Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences

Marine current energy conversion can provide significant electrical power from resource-rich sites. However since no large marine current turbine arrays currently exist, validation of methods for simulating energy extraction relies upon scaled down laboratory experiments. We present results from an experiment using porous fences spanning the width of a recirculating flume to simulate flow through large, regular, multi-row marine current turbine arrays. Measurements of fence drag, free surface elevation drop and velocity distribution were obtained to validate a method for parameterising array drag in the distributed drag approach, which is typically implemented in regional scale models. The effect of array density was also investigated by varying the spacing between fences. Two different inflow conditions were used; the first used the flume bed in its natural state, whilst the second used roughness strips on the flume bed to significantly enhance ambient turbulence intensity to levels similar to those recorded at tidal sites. For realistic array densities (<0.07), a depth averaged formulation of effective array drag coefficient agreed within 10% of that derived from experimental results for both inflow conditions. The validity of the distributed drag approach was shown to be dependent on longitudinal row spacing between porous fences and ambient turbulence intensity, two features that determine the level of wake recovery downstream of each porous fence. Finally a force balance analysis quantified the change in bed drag as a result of the presence of porous fence arrays. Adding arrays to the flow gave an increase in bed drag coefficient of up to 95% which was 20% of the total added bed and array drag coefficient. Results have implications for regional scale hydrodynamic modelling, where array layout along with site specific characteristics such as turbulence intensity and bed profile determine the validity of the distributed drag approach for simulating energy extraction

Assessment of the energy extraction potential at tidal sites around the Channel Islands

Tidal flows around the Channel Islands contain a significant energy resource that if harnessed could provide electrical power to the Channel Islands, the UK and France. We have developed a new 2D hydrodynamic model of the English Channel which gives an improvement to the temporal and spatial resolution of the ambient flow in comparison with previous regional scale resource assessments. The ambient flow was characterised to identify suitable sites, resulting in a reduction in total development area of up to 80% compared with previous studies. Estimates for upper bound energy extraction confirm that Alderney Race contains the majority of the Channel Islands resource, giving a maximum potential of 5.1 GW, which exceeds a previous estimate for the Pentland Firth by 35%. This is followed by Casquets (0.47 GW) and then Big Roussel (0.24 GW). Our work shows that energy extraction at Alderney Race has a constructive impact on the resource at Casquets, and that the sensitivity to added drag at each site with respect to energy extraction is highly dependent on bathymetry and the proximity of coastlines. These results have implications for the overall resource development within the Channel Islands, where regulation is needed to account for site-site interaction

Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences

Marine current energy conversion can provide significant electrical power from resource-rich sites. However since no large marine current turbine arrays currently exist, validation of methods for simulating energy extraction relies upon scaled down laboratory experiments. We present results from an experiment using porous fences spanning the width of a recirculating flume to simulate flow through large, regular, multi-row marine current turbine arrays. Measurements of fence drag, free surface elevation drop and velocity distribution were obtained to validate a method for parameterising array drag in the distributed drag approach, which is typically implemented in regional scale models. The effect of array density was also investigated by varying the spacing between fences. Two different inflow conditions were used; the first used the flume bed in its natural state, whilst the second used roughness strips on the flume bed to significantly enhance ambient turbulence intensity to levels similar to those recorded at tidal sites. For realistic array densities (<0.07), a depth averaged formulation of effective array drag coefficient agreed within 10% of that derived from experimental results for both inflow conditions. The validity of the distributed drag approach was shown to be dependent on longitudinal row spacing between porous fences and ambient turbulence intensity, two features that determine the level of wake recovery downstream of each porous fence. Finally a force balance analysis quantified the change in bed drag as a result of the presence of porous fence arrays. Adding arrays to the flow gave an increase in bed drag coefficient of up to 95% which was 20% of the total added bed and array drag coefficient. Results have implications for regional scale hydrodynamic modelling, where array layout along with site specific characteristics such as turbulence intensity and bed profile determine the validity of the distributed drag approach for simulating energy extraction

Looking back and moving forward

This chapter brings together the research on teacher resilience and approaches to supporting resilience and wellbeing discussed in this volume. As many of the approaches utilised aspects of the BRiTE and Staying BRiTE projects, I highlight common themes as well as the different ways the authors developed and implemented their work to reflect their specific contexts and participants. I also reflect on broader issues related to conceptualisation of resilience, consider where responsibility for resilience lies, and explore future directions. The chapter also provides some insights regarding the collegial collaboration that has made the body of work possible

How sharing can contribute to more sustainable cities

\ua9 2017 by the authors. Recently, much of the literature on sharing in cities has focused on the sharing economy, in which people use online platforms to share underutilized assets in the marketplace. This view of sharing is too narrow for cities, as it neglects the myriad of ways, reasons, and scales in which citizens share in urban environments. Research presented here by the Liveable Cities team in the form of participant workshops in Lancaster and Birmingham, UK, suggests that a broader approach to understanding sharing in cities is essential. The research also highlighted tools and methods that may be used to help to identify sharing in communities. The paper ends with advice to city stakeholders, such as policymakers, urban planners, and urban designers, who are considering how to enhance sustainability in cities through sharing

Current tidal power technologies and their suitability for applications in coastal and marine areas

A considerable body of research is currently being performed to quantify available tidal energy resources and to develop efficient devices with which to harness them. This work is naturally focussed on maximising power generation from the most promising sites, and a review of the literature suggests that the potential for smaller scale, local tidal power generation from shallow near-shore sites has not yet been investigated. If such generation is feasible, it could have the potential to provide sustainable electricity for nearby coastal homes and communities as part of a distributed generation strategy, and would benefit from easier installation and maintenance, lower cabling and infrastructure requirements and reduced capital costs when compared with larger scale projects. This article reviews tidal barrages and lagoons, tidal turbines, oscillating hydrofoils and tidal kites to assess their suitability for small-scale electricity generation in shallow waters. This is achieved by discussing the power density, scalability, durability, maintainability, economic potential and environmental impacts of each concept. The performance of each technology in each criterion is scored against axial-flow turbines, allowing for them to be ranked according to their overall suitability. The review suggests that tidal kites and range devices are not suitable for small-scale shallow water applications due to depth and size requirements respectively. Cross-flow turbines appear to be the most suitable technology, as they have high power densities and a maximum size that is not constrained by water depth

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe