Fiber Optic Measurement Research Articles

Feasibility and Error Analysis of Using Fiber Optic Temperature Measurement Device to Evaluate the Electromagnetic Safety of Hot Bridge Wire EEDs.

Most studies assessing the safety of hot bridge wire EEDs employ temperature sensors that directly use the measurements of the temperature measurement device without analyzing the accuracy of the temperature measurement. This study establishes the response function of the exposed bridge and exposed bridge temperature rise system of hot bridge wire EEDs through the Rosenthal’s temperature rise equation and Laplace transformation as well as experimental tests, and through the response function, the response law and numerical characteristics of the two are compared and analyzed under four typical excitations. Under steady current injection and continuous-wave radiation, both exposed bridge and exposed bridge temperature measurement systems can reach thermal equilibrium, and the equilibrium temperature of both are the same. However, under pulse excitation, the temperature rise measurement value is significantly different from the actual value due to the large difference in response time of the exposed bridge (1 ms) and the exposed bridge temperature measurement device (0.82 s). Studies have shown that under steady current injection and continuous-wave radiation, temperature rise measurements can be directly applied to the safety assessment of hot bridge wire EEDs, while under pulsed conditions, temperature rise measurements cannot be directly applied.

Possibilities of using fiber-optic sensors in the study of oil and gas wells

With an increase in the accuracy of fiber-optic sensors, the possibility of their use in various fields is being formed. In this article, the authors present their own experience in the implementation of fiber-optic technologies in geophysical surveys of wells, indicate current problems and prospects for the development of this direction in the region of activity. Since 2014, LLC “PITC Geofizika” has been actively developing the direction of fiber-optic temperature measurement systems. To date, these are measurements in more than 40 wells (15 wells are being measured at present time). As a result, we can say that today there is already a certain niche in the basket of the geophysical sector, confidently occupied with fiber-optic sensors technologies, but the prospects for the development of this technology are significant and are fully revealed only in the process of work. However, it is worth approaching the implementation of this method only with a complete understanding of the processes occurring in the well.

Optical fiber measurement of local strains in a ribbed bar

AbstractRibbed bars are known for their enhanced bond to concrete. Their ribs make bar section variable along the axis and the strain profile is variable as well, under any given applied force. Such variable strain profile has not been measured so far, thus the stress profile and its effect on the global behavior of the bar cannot be determined. Though optical fibers are an effective means to measure the strains in structural members, their application to the study of bond behavior is still in its infancy. Such an application is the objective of this research project. Specially manufactured partly smooth and partly ribbed bars with optical fibers were tested in pure tension (bare bars) and in the pullout from concrete to investigate the strain profile variability. In the bare bars, the strain measured in the smooth part was constant (as expected), while in the ribbed part higher strains were measured but no localized effects were detected, and the location of the ribs was not identified. Similar behavior was obtained by 3D finite‐element analysis, which merely yielded slight ups and downs at ribs' locations, with an average strain that is similar to the measured strain. However, in the pull‐out tests, the strains were constant in the unbonded smooth part and exhibited an undulating profile in the bonded ribbed part, where the peaks were related to the locations of the ribs. Such promising results motivate further studies to improve the resolution of the proposed technique.

Study on the Law of Influence of Seepage Field Anomalies on Displacement Field Induced by Leakage of Enclosure Structure

The leakage of an enclosure structure will cause abnormal changes in the seepage flow field, which in turn can lead to the deformation of the enclosure structure and affect the surrounding geotechnical body. In this paper, a fiber-optic temperature measurement system is used to detect the location of the seepage points in a station of the Qingdao subway during open pit excavation, and the abnormal variation of the seepage field caused by the seepage points is obtained by numerical calculation and field measurement. Then, numerical simulation is performed to analyze the effects of seepage field anomalies on the deformation of the enclosure structure and surface settlement. It is found that the seepage flow caused by the leakage point has a significant influence on the surface settlement and the deformation of the enclosure structure. With the increase of excavation depth, the deformation of the enclosure structure increases and the maximum deformation position shifts downward. The deformation of the enclosure structure decreases when the leakage point exists. The surface volume also increases gradually with the excavation, and the maximum surface settlement position shifts outward significantly. The settlement range becomes larger when the leakage point exists.

Using Thermal Monitoring and Fibre Optic Measurements to Verify Numerical Models, Soil Parameters and to Determine the Impact of the Implemented Investment on Neighbouring Structures

Numerical modelling using Finite Element Method (FEM) is currently a standard procedure for engineering complex structures and determining structure–subsoil cooperation conditions. It is used for, among others, forecasting displacements, which are the calculation results most easily verified. Numerical modelling is also used to identify the impact on neighbouring structures and design a monitoring system and determine expected values, e.g., displacements. A numerical model enables one to optimally design the monitoring system for a facility under construction and the neighbouring structures through selecting a measurement technology, matching the scope of obtained results or choosing sensor and measurement point locations. The implemented monitoring may be based on various technologies, from thermal monitoring, laser scanning, fibre optic measurements, to classic surveying measurements. The walls must protect the soil from excessive displacement and protect the excavation against groundwater inflow. If the wall is not watertight, deepening the excavation may cause a sudden water inflow. Leak and erosion process thermal monitoring is a proven leak detection method. It is based on the tests utilizing heat and water transfer process relations, which are coupled processes. Another tool for verifying numerical models is the installation of DFOS (Distributed Fibre Optic Sensors) at the stage of executing structural elements (e.g., diaphragm walls, barrettes, foundation slab). It allows one to permanently monitor both temperature and displacements during element execution (concrete curing), and following facility construction and operation stages. The paper presents methods for designing selected monitoring elements of engineering objects, based on calculations using the Finite Element Method. The verification of numerical models, based on data obtained from DFOS, classic surveying measurements and thermal monitoring, is also presented.

An Application of Fiber-Optic Temperature Measurement for Groundwater Behavior Monitoring at Underground Petroleum Stockpiling Base

水封方式による地下石油備蓄基地では，岩盤タンクの周辺に安定した地下水の存在が要求されることから，地下水位は重要な監視項目である。串木野国家石油備蓄基地において，水位観測孔の1孔で地下水位が大きく変化したため，原因調査を行った。水位観測孔には，孔を保護するための塩化ビニル製の有孔管が設置され，有孔管の中には水位計等の監視機器がある。このため孔内環境を乱さない状態で調査が可能な光ファイバを用いた温度検層を実施した。その結果，地下水の流入・流出箇所および水位変化の主たる要因を推定することができ，他の調査結果と整合的であったことから，光ファイバ温度検層は有効な手段であることが分かった。

Fibre optic measurements and model uncertainty quantification for Fe-SMA strengthened concrete structures

This investigation aimed at studying a novel strengthening method using ribbed memory-steel bars by means of quasi-static load experiments and computational modelling of large-scale concrete members in flexure. The first part of the study focussed on the strain in activated and non-activated memory-steel bars measured with a distributed fibre optic measurement system during external loading of strengthened slabs. In the second part, a computational cross-section analysis model was developed and enhanced with two uncertainty quantification methods: sensitivity analysis and Bayesian model calibration.The distributed fibre optic strain measurements enabled detailed monitoring of the peak strains owing to concrete cracking. The strain data was post-processed to obtain axial stress and bond shear stress in proximity to the largest bending crack. The sensitivity analysis provided the relative importance of the calibrated input parameters and their interdependencies. Model calibration quantified the uncertain parameters such as prestress, concrete parameters, and memory-steel constitutive laws, resulting in good accordance between the model and the experiments. The models were validated by independent strain measurements. Parametric studies enabled prediction of the effects of the investigated strengthening method on similar concrete members with different prestress, materials and geometries.

Load Transfer On Bored Pile Foundation Instrumented With Fiber Optic And Concrete Quality Analysis

The problem in the construction method of the bored pile is the contamination of mud or the other contaminant that can cause the modulus of elasticity of concrete to decrease. This research determines the modulus of concrete on a bored pile foundation instrumented with fiber-optic (FO) with a manual calculation based on strain data during loading test, validated with the results of research in the laboratory and numerical analysis. Fiber optic was used to measure the strain along with the pile during the loading test. The bored pile foundation is divided into 12 segments with the same strain characteristics, and then the modulus value is calculated. The result is the modulus value of each segment is different, and the value of the modulus changes along with the increase in strain; the modulus will decrease as the strain increases. This differs from the theory that the modulus has a fixed value approximated by empirical equations. Made a cylindrical concrete sample on both sides, which installed a FO to record the strain during the loading test. The result is true that the modulus is not constant but decreases as the strain increases. It is shown in the result of analysis to fiber-optic measurement data. Created a model in Plaxis2D for validation, and the results are not much different from the manual calculation.

Application of fiber optic measurement in textile‐reinforced concrete testing

AbstractIn research on concrete constructions, fiber optic sensor technology is becoming increasingly important. It enables high‐frequency and quasi‐continuous measurement of temperature and strain distribution. Furthermore, this technology offers the opportunity to determine the crack width within the cross section of specimens and not, as with conventional instrumentation, only from the outside. While experience for application of fiber sensors in steel‐reinforced concrete research already exists for several years, only few findings are available for textile‐reinforced concrete (TRC). This article gives a short overview of the principle of fiber optic sensor technology, presents possible concepts for utilization in TRC testing, and explains the necessary post‐processing steps for the preparation of the measurement results by means of an example from current research. Finally, the results are validated with conventional measuring methods and the applicability and further challenges are discussed.

Diamond protection for reusable ZnO coated fiber-optic measurement head in optoelectrochemical investigation of bisphenol A

Due to the global problem with plastic contaminating the environment, with bisphenol A (BPA) being one of the highest demand, effective monitoring and purification of the pollutants are required. The electrochemical methods constitute a good solution but, due to polymerization of electrochemical oxidation bisphenol A products and their adsorption to the surfaces, measurement head elements are clogged by the formed film. In this research, we propose a nanocrystalline diamond sheet protection for securing elements in direct contact with bisphenol A during electrochemical processes. The solution was presented on the example of a zinc oxide (ZnO) coating deposited on a fiber-optic end-face by Atomic Layer Deposition. Series of optical and electrochemical measurements were performed in a dedicated hybrid setup. The results show that ZnO can be modified during the electrochemistry leading to the drastic change of its properties. Such degradation did not show in case of nanocrystalline diamond sheet-protected sample proving the solution’s effectiveness, giving a possibility of re-using the measurement element and prolonging its lifespan.

Assessing the reliability of the cargo deck of a hovercraft through fiber optic strain measurements

While traditional sensing systems can suffer from low spatial sampling density and often face significant operational challenges in the maritime environments routinely experienced by naval craft, fiber optics provide a distributed sensing solution that is insensitive to many of these environmental stressors. Through the use of fiber optic sensing systems, strain data was collected along the cargo deck of two naval hovercraft during various maneuvers and loading conditions. This work presents a methodology for translating those strain measurements into deflection estimates, and ultimately reliability analyses, through optimization and analytical modeling tools. Specifically, by treating the cargo deck of the hovercraft as a large, thin plate, direct relationships between strain, bending curvature, and deflection can be reliably established. Comparisons of probability distributions of maximum absolute deflections experienced during set maneuvers and loading conditions reveal differences in the response between the two craft. These differences are further explored in the context of reliability indices based on limit deflections.

Multipoint Bending Measurement Using Multicore Fiber Bragg Grating and Two-Photon Absorption Process in Si-APD

We propose and demonstrate a fiber optic multi-point bending measurement system that uses Bragg gratings inscribed along a multi-core fiber (MCF) and a silicon avalanche photodiode (Si-APD) that produces two-photon absorption (TPA) photocurrent for 1.55- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> light. Because the TPA photocurrent from the Si-APD is proportional to the mean square of the optical intensity, the intensity correlation between 1.55- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> probe and reference beams is measured from it without using complex electrical circuits. The proposed system has different lengths of optical fibers between each core of MCF and input/output ends of a single mode fiber optic system, which makes different the correlation signal between the reference beam and the probe beam reflected from different Bragg gratings in MCF. That enables the reflection spectra of all the Bragg gratings in MCF to be separately measured even when they are overlapped in the wavelength domain. As a result, the bending radius and its direction are measured without using multiple detectors or optical switching devices. We conducted proof-of-concept experiments by using a 7-core MCF with almost the same Bragg gratings inscribed in each core at three points along the fiber. We also demonstrated an example of application to shape measurement.

Improving Distributed Fiber-Optic Sensor Measures by Digital Image Correlation: Two-Stage Structural Health Monitoring

Improving Distributed Fiber-Optic Sensor Measures by Digital Image Correlation: Two-Stage Structural Health Monitoring

Examination of Influence of Molding Conditions on Mold Temperature and Strain by Optical Fiber Measurement

Examination of Influence of Molding Conditions on Mold Temperature and Strain by Optical Fiber Measurement

Absolute spectral backscatter measurements of large-core multimode PMMA polymer optical fibers.

To our knowledge, we are the first to measure the absolute value of the backscattering coefficient of a standard 1 mm core-diameter, multimode (MM) step-index (SI) polymethylmethacrylate (PMMA) polymer optical fiber (POF) for the spectral range of 450 nm to 700 nm. Our optical time domain reflectometer (OTDR) setup consists of a femtosecond supercontinuum laser with an acousto-optical filter as a tunable light source with short pulses and a time-correlated single-photon counting system as a receiver with a high dynamic range. The backscattering coefficient is calculated from the ratio between the energy within the fiber end reflex and the distributed backscattering level. We also measured the spectral attenuation with our OTDR setup and compared it with a standardized measurement method. At the attenuation minima within the measured spectral range the backscattering level of a 1 ns pulse is about -46dB at 520 nm, -48dB at 570 nm, and -51 dB at 650 nm. We were also able to show by the observed wavelength dependence that Rayleigh scattering causes a majority of the scattering.

Comparison of Intra Abdominal Pressure Monitoring Techniques and the Effects of the Abdominal Compartment Syndrome

Background: Abdominal compartment syndrome (ACS) is a life-threatening condition that develops in the setting of increasing and uncontrolled intra-abdominal hypertension (IAH), leading to cardiovascular, respiratory, neurologic and/or renal dysfunction. Aims: To establish a porcine model for the evaluation of the effects of IAH on renal blood flow (RBF) and to determine if IVC pressure and/or Camino fiberoptic direct intraabdominal pressure measurements can accurately predict IAPs that have been derived using bladder pressure measurements. Methods: Abdominal laparotomy, placement of IAP and RBF measuring devices, and fascial closure were performed on six adult feeder pigs with a mean body weight of 25 +/- 5 kg. A Transonic Doppler flow probe, a suprapubic bladder catheter, a Camino fiberoptic probe, and a triple lumen central venous catheter were placed and then baseline measurements were taken of renal blood flow, bladder pressure, direct intra-peritoneal Camino pressure and IVC pressure, respectively. Normal saline was then infused into the abdomen to simulate increasing IAP. Following a 5–10-minute stabilization period, all measurements were again taken. Results: The correlation between IVC pressure and bladder pressure was 0.98, with a mean bias of -0.5 (SD 2.0; 95% CI: -0.9, -0.2). The correlation between direct IAP readings by Camino probe and bladder pressure was 0.91, with a mean bias of -3.9 (SD 4.3; 95% CI: -4.6, -3.2). There was a strong negative correlation (-0.95) between RBF and bladder pressure. At an IAP of 20 mmHg, RBF reduced by an average of 45.4% (95% CI: 40%, 50.8%). Upon abdominal decompression, RBF returned to 66.6% (95% CI: 54.3%, 78.9%) of its baseline value. Conclusions: A porcine model is effective in accurately measuring changes in real time RBF. RBF progressively declines as IAP increases, however upon decompression, it fails to achieve complete recovery. IVC pressure measurements correlate well with, and therefore may substitute, the gold standard bladder pressure measurements as representatives of IAP. Keywords: Abdominal Compartment syndrome, renal blood flow, intrabdominal hypertension, bladder pressure

Fiber optic pressure measurement on a complex outer winglet model with active flow control actuators

The next generation of aircraft requires novel approaches on lift increase and drag reduction technologies as active flow control to counter local flow separations. Testing and monitoring its effectiveness in flight require precise pressure evaluation as a possible control input. Pressure-based measurements of local flow separation are challenging utilizing conventional electrical pressure sensors. These sensors might show degradation of their long-term performance in harsh environments, e. g., in real aircraft applications, due to their low overload protection, susceptibility to electromagnetic influences, and corrosion. Fiber optic measurements overcome those challenges and promise to be a robust sensing solution. We investigate the potential application of a novel fiber optic measurement system that monitors the active flow control system's effectiveness. Furthermore, the results are compared to conventional static pressure measurements. Due to the high-frequency capabilities of the fiber optic sensors, the dynamic behavior of the boundary layer separation and vortex generation was captured in the frequency domain. An industry-relevant outer wing was equipped with 25 fiber optic pressure sensors positioned at one wingspan section for this experiment. The experiments were conducted at a Reynolds number Re=1.1⋅106and a Mach number Ma=0.12. Wind tunnel testing results show that fiber optic pressure sensors can measure aerodynamic characteristics and, furthermore, even allow a detailed look at the dynamic behavior.

Evaluation of depth-wise post-gel polymerisation shrinkage behaviour of flowable dental composites

Short fibre reinforced flowable dental composites are gaining acceptance over particulate filled composites due to their competence to impart improved physio-mechanical properties and capability to prevent crack propagation. However, limited research exists to assess their overall post-gel shrinkage behaviour, which is an important factor to determine marginal seal around restoration and hence its longevity. In this paper, depth-wise post-gel shrinkage strain and the resulting factors such as degree of conversion and rheological behaviour of flowable fibre reinforced composite (FRC) containing 5% weight fraction of 5 μm diameter, 350 μm length S-Glass fibres in UDMA/TEGDMA mixture along with 50% strontium filler particles were investigated. Post-gel shrinkage strain was measured using an array of optical fibre Bragg grating sensors (FBGs) of diameter 250 μm and length 1 mm each embedded at three different depths (depth 0 mm, depth 2.5 mm and depth 5 mm from curing light tip) within the flowable dental composite samples. The rheological behaviour during the polymerisation process was carried out using dynamic oscillatory tests. To evaluate the conversion of CC during polymerisation, degree of conversion tests were conducted by using FTIR spectroscopy. The results obtained for FRC samples were further compared with that of particulate filled composite (PFC) samples, with 55% strontium filler particles only within the same resin system. The relationship between post-gel shrinkage strain at different depths, rheological behaviour and degree of conversion was also explored.The experimental results from the sensor embedded materials suggested that the post-gel shrinkage strain was higher at the top surface (depth 0 mm) and was 50% more than at the bottom surface (depth of 5 mm) for dental FRC as well as PFC samples. Further, similar flow behaviour and not significant different (p<0.05) degree of conversion (DC), post-gel shrinkage strain for dental PFC and FRC composites was observed, establishing a convincing positive relationship between all the key factors and further implying that replacement of fibres with fillers did not affect the overall post-gel polymerisation shrinkage behaviour in dental composites. This investigation has also demonstrated that fibre optic sensors-based shrinkage measurements can be an ideal technique to evaluate post-gel shrinkage performance of dental resins with PFCs or FRCs.

Numerical and Experimental Investigation of Temperature Distribution for Dry-Clutches

The temperature rise of the engaging clutch during shifting depends heavily on the transmitted torque. Precisely estimating the clutch temperature not only improves clutch control but also the optimal design of the clutch. However, the contact surface of the friction lining is closed, and the surface temperature is often difficult to measure accurately. In this study, a theoretical model of a two-dimensional transient temperature field for the friction disc has been established. In the radial and axial directions under different launching conditions, the temperature field of a friction disc is investigated. Four stages of clutch engagement have been determined, and finite-element analysis has been used to study the temperature field of a single clutch and to determine its duration.Then, the latest internationally developed distributed optical fiber sensing technology is used to perform measurement tests on the designed dry clutch friction characteristic test rig. The distributed fiber-optic temperature measurement technology can accomplish accurate temperature measurement with fast response speed and can acquire temperature value on different radii of friction discs with high spatial resolution. Such temperature sensing technology is very suitable for clutch working conditions. By analyzing the simulation and experimental results of temperature variation of different radii, different working conditions and different components, an important reference is provided for the establishment of the clutch temperature model and the optimization of the clutch heat dissipation structure design.

Damage Detection at a Reinforced Concrete Specimen with Coda Wave Interferometry.

Reinforced concrete is a widely used construction material in the building industry. With the increasing age of structures and higher loads there is an immense demand for structural health monitoring of built infrastructure. Coda wave interferometry is a possible candidate for damage detection in concrete whose applicability is demonstrated in this study. The technology is based on a correlation evaluation of two ultrasonic signals. In this study, two ways of processing the correlation data for damage detection are compared. The coda wave measurement data are obtained from a four-point bending test at a reinforced concrete specimen that is also instrumented with fibre optic strain measurements. The used ultrasonic signals have a central frequency of 60 kHz which is a significant difference to previous studies. The experiment shows that the coda wave interferometry has a high sensitivity for developing cracks and by solving an inverse problem even multiple cracks can be distinguished. A further specialty of this study is the use of finite elements for solving a diffusion problem which is needed to state the previously mentioned inverse problem for damage localization.