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A method is described using optical fiber technology to measure the vibration characteristics of long slender structures subjected to dynamic disturbances imposed by water or wind generated loads. The method is based on making bending strain measurements at selected locations along the length of lon

A method is described using optical fiber technology to measure the vibration characteristics of long slender structures subjected to dynamic disturbances imposed by water or wind generated loads. The method is based on making bending strain measurements at selected locations along the length of long slender structures such as marine risers or large ropes using fiber optics technology including Optical Time Domain Reflectometry and Bragg diffraction gratings. Engineering interpretation of information obtained from bending strains determines the vibration characteristics including frequency, amplitude, and wave length. Maximum bending strain measurements assess pending structural damage. One application is measurement of vortex induced vibrations (VIV) response of marine risers. The fiber optics based method is also applicable to the measurement of the bending characteristics of spoolable pipe using plastic optical fibers which can be interpreted to assess the pipe structural integrity and to prevent lock-up during deployment into a small diameter annulus.

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What is claimed is: 1. A method for determining the vibration characteristics of long slender structures using maximum bending strain measurements of said long slender structures subjected to dynamic disturbances imposed by water or wind generated dynamic loads, otherwise known as vortex induced vi

What is claimed is: 1. A method for determining the vibration characteristics of long slender structures using maximum bending strain measurements of said long slender structures subjected to dynamic disturbances imposed by water or wind generated dynamic loads, otherwise known as vortex induced vibrations (VIV), comprising: projecting laser light into a single or plurality of independent optical fiber(s) fastened at discrete locations along the longitudinal axis of said long slender structure; reflecting said projected laser light from optical reflective interfaces placed at discrete length segments along the length of each optical fiber in turn creating a reflected laser light data signal; collecting through a fiber optics or electronic data transmission link said reflected laser data signal; receiving and analyzing said collected laser light data signal at electronic optical signal monitoring instrumentation; determining critical bending strains within said discrete length segments along the length of said long slender structure; and calculating at least one of said vibration characteristics of said long slender structure from the determined critical bending strains in order to permit mitigation of damaging effects caused by VIV along said long slender structure through the use of corrective action. 2. The method of claim 1, wherein vibration characteristics include: vibration frequency, vibration amplitude, node-to-node wavelength, and the magnitude of the imposed peak bending strains. 3. The method of claim 1, further comprising: locating the optical fiber(s) along the longitudinal axis and near the exterior or interior surface of said long slender structure. 4. The method of claim 1, further comprising: locating the optical fiber(s) at opposite ends of an imaginary line drawn perpendicular to the longitudinal axis of said long slender structure and through said long slender structure centroid thereby enabling the measurement of said critical bending strains imposed during dynamic loading. 5. The method of claim 1, further comprising: locating multiple sets of longitudinally oriented optical fibers on said long slender structure near opposite ends of an imaginary line drawn perpendicular to the longitudinal axis of said long slender structure and through said long slender structures centroid designed to capture the maximum bending strains imposed during dynamic loading. 6. The method of claim 1, used to measure said bending strains imposed by VIV experienced by metal or composite production and drilling risers, tubing, ropes, and cables deployed in offshore operations in the oil industry. 7. The method of claim 1, further comprising: providing said calculated vibration characteristic information to offshore petroleum drilling and production operations; and using said calculated vibration characteristic information to permit mitigation of potentially damaging effects of VIV in said long slender structure by the adjustment of the axial tension in said long slender structure and the addition of strakes, shrouds, and fairings to said long slender structure. 8. The method of claim 1, wherein said electronic optical signal monitoring instrumentation is capable of measuring the time of flight of light reflected from said optical interfaces; using said time of flight information to determine said critical bending strains. 9. The method of claim 8, wherein said electronic optical signal monitoring instrumentation is optical time domain reflectometry instrumentation. 10. The method of claim 1, wherein said electronic optical signal monitoring instrumentation is optical frequency domain reflectometry instrumentation. 11. The method of claim 1, further comprising: positioning said optical fiber(s) along the longitudinal axis of said long slender structure so as to traverse back and forth between opposite ends of said discrete length segments of said long slender structure along said longitudinal axis to provide greater sensitivity to the measurement of said critical bending strains through the use of time of flight instrumentation. 12. The method of claim 1, wherein the electronic optical signal monitoring instrumentation measures said critical bending strains using Bragg diffraction gratings. 13. The method of claim 1, further comprising: rigidly attaching said optical fiber(s) to the exterior or interior surface of a metal or composite tubular within said long slender structure using a bonding agent; and protecting said rigidly attached optical fiber(s) from damage by hazards imposed in the operating environment by a polymeric or elastomeric external layer. 14. The method of claim 1, wherein said optical fiber(s) used to measure said critical bending strains are constructed of glass or plastic. 15. The method of claim 1, wherein said long slender structures are either a rope or cable; said determined bending strains and said calculated at least one vibration characteristic provide information needed to take action to permit mitigation of the potentially damaging effects of wind or water generated dynamic disturbances. 16. A method for measuring the bending and buckling characteristics of spoolable metal or composite pipe subjected to axial compressive loading during injection into a small diameter annulus, comprising: projecting laser light into a single or plurality of independent optical fiber(s) fastened at discrete locations along the longitudinal axis of said spoolable metal or composite pipe; reflecting said projected laser light from optical reflective interfaces placed at discrete length segments along the length of each optical fiber in turn creating a reflected laser light data signal; collecting through a fiber optics or electronic data transmission link said reflected laser data signal; receiving and analyzing said collected laser light data signal at electronic optical signal monitoring instrumentation; determining critical bending strains within said discrete length segments along the length of said spoolable metal or composite pipe; and calculating at least one bending and buckling characteristic of said spoolable metal or composite pipe from the determined critical bending strains to allow for corrective action to be taken to prevent helical buckling lock-up of said spoolable metal or composite pipe in said small diameter annulus. 17. The method of claim 16, further comprising: locating the optical fiber(s) at opposite ends of an imaginary line drawn perpendicular to the longitudinal axis of said spoolable metal or composite pipe and through said spoolable metal or composite pipe centroid thereby enabling the measurement of said critical bending strains imposed during injection of said spoolable metal or composite pipe into said small diameter annulus. 18. The method of claim 16, further comprising: locating multiple sets of longitudinally oriented optical fibers on said spoolable metal or composite pipe near opposite ends of an imaginary line drawn perpendicular to the longitudinal axis of said spoolable metal or composite pipe and through said spoolable metal or composite pipe centroid designed to capture the maximum bending strains imposed during injection of said spoolable metal or composite pipe into said small diameter annulus. 19. The method of claim 16, further comprising: measuring said critical bending strain in said spoolable metal or composite pipe as said spoolable metal or composite pipe buckles into numerous short wavelength spiral and helical buckles inside said small diameter annulus in response to an axial compressive force imposed to push the spoolable pipe into the annulus by a coiled tubing injector or other injection apparatus. 20. The method of claim 16, further comprising: providing said bending and buckling characteristic information to petroleum drilling and production operations; and using said calculated bending and buckling characteristic information to prevent said spoolable metal or composite pipe from entering a condition of lock-up inside said small diameter annulus by reducing the applied axial compression force to said spoolable metal or composite pipe. 21. The method of claim 16, wherein said electronic optical signal monitoring instrumentation is optical time domain reflectometry strain instrumentation. 22. The method of claim 16, wherein said electronic optical signal monitoring instrumentation is optical frequency domain reflectometry strain instrumentation. 23. The method of claim 16, wherein said electronic optical signal monitoring instrumentation is Bragg diffraction grating strain measurement instrumentation. 24. The method of claim 16, further comprising: positioning said optical fiber(s) along the longitudinal axis of said spoolable metal or composite pipe so as to traverse back and forth between opposite ends of said discrete length segments of said spoolable metal or composite pipe along said longitudinal axis to provide greater sensitivity to the measurement of said critical bending strains through the use of time of flight instrumentation. 25. The method of claim 16, further comprising: rigidly attaching said optical fiber(s) to the exterior or interior surface of said spoolable metal or composite pipe using a bonding agent; and protecting said rigidly attached optical fiber(s) from damage by hazards imposed in the operating environment by a polymeric or elastomeric external layer. 26. The method of claim 16, further comprising: locating the optical fiber(s) along the longitudinal axis and near the exterior or interior surface of said spoolable metal or composite pipes. 27. The method of claim 16, further comprising: integrating said optical fiber(s) into the interior of said spoolable metal or composite pipe following said spoolable metal or composite pipe fabrication; said optical fiber integration method comprising: inserting a cylindrical foil carrier consisting of an outer layer of adhesive; attaching said optical fibers longitudinally into said foil carrier; pressurizing the interior of said foil carrier with a hot fluid or gas in order to cure said adhesive to bond said foil carrier to said spoolable metal or composite pipe. 28. The method of claim 16, further comprising: integrating said optical fiber(s) into the body of said spoolable metal or composite pipe during manufacture. 29. The method of claim 16, further comprising: carrying out said critical bending strain measurements of said spoolable metal or composite pipe in a region of deployment onto and off of a storage spool; providing said measured critical bending strain information in order to asses the structural integrity of the spoolable metal or composite pipe.