Integrated Numerical Modelling System for Extreme Wave Events at the Wave Hub Site

This paper examines an extreme wave event which occurred during a storm at the Wave Hub site in 2012. The extreme wave of 9.57 m height was identified from a time series of the heave data collected by an Oceanor Seawatch Mini II Buoy deployed at the site. An energy density spectrum was derived from this time series and then used to drive a physical model, which represents the extreme wave at 1:20 scale in Plymouth University’s new COAST Lab. The NewWave technique was used to define the input to the physical model. The experiment is reproduced in a numerical wave tank using the fully nonlinear CFD library OpenFOAM® and the wave generation toolbox waves2Foam. Results are evaluated, and issues regarding the predictions of a numerical model that is driven by the NewWave input signal are discussed. This study sets the basis for further research in coupling field data, physical modelling and numerical modelling in a more efficient and balanced way. This will lead to the new approach of composite modelling that will be implemented in future work

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

CCP-WSI Blind Test Series 2: Assessment of focused wave impacts on floating WECs using OpenFOAM

The presented work represents an individual contribution to the CCP-WSI Blind Test Series 2, in which the submitted results are compared against both physical and alternative numerical solutions for varying wave steepness achieved through changes in peak frequency. Reducing the time taken to provide reliable results is critical if computational fluid dynamics (CFD) is to become a routine design tool for offshore renewable energy devices. This can potentially be achieved by simplifying simulation setup, and hence reducing the required man-hours, through standardised `best practice' procedures. Therefore, in the absence of validation data, the scope of this study is to provide a `blind' estimation of numerical accuracy in simulations of focused wave interactions with floating wave energy converters (WECs). The present numerical results are obtained using open-source CFD with waves generated via linear superposition of first order wave components, derived from empty tank data. Two geometries are considered and the effect of wave steepness on surge, heave and pitch motion, along with the load in the mooring, is examined. Based solely on the reproduction of the known empty tank data, the numerical predictions are estimated to be within 10% of the experimental data in peak motion and mooring loads

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

Trends in floating offshore wind platforms: A review of early-stage devices

This study reviews early-stage floating offshore wind turbine (FOWT) platform designs. The 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. The evolution of FOWT platforms is described, and it is shown how FOWT platforms were originally influenced by floating platforms typically used in the oil and gas industry, but FOWT platforms have deviated away from these conventional floater designs to suit the specific needs of the technology. Four phases are defined to characterize chronological shifts in design thinking. There has been a number of alternative cost reduction strategies recently, including (i) specializing the platform to a particular location or environment, (ii) increasing manufacturability, and (iii) designing an innovative platform which diverges further from conventional designs. For the latter strategy, there has been an emergence of multi-turbine platforms, hybrid platforms, platforms which use a combination of stability mechanisms, and hydrodynamically specialized platforms. Finally, potential future trends are discussed, and it is shown that competing priorities for platform designers in the future will likely mean that the design space must compromise between increasing standardization and increasing specialization