Convex Short Crab Claw Fairing for VIV Suppression
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Solution Overview
Problem
Existing fairing devices for reducing vortex-induced vibrations (VIV) in offshore pipelines face challenges such as high drag forces, limited operational stability, and cumbersome deployment and storage issues, which can lead to structural fatigue and increased costs.
Innovation Solution
A new fairing design, the Short Crab Claw (SCC) fairing, which is convexly curved and can rotate to align with ambient currents, featuring a chord length ratio of 1.4 or less and a tail end opening greater than 80% of the standoff height, made from low-corrosive materials like polyethylene or fiberglass, providing superior VIV suppression with reduced drag and improved stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fairing devices are used to suppress VIV, then vortex-induced vibrations are reduced, but drag forces increase significantly
Solution Approach 1:
The fairing employs a convexly curved surface geometry that smoothly guides fluid flow around the cylindrical structure. This curvature design reduces flow separation and wake turbulence, achieving effective VIV suppression while minimizing pressure drag compared to traditional flat or angular fairing configurations
Solution Approach 2:
The fairing utilizes a specific chord length ratio (c/D ≤ 1.4) and tail end opening ratio (>80% of standoff height) that optimize the balance between VIV suppression and drag reduction. These parameter changes create an efficient flow control geometry that maintains stability without excessive drag penalty
2Reliability
If fairings with larger chord length are used to improve VIV suppression, then stability increases, but deployment and storage become more difficult
Solution Approach 1:
The convexly curved fairing design with constrained chord length ratio (c/D ≤ 1.4) creates a compact, aerodynamically efficient geometry that provides sufficient VIV suppression while maintaining small physical dimensions for easy deployment and storage on offshore vessels
Solution Approach 2:
By optimizing the chord length ratio and tail end opening ratio, the fairing achieves the minimum effective size for stability while minimizing overall dimensions. This parameter optimization ensures the fairing is compact enough for practical offshore operations without sacrificing operational stability
3Ease of operation
If fairings are designed with smaller dimensions for easier deployment, then ease of operation improves, but VIV suppression effectiveness decreases
Solution Approach 1:
The fairing uses optimized parameter ranges (chord length ratio c/D ≤ 1.4, tail end opening >80% of standoff height) that maximize VIV suppression efficiency per unit size. These parameter changes ensure effective vibration control even with compact dimensions suitable for offshore deployment
Solution Approach 2:
The convexly curved geometry concentrates flow control effects in a compact form, achieving effective VIV suppression with smaller dimensions. The curved surface efficiently manages boundary layer flow and wake structures, providing high suppression effectiveness relative to the fairing size
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 SCC fairing effectively suppresses VIV across various flow conditions, reduces drag forces, and enhances stability, allowing for easier deployment and storage, thus minimizing operational disruptions and costs associated with offshore drilling operations.
Implementation Method 1
The search for oil and gas reserves over the past several decades has lead to the need for exploration in ever deeper waters. This in turn has lead to the need for offshore producers to build structures that can withstand strong ocean currents that could threaten the structural integrity of pipelines, risers or other immersed components. The VIV oscillations of marine risers are known to increase drag, and have led to structural fatigue. One proven means of suppressing this vibration is the use of fairings and strakes.
Implementation Method 2
These coverings essentially modify the flow along the cylinder, tripping the production of Karman vortices so that they act less coherently or far enough downstream so they interact less with the body.
Data Source
AI summary
A fairing device for the reduction of vortex-induced vibrations or motions and the minimization of drag about a substantially cylindrical element immersed in a fluid medium, comprising; a cylindrical element, a fairing rotatably mounted about the cylindrical element, the fairing comprising a shell with a cylindrical cross-sectional shape with an outer diameter (D) following the outer diameter of the cylindrical element from an upward stagnation point of 0 degrees to at least +/−90 degrees, and which at +/−90 degrees continues as two fin-like portions in an aft direction and defining a chord length (C), further comprising that the fin-like portions are convexly curved aft of +/−90 degrees thus tapering towards each other and defining a tail end opening or gap less than the fairing standoff height.