Fibre Optic Cable Sensing Segmented Strength Member
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Solution Overview
Problem
Conventional fibre optic cable structures used for coherent Rayleigh distributed fibre optic sensing are limited by tensile loads during deployment and operating conditions, such as hydrostatic pressure, which restrict the sensitivity of the optical fibre to detectable changes in optical path length, especially in environments like underwater deployments.
Innovation Solution
A fibre optic cable structure with a cable core fixedly coupled to a longitudinal strength member at periodic points, allowing the cable core to be substantially tension-free between these points, with the strength member taking the load of deployment and pressure, ensuring the optical fibre can freely respond to stimuli without pre-existing tension, enhancing sensitivity to both longitudinal and transverse stimuli.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fibre optic cable structures are used for COTDR sensing, then the cable can be deployed in various environments, but the tensile load and hydrostatic pressure restrict the sensitivity of the optical fibre to detectable changes in optical path length
Solution Approach 1:
The cable core is divided into segments that are periodically fixed to the strength member, creating discrete coupling points. This segmentation allows the cable core to be tension-free between coupling points while maintaining overall structural integrity through the periodic anchoring to the strength member.
Solution Approach 2:
The strength member acts as an intermediary element that carries the tensile load and hydrostatic pressure, protecting the optical fibre in the cable core from these forces. The strength member is periodically coupled to the cable core, allowing it to bear the mechanical loads while enabling the optical fibre to respond freely to stimuli.
2Stability of the object's composition
If the optical fibre is under pre-existing tension from deployment, then the cable structure is stable, but the optical fibre cannot freely respond to stimuli such as acoustic and elastic waves
Solution Approach 1:
By segmenting the coupling between the cable core and strength member into periodic points, the system achieves stability through the anchored segments while allowing the intermediate portions to move freely in response to stimuli, thus maintaining both structural stability and sensing sensitivity.
Solution Approach 2:
The system changes the mechanical state of the optical fibre from a tensioned state during deployment to a tension-free state during operation. The periodic coupling configuration allows the cable core to be slack between coupling points, enabling the optical fibre to respond freely to acoustic and elastic waves without pre-existing tension.
3Measurement precision
If standard fibre optic cables are used, then costs are reduced and existing cables can be reused, but the sensitivity for detecting acoustic and elastic waves is limited
Solution Approach 1:
The strength member serves multiple functions: it provides structural support, carries tensile loads, protects the optical fibre from hydrostatic pressure, and enables the cable to be deployed in various environments. This multi-functionality enhances sensing sensitivity without requiring separate dedicated components for each function.
Solution Approach 2:
The invention changes the mechanical parameters of the cable structure by introducing periodic coupling between the cable core and strength member. This configuration creates tension-free zones in the cable core, enabling the optical fibre to respond sensitively to acoustic and elastic waves while maintaining cable integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly increases the sensitivity of the fibre optic sensor to detectable stimuli, including acoustic and elastic waves, by allowing the optical fibre to change path length without overcoming pre-existing tension, enabling detection of incidents that would be undetectable with conventional cables.
Implementation Method 1
interrogating the sensing optical fibre with coherent optical radiation and detecting and analysing optical radiation which is Rayleigh backscattered from within the sensing fibre
Implementation Method 2
between the fixed coupling points the cable core is free to move with respect to the strength member
Data Source
AI summary
This application relates to fibre optic cables structures which are particularly suited for use for distributed fibre optic sensing. A fibre optic cable structure (300, 500) is described which includes a cable core (301, 501) and a longitudinal strength member (302, 502). The cable core has at least one optical fibre (301a, 501a) and, optionally, one or more surrounding layers (505) and/or a strain transformer. (504) The cable core and is fixedly coupled to the longitudinal strength member at periodic fixed coupling points (303, 503). At the fixed coupling points the cable core has a substantially fixed position with respect to the longitudinal strength member and between the fixed coupling points the cable core is free to move with respect to the strength member. For an operating range of tensile load and pressure, the length (Lcoup) of the cable core between any two adjacent fixed coupling points is greater than the axial distance (Dcoup) along the fibre optic cable structure between the fixed anchoring points.