Enlarged Column Base for Vortex-Induced Motion Mitigation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Deep draft semi-submersible offshore platforms experience significant vortex-induced motion (VIM) due to the increased excitation length of longer columns, leading to damaging vibrations and fatigue damage, which existing designs fail to adequately address.

Innovation Solution

The implementation of enlarged column bases with a horizontal extension that breaks the coherence of vortex shedding, creating interfering vortex flows to reduce the effective VIM excitation length and synchronize vortex shedding between columns, while maintaining comparable buoyancy through inverse proportional reduction in pontoon volume.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If the column length is increased to achieve deep draft configuration, then the platform can operate in deeper waters and provide greater stability, but the vortex-induced motion (VIM) increases due to longer excitation length

Engineering Contradiction:

Improvecolumn lengthVSAvoidvortex-induced motion

Core Design Contradiction:

Length of moving objectVSObject-affected harmful factors

Solution Approach 1:

The invention introduces helical protrusions on the column surface that intentionally generate controlled vortices to disrupt the harmful coherent vortex shedding. The helical geometry converts the harmful VIM effect into beneficial interfering vortex flows that reduce the net vibration amplitude on the column structure

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The helical protrusions are applied locally to the column surface rather than modifying the entire column structure. This localized modification creates vortex-disrupting features at specific locations along the column, particularly in regions where vortex shedding has the greatest impact on VIM

Inventive Principle:

Principle #3Local quality

2Strength

If the column diameter is increased to reduce VIM, then the structural strength improves, but the platform buoyancy and stability are compromised

Engineering Contradiction:

Improvecolumn strengthVSAvoidvortex-induced motion

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

Instead of increasing column diameter to reduce VIM, the invention uses helical protrusions to actively disrupt vortex shedding. This approach maintains the original column dimensions and strength while converting the vortex shedding phenomenon from harmful to beneficial by creating interfering flow patterns

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Device complexity

If conventional column designs are used, then the structural simplicity is maintained, but the vortex shedding coherence remains high causing significant VIM

Engineering Contradiction:

Improvecolumn structureVSAvoidvortex-induced motion

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The helical protrusions transform the simple conventional column into a vortex-disrupting structure. The added geometric complexity of the helical features creates controlled turbulence that interferes with coherent vortex shedding, converting the simplicity drawback into an active VIM mitigation mechanism

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 design effectively lowers VIM by disrupting the coherence of vortex shedding along the column length, reducing the synchronization of vortex shedding and providing additional damping, resulting in smaller VIM excitation and reduced heave load on the platform.

Implementation Method 1

Vortex-Induced-Motion (VIM) or Vortex-Induced Vibrations (VIV) are motions induced on bodies facing an external flow by periodical irregularities of this flow. Vortices are then formed, changing the pressure distribution along the surface.

Methodology Applied

Scientific EffectVortex shedding: Kármán Vortex Street

Implementation Method 2

Fluids present some viscosity, and fluid flow around a body, such as a cylinder in water, will be slowed down while in contact with its surface, forming a boundary layer. At some point, this boundary layer can separate from the body. Vortices are then formed

Methodology Applied

Scientific EffectBoundary layer separation: Boundary Layer

Implementation Method 3

a hull that has sufficient buoyancy to support a work platform above the water surface

Methodology Applied

Scientific EffectBuoyancy: Archimedes' Principle (Buoyancy)

Data Source

PatentEP2637918B1Semi-submersible floating structure for vortex-induced motion performance

Publication Date: 2022.01.05 TECH FRANCE SA

Figure 1
Figure 2A~2B
Figure 2C~2D

AI summary

The disclosure provides a semi - submersible offshore platform (5) with columns (6) having an enlarged base (8) on the bottom of each column with pontoons (10) coupled between the columns. The enlarged column base can be at least as high as a height of the pontoon and on at least embodiment can be about 50% of the draft of the platform. The enlarged base can change a current flow shape around the base and columns for lower VIM. An outside corner of the base can be trimmed at an angle. Alternatively, the lower portions of the columns can be extended horizontally outward to form an effectively enlarged base having similar characteristics. In some embodiments, the pontoon volume can be reduced inversely proportional to the base enlargement to have comparable total buoyancy.