Floating Spar Support Heave Period Extension
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Solution Overview
Problem
Existing spar platforms are not adequately designed to handle long wave periods, leading to unacceptable heave motions and Mathieu instability in maritime areas like the North Atlantic, where wave conditions are more challenging than in areas like the Mexican Gulf.
Innovation Solution
A deep caisson support with an extended portion between the upper and lower sections, featuring internal storage and ballast chambers, stepped or bevelled transitions, and shear plates to increase the heave natural period without enhancing heave rigidity, allowing for increased buoyancy and mass under water while reducing waterline rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the spar support uses a conventional design with buoyancy chambers in the upper part and stabilizing weight in the lower part, then the structure maintains vertical floating position and basic stability, but the heave natural period is too short causing resonance and unacceptable motions in areas with long wave periods (15-19s)
Solution Approach 1:
The support structure is divided into three distinct portions: upper portion with buoyancy chambers, intermediate extended portion with storage and ballast chambers, and lower portion with stabilizing weight. This segmentation allows the intermediate portion to contribute to heave period without compromising the stability functions of the upper and lower portions.
Solution Approach 2:
An intermediate extended portion is added between the upper and lower portions, extending the vertical dimension of the structure. This additional length increases the heave natural period from typically 10-12 seconds to 15-19 seconds or longer, matching the wave periods in harsh maritime areas without affecting the platform's stability.
2Length of moving object
If the spar support increases buoyancy and mass underwater to extend the heave period, then the heave natural period increases, but the waterline rigidity increases which may affect platform performance
Solution Approach 1:
The intermediate extended portion is positioned below the waterline, away from the waterline itself. This local placement allows the structure to gain heave period through increased underwater mass and buoyancy distribution, while the waterline area maintains its original rigidity characteristics through the upper portion's design.
Solution Approach 2:
The intermediate extended portion acts as an intermediary element between the upper buoyancy portion and lower stabilizing weight. It provides the necessary mass and volume adjustment to extend the heave period, while being positioned such that it does not directly increase waterline rigidity.
3Adaptability or versatility
If the spar support is designed for short wave periods (13-15s) as in the Mexican Gulf, then the structure performs well in those conditions, but it cannot handle long wave periods (15-19s) encountered in the North Atlantic
Solution Approach 1:
The key parameter changed is the heave natural period, extended from 10-12 seconds to 15-19 seconds or longer through the addition of the intermediate extended portion. This parameter change allows the platform to match the wave periods in the North Atlantic (15-19s), preventing resonance and improving reliability in long wave conditions.
Solution Approach 2:
The intermediate extended portion serves multiple functions: it increases the heave natural period, provides additional ballast capacity, offers storage space, and maintains structural continuity. This multi-functionality enhances the platform's adaptability to different wave conditions while maintaining overall system reliability.
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 effectively increases the heave natural period, reducing sensitivity to wave periods and instability, enabling spar platforms to operate safely in harsher wave conditions, such as those found in the North Atlantic.
Implementation Method 1
one or more buoyancy chambers in an upper part and a stabilising weight in the spar support's lower part
Implementation Method 2
excitation of heave motion at resonance, and the combination of heave and roll/pitch motions
Implementation Method 3
the forces between the portions are transmitted as shear forces
Implementation Method 4
a stabilising weight in the spar support's lower part
Data Source
AI summary
A support of deep caisson type having a longitudinal axis, for floating installation in a body of water and provided with mooring lines for anchoring to a seabed, has a lower portion in the body of water having a weight element, an upper portion that supports a platform above a water surface, and an extended portion in an area between the upper portion and the lower portion. The extended portion has one or more internal storage chambers and one or more ballast chambers. The storage chambers are arranged closer to the longitudinal axis than the ballast chambers.