129 results found
Avdis A, Candy AS, Hill J, et al., 2018, Efficient unstructured mesh generation for marine renewable energy applications, RENEWABLE ENERGY, Vol: 116, Pages: 842-856, ISSN: 0960-1481
Collins DS, Avdis A, Allison PA, et al., 2017, Tidal dynamics and mangrove carbon sequestration during the Oligo-Miocene in the South China Sea, NATURE COMMUNICATIONS, Vol: 8, ISSN: 2041-1723
Culley DM, Funke SW, Kramer SC, et al., 2017, A surrogate-model assisted approach for optimising the size of tidal turbine arrays, International Journal of Marine Energy, Vol: 19, Pages: 357-373, ISSN: 2214-1669
© 2017 The Authors. The new and costly nature of tidal stream energy extraction technologies can lead to narrow margins of success for a project. The design process is thus a delicate balancing act - to maximise the energy extracted, while minimising cost and risk. Scenario specific factors, such as site characteristics, technological constraints and practical engineering considerations greatly impact upon both the appropriate number of turbines to include within a tidal current turbine array (array size), and the individual locations of those turbines (turbine micro-siting). Both have been shown to significantly impact upon the energy yield and profitability of an array. The micro-siting arrangement for a given number of turbines can significantly influence the power extraction of a tidal farm. Until the layout has been optimised (a process which may incorporate turbine parameters, local bathymetry and a host of other practical, physical, legal, financial or environmental constraints) an accurate forecast of the yield of that array cannot be determined. This process can be thought of as 'tuning' an array to the proposed site to maximise desirable outcomes and mitigate undesirable effects. The influence of micro-siting on the farm performance means that determining the optimal array size needs to be coupled to the micro-siting process. In particular, the micro-siting needs to be repeated for any new trial array size in order to be able to compare the performance of the different farm sizes. Considering the large number of design variables in the micro-siting problem (which includes at least the positions of each turbine) it becomes clear that algorithmic optimisation is a key tool to rigorously determine the optimal array size and layout. This paper proposes a nested optimisation approach for solving the array size and layout problem. The core of this approach consists of two nested optimisation procedures. The 'outer' optimisation determines the array size. At
Funke SW, Farrell PE, Piggott MD, 2017, Reconstructing wave profiles from inundation data, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, Vol: 322, Pages: 167-186, ISSN: 0045-7825
Parkinson SD, Funke SW, Hill J, et al., 2017, Application of the adjoint approach to optimise the initial conditions of a turbidity current with the AdjointTurbidity 1.0 model, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 10, Pages: 1051-1068, ISSN: 1991-959X
Schwedes T, Ham DA, Funke SW, et al., 2017, Mesh dependence in PDE-constrained optimisation an application in tidal turbine array layouts, Publisher: Springer, ISBN: 9783319594835
This section verifies the iteration count estimates by solving the optimisation problem (2.2) numerically. The first experiment investigates the number of optimisation iterations required to solve (2.2) under non-uniform mesh refinement.
Smith R, 2017, Numerical modelling of tsunami generated by deformable submarine slides
Submarine slides can generate tsunami waves that cause significant damage and loss of life. Numerical modelling of submarine slide generated waves is complex and computationally challenging, but is useful to understand the nature of the waves that are generated, and identify the important factors in determining wave characteristics which in turn are used in risk assessments. In this work, the open-source, finite-element, unstructured mesh fluid dynamics framework Fluidity is used to simulate submarine slide tsunami using a number of different numerical approaches. First, three alternative approaches for simulating submarine slide acceleration, deformation and wave generation with full coupling between the slide and water in two dimensions are compared. Each approach is verified against benchmarks from experimental and other numerical studies, at different scales, for deformable submarine slides. There is good agreement to both laboratory results and other numerical models, both with a fixed mesh and a dynamically adaptive mesh, tracking important features of the slide geometry as the simulation progresses. Second, Fluidity is also used in a single-layer Bousinesq approximation in conjunction with a prescribed velocity boundary condition to model the propagation of slide tsunami in two and three dimensions. A new, efficient approach for submarine slide tsunami that accounts for slide dynamics and deformation is developed by imposing slide dynamics, derived from multi-material simulations. Two submarine slides are simulated in the Atlantic Ocean, and these generate waves up to 10 m high at the coast of the British Isles. Results indicate the largest waves are generated in the direction of slide motion. The lowest waves are generated perpendicular to the slide motion. The slide velocity and acceleration are the most important factors in determining wave height. Slides that deform generate higher waves than rigid slides, although this effect is of secondary importance f
du Feu RJ, Funke SW, Kramer SC, et al., 2017, The trade-off between tidal-turbine array yield and impact on flow: A multi-objective optimisation problem, Renewable Energy, Vol: 114, Pages: 1247-1257, ISSN: 1879-0682
This paper introduces a new approach for investigating trade-offs between different societal objectives in the design of tidal-turbine arrays. This method is demonstrated through the trade-off between the yield of an array, and the extent to which that array alters the flow. This is posed as a multi-objective optimisation problem, and the problem is investigated using the array layout optimisation tool OpenTidalFarm. Motivated by environmental concerns, OpenTidalFarm is adapted to not only maximise array yield but also to minimise the effect of the array upon the hydrodynamics of the region, specifically the flow velocity. A linear scalarisation of the multi-objective optimisation problem is solved for a series of different weightings of the two conflicting objectives. Two idealised test scenarios are evaluated and in each case a set of Pareto solutions is found. These arrays are assessed for the power they generate and the severity of change they cause in the flow velocity. These analyses allow for the identification of trade-offs between these two objectives, while the methods proposed can similarly be applied to the two key societal objectives of energy production and conservation, thus providing information that could be valuable to stakeholders and policymakers when making decisions on array design.
Abolghasemi MA, Piggott MD, Spinneken J, et al., 2016, Simulating tidal turbines with multi-scale mesh optimisation techniques, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 66, Pages: 69-90, ISSN: 0889-9746
Adam A, Buchan AG, Piggott MD, et al., 2016, Adaptive Haar wavelets for the angular discretisation of spectral wave models, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 305, Pages: 521-538, ISSN: 0021-9991
Avdis A, Jacobs CT, Mouradian SL, et al., 2016, Meshing ocean domains for coastal engineering applications, Pages: 480-492
As we continue to exploit and alter the coastal environment, the quantification of the potential impacts from planned coastal engineering projects, as well as the minimisation of any detrimental effects through design optimisation, are receiving increasing attention. Geophysical fluid dynamics simulations can provide valuable insight towards the mitigation and prevention of negative outcomes, and as such are routinely used for planning, operational and regulatory reasons. The ability to readily create high-quality computational meshes is critical to such modelling studies as it impacts on the accuracy, efficiency and reproducibility of the numerical results. To that end, most (coastal) ocean modelling packages offer tailored mesh generation utilities. Geographical Information Systems (GIS) offer an ideal framework within which to process data for use in the meshing of coastal regions. GIS have been designed specifically for the processing and analysis of geophysical data and are a popular tool in both the academic and industrial sectors. On the other hand Computer Aided Design (CAD) is the most appropriate tool for designing coastal structures and is usually the user interface to generic three-dimensional mesh generation frameworks. In this paper we combine GIS and CAD with a view towards mesh generation for an impact study of the proposed Swansea Bay Tidal Lagoon project within the Bristol Channel and Severn Estuary. We demonstrate in this work that GIS and CAD can be used in a complementary way to deliver unstructured mesh generation capabilities for coastal engineering applications.
Culley DM, Funke SW, Kramer SC, et al., 2016, Integration of cost modelling within the micro-siting design optimisation of tidal turbine arrays, RENEWABLE ENERGY, Vol: 85, Pages: 215-227, ISSN: 0960-1481
Funke SW, Kramer SC, Piggott MD, 2016, Design optimisation and resource assessment for tidal-stream renewable energy farms using a new continuous turbine approach, Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Jacobs CT, Piggott MD, Kramer SC, et al., 2016, On the validity of tidal turbine array configurations obtained from steady-state adjoint optimisation, ECCOMAS Congress 2016 - Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering, Vol: 4, Pages: 8247-8261
Extracting the optimal amount of power from an array of tidal turbines requires an intricate understanding of tidal dynamics and the effects of turbine placement on the local and regional scale flow. Numerical models have contributed significantly towards this understanding, and more recently, adjoint-based modelling has been employed to optimise the positioning of the turbines in an array in an automated way and improve on simple man-made configurations (e.g. structured grids of turbines) . Adjoint-based optimisation of high-resolution and ideally 3D transient models is generally a very computationally expensive problem. Multiple approaches are therefore used in practice to obtain feasible runtimes: using high viscosity values to obtain a steady-state solution, or a sequence of steady-state solutions for "time-varying" setups; limiting the number of adjoint computations; or reformulating the problem to allow for coarser mesh resolution to make it feasible for resources assessment (e.g.  , ). However, such compromises may affect the reliability of the modelled turbines, their wakes and interactions, and thus bring into question the validity of the computed optimal turbine positions. This work considers a suite of idealised simulations of flow past tidal turbine arrays in a two-dimensional channel. It compares four regular array configurations, detailed by Divett et al.  , with the configuration found through adjoint optimisation in a steady-state, high-viscosity setup. The optimised configuration produces considerably more power than the other configurations (approximately 40% more than the best man-made configuration). The same configurations are then used to produce a suite of transient simulations that do not use constant high-viscosity, and instead use large eddy simulation (LES) to parameterise the resulting turbulent structures. All simulations are performed using OpenTidalFarm . It is shown that the 'low background viscosity'/LES simu
Kramer SC, Piggott MD, 2016, A correction to the enhanced bottom drag parameterisation of tidal turbines, Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Kramer SC, Piggott MD, 2016, A correction to the enhanced bottom drag parameterisation of tidal turbines, Renewable Energy, Vol: 92, Pages: 385-396, ISSN: 1879-0682
Hydrodynamic modelling is an important tool for the development of tidalstream energy projects. Many hydrodynamic models incorporate the effect oftidal turbines through an enhanced bottom drag. In this paper we show thatalthough for coarse grid resolutions (kilometre scale) the resulting force exertedon the flow agrees well with the theoretical value, the force starts decreasingwith decreasing grid sizes when these become smaller than the length scale ofthe wake recovery. This is because the assumption that the upstream velocitycan be approximated by the local model velocity, is no longer valid. Using linearmomentum actuator disc theory however, we derive a relationship between thesetwo velocities and formulate a correction to the enhanced bottom drag formulationthat consistently applies a force that remains close to the theoretical value,for all grid sizes down to the turbine scale. In addition, a better understandingof the relation between the model, upstream, and actual turbine velocity, aspredicted by actuator disc theory, leads to an improved estimate of the usefullyextractable energy. We show how the corrections can be applied (demonstratedhere for the models MIKE 21 and Fluidity) by a simple modification of the dragcoefficient.
Mouradian, Avdis A, Piggott M, et al., 2016, TELEMAC model archive: Integrating open-source tools for the management and visualisation of model data, 23rd TELEMAC-MASCARET User Conference (TUC-2016)
Nunez Rattia JM, Percival JR, Yeager B, et al., 2016, Numerical simulation of scour below pipelines using flexible mesh methods, Pages: 101-108
© 2016 Taylor & Francis Group, London. Evaluating bed morphological structure and evolution (specifically the scoured bed level) accurately using numerical models is critical for analyses of the stability of many marine structures. This paper discusses the performance of an implementation within Fluidity, an open source, general purpose, Computational Fluid Dynamics (CFD) code, capable of handling arbitrary multi-scale unstructured tetrahedral meshes and including algorithms to perform dynamic anisotropic mesh adaptivity. The flexibility over mesh structure and resolution that these capabilities provide makes it potentially highly suitable for coupling the structural scale with larger scale ocean dynamics. In this very preliminary study the solver approach is demonstrated for an idealised scenario. Discontinuous Galerkin finite-element (DG-FEM) based discretisation methods have been used for the hydrodynamics and morphological calculations, and automatic mesh deformation has been utilised to account for bed evolution changes while preserving the validity and quality of the mesh. In future work, the solver will be used in three-dimensional impinging jet and other industrial and environmental scour studies.
Piggott MD, 2016, Thetis
Finite element flow solver for simulating coastal and estuarine flows.
Quattrocchi G, Gorman GJ, Piggott MD, et al., 2016, M2, overtides and compound tides generation in the Strait of Messina: the response of a non-hydrostatic, finite-element ocean model, JOURNAL OF COASTAL RESEARCH, Pages: 657-661, ISSN: 0749-0208
Smith RC, Hill J, Collins GS, et al., 2016, Comparing approaches for numerical modelling of tsunami generation by deformable submarine slides, OCEAN MODELLING, Vol: 100, Pages: 125-140, ISSN: 1463-5003
Vire A, Spinneken J, Piggott MD, et al., 2016, Application of the immersed-body method to simulate wave-structure interactions, EUROPEAN JOURNAL OF MECHANICS B-FLUIDS, Vol: 55, Pages: 330-339, ISSN: 0997-7546
Jacobs CT, Avdis A, Mouradian SL, et al., 2015, Integrating research data management into geographical information systems, CEUR Workshop Proceedings, Vol: 1529, Pages: 7-17, ISSN: 1613-0073
Ocean modelling requires the production of high-fidelity com-putational meshes upon which to solve the equations of motion. The production of such meshes by hand is often infeasible, considering the complexity of the bathymetry and coastlines. The use of Geographical Information Systems (GIS) is therefore a key component to discretising the region of interest and producing a mesh appropriate to resolve the dynamics. However, all data abociated with the production of a mesh must be provided in order to contribute to the overall recomputability of the subsequent simulation. This work presents the integration of re-search data management in QMesh, a tool for generating meshes using GIS. The tool uses the PyRDM library to provide a quick and easy way for scientists to publish meshes, and all data required to regenerate them, to persistent online repositories. These repositories are abigned unique identifiers to enable proper citation of the meshes in journal articles.
Jacobs CT, Avdis A, Mouradian SL, et al., 2015, Integrating Research Data Management into Geographical Information Systems, http://ceur-ws.org/Vol-1529/, 5th International Workshop on Semantic Digital Archives (SDA 2015), Pages: 7-17
Ocean modelling requires the production of high-fidelity computational meshes upon which to solve the equations of motion. The production of such meshes by hand is often infeasible, considering the complexity of the bathymetry and coastlines. The use of Geographical Information Systems (GIS) is therefore a key component to discretising the region of interest and producing a mesh appropriate to resolve the dynamics. However, all data associated with the production of a mesh must be provided in order to contribute to the overall recomputability of the subsequent simulation. This work presents the integration of research data management in QMesh, a tool for generating meshes using GIS. The tool uses the PyRDM library to provide a quick and easy way for scientists to publish meshes, and all data required to regenerate them, to persistent online repositories. These repositories are assigned unique identifiers to enable proper citation of the meshes in journal articles.
Jacobs CT, Goldin TJ, Collins GS, et al., 2015, An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273
Jacobs CT, Piggott MD, 2015, Firedrake-Fluids v0.1: numerical modelling of shallow water flows using an automated solution framework, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 8, Pages: 533-547, ISSN: 1991-959X
Jordan JR, Kimura S, Holland PR, et al., 2015, On the Conditional Frazil Ice Instability in Seawater, JOURNAL OF PHYSICAL OCEANOGRAPHY, Vol: 45, Pages: 1121-1138, ISSN: 0022-3670
Martin-Short R, Hill J, Kramer SC, et al., 2015, .Tidal resource extraction in the Pentland Firth, UK: Potential impacts on flow regime and sediment transport in the Inner Sound of Stroma, RENEWABLE ENERGY, Vol: 76, Pages: 596-607, ISSN: 0960-1481
Piggott MD, 2015, OpenTidalFarm
OpenTidalFarm is an open-source software for simulating and optimising tidal turbine farms.The positioning of the turbines in a tidal farm is a crucial decision. Simulations show that the optimal positioning can increase the power generation of the farm by up to 50% and can therefore determine the viability of a project. However, finding the optimal layout is a difficult process due to the complex flow interactions. OpenTidalFarm solves this problem by applying an efficient optimisation algorithm onto a accurate flow prediction model.
Barnett GL, Funke SW, Piggott MD, 2014, Hybrid global-local optimisation algorithms for the layout design of tidal turbine arrays
Tidal stream power generation represents a promising source of renewableenergy. In order to extract an economically useful amount of power, tens tohundreds of tidal turbines need to be placed within an array. The layout ofthese turbines can have a significant impact on the power extracted and henceon the viability of the site. Funke et al. formulated the question of the bestturbine layout as an optimisation problem constrained by the shallow waterequations and solved it using a local, gradient-based optimisation algorithm.Given the local nature of this approach, the question arises of how optimal thelayouts actually are. This becomes particularly important for scenarios withcomplex bathymetry and layout constraints, both of which typically introducelocally optimal layouts. Optimisation algorithms which find the global optimagenerally require orders of magnitude more iterations than local optimisationalgorithms and are thus infeasible in combination with an expensive flow model.This paper presents an analytical wake model to act as an efficient proxy tothe shallow water model. Based upon this, a hybrid global-local two-stageoptimisation approach is presented in which turbine layouts are first optimisedwith the analytical wake model via a global optimisation algorithm, and furtheroptimised with the shallow water model via a local gradient-based optimisationalgorithm. This procedure is applied to a number of idealised cases and a morerealistic case with complex bathymetry in the Pentland Firth, Scotland. It isshown that in cases where bathymetry is considered, the two-stage optimisationprocedure is able to improve the power extracted from the array by as much as25% compared to local optimisation for idealised scenarios and by as much as12% for the more realistic Pentland Firth scenario whilst in many casesreducing the overall computation time by approximately 35%.
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