Helical Optical Cable Design for Strain-Free Temperature Sensing
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Solution Overview
Problem
Optical fiber cables used in offshore oil pipelines face premature mechanical failure due to excessive stress from mechanical deformation and temperature fluctuations, which affects the accuracy of temperature measurements.
Innovation Solution
The optical cable design features a plurality of cable sensors helically wound around a support with an outer jacket, where each sensor comprises an optical fiber with a deformable material and a flexible tube, allowing the fiber to expand or contract without imposing stress, using equations to determine optimal strain levels and fiber clearance for free movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the optical fiber cable is made rigid to maintain structural integrity, then the cable strength is improved, but the fiber experiences excessive stress during mechanical deformation and temperature fluctuations
Solution Approach 1:
The cable is segmented into multiple independent helically wound sensors rather than a single rigid structure. Each sensor contains an optical fiber that can move independently within its protective tube, allowing the cable to maintain overall structural integrity while individual fibers remain stress-free during deformation
Solution Approach 2:
Each optical fiber is enclosed in a flexible protective tube that allows the fiber to move freely within the tube. This flexible enclosure protects the fiber from mechanical stress while permitting the necessary movement to accommodate cable deformation and thermal expansion/contraction
2Manufacturing precision
If the optical fiber is fixed tightly within the cable structure, then the manufacturing precision is improved, but the fiber cannot accommodate thermal expansion and contraction
Solution Approach 1:
The optical fiber positioning is made dynamic rather than fixed. The fiber is positioned with precision during manufacturing but is allowed to move dynamically within the protective tube to accommodate thermal expansion and contraction, combining manufacturing precision with thermal adaptability
Solution Approach 2:
A protective tube acts as an intermediary between the optical fiber and the cable structure. This intermediary component provides a controlled environment that maintains manufacturing precision while allowing the fiber to move freely in response to thermal changes
3Reliability
If the cable is designed to accommodate fiber movement, then the fiber strain is reduced, but the cable structure becomes more complex
Solution Approach 1:
Multiple functional elements are merged into a single integrated cable structure. The helically wound sensors, protective tubes, and optical fibers are combined in a unified design that accommodates fiber movement without requiring separate complex mechanisms for each function
4Ease of manufacture
If the optical fiber length is exactly matched to the cable length, then the manufacturing simplicity is improved, but the fiber experiences stress during cable deformation
Solution Approach 1:
The optical fiber is intentionally made longer than the cable length to provide a cushion against stress. This excess length acts as a buffer that absorbs the stress generated during cable deformation, preventing the fiber from experiencing damaging tension or compression
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 design reduces strain on the optical fibers, ensuring accurate temperature measurements and long-term reliability by allowing the fibers to move freely within the cable, minimizing stress and maintaining zero strain levels, thus preventing mechanical failure.
Implementation Method 1
These temperature changes will cause the fibers to expand (+) and contract (−). It is desirable to permit the fibers to expand or contract while isolating the sensing optical fibers from mechanical or environmental strain
Implementation Method 2
a plurality of cable sensors helically wound around a support... where the strain in the cable sensor is determined by equations involving pitch diameter and pitch length
Data Source
AI summary
Disclosed herein is an optical cable comprising a support; flexible protective tubes helically wound around the support, each flexible protective tube comprising an optical fiber comprising an optical core; a cladding disposed on the core; and a primary coating external to the cladding; and a deformable material surrounding the optical fiber; an outer jacket surrounding the flexible protective tubes; wherein each optical fiber is about 0.5% to about 1.5% longer than its respective flexible protective tube; wherein an allowable strain on the optical cable with substantially zero stress on the optical fibers is determined by equations (1) and (2) below:ɛ=π2(D+d2)2+p2_π2(D-d2)2+p2_π2dD_-10dD_;(1)ɛ×100=Percentelongationorcontraction;(2)where d is the amount of optical fiber clearance for free movement within the flexible protective tube, D is an average helical diameter of the helically wound flexible protective tubes, and p is an average helical pitch of the helically wound flexible protective tubes.