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  • Journal article
    Davison TM, Derrick JG, Collins GS, Bland PA, Rutherford ME, Chapman DJ, Eakins DEet al., 2017,

    Impact-induced compaction of primitive solar system solids: The need for mesoscale modelling and experiments

    , Procedia Engineering, Vol: 204, Pages: 405-412, ISSN: 1877-7058

    Primitive solar system solids were accreted as highly porous bimodal mixtures of mm-sized chondrules and sub-μm matrix grains. To understand the compaction and lithification of these materials by shock, it is necessary to investigate the process at the mesoscale; i.e., the scale of individual chondrules. Here we document simulations of hypervelocity compaction of primitive materials using the iSALE shock physics model. We compare the numerical methods employed here with shock compaction experiments involving bimodal mixtures of glass beads and silica powder and find good agreement in bulk material response between the experiments and models. The heterogeneous response to shock of bimodal porous mixtures with a composition more appropriate for primitive solids was subsequently investigated: strong temperature dichotomies between the chondrules and matrix were observed (non-porous chondrules remained largely cold, while the porous matrix saw temperature increases of 100’s K). Matrix compaction was heterogeneous, and post-shock porosity was found to be lower on the lee-side of chondrules. The strain in the matrix was shown to be higher near the chondrule rims, in agreement with observations from meteorites. Chondrule flattening in the direction of the shock increases with increasing impact velocity, with flattened chondrules oriented with their semi-minor axis parallel to the shock direction.
  • Journal article
    Collins GS, Lynch E, McAdam R, Davison TMet al., 2017,

    A numerical assessment of simple airblast models of impact airbursts

    , Meteoritics & Planetary Science, Vol: 52, Pages: 1542-1560, ISSN: 1086-9379

    Asteroids and comets 10–100 m in size that collide with Earth disrupt dramatically in the atmosphere with an explosive transfer of energy, caused by extreme air drag. Such airbursts produce a strong blastwave that radiates from the meteoroid's trajectory and can cause damage on the surface. An established technique for predicting airburst blastwave damage is to treat the airburst as a static source of energy and to extrapolate empirical results of nuclear explosion tests using an energy-based scaling approach. Here we compare this approach to two more complex models using the iSALE shock physics code. We consider a moving-source airburst model where the meteoroid's energy is partitioned as two-thirds internal energy and one-third kinetic energy at the burst altitude, and a model in which energy is deposited into the atmosphere along the meteoroid's trajectory based on the pancake model of meteoroid disruption. To justify use of the pancake model, we show that it provides a good fit to the inferred energy release of the 2013 Chelyabinsk fireball. Predicted overpressures from all three models are broadly consistent at radial distances from ground zero that exceed three times the burst height. At smaller radial distances, the moving-source model predicts overpressures two times greater than the static-source model, whereas the cylindrical line-source model based on the pancake model predicts overpressures two times lower than the static-source model. Given other uncertainties associated with airblast damage predictions, the static-source approach provides an adequate approximation of the azimuthally averaged airblast for probabilistic hazard assessment.
  • Journal article
    Morgan JV, 2016,

    The formation of peak rings in large impact craters

    , Science, Vol: 354, Pages: 878-882, ISSN: 0036-8075

    Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.
  • Journal article
    Bhutani G, Brito Parada PR, Cilliers JJ, 2016,

    Polydispersed flow modelling using population balances in an adaptive mesh finite element framework

    , Computers and Chemical Engineering, Vol: 87, Pages: 208-225, ISSN: 1873-4375

    An open-source finite element framework to model multiphase polydispersed flows is presented in this work. The Eulerian–Eulerian method was coupled to a population balance equation and solved using a highly-parallelised finite element code—Fluidity. The population balance equation was solved using DQMOM. A hybrid finite element–control volume method for solving the coupled system of equations was established. To enhance the efficiency of this solver, fully-unstructured non-homogeneous anisotropic mesh adaptivity was applied to systematically adapt the mesh based on the underlying physics of the problem. This is the first time mesh adaptivity has been applied to the external coordinates of the population balance equation for modelling polydispersed flows. Rigorous model verification and benchmarking were also performed to demonstrate the accuracy of this implementation. This finite element framework provides an efficient alternative to model polydispersed flow problems over the other available finite volumeCFD packages.
  • Journal article
    Jackson MD, Percival JR, Mostaghiml P, Tollit BS, Pavlidis D, Pain CC, Gomes JLMA, El-Sheikh AH, Salinas P, Muggeridge AH, Blunt MJet 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 & ENGINEERING, Vol: 18, Pages: 115-132, ISSN: 1094-6470
  • Journal article
    Guo X, Lange M, Gorman G, Mitchell L, Weiland Met al., 2015,

    Developing a scalable hybrid MPI/OpenMP unstructured finite element model

    , COMPUTERS & FLUIDS, Vol: 110, Pages: 227-234, ISSN: 0045-7930
  • Conference paper
    Salinas P, Percival J, Pavlidis D, Xie Z, Gomes J, Pain C, JAckson Met 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
  • Journal article
    Jacobs CT, Goldin TJ, Collins GS, Piggott MD, Kramer SC, Melosh HJ, Wilson CRG, Allison PAet al., 2015,

    An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds

    , JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273
  • Journal article
    Pavlidis D, Gomes JLMA, Salinas P, Pain CC, Tehrani AAK, Moatamedi M, Smith PN, Jones AV, Matar OKet 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
  • Journal article
    Bland PA, Collins GS, Davison TM, Abreu NM, Ciesla FJ, Muxworthy AR, Moore Jet al., 2014,

    Pressure-temperature evolution of primordial solar system solids during impact-induced compaction

    , NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
  • Journal article
    Jacobs CT, Avdis A, Gorman GJ, Piggott MDet 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
  • Journal article
    Mostaghimi P, Tollit BS, Neethling SJ, Gorman GJ, Pain CCet 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
  • Software
    Jacobs CT, Avdis A, Gorman GJ, Piggott MDet 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.
  • Journal article
    Xie Z, Xie Z, 2014,

    Numerical modelling of wind effects on breaking solitary waves

    , European Journal of Mechanics, B/Fluids, Vol: 43, Pages: 135-147, ISSN: 0997-7546

    Wind effects on breaking solitary waves are investigated in this study using a two-phase flow model. The model solves the Reynolds-averaged Navier-Stokes equations with the k - . turbulence model simultaneously for the flows both in the air and water, with the air-water interface calculated by the volume of fluid method. First, the proposed model was validated with the computations of a breaking solitary wave run-up on a 1:19.85 sloping beach in the absence of wind, and fairly good agreement between the computational results and experimental measurements was obtained. Further, detailed information of the water surface profiles, velocity fields, vorticity, turbulent stress, maximum run-up, evolution of maximum wave height, energy dissipation, plunging jet and splash-up phenomena is presented and discussed for breaking solitary waves in the presence of wind. The inclusion of wind alters the air flow structure above water waves, increases the generation of vorticity and turbulent stress, and affects the solitary wave shoaling, breaking and run-up processes. Wind increases the water particle velocities and causes water waves to break earlier and seaward, which agrees with the previous experiment. © 2013 Elsevier Masson SAS. All rights reserved.
  • Journal article
    Buchan AG, Farrell PE, Gorman GJ, Goddard AJH, Eaton MD, Nygaard ET, Angelo PL, Smedley-Stevenson RP, Merton SR, Smith PNet al., 2014,

    The immersed body supermeshing method for modelling reactor physics problems with complex internal structures

    , ANNALS OF NUCLEAR ENERGY, Vol: 63, Pages: 399-408, ISSN: 0306-4549
  • Journal article
    Lamb AR, Gorman GJ, Elsworth D, 2013,

    A fracture mapping and extended finite element scheme for coupled deformation and fluid flow in fractured porous media

    , INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Vol: 37, Pages: 2916-2936, ISSN: 0363-9061
  • Journal article
    Xie Z, Lin B, Falconer RA, Maddux TB, Xie Z, Lin B, Falconer RA, Maddux TBet al., 2013,

    Large-eddy simulation of turbulent open-channel flow over three-dimensional dunes

    , Journal of Hydraulic Research, Vol: 51, Pages: 494-505, ISSN: 0022-1686

    A large-eddy simulation study has been undertaken to investigate the turbulent structure of open-channel flow over three-dimensional (3D) dunes. The governing equations have been discretized using the finite volume method, with the partial cell treatment being implemented in a Cartesian grid form to deal with the 3D dune topography. The simulated free surface elevations, mean flow velocities and Reynolds shear stress distributions have been compared with experimental measurements published in the literature. Relatively close agreement has been obtained between the two sets of results. The predicted mean velocity field and the associated turbulence structure are significantly different from those observed for flows over two-dimensional dunes. The effects of dune three-dimensionality are reflected in spanwise variations of mean flow fields, secondary currents and different distributions of vertical profiles of the double-averaged velocity. Furthermore, large-scale vortical structures, such as spanwise rollers and hairpin-like structures, are predicted in the simulations, with most of them being generated in the concave regions of the 3D dunes. © 2013 International Association for Hydro-Environment Engineering and Research.
  • Journal article
    Buchan AG, Pain CC, Fang F, Navon IMet 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
  • Journal article
    Legler B, Johnson HD, Hampson GJ, Massart BYG, Jackson CA-L, Jackson MD, El-Barkooky A, Ravnas Ret al., 2013,

    Facies model of a fine-grained, tide-dominated delta: Lower Dir Abu Lifa Member (Eocene), Western Desert, Egypt

    , Sedimentology, Vol: 60, Pages: 1313-1356, ISSN: 0037-0746
  • Journal article
    Fang F, Pain CC, Navon IM, Cacuci DG, Chen Xet 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
  • Journal article
    ELSheikh AH, Pain CC, Fang F, Gomes JLMA, Navon IMet 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
  • Journal article
    Baker CMJ, Buchan AG, Pain CC, Tollit BS, Goffin MA, Merton SR, Warner Pet al., 2013,

    Goal based mesh adaptivity for fixed source radiation transport calculations

    , Annals of Nuclear Energy, Vol: 55, Pages: 169-183, ISSN: 0306-4549
  • Journal article
    Merton SR, Buchan AG, Pain CC, Smedley-Stevenson RPet 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
  • Journal article
    Latham J-P, Anastasaki E, Xiang J, 2013,

    New modelling and analysis methods for concrete armour unit systems using FEMDEM

    , Coastal Engineering, Vol: 77, Pages: 151-166

    Rubble mound breakwaters armoured with concrete units rely on collective behaviour between adjacent concrete armour units but existing largely empirical approaches have been unable to provide a detailed understanding of how these gigantic granular systems work. The problem has been that current methods cannot investigate the interdependence of hydraulic and structural stability at the scale of individual units. Numerical methods have the potential to provide such answers but there are many challenges to overcome. We present a solution to the first major bottleneck concerning the solids modelling: the numerical creation of a breakwater trunk section of single layer concrete units with geometrical and mechanical properties that conform to realistic prototype structure placements. Positioning of units is achieved with a new versatile software tool, POSITIT, which incorporates user-defined deposition variables and the initial positioning grid necessary to achieve the required design packing densities. The code Y3D, based on the combined finite-discrete element method, FEMDEM, solves the multi-body mechanics of the problem. First, we show numerically constructed breakwater sections with armour layers of 8 m3 CORE-LOC™ units placed on rock underlayers. The numerically-generated packs are deemed acceptable when examined according to a range of criteria indicative of acceptably placed armour layers, as set by concrete unit designers. Breakwater sections with packing densities ranging from 0.59 to 0.63 are then created. Using a set of analysis tools, local variation in packing density as an indicator of heterogeneity, centroid spacing, unit contacts and orientation of unit axes are presented, together with mechanical information showing the variation in contact forces. For these five packs examined, an increasingly tighter pack was associated with a steady increase in coordination number and a more steeply and accelerating increase in average maximum contact force per
  • Journal article
    Xie Z, 2013,

    Two-phase flow modelling of spilling and plunging breaking waves

    , Applied Mathematical Modelling, Vol: 37, Pages: 3698-3713, ISSN: 0307-904X

    A two-phase flow model, which solves the flow in the air and water simultaneously, has been employed to investigate both spilling and plunging breakers in the surf zone with a focus during wave breaking. The model is based on the Reynolds-averaged Navier-Stokes equations with the k-ε{lunate} turbulence model. The governing equations are solved using the finite volume method, with the partial cell treatment being implemented in a staggered Cartesian grid to deal with complex geometries. The PISO algorithm is utilised for the pressure-velocity coupling and the air-water interface is modelled by the interface capturing method via a high-resolution volume of fluid scheme. Numerical results are compared with experimental measurements and other numerical studies in terms of water surface elevations, mean flow and turbulence intensity, in which satisfactory agreement is obtained. In addition, water surface profiles, velocity and vorticity fields during wave breaking are also presented and discussed. It is shown that the present model is capable of simulating the wave overturning, air entrainment and splash-up processes. © 2012 Elsevier Inc.
  • Journal article
    Xie Z, Lin B, Falconer RA, 2013,

    Large-eddy simulation of the turbulent structure in compound open-channel flows

    , Advances in Water Resources, Vol: 53, Pages: 66-75, ISSN: 0309-1708

    A large-eddy simulation study has been undertaken to investigate the turbulent structure of open-channel flow in an asymmetric compound channel. The dynamic sub-grid scale model has been employed in the model, with the partial cell treatment being implemented using a Cartesian grid structure to deal with the floodplain. The numerical model was used to predict the: primary velocity and secondary currents, boundary shear stress, turbulence intensities, turbulent kinetic energy, and Reynolds stresses. These parameters were compared with experimental measurements published in the literature, with relatively close agreement being obtained between both sets of results. Furthermore, instantaneous flow fields and large-scale vortical structures were predicted and are presented herein. These vortical structures were found to be responsible for the significant lateral exchange of mass and momentum in compound channels. © 2012.
  • Journal article
    Xiao D, Fang F, Du J, Pain CC, Navon IM, Buchan AG, ElSheikh AH, Hu Get 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
  • Journal article
    Warner M, Ratcliffe A, Nangoo T, Morgan J, Umpleby A, Shah N, Vinje V, Stekl I, Guasch L, Win C, Conroy G, Bertrand A, Warner M, Ratcliffe A, Nangoo T, Morgan J, Umpleby A, Shah N, Vinje V, Guasch L, Win C, Stekl I, Conroy G, Bertrand Aet al., 2013,

    Anisotropic 3D full-waveform inversion

    , Geophysics, Vol: 78, Pages: R59-R80

    We have developed and implemented a robust and practical scheme for anisotropic 3D acoustic full-waveform inversion (FWI). We demonstrate this scheme on a field data set, applying it to a 4C ocean-bottom survey over the Tommeliten Alpha field in the North Sea. This shallow-water data set provides good azimuthal coverage to offsets of 7 km, with reduced coverage to a maximum offset of about 11 km. The reservoir lies at the crest of a high-velocity antiformal chalk section, overlain by about 3000 m of clastics within which a low-velocity gas cloud produces a seismic obscured area. We inverted only the hydrophone data, and we retained free-surface multiples and ghosts within the field data. We invert in six narrow frequency bands, in the range 3 to 6.5 Hz. At each iteration, we selected only a subset of sources, using a different subset at each iteration; this strategy is more efficient than inverting all the data every iteration. Our starting velocity model was obtained using standard PSDM model building including anisotropic reflection tomography, and contained epsilon values as high as 20%. The final FWI velocity model shows a network of shallow high-velocity channels that match similar features in the reflection data. Deeper in the section, the FWI velocity model reveals a sharper and more-intense low-velocity region associated with the gas cloud in which low-velocity fingers match the location of gas-filled faults visible in the reflection data. The resulting velocity model provides a better match to well logs, and better flattens common-image gathers, than does the starting model. Reverse-time migration, using the FWI velocity model, provides significant uplift to the migrated image, simplifying the planform of the reservoir section at depth. The workflows, inversion strategy, and algorithms that we have used have broad application to invert a wide-range of analogous data sets.
  • Journal article
    Baker CMJ, Buchan AG, Pain CC, Farrell PE, Eaton MD, Warner Pet 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.
  • Journal article
    Buchan AG, Pain CC, Tollit TS, Gomes JLMA, Eaton MD, Gorman GJ, Cooling CM, Goddard AJH, Nygaard ET, Angelo PL, Smith PNet 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.
  • Journal article
    Ilankoon IMSK, Cole KE, Neethling SJ, 2013,

    Measuring hydrodynamic dispersion coefficients in unsaturated packed beds: Comparison of PEPT with conventional tracer tests

    , CHEMICAL ENGINEERING SCIENCE, Vol: 89, Pages: 152-157, ISSN: 0009-2509
  • Journal article
    Du J, Navon IM, Zhu J, Fang F, Alekseev AKet al., 2013,

    Reduced order modeling based on POD of a parabolized Navier-Stokes equations model II: Trust region POD 4D VAR data assimilation

    , COMPUTERS & MATHEMATICS WITH APPLICATIONS, Vol: 65, Pages: 380-394, ISSN: 0898-1221
  • Journal article
    Fang F, Pain CC, Navon IM, Elsheikh AH, Du J, Xiao Det 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
  • Conference paper
    Vire A, Xiang J, Piggott M, Cotter C, Pain Cet 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
  • Journal article
    Hassan MHA, Johnson HD, Allison PA, Abdullah WHet al., 2013,

    Sedimentology and stratigraphic development of the upper Nyalu Formation (Early Miocence), Sarawak, Malaysia: A mixed wave and tide influenced coastal system

    , Journal of Asian Earth Sciences
  • Journal article
    Goffin MA, Baker CMJ, Buchan AG, Pain CC, Eaton MD, Smith PNet 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.
  • Conference paper
    Lange M, Gorman G, Weiland M, Mitchell L, Southern J, Lange M, Gorman G, Weiland M, Mitchell L, Southern Jet al., 2013,

    Acieving efficient strong scaling with PETSc using hybrid MPI/OpenMP optimisations

    , Publisher: Springer Berlin Heidelberg, Pages: 97-108
  • Conference paper
    Markall GR, Rathgeber F, Mitchell L, Loriant N, Bertolli C, Kelly PHJ, Markall G, Rathgeber F, Ham D, Loriant N, Mitchell L, Bertolli C, Kelly Pet al., 2013,

    Performance-Portable Finite Element Assembly Using PyOP2 and FEniCS

    , International Supercomputing Conference (ISC), Publisher: Springer, Pages: 279-289, ISSN: 0302-9743

    We describe a toolchain that provides a fully automated compilation pathway from a finite element domain-specific language to low-level code for multicore and GPGPU platforms. We demonstrate that the generated code exceeds the performance of the best available alternatives, without requiring manual tuning or modification of the generated code. The toolchain can easily be integrated with existing finite element solvers, providing a means to add performance portable methods without having to rebuild an entire complex implementation from scratch.
  • Journal article
    Brito-Parada PR, Neethling SJ, Cilliers JJ, 2013,

    Modelling the behaviour of the wetting front in non-standard forced foam drainage scenarios

    , Colloids and Surfaces A: Physicochemical and Engineering Aspects
  • Conference paper
    Jordan N, Allison PA, Hill JH, Sutton MDet al., 2012,

    Carbonates, ammonites and the fate of aragonite: a new perspective from the Lower Jurassic of Lyme Regis

    , British Sedimentological Research Group Annual Meeting

    The Lower Jurassic Blue Lias Formation at Lyme Regis, Dorset, preserves a diverse assemblage of invertebrate and vertebrate fossils within rhythmic packages of shales, marls and carbonates. One limestone bed in particular, Bed 29, preserves a unique pavement of very large (up to 72 cm) ammonites, initially buried in carbonate mud before diagenetic cementation. The ammonite accumulation is most likely due to sedimentological condensation but the mechanisms for preserving an aragonitic shell long enough for it to be neomorphosed to calcite on the seabed are a challenge for conventional taphonomic models. It has been suggested that early dissolution of aragonite is a major process in offshore deeper ramp settings, resulting in the removal of sediment prior to lithification. We present field-based evidence for a new model of aragonite preservation within a cyclic oxic-anoxic carbonate environment, using ammonite preservation to track the fate of aragonite in different depositional environments. The carbonate sediment provides a short-term geochemical buffer that militates against the dissolution of aragonite sediment and molluscs, allowing neomorphism to calcite under some conditions. The broader implications of this model for the preservation of molluscan shells and reduced sediment dissolution in carbonate environments under variably oxygenated conditions are evaluated.
  • Journal article
    Hossen MJ, Navon IM, Fang F, 2012,

    A penalized four-dimensional variational data assimilation method for reducing forecast error related to adaptive observations

    , INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Vol: 70, Pages: 1207-1220, ISSN: 0271-2091
  • Conference paper
    Barker DJ, Neethling SJ, Parameswaran G, 2012,

    SPH Simulation of Packed-beds and ColumnsApplied to Heap-leaching

    , CFD 2012
  • Journal article
    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.
  • Journal article
    Viré A, Xiang J, Milthaler F, Farrell P, Piggott MD, Latham JP, Pavlidis D, Pain CCet al., 2012,

    Modelling of fluid–solid interactions using an adaptive mesh fluid model coupled with a combined finite–discrete element model

    , Ocean Dynamics
  • Journal article
    Buchan AG, Pain CC, Umpleby AP, Smedley-Stevenson RPet 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
  • Journal article
    Morris G, Neethling SJ, Cilliers JJ, 2012,

    Identifying the Transition Capillary Pressure of a Superhydrophobic Surface Containing Cylindrical Rods

    , CHEMISTRY LETTERS, Vol: 41, Pages: 1303-1305, ISSN: 0366-7022
  • Journal article
    Neethling SJ, Cilliers JJ, 2012,

    Grade-recovery curves: A new approach for analysis of and predicting from plant data

    , MINERALS ENGINEERING, Vol: 36-38, Pages: 105-110, ISSN: 0892-6875
  • Journal article
    Buchan A, Eaton MD, Goddard AJH, Pain CCet 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.
  • Journal article
    Xie Z, 2012,

    Numerical study of breaking waves by a two-phase flow model

    , International Journal for Numerical Methods in Fluids, Vol: 70, Pages: 246-268, ISSN: 0271-2091

    A two-phase flow model, which solves the flow in the air and water simultaneously, is presented for modelling breaking waves in deep and shallow water, including wave pre-breaking, overturning and post-breaking processes. The model is based on the Reynolds-averaged Navier-Stokes equations with the k -ε turbulence model. The governing equations are solved by the finite volume method in a Cartesian staggered grid and the partial cell treatment is implemented to deal with complex geometries. The SIMPLE algorithm is utilised for the pressure-velocity coupling and the air-water interface is modelled by the interface capturing method via a high resolution volume of fluid scheme. The numerical model is validated by simulating overturning waves on a sloping beach and over a reef, and deep-water breaking waves in a periodic domain, in which good agreement between numerical results and available experimental measurements for the water surface profiles during wave overturning is obtained. The overturning jet, air entrainment and splash-up during wave breaking have been captured by the two-phase flow model, which demonstrates the capability of the model to simulate free surface flow and wave breaking problems. © 2011 John Wiley & Sons, Ltd.
  • Journal article
    Solano JMS, Jackson MD, Sparks RSJ, Blundy JD, Annen Cet al., 2012,

    Melt Segregation in Deep Crustal Hot Zones: a Mechanism for Chemical Differentiation, Crustal Assimilation and the Formation of Evolved Magmas

    , Journal of Petrology, Vol: 53, Pages: 1999-2026, ISSN: 1460-2415

    Mantle-derived basaltic sills emplaced in the lower crust provide amechanism for the generation of evolved magmas in deep crustal hotzones (DCHZ).This study uses numerical modelling to characterizethe time required for evolved magma formation, the depth and temperatureat which magma formation occurs, and the composition ofthe magma.The lower crust is assumed to comprise amphibolite. Inan extension of previous DCHZ models, the new model couples heattransfer during the repetitive emplacement of sills with mass transfervia buoyancy-driven melt segregation along grain boundaries.The resultsshed light on the dynamics of DCHZ development and evolution.TheDCHZ comprises a mush of crystals plus interstitial melt,except when a new influx of basaltic magma yields a short-lived(20^200 years) reservoir of melt plus suspended crystals (magma).Melt segregation and accumulation within the mush yields two contrastingmodes of evolved magma formation, which operate over timescalesof c. 10 kyr-1 Myr, depending upon emplacement rate andstyle. In one, favoured by emplacement via over-accretion, or emplacementat high rates, evolved magma forms in the crust overlying theintruded basalt sills, and is composed of crustal partial melt, and residualmelt that has migrated upwards out of the crystallizingbasalt. In the other, favoured by emplacement via under- orintra-accretion, or by emplacement at lower rates, evolved magmaforms in the intruded basalt, and the resulting magma is composedprimarily of residual melt. In all cases, the upward migration ofbuoyant melt yields cooler and more evolved magmas, which arebroadly granitic in composition. Chemical differentiation is thereforedriven by melt migration, because the melt migrates through, andchemically equilibrates with, partially molten rock at progressivelylower temperatures. Crustal assimilation occurs during partial melting,and mixing of crustal and residual melt occurs when residualmelt migrates into the partially molten crust, yielding

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