Despite the extensive use of distributed fiber optic sensing(DFOS)in monitoring underground structures,its potential in detecting structural anomalies,such as cracks and cavities,is still not fully understood.To contr...Despite the extensive use of distributed fiber optic sensing(DFOS)in monitoring underground structures,its potential in detecting structural anomalies,such as cracks and cavities,is still not fully understood.To contribute to the identification of defects in underground structures,this study conducted a four-point bending test of a reinforced concrete(RC)beam and uniaxial loading tests of an RC specimen with local cavities.The experimental results revealed the disparity in DFOS strain spike profiles between these two structural anomalies.The effectiveness of DFOS in the quantification of crack opening displacement(COD)was also demonstrated,even in cases where perfect bonding was not achievable between the cable and structures.In addition,DFOS strain spikes observed in two diaphragm wall panels of a twin circular shaft were also reported.The most probable cause of those spikes was identified as the mechanical behavior associated with local concrete contamination.With the utilization of the strain profiles obtained from laboratory tests and field monitoring,three types of multi-classifiers,based on support vector machine(SVM),random forest(RF),and backpropagation neural network(BP),were employed to classify strain profiles,including crack-induced spikes,non-crack-induced spikes,and non-spike strain profiles.Among these classifiers,the SVM-based classifier exhibited superior performance in terms of accuracy and model robustness.This finding suggests that the SVM-based classifier holds promise as a potential solution for the automatic detection and classification of defects in underground structures during long-term monitoring.展开更多
Phase-sensitive Optical Time-Domain Reflectometer(φ-OTDR)technology facilitates the real-time detection of vibration events along fiber optic cables by analyzing changes in Rayleigh scattering signals.This technology...Phase-sensitive Optical Time-Domain Reflectometer(φ-OTDR)technology facilitates the real-time detection of vibration events along fiber optic cables by analyzing changes in Rayleigh scattering signals.This technology is widely used in applications such as intrusion monitoring and structural health assessments.Traditional signal processing methods,such as Support Vector Machines(SVM)and K-Nearest Neighbors(KNN),have limitations in feature extraction and classification in complex environments.Conversely,a single deep learning model often struggles with capturing long time-series dependencies and mitigating noise interference.In this study,we propose a deep learning model that integrates Convolutional Neural Network(CNN),Long Short-Term Memory Network(LSTM),and Transformer modules,leveraging φ-OTDR technology for distributed fiber vibration sensing event recognition.The hybrid model combines the CNN's capability to extract local features,the LSTM's ability to model temporal dynamics,and the Transformer's proficiency in capturing global dependencies.This integration significantly enhances the accuracy and robustness of event recognition.In experiments involving six types of vibration events,the model consistently achieved a validation accuracy of 0.92,and maintained a validation loss of approximately 0.2,surpassing other models,such as TAM+BiLSTM and CNN+CBAM.The results indicate that the CNN+LSTM+Transformer model is highly effective in handling vibration signal classification tasks in complex scenarios,offering a promising new direction for the application of fiber optic vibration sensing technology.展开更多
Distributed fiber optic sensors(DFOSs)possess the capability to measure strain and temperature variations over long distances,demonstrating outstanding potential for monitoring underground infrastructure.This study pr...Distributed fiber optic sensors(DFOSs)possess the capability to measure strain and temperature variations over long distances,demonstrating outstanding potential for monitoring underground infrastructure.This study presents a state-of-the-art review of the DFOS applications for monitoring and assessing the deformation behavior of typical tunnel infrastructure,including bored tunnels,conventional tunnels,as well as immersed and cut-and-cover tunnels.DFOS systems based on Brillouin and Rayleigh scattering principles are both considered.When implementing DFOS monitoring,the fiber optic cable can be primarily installed along transverse and longitudinal directions to(1)measure distributed strains by continuously adhering the fiber to the structure’s surface or embedding it in the lining,or(2)measure point displacements by spot-anchoring it on the lining surface.There are four critical aspects of DFOS monitoring,including proper selection of the sensing fiber,selection of the measuring principle for the specific application,design of an effective sensor layout,and establishment of robust field sensor instrumentation.These four issues are comprehensively discussed,and practical suggestions are provided for the implementation of DFOS in tunnel infrastructure monitoring.展开更多
This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumf...This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage.The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface.The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation,detects initialization of microcrack nucleation,and identifies strain localization within the specimen.The DFOSS well observes the effects of rock heterogeneity on rock deformation.The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning.The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.展开更多
Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most o...Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.展开更多
A simple distributed optical fiber sensing system used to monitor vibration signal has an additional sub-loop eoupled with main ring by a 3 dB coupler. This paper compares three outputting interfered beams, each of th...A simple distributed optical fiber sensing system used to monitor vibration signal has an additional sub-loop eoupled with main ring by a 3 dB coupler. This paper compares three outputting interfered beams, each of them travels in the sub-ring 0, 1, 2 times, separately. Using the simultaneous equations produced by those three outputs, we find the relation between the interference lights and vibration signal＇s characteristics, such as frequency, amplitude and position. Through simplifying and calculating, the vibration position can be obtained finally.展开更多
The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandw...The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandwidth （〈10 MHz） ECL laser and is pumped by the tunable power 1427.2 nm fiber Raman laser. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber Raman amplifier and fiber Brillouin amplifier. The SBS lines total gain is a production of the gain of Raman and the gain of Brillouin amplifier. In experiment, the gain of SBS is about 42 dB and the saturation gain of 25 Ion G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.展开更多
For distributed fiber Raman amplifiers（DFRAs）, stimulated Brillouin scattering（SBS） can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain sa...For distributed fiber Raman amplifiers（DFRAs）, stimulated Brillouin scattering（SBS） can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 m W forward pump is as low as 0 d Bm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 d B, and the correction factor is 0.25 d B, in which the modulation frequency is high enough. Additionally, the factor is 1.767 d B for the modulation frequency of 25 MHz. On this basis,phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.展开更多
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...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.展开更多
The principle of optical time-domain reflection localization limits the sensing spatial resolution of Raman distributed optical fiber sensing.We provide a solution for a Raman distributed optical fiber sensing system ...The principle of optical time-domain reflection localization limits the sensing spatial resolution of Raman distributed optical fiber sensing.We provide a solution for a Raman distributed optical fiber sensing system with kilometer-level sensing distance and submeter spatial resolution.Based on this,we propose a Raman distributed optical fiber sensing scheme based on chaotic pulse cluster demodulation.Chaotic pulse clusters are used as the probe signal,in preference to conventional pulsed or chaotic single-pulse lasers.Furthermore,the accurate positioning of the temperature variety region along the sensing fiber can be realized using chaotic pulse clusters.The proposed demodulation scheme can enhance the signal-to-noise ratio by improving the correlation between the chaotic reference and the chaotic Raman anti-Stokes scattering signals.The experiment achieved a sensing spatial resolution of 30 cm at a distributed temperature-sensing distance of∼6.0 km.Furthermore,we explored the influence of chaotic pulse width and detector bandwidth on the sensing spatial resolution.In addition,the theoretical experiments proved that the sensing spatial resolution in the proposed scheme was independent of the pulse width and sensing distance.展开更多
The distributed fiber optic sensing system,known for its high sensitivity and wide-ranging measurement capabilities,has been widely used in monitoring underground gas pipelines.It primarily serves to perceive vibratio...The distributed fiber optic sensing system,known for its high sensitivity and wide-ranging measurement capabilities,has been widely used in monitoring underground gas pipelines.It primarily serves to perceive vibration signals induced by external events and to effectively provide early warnings of potential intrusion activities.Due to the complexity and diversity of external intrusion events,traditional deep learning methods can achieve event recognition with an average accuracy exceeding 90%.However,these methods rely on large-scale datasets,leading to significant time and labor costs during the data collection process.Additionally,traditional methods perform poorly when faced with the scarcity of low-frequency event samples,making it challenging to address these rare occurrences.To address this issue,this paper proposes a small-sample learning model based on triplet learning for intrusion event recognition.The model employs a 6-way 20-shot support set configuration and utilizes the KNN clustering algorithm to assess the model's performance.Experimental results indicate that the model achieves an average accuracy of 91.6%,further validating the superior performance of the triplet learning model in classifying external intrusion events.Compared to traditional methods,this approach not only effectively reduces the dependence on large-scale datasets but also better addresses the classification of low-frequency event samples,demonstrating significant application potential.展开更多
Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design o...Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design optimization of variable stiffness of fiber-reinforced composite laminates has attracted widespread attention from scholars and industry. In these aerospace composite structures, numerous cutout panels and shells serve as access points for maintaining electrical, fuel, and hydraulic systems. The traditional fiber-reinforced composite laminate subtractive drilling manufacturing inevitably faces the problems of interlayer delamination, fiber fracture, and burr of the laminate. Continuous fiber additive manufacturing technology offers the potential for integrated design optimization and manufacturing with high structural performance. Considering the integration of design and manufacturability in continuous fiber additive manufacturing, the paper proposes linear and nonlinear filtering strategies based on the Normal Distribution Fiber Optimization (NDFO) material interpolation scheme to overcome the challenge of discrete fiber optimization results, which are difficult to apply directly to continuous fiber additive manufacturing. With minimizing structural compliance as the objective function, the proposed approach provides a strategy to achieve continuity of discrete fiber paths in the variable stiffness design optimization of composite laminates with regular and irregular holes. In the variable stiffness design optimization model, the number of candidate fiber laying angles in the NDFO material interpolation scheme is considered as design variable. The sensitivity information of structural compliance with respect to the number of candidate fiber laying angles is obtained using the analytical sensitivity analysis method. Based on the proposed variable stiffness design optimization method for complex perforated composite laminates, the numerical examples consider the variable stiffness design optimization of typical non-perforated and perforated composite laminates with circular, square, and irregular holes, and systematically discuss the number of candidate discrete fiber laying angles, discrete fiber continuous filtering strategies, and filter radius on structural compliance, continuity, and manufacturability. The optimized discrete fiber angles of variable stiffness laminates are converted into continuous fiber laying paths using a streamlined process for continuous fiber additive manufacturing. Meanwhile, the optimized non-perforated and perforated MBB beams after discrete fiber continuous treatment, are manufactured using continuous fiber co-extrusion additive manufacturing technology to verify the effectiveness of the variable stiffness fiber optimization framework proposed in this paper.展开更多
Distributed fiber sensing possesses the unique ability to measure the distributed profile of an environmental quantity along many tens of kilometers with spatial resolutions in the meter or even centimeter scale.This ...Distributed fiber sensing possesses the unique ability to measure the distributed profile of an environmental quantity along many tens of kilometers with spatial resolutions in the meter or even centimeter scale.This feature enables distributed sensors to provide a large number of resolved points using a single optical fiber.However,in current systems,this number has remained constrained to a few hundreds of thousands due to the finite signal-to-noise ratio(SNR)of the measurements,which imposes significant challenges in the development of more performing sensors.Here,we propose and experimentally demonstrate an ultimately optimized distributed fiber sensor capable of resolving 2100000 independent points,which corresponds to a one-orderof-magnitude improvement compared to the state-of-the-art.Using a Brillouin distributed fiber sensor based on phase-modulation correlation-domain analysis combined with temporal gating of the pump and time-domain acquisition,a spatial resolution of 8.3 mm is demonstrated over a distance of 17.5 km.The sensor design addresses the most relevant factors impacting the SNR and the performance of medium-to-long range sensors as well as of sub-meter spatial resolution schemes.This step record in the number of resolved points could be reached due to two theoretical models proposed and experimentally validated in this study:one model describes the spatial resolution of the system and its relation with the sampling interval,and the other describes the amplitude response of the sensor,providing an accurate estimation of the SNR of the measurements.展开更多
In this paper,we present an application of distributed fiber optic sensor(DFOS)technology to measure the strain of a continuous flight auger(CFA)test pile with a central reinforcement bar bundle,during a static load t...In this paper,we present an application of distributed fiber optic sensor(DFOS)technology to measure the strain of a continuous flight auger(CFA)test pile with a central reinforcement bar bundle,during a static load test carried out in London.Being distributed in nature,DFOS gives much more information about the pile performance as compared to traditional point sensors,such as identifying cross-sectional irregularities or other anomalies.The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation(contraction),shaft friction,and tip resistance under various loads.Based on this pile load test,a finite element(FE)analysis was performed using a one-dimensional nonlinear load-transfer model.Calibrated by the shaft friction and tip resistance derived from the monitored data,the FE model was able to simulate the pile and soil performance during the load testing with good accuracy.The effect of the reinforcement cage and central reinforcement bar bundle were investigated,and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%.展开更多
Brillouin scattering based optical fiber sensors(BOFS)have the unique advantages over other sensors such as long distance,fully distributed,and multi-parameter sensing.The progresses on the development of BOFS technol...Brillouin scattering based optical fiber sensors(BOFS)have the unique advantages over other sensors such as long distance,fully distributed,and multi-parameter sensing.The progresses on the development of BOFS technology in Nanjing University are reviewed.The key technologies to make BOFS with ultra-long distance,high spatial resolution,and fast measuring speed are discussed and realized.展开更多
A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filte...A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.展开更多
Multicore fiber(MCF)which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light t...Multicore fiber(MCF)which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light transmission in multiple spatial channels.Different from the situation in standard single mode fiber(SMF),the fiber bending gives rise to tangential strain in off-center cores,and this unique feature has been employed for directional bending and shape sensing,where strain measurement is achieved by using either fiber Bragg gratings(FBGs),optical frequency-domain reflectometry(OFDR)or Brillouin distributed sensing technique.On the other hand,the parallel spatial cores enable space-division multiplexed(SDM)system configuration that allows for the multiplexing of multiple distributed sensing techniques.As a result,multi-parameter sensing or performance enhanced sensing can be achieved by using MCF.In this paper,we review the research progress in MCF based distributed fiber sensors.Brief introductions of MCF and the multiplexing/de-multiplexing methods are presented.The bending sensitivity of off-center cores is analyzed.Curvature and shape sensing,as well as various SDM distributed sensing using MCF are summarized,and the working principles of diverse MCF sensors are discussed.Finally,we present the challenges and prospects of MCF for distributed sensing applications.展开更多
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 compatibil...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.展开更多
Presented here is long-range distributed vibration sensing based on internal-modulation optical frequency domain reflectometry(OFDR).In the proposed system with internal modulation,a silicon-based photonic-chip laser i...Presented here is long-range distributed vibration sensing based on internal-modulation optical frequency domain reflectometry(OFDR).In the proposed system with internal modulation,a silicon-based photonic-chip laser is used as the laser source,and by controlling the output voltage curve of an arbitrary waveform generator to induce temperature change in the external cavity of the laser,a 10-GHz optical frequency tuning range is achieved.The complexity of the proposed internal-modulation system is lower than that of the traditional external-modulation OFDR system that combines a narrow-linewidth laser with a single-sideband modulator to achieve wavelength tuning.Cross-correlation analysis is used as a sensing mechanism to evaluate the similarity between Rayleigh scatter signals and to achieve vibration event localization.Experimental comparison is made of the vibration sensing performance of the external-and internal-modulation systems,and for a vibration event generated at a distance of 100.95 km,they locate it with a sensing spatial resolution of 43.0 m and 16.8 m,respectively.The results indicates that the proposed distributed vibration sensing based on internal modulation has better sensing performance and lower complexity compared to the traditional external-modulation system.In addition,the proposed system is single-ended and involves no optical amplification,which makes it very suitable for ultra-long-range sensing.展开更多
Underground mine pillars provide natural stability to the mine area,allowing safe operations for workers and machinery.Extensive prior research has been conducted to understand pillar failure mechanics and design safe...Underground mine pillars provide natural stability to the mine area,allowing safe operations for workers and machinery.Extensive prior research has been conducted to understand pillar failure mechanics and design safe pillar layouts.However,limited studies(mostly based on empirical field observation and small-scale laboratory tests)have considered pillar-support interactions under monotonic loading conditions for the design of pillar-support systems.This study used a series of large-scale laboratory compression tests on porous limestone blocks to analyze rock and support behavior at a sufficiently large scale(specimens with edge length of 0.5 m)for incorporation of actual support elements,with consideration of different w/h ratios.Both unsupported and supported(grouted rebar rockbolt and wire mesh)tests were conducted,and the surface deformations of the specimens were monitored using three-dimensional(3D)digital image correlation(DIC).Rockbolts instrumented with distributed fiber optic strain sensors were used to study rockbolt strain distribution,load mobilization,and localized deformation at different w/h ratios.Both axial and bending strains were observed in the rockbolts,which became more prominent in the post-peak region of the stress-strain curve.展开更多
基金support from the Open Research Project Programme of the State Key Laboratory of Internet of Things for Smart City,University of Macao (Grant No.SKL-IoTSC (UM)-2021-2023/ORPF/A19/2022)the General Research Fund project from Research Grants Council of Hong Kong Special Administrative Region Government of China (Grant No.15214722)the Start-up Fund from The Hong Kong Polytechnic University (Grant No.BD88).
文摘Despite the extensive use of distributed fiber optic sensing(DFOS)in monitoring underground structures,its potential in detecting structural anomalies,such as cracks and cavities,is still not fully understood.To contribute to the identification of defects in underground structures,this study conducted a four-point bending test of a reinforced concrete(RC)beam and uniaxial loading tests of an RC specimen with local cavities.The experimental results revealed the disparity in DFOS strain spike profiles between these two structural anomalies.The effectiveness of DFOS in the quantification of crack opening displacement(COD)was also demonstrated,even in cases where perfect bonding was not achievable between the cable and structures.In addition,DFOS strain spikes observed in two diaphragm wall panels of a twin circular shaft were also reported.The most probable cause of those spikes was identified as the mechanical behavior associated with local concrete contamination.With the utilization of the strain profiles obtained from laboratory tests and field monitoring,three types of multi-classifiers,based on support vector machine(SVM),random forest(RF),and backpropagation neural network(BP),were employed to classify strain profiles,including crack-induced spikes,non-crack-induced spikes,and non-spike strain profiles.Among these classifiers,the SVM-based classifier exhibited superior performance in terms of accuracy and model robustness.This finding suggests that the SVM-based classifier holds promise as a potential solution for the automatic detection and classification of defects in underground structures during long-term monitoring.
基金Supported by Key Laboratory of Space Active Optical-Electro Technology of Chinese Academy of Sciences(2021ZDKF4)。
文摘Phase-sensitive Optical Time-Domain Reflectometer(φ-OTDR)technology facilitates the real-time detection of vibration events along fiber optic cables by analyzing changes in Rayleigh scattering signals.This technology is widely used in applications such as intrusion monitoring and structural health assessments.Traditional signal processing methods,such as Support Vector Machines(SVM)and K-Nearest Neighbors(KNN),have limitations in feature extraction and classification in complex environments.Conversely,a single deep learning model often struggles with capturing long time-series dependencies and mitigating noise interference.In this study,we propose a deep learning model that integrates Convolutional Neural Network(CNN),Long Short-Term Memory Network(LSTM),and Transformer modules,leveraging φ-OTDR technology for distributed fiber vibration sensing event recognition.The hybrid model combines the CNN's capability to extract local features,the LSTM's ability to model temporal dynamics,and the Transformer's proficiency in capturing global dependencies.This integration significantly enhances the accuracy and robustness of event recognition.In experiments involving six types of vibration events,the model consistently achieved a validation accuracy of 0.92,and maintained a validation loss of approximately 0.2,surpassing other models,such as TAM+BiLSTM and CNN+CBAM.The results indicate that the CNN+LSTM+Transformer model is highly effective in handling vibration signal classification tasks in complex scenarios,offering a promising new direction for the application of fiber optic vibration sensing technology.
基金funding support from Rijkswaterstaat,the Netherlands,and European Union’s Horizon 2020 Research and Innovation Programme(Project SAFE-10-T under Grant No.723254)China Scholarship Council,and National Natural Science Foundation of China(Grant No.42225702).
文摘Distributed fiber optic sensors(DFOSs)possess the capability to measure strain and temperature variations over long distances,demonstrating outstanding potential for monitoring underground infrastructure.This study presents a state-of-the-art review of the DFOS applications for monitoring and assessing the deformation behavior of typical tunnel infrastructure,including bored tunnels,conventional tunnels,as well as immersed and cut-and-cover tunnels.DFOS systems based on Brillouin and Rayleigh scattering principles are both considered.When implementing DFOS monitoring,the fiber optic cable can be primarily installed along transverse and longitudinal directions to(1)measure distributed strains by continuously adhering the fiber to the structure’s surface or embedding it in the lining,or(2)measure point displacements by spot-anchoring it on the lining surface.There are four critical aspects of DFOS monitoring,including proper selection of the sensing fiber,selection of the measuring principle for the specific application,design of an effective sensor layout,and establishment of robust field sensor instrumentation.These four issues are comprehensively discussed,and practical suggestions are provided for the implementation of DFOS in tunnel infrastructure monitoring.
基金support from the Institute of Crustal Dynamics,China Earthquake Administration(Grant No.ZDJ2016-20 and ZDJ2019-15)。
文摘This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage.The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface.The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation,detects initialization of microcrack nucleation,and identifies strain localization within the specimen.The DFOSS well observes the effects of rock heterogeneity on rock deformation.The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning.The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.
基金funding support from the Israeli Ministry of Housing and Construction(Grant No.2028286).
文摘Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.
文摘A simple distributed optical fiber sensing system used to monitor vibration signal has an additional sub-loop eoupled with main ring by a 3 dB coupler. This paper compares three outputting interfered beams, each of them travels in the sub-ring 0, 1, 2 times, separately. Using the simultaneous equations produced by those three outputs, we find the relation between the interference lights and vibration signal＇s characteristics, such as frequency, amplitude and position. Through simplifying and calculating, the vibration position can be obtained finally.
基金supported by the National Natural Science Foundation under Grant No. 60608009Zhejiang Science Foundation under Grant No. Y107091.
文摘The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandwidth （〈10 MHz） ECL laser and is pumped by the tunable power 1427.2 nm fiber Raman laser. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber Raman amplifier and fiber Brillouin amplifier. The SBS lines total gain is a production of the gain of Raman and the gain of Brillouin amplifier. In experiment, the gain of SBS is about 42 dB and the saturation gain of 25 Ion G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.
基金Project supported by the National Natural Science Foundation of China(Grant No.61177073)the Major Application Basic Research Project of National University of Defense Technology,China(Grant No.ZDYYJCYJ20140701)
文摘For distributed fiber Raman amplifiers（DFRAs）, stimulated Brillouin scattering（SBS） can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 m W forward pump is as low as 0 d Bm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 d B, and the correction factor is 0.25 d B, in which the modulation frequency is high enough. Additionally, the factor is 1.767 d B for the modulation frequency of 25 MHz. On this basis,phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.
基金supported by the National Natural Science Foundation of China under Grant No. 60377021partially supported by Program for New Century Excellent Talents in University under Grant. No. NCET-07-0152Sichuan Scientific Funds for Young Researchers under Grant No. 08ZQ026-012.
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.U23A20375 and 62075151)the National Key Research and Development Program of China(Grant No.202103021223042).
文摘The principle of optical time-domain reflection localization limits the sensing spatial resolution of Raman distributed optical fiber sensing.We provide a solution for a Raman distributed optical fiber sensing system with kilometer-level sensing distance and submeter spatial resolution.Based on this,we propose a Raman distributed optical fiber sensing scheme based on chaotic pulse cluster demodulation.Chaotic pulse clusters are used as the probe signal,in preference to conventional pulsed or chaotic single-pulse lasers.Furthermore,the accurate positioning of the temperature variety region along the sensing fiber can be realized using chaotic pulse clusters.The proposed demodulation scheme can enhance the signal-to-noise ratio by improving the correlation between the chaotic reference and the chaotic Raman anti-Stokes scattering signals.The experiment achieved a sensing spatial resolution of 30 cm at a distributed temperature-sensing distance of∼6.0 km.Furthermore,we explored the influence of chaotic pulse width and detector bandwidth on the sensing spatial resolution.In addition,the theoretical experiments proved that the sensing spatial resolution in the proposed scheme was independent of the pulse width and sensing distance.
基金Supported by the Scientific Research and Technology Development Project of Petrochina Southwest Oil and Gas Field Company(20230307-02)。
文摘The distributed fiber optic sensing system,known for its high sensitivity and wide-ranging measurement capabilities,has been widely used in monitoring underground gas pipelines.It primarily serves to perceive vibration signals induced by external events and to effectively provide early warnings of potential intrusion activities.Due to the complexity and diversity of external intrusion events,traditional deep learning methods can achieve event recognition with an average accuracy exceeding 90%.However,these methods rely on large-scale datasets,leading to significant time and labor costs during the data collection process.Additionally,traditional methods perform poorly when faced with the scarcity of low-frequency event samples,making it challenging to address these rare occurrences.To address this issue,this paper proposes a small-sample learning model based on triplet learning for intrusion event recognition.The model employs a 6-way 20-shot support set configuration and utilizes the KNN clustering algorithm to assess the model's performance.Experimental results indicate that the model achieves an average accuracy of 91.6%,further validating the superior performance of the triplet learning model in classifying external intrusion events.Compared to traditional methods,this approach not only effectively reduces the dependence on large-scale datasets but also better addresses the classification of low-frequency event samples,demonstrating significant application potential.
基金supports for this research were provided by the National Natural Science Foundation of China(No.12272301,12002278,U1906233)the Guangdong Basic and Applied Basic Research Foundation,China(Nos.2023A1515011970,2024A1515010256)+1 种基金the Dalian City Supports Innovation and Entrepreneurship Projects for High-Level Talents,China(2021RD16)the Key R&D Project of CSCEC,China(No.CSCEC-2020-Z-4).
文摘Fiber-reinforced composites are an ideal material for the lightweight design of aerospace structures. Especially in recent years, with the rapid development of composite additive manufacturing technology, the design optimization of variable stiffness of fiber-reinforced composite laminates has attracted widespread attention from scholars and industry. In these aerospace composite structures, numerous cutout panels and shells serve as access points for maintaining electrical, fuel, and hydraulic systems. The traditional fiber-reinforced composite laminate subtractive drilling manufacturing inevitably faces the problems of interlayer delamination, fiber fracture, and burr of the laminate. Continuous fiber additive manufacturing technology offers the potential for integrated design optimization and manufacturing with high structural performance. Considering the integration of design and manufacturability in continuous fiber additive manufacturing, the paper proposes linear and nonlinear filtering strategies based on the Normal Distribution Fiber Optimization (NDFO) material interpolation scheme to overcome the challenge of discrete fiber optimization results, which are difficult to apply directly to continuous fiber additive manufacturing. With minimizing structural compliance as the objective function, the proposed approach provides a strategy to achieve continuity of discrete fiber paths in the variable stiffness design optimization of composite laminates with regular and irregular holes. In the variable stiffness design optimization model, the number of candidate fiber laying angles in the NDFO material interpolation scheme is considered as design variable. The sensitivity information of structural compliance with respect to the number of candidate fiber laying angles is obtained using the analytical sensitivity analysis method. Based on the proposed variable stiffness design optimization method for complex perforated composite laminates, the numerical examples consider the variable stiffness design optimization of typical non-perforated and perforated composite laminates with circular, square, and irregular holes, and systematically discuss the number of candidate discrete fiber laying angles, discrete fiber continuous filtering strategies, and filter radius on structural compliance, continuity, and manufacturability. The optimized discrete fiber angles of variable stiffness laminates are converted into continuous fiber laying paths using a streamlined process for continuous fiber additive manufacturing. Meanwhile, the optimized non-perforated and perforated MBB beams after discrete fiber continuous treatment, are manufactured using continuous fiber co-extrusion additive manufacturing technology to verify the effectiveness of the variable stiffness fiber optimization framework proposed in this paper.
基金supported by the Swiss National Science Foundation through the project 200021-134546the Swiss State Secretariat for Education,Research and Innovation(SERI)through the project COST C10.0093.
文摘Distributed fiber sensing possesses the unique ability to measure the distributed profile of an environmental quantity along many tens of kilometers with spatial resolutions in the meter or even centimeter scale.This feature enables distributed sensors to provide a large number of resolved points using a single optical fiber.However,in current systems,this number has remained constrained to a few hundreds of thousands due to the finite signal-to-noise ratio(SNR)of the measurements,which imposes significant challenges in the development of more performing sensors.Here,we propose and experimentally demonstrate an ultimately optimized distributed fiber sensor capable of resolving 2100000 independent points,which corresponds to a one-orderof-magnitude improvement compared to the state-of-the-art.Using a Brillouin distributed fiber sensor based on phase-modulation correlation-domain analysis combined with temporal gating of the pump and time-domain acquisition,a spatial resolution of 8.3 mm is demonstrated over a distance of 17.5 km.The sensor design addresses the most relevant factors impacting the SNR and the performance of medium-to-long range sensors as well as of sub-meter spatial resolution schemes.This step record in the number of resolved points could be reached due to two theoretical models proposed and experimentally validated in this study:one model describes the spatial resolution of the system and its relation with the sampling interval,and the other describes the amplitude response of the sensor,providing an accurate estimation of the SNR of the measurements.
基金The authors thank the EPSRC and Innovate UK for funding this research through the Cambridge Centre for Smart Infrastructure and Construction(CSIC)Innovation and Knowledge Centre(EPSRC grand reference number EP/L010917/1)We thank Professor Kenichi Soga(UC Berkeley)for providing valuable input to this research.We would also like to acknowledge the contribution of Angus Cameron from Environmental Scientifics Group.
文摘In this paper,we present an application of distributed fiber optic sensor(DFOS)technology to measure the strain of a continuous flight auger(CFA)test pile with a central reinforcement bar bundle,during a static load test carried out in London.Being distributed in nature,DFOS gives much more information about the pile performance as compared to traditional point sensors,such as identifying cross-sectional irregularities or other anomalies.The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation(contraction),shaft friction,and tip resistance under various loads.Based on this pile load test,a finite element(FE)analysis was performed using a one-dimensional nonlinear load-transfer model.Calibrated by the shaft friction and tip resistance derived from the monitored data,the FE model was able to simulate the pile and soil performance during the load testing with good accuracy.The effect of the reinforcement cage and central reinforcement bar bundle were investigated,and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%.
基金This work was supported by National Basic Research Program of China(973 Program)under Grant No.2010CB327803 and National Natural Science Foundation of China(61027617).
文摘Brillouin scattering based optical fiber sensors(BOFS)have the unique advantages over other sensors such as long distance,fully distributed,and multi-parameter sensing.The progresses on the development of BOFS technology in Nanjing University are reviewed.The key technologies to make BOFS with ultra-long distance,high spatial resolution,and fast measuring speed are discussed and realized.
基金Project supported by the Innovation Program of Education Commission of Shanghai Municipality (Grant No.10YZ19)the Shanghai Leading Academic Discipline Project (Grant No.S30108)the Shanghai Key Laboratory of Specialty Fiber Optics and Optical Access Networks (Grant No.SKLSFO200903)
文摘A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.
文摘Multicore fiber(MCF)which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light transmission in multiple spatial channels.Different from the situation in standard single mode fiber(SMF),the fiber bending gives rise to tangential strain in off-center cores,and this unique feature has been employed for directional bending and shape sensing,where strain measurement is achieved by using either fiber Bragg gratings(FBGs),optical frequency-domain reflectometry(OFDR)or Brillouin distributed sensing technique.On the other hand,the parallel spatial cores enable space-division multiplexed(SDM)system configuration that allows for the multiplexing of multiple distributed sensing techniques.As a result,multi-parameter sensing or performance enhanced sensing can be achieved by using MCF.In this paper,we review the research progress in MCF based distributed fiber sensors.Brief introductions of MCF and the multiplexing/de-multiplexing methods are presented.The bending sensitivity of off-center cores is analyzed.Curvature and shape sensing,as well as various SDM distributed sensing using MCF are summarized,and the working principles of diverse MCF sensors are discussed.Finally,we present the challenges and prospects of MCF for distributed sensing applications.
基金supported by the National Natural Science Foundation of China under Grant No. 60608009Science Foundation of Zhejiang Province under Grant No. Y107091 and ScienceTechnology Department of Zhejiang Province under Grant No. 2008C21172.
文摘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.
基金supported by the 34th Research Institute of CETC Funding(Grant No.K134002021S604)the New Technology Research University Cooperation Project of the 34th Research Institute of CETC(Grant No.2021-1200-05-001900).
文摘Presented here is long-range distributed vibration sensing based on internal-modulation optical frequency domain reflectometry(OFDR).In the proposed system with internal modulation,a silicon-based photonic-chip laser is used as the laser source,and by controlling the output voltage curve of an arbitrary waveform generator to induce temperature change in the external cavity of the laser,a 10-GHz optical frequency tuning range is achieved.The complexity of the proposed internal-modulation system is lower than that of the traditional external-modulation OFDR system that combines a narrow-linewidth laser with a single-sideband modulator to achieve wavelength tuning.Cross-correlation analysis is used as a sensing mechanism to evaluate the similarity between Rayleigh scatter signals and to achieve vibration event localization.Experimental comparison is made of the vibration sensing performance of the external-and internal-modulation systems,and for a vibration event generated at a distance of 100.95 km,they locate it with a sensing spatial resolution of 43.0 m and 16.8 m,respectively.The results indicates that the proposed distributed vibration sensing based on internal modulation has better sensing performance and lower complexity compared to the traditional external-modulation system.In addition,the proposed system is single-ended and involves no optical amplification,which makes it very suitable for ultra-long-range sensing.
基金the funding support from Alpha Foundation for the Improvement of Mine Safety and Health Inc.(ALPHAFOUNDATION,Grant No.AFC820-52)。
文摘Underground mine pillars provide natural stability to the mine area,allowing safe operations for workers and machinery.Extensive prior research has been conducted to understand pillar failure mechanics and design safe pillar layouts.However,limited studies(mostly based on empirical field observation and small-scale laboratory tests)have considered pillar-support interactions under monotonic loading conditions for the design of pillar-support systems.This study used a series of large-scale laboratory compression tests on porous limestone blocks to analyze rock and support behavior at a sufficiently large scale(specimens with edge length of 0.5 m)for incorporation of actual support elements,with consideration of different w/h ratios.Both unsupported and supported(grouted rebar rockbolt and wire mesh)tests were conducted,and the surface deformations of the specimens were monitored using three-dimensional(3D)digital image correlation(DIC).Rockbolts instrumented with distributed fiber optic strain sensors were used to study rockbolt strain distribution,load mobilization,and localized deformation at different w/h ratios.Both axial and bending strains were observed in the rockbolts,which became more prominent in the post-peak region of the stress-strain curve.
