Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta

By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition temperature, Tc, and room temperature. Below Tc the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.Comment: 17 pages, 1 table, 5 figures, submitted to PR

Supplementary information on early-stage floating offshore wind platform designs

This document serves as supplementary information to the authors' review paper on early-stage floating offshore wind turbine (FOWT) platform designs. The review paper is the second part in a study on FOWT platform designs, following a review of FOWT platforms which currently have or have previously had a prototype, demonstration, or farm scale project at-sea. The present review covers 86 past and current early-stage platform designs, ranging from early conceptual designs to platforms which have undergone lab tests simulating extreme conditions. In this supplementary information document, more details are provided about all 86 platforms reviewed. For each device, the following is included (if available): (i) a description of the platform and its unique features, (ii) a rough timeline of development, (iii) design goals and constraints, (iv) evolution of the design, (v) lab testing information, and (vi) published dimensions. Two sections are included: one section contains the platforms that are no longer in development (i.e., there has been no new development since 2018), and the other section contains the platforms still in development today. Within each sub-section, platforms designed to hold a single turbine are presented first, then platforms designed to hold multiple turbines, and finally hybrid platforms

The Normal State Resistivity of Grain Boundaries in YBa2Cu3O7-delta

Using an optimized bridge geometry we have been able to make accurate measurements of the properties of YBa2Cu3O7-delta grain boundaries above Tc. The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band-bending allows us to estimate the height of the potential barrier present at the grain boundary interface.Comment: 11 pages, 3 figure

Time-Splitting Coupling of WaveDyn with OpenFOAM by Fidelity Limit Identified from a WEC in Extreme Waves

Survivability assessment is the complexity compromising Wave energy development. The present study develops a hybrid model aiming to reduce computational power while maintaining accuracy for survivability assessment of a Point-Absorber (PA) Wave Energy Converter (WEC) in extreme Wave Structure Interaction (WSI). This method couples the fast inviscid linear potential flow time-domain model WaveDyn (1.2, DNV-GL, Bristol, UK) with the fully nonlinear viscous Navier–Stokes Computational Fluid Dynamics (CFD) code OpenFOAM (4.2, OpenFOAM.org, London, UK). The coupling technique enables the simulation to change between codes, depending on an indicator relating to wave steepness identified as a function of the confidence in the linear model solution. During the CFD part of the simulation, the OpenFOAM solution is returned to WaveDyn via an additional load term, thus including viscous effects. Developments ensure a satisfactory initialisation of CFD simulation to be achieved from a ‘hot-start’ time, where the wave-field is developed and the device is in motion. The coupled model successfully overcomes identified inaccuracies in the WaveDyn code due to the inviscid assumption and the high computational cost of the OpenFOAM code. Experimental data of a PA response under extreme deterministic events (NewWave) are used to assess WaveDyn’s validity limit as a function of wave steepness, in order to validate CFD code and develop the coupling. The hybrid code demonstrates the applicability of WaveDyn validity limit and shows promising results for long irregular sea-state applications

Feasibility study of mooring lines design for a floating tidal turbine platform using double hull structure

The aim of this paper is to study the mooring tension characteristics on a tidal energy converter (TIC) platform considering i) a horizontal and ii) a vertical tidal turbine. The study examines numerically the feasibility of a catenary mooring line for a modular tidal energy platform. A modular platform is designed and modelled with two floating hulls and anchored by studlink catenary mooring chains on the seabed. Vertical and horizontal axis turbines which have similar Cp are selected and modelled separately. The effect of those turbines on the mooring system are compared and the results informs lifetime of the mooring component for each turbine connection. The hydrodynamic model with no turbine is firstly developed and validated against an experiment with 1:12 scale ratio. The starboard fore mooring line tension, platform surge and pitch displacements are validated against the experiment. The model results show identical signal frequency with slightly different magnitude from the experiment. The mooring tension under vertical and horizontal tidal turbine operations in the particular environment is further examined. The result shows that the mooring line using selected vertical axis turbine experiences higher tension. For platform motions, the horizontal turbine generates slightly larger displacement in surge. However the pitch motion record shows equal displacement under both turbine operations. The selected vertical axis tidal turbine also produces longer lifetime mooring components

A randomised trial of an internet weight control resource: The UK Weight Control Trial [ISRCTN58621669]

BACKGROUND: Obesity treatment is notoriously unsuccessful and one of the barriers to successful weight loss reported by patients is a lack of social support. The Internet offers a novel and fast approach to the delivery of health information, enabling 24-hour access to help and advice. However, much of the health information available on the Internet is unregulated or not written by qualified health professionals to provide unbiased information. The proposed study aims to compare a web-based weight loss package with traditional dietary treatment of obesity in participants. The project aims to deliver high quality information to the patient and to evaluate the effectiveness of this information, both in terms of weight loss outcomes and cost-effectiveness. METHODS: This study is a randomised controlled trial of a weight loss package against usual care provided within General Practice (GP) surgeries in Leeds, UK. Participants will be recruited via posters placed in participating practices. A target recruitment figure of 220 will enable 180 people to be recruited (allowing for 22% dropout). Participants agreeing to take part in the study will be randomly allocated using minimisation to either the intervention group, receiving access to the Internet site, or the usual care group. The primary outcome of the study will be the ability of the package to promote change in BMI over 6 and 12 months compared with traditional treatment. Secondary outcomes will be the ability of the Internet package to promote change in reported lifestyle behaviours. Data will be collected on participant preferences, adherence to treatment, health care use and time off work. Difference in cost between groups in provision of the intervention and the cost of the primary outcome will also be estimated. CONCLUSION: A positive result from this study would enhance the repertoire of treatment approaches available for the management of obesity. A negative result would be used to inform the research agenda and contribute to redefining future strategies for tackling obesity

Loads on a point-absorber wave energy converter in regular and focused extreme wave events

Accurate modeling and prediction of extreme loads for survivability is of crucial importance if wave energy is to become commercially viable. The fundamental differences in scale and dynamics from traditional offshore structures, as well as the fact that wave energy has not converged around one or a few technologies, implies that it is still an open question how the extreme loads should be modeled. In recent years, several methods to model wave energy converters in extreme waves have been developed, but it is not yet clear how the different methods compare. The purpose of this work is the comparison of two widely used approaches when studying the response of a point-absorber wave energy converter in extreme waves, using the open-source CFD software OpenFOAM. The equivalent design-waves are generated both as equivalent regular waves and as focused waves defined using NewWave theory. Our results show that the different extreme wave modeling methods produce different dynamics and extreme forces acting on the system. It is concluded that for the investigation of point-absorber response in extreme wave conditions, the wave train dynamics and the motion history of the buoy are of high importance for the resulting buoy response and mooring forces

Numerical Modelling of a Floating OWC-WEC Using CFD

Economical conversion of ocean waves into electricity remains a challenge for the marine engineering community. Consequently the wave energy industry has yet to converge on a solution for the design of an effective Wave Energy Converter (WEC). Among the concepts proposed, devices incorporating an Oscillating Water Column (OWC) have proven popular with developers and many of the most technologically ready devices are OWC-based WECs. Furthermore, the key benefits of OWC-WECs, including simplicity and strong reliability/survival characteristics, make such devices ideal candidates for co-located installations. Due to the increasing interest in OWC-type WECs, the numerical tools used in WEC development need to be adapted to accommodate the unique characteristics of these devices. The aim of this study is to ascertain the key challenges involved in simulating a floating OWC-WEC in a fully nonlinear Navier-Stokes solver and suggest potential improvements to the modelling process. An existing tool, developed for simple point-absorbers [1], has been adapted in order to reproduce a physical heave decay test involving a freely-floating, 1:40 scale model OWC-WEC. As anticipated, the Power Take-Off (PTO) is the key area of interest. At scale the PTO is approximated using an orifice plate to restrict the flow of air and provide a pressure head across the plate equivalent to that of a scaled turbine (used in the full-scale PTO). Crucially, the orifice plate accelerates the flow of air resulting in high velocity jets that would not otherwise be present at full-scale. Therefore, in addition to the complexities associated with properly representing the compressibility of the air in the internal chamber, an exact numerical model of the scale OWC-WEC must accommodate relatively high speed air flow. Extreme heterogeneity in the velocity field, such as that caused by the accelerated flow through the orifice plate, is a significant issue for mesh-based Navier-Stokes solvers (Fig. 1). In order to correctly capture the flow in the high-velocity region the mesh resolution has to be increased. Furthermore, in order to retain simulation stability, i.e. satisfy the Courant condition, the time-resolution must also be increased. Consequently, the CPU cost of such simulations rapidly becomes excessive, rendering these methods inappropriate for routine design processes. In order to make use of these high fidelity tools in the design process of OWC-WECs an alternative method to describe the PTO is required