Coordinateurs du projet
Context
The SEM-REV test site, operated by Centrale Nantes and the CNRS through the LHEEA research laboratory, has all the offshore and onshore equipment needed to develop, under operational conditions, a full-scale demonstrator for recovering marine energy, mainly from offshore waves and wind. SEM-REV is equipped with oceanographic measurement instruments, the electrical infrastructure connecting the system to the coast (power cable and underwater connection hub), an electrical and communications substation connected to the ENEDIS network, and an onshore base located in Le Croisic.
One of SEM-REV’s research activities is to increase knowledge of the marine environment in order to better understand the potential environmental impacts of installing MRE demonstrators and to assess the effects of the environment on MRE devices.
The position of floating devices (oceanographic instruments, marker buoys, and demonstrators) installed in the SEMREV zone is maintained by numerous pieces of equipment (moorings, anchors) installed on the seabed and subject to sedimentary movements. The electrical equipment (connection hub, export cable terminations, and dynamic cables) linked to the export of MRE production is laid on the seabed. A better understanding of the morphodynamic processes on site is necessary in order to understand the scouring phenomena around submerged structures and to better anticipate abrasion phenomena and the associated risks.
An electrical power export cable used to transport electricity between the test site and the onshore delivery station is buried along almost the entire route. As part of the site’s environmental monitoring and to ensure that the cable is not at risk of surfacing, the XYZ position of the export cable was monitored using a TSS detector, and initial results indicate that the cable’s burial depth has changed. In order to monitor the burial depths of the cable and reduce the costs associated with TSS measurement campaigns, ECN wishes to evaluate the morphodynamic processes along the cable route at different spatial and temporal scales.
Scientific breakthroughs and innovation
This project aims, as part of a six-month internship for students with a master’s degree, to first conduct a bibliographic study of the complex hydro-sedimentary processes in the area and to analyze morphological changes and their classification based on various hydro-sedimentary data sets and sources acquired in recent years by SEM-REV. The second part of the project will consist of applying a regional-scale digital hydro-sedimentary model to assess its ability to account for bathymetric changes in sensitive areas under different oceanographic and meteorological scenarios.
Expected technical and economic impact
A better understanding of the morphodynamic processes at the SEMREV sea test site is needed in order to understand the scouring phenomena around submerged structures and to better anticipate abrasion phenomena and the associated risks.
Demonstrator
Given the significant challenges associated with the smooth operational functioning of the sea test site, the morphodynamic complexity of the area, and the environmental monitoring efforts that have benefited the SEM-REV site in recent years, the domain provides an innovative framework for research and the application of methodologies and tools for understanding the processes at work.
Results
- The changes in sedimentation resulting from TSS measurement campaigns using mobile ROVs in the water column or rolling on the seabed do not appear to be usable as such, despite the accuracy claimed by the various service providers and manufacturers. Provided that the cable remains stationary over time in the sediment layer, the TSS data on changes is not consistent with independent bathymetric surveys carried out in the area.
- Bathymetric monitoring of the area provides a consistent database of changes. Measurement biases and errors are in the order of tens of centimeters and indistinguishable from most morphodynamic movements in the area.
- However, local and occasional inaccuracies do affect some readings.
- Numerical models combining coastal circulation and sea states, once considered as a complement to field surveys, do not currently seem capable of effectively reproducing hydrodynamic forces for the study of sedimentary processes in this intermediate depth zone.
Perspectives
This project has demonstrated a need for the development of new techniques for processing bathymetric data, or proven, reliable, and cost-effective systems for monitoring cable burial.