Imperial College London

Stephan Kramer

Faculty of EngineeringDepartment of Earth Science & Engineering

Research Fellow
 
 
 
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Contact

 

s.kramer Website CV

 
 
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Location

 

4.85Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
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83 results found

Clare MCA, Wallwork JG, Kramer SC, Weller H, Cotter CJ, Piggott MDet al., 2022, Multi-scale hydro-morphodynamic modelling using mesh movement methods, GEM: International Journal on Geomathematics, Vol: 13, ISSN: 1869-2672

Hydro-morphodynamic modelling is an important tool that can be used in the protection of coastal zones. The models can be required to resolve spatial scales ranging from sub-metre to hundreds of kilometres and are computationally expensive. In this work, we apply mesh movement methods to a depth-averaged hydro-morphodynamic model for the first time, in order to tackle both these issues. Mesh movement methods are particularly well-suited to coastal problems as they allow the mesh to move in response to evolving flow and morphology structures. This new capability is demonstrated using test cases that exhibit complex evolving bathymetries and have moving wet-dry interfaces. In order to be able to simulate sediment transport in wet-dry domains, a new conservative discretisation approach has been developed as part of this work, as well as a sediment slide mechanism. For all test cases, we demonstrate how mesh movement methods can be used to reduce discretisation error and computational cost. We also show that the optimum parameter choices in the mesh movement monitor functions are fairly predictable based upon the physical characteristics of the test case, facilitating the use of mesh movement methods on further problems.

Journal article

Halilovic S, Böttcher F, Kramer S, Piggott M, Zosseder K, Hamacher Tet al., 2022, Well layout optimization for groundwater heat pump systems using the adjoint approach, Energy Conversion and Management, Vol: 268, ISSN: 0196-8904

Groundwater heat pump systems cause thermal anomalies in the aquifer that can impact upon downstream systems and reduce their efficiency. Therefore, it is important to optimally position the extraction and injection wells of such systems to avoid negative interactions and maximize the thermal potential of the aquifer. This paper presents a new method to determine optimal well layouts of groundwater heat pumps using the adjoint approach, which is an efficient way to solve the underlying PDE-constrained optimization problem. An integral part of the method is the numerical groundwater simulation, which here is based on the finite element method. In addition, a multi-start initialization strategy is introduced in an attempt tobetter reach the global optimum. The method is applied to a real case study with 10 groundwater heat pumps, i.e. 20 wells, and two optimization scenarios with different natural groundwater temperatures. In both scenarios, the optimization method successfully determines a well layout that maximizes groundwater temperatures at all extraction wells. Comparing the results from these scenarios demonstrates that hydro-geological conditions can have a significant impact on the optimal well layout. The proposed method is equally applicable to systems with multiple extraction and injection wells and can be extended to various other shallow geothermal applications, such as combined heating and cooling systems.

Journal article

Pan W, Kramer SC, Piggott MD, Yu Xet al., 2022, Modeling landslide generated waves using the discontinuous finite element method, International Journal for Numerical Methods in Fluids, Vol: 94, Pages: 1-33, ISSN: 0271-2091

A new two-layer model for impulsive wave generation by deformable granular landslides is developed based upon a discontinuous Galerkin finite element discretization. Landslide motion is modeled using a depth-averaged formulation for a shallow subaerial debris flow, which considers the bed curvature represented by the local slope angle variable and accounts for inter-granular stresses using Coulomb friction. Wave generation and propagation are simulated with the three-dimensional non-hydrostatic coastal ocean model Thetis to accurately capture key features such as wave dispersion. Two different techniques are used in treating wetting and drying (WD) processes during the landslide displacement and wave generation, respectively. For the lower-layer landslide motion across the dry bed a classical thin-layer explicit WD method is implemented, while for the resulting free-surface waves interacted with the moving landslide an implicit WD scheme is utilized to naturally circumvent the artificial pressure gradient problem which may appear in the dynamic interaction between the landslide and water if using the thin-layer method. The two-layer model is validated using a suite of test cases, with the resulting good agreement demonstrating its capability in describing both the complex behaviors of granular landslides from initiation to deposition, and the consequent wave generation and propagation.

Journal article

Davies DR, Kramer SC, Ghelichkhan S, Gibson Aet al., 2022, Towards automatic finite-element methods for geodynamics via Firedrake, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 15, Pages: 5127-5166, ISSN: 1991-959X

Journal article

Duvernay T, Davies DR, Mathews CR, Gibson AH, Kramer SCet al., 2022, Continental Magmatism: The Surface Manifestation of Dynamic Interactions Between Cratonic Lithosphere, Mantle Plumes and Edge-Driven Convection, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 23

Journal article

Clare MCA, Kramer SC, Cotter CJ, Piggott MDet al., 2022, Calibration, inversion and sensitivity analysis for hydro-morphodynamic models through the application of adjoint methods, Computers and Geosciences, Vol: 163, Pages: 1-13, ISSN: 0098-3004

The development of reliable, sophisticated hydro-morphodynamic models is essential for protecting the coastal environment against hazards such as flooding and erosion. There exists a high degree of uncertainty associated with the application of these models, in part due to incomplete knowledge of various physical, empirical and numerical closure related parameters in both the hydrodynamic and morphodynamic solvers. This uncertainty can be addressed through the application of adjoint methods. These have the notable advantage that the number and/or dimension of the uncertain parameters has almost no effect on the computational cost associated with calculating the model sensitivities. Here, we develop the first freely available and fully flexible adjoint hydro-morphodynamic model framework. This flexibility is achieved through using the pyadjoint library, which allows us to assess the uncertainty of any parameter with respect to any model functional, without further code implementation. The model is developed within the coastal ocean model Thetis constructed using the finite element code-generation library Firedrake. We present examples of how this framework can perform sensitivity analysis, inversion and calibration for a range of uncertain parameters based on the final bedlevel. These results are verified using so-called dual-twin experiments, where the ‘correct’ parameter value is used in the generation of synthetic model test data, but is unknown to the model in subsequent testing. Moreover, we show that inversion and calibration with experimental data using our framework produces physically sensible optimum parameters and that these parameters always lead to more accurate results. In particular, we demonstrate how our adjoint framework can be applied to a tsunami-like event to invert for the tsunami wave from sediment deposits.

Journal article

Zhang J, Zhang C, Angeloudis A, Kramer SC, He R, Piggott MDet al., 2022, Interactions between tidal stream turbine arrays and their hydrodynamic impact around Zhoushan Island, China, Ocean Engineering, Vol: 246, Pages: 1-13, ISSN: 0029-8018

Tidal currents represent an attractive renewable energy source particularly because of their predictability. Prospective tidal stream development sites are often co-located in close proximity. Under such circumstances, in order to maximise the exploitation of the resource, multiple tidal stream turbine arrays working in tandem would be needed. In this paper, a continuous array optimisation approach based on the open source coastal ocean modelling framework Thetis is applied to derive optimal configurations for four turbine arrays around Zhoushan Islands, Zhejiang Province, China. Alternative optimisation scenarios are tested to investigate interactions between the turbine arrays and their hydrodynamic footprint. Results show that there are no obvious competition effects between these four arrays around Hulu and Taohua Island. However, significant interactions could arise among the three turbine arrays situated around Hulu Island, with a maximum decrease in average power of 42.2%. By optimising all turbine arrays simultaneously, the competition effects can be minimised and the cost of energy reduced as less turbines are required to deliver an equivalent energy output. As for the potential environmental impact, it is found that the turbine array around Taohua Island would affect a larger area than turbine arrays around Hulu Island.

Journal article

Mackie L, Kramer SC, Piggott MD, Angeloudis Aet al., 2021, Assessing impacts of tidal power lagoons of a consistent design, OCEAN ENGINEERING, Vol: 240, ISSN: 0029-8018

Journal article

Duvernay T, Davies DR, Mathews CR, Gibson AH, Kramer SCet al., 2021, Linking Intraplate Volcanism to Lithospheric Structure and Asthenospheric Flow, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 22

Journal article

Zhang C, Kramer SC, Angeloudis A, Zhang J, Lin X, Piggott MDet al., 2021, Improving tidal turbine array performance through the optimisation of layout and yaw angles, European Wave and Tidal Energy Conference, Pages: 2205-1-2205-7-2205-1-2205-7, ISSN: 2706-6932

Tidal stream currents change in magnitude and direction during flood and ebb tides. Setting the most appropriate yaw angles for a tidal turbine is not only important to account for the performance of a single turbine, but can also be significant for the interactions between the turbines within an array. In this paper, a partial differentiation equation (PDE) constrained optimisation approach is established based on the Thetis coastal ocean modelling framework. The PDE constraint takes the form here of the two-dimensional, depth-averaged shallow water equations which are used to simulate tidal elevations and currents in the presence of tidal stream turbine arrays. The Sequential Least Squares Programming (SLSQP) algorithm is applied with a gradient obtained via the adjoint method in order to perform design optimisation. An idealised rectangular channel test case is studied to demonstrate this optimisation framework. Located in the centre of the computational domain, turbine arrays comprised of 12 turbines are tested in aligned and staggered layouts. The setups are initially optimised based on their yaw angles alone; their locations and yaw angles are also optimized simultaneously to improve the array overall performance. Results indicate that for the aligned turbine array case, the energy output can be increased by approximately 80% when considering yaw angle optimisation alone. For the staggered turbine array, the increase is approximately 30%. The yaw optimised staggered array is able to outperform the yaw optimised aligned array by approximately 8%. If both layout and the yaw angles of the turbines are considered within the optimisation then the increase is more significant compared with optimising yaw angle alone.

Conference paper

Goss ZL, Coles DS, Kramer SC, Piggott MDet al., 2021, Efficient economic optimisation of large-scale tidal stream arrays, Applied Energy, Vol: 295, Pages: 1-17, ISSN: 0306-2619

As the tidal energy industry moves from demonstrator arrays comprising just a few turbines to large-scale arrays made up of potentially hundreds of turbines, there is a need to optimise both the number of turbines and their spatial distribution in order to minimise cost of energy. Optimising array design manually may be feasible for small arrays, but becomes an impractically large approach when the number of devices is high, especially if taking into account both the cost effectiveness of each turbine and also the coupled nature of the turbine locations and the local as well as far-field hydrodynamics.Previous work has largely focused on producing computational tools to automatically design the size and layout of large-scale tidal turbine arrays to optimise power. There has been some limited preliminary work to incorporate costs into these models, in order to improve the economic viability of tidal arrays. This paper provides the first in depth implementation and analysis of economic functionals, based upon metrics such as break even power and levelised cost of energy, used for design of explicit array sizing and spatial variation.The addition of these new economic functionals introduces complexity by increasing the number of inputs to the model, each of which are subject to their own uncertainty in value. For this reason, sensitivity analysis becomes both more important as well as more difficult to undertake. This paper presents a novel rapid methodology for deriving the optimal array design (number of turbines and their spatial distribution throughout the farm area) to minimise cost functionals, and its sensitivity to variations in the economic inputs. Importantly, the new aspects of this method introduced here do not rely on repeated model runs and iterative optimisation, two aspects that typically prove to be impractically expensive computationally. This more readily allows for the impact of changes in investor priorities to be investigated. It is also shown tha

Journal article

Kramer S, Davies R, Wilson C, 2021, Analytical solutions for mantle flow in cylindrical and spherical shells, Geoscientific Model Development, Vol: 14, Pages: 1899-1919, ISSN: 1991-959X

Computational models of mantle convection must accurately represent curved boundaries and the associated boundary conditions of a 3-D spherical shell, bounded by Earth's surface and the core–mantle boundary. This is also true for comparable models in a simplified 2-D cylindrical geometry. It is of fundamental importance that the codes underlying these models are carefully verified prior to their application in a geodynamical context, for which comparisons against analytical solutions are an indispensable tool. However, analytical solutions for the Stokes equations in these geometries, based upon simple source terms that adhere to physically realistic boundary conditions, are often complex and difficult to derive. In this paper, we present the analytical solutions for a smooth polynomial source and a delta-function forcing, in combination with free-slip and zero-slip boundary conditions, for both 2-D cylindrical- and 3-D spherical-shell domains. We study the convergence of the Taylor–Hood (P2–P1) discretisation with respect to these solutions, within the finite element computational modelling framework Fluidity, and discuss an issue of suboptimal convergence in the presence of discontinuities. To facilitate the verification of numerical codes across the wider community, we provide a Python package, Assess, that evaluates the analytical solutions at arbitrary points of the domain.

Journal article

Pan W, Kramer SC, Piggott MD, 2021, A sigma-coordinate non-hydrostatic discontinuous finite element coastal ocean model, Ocean Modelling, Vol: 157, Pages: 1-21, ISSN: 1463-5003

A𝜎-coordinate non-hydrostatic coastal ocean model is developed using the discontinuous Galerkin fi-nite element method. With the selection of the low-order piecewise-constant PDG0and piecewise-linearPDG1discretisations in the vertical for the velocity and pressure fields, respectively, the proposed𝜎-coordinatemodel can naturally retain the wave dispersion characteristics of the widely-adopted multi-layer approach ofZijlema and Stelling (2005), which is demonstrated through both mathematical derivation and numerical tests.Under the finite element approach, higher-order vertical discretisation choices can also be readily made whichcan reduce the number of vertical layers required for the accurate representation of wave dispersion. Themodel is verified and validated through comparisons against a series of test cases with analytical solutions orexperimental measurements. All the comparisons demonstrate good agreement, indicating that the proposedmodel can accurately represent dispersive barotropic surface waves with as few as one vertical layer, and cansimulate baroclinic internal waves with reasonable accuracy using relatively coarse mesh resolution. It is alsodemonstrated that consistency in the coupling of barotropic and baroclinic flows can be properly ensured.

Journal article

Kramer S, Wilson C, Davies R, Funke SW, Greaves T, Avdis A, Lange M, Candy A, Cotter CJ, Pain C, Percival J, Mouradian S, Bhutani G, Gorman G, Gibson A, Duvernay T, Guo X, Maddison JR, Rathgeber F, Farrell P, Weiland M, Robinson D, Ham DA, Goffin M, Piggott M, Gomes J, Dargaville S, Everett A, Jacobs CT, Cavendish ABet al., 2020, FluidityProject/fluidity: New test cases "Analytical solutions for mantle flow in cylindrical and spherical shells"

This release adds new test cases described in the GMD paper "Analytical solutions for mantle flow in cylindrical and spherical shells"

Software

Angeloudis A, Kramer SC, Hawkins N, Piggott MDet al., 2020, On the potential of linked-basin tidal power plants: An operational and coastal modelling assessment, Renewable Energy, Vol: 155, Pages: 876-888, ISSN: 0960-1481

Single-basin tidal range power plants have the advantage of predictable energy outputs, but feature non-generation periods in every tidal cycle. Linked-basin tidal power systems can reduce this variability and consistently generate power. However, as a concept the latter are under-studied with limited information on their performance relative to single-basin designs. In addressing this, we outline the basic principles of linked-basin power plant operation and report results from their numerical simulation. Tidal range energy operational models are applied to gauge their capabilities relative to conventional, single-basin tidal power plants. A coastal ocean model (Thetis) is then refined with linked-basin modelling capabilities. Simulations demonstrate that linked-basin systems can reduce non-generation periods at the expense of the extractable energy output relative to conventional tidal lagoons and barrages. As an example, a hypothetical case is considered for a site in the Severn Estuary, UK. The linked-basin system is seen to generate energy 80–100% of the time over a spring-neap cycle, but harnesses at best 30% of the energy of an equivalent-area single-basin design.

Journal article

Pan W, Kramer S, Kärnä T, Piggott Met al., 2020, Comparing non-hydrostatic extensions to a discontinuous finite element coastal ocean model, Ocean Modelling, Vol: 151, ISSN: 1463-5003

The unstructured mesh, discontinuous Galerkin finite element discretisation based coastal ocean model, Thetis, has been extended to include non-hydrostatic (buoyancy-driven and free surface) dynamics. Two alternative approaches to achieve this are described in this work. The first (a 3D based algorithm) makes use of prismatic element based meshes and uses a split-step pressure projection method for baroclinic and barotropic modes, while the second (a 2D based algorithm) adopts a novel multi-layer approach to convert a 3D problem into a combination of multiple 2D computations with only 2D triangle meshes required. Model development is carried out at high-level with the Firedrake library, using code generation techniques to automatically produce low-level code for the discretised model equations in an efficient and rapid manner. Through comparisons against several barotropic/baroclinic test cases where non hydrostatic effects are important, the implemented approaches are verified and validated, and the proposed algorithms compared. Depending on whether the problems are dominated by dispersive, baroclinic or barotropic features, recommendation are given over the use of full 3D or multi-layer 2D based approaches to achieve optimal computational accuracy and efficiency. It is demonstrated that while in general the 2D approach is well-suited for barotropic problems and dispersive free surface waves, the 3D approach is more advantageous for simulating baroclinic buoyancy-driven flows due in part to the high vertical resolution typically required to represent the active tracer fields. Keywords: Discontinuous Galerkin, Finite element, Unstructured mesh, Baroclinic flow, Non-hydrostatic, Dispersion, Free surface

Journal article

Kramer S, Kärnä T, Hill J, Funke SWet al., 2020, stephankramer/uptide: First release of uptide v1.0

python package for tidal calculations

Software

Kramer S, 2020, stephankramer/assess: Version 1.0

First release of Assess, a python package that implements a number of analytical solutions to the Stokes equations in cylindrical and spherical shell domains. Documentation available from https://assess.readthedocs.io/

Software

Wallwork JG, Barral N, Kramer SC, Ham DA, Piggott MDet al., 2020, Goal-oriented error estimation and mesh adaptation for shallow water modelling, SN Applied Sciences, Vol: 2, Pages: 1-11, ISSN: 2523-3971

This study presents a novel goal-oriented error estimate for the nonlinear shallow water equations solved using a mixed discontinuous/continuous Galerkin approach. This error estimator takes account of the discontinuities in the discrete solution and is used to drive two metric-based mesh adaptation algorithms: one which yields isotropic meshes and another which yields anisotropic meshes. An implementation of these goal-oriented mesh adaptation algorithms is described, including a method for approximating the adjoint error term which arises in the error estimate. Results are presented for simulations of two model tidal farm configurations computed using the Thetis coastal ocean model (Kärnä et al. in Geosci Model Dev 11(11):4359–4382, 2018). Convergence analysis indicates that meshes resulting from the goal-oriented adaptation strategies permit accurate QoI estimation using fewer computational resources than uniform refinement.

Journal article

Kärnä T, Kramer S, Mitchell L, Angeloudis A, Ham DA, Barral N, McRae ATTet al., 2020, thetisproject/thetis: Thetis coastal ocean model

This version is used in paper "A comparison of Bayesian inference and gradient-based approaches for friction parameter estimation."This release is specifically created to document the version of Thetis used in a particular set of experiments. Please do not cite this as a general source for Thetis. See https://thetisproject.org/publications.html for how to cite Thetis in your work.

Software

Du Feu R, funke S, Kramer S, hill J, Piggott Met al., 2019, The trade-off between tidal-turbine array yield and environmental impact: A habitat suitability modelling approach, Renewable Energy, Vol: 143, Pages: 390-403, ISSN: 1879-0682

In the drive towards a carbon-free society, tidal energy has the potential to become a valuable part of the UK energy supply. Developments are subject to intense scrutiny, and potential environmental impacts must be assessed. Unfortunately many of these impacts are still poorly understood, including the implications that come with altering the hydrodynamics. Here, methods are proposed to quantify ecological impact and to incorporate its minimisation into the array design process. Four tidal developments in the Pentland Firth are modelled with the array optimisation tool OpenTidalFarm, that designs arrays to generate the maximum possible profit. Maximum entropy modelling is used to create habitat suitability maps for species that respond to changes in bedshear stress. Changes in habitat suitability caused by an altered tidal regime are assessed. OpenTidalFarm is adapted to simultaneously optimise array design to maximise both this habitat suitability and to maximise the profit of the array. The problem is thus posed as a multi-objective optimisation problem, and a set of Pareto solutions found, allowing trade-offs between these two objectives to be identified. The methods proposed generate array designs that have reduced negative impact, or even positive impact, on the habitat suitability of specific species or habitats of interest.

Journal article

Davies DR, Valentine AP, Kramer SC, Rawlinson N, Hoggard MJ, Eakin CM, Wilsons CRet al., 2019, Earth's multi-scale topographic response to global mantle flow, NATURE GEOSCIENCE, Vol: 12, Pages: 845-+, ISSN: 1752-0894

Journal article

Goss Z, Warder S, Angeloudis A, Kramer S, Avdis A, Piggott Met al., 2019, Tidal modelling with Thetis: preliminary English Channel benchmarking, Tidal modelling with Thetis: preliminary English Channelbenchmarking

This report describes the application and benchmarking of the Thetis coastal ocean model fortidal modelling, and makes use of a test case based upon the English Channel. Comparisonsare made between model predictions and tide gauge data at a number of locations across theEnglish Channel. A preliminary investigation of the impact of mesh resolution and bathymetrydata is given. A demonstration is also provided of Thetis’s ability to use adjoint technologyto optimise model predictions through the assimilation of observational data. In the examplepresented here the bottom friction field is optimised to provide an improved match betweenthe model results and tide gauge data. This adjoint based optimisation capability may alsobe used to optimise the location, size and design of tidal power generation schemes.

Report

Vouriot C, Angeloudis A, Kramer S, Piggott Met al., 2019, Fate of large-scale vortices in idealized tidal lagoons, Environmental Fluid Mechanics, Vol: 19, Pages: 329-348, ISSN: 1567-7419

The generation and evolution of tidally-induced vortices in coastal and estuarine regions can influence water quality and sedimentary processes. These effects must be taken into consideration in the development of coastal reservoirs, barrages and lagoons, among other environmental flow applications. Results are presented here on the fate of large-scale vortices within confined tidally-forced domains. A computational approach is employed using the Thetis depth-averaged coastal ocean modeling framework. Initially, two test cases serve to demonstrate model capability in capturing the formation of dipoles downstream of oscillatory flow channels. Diagnostic quantities of vorticity and localized circulation are used to track the 2-D vortex evolution and dissipation. This approach is then applied to tidal lagoon geometries, where flows through the inlet induce a pair of counter rotating vortices (dipoles). Idealized model geometries and inlet conditions are used to determine the impact of three design parameters on large-scale vortical structures: (a) the lagoon geometry aspect ratio in the horizontal plane, (b) the inlet width and (c) the bathymetry profile as the coastline is approached. The dependence of vortex flushing behavior on the dimensionless ratio Wi/UT (where Wi is the width of the inlet channel, U is the maximum velocity and T is the tidal period) is reaffirmed, while the side walls and the sloping bathymetry are found to affect the vortex dissipation process.

Journal article

Walker DW, Kramer SC, Biebl FRA, Ledger PD, Brown Met al., 2019, Accelerating magnetic induction tomography-based imaging through heterogeneous parallel computing, Concurrency Computation, ISSN: 1532-0626

© 2019 John Wiley & Sons, Ltd. Magnetic Induction Tomography (MIT) is a non-invasive imaging technique, which has applications in both industrial and clinical settings. In essence, it is capable of reconstructing the electromagnetic parameters of an object from measurements made on its surface. With the exploitation of parallelism, it is possible to achieve high quality inexpensive MIT images for biomedical applications on clinically relevant time scales. In this paper we investigate the performance of different parallel implementations of the forward eddy current problem, which is the main computational component of the inverse problem through which measured voltages are converted into images. We show that a heterogeneous parallel method that exploits multiple CPUs and GPUs can provide a high level of parallel scaling, leading to considerably improved runtimes. We also show how multiple GPUs can be used in conjunction with deal.II, a widely-used open source finite element library.

Journal article

Rathgeber F, Mitchell L, Luporini F, Ham D, Markall G, Homolya M, tj-sun, Barton N, Dearman H, Gibson T, gbts, Wechsung F, Kramer S, Funke SW, Shapero D, Kirby R, Lange M, Sato K, Russell F, Fangyi Zet al., 2019, OP2/PyOP2: Framework for performance-portable parallel computations on unstructured meshes

This release is specifically created to document the version of PyOP2 used in a particular set of experiments using Firedrake. Please do not cite this as a general source for Firedrake or any of its dependencies. Instead, refer to https://www.firedrakeproject.org/citing.html

Software

Pan W, Kramer S, Piggott M, 2019, Multi-layer non-hydrostatic free surface modelling using the discontinuous Galerkin method, Ocean Modelling, Vol: 134, Pages: 68-83, ISSN: 1463-5003

A multi-layer non-hydrostatic version of the unstructured mesh, discontinuous Galerkinfinite element based coastal ocean model, Thetis, is developed. This is accomplishedusing the PDE solver framework, Firedrake, which is used to automatically produce thecode for the discretised model equations in a rapid and efficient manner. The motivationfor this work is a need to accurately simulate dispersive nearshore free surface processes.In order to resolve both frequency dispersion and non-linear effects accurately, additional non-hydrostatic terms are included in the layer-integrated hydrostatic equations,producing a form similar to the layered non-linear shallow water equations, but withextra vertical velocities at the layer interfaces. An implementation process is adoptedto easily handle the inter-layer connection, i.e. the governing equations are transformedinto a depth-integrated system through the introduction of depth-averaged variables.The model is verified and validated through comparisons against several idealisedand experimentally-based test cases. All the comparisons demonstrate good agreement,showing that the developed non-hydrostatic model has excellent capabilities in representing coastal wave phenomena including shoaling, refraction and diffraction of dispersive short waves, as well as propagation, run-up and inundation of non-linear tsunamiwaves.

Journal article

Angeloudis A, Hawkins N, Kramer SC, Piggott MDet al., 2019, Comparison of twin-basin lagoon systems against conventional tidal power plant designs, Pages: 159-168

Tidal power plant proposals present opportunities to deliver sustainable energy to the national grid in the UK and beyond. Multiple designs have been considered over the years that seek to competitively balance economic, environmental and technical challenges. Tidal range power plants have the advantage of reliable and predictable energy outputs with a certain degree of flexibility but typically feature non-generation periods in every tidal cycle. Twin-basin systems present an alternative that can significantly reduce this variability but very little information has been reported in terms of their performance to-date. In this work a coastal ocean modelling framework has been coupled with twin-basin and tidal power plant operation algorithms and is applied to compare tidal energy options. Results suggest that through use of a twin basin system the non-generation time can be substantially reduced at a notable expense to the overall energy output relative to conventional tidal lagoons and barrages.

Conference paper

Goss ZL, Piggott MD, Kramer SC, Avdis A, Angeloudis A, Cotter CJet al., 2019, Competition effects between nearby tidal turbine arrays—optimal design for alderney race, Pages: 255-262

Tidal renewable energy can be described as a fledgling industry, with the world’s pilot tidal stream turbine array only recently installed. Full-sized arrays will be developed if they prove their economic, engineering and environmental viability. Reliable numerical tools are needed to optimise power yields in arrays of potentially hundreds of turbines and assess viability of new sites and designs. To demonstrate our capability to optimise the number of turbines and their spatial distribution in a region, we focus on a test case based upon the Alderney Race. The site contains the majority of the Channel Islands resource with plans from both France and Alderney to develop adjacent arrays that could impact on each other. We present a shallow-water model of the English Channel using the Thetis ocean model. Together with the hydrodynamics modelling we employ adjoint technology to optimise the micrositing of turbines for a set of scenarios.

Conference paper

Mitchell L, Ham D, Gibson T, Rathgeber F, Homolya M, McRae ATT, Fangyi Z, Cotter CJ, Lange M, Andrej J, Luporini F, Kirby R, Wechsung F, Paganini A, Poulin FJ, Roy T, Hawkes C, Salwa T, Kalogirou A, Karna T, Greaves T, tj-sun, Gregory A, Kramer S, Funke SW, Busing H, McBain G, Mueller EHet al., 2018, firedrakeproject/firedrake: an automated finite element system

This release is specifically created to document the version of firedrake used in a particular set of experiments using Firedrake. Please do not cite this as a general source for Firedrake or any of its dependencies. Instead, refer to https://www.firedrakeproject.org/citing.html

Software

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

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