Helical Strake Flow Modifier for Cylindrical VIV and Drag Reduction
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Solution Overview
Problem
Cylindrical structures such as marine risers, umbilicals, and pipelines experience vortex-induced vibration (VIV) and increased drag when immersed in fluid media, leading to reduced operating life due to fatigue, and existing flow modification devices are either impractical for handling or time-consuming to deploy.
Innovation Solution
A flow modification device with an elongate body featuring raised body portions, such as curved or helically arranged ridges, that reduce VIV and drag by altering vortex formation when connected to cylindrical elements, and can be securely attached using releasable straps or clamping mechanisms, allowing for efficient deployment and reduced fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If helical strakes are used to reduce VIV, then VIV severity is reduced to very small levels, but the device becomes large and impractical to handle
Solution Approach 1:
The flow modification device is divided into multiple discrete raised body portions (ridges) spaced along the elongate body, rather than using continuous large helical strakes. This segmentation allows the device to maintain VIV reduction effectiveness while being divided into smaller, more manageable sections that are easier to handle and deploy.
Solution Approach 2:
Instead of applying a uniform large-scale helical structure, the invention uses localized raised body portions with specific dimensions (height between 2% and 10% of body diameter) positioned at specific intervals. This local modification approach maintains effectiveness while significantly reducing overall device size and handling difficulty.
2Reliability
If rigid fairings are used to suppress VIV, then VIV is reduced by streamlining flow, but the clamping process becomes time consuming
Solution Approach 1:
The device transitions from a rigid fairing that requires complex clamping to a more flexible design using releasable straps or clamping mechanisms that can be quickly applied and removed. This dynamic attachment system maintains VIV suppression effectiveness while dramatically reducing deployment and retrieval time.
Solution Approach 2:
The flow modification device is designed for temporary attachment that allows quick deployment and easy removal. The releasable attachment mechanism enables the device to be rapidly installed before operations and quickly removed afterward, minimizing time loss and allowing the cylindrical element to be reused without permanent modification.
3Adaptability or versatility
If drilling risers undergo deployment and retrieval operations, then operational flexibility is maintained, but large helical strake devices cannot be easily handled
Solution Approach 1:
By segmenting the flow modification device into smaller raised body portions spaced along the elongate body, the device becomes lightweight and flexible enough to be easily deployed and retrieved with drilling risers, maintaining operational flexibility while enabling practical handling.
Solution Approach 2:
The elongate body with raised portions creates a flexible flow modification structure that can conform to the cylindrical element and be easily maneuvered during deployment and retrieval operations, unlike rigid large helical strakes.
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 device effectively suppresses VIV and drag on cylindrical elements, enhancing their operational life by altering vortex shedding patterns and reducing peak loading, while being practical for deployment and handling due to its design and attachment methods.
Implementation Method 1
cylindrical structures such as marine risers, umbilicals, cables, and pipelines will generally be subject to vortex-induced vibration excitation when immersed in a flowing fluid medium
Implementation Method 2
Rigid fairings aim to suppress VIV by streamlining and delaying separation of the flow about the cylindrical structure
Implementation Method 3
Flow modification devices have been developed to reduce the level or severity of VIV on cylindrical structures
Data Source
AI summary
A flow modification device connectable to a generally cylindrical element adapted for immersion in a fluid medium is provided. The device comprises an elongate body having a length and a generally circular cross-section; a plurality of raised body portions disposed about and extending along the length of the elongate body, the raised body portions having a height between 2% and 10% of a diameter of the body; and an aperture extending through the length of the elongate body, the aperture being adapted to receive the generally cylindrical element such that the flow modification device is arranged about the cylindrical element. The plurality of raised body portions are helically arranged or twisted about a longitudinal axis of the elongate body and are adapted to reduce vortex-induced vibration and/or drag on the cylindrical element when the device is connected to the cylindrical element and the connected device and cylindrical element are immersed in the fluid medium and there is relative movement between the connected device and cylindrical element and the fluid medium.