148 results found
Du Feu R, funke S, Kramer S, et 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.
Goss Z, Warder S, Angeloudis A, et 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.
Deskos G, Laizet S, Piggott M, 2019, Turbulence-resolving simulations of wind turbine wakes, Renewable Energy, Vol: 134, Pages: 989-1002, ISSN: 1879-0682
Turbulence-resolving simulations of wind turbine wakes are presented using a high-order flow solver combined with both a standard and a novel dynamic implicit spectral vanishing viscosity (iSVV and dynamic iSVV) model to account for subgrid-scale (SGS) stresses. The numerical solutions are compared against wind tunnel measurements, which include mean velocity and turbulent intensity profiles, as well as integral rotor quantities such as power and thrust coefficients. For the standard (also termed static) case the magnitude of the spectral vanishing viscosity is selected via a heuristic analysis of the wake statistics, while in the case of the dynamic model the magnitude is adjusted both in space and time at each time step. The study focuses on examining the ability of the two approaches, standard (static) and dynamic, to accurately capture the wake features, both qualitatively and quantitatively. The results suggest that the static method can become over-dissipative when the magnitude of the spectral viscosity is increased, while the dynamic approach which adjusts the magnitude of dissipation locally is shown to be more appropriate for a non-homogeneous flow such that of a wind turbine wake.
Vouriot C, Angeloudis A, Kramer S, et 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.
Harcourt F, Angeloudis A, Piggott M, 2019, Utilising the ﬂexible generation potential of tidal range power plants to optimise economic value, Applied Energy, Vol: 237, Pages: 873-884, ISSN: 0306-2619
Tidal range renewable power plants have the capacity to deliver predictableenergy to the electricity grid, subject to the known variability of the tides.Tidal power plants inherently feature advantages that characterise hydro-powermore generally, including a lifetime exceeding alternative renewable energy technologies and relatively low Operation & Maintenance costs. Nevertheless, thetechnology is typically inhibited by the significant upfront investment associatedwith capital costs. A key aspect that makes the technology stand out relativeto other renewable options is the partial flexibility it possesses over the timingof power generation. In this study we provide details on a design methodologytargeted at the optimisation of the temporal operation of a tidal range energystructure, specifically the Swansea Bay tidal lagoon that has been proposedwithin the Bristol Channel, UK. Apart from concentrating on the classical incentive of maximising energy, we formulate an objective functional in a mannerthat promotes the maximisation of income for the scheme from the Day-Aheadenergy market. Simulation results demonstrate that there are opportunities toexploit the predictability of the tides and flexibility over the precise timing ofpower generation to incur a noticeable reduction in the subsidy costs that are often negotiated with regulators and governments. Additionally, we suggest thatthis approach should enable tidal range energy to play a more active role inensuring security of supply in the UK. This is accentuated by the income-basedoptimisation controls that deliver on average more power over periods whendemand is higher. For the Swansea Bay tidal lagoon case study a 23% increaseis observed in the income obtained following the optimisation of its operationcompared to a non-adaptive operation. Similarly, a 10% increase relative toan energy-maximisation approach over a year’s operation suggests that simplymaximising energy generation in a setting where power
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.
Deskos G, Piggott MD, Laizet S, 2019, Development and validation of the higher-order finite-difference wind farm simulator, winc3d, Pages: 721-728
© 2019 Taylor & Francis Group, London. High-fidelity wind farm models typically employ Large–Eddy Simulation (LES) formulations and turbine parametrisations (e.g. actuator disc models) to resolve the turbine wakes at spatial and temporal scales so that all flow features of engineering importance are well–captured. Such features include the low frequency dynamic wake meandering, which plays a key role in the fatigue loading expe-rienced by downstream turbines clustered in arrays. By the term ‘Wind Farm Simulator’ (WFS) we refer to an integrated framework which offers these capabilities and can be used as a research tool to study wake–to–wake and turbine–to–wake interactions. In this work, we present a validation study for WInc3D, a WFS based on the powerful, sixth-order finite-difference flow solver, incompact3d. For our validation study, we use operational scenarios from the Horns Rev offshore wind farm. The comparison of the present model with existing Supervisory Control and Data Acquisition (SCADA) measurements and previous LES studies shows an overall good agreement.
Goss ZL, Piggott MD, Kramer SC, et al., 2019, Competition effects between nearby tidal turbine arrays—optimal design for alderney race, Pages: 255-262
© 2019 Taylor & Francis Group, London. 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.
Angeloudis A, Hawkins N, Kramer SC, et al., 2019, Comparison of twin-basin lagoon systems against conventional tidal power plant designs, Pages: 159-168
© 2019 Taylor & Francis Group, London. 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.
Nunez Rattia JM, Percival J, Neethling S, et al., 2018, Modelling local scour near structures with combined mesh movement and mesh optimisation, Journal of Computational Physics, Vol: 375, Pages: 1220-1237, ISSN: 0021-9991
This paper develops a new implementation coupling optimisation-based anisotropic mesh adaptivity algorithms to a moving mesh numerical scour model, considering both turbulent suspended and bedload sediment transport. The significant flexibility over mesh structure and resolution, in space and time, that the coupling of these approaches provides makes this framework highly suitable for resolving individual marine structure scales with larger scale ocean dynamics. The use of mesh optimisation addresses the issue of poor mesh quality and/or inappropriate resolution that have compromised existing modelling approaches that apply mesh movement strategies alone, especially in the case of extreme scour. Discontinuous Galerkin finite element-based discretisation methods and a Reynolds Averaged Navier–Stokes-based turbulent modelling approach are used for the hydrodynamic fluid flow. In this work the model is verified in two dimensions for current-dominated scour near a horizontal pipeline. Combined adaptive mesh movement and anisotropic mesh optimisation is found to maintain both the quality and validity of the mesh in response to morphological bed evolution changes, even in the case where it is severely constrained by nearby structures.
Deskos G, Piggott M, 2018, Mesh-adaptive simulations of horizontal-axis turbine arrays using the actuator line method, Wind Energy, Vol: 21, Pages: 1266-1281, ISSN: 1095-4244
Numerical models of the flow and wakes due to turbines operating within a real-scale offshore wind farm can lead to a prohibitively large computational cost, particularly when considering blade-resolved simulations. With the introduction of turbine parametrisations such as the actuator disk (ADM) or the actuator line (ALM) models this problem has been partially addressed, yet the computational cost associated with these simulations remains high. In this work we present an implementation and validation of an ALM within the mesh-adaptive 3D fluid dynamics solver, Fluidity, under a uRANS-based turbulence modelling approach. A key feature of this implementation is the use of mesh optimization techniques which allow for the automatic refinement or coarsening of the mesh locally according to the resolution needed by the fluid flow solver. The model is first validated against experimental data from wind tunnel tests. Finally, we demonstrate the benefits of mesh-adaptivity by considering flow past the Lillgrund offshore wind farm.
Collins D, Alvdis A, Allison P, et al., 2018, Controls on tidal sedimentation and preservation: insights from numerical tidal modelling in the late oligocene–miocene South China sea, Southeast Asia, Sedimentology, Vol: 65, Pages: 2468-2505, ISSN: 0037-0746
Numerical tidal modelling, when integrated with other geological datasets, can significantly inform the analysis of physical sedimentation processes and the depositional and preservational record of ancient tide-influenced shoreline–shelf systems. This is illustrated in the Oligo–Miocene of the South China Sea (SCS), which experienced significant changes in basin physiography and where tide-influenced, shoreline–shelf deposition is preserved in ca 10 sub-basins. Palaeogeographic reconstructions, palaeotidal modelling and regional sedimentary facies analysis have been integrated in order to evaluate the spatial–temporal evolution and physiographic controls on tidal sedimentation and preservation during the ca 25 Myr Oligo–Miocene record in the SCS. Palaeotidal modelling, using an astronomically forced and global tidal model (Fluidity) at a maximum 10 km resolution, indicates that spring tides along Late Oligocene–Middle Miocene coastlines were predominantly mesotidal– macrotidal and capable of transporting sand, which reflects two main conditions: (1) increased tidal inflow through wider ocean connections to the Pacific Ocean; and (2) tidal amplification resulting from constriction of the tidal wave in a ‘blind gulf’ type of basin morphology. Since the Middle–Late Miocene, a reduction in the amplitude and strength of tides in the SCS was mainly due to diminishing tidal inflow from the Pacific Ocean caused by the northward movement of the Philippines and Izu-Bonin-Mariana arc. Sensitivity tests to palaeogeographic and palaeobathymetric uncertainty indicate that regional–scale (100–1000s29 km) palaeogeographic changes influencing tidal inflow versus outflow can override local30scale (1–100s km) changes to tidal resonance and convergence effects (funnelling and shoaling), such as shelf width and shoreline geometry. Palaeotidal model results compare favourably to the distribution and sedimenta
Neill SP, Angeloudis A, Robins PE, et al., 2018, Tidal range energy resource and optimization - past perspectives and future challenges, Renewable Energy, Vol: 127, Pages: 763-778, ISSN: 0960-1481
Tidal energy is one of the most predictable forms of renewable energy. Although there has been much commercial and R&D progress in tidal stream energy, tidal range is a more mature technology, with tidal range power plants having a history that extends back over 50 years. With the 2017 publication of the “Hendry Review” that examined the feasibility of tidal lagoon power plants in the UK, it is timely to review tidal range power plants. Here, we explain the main principles of tidal range power plants, and review two main research areas: the present and future tidal range resource, and the optimization of tidal range power plants. We also discuss how variability in the electricity generated from tidal range power plants could be partially offset by the development of multiple power plants (e.g. lagoons) that are complementary in phase, and by the provision of energy storage. Finally, we discuss the implications of the Hendry Review, and what this means for the future of tidal range power plants in the UK and internationally.
Kärnä T, Kramer SC, Mitchell L, et al., 2018, Thetis coastal ocean model: discontinuous Galerkin discretization for the three-dimensional hydrostatic equations, Geoscientific Model Development, Vol: 11, Pages: 4359-4382, ISSN: 1991-959X
Unstructured grid ocean models are advantageous for simulating the coastal ocean and river-estuary-plume systems. However, unstructured grid models tend to be diffusive and/or computationally expensive which limits their applicability to real life problems. In this paper, we describe a novel discontinuous Galerkin (DG) finite element discretization for the hydrostatic equations. The formulation is fully conservative and second-order accurate in space and time. Monotonicity of the advection scheme is ensured by using a strong stability preserving time integration method and slope limiters. Compared to previous DG models advantages include a more accurate mode splitting method, revised viscosity formulation, and new second-order time integration scheme. We demonstrate that the model is capable of simulating baroclinic flows in the eddying regime with a suite of test cases. Numerical dissipation is well-controlled, being comparable or lower than in existing state-of-the-art structured grid models.
Piggott MD, Optimisation of tidal stream turbine arrays within the Alderney Race, European Wave and Tidal Energy Conference
Tidal range power plants represent an attractive approach for the large-scale generation of electricity from the marine environment. Even though the tides and by extension the available energy resource are predictable, they are also variable in time. This variability poses a challenge regarding the optimal transient control of power plants. We consider simulation methods which include the main modes of operation of tidal power plants, along with algorithms to regulate the timing of these. This paper proposes a framework where simplified power plant operation models are coupled with gradient-based optimisation techniques to determine the optimal control strategy over multiple tidal cycles. The optimisation results inform coastal ocean simulations that include tidal power plants to gauge whether the benefits of an adaptive operation are preserved once their hydrodynamic impacts are also taken into consideration. The combined operation of two prospective tidal lagoon projects within the Bristol Channel and the Severn Estuary is used as an example to demonstrate the potential benefits of an energy maximisation optimisation approach. For the case studies considered, the inclusion of pumping and an adaptive operation is shown to deliver an overall increase in energy output of 20–40% compared to a conventional two-way uniform operation. The findings also demonstrate that smaller schemes stand to gain more from operational optimisation compared to designs of a larger scale.
Piggott MD, Comparison of 0-D, 1-D and 2-D model capabilities for tidal range energy resource assessments, European Wave and Tidal Energy Conference
van Sebille E, Griffies SM, Abernathey R, et al., 2017, Lagrangian ocean analysis: fundamentals and practices, Ocean Modelling, Vol: 121, Pages: 49-75, ISSN: 1463-5003
Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
Avdis A, Candy AS, Hill J, et al., 2017, Efficient unstructured mesh generation for marine renewable energy applications, Renewable Energy, Vol: 116, Pages: 842-856, ISSN: 0960-1481
Renewable energy is the cornerstone of preventing dangerous climate change whilst maintaining a robust energy supply. Tidal energy will arguably play a critical role in the renewable energy portfolio as it is both predictable and reliable, and can be put in place across the globe. However, installation may impact the local and regional ecology via changes in tidal dynamics, sediment transport pathways or bathymetric changes. In order to mitigate these effects, tidal energy devices need to be modelled in order to predict hydrodynamic changes. Robust mesh generation is a fundamental component required for developing simulations with high accuracy. However, mesh generation for coastal domains can be an elaborate procedure. Here, we describe an approach combining mesh generators with Geographical Information Systems. We demonstrate robustness and efficiency by constructing a mesh with which to examine the potential environmental impact of a tidal turbine farm installation in the Orkney Islands. The mesh is then used with two well-validated ocean models, to compare their flow predictions with and without a turbine array. The results demonstrate that it is possible to create an easy-to-use tool to generate high-quality meshes for combined coastal engineering, here tidal turbines, and coastal ocean simulations.
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.
du Feu RJ, Funke SW, Kramer SC, et al., 2017, The trade-off between tidal-turbine array yield and impact on flow: A multi-objective optimisation problem, Renewable Energy, Vol: 114, Pages: 1247-1257, ISSN: 1879-0682
This paper introduces a new approach for investigating trade-offs between different societal objectives in the design of tidal-turbine arrays. This method is demonstrated through the trade-off between the yield of an array, and the extent to which that array alters the flow. This is posed as a multi-objective optimisation problem, and the problem is investigated using the array layout optimisation tool OpenTidalFarm. Motivated by environmental concerns, OpenTidalFarm is adapted to not only maximise array yield but also to minimise the effect of the array upon the hydrodynamics of the region, specifically the flow velocity. A linear scalarisation of the multi-objective optimisation problem is solved for a series of different weightings of the two conflicting objectives. Two idealised test scenarios are evaluated and in each case a set of Pareto solutions is found. These arrays are assessed for the power they generate and the severity of change they cause in the flow velocity. These analyses allow for the identification of trade-offs between these two objectives, while the methods proposed can similarly be applied to the two key societal objectives of energy production and conservation, thus providing information that could be valuable to stakeholders and policymakers when making decisions on array design.
Deskos G, Abolghasemi AA, Piggott MD, Wake predictions from two turbine parametrisation models using mesh-optimisation techniques, European Wave and Tidal Energy Conference, ISSN: 2309-1983
Culley DM, Funke SW, Kramer SC, et al., 2017, A surrogate-model assisted approach for optimising the size of tidal turbine arrays, International Journal of Marine Energy, Vol: 19, Pages: 357-373, ISSN: 2214-1669
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
Collins DS, Avdis A, Allison PA, et al., 2017, Tidal dynamics and mangrove carbon sequestration during the Oligo–Miocene in the South China Sea, Nature Communications, Vol: 8, ISSN: 2041-1723
Modern mangroves are among the most carbon-rich biomes on Earth, but their long-term (≥106 yr) 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 optimised 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 4000 Gt (equivalent to 2000 ppm 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.
Funke SW, Farrell PE, Piggott MD, 2017, Reconstructing wave profiles from inundation data, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, Vol: 322, Pages: 167-186, ISSN: 0045-7825
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: 1991-9603
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
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.
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