Eight re-configurable, synchronized resonant cavity time-division- multiplexed FBG sensor interrogators provide 16,800 high-resolution measurements-per-second from 280 axially embedded strain sensors, for the analysis of vortex-shedding-induced vibration and bending in a composite oil riser pipe

Bennion, Ian

Everall, Lorna A.

Lloyd, Glynn D.

Sugden, Kate

English

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Re-configurable multi-channel high-speed FBG strain sensing system for vibration analysis in oil risers

Eight re-configurable, synchronized resonant cavity time-division-multiplexed FBG sensor interrogators provide 16,800 high-resolution measurements-per-second from 280 axially embedded strain sensors, for the analysis of vortex-shedding-induced vibration and bending in a composite oil riser pipe

Lloyd, G.D.

Everall, L.A.

Sugden, K.

Bennion, I.

Coventry University Pure Portal

Re-configurable, multi-channel, high-speed FBG strain sensing system for vibration analysis in oil risers

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PROCEEDINGS OF SPIESPIEDigitalLibrary.org/conference-proceedings-of-spieRe-configurable multi-channel high-speed FBG strain sensing system forvibration analysis in oil risersGlynn D. Lloyd, Lorna A. Everall, Kate Sugden, IanBennionGlynn D. Lloyd, Lorna A. Everall, Kate Sugden, Ian Bennion, "Re-configurablemulti-channel high-speed FBG strain sensing system for vibration analysis inoil risers," Proc. SPIE 5855, 17th International Conference on Optical FibreSensors,  (23 May 2005); doi: 10.1117/12.623801Event: 17th International Conference on Optical Fibre Sensors, 2005, Bruges,BelgiumDownloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 08 Nov 2019  Terms of Use: https://www.spiedigitallibrary.org/terms-of-useRe-configurable, multi-channel, high-speed FBG strain sensing systemfor vibration analysis in oil risersGlynn D. Lloyd*a, Lorna A. Everalla, Kate Sugdenb, Ian BennionbaInsensys Limited, 6 & 7 Compass Point, Hamble, Southampton, Hampshire, SO31 4RA, UKbPhotonics Research Group, Aston University, Aston Triangle, Birmingham, B4 7ET, UKABSTRACTEight re-configurable, synchronized resonant cavity time-division-multiplexed FBG sensor interrogators provide 16,800high-resolution measurements-per-second from 280 axially embedded strain sensors, for the analysis of vortex-shedding-induced vibration and bending in a composite oil riser pipe.Keywords: Resonant cavity, time-division-multiplexing, FBG strain sensing, vibration analysis1. INTRODUCTIONThe use of fiber Bragg gratings (FBGs) for the embedded strain sensing of composite materials is well established andhas been the focus of numerous review papers [1, 2]. For many ‘smart-structures’ fewer than twenty strain sensors areneeded and the interrogation rate can be just a few Hertz, but some reported systems have employed much higherinterrogation frequencies for vibration analysis. In this paper the authors report the development of a multi-channelresonant cavity time-division-multiplexed (TDM) FBG strain measurement system for analysis of the vibration andbending induced in a vertically oriented, composite, oil riser pipe.Vibration and bending in oil risers results from vortex shedding, which is created by the strong marine currents presentin locations where the pipes are deployed. The exact nature of this resonance, and its consequences, are exceedinglycomplex and so the construction and verification of mathematical models to predict this behavior requires the collectionof experimental data.To collect such data a model riser pipe was manufactured in glass-fiber composite and was fitted with numerousembedded FBG strain sensors. This was then attached to a ‘sinker’ weight and towed vertically through the sea at arange of controlled velocities to simulate real marine conditions. During this towing the reported strain measurementsystem was employed in numerous software-selectable interrogation modes to collect extensive strain data. This datawas subsequently processed to produce crucial vibration and curvature information for mathematical model verification.2. SYSTEM CONFIGURATIONThe modes of oscillation and resonance of a riser pipe can occur both across and in the direction of the dominant marinecurrent, and can also vary considerably in frequency and amplitude, and with depth. Therefore, sensors were required atshort intervals along the full length of the pipe and at multiple locations around the circumference. Additionally, due tothe high level of induced strain from self-weight and deployment, coupled with the criterion for full vibration andcurvature data, each of the sensors was required to deliver absolute strain measurement with high resolution, across alarge strain range.Figure 1 shows the composite pipe and the position of eight separate fiber sensor arrays. Each array contained 35identical FBG sensors, which were embedded into the model pipe during its manufacture. The fibers were orientated at45° intervals around the circumference, such that sensors from each fiber were co-located at equal spacing in the axialdirection. The sensors were manufactured in singlemode fiber and were all of 4% reflectivity, with a nominal zero-strain central wavelength of 1550nm.* Email: glynn.lloyd@insensys.com; Tel: +44 2380 604300; Fax: +44 2380 604301; Website: www.insensys.com17th International Conference on Optical Fibre Sensors, Marc Voet, Reinhardt Willsch,Wolfgang Ecke, Julian Jones, Brian Culshaw, eds., Proceedings of SPIE Vol. 5855(SPIE, Bellingham, WA, 2005) · 0277-786X/05/$15 · doi: 10.1117/12.623801218Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 08 Nov 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-useFigure 1. A schematic of the composite riser pipe showing the location of the 280 FBG strain sensorsTo accurately resolve the curvature and vibration information into both direction and magnitude it was crucial that themeasurement from each sensor was accurately timed and deterministic. In particular, to minimize uncertainty error inthe bending analysis, it was highly preferential to provide simultaneous measurement of each set of co-located sensors(i.e. those located at the same position with respect to length along the pipe).To achieve this criterion with microsecond timing precision each sensor array was connected to a separate resonantcavity TDM interrogator and then all eight interrogators were hardware synchronized to the output signal from aseparate synchronizer board. The actual circuit configuration for a single interrogator is shown in Figure 2. This wassimilar to that presented in our previous work [3, 4], but in this instance a diffractive element spectrometer was used inpreference to the ratiometric filter. The use of this resonant cavity architecture provided numerous advantages in termsof both performance and cost, which included:• The ability to interrogate 35 sensors per fiber, with a full 10,000sensing range for each sensor• A high sensing resolution per sensor of <3, with low signal noise of <4(RMS)• A very high interrogation rate of 2,100 measurements per second (per interrogator)The use of identical, low reflectivity ‘commodity’ sensors also provided considerable cost savings, since this removedthe requirement for bespoke array design, allowed the use of through-coating grating fabrication and enabled simplersystem deployment.A further inherent advantage of the resonant cavity TDM interrogation technique was an ability to easily re-configurethe sensor configuration, on a per-test basis, to match the changing data requirements of the research; by simpleadjustment of software controls on a graphical user interface the sensor configuration could be changed from using asingle sensor (per array) at an interrogation rate of 2,100 Hz per sensor, through to measurement of all 280 sensors at arate of 60 Hz per sensor.Figure 2. An overview of a single resonant cavity TDM FBG sensor interrogator8 axially embedded fibreslocated at 45° intervalsaround the circumferenceComposite oil riser pipeEach fibres contains 35 sensors thatare co-located at equal intervalsalong the pipes lengthProgrammablepulse generatorHigh speedSOA driver01100111SOAFibreRear ReflectorCoupler100mFBG SensorsSpectrometerSpectrometerinterfaceEmbedded control systemSystem address and data busUSBSyncProc. of SPIE Vol. 5855     219Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 08 Nov 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-useFigure 3 shows the electrical and optical configuration for the complete sensor system. The 8 sensor arrays are shownconnected to 8 interrogators, which were then connected in pairs to 4 single board computers (SBCs) via a USBinterface. The SBCs were loaded with an embedded Linux operating system and communicated with a Windows-basedgraphical host PC via a local TCP/IP Ethernet network. Also connected to the network was the hardware synchronizerunit, which was constructed from a low-cost, 8-bit micro-controller.Figure 3. An overview of the complete interrogation system, showing the eight synchronized resonant cavityinterrogators, the networked single board computers and the eight FBG arrays (each containing 35 identical,low-reflectivity sensors)Figure 4 shows an internal and external view of the completed interrogation system, which was mounted into a 19”cabinet enclosure and connected to the model riser pipe using a multi-way waterproof optical connector.The complete interrogator system was housed in a standard 19” instrument rack8 arrays of 35sensorsUSBLinux SBCUSBUSBLinux SBCUSBUSBLinux SBCUSBUSBLinux SBCUSBWindows host PC8 resonant cavityinterrogatorsMicro-controllerbased synchroniser4 networked singleboard computersEthernethubSync220     Proc. of SPIE Vol. 5855Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 08 Nov 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-useFigure 4. Photographs showing, (a) the internal and (b the external view of the complete interrogation system,when mounted in the 19” rack enclosure3. CONCLUSIONThe time-division-multiplexing of 280 identical wavelength, low reflectivity, low-cost FBG sensors using multiplehardware-synchronized resonant cavity interrogators has been used to provide precisely timed, high speed, simultaneousstrain measurement across 8 separate fiber channels, for the analysis of vibration and bending in oil riser pipes.By providing versatile control software and using all-solid-state interrogators that were capable of delivering acombined 16,800 measurements per second, tailoring of the sensor configuration from just eight active sensorsinterrogated at 2,100Hz, through to the measurement of all 280 sensors at 60Hz each, was possible without anycompromise on the 10,000strain range and micro-strain resolution of each sensor.ACKNOWLEDGEMENTSThe authors would like to acknowledge their colleagues at Insensys Limited for their valuable contributions to thiswork. Glynn Lloyd would like to thank UK EPSRC for partially funding his work.REFERENCES1 A. D. Kersey, M. A. Devis, H. J. Patrick, M. LeBlanc, K. P. Koo, C. G. Askins, M. A. Putnam and E. J. Friebele,“Fiber grating sensors”, J. Lightwave Technol., vol.15, 1997, pp.1442-14632 K. Lau, L. Yuan, L. Zhou, J. Wu, C. Woo, ‘Strain monitoring in FRP laminates and concrete beams using FBGsensors’, Composite Structures, vol.51, 2001, pp.9-203 G. D. Lloyd, L. A. Everall, K. Sugden and I. Bennion, “Resonant cavity time-division-mulitplexed fibre Bragg gratingsensor interrogator”, IEEE Photon. Technol. Lett., vol.16, no.10, 2004, pp.2323-23254 G. D. Lloyd, L. A. Everall, K. Sugden and I. Bennion, “Resonant cavity based fibre Bragg grating sensor interrogationusing ratiometric detection”, Opt. Commun. (in press)Proc. of SPIE Vol. 5855     221Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 08 Nov 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use

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Re-configurable, multi-channel, high-speed FBG strain sensing system for vibration analysis in oil risers

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