Matthias Fabian

Fiber Bragg Grating-Based System for 2-D Analysis of Vibrational Modes of a Steel Propeller Blade

This paper reports results obtained using fiber Bragg grating (FBG)-based sensors to investigate the displacement mode shapes of a cantilevered steel propeller blade, using FBG arrays for vibration monitoring for the first time. The experimental data obtained are cross compared with those from a finite element analysis of the same blade, undertaken using proprietary software. In the experimental configuration used, a network of gratings, forming a series of sensor arrays, was mounted on the blade under study to monitor its bending modes, while a further set was mounted perpendicular to this array to monitor torsional modes. To obtain the shape of the strain modes generated in the blade at specific frequencies, the dynamic response of the FBG arrays, as a function of time, was captured and then processed using Fourier transform algorithms to show the natural frequencies of the blade. As a result, the displacement modes shapes for the bending, torsional, and coupled modes of the first nine natural frequencies of the plate were obtained. The experimental data show very good agreement with theoretical analysis. This paper demonstrates the potential of using the lightweight, minimally invasive sensing technique described for the analysis of propeller blades and, thus, illustrating an effective method to overcome the deleterious effects of propellers seen in some commercial propeller designs.

Novel Sensor Design Using Photonic Crystal Fibres for Monitoring the Onset of Corrosion in Reinforced Concrete Structures

In this paper, a novel sensing technique has been designed and investigated for the direct, in situ detection of steel corrosion distributed in reinforced concrete structures. At present, structural health monitoring in reinforced concrete structures is generally focused on monitoring the corrosion risk of the reinforcing steel. It is of significant importance, however, to inform industry of both the onset of corrosion and the corrosion rate as these are key contributors to structural degradation and thus evaluating the service life of the structures. This paper aims to address the above challenges by describing a novel corrosion sensor design using birefringent photonic crystal fibres. The technique exploits fully both the birefringence of the fibres for force/pressure measurement and their very low temperature sensitivity to detect the onset of corrosion. This new type of sensor not only determines the onset of corrosion but also allows for better monitoring along the length of a reinforcement bar.

Underwater Free-Vibration Analysis of Full-Scale Marine Propeller Using a Fiber Bragg Grating-Based Sensor System

A detailed experimentally-based study has been carried out on instrumented, full-scale marine propeller blades in order to investigate their vibration behaviour, both in air and underwater. To obtain data with minimum perturbation to the characteristics of the blades, a fiber Bragg grating-based sensor network system was designed and implemented, for the first time. The individual vibration frequencies at each measurement point and thus the broader vibration patterns seen for each of the blades were obtained, with excitation both in air and in water and the results are compared favourably with those obtained from finite-element analysis. The vibration patterns obtained show that the same modes of vibration occur in air and in water, although in some natural frequencies, the mode order is seen to change from one blade to another on the same propeller. The extensive performance survey carried out and experimental data obtained have also shown that while the effect of the added mass of water on the natural frequencies of the blades in the fundamental modes is considerable, this effect diminishes as the natural frequencies of the blades increase. The results obtained from the optical fiber sensor network were compared with those from previous work in this area using different and less satisfactory techniques and it was confirmed that the ratio of the natural frequencies in water to those in air increases in a linear manner as the frequencies were increasing. In addition, the natural frequencies of a blade were measured under different depths of propeller immersion.

Transverse force sensitivity of joint photonic crystal fibres

Further to the previous investigation of four types of photonic crystal fibres (PCFs) for their respective force/pressure sensitivity and the conclusion made that the PCF with lower birefringence demonstrates higher force/pressure sensitivity, this work is focused on the investigation of the pressure/force sensitivities of any two joint PCFs when they are fusion-spliced together. To obtain an optimum output, a polarization controller is used in a fibre loop mirror configuration to ensure two joint PCFs having the same birefringence angle. The results obtained show that the sensitivity of the joint fibres is lower than that of a single PCF with low and medium birefringence but more sensitive than that of a single PCF with high birefringence.

Vibration measurement of electrical machines using integrated fibre Bragg gratings

In this paper a method to track the rotating force vector set up within the air-gap of radial flux rotating electrical machines using fibre Bragg gratings is reported. The proposed technique offers the potential for simultaneous rotor speed and position monitoring. This specific sensor design, together with other FBG-based multi-parameter measurements, is aimed to create an all-optical sensor solution for electrical machines, reducing the component count of existing systems and addressing noise issues traditionally associated with electrical sensors used. In this work, an optical fibre sensor system has been successfully integrated into an off-the-shelf four-pole 11kW induction motor.

Reinforced concrete structural corrosion monitoring using Hi-Bi photonic crystal fibres in a fiber loop structure

A novel sensing approach has been developed for in-situ corrosion monitoring of steel in reinforced concrete structures, using a fibre loop interferometer sensor system based on a Hi-Bi photonic crystal fibre (PCF). To do so an accurate fibre alignment procedure has been implemented in order to improve the performance of the sensor system embedded into the concrete structure when it is subjected to an accelerated corrosion test. The positive results obtained have confirmed the effectiveness of such a sensor system for applications in structural health monitoring.

Comprehensive Monitoring of Electrical Machine Parameters Using an Integrated Fiber Bragg Grating-Based Sensor System

In this paper, a multiparameter, multisensor system for comprehensive electrical machine condition monitoring has been developed and the results of an evaluation reported. The fiber Bragg grating-based system developed allows for the simultaneous monitoring of key parameters including machine vibration, rotor speed, torque, spin direction, temperature distribution along the stator windings and on the rotor surface as well as the stator wave frequency. This all-optical sensing solution has been designed to be compatible with being fitted in the tight confines of an electric motor and uses the optical nature of the measurement and the insulating nature of the sensor material to avoid problems of electrical interference. The system reduces the component count over conventional sensor systems, i.e., all sensing elements are contained within the machine and operated by a single sensing interrogation unit, thereby reducing cost and allowing for a convenient interface for the user. The design of the system is presented, as are results on the testing and evaluation of the device the sensing system has been successfully integrated into and tested on a permanent magnet motor prototype.

Use of DIC and AE for Monitoring Effective Strain and Debonding in FRP and FRCM-Retrofitted RC Beams

AbstractThe effective strain in composites, along with their potential rupture and debonding, plays a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams. However, only limited experimental data on these phenomena are available, mainly because of the inadequacy of traditional deformation and strain measurement techniques. This paper presents a comparative analysis of instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials, FRPs (fiber-reinforced polymers), and FRCMs (fiber-reinforced cementitious mortars). It also considers strain gauges, fiber Bragg grating (FBG) sensors, LVDTs, digital image correlation (DIC), and acoustic emission (AE) sensors for monitoring strain, displacement, cracking, and debonding. Experiments on six beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring is shown to match the perf...

A temperature compensated fibre Bragg grating (FBG)-based sensor system for condition monitoring of electrified railway pantograph

This paper presents the results obtained from fibre Bragg grating (FBG) sensors integrated into a railway current-collecting pantograph for accurate measurement of contact force and contact location when it is subjected to various temperature conditions. The temperature change of the pantograph is simulated, at the industrial laboratory of Brecknell Willis in the UK, by changing the DC current applied to pantograph from 0 to 1500 A. This test is primarily designed to verify the effectiveness of the temperature compensation mechanism built in the FBG sensor design. For this verification, 3 thermocouples co-located with the FBG sensor packages are used to measure the temperature change seen from 25 °C to 55 °C. The tests were repeated several times and the sensor system has shown its temperature-independence, confirming that the intrinsic cross-sensitivity of FBGs to temperature variation for strain measurement has been fully compensated through the use of this innovative sensor design and data processing.

Optical fibre sensing: A solution for industry

Optical fibres have been explored widely for their sensing capability to meet increasing industrial needs, building on their success in telecommunications. This paper provides a review of research activities at City University of London in response to industrial challenges through the development of a range of fibre Bragg grating (FBG)-based sensors for transportation structural monitoring. For marine propellers, arrays of FBGs mapped onto the surface of propeller blades allow for capturing vibrational modes, with reference to simulation data. The research funded by EU Cleansky programme enables the development of self-sensing electric motor drives to support ‘More Electric Aircraft’ concept. The partnership with Faiveley Brecknell Willis in the UK enables the integration of FBG sensors into the railway current-collecting pantographs for real-time condition monitoring when they are operating under 25kV conditions.