Session: 06-13-01 Towed and Undersea Cables and Pipes, Mooring, and Buoy Technology

Paper Number: 80516

80516 - Numerical and Empirical Based Fatigue Life Analyses of Submarine Cables Under Hydrodynamic Loads 

High-voltage submarine cables are widely used either to establish energy connections between offshore installations or to connect offshore structures to an onshore grid. For the most part, these cables are typically installed around 1.5 metres beneath the sea flow. However, near the respective offshore foundation structure cables must be elevated above sea floor level, often creating significant free spans, especially for floating platforms. Thus, parts of these cables are exposed to considerable transient hydrodynamic loads, caused by waves and currents resulting in significant deflections. Since failures of subsea cables lead to time-consuming repairs and high economic losses, it should be ensured that the resulting stresses on the free span cannot cause premature fatigue damage during the desired lifetime.

In order to perform meaningful fatigue life analyses and estimate the state of fatigue of existing submarine cables, detailed knowledge of the fluid-structure interaction for a variety of load cases as well as reliable data on the fatigue behaviour of the complex overall cable is required. To protect the conductor, submarine export cables consist of several layers. Here, a lead sheathing ensures complete radial water tightness. Regarding transient loads, due to the low fatigue resistance of lead this layer turnes out to be the weak point of the cable geometry. Accordingly, experimental investigations on full-scale cables are carried out in order to determine the cable’s stress-cycle curve.

Fully flexible, nonlinear time domain simulations are then used to determine transient stress distributions within the cable for defined load cases. Here, a non-linear model based on reduced finite element structures was developed and implemented. Finally, based on the fatigue data previously determined during the experiments, a damage analysis is carried out using rainflow-counting.

Presenting Author: Christoph Otto University of Rostock

Authors:

Clemens Schütt University of Rostock
Christoph Otto University of Rostock
Sascha Kosleck University of Rostock