B3 - Moorings, anchors and foundations
B - Fluid-structure Seabed Interaction
Foundation and station-keeping systems are a major fraction of ORE system costs and critical to system response.
Novel and higher performance mooring arrangements, lines, foundations and anchor systems will reduce the costs of support and station keeping, and optimise the dynamic response of wave devices
Context And Need
For all ORE systems, multiple devices and the connecting electrical infrastructure require support or station keeping. Station-keeping requires systems of mooring lines and anchor or foundation types for a range of bed conditions. Fixed devices require foundations that provide adequate strength and stiffness. Design methods have been developed for a range of water depths, aided by knowledge transfer from other offshore engineering sectors. However, typically, the mooring and foundation systems will comprise a significant fraction of the total system costs, particularly in deeper water. Reducing these infrastructure costs is important for overall cost reduction.
Likely to require: new materials, better modelling approaches to capture the integrated behaviour of the mooring system with the floating structure, new foundation types particularly for high-energy environments.
New concepts and materials for moorings; design of coupled mooring and foundation systems and coupling mooring analysis and hydrodynamics for floating offshore wind and wave devices. Mooring systems for arrays including shared moorings and systems with multiple devices per foundation
The mooring and foundation system can be a significant part of a fixed or floating structure, in shallow water, but as water depths increase these costs generally increase significantly. Deployment of wave and tidal systems is contingent on a suitable anchoring / foundation system. Self-installing systems or novel ideas may be needed to reduce costs.
There has been significant research completed worldwide on mooring and foundation systems for fixed and floating oil and gas structures. This research should be leveraged for ORE. Recent work on anchoring includes work on driven pile design (e.g. PISA, ALPACA) as well as on screwpile design (Supergen Wind funded project).
Active research projects:
- FLOTANT (Innovative, low cost, low weight and safe floating wind technology optimized for deep water wind sites): The main objective of FLOTANT is the development of innovative solutions to improve the robustness and cost-efficiency of 10+MW wind turbine generators in deep waters (100-600m). This goal will be achieved through the design and test of specific components, as well as the assessment and optimisation of the construction, installation, operation and decommissioning techniques, in line with state-of-the-art practices and environmental constraints. Biostabilisation of sediments for erosion prevention: a cost-effective and sustainable solution: Biostabilisation artificially induces cohesion in sediments to produce highly resilient substrata to complement or replace traditional, hard-engineered scour prevention methods. It employs inert, natural biological polymers - 'biopolymers' - to inhibit particle movement, thereby increasing the sediment's resistance to erosion. A cost-effective and sustainable solution to a ubiquitous engineering problem.
- Marine Energy Engineering Centre of Excellence MEECE - The Marine Energy Engineering Centre of Excellence is advancing the Welsh marine and offshore renewable energy sectors. Research, technology innovation and testing and demonstration, reduced cost of energy, improved reliability, and supporting the Welsh supply chain.
Previous research includes:
- Development of screw anchors for floating Marine Renewable Energy system arrays incorporating anchor sharing: This project investigated the use of screw anchors for ORE applications (wind, wave, tidal). Results combine centrifuge modelling and FE analyses to calculate the anchor capacity, incorporating some installation effects. A simplified design method has been developed to fast assess the anchor capacity and optimise its geometry. Further information can be found here.
- A review of potential impacts of submarine power cables on the marine environment: Knowledge gaps, recommendations and future directions: Submarine power cables (SPC) have been in use since the mid-19th century, but environmental concerns about them are much more recent. With the development of marine renewable energy technologies, it is vital to understand their potential impacts. The commissioning of SPC may temporarily or permanently impact the marine environment through habitat damage or loss, noise, chemical pollution, heat and electromagnetic field emissions, risk of entanglement, the introduction of artificial substrates, and the creation of reserve effects. While growing numbers of scientific publications focus on impacts of the marine energy harnessing devices, data on impacts of associated power connections such as SPC are scarce and knowledge gaps persist. The present study (1) examines the different categories of potential ecological effects of SPC during installation, operation and decommissioning phases and hierarchizes these types of interactions according to their ecological relevance and existing scientific knowledge, (2) identifies the main knowledge gaps and needs for research, and (3) sets recommendations for better monitoring and mitigation of the most significant impacts. Overall, ecological impacts associated with SPC can be considered weak or moderate, although many uncertainties remain, particularly concerning electromagnetic effects.
Supergen ORE Hub Flexible funding Research
- Cost Effective Methods of Installing Offshore Wind Infrastructure
Lead Institution: Aberdeen University
This collaborative research proposal addresses a need for the development of novel, more efficient and cost effective methods for the installation of offshore windfarms. This is especially important in the context of the quest for obtaining Net Zero goals in the UK and is also of interest for temporary power supply during decommissioning of offshore Oil & Gas assets. The project builds on patented pumpable variable buoyancy technology (Deepbuoy), based on noncompressible liquids (deployable at depths up to 3000 m), incorporated into the Underwater Lifting System (ULS), developed and validated through the Knowledge Transfer Partnership project funded by Innovate UK to Technology Readiness Level 5. The proposed research programme will be underpinned by detailed modelling studies utilizing a state-of-the-art, real-time, real-physics Marine Simulator. This will be used to build models of the Deepbuoy technology to assess its applicability, benefits in terms of costs and reduced carbon footprint for installation of wind farms infrastructure.
This project will also benefit from support Offshore Renewable Energy Catapult's Floating Offshore Wind Centre of Excellence (FoW CoE).
- SharEd Anchor Multidirectional Load Envelopes with Strength Synthesis (SEAMLESS)
Lead Institution: Southampton University
This project addresses cost reduction in mooring/anchoring which is highlighted as an important research priority for floating wave and wind energy. Anchor sharing, by reducing the number of installed anchors, reduces capital expenditure of floating ORE farms that require hundreds of anchorages. The goal of this project is to identify a method for shared anchor geometry optimisation and develop new design guidance to unlock performance gains. This will be achieved by answering two fundamental questions: 'What threshold level of upwards cyclic load can be sustained without significant ratcheting?' and 'How does the stress history of vertical-lateral load interactions affect the capacity?'. To address these questions, and create a framework for design solutions, this project will identify realistic shared-type loading and use a geotechnical centrifuge to apply these to caisson anchors in dense sand, representative of UK and European seabeds. Additional data from pressure sensors and X-ray tomography of the centrifuge samples alongside element level cyclic direct shear tests (CDSS) will be combined to study the fundamental mechanisms underlying the anchor-scale behaviour. A predictive framework for capacity variations and ratcheting quantification will be developed to create V-H failure envelopes combined with cyclic degradation/enhancement diagrams, extending current practice.
- ALPHA: Numerical Analysis of Laterally Loaded Piles Divided in Chalk
Lead Institution: Imperial College London
Chalk, which can behave as a weak rock, can also be de-structured into a soft putty under pile driving or severe cyclic loading. Recent difficulties experienced offshore in chalk have highlighted an urgent need for more accurate and reliable design tools to enable robust and cost-effective foundation design for offshore wind energy developments involving this highly problematic geomaterial. This project will use pre-collected data to develop a novel numerical analysis to capture the behaviour of both individual chalk elements and full-scale offshore piles.
We would also like to invite UK researchers and industry stakeholders within ORE to submit links to research projects, both past and present, for inclusion within the landscape.
Therefore, if you have a UK-based research project within an area of ORE that you feel is relevant to a specific research theme or challenge within the Research Landscape, click HERE to submit your research project to the research landscape
PhD projects in Offshore Renewable Energy
In order to better understand the breadth of ORE research currently being conducted in the UK, the Supergen ORE Hub has collated from its academic network, UK Centres for Doctoral Training and Industrial partners, a list of PhDs currently being undertaken in ORE.