How stick-slip bending stiffness improves subsea performance and helped avoid costly delays.
We use OrcaFlex extensively for subsea cable analysis. It’s a powerful tool – but like any digital twin, its accuracy depends on the inputs you feed it.
Following a recent analysis project on an offshore wind cable installation, we encountered an unexpected limitation. Some simulation cases flagged low wave height operating limits. We looked closer and spotted a critical assumption.
Why accurate bending stiffness modelling matters
As subsea power cables are installed, vessel motion travels down the cable as a wave. This wave can concentrate stress at the seabed touchdown point, causing curvature beyond safe design limits.
When this happens, safe weather windows shrink. Installation gets delayed. Costs go up.
We initially assumed linear bending stiffness – a common approach in OrcaFlex cable modelling. But for this case, it was an assumption worth challenging.
Using stick-slip stiffness for realistic cable response
Instead of defaulting to linear stiffness, we introduced a stick-slip bending stiffness model, based on real test data. This better represents physical behaviour, where the cable initially resists bending due to internal friction, then becomes more flexible once the friction is overcome.
That friction absorbs energy, and it fundamentally changes the system response.
Stick-slip modelling results
Watch the short comparison video.
The stick-slip model damped the compressive wave – preventing the ‘snake effect’ from travelling up the cable. This reduced peak curvature near the touchdown and increased the cable’s tension response.
Key result:
✅ Peak curvature reduced by a factor of 2 to 4
✅ Better installation performance
✅ Larger safe weather windows
Lessons for cable installation engineering
Every subsea cable installation model involves assumptions. However, those assumptions must accurately reflect reality, especially for critical parameters such as bending stiffness.
Using accurate, validated stick-slip data could mean the difference between executing a smooth cable lay and facing costly vessel standby days.
Want to reduce risk in your cable installation projects?
We’re happy to share the full model and the paper from which our data originated.
Email us at renewables@apollo.engineer to request the files.
Acknowledgements
Thanks to Stefan Schlomilch for the original insight on compressive wave behaviour in cables, and to Rupert Raymond for his insight into the problem.