Shell-Based Mooring Compressive Element for Variable Stiffness
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Solution Overview
Problem
Mooring systems for floating offshore wind turbines and tidal turbines face challenges in shallow waters due to high background thrust loads, leading to increased stiffness and high variable loads, which require larger and more expensive components, and result in undesirable stress-strain behavior and fatigue issues.
Innovation Solution
A compressive element comprising a plurality of shells with different annular portions and a central section, arranged to change stiffness response based on compression, allowing for a high stiffness at low thrust values and lower stiffness at higher thrust values, thereby providing a more desirable stress-strain response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional catenary chain systems are used in shallow water, then the mooring system can provide restoring force, but the system becomes excessively stiff under high background thrust, leading to high variable loads and fatigue
Solution Approach 1:
The mooring system transitions from a static catenary chain configuration to a dynamic system where the compressive element actively adjusts its stiffness characteristics. The compressive element allows the mooring line to transition between different geometric configurations, enabling the system to adapt its mechanical properties in response to varying environmental conditions and thrust loads.
Solution Approach 2:
The system changes the effective stiffness parameter of the mooring line by introducing a compressive element that can alter the mechanical behavior of the line. This allows the system to operate with lower stiffness under high background thrust conditions, reducing variable loads, while maintaining adequate restoring force when needed.
2Length of moving object
If the mooring line is made longer to allow for platform motion in shallow water, then the system can accommodate surge, but the line becomes more susceptible to seabed contact and the system stiffness increases
Solution Approach 1:
The compressive element acts as an intermediary component between the mooring line and the platform, providing a controlled mechanism for length adjustment and stiffness management. This intermediary device allows the system to achieve the necessary travel range without requiring excessively long mooring lines that would increase stiffness and seabed contact risk.
3Reliability
If larger mooring components are used to handle high variable loads, then the system can withstand extreme conditions, but the component cost and installation complexity increase significantly
Solution Approach 1:
The compressive element modifies the load parameters transmitted through the mooring system by reducing peak variable loads through its stiffness-modulating behavior. This allows the use of smaller, more cost-effective components while maintaining adequate reliability, as the system dynamically manages load transmission rather than requiring oversized components to handle all possible load conditions.
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 compressive element reduces the risk of failure by managing high wave conditions with lower component costs and minimizing fatigue, allowing for continuous elongation of the mooring line while maintaining structural integrity.
Implementation Method 1
when a compressive stress is applied to the compressive element substantially in the direction of the central axis, the compressive element is compressed
Implementation Method 2
the compressive element is arranged such that when the compressive stress applied to the compressive element causes the compressive element to be compressed by a particular fraction of an uncompressed length of the compressive element, the central section of one of the plurality of shells contacts the central section of an adjacent shell of the plurality of shells
Data Source
AI summary
A compressive element for a mooring component includes multiple shells. Each shell has first and second annular portions, and a central section that extends between the first and second annular portions. The first and second annular portions lie in a plane that is perpendicular to a central axis of the compressive element. The first annular portion has a maximum dimension in a direction perpendicular to the central axis that is greater than a corresponding maximum dimension of the second annular portion. The shells are arranged along the central axis such that the first or second annular portion of one shell is joined to the first or second annular portion of an adjacent shell. The compressive element is arranged such that when a compressive stress causes the compressive element to be compressed, the central section of one shell contacts the central section of an adjacent shell.