Shallow Water System Subsea Structure Positioning
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Solution Overview
Problem
Existing shallow water systems face challenges in protecting flexible transporting units from over-bending, touching down, and stretching due to significant movements of weathervaning vessels under weather influences, especially in shallow waters, where the subsea structure's positioning is restricted, leading to potential damage.
Innovation Solution
The shallow water system allows the subsea structure to be positioned further from the seabed than the keel height, with a safety margin to prevent collisions, enabling a larger surplus length for flexible transporting units and reducing the risk of damage by arranging the subsea structure within an exclusion zone that accounts for the vessel's movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the subsea structure is positioned close to the seabed to minimize flexible transporting unit length, then the system complexity is reduced, but the risk of collision with the weathervaning vessel increases under weather conditions
Solution Approach 1:
The patent positions the subsea structure horizontally away from the vertical centerline of the weathervaning vessel, using the horizontal dimension to create safety distance. This allows the structure to be close to the seabed while maintaining adequate clearance from the vessel's movement path, resolving the contradiction between minimizing flexible unit length and preventing collision.
2Reliability
If the subsea structure is positioned further from the seabed to increase safety margin, then collision risk is reduced, but the flexible transporting units become more susceptible to over-bending and stretching
Solution Approach 1:
Instead of increasing vertical distance from the seabed, the patent uses horizontal positioning to achieve safety. The subsea structure is placed at a horizontal distance from the vessel's vertical centerline, which provides collision safety without increasing the vertical span that the flexible transporting units must cover, thus avoiding over-bending and stretching issues.
3Adaptability or versatility
If the flexible transporting units are arranged in wave configuration to provide surplus length, then the vessel's movement freedom is improved, but the units may still touch down and drag across the seabed under extreme conditions
Solution Approach 1:
The patent pre-position the subsea structure at a horizontal distance from the vessel's expected movement path, establishing a safety zone before extreme weather conditions occur. This preliminary positioning ensures that even when the vessel moves significantly due to weather, the flexible transporting units maintain adequate clearance and do not touch down on the seabed.
Solution Approach 2:
The patent transitions from vertical safety margins to horizontal safety margins. By positioning the subsea structure horizontally away from the vessel's vertical centerline, it creates a safety buffer that accommodates vessel movement without requiring excessive flexible unit length or wave configurations that could lead to seabed contact.
Data Source
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AI summary
The invention relates to a shallow water system comprising a floating weathervaning vessel (3) with a topside hang-off structure, a subsea structure and at least one flexible transporting unit (2) extending from the topside hang-off structure to the subsea structure (1). The weathervaning vessel (3) has a bow with a lowermost bow midpoint. The weathervaning vessel is moored such that at still water it can weathervane around a weathervaning vertical centre line, such that the position of the lowermost bow midpoint follows an annular lowermost bow line which defines a vertical tube shaped border to a lowermost bow midpoint exclusion zone (LE-zone). The subsea structure (1) is arranged in said LE-zone. The weathervaning vertical centre line (9) is preferably the nominal weathervaning vertical centre line. The weathervaning vessel (3) is generally a line moored weathervaning vessel. The shallow water system of the invention provides a simple system for design with a high safety against damaging of flexible transporting unit (2). The shallow water system is in particular beneficial for use at very shallow water.