Left in the wake: assessing the impact of sediment mobility in the wake of offshore wind infrastructure

Project Description:

This PhD scholarship is offered by the EPSRC Centre for Doctoral Training in Offshore Wind Energy Sustainability and Resilience; a partnership between the Universities of Durham, Hull, Loughborough and Sheffield. The project is sponsored by industry partner, The Turbidites Research Group (TRG). The successful applicant will undertake six-months of training with the rest of the CDT cohort at the University of Hull before continuing their PhD research at Loughborough University.

Offshore wind is a core component of global solutions to net-zero. However, a prerequisite is that offshore wind is sustainable and developed in an environmentally friendly manner. A key challenge within offshore wind is the development of new fixed bottom offshore windfarms, globally, and the decommissioning and repowering of extant wind farms close to end of life, in particular in the southern North Sea. Both these scenarios entail installation of much larger infrastructure, at greater extents, in more morphodynamically active areas than have currently been constructed.

(Re-)development of morphodynamically active shallow water sites by new offshore wind is important. Development of such sites suffers from the potential risks of scour by the marine environment, but also impacts the marine environment itself. Enhanced vertical mixing results in increased sediment suspension within the water column. The increase in suspended sediment concentration (water turbidity) is widely known to affect marine ecosystem functions, including reducing prey capture rates (Ortega et al., 2020), and the occurrence of phytoplankton blooms (May et al., 2003).

Within current windfarms, enhanced vertical mixing is sufficiently strong to generate sediment plumes that reach the water surface, and are visible from space. These plumes trace the turbulent wakes in the lee of offshore wind infrastructure (Bailey et al. 2024). It is hypothesised that the size of these wakes scales with the number of wind farm structures (van der Molen et al., 2014). However, the scale of observed sediment plumes is several kilometres; this is as much as an order of magnitude larger than the expected length scales over which coherent wakes may be expected to persist.

Therefore, to understand potential ecological implications, there is a need to understand the physical processes that enable the enigmatic extent of these plumes. In particular, with the ecological importance of increased turbidity, consideration needs to placed on the impact of plume buoyancy as a control on 3D flow dynamics. Further, the problem is complicated by its range of scales: from water depth at metre scales to development over hundreds of kilometres; whilst time scales may vary over two orders of magnitude between settling times and semidiurnal tides.

Research to date has focussed on field studies and remote observations (Vanhellmont & Ruddick, 2014; Bailey et al., 2024). Existing field data reveals the presence, distribution, and to some extent, the turbid concentration of sediment wakes (Bailey et al., 2024). These have evidenced that sediment from the seabed is drawn upwards from tidal flow interactions with sea-bed infrastructure through complex fluid-structure interactions. Many studies have quantified the water flow and turbulence (hydrodynamics) around cylinders and wind turbine foundations, but coupled assessment of associated water column sediment plume evolution and its properties is limited. Here, this project will develop both novel data and methods to enable advanced predictions of the spatial and temporal distribution and turbidity of sediment plumes around offshore wind infrastructure. Such advances are critical for understanding how turbid sediment plumes develop and persist around generic seafloor obstacles from nature to the industry, including: dunes, ridges and sills; pipelines and cables; bridges and tunnels; and geofluid extraction and storage infrastructure.

Critically, there is a poor understanding of the fundamental physics associated with sediment transport dynamics in the lee of offshore wind infrastructure and other seafloor obstacles. Due to the potentially high sediment concentrations in such flows, acoustic techniques are most commonly adopted during experimental studies, which are poor at quantifying three-dimensional small scale turbulent fluid motion. Similarly, the numerical techniques often adopted for simulating sediment transport flows at scale adopt sweeping assumptions about turbulent transport dynamics and sediment properties (e.g., turbulence closures within buoyancy driven flows).

This project will overcome these issues by conducting the first experiments to resolve particle transport processes around fixed bottom offshore wind foundations in high fidelity. Further, the project will collaborate with project partner TRG in development of a globally leading computational fluid dynamics model to simulate sediment transport across a range of scales.

Numerical simulations will be based on a cutting-edge Lattice Boltzmann (LB) framework. Here experiments will act to benchmark model development. Recently this method has been demonstrated as being uniquely capable of performing highly scalable, high accuracy simulations of buoyancy driven flows at large-scale (Adekanye et al., 2022).

Project partner TRG (The Turbidites Research Group), is a Joint Industry Project run for over 30-years from the University of Leeds. It has specialised in academic-industry knowledge exchange, research and innovation on deep water sediment laden density driven flows with the global energy industry. Through the TRG, the student will have opportunity to engage with a wide range of research and industry partners, including through biannual (international) workshops.

Training and development

You will benefit from a taught programme, giving you a broad understanding of the breadth and depth of current and emerging offshore wind sector needs. This begins with an intensive six-month programme at the University of Hull for the new student intake, drawing on the expertise and facilities of all four academic partners. It is supplemented by Continuing Professional Development (CPD), which is embedded throughout your 4-year research scholarship.

To aid learning and development of LB methods the successful student will be supported in attending an extended placement with the TRG at the University of Leeds, working with TRG advisor Dr Amirul Khan. Moreover, the student will be afforded overseas placement opportunities. For example, relevant summer schools, or to carry out additional experiments. These include opportunities to visit the University of Illinois Urbana-Champaign, USA, to evaluate the flow field dynamics inside monopile arrays using novel Refractive Index Matching (RIM) modelling techniques.

The prospective student is supported to become an established researcher with key transferable skills for use beyond the PhD programme. This includes but is not limited to opportunities to: undertake specialised training in CFD, management development, Safe AI training, present at international conferences, engage with industry partners and undertake an internship or policy internship in government.

Entry requirements

If you have received a First-class Honours degree, or a 2:1 Honours degree and a Masters, or a Distinction at Masters level with any undergraduate degree (or the international equivalents) in engineering, computer science, mathematics and statistics, or physics, we would like to hear from you.

If your first language is not English, or you require Tier 4 student visa to study, you will be required to provide evidence of your English language proficiency level that meets the requirements of the Aura CDT’s academic partners. This course requires academic IELTS 7.0 overall, with no less than 6.0 in each skill.

For more information visit www.auracdt.hull.ac.uk. If you have a direct question about the project, you may email auracdt@hull.ac.uk or the project supervisor.

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Funding

The CDT is funded by the EPSRC, allowing us to provide scholarships that cover fees plus a stipend set at the UKRI nationally agreed rates. These are currently circa £19,795 per annum at 2025/26 rates and will increase in line with the EPSRC guidelines for the subsequent years (subject to progress).

Eligibility

Research Council funding for postgraduate research has residence requirements. Our CDT scholarships are available to Home (UK) Students. To be considered a Home student, and therefore eligible for a full award, a student must have no restrictions on how long they can stay in the UK and have been ordinarily resident in the UK for at least 3 years prior to the start of the scholarship (with some further constraint regarding residence for education). For full eligibility information, please refer to the EPSRC website.

We also allocate a number of scholarships for International Students per cohort.