3D Dampers for Subsea Catenary Line Motion Suppression
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Solution Overview
Problem
Offshore engineering catenary lines experience significant dynamic bending stresses, axial loads, and buckling due to dynamic motions and hydrodynamic forces, leading to reduced fatigue life and increased costs associated with complex line configurations and high installation loads in deepwater conditions.
Innovation Solution
The implementation of dynamics decoupling, damping, buoyancy, mass, and added mass modifying devices along the catenary line near the seabed, optimizing buoyancy, submerged weight, and drag to reduce dynamic motions without increasing line length, and utilizing novel buoyancy shapes to suppress Vortex Induced Vibrations and dynamic excitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex line configurations are used to reduce dynamic motions, then dynamic tension and buckling are reduced, but device complexity and installation costs increase
Solution Approach 1:
The patent modifies physical parameters of the catenary line by adding devices that change buoyancy, mass, and drag characteristics. These parameter changes alter the dynamic response of the line without requiring complex reconfiguration of the entire line system, thereby improving fatigue life while controlling complexity.
Solution Approach 2:
Rather than modifying the entire line configuration, the patent applies localized modifications at specific positions along the catenary line. The devices are positioned to create local changes in buoyancy and mass distribution, which effectively reduce dynamic motions and buckling without requiring complex changes throughout the entire line system.
2Strength
If traditional motion suppression methods are used, then dynamic bending stresses are reduced, but installation loads and costs increase
Solution Approach 1:
The patent employs devices that provide buoyant forces to counteract the weight and dynamic loads of the catenary line. These buoyancy devices effectively reduce the installation loads by providing upward counterbalancing forces, while also reducing dynamic bending stresses during operation, thereby improving fatigue resistance without excessive installation weight.
3Reliability
If line length is increased to reduce dynamic effects, then dynamic tension is reduced, but productivity and installation efficiency decrease
Solution Approach 1:
Instead of increasing line length to reduce dynamic effects, the patent changes other physical parameters of the line system by incorporating devices that modify buoyancy, mass, and drag. This allows dynamic tension to be reduced through parameter modification rather than geometric extension, maintaining installation efficiency while improving fatigue life.
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
This approach reduces dynamic tension, increases the minimum dynamic radius of curvature, enhances fatigue life, and decreases the range of stress components, effectively mitigating buckling and fatigue damage while maintaining acceptable installation costs.
Implementation Method 1
The implementation of dynamics decoupling, damping, buoyancy, mass, and added mass modifying devices along the catenary line near the seabed, optimizing buoyancy, submerged weight, and drag
Implementation Method 2
optimizing buoyancy, submerged weight, and drag to reduce dynamic motions without increasing line length
Implementation Method 3
The implementation of dynamics decoupling, damping, buoyancy, mass, and added mass modifying devices along the catenary line
Data Source
AI summary
This invention introduces three-dimensional (3D) damper arrangements that are used to suppress dynamic motions of a subsea line like a riser, on which the dampers are installed. Damping surfaces (shapes) are mounted on the line so that their combined drag per line unit length dampens motions in 3 mutually perpendicular directions: axial, in-plane (IP) and out-of-plane (OOP). 3D suppression is provided by integral 3D dampers or by combining IP-OOP dampers like strakes with neighboring axial dampers. Increased line motions suppression is achieved by decoupling, particularly on dampers mounted in regions of high line curvature and/or small effective tension. This invention also presents Short Lazy Wave (SLW) configurations of rigid catenary risers, which are also used to suppress dynamic motions. 3D dampers can be used together with SLWs. Motion suppression is introduced to reduce dynamic stresses and to increase fatigue life of the lines.