127 results found
Abolghasemi M, Piggott MD, Spinneken J, et al., Simulating tidal turbines with mesh optimisation and RANS turbulence models, 2015 European Wave and Tidal Energy Conference
Avdis A, Jacobs CT, Hill J, et al., Shoreline and Bathymetry Approximation in Mesh Generation for Tidal Renewable Simulations, European Wave and Tidal Conference Series
Due to the fractal nature of the domain geometry in geophysical flow simulations, a completely accurate description of the domain in terms of a computational mesh is frequently deemed infeasible. Shoreline and bathymetry simplification methods are used to remove small scale details in the geometry, particularly in areas away from the region of interest. To that end, a novel method for shoreline and bathymetry simplification is presented. Existing shoreline simplification methods typically remove points if the resultant geometry satisfies particular geometric criteria. Bathymetry is usually simplified using traditional filtering techniques, that remove unwanted Fourier modes. Principal Component Analysis (PCA) has been used in other fields to isolate small-scale structures from larger scale coherent features in a robust way, underpinned by a rigorous but simple mathematical framework. Here we present a method based on principal component analysis aimed towards simplification of shorelines and bathymetry. We present the algorithm in detail and show simplified shorelines and bathymetry in the wider region around the North Sea. Finally, the methods are used in the context of unstructured mesh generation aimed at tidal resource assessment simulations in the coastal regions around the UK.
Avdis A, Jacobs CT, Hill J, et al., Shoreline and Bathymetry Approximation in Mesh Generation for Tidal Renewable Simulations
Due to the fractal nature of the domain geometry in geophysical flowsimulations, a completely accurate description of the domain in terms of acomputational mesh is frequently deemed infeasible. Shoreline and bathymetrysimplification methods are used to remove small scale details in the geometry,particularly in areas away from the region of interest. To that end, a novelmethod for shoreline and bathymetry simplification is presented. Existingshoreline simplification methods typically remove points if the resultantgeometry satisfies particular geometric criteria. Bathymetry is usuallysimplified using traditional filtering techniques, that remove unwanted Fouriermodes. Principal Component Analysis (PCA) has been used in other fields toisolate small-scale structures from larger scale coherent features in a robustway, underpinned by a rigorous but simple mathematical framework. Here wepresent a method based on principal component analysis aimed towardssimplification of shorelines and bathymetry. We present the algorithm in detailand show simplified shorelines and bathymetry in the wider region around theNorth Sea. Finally, the methods are used in the context of unstructured meshgeneration aimed at tidal resource assessment simulations in the coastalregions around the UK.
Barral N, Knepley MG, Lange M, et al., Anisotropic mesh adaptation in Firedrake with PETSc DMPlex
Despite decades of research in this area, mesh adaptation capabilities arestill rarely found in numerical simulation software. We postulate that theprimary reason for this is lack of usability. Integrating mesh adaptation intoexisting software is difficult as non-trivial operators, such as error metricsand interpolation operators, are required, and integrating available adaptiveremeshers is not straightforward. Our approach presented here is to firstintegrate Pragmatic, an anisotropic mesh adaptation library, into DMPlex, aPETSc object that manages unstructured meshes and their interactions withPETSc's solvers and I/O routines. As PETSc is already widely used, this willmake anisotropic mesh adaptation available to a much larger community. As ademonstration of this we describe the integration of anisotropic meshadaptation into Firedrake, an automated Finite Element based system for theportable solution of partial differential equations which already uses PETScsolvers and I/O via DMPlex. We present a proof of concept of this integrationwith a three-dimensional advection test case.
Deskos G, Abolghasemi AA, Piggott MD, Wake predictions from two turbine parametrisation models using mesh-optimisation techniques, European Wave and Tidal Energy Conference, ISSN: 2309-1983
Deskos G, Piggott MD, Mesh-adaptive simulations of horizontal-axis turbine arrays using the actuator line method, arXiv:1710.03202
Funke SW, Kramer SC, Piggott MD, Design optimisation and resource assessment for tidal-stream renewable energy farms using a new continuous turbine approach, Renewable Energy, ISSN: 1879-0682
This paper presents a new approach for optimising the design of tidal stream turbine farms. In this approach, the turbine farm is represented by a turbine density function that specifies the number of turbines per unit area and an associated continuous locally-enhanced bottom friction field. The farm design question is formulated as a mathematical optimisation problem constrained by the shallow water equations and solved with efficient, gradient-based optimisation methods. The resulting method is accurate, computationally efficient, allows complex installation constraints, and supports different goal quantities such as to maximise power or profit. The outputs of the optimisation are the optimal number of turbines, their location within the farm, the overall farm profit, the farm's power extraction, and the installation cost.We demonstrate the capabilities of the method on a validated numerical model of the Pentland Firth, Scotland. We optimise the design of four tidal farms simultaneously, as well as individually, and study how farms in close proximity may impact upon one another.
Hill J, Avdis A, Mouradian S, et al., Was Doggerland catastrophically flooded by the Mesolithic Storegga tsunami?
Myths and legends across the world contain many stories of deluges andfloods. Some of these have been attributed to tsunami events. Doggerland in thesouthern North Sea is a submerged landscape thought to have been heavilyaffected by a tsunami such that it was abandoned by Mesolithic humanpopulations at the time of the event. The tsunami was generated by the Storeggasubmarine landslide off the Norwegian coast which failed around 8150 years ago.At this time there were also rapid changes in sea level associated withdeglaciation of the Laurentide ice sheet and drainage of its large proglaciallakes, with the largest sea level jumps occurring just prior to the Storeggaevent. The tsunami affected a large area of the North Atlantic leavingsedimentary deposits across the region, from Greenland, through the Faroes, theUK, Norway and Denmark. From these sediments, run-up heights of up to 20 metreshave been estimated in the Shetland Isles and several metres on mainlandScotland. However, sediments are not preserved everywhere and so reconstructinghow the tsunami propagated across the North Atlantic before inundating thelandscape must be performed using numerical models. These models can also beused to recreate the tsunami interactions with now submerged landscapes, suchas Doggerland. Here, the Storegga submarine slide is simulated, generating atsunami which is then propagated across the North Atlantic and used toreconstruct the inundation on the Shetlands, Moray Firth and Doggerland. Theuncertainty in reconstructing palaeobathymetry and the Storegga slide itselfresults in lower inundation levels than the sediment deposits suggest. Despitethese uncertainties, these results suggest Doggerland was not as severelyaffected as previous studies implied. It is suggested therefore that theabandonment of Doggerland was primarily caused by rapid sea level rise prior tothe tsunami event.
Avdis A, Candy AS, Hill J, et al., 2017, Efficient unstructured mesh generation for marine renewable energy applications, Renewable Energy, 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, ISSN: 2214-1669
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: 0960-1481
© 2017 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
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