C-Semi Platform Hydrodynamic Motion Reduction
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Solution Overview
Problem
Conventional semi-submersible hulls for offshore oil and gas drilling and production face limitations such as large heave, roll, and pitch motions, inability to support steel catenary risers in extreme weather, and susceptibility to vortex-induced vibrations, which lead to fatigue and operational constraints.
Innovation Solution
A circular cylindrical semi-submersible (C-Semi) platform with a generally circular toroidal pontoon and columns of equal cross-sectional area, where the pontoon diameter is greater than the column spacing, and optional helical strakes on columns to mitigate vortex-induced motions, allowing for steel catenary risers and dry tree production applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional semi-submersible hulls are used, then the structure is simple and easy to manufacture, but the platform experiences large heave, roll and pitch motions
Solution Approach 1:
The patent applies spheroidality by using a circular cylindrical pontoon instead of a conventional square pontoon structure. This curved geometry reduces vortex-induced vibrations and improves hydrodynamic performance, thereby minimizing platform motions while maintaining structural integrity
2Force
If deep draft variants are developed to reduce motion effects, then wave forces are reduced, but the structure becomes operationally limited and manufacturing becomes more difficult
Solution Approach 1:
The patent optimizes the draft-to-column-spacing ratio parameter to achieve minimal platform motions without requiring excessive draft depth. By carefully selecting geometric parameters (pontoon diameter, column spacing, draft), the design achieves operational flexibility while reducing wave forces through optimized hydrodynamic characteristics
3Strength
If columns without strakes are used, then the structure is simpler, but vortex-induced vibrations cause fatigue damage
Solution Approach 1:
The patent converts the harmful vortex-induced vibrations into a beneficial effect by adding helical strakes to the columns. These strakes disrupt vortex formation and convert the potentially damaging periodic forces into beneficial turbulent flow patterns, reducing fatigue damage while maintaining column structural integrity
4Stability of the object's composition
If dual column configuration is used, then motion performance improves at deeper draft, but design and fabrication complexity increases
Solution Approach 1:
The patent employs asymmetric column placement relative to the circular pontoon, positioning columns at optimized angular intervals rather than symmetric spacing. This asymmetric arrangement optimizes hydrodynamic performance and minimizes platform motions while maintaining a simpler single-row column configuration compared to dual-column designs
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 C-Semi platform minimizes wave, current, and vortex-induced motions, improving hull and riser system performance, reducing costs and risks in offshore oil and gas field development, and enhancing structural integrity by redistributing wave forces and reducing fatigue damage.
Implementation Method 1
strong sub-surface currents can cause vortex-induced vibrations (VIV). A structure that has prolonged exposure to VIV can experience fatigue damage to components
Implementation Method 2
The C-Semi platform minimizes wave, current, and vortex-induced motions, improving hull and riser system performance
Data Source
AI summary
An offshore floating structure (10) for the drilling and production of oil and gas includes a generally circular toroidal, hollow pontoon (11) of substantially the same radial width throughout a perimeter of the pontoon. The offshore floating structure includes a plurality of columns (12) of substantially a same cross-sectional area, each coupled at a coupling point, on a bottom end thereof to the pontoon at an equidistant point along the perimeter of the pontoon, and adapted to be coupled on a top end to a deck structure. The diameter (23) from a center of the radial width of the pontoon is greater than a distance (21) from a center of one column to a center of an adjacent column.