该传感器可以用于25 Hz以下的低频目标的振动测量.     

基于相移布喇格光纤光栅的折射率传感实验研究

利用图解法求解光纤特征方程,获得腐蚀过程和传感过程中光纤光栅的光谱特性,设计了光纤光栅的部分腐蚀方案,采用氢氟酸溶液腐蚀制作相移布喇格光纤光栅。对光纤光栅进行部分腐蚀,将形成相移光纤光栅。根据相移光纤光栅的特性,讨论了利用反射光光强解调的方式,该方式具有结构简单且对温度不敏感的优点。     

Femtosecond laser-inscribed fiber Bragg gratings for strain monitoring in power cables of offshore wind turbines

A fiber Bragg grating sensor system used for monitoring the effects of strain on the power cable of an offshore wind turbine is presented. The Bragg grating structure was inscribed into coated nonphotosensitive standard telecommunication fibers using an IR femtosecond laser and the point-by-point writing technique. Because of the presence of the protective coating of the fiber, the mechanical stability of the resultant sensor device is better than that of a sensor consisting of a bare fiber. A system containing this sensing element was to our knowledge for the first time successfully installed and tested in an offshore wind turbine prototype (REpower 6M, REpower Systems, AG, Germany) in February 2010, near Ellh?ft (Germany). The fabrication process of the fiber Bragg gratings, measurement results of the online monitoring, and a comparison between the sensor signal and commonly used sensing techniques are presented.     

用纤内Bragg光栅进行动态应变测量的研究

描述了用纤内Bragg光栅进行动态应变测量研究的意义，原理和方法，提出了两种用纤内Bragg光栅动态应变测量时进行Bragg波长偏移量的解调方法；光干涉相位检测Bragg光栅反射波长偏移的解调方法和用DWDM密集波分复用器解调Bragg波长的方法，前者适用于高频宽带动态应变测量，后者适用于有限频率或中等频率响应的动态应变测量。     

利用WDM光纤耦合器的光纤光栅传感解调技术

根据 WDM 光纤耦合器波长解调方案的工作原理、偏振特性以及影响系统波长分辨力的因素,提出一种改进的利用 WDM 光纤耦合器的光纤光栅传感解调技术。该技术在原技术的基础上,采用偏振控制器控制入射光偏振状态,提高了解调的精度和稳定性。对 WDM 光纤耦合器的多次波长扫描结果表明,采用偏振控制器后,其波长误差可减小到 5pm 左右。实验采用 1540/1560nm的 WDM 光纤耦合器对单点光纤光栅应变传感器进行静态解调,结果表明:按此技术开发的解调系统具有 0.01nm 波长分辨力和 10nm 的波长线性解调范围。     

Response of fiber Bragg gratings to longitudinal ultrasonic waves

In the last years, fiber optic sensors have been widely exploited for several sensing applications, including static and dynamic strain measurements up to acoustic detection. Among these, fiber Bragg grating sensors have been indicated as the ideal candidate for practical structural health monitoring in light of their unique advantages over conventional sensing devices. Although this class of sensors has been successfully tested for static and low-frequency measurements, the identification of sensor performances for high-frequency detection, including acoustic emission and ultrasonic investigations, is required. To this aim, the analysis of feasibilty on the use of fiber Bragg grating sensors as ultrasonic detectors has been carried out. In particular, the response of fiber Bragg gratings subjected to the longitudinal ultrasonic (US) field has been theoretically and numerically investigated. Ultrasonic field interaction has been modeled, taking into account the direct deformation of the grating pitch combined with changes in local refractive index due to the elasto-optic effect. Numerical results, obtained for both uniform and Gaussian-apodized fiber Bragg gratings, show that the grating spectrum is strongly influenced by the US field in terms of shape and central wavelength. In particular, a key parameter affecting the grating response is the ratio between the US wavelength and the grating length. Normal operation characterized by changes in wavelength of undistorted Bragg peak is possible only for US wavelengths longer than the grating length. For US wavelengths approaching the grating length, the wavelength change is accompanied by subpeaks formation and main peak amplitude modulation. This effect can be attributed to the nonuniformity of the US perturbation along the grating length. At very high US frequencies, the grating is not sensitive any longer. The results of this analysis provide useful tools for the design of grating-based ultrasound sensors for meeting specific requirements in terms of field intensity and frequencies.     

Theoretical investigation on the temperature characteristics of liquid-cladding micro/nanofiber Bragg grating

Based on the functions of the effective refractive index of fundamental mode in step-index fiber, a theoretical mode about the Bragg wavelength shift of micro/nanofiber Bragg grating (MNFBG) is presented. The numerical simulation results demonstrate, for a MNFBG with given radius, the Bragg wavelength shifts to short wavelength as ambient temperature increases, and the reason results from the effective index decreasing with the increase of ambient temperature. Moreover, with the reduction of fiber-core radius, as well as the increase of ambient index and its thermo-optic coefficient, the temperature sensitivity, linearity and linear response range of the temperature-dependent Bragg wavelength shift are improved obviously. Especially for a MNFBG with fiber radius smaller than 0.5?μm, the linearity of Bragg wavelength shifting with temperature will be close to the theoretical limit, and the temperature sensitivity is proportional to the thermo-optic coefficient of the ambient liquid. Compared with the temperature properties of conventional fiber Bragg grating (FBG), all the results will provide much theoretical guides for FBG applied in fiber sensing and communication.     

Advanced cure monitoring by optoelectronic multifunction sensing system

In this work, a dual functionality fiber optic sensing system for thermoset cure monitoring has been developed and successfully tested. Principle of operation relies on the use of a standard optical fiber in single ended configuration containing a single in-fiber Bragg grating. The change in refractive index directly related to material density at fiber end and the variation in the wavelength reflected by the fiber grating have been monitored simultaneously, throughout an In-Mould curing process of an epoxy resin. A compact and low cost in-fiber dual wavelength demodulation system has been developed and experimental results demonstrate the capability to on line identify the degree of cure, gel point, residual stresses and the glass transition temperature of the cured resin.