Subsea Buoy Tether Connector Flex Joint Fatigue Reduction
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Solution Overview
Problem
The existing tensioning systems for subsea buoys in hybrid riser systems face challenges in accurately predicting tether extension due to high tension, thermal expansion, and wear, leading to stress concentrations and potential premature failure of top chains, while also increasing the size, weight, and cost of hang-off porches due to the need for large spherical bearings to accommodate varying tether angles.
Innovation Solution
A top connector system featuring a pivot axis with a flex joint and a lever member that can pivot independently, allowing for micro-angular movement responsiveness and reducing friction, combined with a chain stop mechanism and tensioner unit for efficient tension management, which minimizes bending fatigue and wear by using a resilient annular bush and adjustable chain guides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If large spherical bearings are used to accommodate varying tether angles, then the ability to adapt to angle variations is improved, but the size, weight, and cost of hang-off porches increases
Solution Approach 1:
The system is divided into separate functional components: a pivot axis for angular movement, a flex joint for micro-angular adjustments, and a lever member for tension application. This segmentation allows each component to be optimized independently, reducing the overall size and weight compared to a single large spherical bearing.
Solution Approach 2:
The pivot axis and lever member are designed to dynamically adjust to varying tether angles through controlled movement. The lever member can pivot independently to follow the tether's departure angle while maintaining tension, replacing the need for oversized static spherical bearings.
2Adaptability or versatility
If spherical bearings are used to accommodate dynamic angle variations, then adaptability is improved, but friction and wear increase
Solution Approach 1:
The traditional spherical bearing mechanism is replaced with a pivot axis and lever member system that uses controlled pivoting and flex joint deformation instead of rolling contact. This substitution reduces friction and wear by eliminating the sliding and rolling surfaces inherent in spherical bearings.
Solution Approach 2:
The flex joint introduces micro-angular movement capability that changes the operational parameters of the system. By allowing small angular adjustments through flex joint deformation, the system reduces the demand for large angular movements that would generate friction and wear in traditional bearing systems.
3Area of stationary object
If the pivot axis is positioned far from the side shell to avoid clashing, then clearance is improved, but the size and weight of hang-off porches increases
Solution Approach 1:
The lever member is designed to pivot in a different spatial dimension, allowing the top of the lever to move laterally away from the side shell during extreme angles. This dimensional movement provides the necessary clearance without requiring the pivot axis to be positioned far from the side shell, thus reducing porch size and weight.
Solution Approach 2:
The lever member dynamically adjusts its position during operation, moving laterally to avoid clashing with the side shell when the tether adopts extreme departure angles. This dynamic movement provides the necessary clearance without requiring a fixed large distance from the side shell.
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
The solution reduces the size and weight of hang-off porches, enhances chain fatigue life, and maintains tether alignment, achieving a projected chain bending fatigue life of over 16,000 years, effectively addressing the limitations of spherical bearings in accommodating dynamic angle variations and tension changes.
Implementation Method 1
a flex joint allowing for micro-angular movement responsiveness and reducing friction, combined with a chain stop mechanism and tensioner unit for efficient tension management, which minimizes bending fatigue and wear by using a resilient annular bush
Implementation Method 2
The articulating member and the socket have complementary part-spherical bearing surfaces that together define a ball-and-socket joint. The spherical bearing allows the tensioning module to adapt to varying inclinations of the departure axis of the associated tether.
Data Source
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AI summary
A top connector (12) for a tether (16) of a subsea buoy (10) comprises a support (46), a lever member (60) movable about a pivot axis, and a chain stop mechanism (64) mounted on the lever member (60) to be situated below the pivot axis in use. The lever member (60) is pivotably connected to the support (46) via a flex joint (58) arranged to bear a tensile load exerted by a top chain (22) of the tether (16) when engaged with the chain stop mechanism (64). The flex joint (58) improves bending fatigue life of the top chain (22). A frame (30) extends upwardly from the support (46) to carry a sheave (32) for the top chain (22). A pivotably connected lever member (62) extends downwardly from the support (46). The lever member (62) is pivotable relative to the support (46) and the frame (30), allowing a compact arrangement that avoids the frame (30), the top chain (22) or the sheave (32) clashing with the shell (14) of the buoy (10).