Dual Axis Chain Support for Offshore Mooring Fatigue Reduction
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Solution Overview
Problem
Existing mooring systems for offshore structures face issues with fatigue damage due to out-of-plane bending, limited rotation capabilities, and inefficient length adjustment, particularly in designs that do not minimize uplift forces and chain misalignment during installation and tensioning.
Innovation Solution
A dual-axis chain support system featuring an elongated hawse pipe pivotally connected to a hollow trunnion block with two pairs of trunnions for perpendicular rotation, a chain latch at the lower end to prevent rotation impediments, and a guide radius to distribute load and reduce bending stresses, allowing for adjustable mooring line length and minimal assembly width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the chain latch is mounted on the upper end of the hawse pipe for easy accessibility, then the chain inside the trunnion block becomes taut and impedes the rotations of the hawse pipe around the lower pair of trunnions
Solution Approach 1:
The chain latch is inverted from its conventional upper-end mounting to lower-end mounting on the hawse pipe. This inversion resolves the contradiction by placing the latch where it cannot impede rotation while still being accessible for operation during installation and maintenance.
2Area of stationary object
If the hawse pipe is shortened to reduce assembly width, then the torque generated by small angles between captive and free chain links becomes insufficient to rotate the hawse pipe around the trunnions
Solution Approach 1:
The hawse pipe is extended in the longitudinal dimension to compensate for the reduced width. This dimensional change ensures that sufficient torque is generated through the elongated lever arm to rotate the hawse pipe around the trunnions, even when the assembly width is minimized.
3Adaptability or versatility
If the chain support allows large vertical angle variations at the lower end, then misalignment of the assembly with the mooring line occurs
Solution Approach 1:
The chain support employs dynamic rotation capabilities around two perpendicular axes, allowing the assembly to adapt to varying vertical angles while maintaining proper alignment. The dual-axis rotation mechanism dynamically adjusts the orientation to accommodate angle variations without causing misalignment.
4Ease of manufacture
If the mooring line length is adjusted before rod connection on board another vessel, then the adjustment process becomes complex and time-consuming
Solution Approach 1:
The chain latch mechanism enables self-service length adjustment of the mooring line directly at the chain support location. The operator can independently add or remove chain links and secure them using the latch, eliminating the need for pre-adjustment on another vessel and reducing installation complexity and time.
Data Source
AI summary
A chain support 11, hinged on two perpendicular axes 5, 6 which allows chain movement in two perpendicular planes. The chain support provides an improved arrangement to allow chain 4 to be pulled through the center of the apparatus to a desired length after which the chain is removably secured to the chain support.