The Problem

Cable protection systems (CPS) are a requirement on the vast majority of offshore windfarms. They are designed to protect the power cable between the hang-off deck and the transition into burial. It is important that the manufacturers, installers and buyers of these systems have confidence that they perform as designed and give the required protection throughout the design life. However, these systems exhibit complex structural behaviour and if this is not properly quantified then the results of any analysis will be invalid.

The Solution

AgileTek have developed detailed analysis models for each element of the CPS:

HANG-OFF

Cable hang-off is modelled from the point at which the armour wires are fixed in translation and rotation. The part of the cable inside the monopile is shielded from environmental loading but is allowed to be influenced by CPS movement at the monopile interface.

LATCH

Some Cable Protection Systems require a latched interface. But when this is required, the latch body must be smaller than the hole within the monopile in order to allow installation, which introduces a complex boundary condition at the interface whereby the latch is allowed to rotate in vertical and horizontal planes by differing amounts. Modelling this condition is achieved in our global models with interconnected rotational constraints.

This allows us to determine the precise combination of shear force, axial force and bend moment at each point in the latch assembly, and we can then put models into local structural FEA which exhibit hyperelastic material behaviour. This way the extreme loads in every single latch component can be verified against design limits.

BEND LIMITING

The bend limiting components will exhibit complex non-linear behaviour. Using an arbitrary relationship here can result in under or over estimation of loads at various points in the system. We use local FEA models to determine the exact relationship between curvature and restoring moments which we then can use in our global models.