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22

At the recent Renewable UK

Global Offshore Wind

conference and exhibition Terry

Griffiths, Director at Aurora

Offshore Engineering (and more

importantly, a founding member

of the SUT Perth Branch), talked

on the topic of "Thar be

Dragons", sharing lessons

learned from solving really

difficult design and integrity

problems for over 4000km and

22GW of subsea cable projects

across the globe.

In many ways, the rise of the wind

industry has built on the

inherited methods developed

over many decades by the

offshore oil and gas industry and

has been motivated as much by

environmental concerns about

the need to transition to

sustainable and renewable

sources of energy, as it is based

on energy security concerns. The

offshore industry has also been

transitioning as work

opportunities in the renewables

sector grow.

While the specifics and

economics between these

industries are different, it did not

take established offshore

companies long to exploit this

market. This has an added bonus

that there are to be considerably

more turbines than conventional

offshore oil installations. There

are very broad similarities.

Instead of production platform

jackets read offshore substation

jackets. Instead of oil pipelines,

read subsea cables. And this,

contends Terry, is a trap the

industry is sleepwalking into.

THAR BE DRAGONS

“We need to stop thinking about

subsea power cables as just small

oil and gas pipelines,” he said.

“A fundamental difference is that

because of the small diameter,

typically subsea cables have

Keulegan-Carpenter (KC)

numbers (a quantity describing

the relative importance of the

drag) that are in the range of 200

to 500. The typical oil and gas

pipelines, however, have a KC

number that's in the range of 30

to 50.

“Subsea cables also typically

have much smaller Reynolds

numbers, so the hydrodynamic

models that we've inherited from

the oil and gas industry are not

correct for subsea cables, and

using these engineering formulae

can result in fundamental errors

in the physics that is very relevant

to the design.”

“The reason the way pipeline

engineering has evolved because

of the hydrocarbon fluids they

Pipeline with rock bag

NEWS

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