Publications
420 results found
Xiao D, Fang F, Pain C, et al., 2015, Non-intrusive reduced-order modelling of the Navier-Stokes equations based on RBF interpolation, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Vol: 79, Pages: 580-595, ISSN: 0271-2091
Dargaville S, Goffin MA, Buchan AG, et al., 2015, Solving the Boltzmann transport equation with multigrid and adaptive space/angle discretisations, ANNALS OF NUCLEAR ENERGY, Vol: 86, Pages: 99-107, ISSN: 0306-4549
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- Citations: 9
Adam A, Buchan AG, Piggott MD, et al., 2015, Adaptive Haar wavelets for the angular discretisation of spectral wave models, Journal of Computational Physics, Vol: 305, Pages: 521-538, ISSN: 1090-2716
A new framework for applying anisotropic angular adaptivity in spectral wave modelling is presented. The angular dimension of the action balance equation is discretised with the use of Haar wavelets, hierarchical piecewise-constant basis functions with compact support, and an adaptive methodology for anisotropically adjusting the resolution of the angular mesh is proposed. This work allows a reduction of computational effort in spectral wave modelling, through a reduction in the degrees of freedom required for a given accuracy, with an automated procedure and minimal cost.
Zheng J, Zhu J, Wang Z, et al., 2015, Towards a new multiscale air quality transport model using the fully unstructured anisotropic adaptive mesh technology of Fluidity (version 4.1.9), Geoscientific Model Development, ISSN: 1991-9603
Abushaikha AS, Blunt MJ, Gosselin OR, et al., 2015, Interface control volume finite element method for modelling multi-phase fluid flow in highly heterogeneous and fractured reservoirs, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 298, Pages: 41-61, ISSN: 0021-9991
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- Citations: 32
Buchan AG, Calloo AA, Goffin MG, et al., 2015, A POD reduced order model for resolving angular direction in neutron/photon transport problems, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 296, Pages: 138-157, ISSN: 0021-9991
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- Citations: 65
Xiao D, Fang F, Buchan AG, et al., 2015, Non-intrusive reduced order modelling of the Navier-Stokes equations, Computer Methods in Applied Mechanics and Engineering, Vol: 293, Pages: 522-541, ISSN: 0045-7825
This article presents two new non-intrusive reduced order models based upon proper orthogonal decomposition (POD) for solving the Navier–Stokes equations. The novelty of these methods resides in how the reduced order models are formed, that is, how the coefficients of the POD expansions are calculated. Rather than taking a standard approach of projecting the underlying equations onto the reduced space through a Galerkin projection, here two different techniques are employed. The first method applies a second order Taylor series to calculate the POD coefficients at each time step from the POD coefficients at earlier time steps. The second method uses a Smolyak sparse grid collocation method to calculate the POD coefficients, where again the coefficients at earlier time steps are used as the inputs. The advantage of both approaches are that they are non-intrusive and so do not require modifications to a system code; they are therefore very easy to implement. They also provide accurate solutions for modelling flow problems, and this has been demonstrated by the simulation of flows past a cylinder and within a gyre. It is demonstrated that accuracy relative to the high fidelity model is maintained whilst CPU times are reduced by several orders of magnitude in comparison to high fidelity models.
Jackson MD, Percival JR, Mostaghiml P, et al., 2015, Reservoir modeling for flow simulation by use of surfaces, adaptive unstructured meshes, and an overlapping-control-volume finite-element method, SPE Reservoir Evaluation and Engineering, Vol: 18, Pages: 115-132, ISSN: 1094-6470
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 multiscale geologic heterogeneity and the prediction of flow through that heterogeneity. The research builds on more than 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.Geologic heterogeneities, whether structural, stratigraphic, sedimentologic, or diagenetic in origin, are represented as discrete volumes bounded by surfaces, without reference to a predefined grid. Petrophysical properties are uniform within the geologically defined rock volumes, rather than within grid cells. The resulting model is discretized for flow simulation by use of an unstructured, tetrahedral mesh that honors the architecture of the surfaces. This approach allows heterogeneity over multiple length-scales to be explicitly captured by use of fewer cells than conventional corner-point or unstructured grids.Multiphase flow is simulated by use of 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 dynamic adaptive-mesh optimization and efficient parallelization. Within each rock volume, the mesh coarsens and refines to capture key flow processes during a simulation, and also preserves the surface-based representation of geologic heterogeneity. Computational effort is thus focused on regions of the model where it is most required.After valid
Mostaghimi P, Percival JR, Pavlidis D, et al., 2015, Anisotropic Mesh Adaptivity and Control Volume Finite Element Methods for Numerical Simulation of Multiphase Flow in Porous Media, MATHEMATICAL GEOSCIENCES, Vol: 47, Pages: 417-440, ISSN: 1874-8961
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- Citations: 35
Vire A, Xiang J, Pain CC, 2015, An immersed-shell method for modelling fluid-structure interactions, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 373, ISSN: 1364-503X
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- Citations: 18
Salinas P, Percival J, Pavlidis D, et al., 2015, A discontinuous overlapping control volume finite element method for multi-phase porous media flow using dynamic unstructured mesh optimization, SPE Reservoir Simulation Symposium
Su K, Latham J-P, Pavlidis D, et al., 2015, Multiphase flow simulation through porous media with explicitly resolved fractures, Geofluids, Vol: 15, Pages: 592-607, ISSN: 1468-8123
Accurate simulation of multiphase flow in fractured porous media remains a challenge. An important problem is the representation of the discontinuous or near discontinuous behaviour of saturation in real geological formations. In the classical continuum approach, a refined mesh is required at the interface between fracture and porous media to capture the steep gradients in saturation and saturation-dependent transport properties. This dramatically increases the computational load when large numbers of fractures are present in the numerical model. A discontinuous finite element method is reported here to model flow in fractured porous media. The governing multiphase porous media flow equations are solved in the adaptive mesh computational fluid dynamics code IC-FERST on unstructured meshes. The method is based on a mixed control volume – discontinuous finite element formulation. This is combined with the PN+1DG-PNDG element pair, which has discontinuous (order N+1) representation for velocity and discontinuous (order N) representation for pressure. A number of test cases are used to evaluate the method's ability to model fracture flow. The first is used to verify the performance of the element pair on structured and unstructured meshes of different resolution. Multiphase flow is then modelled in a range of idealised and simple fracture patterns. Solutions with sharp saturation fronts and computational economy in terms of mesh size are illustrated.
Goffin MA, Buchan AG, Dargaville S, et al., 2015, Goal-based angular adaptivity applied to a wavelet-based discretisation of the neutral particle transport equation, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 281, Pages: 1032-1062, ISSN: 0021-9991
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- Citations: 14
Salinas P, Percival JR, Pavlidis D, et al., 2015, A new approach to reservoir modeling and simulation using boundary representation, adaptive unstructured meshes and the discontinuous overlapping control volume finite element method, Pages: 241-245
We present a new, high-order, control-volume-finite-element (CVFE) method with discontinuous Nthorder representation for pressure and (N+1)th-order for velocity. The method conserves mass and ensures that the extended Darcy equations for multi-phase flow are exactly enforced, but does not require the use of control volumes (CVs) that span domain boundaries. We demonstrate that the approach, amongst other features, accurately preserves sharp saturation changes associated with high aspect ratio geologic features such as fractures and mudstones, allowing efficient simulation of flow in highly heterogeneous models. Moreover, in conjunction with dynamic mesh optimization, in which the mesh adapts in space and time to key solution fields such as pressure, velocity or saturation whilst honoring a surface-based representation of the underlying geologic heterogeneity, accurate solutions are obtained at significantly lower computational cost than an equivalent fine, fixed mesh and conventional CVFE methods. The work presented is significant for two reasons. First, it resolves a longstanding problem associated with the use of classical CVFE methods to model flow in highly heterogeneous porous media; second, it reduces computational cost/increases solution accuracy through the use of dynamic mesh optimization without compromising parallelization.
Angeli P, Azzopardi BJ, Hewakandamby B, et al., 2015, Multi-scale exploration of multiphase physics in flows (MEMPHIS): A framework for the next-generation predictive tools for multiphase flows, Pages: 242-249
Ins 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 micro-fluidics, 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, model-driven experimentation, to maximise prediction accuracy. The framework also involves massively-parallelisable 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.
Guo L, Xiang J, Latham JP, et al., 2015, Numerical simulation of hydraulic fracturing using a three-dimensional fracture model coupled with an adaptive mesh fluid model, Pages: 2170-2179
A three-dimensional fracture model developed in the context of the combined finite-discrete element method is incorporated into a two-way fluid-solid coupling model. The fracture model is capable of simulating the whole fracturing process. It includes pre-peak hardening deformation, post-peak strain softening, transition from continuum to discontinuum, and the explicit interaction between discrete fracture surfaces, for both tensile and shear fracture initiation and propagation. The fluid-solid coupling model can simulate the interactions between moving fluids and multi-body solids. By incorporating the fracture model into the coupling model, a methodology of using the new coupling model to capture fracturing behaviour of solids in fluid-solid coupling simulations is proposed. To solve the problem in the coupling model of having adaptive continuous meshes being used by the fluid code and discontinuous meshes in the solid code, a scheme to convert different meshes is developed. A single fracture propagation driven by fluid pressures is simulated and the results show that the modelling obtains the correct critical load and propagation direction for fluid-driven fracturing. Several important phenomena, such as stress concentration ahead of the fracture tip, adaptive refinement of fluid mesh as a response to the fracture propagation and fluids flowing into fractures, are properly captured.
Mostaghimi P, Kamali F, Jackson MD, et al., 2015, A dynamic mesh approach for simulation of immiscible viscous fingering, Pages: 1537-1548
Viscous fingering is a major concern in the water flooding of heavy oil reservoirs. Traditional reservoir simulators employ low-order finite volume/difference methods on structured grids to resolve this phenomenon. However, their approach suffers from a significant numerical dispersion error due to insufficient mesh resolution which smears out some important features of the flow. We simulate immiscible incompressible two phase displacements and propose use of unstructured control volume finite element (CVFE) methods for capturing viscous fingering in porous media. Our approach uses anisotropic mesh adaptation where the mesh resolution is optimized based on the evolving flow features. The adaptive algorithm uses a metric tensor field based on solution interpolation error estimates to locally control the size and shape of elements in the metric. We resolve the viscous fingering patterns accurately and reduce the numerical dispersion error significantly. The mesh optimization, generates an unstructured coarse mesh in other regions of the computational domain where a high resolution is not required. We analyze the computational cost of mesh adaptivity on unstructured mesh and compare its results with those obtained by a commercial reservoir simulator based on the finite volume methods.
Pavlidis D, Gomes JLMA, Xie Z, et al., 2015, Numerical modelling of melt behaviour in the lower vessel head of a nuclear reactor, IUTAM SYMPOSIUM ON MULTIPHASE FLOWS WITH PHASE CHANGE: CHALLENGES AND OPPORTUNITIES, Vol: 15, Pages: 72-77, ISSN: 2210-9838
Pavlidis D, Gomes JLMA, Salinas P, et al., 2015, Numerical modelling of debris bed water quenching, IUTAM SYMPOSIUM ON MULTIPHASE FLOWS WITH PHASE CHANGE: CHALLENGES AND OPPORTUNITIES, Vol: 15, Pages: 64-71, ISSN: 2210-9838
Xie Z, Pavlidis D, Percival JR, et al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, 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.
Xie Z, Pavlidis D, Percival JR, et al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, ISSN: 0301-9322
© 2013 Elsevier Ltd. 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.
Percival JR, Pavlidis D, Xie Z, et al., 2014, Control volume finite element modelling of segregation of sand and granular flows in fluidized beds, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 191-199, ISSN: 0301-9322
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- Citations: 5
Pavlidis D, Xie Z, Percival JR, et al., 2014, Two- and three-phase horizontal slug flow simulations using an interface-capturing compositional approach, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 85-91, ISSN: 0301-9322
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- Citations: 26
Fang F, Zhang T, Pavlidis D, et al., 2014, Reduced order modelling of an unstructured mesh air pollution model and application in 2D/3D urban street canyons, Atmospheric Environment, Vol: 96, Pages: 96-106, ISSN: 1352-2310
A novel reduced order model (ROM) based on proper orthogonal decomposition (POD) has been developed for a finite-element (FE) adaptive mesh air pollution model. A quadratic expansion of the non-linear terms is employed to ensure the method remained efficient. This is the first time such an approach has been applied to air pollution LES turbulent simulation through three dimensional landscapes. The novelty of this work also includes POD's application within a FE-LES turbulence model that uses adaptive resolution. The accuracy of the reduced order model is assessed and validated for a range of 2D and 3D urban street canyon flow problems. By comparing the POD solutions against the fine detail solutions obtained from the full FE model it is shown that the accuracy is maintained, where fine details of the air flows are captured, whilst the computational requirements are reduced. In the examples presented below the size of the reduced order models is reduced by factors up to 2400 in comparison to the full FE model while the CPU time is reduced by up to 98% of that required by the full model.
Goffin MA, Buchan AG, Belme AC, et al., 2014, Goal-based angular adaptivity applied to the spherical harmonics discretisation of the neutral particle transport equation, ANNALS OF NUCLEAR ENERGY, Vol: 71, Pages: 60-80, ISSN: 0306-4549
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- Citations: 20
Merton SR, Smedley-Stevenson RP, Pain CC, et al., 2014, Adjoint eigenvalue correction for elliptic and hyperbolic neutron transport problems, PROGRESS IN NUCLEAR ENERGY, Vol: 76, Pages: 1-16, ISSN: 0149-1970
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- Citations: 3
Mostaghimi P, Tollit BS, Neethling SJ, et al., 2014, A control volume finite element method for adaptive mesh simulation of flow in heap leaching, JOURNAL OF ENGINEERING MATHEMATICS, Vol: 87, Pages: 111-121, ISSN: 0022-0833
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- Citations: 25
Che Z, Fang F, Percival J, et al., 2014, An ensemble method for sensor optimisation applied to falling liquid films, International Journal of Multiphase Flow, Vol: 67, Pages: 153-161, ISSN: 1879-3533
Multiphase flow problems are often extremely complex due to their strong nonlinearity. To study multiphase flow, it is important to simulate or measure key parameters accurately, such as pressure drops and flow rates. Therefore, it is essential to place the sensors at the locations with high impact, and to avoid locations with low impact, where impact is determined by a function such as one of the key variables like pressure drop or flow rate. In this paper, an ensemble method is used to optimise sensor locations for falling film problems based on an importance map. The importance map can identify the important regions according to a target function. The sensor locations are selected based on the importance map, the variation of the variables, and the costs of performing the measurements. We demonstrate the approach by applying data assimilation and show that the optimised sensor locations can significantly improve the data assimilation results. Through sensitivity analysis, sensor optimisation, and data assimilation, this study, for the first time, provides a systematic linkage between the experiments and the models for falling film problems. It also presents a new goal or target based method for sensor placement. This method can be extended to other complex multiphase flow problems.
Jewer S, Buchan AG, Pain CC, et al., 2014, An immersed body method for coupled neutron transport and thermal hydraulic simulations of PWR assemblies, ANNALS OF NUCLEAR ENERGY, Vol: 68, Pages: 124-135, ISSN: 0306-4549
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- Citations: 5
Sakai M, Abe M, Shigeto Y, et al., 2014, Verification and validation of a coarse grain model of the DEM in a bubbling fluidized bed, CHEMICAL ENGINEERING JOURNAL, Vol: 244, Pages: 33-43, ISSN: 1385-8947
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- Citations: 177
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