Publications
209 results found
Piggott MD, 2014, Fluidity
Fluidity is an open source, general purpose, multi-phase computational fluid dynamics code capable of numerically solving the Navier-Stokes equation and accompanying field equations on arbitrary unstructured finite element meshes in one, two and three dimensions.It is used in a number of different scientific areas including geophysical fluid dynamics, computational fluid dynamics, ocean modelling and mantle convection. It uses a finite element/control volume method which allows arbitrary movement of the mesh with time dependent problems, allowing mesh resolution to increase or decrease locally according to the current simulated state. It has a wide range of element choices including mixed formulations.Fluidity is parallelised using MPI and is capable of scaling to many thousands of processors. Other innovative and novel features are a user-friendly GUI and a python interface which can be used to calculate diagnostic fields, set prescribed fields or set user-defined boundary conditions.
Barnett GL, Funke SW, Piggott MD, 2014, Hybrid global-local optimisation algorithms for the layout design of tidal turbine arrays
Tidal stream power generation represents a promising source of renewableenergy. In order to extract an economically useful amount of power, tens tohundreds of tidal turbines need to be placed within an array. The layout ofthese turbines can have a significant impact on the power extracted and henceon the viability of the site. Funke et al. formulated the question of the bestturbine layout as an optimisation problem constrained by the shallow waterequations and solved it using a local, gradient-based optimisation algorithm.Given the local nature of this approach, the question arises of how optimal thelayouts actually are. This becomes particularly important for scenarios withcomplex bathymetry and layout constraints, both of which typically introducelocally optimal layouts. Optimisation algorithms which find the global optimagenerally require orders of magnitude more iterations than local optimisationalgorithms and are thus infeasible in combination with an expensive flow model.This paper presents an analytical wake model to act as an efficient proxy tothe shallow water model. Based upon this, a hybrid global-local two-stageoptimisation approach is presented in which turbine layouts are first optimisedwith the analytical wake model via a global optimisation algorithm, and furtheroptimised with the shallow water model via a local gradient-based optimisationalgorithm. This procedure is applied to a number of idealised cases and a morerealistic case with complex bathymetry in the Pentland Firth, Scotland. It isshown that in cases where bathymetry is considered, the two-stage optimisationprocedure is able to improve the power extracted from the array by as much as25% compared to local optimisation for idealised scenarios and by as much as12% for the more realistic Pentland Firth scenario whilst in many casesreducing the overall computation time by approximately 35%.
Jacobs CT, Avdis A, Gorman GJ, et al., 2014, PyRDM: A Python-based Library for Automating the Management and Online Publication of Scientific Software and Data, Journal of Open Research Software, Vol: 2, ISSN: 2049-9647
Parkinson SD, Hill J, Piggott MD, et al., 2014, Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 7, Pages: 1945-1960, ISSN: 1991-959X
Jacobs CT, Piggott MD, 2014, Firedrake-Fluids v0.1: numerical modelling of shallow water flows using a performance-portable automated solution framework, Geoscientific Model Development Discussions, Vol: 7, Pages: 5699-5738, ISSN: 1991-9611
Jacobs CT, Avdis A, Gorman GJ, et al., 2014, PyRDM
PyRDM is a Python-based library for research data management (RDM). It facilitates the automated publication of scientific software and associated input and output data.
Hill J, Popova EE, Ham DA, et al., 2014, Adapting to life: ocean biogeochemical modelling and adaptive remeshing, Ocean Science, Vol: 10, Pages: 323-343
An outstanding problem in biogeochemical modelling of the ocean is that many of the key processes occur intermittently at small scales, such as the sub-mesoscale, that are not well represented in global ocean models. This is partly due to their failure to resolve sub-mesoscale phenomena, which play a significant role in vertical nutrient supply. Simply increasing the resolution of the models may be an inefficient computational solution to this problem. An approach based on recent advances in adaptive mesh computational techniques may offer an alternative. Here the first steps in such an approach are described, using the example of a simple vertical column (quasi-1-D) ocean biogeochemical model. We present a novel method of simulating ocean biogeochemical behaviour on a vertically adaptive computational mesh, where the mesh changes in response to the biogeochemical and physical state of the system throughout the simulation. We show that the model reproduces the general physical and biological behaviour at three ocean stations (India, Papa and Bermuda) as compared to a high-resolution fixed mesh simulation and to observations. The use of an adaptive mesh does not increase the computational error, but reduces the number of mesh elements by a factor of 2–3. Unlike previous work the adaptivity metric used is flexible and we show that capturing the physical behaviour of the model is paramount to achieving a reasonable solution. Adding biological quantities to the adaptivity metric further refines the solution. We then show the potential of this method in two case studies where we change the adaptivity metric used to determine the varying mesh sizes in order to capture the dynamics of chlorophyll at Bermuda and sinking detritus at Papa. We therefore demonstrate that adaptive meshes may provide a suitable numerical technique for simulating seasonal or transient biogeochemical behaviour at high vertical resolution whilst minimising the number of elements in the mesh. M
Funke SW, Farrell PE, Piggott MD, 2014, Tidal turbine array optimisation using the adjoint approach, Renewable Energy, Vol: 63, Pages: 658-673, ISSN: 0960-1481
Oceanic tides have the potential to yield a vast amount of renewable energy. Tidal stream generators are one of the key technologies for extracting and harnessing this potential. In order to extract an economically useful amount of power, hundreds of tidal turbines must typically be deployed in an array. This naturally leads to the question of how these turbines should be configured to extract the maximum possible power: the positioning and the individual tuning of the turbines could significantly influence the extracted power, and hence is of major economic interest. However, manual optimisation is difficult due to legal site constraints, nonlinear interactions of the turbine wakes, and the cubic dependence of the power on the flow speed. The novel contribution of this paper is the formulation of this problem as an optimisation problem constrained by a physical model, which is then solved using an efficient gradient-based optimisation algorithm. In each optimisation iteration, a two-dimensional finite element shallow water model predicts the flow and the performance of the current array configuration. The gradient of the power extracted with respect to the turbine positions and their tuning parameters is then computed in a fraction of the time taken for a flow solution by solving the associated adjoint equations. These equations propagate causality backwards through the computation, from the power extracted back to the turbine positions and the tuning parameters. This yields the gradient at a cost almost independent of the number of turbines, which is crucial for any practical application. The utility of the approach is demonstrated by optimising turbine arrays in four idealised scenarios and a more realistic case with up to 256 turbines in the Inner Sound of the Pentland Firth, Scotland.
Jordan JR, Holland PR, Jenkins A, et al., 2014, Modeling ice-ocean interaction in ice-shelf crevasses, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 119, Pages: 995-1008, ISSN: 2169-9275
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- Citations: 14
Hiester HR, Piggott MD, Farrell PE, et al., 2014, Assessment of spurious mixing in adaptive mesh simulations of the two-dimensional lock-exchange, Ocean Modelling, Vol: 73, Pages: 30-44, ISSN: 1463-5003
Jacobs CT, Collins GS, Piggott MD, et al., 2014, MULTIPHASE FLOW MODELLING OF EXPLOSIVE VOLCANIC ERUPTIONS USING AN ADAPTIVE UNSTRUCTURED MESH-BASED APPROACH, 11th World Congress on Computational Mechanics (WCCM) / 5th European Conference on Computational Mechanics (ECCM) / 6th European Conference on Computational Fluid Dynamics (ECFD), Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 7406-7417
Vire A, Spinneken J, Piggott MD, et al., 2014, MODELLING OF WAVES AND WAVE-STRUCTURE INTERACTIONS USING NON-LINEAR NUMERICAL MODELS, 11th World Congress on Computational Mechanics (WCCM) / 5th European Conference on Computational Mechanics (ECCM) / 6th European Conference on Computational Fluid Dynamics (ECFD), Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 2138-2148
Vire A, Jiang J, Piggott MD, et al., 2014, Towards the Numerical Modelling of Floating Offshore Renewables, Fluid-Structure-Sound Interactions and Control, Editors: Zhou, Yang, Huang, Hodges, Publisher: Springer Berlin Heidelberg, Pages: 413-417, ISBN: 978-3-642-40370-5
Kimura S, Candy AS, Holland PR, et al., 2013, Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves, Ocean Modelling, Vol: 67, Pages: 39-51, ISSN: 1463-5003
Oishi Y, Piggott MD, Maeda T, et al., 2013, Three-dimensional tsunami propagation simulations using an unstructured mesh finite element model, Journal of Geophysical Research: Solid Earth, Vol: 118, Pages: 2998-3018, ISSN: 2169-9313
Vire A, Xiang J, Piggott M, et al., 2013, Towards the fully-coupled numerical modelling of floating wind turbines, 10th Deep Sea Offshore Wind R and D Conference (DeepWind), Publisher: ELSEVIER SCIENCE BV, Pages: 43-51, ISSN: 1876-6102
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- Citations: 12
Vire A, Xiang J, Piggott M, et al., 2013, Numerical Modelling of Fluid-structure Interactions for Floating Wind Turbine Foundations, Twenty-third International Offshore and Polar Engineering Conference, Pages: 377-382
The aim of this study is to model the interactions between fluids and solids using fully nonlinear models. Non-linearity is important in the context of floating wind turbines, for example, to model breaking waves impacting on the structure and the effect of the solid’s elasticity. In this work, the fluid- and solid-dynamics equations are solved using separate finite-element models, which are coupled at every time step. This enables the mutual interactions between fluids and moving solids to be modelled. Importantly, the coupling algorithm ensures that the action-reaction principle is satisfied at a discrete level, independently of the order of representation of the discrete fields in each model. To the authors’ knowledge, the present algorithm is novel in that it can simultaneously handle (i) non-matching fluid and solid meshes, (ii) different polynomial orders of the basis functions on each mesh, and (iii) different fluid and solid time steps. Results are shown for: (i) a bottom-mounted pile subjected to small-amplitude waves in a numerical wave tank, and (ii) a truncated pile floating at an interface between air and water.
Jacobs CT, Collins GS, Piggott MD, et al., 2013, Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes, Geophysical Journal International, Vol: 192, Pages: 647-665
Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adapt
Milthaler FFM, Gorman GJ, Piggott MD, 2012, Reducing spurious drag forces when using mesh adaptivity in CFD, ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers, Pages: 5621-5640
This work explores the impact of mesh adaptivity methods in combination with fixed as well as adaptive timestepping when modelling fluid dynamical systems that are sensitive to minor changes in the fluid's pressure and velocity. Here the diagnostic of interest for fluidsolid interaction modelling is the drag force. Depending on the solid's properties, even minor unphysical abrupt changes, so-called peaks, in the drag force - due to mesh adaptivity - could lead to a major disturbance in the model. For such systems the need naturally arises to reduce these peaks to a certain degree, until the sudden changes are small enough to be neglected. Hence, in this paper a variety of approaches are described and compared against one another, that aim to reduce these peaks. Moreover, further studies show the relation between the peaks in the drag force to the timestep, and pressure. The 3D-CFD software Fluidity, which uses an arbitrarily unstructured mesh, and a 3D mesh optimization algorithm was used for this case-study.
VirĂ© A, Xiang J, Milthaler F, et al., 2012, Modelling of fluid–solid interactions using an adaptive mesh fluid model coupled with a combined finite–discrete element model, Ocean Dynamics
Spinneken J, Heller V, Kramer S, et al., 2012, Assessment of an Advanced Finite Element Tool for the Simulation of Fully-nonlinear Gravity Water Waves, The 22nd International Ocean and Polar Engineering Conference
The aim of the present study is to provide a rigorous analysis of the water wave modelling capabilities of the advanced multipurpose CFD code Fluidity. This code has been developed atImperial College London over a large number of years and benefits from an open source GNU license. In contrast to similar studies adopting closed-source in-house or commercial solutions,the results presented herein may be verified by any computer literate reader. The investigation focuses on the simulation of gravity water waves; their detailed understanding being fundamental to the design of many offshore (marine) solutions, including the emerging fields of wave energy conversion and floatingoffshore wind applications. Both small amplitude (linear hydrodynamics) and finite amplitude (nonlinear hydrodynamics) regular waves are simulated in a 2D Numerical Wave Tank (NWT). First, and assessment of the NWT’s capabilities in accurately modelling wave propagation and wave energy conservation of linear waves is undertaken. Subsequently, the simulated wave field is directly compared with results obtained from linear wavemaker theory. For the purpose of the nonlinear wave investigation, two wave generation techniques are adopted, and comparisons with a high-order potential flow theory are made. The overall agreement between the simulation results and theory was found to be very good.
Bull JR, Piggott MD, Pain CC, 2012, A finite element LES methodology for anisotropic in-homogeneous meshes, 7th International Symposium on Turbulence Heat and Mass Transfer (THMT), Publisher: BEGELL HOUSE, INC, Pages: 1516-1527
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- Citations: 3
Hill J, Piggott MD, Ham DA, et al., 2012, On the performance of a generic length scale turbulence model within an adaptive finite element ocean model, Ocean Modelling, Vol: 56, Pages: 1-15
Research into the use of unstructured mesh methods for ocean modelling has been growing steadily in the last few years. One advantage of using unstructured meshes is that one can concentrate resolution where it is needed. In addition, dynamic adaptive mesh optimisation (DAMO) strategies allow resolution to be concentrated when this is required. Despite the advantage that DAMO gives in terms of improving the spatial resolution where and when required, small-scale turbulence in the oceans still requires parameterisation. A two-equation, generic length scale (GLS) turbulence model (one equation for turbulent kinetic energy and another for a generic turbulence length-scale quantity) adds this parameterisation and can be used in conjunction with adaptive mesh techniques. In this paper, an implementation of the GLS turbulence parameterisation is detailed in a non-hydrostatic, finite-element, unstructured mesh ocean model, Fluidity-ICOM. The implementation is validated by comparing to both a laboratory-scale experiment and real-world observations, on both fixed and adaptive meshes. The model performs well, matching laboratory and observed data, with resolution being adjusted as necessary by DAMO. Flexibility in the prognostic fields used to construct the error metric used in DAMO is required to ensure best performance. Moreover, the adaptive mesh models perform as well as fixed mesh models in terms of root mean square error to observation or theoretical mixed layer depths, but uses fewer elements and hence has a reduced computational cost.
Gorman GJ, Southern J, Farrell PE, et al., 2012, Hybrid OpenMP/MPI anisotropic mesh smoothing, International Conference on Computational Science (ICCS), Publisher: ELSEVIER SCIENCE BV, Pages: 1513-1522, ISSN: 1877-0509
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- Citations: 13
Southern J, Gorman GJ, Piggott MD, et al., 2011, Parallel anisotropic mesh adaptivity with dynamic load balancing for cardiac electrophysiology, Journal of Computational Science, Vol: 3, Pages: 8-16
Gomes JLMA, Pain CC, Eaton MD, et al., 2011, Coupled neutronics-fluids modelling of criticality within a MOX powder system, PROGRESS IN NUCLEAR ENERGY, Vol: 53, Pages: 523-552, ISSN: 0149-1970
Investigation of nuclear criticality in powder systems is necessary for the assessment of industrial plant integrity and potential radiation impacts on worker and the public health. For nuclear fuel processing, to produce fuel pellets, MOX (UO2 + PuO2) and zinc stearate (lubricant) powders are homogenised in a stirred vessel. The coupled multi-fluids (multiphase and multi-component) and neutron-radiation transport FETCH model was extended to simulate reactivity feedback mechanisms and to assess safety and potential risks of criticality incursions in 2-3D systems. This work has strengthened links with the Japan Atomic Energy Agency (JAEA), led to consultancy work with Japanese National Labs and work with Tokyo University that led on to the Todai Forum and the core to core program with Japan.
Hiester H, Piggott MD, Allison PA, 2011, The impact of mesh adaptivity on the gravity current front speed in a two-dimensional lock-exchange, Ocean Modelling, ISSN: 1463-5003
Nelson R, Piggott M, Wilson C, et al., 2011, Compressible Flows on Adaptive and Unstructured Meshes with FLUIDITY, 6th International Conference on Fluid Mechanics, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
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