Publications
209 results found
McManus TM, Percival JR, Yeager BA, et al., 2017, Moving mesh methods in Fluidity and Firedrake, Archer report eCSE06-1
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: 1991-9603
Turbidity currents are one of the main drivers ofsediment transport from the continental shelf to the deepocean. The resulting sediment deposits can reach hundredsof kilometres into the ocean. Computer models that simulateturbidity currents and the resulting sediment deposit can helpus to understand their general behaviour. However, in orderto recreate real-world scenarios, the challenge is to find theturbidity current parameters that reproduce the observationsof sediment deposits.This paper demonstrates a solution to the inverse sedimenttransportation problem: for a known sedimentary deposit, thedeveloped model reconstructs details about the turbidity cur-rent that produced the deposit. The reconstruction is con-strained here by a shallow water sediment-laden density cur-rent model, which is discretised by the finite-element methodand an adaptive time-stepping scheme. The model is differ-entiated using the adjoint approach, and an efficient gradient-based optimisation method is applied to identify the turbidityparameters which minimise the misfit between the modelledand the observed field sediment deposits. The capabilities ofthis approach are demonstrated using measurements taken inthe Miocene Marnoso-arenacea Formation (Italy). We findthat whilst the model cannot match the deposit exactly dueto limitations in the physical processes simulated, it providesvaluable insights into the depositional processes and repre-sents a significant advance in our toolset for interpreting tur-bidity current deposits.
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
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
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- Citations: 36
Abolghasemi M, 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: 1095-8622
Embedding tidal turbines within simulations of realistic large-scale tidal flows is a highly multi-scale problem that poses significant computational challenges. Here this problem is tackled using actuator disc momentum (ADM) theory and Reynolds-averaged Navier-Stokes (RANS) with, for the first time, dynamically adaptive mesh optimisation techniques. Both k-ω and k-ω SST RANS models have been developed within the Fluidity framework, an adaptive mesh CFD solver, and the model is validated against two sets of experimental flume test results. A brief comparison against a similar OpenFOAM model is presented to portray the benefits of the finite element discretisation scheme employed in the Fluidity ADM model. This model has been developed with the aim that it will be seamlessly combined with larger numerical models simulating tidal flows in realistic domains. This is where the mesh optimisation capability is a major advantage as it enables the mesh to be refined dynamically in time and only in the locations required, thus making optimal use of limited computational resources.
Funke SW, Kramer SC, Piggott MD, 2016, 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.
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)
Kramer SC, Piggott MD, 2016, A correction to the enhanced bottom drag parameterisation of tidal turbines, RENEWABLE ENERGY, Vol: 92, Pages: 385-396, ISSN: 0960-1481
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- Citations: 26
Jacobs CT, Piggott MD, Kramer SC, et al., 2016, On the validity of tidal turbine array configurations obtained from steady-state adjoint optimisation, VII European Congress on Computational Methods in Applied Sciences and Engineering, Publisher: ECCOMAS Proceedia, 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) [1]. 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. [2] , [3]). 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. [4] , 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 [1]. It is shown that the 'low background viscosity'/LES simu
Nunez Rattia JM, Percival JR, Yeager B, et al., 2016, Numerical simulation of scour below pipelines using flexible mesh methods, The 8th International Conference on Scour and Erosion, Pages: 101-108
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.
Avdis A, Jacobs CT, Mouradian SL, et al., 2016, Meshing ocean domains for coastal engineering applications, ECCOMAS Congress 2016, 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.
Deskos G, Spinneken J, Piggott MD, 2016, Impact of the free surface proximity on the performance of a single Tidal Stream Turbine: A Vortex Filament Approach, 5th Oxford Tidal Energy Workshop
In the present work, a single Horizontal Axis Tidal Turbine (HATT) is placed in an infinite widthopen-channel and is subject to a uniform free stream velocity. The Vortex Filament Method is used to model theturbine loading and the wake behind it while the free surface deformation is modelled using a panel methodbased on linear wave theory [1]. For the simulations presented here, an enhanced version of the mid-fidelityopen source code CACTUS is used. Results for the power coefficient ܥ are reported for a large number of TipSpeed Ratios ߣ and for two above turbine clearance scenarios. The extracted results are compared withexperimental data [2] showing a good agreement for a broad range of ߣ
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
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- Citations: 1
Smith R, 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
Tsunami generated by submarine slides are arguably an under-consideredrisk in comparison to earthquake-generated tsunami. Numerical simulationsof submarine slide-generated waves can be used to identify the important factorsin determining wave characteristics. Here we use Fluidity, an open sourcefinite element code, to simulate waves generated by deformable submarineslides. Fluidity uses flexible unstructured meshes combined with adaptivitywhich alters the mesh topology and resolution based on the simulationstate, focussing or reducing resolution, when and where it is required. Fluidityalso allows a number of different numerical approaches to be taken tosimulate submarine slide deformation, free-surface representation, and wavegeneration within the same numerical framework. In this work we use amulti-material approach, considering either two materials (slide and waterwith a free surface) or three materials (slide, water and air), as well as asediment model (sediment, water and free surface) approach. In all casesthe slide is treated as a viscous fluid. Our results are shown to be consistentwith laboratory experiments using a deformable submarine slide, anddemonstrate good agreement when compared with other numerical models.The three different approaches for simulating submarine slide dynamics andtsunami wave generation produce similar waveforms and slide deformationgeometries. However, each has its own merits depending on the application.Mesh adaptivity is shown to be able to reduce the computational cost withoutcompromising the accuracy of results.
Piggott MD, 2016, Thetis
Finite element flow solver for simulating coastal and estuarine flows.
Vire A, Spinneken J, Piggott MD, et al., 2016, Application of the immersed-body method to simulatewave–structure interactions, European Journal of Mechanics B: Fluids, Vol: 55, Pages: 330-339, ISSN: 1873-7390
This study aims at demonstrating the capability of the immersed-body method to simulate wave–structure interactions using a non-linear finite-element model. In this approach, the Navier–Stokes equations are solved on an extended mesh covering the whole computational domain (i.e. fluids and structure). The structure is identified on the extended mesh through a nonzero solid-concentration field, which is obtained by conservatively mapping the mesh discretising the structure onto the extended mesh. A penalty term relaxes the fluid and structural velocities to one another in the regions covered by the structure. The paper is novel in that it combines the immersed-body method with wave modelling and mesh adaptivity. The focus of the paper is therefore on demonstrating the capability of this new methodology in reproducing well-established test cases, rather than investigating new physical phenomena in wave–structure interactions. Two cases are considered for a bottom-mounted pile. First, the pile is placed in a numerical wave tank, where propagating waves are modelled through a free-surface boundary condition. For regular and irregular waves, it is shown that the wave dynamics are accurately modelled by the computational fluid dynamics model and only small discrepancies are observed in the close vicinity of the structure. Second, the structure is subjected to a dam-break wave impact obtained by removing a barrier between air and water. In that case, an additional advection equation is solved for a fluid-concentration field that tracks the evolution of the air–water interface. It is shown that the load associated with the wave impact on the structure compares well with existing numerical and experimental data.
Robinson D, Wood M, Piggott M, et al., 2016, CFD modelling of marine discharge mixing and dispersion, JOURNAL OF APPLIED WATER ENGINEERING AND RESEARCH, Vol: 4, Pages: 152-162, ISSN: 2324-9676
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- Citations: 13
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.
Adam A, Buchan AG, Piggott MD, et al., 2015, Adaptive Haar wavelets for the angular discretisation of spectral wave models, Journal of Computational Physics, Vol: 305, Pages: 521-538, ISSN: 1090-2716
A new framework for applying anisotropic angular adaptivity in spectral wave modelling is presented. The angular dimension of the action balance equation is discretised with the use of Haar wavelets, hierarchical piecewise-constant basis functions with compact support, and an adaptive methodology for anisotropically adjusting the resolution of the angular mesh is proposed. This work allows a reduction of computational effort in spectral wave modelling, through a reduction in the degrees of freedom required for a given accuracy, with an automated procedure and minimal cost.
Culley DM, Funke SW, Kramer SC, et al., 2015, Integration of cost modelling within the micro-siting design optimisation of tidal turbine arrays, Renewable Energy, Vol: 85, Pages: 215-227, ISSN: 1879-0682
The location of individual turbines within a tidal current turbine array – micro-siting – can have a significant impact on the power that the array may extract from the flow. Due to the infancy of the industry and the challenges of exploiting the resource, the economic costs of realising industrial scale tidal current energy projects are significant and should be considered as one of the key drivers of array design. This paper proposes a framework for the automated design of tidal current turbine arrays in which costs over the lifespan of the array may be modelled and considered as part of the design optimisation process. To demonstrate this approach, the cost of sub-sea cabling is incorporated by implementing a cable-routing algorithm alongside an existing gradient-based array optimisation algorithm. Three idealised test scenarios are used to demonstrate the effects of a financial-return optimising design approach as contrasted with a power maximisation approach.
Avdis A, Jacobs CT, Hill J, et al., 2015, Shoreline and Bathymetry Approximation in Mesh Generation for Tidal Renewable Simulations, European Wave & Tidal Energy
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.
Abolghasemi M, Piggott MD, Spinneken J, et al., 2015, Simulating tidal turbines with mesh optimisation and RANS turbulence models, 2015 European Wave and Tidal Energy Conference
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
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- Citations: 11
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
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- Citations: 96
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.
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, 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
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- Citations: 9
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
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- Citations: 11
Kimura S, Holland PR, Jenkins A, et al., 2014, The Effect of Meltwater Plumes on the Melting of a Vertical Glacier Face, JOURNAL OF PHYSICAL OCEANOGRAPHY, Vol: 44, Pages: 3099-3117, ISSN: 0022-3670
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- Citations: 55
Hill J, Collins GS, Avdis A, et al., 2014, How does multiscale modelling and inclusion of realistic palaeobathymetry affect numerical simulation of the Storegga Slide tsunami?, Ocean Modelling, Vol: 83, Pages: 11-25, ISSN: 1463-5003
The ∼8.15 ka Storegga submarine slide was a large (∼3000 km3), tsunamigenic slide off the coast of Norway. The resulting tsunami had run-up heights of around 10–20 m on the Norwegian coast, over 12 m in Shetland, 3–6 m on the Scottish mainland coast and reached as far as Greenland. Accurate numerical simulations of Storegga require high spatial resolution near the coasts, particularly near tsunami run-up observations, and also in the slide region. However, as the computational domain must span the whole of the Norwegian-Greenland sea, employing uniformly high spatial resolution is computationally prohibitive. To overcome this problem, we present a multiscale numerical model of the Storegga slide-generated tsunami where spatial resolution varies from 500 m to 50 km across the entire Norwegian-Greenland sea domain to optimally resolve the slide region, important coastlines and bathymetric changes. We compare results from our multiscale model to previous results using constant-resolution models and show that accounting for changes in bathymetry since 8.15 ka, neglected in previous numerical studies of the Storegga slide-tsunami, improves the agreement between the model and inferred run-up heights in specific locations, especially in the Shetlands, where maximum run-up height increased from 8 m (modern bathymetry) to 13 m (palaeobathymetry). By tracking the Storegga tsunami as far south as the southern North sea, we also found that wave heights were high enough to inundate Doggerland, an island in the southern North Sea prior to sea level rise over the last 8 ka.
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