STRUCTURE MONITORING
First Claim
1. A method of monitoring the position of a structure using an optical fiber distributed acoustic sensor deployed in a known relationship with respect to the structure such that a known part of the optical fiber corresponds to a known part of the structure, the method comprising:
- using the optical fiber as a distributed acoustic sensor to detect, at a plurality of acoustic sensor positions along the fibre, acoustic signals emitted by a plurality of acoustic sources deployed at known positions in an area in which the structure to be monitored is located;
calculating relative positions of a plurality of the acoustic sensors in dependence on the detected acoustic signals from the acoustic sources; and
from the calculated positions of the sensors along the fibre, determining a shape, or shape and position, of the structure in dependence on the known relationship between the fiber and the structure.
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Accused Products
Abstract
A method and apparatus for monitoring a structure using an optical fiber based distributed acoustic sensor (DAS) extending along the length of the structure. The DAS is able to resolve a separate acoustic signal with a spatial resolution of 1 m along the length of the fibre, and hence is able to operate with an acoustic positioning system to determine the position of the riser with the same spatial resolution. In addition, the fiber can at the same time also detect much lower frequency mechanical vibrations in the riser, for example such as resonant mode vibrations induced by movement in the surrounding medium. By using vibration detection in combination with acoustic positioning then overall structure shape monitoring can be undertaken, which is useful for vortex induced vibration (VIV) visualisation, fatigue analysis, and a variety of other advanced purposes. The structure may be a sub-sea riser.
76 Citations
20 Claims
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1. A method of monitoring the position of a structure using an optical fiber distributed acoustic sensor deployed in a known relationship with respect to the structure such that a known part of the optical fiber corresponds to a known part of the structure, the method comprising:
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using the optical fiber as a distributed acoustic sensor to detect, at a plurality of acoustic sensor positions along the fibre, acoustic signals emitted by a plurality of acoustic sources deployed at known positions in an area in which the structure to be monitored is located; calculating relative positions of a plurality of the acoustic sensors in dependence on the detected acoustic signals from the acoustic sources; and from the calculated positions of the sensors along the fibre, determining a shape, or shape and position, of the structure in dependence on the known relationship between the fiber and the structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14)
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11. A method according to claim 11, wherein the passive acoustic monitoring comprises detecting acoustic events having an energy greater than a predetermined energy threshold.
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15. A system for monitoring the position of a structure, comprising:
an optical fiber distributed acoustic sensor system deployed in a known relationship with respect to the structure such that a known part of the optical fiber corresponds to a known part of the structure, the sensor system further comprising a processor arranged to perform the following; i) use the optical fiber as a distributed acoustic sensor to detect, at a plurality of acoustic sensor positions along the fibre, acoustic signals emitted by a plurality of acoustic sources deployed at known positions in an area in which the structure to be monitored is located; ii) calculate relative positions of a plurality of the acoustic sensors in dependence on the detected acoustic signals from the acoustic sources; and iii) from the calculated positions of the sensors along the fibre, determine a shape, or shape and position, of the structure in dependence on the known relationship between the fiber and the structure. - View Dependent Claims (16, 17, 18, 19, 20)
Specification