DEEPSEA employs in-house models to perform structural assessments of flexibles as part of the design process and regularly undertakes these engineering activities for flexible pipe suppliers .
The following key structural properties are included:
- Axial, torsional and radial stiffnesses
- Load coupling and torsional balance
- Load sharing of the internal components for given loading
These can be used in the global dynamic analyses as well as the fatigue assessment. Other important structural behaviour includes:
- Bending moment changes depending on curvature
- Critical curvature delimits this behaviour
- Helical component slippage initiates at neutral axis
- Components at extreme positions may not slide
- Inter-component friction & contact pressure influence speed of transition from no slip to full slip condition for a component
Internal friction affects the local structural analysis and is therefore an important phenomenon to correctly model. There are two conditions:
- No slip
- Full slip – component no longer contributes to bending stiffness
Most models assume slip occurs everywhere for a helical component once the critical curvature is exceeded. DEEPSEA’s model accounts for the gradual progression of slip regions and therefore results in a more accurate value for the bending stiffness.
This tends to increase the stress in a helical component and therefore must be considered to assure conservative results.
Umbilicals
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