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EGFoRMEG: Enhanced Gravity Foundations on Rock for Marine Energy Generators

  • Supervisors: Dr. Michael Brown (University of Dundee) & Ana Ivanovic (University of Aberdeen)
  • Sponsor Company: Lloyd’s Register EMEA
  • PhD Student: Andreas Ziogos 

Investigations of the costs associated with the installation of marine energy generators (tidal stream, wave bobbing units and offshore wind) all highlight that foundation/anchoring installation (and mooring) make up to 25-30% of the cost of manufacture and installation of the devices. This figure is very high and needs to be reduced to improve financial viability of marine energy generators. In the case of tidal stream, the main reason for these large costs is that many marine generation systems are either large working prototypes or at the field study stage where a small number of generator configurations have been trialled. This has resulted in bespoke foundation systems that have to be installed in difficult conditions using surface techniques in parallel with divers. This limits the mobility of the generators and may make recovery for repair/maintenance difficult.

One simple alternative would be to design the foundation as a gravity base where resistance to loading is provided by the self-weight of the device and the interface friction between the seabed and the foundation. Tidal stream energy projects need to be located in areas of strong tidal currents. This often means that the seabed sediment has been scoured away by currents leaving exposed rock. Very little work has been done to assess the interface friction between steel foundations and rock meaning that quite conservative design is required leading to unnecessary cost increases. The nature of the problem is not only limited to marine energy but also exists in both onshore and offshore wind energy projects where the wind turbine foundations are formed by gravity bases.

The objective of the project is to develop a greater understanding of the material controls on the foundation interface behaviour of gravity based foundations on rock. The outcome of the research will be to develop a database of rock/foundation interface properties and improved design procedures that will lead to less conservative design for marine energy generators. It is hoped that through the research modifications to gravity based foundations on rock will also be developed that will enhance their capacity. The use of gravity based systems will allow the movement of generators with low associated costs and will negate the need for costly permanent anchoring systems. Understanding the current limitations of gravity structures will also allow the development of cost effective foundation modifications that will extend the safe working window of the system and allow deployment in more onerous stream conditions without risk to the generator and associated infrastructure.