122 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
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.
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.
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, Pages: 15698-15698, ISSN: 2041-1723
Modern mangroves are among the most carbon-rich biomes on Earth, but their long-term (≥10(6) years) impact on the global carbon cycle is unknown. The extent, productivity and preservation of mangroves are controlled by the interplay of tectonics, global sea level and sedimentation, including tide, wave and fluvial processes. The impact of these processes on mangrove-bearing successions in the Oligo-Miocene of the South China Sea (SCS) is evaluated herein. Palaeogeographic reconstructions, palaeotidal modelling and facies analysis suggest that elevated tidal range and bed shear stress optimized mangrove development along tide-influenced tropical coastlines. Preservation of mangrove organic carbon (OC) was promoted by high tectonic subsidence and fluvial sediment supply. Lithospheric storage of OC in peripheral SCS basins potentially exceeded 4,000 Gt (equivalent to 2,000 p.p.m. of atmospheric CO2). These results highlight the crucial impact of tectonic and oceanographic processes on mangrove OC sequestration within the global carbon cycle on geological timescales.
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
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 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
© 2017 Elsevier B.V. This paper applies variational data assimilation to inundation problems governed by the shallow water equations with wetting and drying. The objective of the assimilation is to recover an unknown time-varying wave profile at an open ocean boundary from inundation observations. This problem is solved with derivative-based optimisation and an adjoint wetting and drying scheme to efficiently compute sensitivity information. The capabilities of this approach are demonstrated on an idealised sloping beach setup in which the profile of an incoming wave is reconstructed from wet/dry interface observations. The method is robust to noise in the observations if a regularisation term is added to the optimisation objective. Finally, the method is applied to a laboratory experiment of the Hokkaido-Nansei-Oki tsunami, where the wave profile is reconstructed with a relative L ∞ error of less than 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: 1991-959X
© 2017 Author(s). Turbidity currents are one of the main drivers of sediment transport from the continental shelf to the deep ocean. The resulting sediment deposits can reach hundreds of kilometres into the ocean. Computer models that simulate turbidity currents and the resulting sediment deposit can help us to understand their general behaviour. However, in order to recreate real-world scenarios, the challenge is to find the turbidity current parameters that reproduce the observations of sediment deposits. This paper demonstrates a solution to the inverse sediment transportation problem: for a known sedimentary deposit, the developed model reconstructs details about the turbidity current that produced the deposit. The reconstruction is constrained here by a shallow water sediment-laden density current model, which is discretised by the finite-element method and an adaptive time-stepping scheme. The model is differentiated using the adjoint approach, and an efficient gradient-based optimisation method is applied to identify the turbidity parameters which minimise the misfit between the modelled and the observed field sediment deposits. The capabilities of this approach are demonstrated using measurements taken in the Miocene Marnoso-arenacea Formation (Italy). We find that whilst the model cannot match the deposit exactly due to limitations in the physical processes simulated, it provides valuable insights into the depositional processes and represents a significant advance in our toolset for interpreting turbidity current deposits.
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
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
© 2016 The Authors 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 lim ited computational resources.
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
© 2015 The Authors. 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.
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
© 2015 The Authors. 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.
Funke SW, Kramer SC, Piggott MD, et al., 2016, Design optimisation and resource assessment for tidal-stream renewable energy farms using a new continuous turbine approach, Publisher: PERGAMON-ELSEVIER SCIENCE LTD
© 2016 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.
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, 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.
Kramer SC, Piggott MD, Kramer SC, et al., 2016, A correction to the enhanced bottom drag parameterisation of tidal turbines, Publisher: PERGAMON-ELSEVIER SCIENCE LTD
© 2016 The Authors. Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.
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, Vol: 1, Pages: 657-661, ISSN: 0749-0208
© Coastal Education and Research Foundation, Inc. 2016. The nonlinear interactions between the main tidal constituents and geographical constraints are investigated using Fluidity-ICOM, a non-hydrostatic finite-element ocean model that was implemented in the region of the Strait of Messina (Mediterranean Sea). As a first crucial approach, the barotropic tidal dynamics was investigated and the model solution was interpreted in terms of tidal maps and spectra obtained by harmonic analysis of the sea surface elevation. The model domain is represented by an unstructured mesh with variable spatial resolution ranging from two kilometres to fifty meters, in order to resolve the shoreline in the inner part of the Strait. Amplitudes and phases of the main diurnal and semidiurnal tides were prescribed at the off-shore open boundaries. A calibration procedure was carried out with available observations in order to provide a suitable parameterization for bottom drag coefficient and horizontal viscosities. The results gave clear indication that over-harmonics and compound tides are generated in the Strait. The generation mechanism, geographical localization and intensity of these phenomena were described to provide groundwork for further model analyses that would clarify the role of shallow water tides in modifying the hydrological setup in proximity of sea straits.
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
© 2016 The Authors. Tsunami generated by submarine slides are arguably an under-considered risk in comparison to earthquake-generated tsunami. Numerical simulations of submarine slide-generated waves can be used to identify the important factors in determining wave characteristics. Here we use Fluidity, an open source finite element code, to simulate waves generated by deformable submarine slides. Fluidity uses flexible unstructured meshes combined with adaptivity which alters the mesh topology and resolution based on the simulation state, focussing or reducing resolution, when and where it is required. Fluidity also allows a number of different numerical approaches to be taken to simulate submarine slide deformation, free-surface representation, and wave generation within the same numerical framework. In this work we use a multi-material approach, considering either two materials (slide and water with a free surface) or three materials (slide, water and air), as well as a sediment model (sediment, water and free surface) approach. In all cases the slide is treated as a viscous fluid. Our results are shown to be consistent with laboratory experiments using a deformable submarine slide, and demonstrate good agreement when compared with other numerical models. The three different approaches for simulating submarine slide dynamics and tsunami wave generation produce similar waveforms and slide deformation geometries. However, each has its own merits depending on the application. Mesh adaptivity is shown to be able to reduce the computational cost without compromising the accuracy of results.
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
© 2015 The Authors 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.
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, 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
© 2014. Laboratory experiments and numerical simulations have shown that volcanic ash particles immersed in water can either settle slowly and individually, or rapidly and collectively as particle-laden plumes. The ratio of timescales for individual and collective settling, in the form of analytical expressions, provides a dimensionless quantitative measure of the tendency for such plumes to grow and persist which has important implications for determining particle residence times and deposition rates. However, existing measures in the literature assume that collective settling obeys Stokes' law and is therefore controlled by the balance between gravitational forces and viscous drag, despite plume development actually being controlled by the balance between gravitational forces and inertial drag even in the absence of turbulence during early times. This paper presents a new measure for plume onset which takes into account the inertial drag-controlled (rather than viscous drag-controlled) nature of plume growth and descent. A parameter study comprising a set of numerical simulations of small-scale volcanic ash particle settling experiments highlights the effectiveness of the new measure and, by comparison with an existing measure in the literature, also demonstrates that the timescale of collective settling is grossly under-estimated when assuming that plume development is slowed by viscous drag. Furthermore, the formulation of the new measure means that the tendency for plumes to form can be estimated from the thickness and concentration of the final deposit; the magnitude and duration of particle flux across the water's surface do not need to be known. The measure therefore permits the residence times of particles in a large body of water to be more accurately and practically determined, and allows the improved interpretation of layers of volcaniclastic material deposited at the seabed.
Jacobs CT, Piggott MD, Jacobs CT, et al., 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
© Author(s) 2015. This model description paper introduces a new finite element model for the simulation of non-linear shallow water flows, called Firedrake-Fluids. Unlike traditional models that are written by hand in static, low-level programming languages such as Fortran or C, Firedrake-Fluids uses the Firedrake framework to automatically generate the model's code from a high-level abstract language called Unified Form Language (UFL). By coupling to the PyOP2 parallel unstructured mesh framework, Firedrake can then target the code towards a desired hardware architecture to enable the efficient parallel execution of the model over an arbitrary computational mesh. The description of the model includes the governing equations, the methods employed to discretise and solve the governing equations, and an outline of the automated solution process. The verification and validation of the model, performed using a set of well-defined test cases, is also presented along with a road map for future developments and the solution of more complex fluid dynamical systems.
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
© 2015 American Meteorological Society. It has been suggested that the presence of frazil ice can lead to a conditional instability in seawater. Any frazil forming in the water column reduces the bulk density of a parcel of frazil-seawater mixture, causing it to rise. As a result of the pressure decrease in the freezing point, this causes more frazil to form, causing the parcel to accelerate, and so on. This study uses linear stability analysis and a nonhydrostatic ocean model to study this instability. The authors find that frazil ice growth caused by the rising of supercooled water is indeed able to generate a buoyancy-driven instability. Even in a gravitationally stable water column, the frazil ice mechanism can still generate convection. The instability does not operate in the presence of strong density stratification, high thermal driving (warm water), a small initial perturbation, high background mixing, or the prevalence of large frazil ice crystals. In an unstable water column, the instability is not necessarily expressed in frazil ice at all times; an initial frazil perturbation may melt and refreeze. Given a large enough initial perturbation, this instability can allow significant ice growth. A model shows frazil ice growth in an Ice Shelf Water plume several kilometers from an ice shelf, under similar conditions to observations of frazil ice growth under sea ice. The presence of this instability could be a factor affecting the growth of sea ice near ice shelves, with implications for Antarctic Bottom Water formation.
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