Publications
420 results found
Xie Z, Pavlidis D, Percival JR, et al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, ISSN: 0301-9322
Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.
Xiao D, Fang F, Buchan AG, et al., 2014, Non-linear model reduction for the Navier-Stokes equations using residual DEIM method, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 263, Pages: 1-18, ISSN: 0021-9991
Angeli P, Azzopardi BJ, Hewakandamby B, et al., 2014, Multi-scale exploration of multiphase physics in flows (MEMPHIS): A framework for the next-generation predictive tools for multiphase flows, Pages: 231-238
In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.
Angeli P, Azzopardi BJ, Hewakandamby B, et al., 2014, The next-generation predictive tools for multiphase flows, Pages: 221-228
In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.
Latham JP, Xiang J, Anastasaki E, et al., 2014, Numerical modelling of forces, stresses and breakages of concrete armour units, ISSN: 0161-3782
Numerical modelling has the potential to probe the complexity of the interacting physics of rubble mound armour systems. Through forward modelling of armour unit packs, stochastic variables such as unit displacement and maximum contact force per unit during an external oscillatory disturbance can be predicted. The combined finite-discrete element method (FEMDEM) is a multi-body method ideally suited to model the behaviour of the armour layer system and the stresses generated within complex shape units. In this paper we highlight the latest developments made with the application of FEMDEM technology to breakwater modelling including realistic rock underlayer and concrete unit layer topologies, maximum contact force distributions, internal unit stresses, fracture and unit breakages. Finally, fully coupled wave and multi-body armour unit motion with internal dynamic stress generation is illustrated.
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
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
Ardjmandpour N, Pain CC, Fang F, et al., 2014, Reduced order borehole induction modelling, INTERNATIONAL JOURNAL OF COMPUTATIONAL FLUID DYNAMICS, Vol: 28, Pages: 140-157, ISSN: 1061-8562
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- Citations: 3
Buchan AG, Pain CC, Fang F, et al., 2013, A POD reduced-order model for eigenvalue problems with application to reactor physics, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 95, Pages: 1011-1032, ISSN: 0029-5981
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- Citations: 51
Fang F, Pain CC, Navon IM, et al., 2013, The independent set perturbation method for efficient computation of sensitivities with applications to data assimilation and a finite element shallow water model, Computers & Fluids, Vol: 76, Pages: 33-49, ISSN: 0045-7930
Baker CMJ, Buchan AG, Pain CC, et al., 2013, Goal based mesh adaptivity for fixed source radiation transport calculations, Annals of Nuclear Energy, Vol: 55, Pages: 169-183, ISSN: 0306-4549
ELSheikh AH, Pain CC, Fang F, et al., 2013, Parameter estimation of subsurface flow models using iterative regularized ensemble Kalman filter, STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT, Vol: 27, Pages: 877-897, ISSN: 1436-3240
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- Citations: 33
Merton SR, Buchan AG, Pain CC, et al., 2013, An adjoint-based method for improving computational estimates of a functional obtained from the solution of the Boltzmann Transport Equation, ANNALS OF NUCLEAR ENERGY, Vol: 54, Pages: 1-10, ISSN: 0306-4549
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- Citations: 1
Xiao D, Fang F, Du J, et al., 2013, Non-linear Petrov–Galerkin methods for reduced order modelling of the Navier–Stokes equations using a mixed finite element pair, Computer Methods in Applied Mechanics and Engineering, Vol: 255, Pages: 147-157, ISSN: 0045-7825
Buchan AG, Pain CC, Tollit TS, et al., 2013, Simulated spatially dependent transient kinetics analysis of the Oak Ridge Y12 plant criticality excursion, Progress in Nuclear Energy, Vol: 63, Pages: 12-21
In June 1958 an accidental nuclear excursion occurred in the C-1 Wing of building 9212 in a process facility designed to recover enriched Uranium U(93) from various solid wastes. The accident was caused by the inadvertent flow of enriched uranyl nitrate into a 55 gallon drum which established a prompt critical nuclear excursion. Following the initial fission spike the nuclear system oscillated in power. The reaction was eventually terminated by the additional water which was flowing into the drum. The criticality excursion was estimated to have lasted approximately 20 min based upon nearby radiation measurement equipment with an estimated total fission yield of 1.3 × 1018 fissions of which the first fission spike contributed 6 × 1016 fissions.The traces from the radiation measurement devices indicated that most of the fissions occurred in the first 2.8 min, in which case the average power required for the observed fission yield was approximately 220 kW. After the first 2.8 min the system was postulated to have boiled causing a sharp decrease in density and reactivity of the system. This boiling probably reduced the power output from the system to a low level for the final 18 min of the excursion. This paper will aim to investigate the subsequent evolution of the Y12 excursion using the fundamentally based spatially dependent neutron/multiphase CFD kinetics simulation tool - FETCH. The reconstruction of the Y12 excursion using FETCH will follow the evolution of the excursion up until the uranyl nitrate starts to boil. The results of the FETCH simulation are presented and compared against the known measurements of the excursion from the radiation detection instruments located near the drum.
Baker CMJ, Buchan AG, Pain CC, et al., 2013, Multimesh anisotropic adaptivity for the Boltzmann transport equation, Annals of Nuclear Energy, Vol: 53, Pages: 411-426
This article presents a new adaptive finite element based method for the solution of the spatial dimensions of the Boltzmann transport equation. The method applies a curvature based error metric to locate the under and over resolved regions of a solution and this, in turn, is used to guide the refinement and coarsening of the spatial mesh. The error metrics and re-meshing procedures are designed such that they enable anisotropic resolution to form in the mesh should it be appropriate to do so. The adaptive mesh enables the appropriate resolution to be applied throughout the whole domain of a problem and so increase the efficiency of the solution procedure. Another new approach is also described that allows independent adaptive meshes to form for each of the energy group fluxes. The use of independent meshes can significantly improve computational efficiency when solving problems where the different group fluxes require high resolution over different regions. The mesh to mesh interpolation is made possible through the use of a ‘supermeshing’ procedure that ensures the conservation of particles when calculating the group to group scattering sources. Finally it is shown how these methods can be incorporated within a solver to resolve both fixed source and eigenvalue problems. A selection of both fixed source and eigenvalue problems are solved in order to demonstrate the capabilities of these methods.
Fang F, Pain CC, Navon IM, et al., 2013, Non-linear Petrov-Galerkin methods for reduced order hyperbolic equations and discontinuous finite element methods, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 234, Pages: 540-559, ISSN: 0021-9991
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- Citations: 47
Jackson MD, Gomes JLMA, Mostaghimi P, et al., 2013, Reservoir modeling for flow simulation using surfaces, adaptive unstructured meshes and control-volume-finite-element methods, Pages: 774-792
We present new approaches to reservoir modeling and flow simulation that dispose of the pillar-grid concept that has persisted since reservoir simulation began. This results in significant improvements to the representation of multi-scale geological heterogeneity and the prediction of flow through that heterogeneity. The research builds on 20+ years of development of innovative numerical methods in geophysical fluid mechanics, refined and modified to deal with the unique challenges associated with reservoir simulation. Geological heterogeneities, whether structural, stratigraphic, sedimentologic or diagenetic in origin, are represented as discrete volumes bounded by surfaces, without reference to a pre-defined grid. Petrophysical properties are uniform within the geologically-defined rock volumes, rather than within grid-cells. The resulting model is discretized for flow simulation using an unstructured, tetrahedral mesh that honors the architecture of the surfaces. This approach allows heterogeneity over multiple length-scales to be explicitly captured using fewer cells than conventional corner-point or unstructured grids. Multiphase flow is simulated using a novel mixed finite element formulation centered on a new family of tetrahedral element types, PN(DG)-PN+1, which has a discontinuous Nth-order polynomial representation for velocity and a continuous (order N+1) representation for pressure. This method exactly represents Darcy force balances on unstructured meshes and thus accurately calculates pressure, velocity and saturation fields throughout the domain. Computational costs are reduced through (i) efficient parallelization and (ii) automatic mesh adaptivity in time and space. Within each rock volume, the mesh coarsens and refines to capture key flow processes, whilst preserving the surface-based representation of geological heterogeneity. Computational effort is thus focused on regions of the model where it is most required. Having validated the approach aga
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.
Goffin MA, Baker CMJ, Buchan AG, et al., 2013, Minimising the error in eigenvalue calculations involving the Boltzmann transport equation using goal-based adaptivity on unstructured meshes, Journal of Computational Physics, Vol: 242, Pages: 726-762
This article presents a method for goal-based anisotropic adaptive methods for the finite element method applied to the Boltzmann transport equation. The neutron multiplication factor, keff, is used as the goal of the adaptive procedure. The anisotropic adaptive algorithm requires error measures for keff with directional dependence. General error estimators are derived for any given functional of the flux and applied to keff to acquire the driving force for the adaptive procedure. The error estimators require the solution of an appropriately formed dual equation. Forward and dual error indicators are calculated by weighting the Hessian of each solution with the dual and forward residual respectively. The Hessian is used as an approximation of the interpolation error in the solution which gives rise to the directional dependence. The two indicators are combined to form a single error metric that is used to adapt the finite element mesh. The residual is approximated using a novel technique arising from the sub-grid scale finite element discretisation. Two adaptive routes are demonstrated: (i) a single mesh is used to solve all energy groups, and (ii) a different mesh is used to solve each energy group. The second method aims to capture the benefit from representing the flux from each energy group on a specifically optimised mesh. The keff goal-based adaptive method was applied to three examples which illustrate the superior accuracy in criticality problems that can be obtained.
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
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
Buchan AG, Pain CC, Umpleby AP, et al., 2012, A sub-grid scale finite element agglomeration multigrid method with application to the Boltzmann transport equation, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 92, Pages: 318-342, ISSN: 0029-5981
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- Citations: 7
Buchan A, Eaton MD, Goddard AJH, et al., 2012, Simulated transient dynamics and heat transfer characteristics of the water boiler nuclear reactor SUPO with cooling coil heat extraction, Annals of nuclear energy, Vol: 48, Pages: 68-83
The term “water boiler” reactor refers to a type of aqueous homogeneous reactor (AHR) that was designed, built and operated by Los Alamos in the 1940s. This was the first type of liquid fuelled reactor and the first to be fuelled with enriched Uranium. For security reasons the term “water boiler” was adopted and three versions were built: LOPO (for low power), HYPO (for high power) and SUPO (for super power) which were spherical shaped reactor vessels. The name was appropriate as the reactors appeared to boil although this was actually due to the release of radiolytic gas bubbles; although SUPO was operated during some studies close to the boiling point of uranyl nitrate. The final water boiler “SUPO” was operated almost daily as a neutron source from 1951 until its deactivation in 1974-23 years of safe, reliable operation. Many of the key neutron measurements needed in the design of the early atomic weapons were made using LOPO, HYPO and SUPO. More recently SUPO has been considered as a benchmark for quasi-steady-state operation of AHRs with internal cooling structures.This paper presents modelling and analysis of the coupled neutronic and fluid time dependent characteristics of the SUPO reactor. In particular the quasi-steady-state dynamics of SUPO have been investigated together with its heat transfer characteristics. In the simulations presented the SUPO reactor is modelled using the spatially dependent neutron/multiphase CFD simulation tool, FETCH, at a quasi-steady-state power of 25 kW. SUPO also possessed a cooling coil system that fed cooling water through the reactor for the extraction of the fission and decay heat. This cooling system, and the heat extraction, is modelled in the simulations using a new sub-modelling approach that is detailed here. The results from this simulation, such as gas fraction, gas generation rate, coolant rate and average temperature, are compared against the available experimental information.
Sakai M, Takahashi H, Pain CC, et al., 2012, Study on a large-scale discrete element model for fine particles in a fluidized bed, ADVANCED POWDER TECHNOLOGY, Vol: 23, Pages: 673-681, ISSN: 0921-8831
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- Citations: 106
Baker CMJ, Buchan AG, Pain CC, et al., 2012, Quadratic inner element subgrid scale discretisation of the Boltzmann transport equation, Annals of Nuclear Energy, Vol: 45, Pages: 124-137
This paper explores the application of the inner element subgrid scale method to the Boltzmann transport equation using quadratic basis functions. Previously, only linear basis functions for both the coarse scale and the fine scale were considered. This paper, therefore, analyses the advantages of using different coarse and subgrid basis functions for increasing the accuracy of the subgrid scale method. The transport of neutral particle radiation may be described by the Boltzmann transport equation (BTE) which, due to its 7 dimensional phase space, is computationally expensive to resolve. Multi-scale methods offer an approach to efficiently resolve the spatial dimensions of the BTE by separating the solution into its coarse and fine scales and formulating a solution whereby only the computationally efficient coarse scales need to be solved. In previous work an inner element subgrid scale method was developed that applied a linear continuous and discontinuous finite element method to represent the solution’s coarse and fine scale components. This approach was shown to generate efficient and stable solutions, and so this article continues its development by formulating higher order quadratic finite element expansions over the continuous and discontinuous scales. Here it is shown that a solution’s convergence can be improved significantly using higher order basis functions. Furthermore, by using linear finite elements to represent coarse scales in combination with quadratic fine scales, convergence can also be improved with only a modest increase in computational expense.
Nygaard ET, Pain CC, Eaton MD, et al., 2012, Steps Towards Verification and Validation of the FETCH Code for Level 2 Analysis, Design and Optimization of Aqueous Homogeneous Reactors, PHYSOR
Saunders JH, Jackson MD, Pain CC, et al., 2012, Streaming potentials in hydrocarbon reservoir conditions, Geophysics, Vol: 77, Pages: E77-E90
Brito-Parada PR, Kramer SC, Wilson CR, et al., 2012, A finite element formulation to model the flow of flotation foams
Du J, Fang F, Pain CC, et al., 2012, POD reduced-order unstructured mesh modelling applied to 2D and 3D fluid flow, Computers & Mathematics with Applications
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