Distributed optical fiber acoustic sensor for in situ monitoring of marine natural gas hydrates production for the first time in the Shenhu Area,China

The distributed acoustic sensor(DAS)uses a single optical cable as the sensing unit,which can capture the acoustic and vibration signals along the optical cable in real-time.So it is suitable for monitoring downhole production activities in the process of oil and gas development.The authors applied the DAS system in a gas production well in the South China Sea for in situ monitoring of the whole wellbore for the first time and obtained the distributed acoustic signals along the whole wellbore.These signals can clearly distinguish the vertical section,curve section,and horizontal production section.The collected acoustic signal with the frequency of approximately 50 Hz caused by the electric submersible pump exhibit a signal-to-noise ratio higher than 27 dB.By analyzing the acoustic signals in the production section,it can be located the layers with high gas production rates.Once an accurate physical model is built in the future,the gas production profile will be obtained.In addition,the DAS system can track the trajectory of downhole tools in the wellbore to guide the operation.Through the velocity analysis of the typical signals,the type of fluids in the wellbore can be distinguished.The successful application of the system provides a promising whole wellbore acoustic monitoring tool for the production of marine gas hydrate,with a good application prospect.

Network Integration of Distributed Optical Fiber Temperature Sensor

The integration of distributed optical fiber temperature sensor with supervisory control and data acquisition （SCADA） system is proposed and implemented. In the implementation of the integration, both the compatibility with traditional system and the characteristics of distributed optical fiber temperature sensor is considered before Modbus TCP/IP protocol is chosen. The protocol is implemented with open source component Indy. The Modbus TCP/IP protocol used in the system is proved to be fast and robust.

Feasibility study on sinkhole monitoring with fiber optic strain sensing nerves

Anthropogenic activity-induced sinkholes pose a serious threat to building safety and human life nowadays.Real-time detection and early warning of sinkhole formation are a key and urgent problem in urban areas.This paper presents an experimental study to evaluate the feasibility of fiber optic strain sensing nerves in sinkhole monitoring.Combining the artificial neural network(ANN)and particle image velocimetry(PIV)techniques,a series of model tests have been performed to explore the relationship between strain measurements and sinkhole development and to establish a conversion model from strain data to ground settlements.It is demonstrated that the failure mechanism of the soil above the sinkhole developed from a triangle failure plane to a vertical failure plane with increasing collapse volume.Meanwhile,the soil-embedded fiber optic strain sensing nerves allowed deformation monitoring of the ground soil in real time.Furthermore,the characteristics of the measured strain profiles indicate the locations of sinkholes and the associated shear bands.Based on the strain data,the ANN model predicts the ground settlement well.Additionally,micro-anchored fiber optic cables have been proven to increase the soil-to-fiber strain transfer efficiency for large deformation monitoring of ground collapse.

Distributed Fiber Optic Monitoring and Stability Analysis of a Model Slope under Surcharge Loading

In the discipline of geotechnical engineering, fiber optic sensor based distributed monitoring has played an increasingly important role over the past few decades. Compared with conventional sensors, fiber optic sensors have a variety of exclusive advantages, such as smaller size,higher precision, and better corrosion resistance.These innovative monitoring technologies have been successfully applied for performance monitoring of geo-structures and early warning of potential geohazards around the world. In order to investigate their ability to monitor slope stability problems, a medium-sized model of soil nailed slope has been constructed in laboratory. The fully distributed Brillouin optical time-domain analysis(BOTDA)sensing technology was employed to measure the horizontal strain distributions inside the model slope.During model construction, a specially designed strain sensing fiber was buried in the soil mass.Afterward, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and a reaction frame. During testing, an NBX-6050 BOTDA sensing interrogator was used to collect the fiber optic sensing data. The test results have been analyzed in detail, which shows that the fiber optic sensors can capture the progressive deformation and failure pattern of the model slope. The limit equilibrium analyses were also conducted to obtain the factors of safety of the slope under different surface loadings. It is found that the characteristic maximum strains can reflect the stability of the model slope and an empirical relationship was obtained. This study verified the effectiveness of the distributed BOTDA sensing technology in performance monitoring of slope.

Landslide Monitoring Based on High-Resolution Distributed Fiber Optic Stress Sensor

A landslide monitoring application is presented by using a high-resolution distributed fiber optic stress sensor. The sensor is used to monitor the intra-stress distribution and variations in landslide bodies, and can be used for the early warning of the occurrence of the landslides. The principle of distributed fiber optic stress sensing and the intra-stress monitoring method for landslides are described in detail. By measuring the distributed polarization mode coupling in the polarization-maintaining fiber, the distributed fiber stress sensor with stress measuring range 0 to 15 MPa, spatial resolution 10 cm and measuring range 0.5 km, is designed. The warning system is also investigated experimentally in the field trial.

The Design of Fiber Bragg Grating Temperature Measurement System Based on Labview

The paper made a research on the fiber Bragg grating sensor demodulation system, which was based on virtual instrument labview and it developed a friendly upper monitor software. Based on the LM algorithm, the software realized rapid and accurate spectral data fitting, improving dynamic characteristics and measuring precision of the system. Depending on different fiber Bragg grating sensors, it can realize flexible calibration. It has the functions of collection, display and data storage, which can flexibly design alarm threshold according to the practical application. The fiber Bragg grating sensors can be identified by the software so that the distributed network, with large capacity optical fiber sensing, can be achieved.

冻融条件下路基温度场和湿度场分布式感知试验

搭建土体冻融多物理场感知室内试验装置,布设传统点式传感器和分布式光纤,对土体冻融过程中路基温度场、湿度场和变形情况开展试验监测,探究单端冻结、双端融化条件下土体温度场和湿度场的分布式感知特征,验证主动加热分布式光纤技术的监测效果。试验结果表明,-15℃单端冻结条件下,土体冻结过程按降温速率分为快速冷却、逐步降温、稳定平衡三阶段,冻结锋面逐渐下移,最大冻深约占土柱高度的35%。孔隙水受冻胀迁移力影响向冻结锋面移动,引起冻融前后土体湿度场重分布,并导致土体冻胀变形,变形量为土体最大冻深的7.8%~10.9%。分布式光纤可准确得到冻融过程中土体温度场、湿度场变化特征,识别土体内冻结区域范围,温度、湿度监测拟合优度R2分别达0.98和0.94。

煤层采动巨厚松散层全断面监测及内部变形特征

开采沉陷是煤炭资源井工开发利用所面临的主要环境地质问题,尤其对于我国东部高潜水位矿区而言,巨厚松散层的移动变形控制与采动减损评价备受关注。为了研究巨厚松散层内部移动机制,明确其对地表移动变形影响,以淮南新集矿区某井田为研究区,通过采用分布式光纤与并行电法联合测试技术,构建超过600 m深度全断面钻孔监测系统,探究巨厚松散层变形特征和内部移动规律。全断面监测系统能够获取煤层采动区域巨厚松散层内部应变、位移信息及监测钻孔周围电阻率变化情况,量化地层监测断面松散层内部移动变形时空关系和渗流场变化数据,分析松散层内地层变形特征与发育形态。研究结果表明:多参量联合测试技术的应用,显著提高了对巨厚松散层移动变形的监测效率和变形定位的准确性,获得了工作面回采位置与松散层内部变形时空演变关系。并根据松散层变形特征,将采动影响过程划分为超前影响期、弱采动影响期、强采动影响期、采后沉稳期4个阶段,揭示了超前影响变形表现“台阶状”形态与采动影响期的“反向3字型”移动特征,同时分析了“反向3字型”移动模式的构成条件、影响因素。基于全断面监测数据,提出巨厚松散层变形多场可测信息量化评价方法,阐明了巨厚松散层在煤层开采过程中存在分层应力积累与释放的规律。研究内容为巨厚松散层内部移动变形的精细化监测分析提供重要的技术支持。全断面监测技术的应用,也可为采动损害过程监测与评价、矿山生态源头减损与减沉、沉陷区土地规划与复垦以及松散层内注浆改造等提供参考。

预应力混凝土梁腐蚀断丝水下监测试验研究

采用人工通电加速腐蚀的方法模拟混凝土梁内预应力钢筋的自然断裂过程从而获得真实的断丝声发射信号,应用高频声发射传感器和分布式光纤监测系统从水下采集预应力钢筋断裂时产生的声信号,分析信号的时频域特征和时域统计特征参数,结果表明:断丝信号的超声波段在水中传播时发生频散,应采用20 kHz以下的时域统计特征识别断丝信号;铠装光缆可以接收到在水中传播的断丝信号,其在时频图上表现为一条竖直的条带,并且能量主要集中分布于100~200 Hz。采用时域统计特征参数分析光纤监测信号时,需要设定较小的门槛值截取信号进行分析;对于光纤水声监测工况来说,峰值指标的信噪比较低,裕度和峭度指标更适合于用来识别断丝信号。该研究为开发预应力混凝土结构断丝水下声光纤监测系统奠定了基础。

光纤传感技术在油气田开发中的应用

分布式光纤监测技术在油气田开发中具有无可比拟的优势。从分布式光纤传感技术基本原理和井中布设方式出发,介绍了光纤传感技术在水力压裂、连续油管产液剖面测试、邻井压裂监测、油气井注采监测、储气库安全监测和套损监测等多个石油工程领域应用情况。整体表明光纤监测是一种经济高效的监测技术,具备实时监控油气井全生命周期的潜力,是具有科学性、时代特性和安全高效的生产测井技术。同时指出分布式光纤传感技术在油田应用的未来发展应聚焦于提升传感器性能、丰富光纤监测场景应用、提高资料处理解释水平能力,降低应用成本,进一步发挥光纤在油气田开发中的作用。

基于光纤传感技术的工程监测应用研究

光纤传感技术作为当前热门技术之一,在工程监测领域有着许多重要应用。通过探讨光纤传感技术在工程形变监测中的应用案例,展示了其在工程监测领域的重要性。光纤传感技术利用光纤作为传感元件,可以实现对形变的连续、实时监测,并提供高精度的监测数据。通过布设应变光缆和温度补偿光缆,在合璧津高速公路K134段高架桥上进行了监测实验。结果表明,光纤传感技术能够准确评估结构的变形情况,并通过温度补偿算法消除了温度变化对数据的影响。通过几何方法计算沉降位移,可以实现对沉降位移的估算。

边坡全维度监测技术与模型试验研究

中国是世界上地质灾害最严重的国家之一,其中滑坡常年位于各类地质灾害首位,因此对滑坡灾害进行深层次的研究至关重要。边坡工程常常会受到人类工程活动与自然地质作用叠加效应的影响,从而增加了对边坡变形失稳机理的科学认知难度。为精准掌握边坡状态信息与变形失稳过程,可通过建立全维度的监测体系以实现边坡状态信息的动态解译与表征,据此获得更加精准、可靠、直观的边坡稳定性评价依据。文章围绕边坡破坏模式及典型边坡监测技术,在厘清边坡变形演化过程的基础上,对边坡“天—空—地—体”一体化监测技术体系进行了全面分析;概述性总结了基于DFOS的边坡监测技术,重点阐述了基于DFOS的边坡多源多场监测研究思路与实施路径;系统性梳理了基于典型监测技术与DFOS技术的边坡物理模型试验研究过程与结果,以期为开展边坡加固方案设计与防灾减灾控灾提供重要的参考依据。

DT-CWT-LMS自适应降噪模型构建及其在隧道监测工程中的应用

针对隧道工程监测现场应用布里渊光时域反射仪(BOTDR)系统存在的问题,提出基于双树复小波变换(DT-CWT)和改进的LMS算法的组合降噪模型,用于对BOTDR分布式光纤监测信号进行降噪处理。首先,基于双树复小波变换算法分解原始信号;然后,使用样本熵作为目标函数自动选择最优小波分解层数的模型,并基于优化双曲余弦函数改进LMS算法的收敛速度和收敛性;最后,为验证所提出算法的有效性,进行BOTDR温度信号降噪试验。试验结果表明:1)DT-CWT-LMS算法的降噪效果明显优于传统的小波阈值降噪方法,在6个温度梯度上的平均SNR值比WDD、EMT、EMD分别高出43.98%、17.5%、8.4%,平均RMSE值分别降低33.18%、17.14%、9.23%,平均SE值分别降低29.04%、21.17%、20.67%。为验证所提算法在工程现场的有效性,依托北京地铁隧道监测项目,使用DT-CWT-LMS算法对光纤监测信号进行降噪研究,降噪后信号的样本熵平均降低幅为64.03%;2)和常规WDD、EMT、EMD 3种方法相比,DT-CWT-LMS算法在3条光纤上的表现均优于其他3种算法,在1号、2号、3号光纤上的SNR指标比其他3种算法的平均值分别高出22%、38%、27%,说明该算法可作为隧道工程光纤监测信号的一种有效降噪方法。

飞行器结构健康监测技术研究进展

结构健康监测技术有望在飞行器设计、服役和维护中发挥关键作用,提高飞行器结构效率,确保飞行器结构的安全性和可靠性。本文首先概述结构健康监测的基本概念及其适用范围,强调其在航空航天领域中的重要性。随后,针对结构健康监测技术在飞行器典型结构中的研究工作情况,重点围绕冲击监测、超声导波损伤监测以及光纤传感器应变监测等先进技术进行详细讨论,总结国内外研究现状、技术能力以及典型应用。最后,指出飞行器结构健康监测面临的挑战性问题,展望该技术在航空航天领域的应用前景。

高填方引调水工程渗漏连续监测方法研究

针对高填方引调水工程提出适于工程结构破坏预警的方法。通过建立室内试验模型在强透水层砂砾石层与弱透水层黏土层之间增设不透水层,分层埋设加热电缆和分布式光纤得到不同工况下渗透破坏的监测数据,对比分析增设不透水层以后的渗透破坏试验结果、现象及渗透路径的变化,确定渗漏破坏与光纤监测数据之间的关联。采用分布式光纤可以测量得到堤基土体的温度场,根据温度的差异,可以判断得到堤基可能发生管涌且已经发生管涌的位置;不同程度的渗漏破坏,对应不同的温度场,渗流流量越大,温度场的差异越明显。

基于分布式光纤的蜂窝夹层结构脱粘损伤监测

航空航天蜂窝夹层结构服役环境恶劣,需要发展相应的结构健康监测技术以保证结构的安全运行。脱粘损伤因发生在内部胶层而难以监测,该文采用埋入胶层的分布式光纤传感器对蜂窝夹层结构脱粘损伤进行监测。在预埋损伤监测试验中采用高强光纤和边界浅槽的方式提高传感器存活效率,得到脱粘损伤应变特征。采用参数化建模方式对不同损伤位置进行大量有限元模拟,加入白噪声后得到含有脱粘损伤特征的13500组数据。将模拟数据代入卷积神经网络进行训练,训练后的网络对试验损伤数据的识别准确率达到98.84%。该方法能够识别20 mm^(2)脱粘损伤,同时定位平均误差小于4 mm。

基于分布式光纤传感与U-Net网络的复合材料分层损伤定量识别方法

结构健康监测(SHM)是确保飞行器复合材料结构安全性和完整性的重要手段。基于背向瑞利散射的分布式光纤传感器可以通过测量高密度的应变分布为复合材料损伤监测提供数据支持。然而,结构应变分布特征和损伤的映射关系较为复杂,无法直接根据应变分布准确判定损伤的定量信息。另外,分布式光纤传感器数据量大,通过人为分析应变数据识别损伤较为耗时且准确性偏低。为了应对这一挑战,提出了一种基于分布式光纤传感数据与U-Net神经网络的智能损伤识别方法,旨在自动精确识别复合材料中常见的分层损伤。首先,通过有限元仿真构建U-Net神经网络的训练集与验证集;随后进行含分层损伤复合材料板的悬臂加载试验,通过分布式光纤传感器采集结构应变分布数据作为测试集。损伤识别结果表明,U-Net神经网络可以对分层损伤的位置、尺寸与形状进行较为精确的定量识别。

光加热光纤光栅阵列液位测量方法研究

安全可靠的液位测量是现代工业领域的重要技术需求之一,提出一种基于光加热光纤光栅阵列的液位测量方法,即利用泵浦光加热掺钴光纤,控制温度场,利用光栅阵列测量温度场分布,由于气液导热性能的差别,气液界面处温度突变,从而确定液位。实验中,将掺钴光纤与密集光栅阵列紧密固定在一起,将1.5 W的泵浦光输入衰减系数分别为0.71 dB/cm和0.28 dB/cm的掺钴光纤中,沿着光传播的方向,温度变化均呈指数函数衰减。液位测量的精度与范围由主要取决于泵浦光功率、掺钴光纤吸收系数,经对比最终选定0.28 dB/cm的掺钴光纤作为液位实验的加热光纤。实验测量了不同液位下的温度场分布,证明了利用测量温度分布来测量液位的可行性,液位变化范围0~88 mm以内的误差为2 mm。所提出的传感系统结构简单,成本低廉,在液位测量方面具有潜在的应用价值。