Review of Fiber Optic Sensors for Structural Fire Engineering

Reliable and accurate measurements of temperature and strain in structures subjected to fire can be difficult to obtain using traditional sensing technologies based on electrical signals. Fiber optic sensors, which are based on light signals, solve many of the problems of monitoring structures in high temperature environments; however, they present their own challenges. This paper, which is intended for structural engineers new to fiber optic sensors, reviews various fiber optic sensors that have been used to make measurements in structure fires, including the sensing principles, fabrication, key characteristics, and recently-reported applications. Three categories of fiber optic sensors are reviewed: Grating-based sensors, interferometer sensors, and distributed sensors

Sensing Applications in Aircrafts Using Polymer Optical Fibres

We report on recent advances in the use of inexpensive polymer optical fibres (POFs) for sensing applications in avionics. The sensors analysed in this manuscript take advantage of the unique properties of polymers, such as high flexibility, elasticity, and sensitivity, and they range from strain, elongation, and vibration interrogators to level and temperature meters, leading to cost-effective techniques for structural health monitoring in aircraft structures. We also highlight recent power-supply methods using Power-over-POF in order to feed sensors remotely, and we discuss the constraints imposed by connectors on the performance of POF networks in aircrafts

Advances in structural analysis and process monitoring of thermoplastic composite pipes.

Thermoplastic composite pipes (TCP) in comparison to other pipes have proven beneficial features due to its flexibility which includes being fit for purpose, lightweight and no corrosion. However, during the manufacturing of TCP which involves the consolidation process, certain defects may be induced in it because of certain parameters, and this can affect the performance of the pipe in the long run as the induced defects might lead to in-service defects. Current techniques used in the industry are facing challenges with on-the-spot detection in a continuous manufacturing system. In TCP manufacturing process, the pipe is regularly monitored. When a defect is noticed, the whole process stops, and the appropriate action is taken. However, shutting down the process is costly; hence it is vital to decrease the downtime during manufacturing to the barest minimum. The solutions include optimizing the process for reduction in the manufacturing defects amount and thoroughly understanding the effect of parameters which causes certain defect types in the pipe. This review covers the current state-of-the-art and challenges associated with characterizing the identified manufacturing induced defects in TCP. It discusses and describes all effective consolidation monitoring strategy for early detection of these defects during manufacturing through the application of suitable sensing technology that is compatible with the TCP. It can be deduced that there is a correlation between manufacturing process to the performance of the final part and selection of characterization technique as well as optimizing process parameters

Contributions to the development of distributed sensors based on stimulated Brillouin scattering

RESUMEN: El objetivo principal de esta tesis es contribuir al desarrollo y la mejora del rendimiento de los sensores distribuidos basados en la dispersión Brillouin. Durante el desarrollo de este trabajo se han considerado diferentes áreas de mejora. En primer lugar, se han propuesto diversas configuraciones experimentales para superar algunas de las limitaciones típicas que tienen estos sensores, como son los efectos no locales en los sensores BOTDA o la aparición de sub-picos en el espectro de ganancia de Brillouin en sistemas basados en el dominio de frecuencia. Otro objetivo principal de este trabajo es aplicar diferentes enfoques de procesado para resolver problemáticas aún no resueltas, como la discriminación entre las medidas de temperatura y las de deformación obtenidas con los sensores Brillouin. Además, también se han estudiado algunos métodos alternativos al método tradicional basado en la aplicación de ajustes Lorentzianos para estimar el cambio de la frecuencia Brillouin. Finalmente, este trabajo también ha tratado de contribuir a la validación de los conocimientos adquiridos mediante la validación en escenarios reales, como aplicaciones de alta temperatura o detección de fugas en tuberías.ABSTRACT: The main objective of this thesis dissertation is to contribute to the development and improvement in the performance of distributed sensors based on Brillouin scattering. Different areas of improvement have been considered during the development of this work. First of all, various different experimental configurations have been proposed to overcome some traditional limitations of these sensors, such as non-local effects on Brillouin optical time domain analysis (BOTDA) sensors or appearance of sub-peaks on the Brillouin gain measured with systems based on the frequency domain. Another main objective of this work is applying different processing approaches in an attempt to solve open problems such as the discrimination between temperature and strain measurements obtained with Brillouin sensors. Additionally, it would be interesting to provide some faster and alternative methods to estimate the Brillouin shift in comparison to traditional method based on applying Lorentzian fittings. Finally, this work has also tried to contribute to the validation of the acquired knowledge by performing validations in real scenarios, such as high-temperature applications or leakage detection in pipelines.This work has been supported by the funding of the following entities and actions: • Universidad de Cantabria through the research grant Programa de Personal Investigador en Formación Predoctoral and research stays grants in Pamplona, Spain and in Aversa, Italy. • Agencia Estatal de Investigación through research project Sensores fotónicos para seguirdad y protección (TEC2016-76021-C2-2-R). • Ministerio de Economía y Competitividad through research project Sensores de fibra óptica para seguirdad y protección (TEC2013-47264-C2-1-R). • Gobierno de Cantabria through research project Detección de fugas en autovías del agua mediante sensores ópticos (FASO). • Fundación TTI through a research grant Patrocinio de actividades formativas en investigación científica y técnica. • Cost action td1001: Novel and reliable optical fibre sensor systems for future security and safety applications (OFSESA) through a research grant for a short term scientific mission to Aversa, Italy and through two grants for summer schools

Dual-wavelength speckle-based SI-POF sensor for cost-effective detection of microvibrations

In this work, a novel method for cost-effective remote sensing of microvibrations is presented. The proposed technique detects periodical changes in the spatial distribution of energy on the speckle pattern at the endface of a SI-POF. By employing a dual-wavelength approach it is possible to increase the system sensitivity without changing its maximum mean squared error, which increases the system accuracy as well as its resolution. The system operates in reflective configuration providing a centralized interrogation scheme. The speckle pattern of both wavelengths is demultiplexed at the fiber end before being directly recorded by an off-the-shelf and a cost-effective webcam. The changes in the intensity distribution are processed at the remote interrogation unit. The proposed system is able to detect instantaneous and periodic microvibrations (with amplitudes ranging from 1 to 6 mu m) localized farther than 9 m from the remote interrogation unit.This work was supported in part by the Spanish Ministry of Economy and in part by the European Union Development Fund under grant TEC2015-63826-C3-2-R (MINECO/FEDER), and in part by the Comunidad de Madrid under grant S2013/MIT-2790

Assessment of fiber Bragg grating sensors for monitoring shaft vibrations of hydraulic turbines

The structural dynamic response of hydraulic turbines needs to be continuously monitored to predict incipient failures and avoid catastrophic breakdowns. Current methods based on traditional off-board vibration sensors mounted on fixed components do not permit inferring loads induced on rotating parts with enough accuracy. Therefore, the present paper assesses the performance of fiber Bragg grating sensors to measure the vibrations induced on a rotating shaft–disc assembly partially submerged in water resembling a hydraulic turbine rotor. An innovative mounting procedure for installing the sensors is developed and tested, which consists of machining a thin groove along a shaft line to embed a fiber-optic array that can pass through the bearings. At the top of the shaft, a rotary joint is used to extract, in real time, the signals to the interrogator. The shaft strain distribution is measured with high spatial resolution at different rotating speeds in air and water. From this, the natural frequencies, damping ratios, and their associated mode shapes are quantified at different operating conditions. Additionally, the change induced in the modes of vibration by the rotation effects is well captured. All in all, these results validate the suitability of this new fiber-optic technology for such applications and its overall better performance in terms of sensitivity and spatial resolution relative to traditional equipment. The next steps will consist of testing this new sensing technology in actual full-scale hydraulic turbines.This work was supported by the funding received from the European Union’s Horizon H2020 research and innovation program (grant agreement no: 814958) and by the I+D+i project SYNERGY PID2020-118310RBI00 funded by the MCIN/AEI/10.13039/501100011033.Peer ReviewedPostprint (published version