Assessing the mechanical stresses of dynamic cables for floating offshore wind applications

D G Young,L Johanning,Q Li,C Ng,S Oterkus

doi:10.1088/1742-6596/1102/1/012016

Abstract

Offshore wind farms are progressing further offshore and into deeper waters, presenting the need for new substructures, including floating offshore wind turbines. These floating turbines will require dynamic cables to run through the water column, exposing them to the dynamic loadings of the marine environment. This paper presents a tool which models the stresses across a dynamic cable cross section’s insulation layers when attached to a floating wind platform. Differing wave, wind and current flow conditions are applied and their impact on the stress distributions of the dynamic cable’s insulation layers are presented. Finally from these stress histories, accumulated fatigue damage of the insulation is calculated and presented. The outcome of this can be used to estimate fatigue damage of a cable components cross section at any point along the cable length, and aid in cable installation configuration decisions.

Highlights

Offshore wind farms are progressing to having larger turbines installed as a cost effective means to reduce the cost of energy
Floating platform wind turbines are envisioned to be installed in water depths ranging from 50m to 200m, with the Carbon Trust estimating up to 90MW of floating wind farms are to be installed in UK waters by the end of 2018 [1]
This paper presents an assessment of the marine environment at a chosen site and presents a model which determines how the mechanical stresses across the cable cross section distribute when installed in this environment

Summary

Introduction

Offshore wind farms are progressing to having larger turbines installed as a cost effective means to reduce the cost of energy. These larger wind farms are moving further from shore and into deeper water depths. Floating platforms will introduce new challenges for the umbilical, or array, cables that hang from the base of the platform to the seabed This cable installation arrangement will expose the cables to the dynamic forces of the environment they would be installed in, including the actions of the waves, current flows and movement of the platform itself in response to wind/turbine interactions. Cables exposed to dynamic environmental loadings will experience dynamic mechanical stresses across their cross sections and along their length. This is a new operating consideration as traditional fixed bottom platforms have allowed cables to operate statically

Results

Discussion

Conclusion