CFD Analysis and Optimisation of StrakesOn Rotating and Stationary Equipment

David HuttonGraduate EngineerNeptune Subsea Engineering

Introduction

Problem overview

Current products

Development of Neptune VSS design

– Specialised design for a rotating scenario

Problem Overview

Planned drilling operations with currents in region of 4-6 knots.

Water depth of 1800m

Currently, conditions cause excessive vibrations in the drill due to vortex induced vibrations (VIV), leading to it being damaged after just 6 hours while stationary in the water

This lead to the need for a VIV suppressive device that can work in both a rotating and stationary domain

Current Products

Currently, Neptune Subsea Engineering (NSE) offer strakes that have been proven to be extremely effective in mitigating VIV on landing strings and risers

Multiple specifications made – each developed specifically for the environmental conditions and geometry of the pipe

Development of Drill Pipe Strake

Strakes are a widely used device for mitigating VIV, but designing and simulating the conditions are vital to ensure that the design works for each situation

There is no one size fits all solution, especially when increasing the complexity by adding the rotation of the drill pipe

Although the drill pipe will be rotating, most of the time it will be stationary so the strake must be able to cope with both scenarios

Literature was used alongside CFD results to create new strakes designs, although rotating drill pipe strakes seem somewhat unresearched in publicised papers

Starting point for the design process was the current design used in the North Sea

Strake Simulations on Stationary Pipe

Firstly, the suitability of the current strake in a higher current was tested, as previously it was only simulated up to 3 knots

These conditions were also analysed for a plain drill pipe

Clear reduction in force oscillations after the addition of a strake

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Lift

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Time (s)

Lift Force Comparison at 3m/s

Drill Pipe

Current Strake

Strake Simulations on Rotating Pipe

After proving once again that the current design significantly reduces force oscillations and therefore VIV on a stationary drill pipe, rotation could now be added to further analyse the design

The results did not follow the hypothesis, the strake made the force oscillations larger and therefore would likely increase the damage on a rotating drill pipe

This opened up a new area of exploration – a design that can handle the rotating drill pipe better than the plain drill pipe

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Lift

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Time (s)

Lift Force Comparison at 2m/s

Drill Pipe

CurrentStrake

Strake Simulations on Rotating Pipe

New strakes were designed, altering the fin angles by adjusting the pitch length

A variety of fin heights were also introduced to decrease the drag force seen by the drill pipe, but the focus remained on the lift force

Design 2 appeared to be the best design, but had to be analysed on a stationary pipe

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Lift

(N

)

Time (s)

Lift Force Comparison at 2m/s

Drill Pipe

Current Strake

Design 1

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Design 3

Strake Simulations on Stationary Pipe

The new design was now simulated on a stationary drill pipe, to ensure the strake was versatile and could be utilised in multiple conditions

Although oscillations were shown, they depleted with time. On the contrary, the pipe oscillations were cyclic – agreeing with vibrations experienced on the rig

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Lift

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Time (s)

Lift Force Comparison

Design 2Stationary

Pipe Stationary

Development of Drill Pipe Strake

Animations can be extracted from the simulation for the flow around the plain pipe and strake

Conclusion

Rather than offering an off the shelf solution, a specialised solution was developed using CFD to reach a finalised geometry

Adapted design to include a helical cut, compared to the traditional axial cut to allow for a longer strake and reduced installation time/personnel

Strakes are currently in manufacture – combining previous experiences to increase longevity of the design to cope with extremely hard conditions

First-off strakes were successfully tested in compression up to 70 tonnes and in a combined compression and sliding test up to 30 tonnes and saw no damage or movement on the drill pipe

Thank you, Any Questions?