Development of a method combining numerical modelling and fibre-optic measurements to determine the mechanical state of submarine power cables of floating wind turbines

Supervisors: P. Cartraud

GeM, Institut de Recherche en Génie Civil et Mécanique, UMR CNRS 6183, Ecole Centrale de Nantes, Nantes, France

1. Introduction and background

The submarine power cables that transmit the energy produced by offshore wind turbines are exposed to the loadings of underwater installation, external attack and those resulting from hydrodynamic forces and the movement of the turbine platform. Each year, cable-related losses account for an average of 77% of the total cost of losses on offshore wind farms worldwide. 

This Ph.D is part of a project funded by the French Environment and Energy Management Agency (ADEME). The aim is to develop a system for modelling, monitoring and predicting the remaining structural lifetime of submarine cables for marine renewable energies. The project partners are Febus Optics, EDF R&D, the Open-C Foundation and Centrale Nantes.

The project is based on a technology for measuring deformation using an optical fibre embedded in the cable. Currently, the specific arrangement of the optical fibres alters the mechanical transfer between the fibres and the various components of the cable. As a result, deformation measurements from the optical fibres alone are insufficient to fully characterize the mechanical state of the cable. This issue has received limited attention to date. It is highly dependent on the cable design and its complexity, which varies from one installation to another. This constitutes a significant obstacle to the use of fibre-optic measurements.

2.        Description of the Ph.D

In this context, the objective of the Ph.D is to enhance these measurements with numerical simulation results to fully determine the state of the cable. 

However, numerical modelling of submarine power cables remains challenging [1-2], due to their numerous components, some of which have helical geometries, and due to contact non-linearities, which lead to non-linear bending behavior. Additionally, some data (such as the initial stress state, friction coefficients, etc.) are not well known. Furthermore, it is not feasible to use a cable model representing all the details of its structure to analyze a cable several tens of meters long, as this would result in prohibitive computation times.

Therefore, it is necessary to rely on multi-scale approaches that combine detailed local models [3-4] to accurately represent the cable's components, and simplified global models to determine its overall response.

The main objective of the Ph.D is to use these two models, along with optical fibre measurements, to characterize the complete response of the cable. A methodology to achieve this objective will be established.

The development and validation of this methodology will take place in several stages through tests:

• in the laboratory under controlled conditions on a model cable, through mechanical tests (tensile, bending),
• in a wave basin, at a reduced scale, considering various sea states,
• at sea, at full scale.

The tests in the basin and at sea will be modeled using a code developed by EDF R&D, in which the cable’s non-linear mechanical model will be coupled with a hydro-aero-servo-elastic code [5], [6], [7] that accounts for the entire system (wind turbine, platform, cables, and fluid environment).

Once the overall methodology has been validated, it can also be used to assess the local stresses in the cable components, from which the lifetime of the components can be estimated.

The ultimate goal of the Ph.D is to combine fibre-optic measurements with the results of numerical modelling to better assess cumulative fatigue, ideally updating the cable’s service life consumption.

The main skills required for this Ph.D are:

• continuum and structural mechanics,
• numerical and finite element methods.

The person recruited will be present at these tests. However, his/her primary task will be to model the cable at different scales and implement the overall methodology.

Previous work on the local and global modelling of electrical cables has already been performed at GeM at Centrale Nantes and will serve as a starting point for this Ph.D. The work will also be based on software developments carried out at EDF R&D.

Main references:

[1] Cerik, B. C., & Huang, L. (2024). Recent advances in mechanical analysis and design of dynamic power cables for floating offshore wind turbines. Ocean Engineering, 311, 118810.

[2] Fang, P., Li, X., Jiang, X., Hopman, H., & Bai, Y. (2025). Methods for the local mechanical analysis of submarine power cables: A systematic literature review. Marine Structures, 101, 103763.

[3] Ménard, F., & Cartraud, P. (2023). A computationally efficient finite element model for the analysis of the non-linear bending behaviour of a dynamic submarine power cable. Marine Structures, 91, 103465.

[4] Fang, P., Li, X., Jiang, X., Hopman, H., & Bai, Y. (2023). Bending study of submarine power cables based on a repeated unit cell model. Engineering Structures, 293, 116606.

[5] Antonutti, R., Peyrard, C., Incecik, A., Ingram, D., Johanning, L. (2023). Dynamic mooring simulation with Code_Aster with application to a floating wind turbine. Ocean Engineering, 151 (2018) 366–377.

[6] https://www.edf.fr/groupe-edf/inventer-lavenir-de-lenergie/rd-un-savoir-faire-mondial/toutes-les-actualites-de-la-rd/la-rd-dedf-aux-cotes-de-edf-renouvelables-sur-leolien-en-mer-flottant

[7] https://www.sintef.no/globalassets/project/eera-deepwind-2025/presentasjoner/7b-marine-operations_coquio.pdf

Centrale Nantes provides initial and continuing education for engineers in the scientific, technological and economic fields, as well as in the social and human sciences. It provides research training leading to doctorates and other national postgraduate degrees.

Centrale Nantes conducts fundamental and applied research in scientific and technical fields. It contributes to the development of the results obtained, to the dissemination of scientific and technical information and to international cooperation.

On its campus, the school has 2,200 students (engineering students, continuing education students, masters and doctoral students) and 400 research staff, including 150 teacher-researchers and researchers who belong to research laboratories.

GeM is a joint Research Center of Centrale Nantes, University of Nantes and CNRS (French National Research Center). It brings together the expertise of the Nantes Saint-Nazaire area in the field of civil engineering, mechanics of materials and processes, modeling and simulation in structural mechanics.

GeM gathers around 240 people, with 80 faculty members, 50 administrative and support staff, around 100 doctoral students and 10 post-doc.

GeM is also involved at Master level, and offers several Master programs in mechanics, civil engineering, and marine technology.

The research activities at GeM aim to develop innovative manufacturing processes, simulation tools suited for the design of parts, engineering structures and products lifecycle management, taking into account the influence of severe loadings and environmental actions.

The Ph.D requires skills in continuum and structural mechanics, as well as numerical and finite element methods.