Fiber Optic Measurement Research Articles

Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 2. Measurement of shape

Optical fibre strain and shape measurement sensors were deployed on a rotor blade during a full-speed helicopter ground run, with real-time data wirelessly streamed from rotor hub-mounted sensor interrogators. In part 2 of a 2-part paper series, two-dimensional direct fibre-optic shape sensing (DFOSS), using fibre segment interferometry-based interrogation is investigated. The concept of blade shape change visualisation over one rotation period using rotation displacement surfaces is introduced and the usefulness of DFOSS data to gain additional insights by determining operational modal frequencies independently for both horizontal and vertical vibration directions of the blade is demonstrated.

Research on the performance of a fiber optical current transformer for high voltage filtering capacitor unbalanced current measurement

Subject of study. A fiber-optic measurement scheme for the unbalanced current of a high-voltage filtering capacitor is proposed, where an all-fiber temperature sensor based on temperature birefringence is presented to realize the real-time correction of temperature errors. Method. Prototypes of an all-fiber filter unbalanced fiber optical current transformer type and a magneto-optical crystal type with a rated current of 1 A and a rated voltage of 258 kV have been developed and performance tested. Main results. After temperature correction, the accuracy of the all-fiber filter unbalanced fiber optical current transformer type in the range of −40∘C to 70°C meets the error limit requirements of class 0.2 specified in the Chinese Standard GB/T 20840.8-2007 (Instrument transformers—Part 8: Electronic current transformers standard), whose accuracy, integration, reliability, and anti-interference ability are better than the magneto-optical crystal type. The proposed scheme has the ability of small current (less than 20 mA) measurement in high voltage (more than 110 kV) scenarios.

Thermo‐mechanical experiments on reinforced concrete beams: Assessing thermal, mechanical, and mixed impacts on fiber optic measurements

AbstractStrain and temperature measurements on reinforced concrete structures with Rayleigh‐based fiber optic sensors (FOS) promise dense data networks of crucial structural parameters. In this context, the measurement of temperature and mechanical strain is invariably intertwined, precipitating in a frequency shift recorded via FOS. Consecutive experiments were carried out on reinforced concrete beams under mechanical, thermal, and thermo‐mechanical loading. Basic analysis of fiber optics equations indicates the sensitivities toward both influences. These are quantified and juxtaposed in experiments, first separately and subsequently combined. As concerns temperature measurement, the slightest tensile forces exerted onto the FOS may engender distortions of several degrees Celsius. Conversely, strain measurements are affected by temperature changes to a lesser degree. Nevertheless, the level of strain to be sensed and the severity of corrupting temperature shifts must be carefully weighted. The article raises awareness for the coupling of temperature and strain and enables the practitioner to identify and assess perturbations.

Design Framework and Laboratory Experiments for Helix and Slinky Type Ground Source Heat Exchangers for Retrofitting Projects

The focus of the experimental work was on shallow spiral geothermal heat exchanger configurations. Real-scale experiments were carried out for vertically oriented spiral collectors (helix) in sand and soil. One objective was to develop a measurement concept in laboratory environment to create a framework for a validated database. This database serves as the basis for further and new development of engineering design tools. To achieve the highest possible data-point density in the observed environment, temperature sensors and a fiber-optic temperature measurement system (DTS) were used. Soil probes were taken in situ before and after the measurements and analyzed at a thermophysical laboratory to determine material properties. The heat flow was controlled by an electric heating cable, which was installed in the form of a spiral-shaped heat exchanger in a 1 m³ container. To guarantee constant boundary conditions, the measurements were carried out in a climate chamber at a defined ambient temperature. The evaluation of the transient response behavior is spatially resolved. The results are coordinate-based temperature points, which describe temperature gradients in all axes of the container over time, which are combined with known soil properties. The collected data was used to develop computational fluid dynamic (CFD) models, which are used to extend the variety of geometry and soil configurations for developing new design tools.

Experimental methods in chemical engineering: Optical fibre probes in multiphase systems

AbstractAs much as 75% of the raw materials in the chemical industry and 50% of consumer products are in the form of powders or granular solids. Gasification, pyrolysis, coating, granulation, drying, and mixing are examples of processes in which particles contact fluids. Researchers examine the hydrodynamics of these fluid–solid systems with pressure signals, acoustics, tomography, radioactive particle tracking, optical fibre measurements, and spectroscopy. Among these techniques, fibre optic probes are simple, inexpensive, and sensitive (spatial resolution of 100 μm) and have sampling frequencies of Hz. Optical probes measure local hydrodynamic properties, including particle velocity, solids fraction, and voids, which are difficult to measure in heterogeneous systems like spouted beds, risers, and turbulent fluidized beds. Light from a fibre optic bundle illuminates a specific volume, and fibres from the same or separate bundle return the reflected or transmitted photons to a detector (visible, near‐infrared spectroscopy, or Raman). Sample MATLAB codes included herein together with sample experimental data demonstrate how to process raw signals for gas/solids/and bubble holdup, particle and bubble velocity, bubble size, and solids flux.

Impacts of Micro-Deviations of Aperture on the Characteristics of Collision Atomization Field

As the final flow channel of the liquid rocket engine, the manufacturing of impinging atomization nozzles has become a critical link in the manufacture of impinging atomization components. At present, the high-precision machining of millimeter nozzles in large-scale production is quite difficult, which inevitably leads to the diversity of internal flow field and atomization field parameters. In this investigation, the influence of the diameter deviation of impinging nozzles on the atomization field is analyzed by experiment. The transparent nozzle is installed in a typical colliding atomizer. The ultra-precision measurement is carried out by the optical fiber measurement system and the flow field in the nozzle is visualized. The information of atomized droplets in the atomization field is assembled by the laser interferometric particle imaging technology (IPI). The experimental results indicate that the micro-deviations of the collision aperture have a profound influence on the cavitation state of the flow field in the nozzles and the atomization characteristics (droplet diameter and atomization cone angle) of the atomization field.

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