Dog Bone Pontoon for Semi-Submersible Heave Reduction
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Solution Overview
Problem
Conventional semi-submersible offshore platforms face challenges in achieving acceptable heave characteristics in lower draft applications while maintaining cost-effectiveness, as increasing draft improves stability but complicates assembly and increases material costs, and existing designs are inefficient in minimizing motion and riser fatigue.
Innovation Solution
A semi-submersible offshore structure featuring a 'dog bone' shaped pontoon with varying width and surface area ratios, optimized to reduce heave motion and material usage, comprising a first and second vertical column with a buoyant hull and elongate horizontal pontoon having specific node and intermediate section dimensions, which reduces the pontoon's surface area and width ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the draft of a semi-submersible offshore platform is increased to improve stability and reduce motion, then stability and motion reduction are improved, but assembly complexity and material costs increase
Solution Approach 1:
The pontoon is divided into multiple compartments (first compartment, second compartment, third compartment) separated by bulkheads, allowing independent buoyancy control of each section. This segmentation enables the platform to achieve desired stability characteristics while maintaining a manageable draft for assembly, as each compartment can be independently ballasted during operation rather than requiring the entire structure to be at operational draft during assembly.
Solution Approach 2:
The patent employs variable cross-sectional area along the pontoon length, with the intermediate section having a different area than the end sections. This geometric parameter variation optimizes the buoyancy distribution and stability characteristics without requiring an overall increase in draft, thereby improving stability while maintaining assembly feasibility.
2Object-affected harmful factors
If the draft of a semi-submersible offshore platform is increased to reduce heave motion, then heave motion is reduced, but material requirements and costs increase
Solution Approach 1:
By segmenting the pontoon into multiple buoyancy compartments with independent ballasting capability, the system can optimize the vertical buoyancy distribution to reduce heave motion. The segmented design allows strategic placement of buoyancy volumes at different depths without requiring a uniform increase in overall draft, thereby reducing material requirements compared to a solid homogeneous structure.
Solution Approach 2:
The pontoon utilizes a composite structure combining buoyant materials (for flotation) with ballast water (for stability and motion control). This composite approach allows the structure to achieve desired heave characteristics through the interaction of buoyant forces and ballast weight, rather than requiring increased structural material throughout the entire draft.
3Ease of manufacture
If conventional pontoon designs are used with uniform cross-section, then manufacturing is simpler, but heave characteristics are inadequate in lower draft applications
Solution Approach 1:
The pontoon design implements local quality variations along its length, with end sections having different cross-sectional areas than the intermediate section. This localized geometric variation optimizes the hydrodynamic characteristics and heave response in specific regions, achieving superior overall heave characteristics compared to uniform designs, while the modular compartmented structure maintains reasonable manufacturability.
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 optimized design results in reduced heave motion and material requirements, facilitating easier assembly and operation in shallower draft conditions with improved stability and reduced riser fatigue, while maintaining structural integrity and cost-effectiveness.
Implementation Method 1
a buoyant hull coupled to the equipment deck and extending below the surface of the water
Implementation Method 2
the surface area of the upper and lower surfaces of the pontoons can be increased, resulting in the vessel having a greater added mass, and hence, increased resistance to movement through the water and heave natural period
Data Source
AI summary
A semi-submersible offshore structure for offshore operations. In an embodiment, the structure comprises a buoyant hull. The hull comprises a first elongate horizontal pontoon having a longitudinal axis, a first end, and a second end. The pontoon includes a first node disposed at the first end of the pontoon, a second node disposed at the second end of the pontoon, and an intermediate section extending axially from the first node to the second node. Moreover, the first node has a width W1, the second node has a width W2, and the intermediate section has a width W3 measured perpendicular to the longitudinal axis in bottom view. The width W3 varies moving axially from the first node to the second node.