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  • JOURNAL ARTICLE
    Buchan AG, Farrell PE, Gorman GJ, Goddard AJH, Eaton MD, Nygaard ET, Angelo PL, Smedley-Stevenson RP, Merton SR, Smith PN, Buchan AG, Farrell PE, Gorman GJ, Goddard AJH, Eaton MD, Nygaard ET, Angelo PL, Smedley-Stevenson RP, Merton SR, Smith PN, 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

    This article describes a new immersed body method for the efficient modelling of complex reactor physics problems. The approach is based on a projection method that maps geometric diagnostics of internal bodies onto practical computational meshes. It applies a recently developed supermeshing algorithm originally developed for data transfer problems to parameterise the effects of internal bodies on the reactor dynamics. This projects meshes of internal bodies onto a mesh that encompasses the entire problem domain. With this mapping, all necessary information about the intersection of an element with the internal body is known. This includes information about the volume, surface area and distances along the internal bodies; importantly, these quantities are always conserved. The appropriate material cross-sections for each element are then calculated from the volume information to account for all the internal bodies they contain. This in turn enables the problem to be solved efficiently on meshes that are practical to generate. The method is demonstrated on two eigenvalue problems where the domain contains fuel pins, cooling pipes, control rods and guide tubes. The first problem is used to demonstrate convergence when the mesh fully resolves the internal bodies and the geometric details of the problem are completely recovered. The second problem models the SUPO (Super POwer) solution reactor which contains many complex and detailed internal components. It is shown that the internal structures of the problem can be parameterised efficiently without the use of computationally expensive geometry-conforming meshes. © 2013 Elsevier Ltd. All rights reserved.

  • JOURNAL ARTICLE
    Williams DA, O'Brien DP, Schenk PM, Denevi BW, Carsenty U, Marchi S, Scully JEC, Jaumann R, De Sanctis MC, Palomba E, Ammannito E, Longobardo A, Magni G, Frigeri A, Russell CT, Raymond CA, Davison TM, Williams DA, O'Brien DP, Schenk PM, Denevi BW, Carsenty U, Marchi S, Scully JEC, Jaumann R, De Sanctis MC, Palomba E, Ammannito E, Longobardo A, Magni G, Frigeri A, Russell CT, Raymond CA, Davison TM, Williams DA, O'Brien DP, Schenk PM, Denevi BW, Carsenty U, Marchi S, Scully JEC, Jaumann R, De Sanctis MC, Palomba E, Ammannito E, Longobardo A, Magni G, Frigeri A, Russell CT, Raymond CA, Davison TM, Williams DA, O'Brien DP, Schenk PM, Denevi BW, Carsenty U, Marchi S, Scully JEC, Jaumann R, De Sanctis MC, Palomba E, Ammannito E, Longobardo A, Magni G, Frigeri A, Russell CT, Raymond CA, Davison TM, Williams DA, O'Brien DP, Schenk PM, Denevi BW, Carsenty U, Marchi S, Scully JEC, Jaumann R, De Sanctis MC, Palomba E, Ammannito E, Longobardo A, Magni G, Frigeri A, Russell CT, Raymond CA, Davison TM, Dawn Science Teamet al., 2014,

    Lobate and flow-like features on asteroid Vesta

    , Planetary and Space Science, Vol: 103, Pages: 24-35, ISSN: 0032-0633

    © 2013 Elsevier Ltd. All rights reserved. We studied high-resolution images of asteroid Vesta's surface (~70 and 20-25 m/pixel) obtained during the High- and Low-Altitude Mapping Orbits (HAMO, LAMO) of NASA's Dawn mission to assess the formation mechanisms responsible for a variety of lobate, flow-like features observed across the surface. We searched for evidence of volcanic flows, based on prior mathematical modeling and the well-known basaltic nature of Vesta's crust, but no unequivocal morphologic evidence of ancient volcanic activity has thus far been identified. Rather, we find that all lobate, flow-like features on Vesta appear to be related either to impact or erosional processes. Morphologically distinct lobate features occur in and around impact craters, and most of these are interpreted as impact ejecta flows, or possibly flows of impact melt. Estimates of melt production from numerical models and scaling laws suggests that large craters like Marcia (~60 km diameter) could have potentially produced impact melt volumes ranging from tens of millions of cubic meters to a few tens of cubic kilometers, which are relatively small volumes compared to similar-sized lunar craters, but which are consistent with putative impact melt features observed in Dawn images. There are also examples of lobate flows that trend downhill both inside and outside of crater rims and basin scarps, which are interpreted as the result of gravity-driven mass movements (slumps and landslides).

  • JOURNAL ARTICLE
    Baker CMJ, Buchan AG, Pain CC, Farrell PE, Eaton MD, Warner P, Baker CMJ, Buchan AG, Pain CC, Farrell PE, Eaton MD, Warner P, 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, ISSN: 0306-4549

    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
    Baker CMJ, Buchan AG, Pain CC, Tollit BS, Goffin MA, Merton SR, Warner P, Baker CMJ, Buchan AG, Pain CC, Tollit BS, Goffin MA, Merton SR, Warner P, 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
    Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJet al., 2013,

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

    , COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, Vol: 438, Pages: 21-27, ISSN: 0927-7757

    Forced foam drainage experiments, in which liquid is added at a constant rate at the top of the foam, are studied numerically. The aim of these experiments is to investigate the change in liquid fraction as the resulting drainage wave propagates through the system. A finite element implementation of the foam drainage equation is used to carry out two-dimensional simulations, taking advantage of mesh adaptivity techniques to accurately resolve the dynamics of the wetting front. First, the effects of changes in the liquid addition area at the top of a rectangular container are studied, showing that the variation of the position of the wave front exhibits a power law with time not only for the vertical displacement but also for the horizontal propagation. Then, for uniform addition scenarios, the effect of changes in the geometry of the container are analysed, finding that a power law also describes well the position of the different regions of the drainage wave with time. © 2013 Elsevier B.V.

  • JOURNAL ARTICLE
    Buchan AG, Pain CC, Fang F, Navon IM, 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
    Buchan AG, Pain CC, Tollit BS, Gomes JLMA, Eaton MD, Gorman GJ, Cooling CM, Goddard AJH, Nygaard ET, Angelo PL, Smith PN, Buchan AG, Pain CC, Tollit BS, Gomes JLMA, Eaton MD, Gorman GJ, Cooling CM, Goddard AJH, Nygaard ET, Angelo PL, Smith PN, Buchan AG, Pain CC, Tollit BS, Gomes JLMA, Eaton MD, Gorman GJ, Cooling CM, Goddard AJH, Nygaard ET, Angelo PL, Smith PN, 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, ISSN: 0149-1970

    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 × 10 18 fissions of which the first fission spike contributed 6 × 10 16 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. © 2012 Elsevier Ltd. All rights reserved.

  • JOURNAL ARTICLE
    Davison TM, O'Brien DP, Ciesla FJ, Collins GS, Davison TM, O'Brien DP, Ciesla FJ, Collins GS, Davison TM, O'Brien DP, Ciesla FJ, Collins GS, Davison TM, Ciesla FJ, Collins GS, O'Brien DP, Davison TM, O'Brien DP, Ciesla FJ, Collins GS, Davison TM, O'Brien DP, Ciesla FJ, Collins GSet al., 2013,

    The early impact histories of meteorite parent bodies

    , Meteoritics and Planetary Science, Vol: 48, Pages: 1894-1918, ISSN: 1086-9379

    We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces — compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 -- 5\% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75\% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.

  • JOURNAL ARTICLE
    Du J, Fang F, Pain CC, Navon IM, Zhu J, Ham DA, Du J, Fang F, Pain CC, Navon IM, Zhu J, Ham DA, Du J, Fang F, Pain CC, Navon IM, Zhu J, Ham DA, Du J, Fang F, Pain CC, Navon IM, Zhu J, Ham DAet al., 2013,

    POD reduced-order unstructured mesh modeling applied to 2D and 3D fluid flow

    , COMPUTERS & MATHEMATICS WITH APPLICATIONS, Vol: 65, Pages: 362-379, ISSN: 0898-1221

    A new scheme for implementing a reduced order model for complex mesh-based numerical models (e.g. finite element unstructured mesh models), is presented. The matrix and source term vector of the full model are projected onto the reduced bases. The proper orthogonal decomposition (POD) is used to form the reduced bases. The reduced order modeling code is simple to implement even with complex governing equations, discretization methods and nonlinear parameterizations. Importantly, the model order reduction code is independent of the implementation details of the full model code. For nonlinear problems, a perturbation approach is used to help accelerate the matrix equation assembly process based on the assumption that the discretized system of equations has a polynomial representation and can thus be created by a summation of pre-formed matrices. In this paper, by applying the new approach, the POD reduced order model is implemented on an unstructured mesh finite element fluid flow model, and is applied to 3D flows. The error between the full order finite element solution and the reduced order model POD solution is estimated. The feasibility and accuracy of the reduced order model applied to 3D fluid flows are demonstrated. © 2012 Elsevier Ltd. All rights reserved.

  • JOURNAL ARTICLE
    Du J, Navon IM, Zhu J, Fang F, Alekseev AK, 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
    ELSheikh AH, Pain CC, Fang F, Gomes JLMA, Navon IM, 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
    Fang F, Pain CC, Navon IM, Cacuci DG, Chen X, Fang F, Pain CC, Navon IM, Cacuci DG, Chen X, 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
    Fang F, Pain CC, Navon IM, Elsheikh AH, Du J, Xiao D, 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
  • JOURNAL ARTICLE
    Goffin MA, Baker CMJ, Buchan AG, Pain CC, Eaton MD, Smith PN, 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: 726-752, ISSN: 0021-9991
  • JOURNAL ARTICLE
    Hassan MHA, Johnson HD, Allison PA, Abdullah WH, Amir Hassan MH, Johnson HD, Allison PA, Abdullah WH, Hassan MHA, Johnson HD, Allison PA, Abdullah WHet al., 2013,

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

    , JOURNAL OF ASIAN EARTH SCIENCES, Vol: 76, Pages: 301-311, ISSN: 1367-9120
  • JOURNAL ARTICLE
    Ilankoon IMSK, Cole KE, Neethling SJ, Ilankoon IMSK, Cole KE, Neethling SJ, Ilankoon IMSK, Cole KE, Neethling SJet al., 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

    Hydrodynamic dispersion has a major impact on mass transport within packed bed and porous media systems. In this paper, dispersion coefficients of neutrally buoyant tracer particles located with positron emission particle tracking (PEPT) are compared to results obtained using a conventional salt tracer experiment. It is demonstrated that the axial dispersion coefficients obtained from PEPT are very similar to those obtained using the salt tracer. The PEPT method has the advantage that the details of the flow behaviour can be observed, thus allowing analysis of the mechanisms at work to be carried out. In addition, the radial dispersion coefficient was obtained with PEPT, which is hard to obtain using conventional salt tracer tests. The main drawback with the PEPT method is that very low flow rates could not be studied as these result in very low saturations, which causes the tracer particle to become stuck. In this work the tracer particles used are 400μm in diameter, though as the tracer fabrication technology improves, the size of tracer available will continue to decrease, allowing a wider range of conditions and particle beds to be studied. © 2012 Elsevier Ltd.

  • JOURNAL ARTICLE
    Jacobs CT, Collins GS, Piggott MD, Kramer SC, Wilson CRG, Jacobs CT, Collins GS, Piggott MD, Kramer SC, Wilson CRG, Jacobs CT, Collins GS, Piggott MD, Kramer SC, Wilson CRG, Jacobs CT, Collins GS, Piggott MD, Kramer SC, Wilson CRGet al., 2013,

    Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes

    , GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 192, Pages: 647-665, ISSN: 0956-540X

    Small-scale experiments of volcanic ash particle settling in water have demonstrated thatash 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 anadaptive 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 theturbulent flow regime, which has a significant impact on entrainment and settling rates. Meshadaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlightingthe benefits of an adaptive u

  • JOURNAL ARTICLE
    Kimura S, Candy AS, Holland PR, Piggott MD, Jenkins A, Kimura S, Candy AS, Holland PR, Piggott MD, Jenkins A, Kimura S, Candy AS, Holland PR, Piggott MD, Jenkins A, Kimura S, Candy AS, Holland PR, Piggott MD, Jenkins Aet 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

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification. © 2013 Elsevier Ltd.

  • JOURNAL ARTICLE
    Lamb AR, Gorman GJ, Elsworth D, Lamb AR, Gorman GJ, Elsworth D, Lamb AR, Gorman GJ, Elsworth D, Lamb AR, Gorman GJ, Elsworth Det al., 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

    This paper presents a fracture mapping (FM) approach combined with the extended finite element method (XFEM) to simulate coupled deformation and fluid flow in fractured porous media. Specifically, the method accurately represents the impact of discrete fractures on flow and deformation, although the individual fractures are not part of the finite element mesh. A key feature of FM-XFEM is its ability to model discontinuities in the domain independently of the computational mesh. The proposed FM approach is a continuum-based approach that is used to model the flow interaction between the porous matrix and existing fractures via a transfer function. Fracture geometry is defined using the level set method. Therefore, in contrast to the discrete fracture flow model, the fracture representation is not meshed along with the computational domain. Consequently, the method is able to determine the influence of fractures on fluid flow within a fractured domain without the complexity of meshing the fractures within the domain. The XFEM component of the scheme addresses the discontinuous displacement field within elements that are intersected by existing fractures. In XFEM, enrichment functions are added to the standard finite element approximation to adequately resolve discontinuous fields within the simulation domain. Numerical tests illustrate the ability of the method to adequately describe the displacement and fluid pressure fields within a fractured domain at significantly less computational expense than explicitly resolving the fracture within the finite element mesh. © 2013 John Wiley & Sons, Ltd.

  • CONFERENCE PAPER
    Lange M, Gorman G, Weiland M, Mitchell L, Southern J, Lange M, Gorman G, Weiland M, Mitchell L, Southern J, Lange M, Gorman G, Weiland M, Mitchell L, Southern J, Lange M, Gorman G, Weiland M, Mitchell L, Southern Jet al., 2013,

    Achieving efficient strong scaling with PETSc using hybrid MPI/OpenMP optimisation

    , Publisher: Springer Berlin Heidelberg, Pages: 97-108, ISSN: 0302-9743

    The increasing number of processing elements and decreasing memory to core ratio in modern high-performance platforms makes efficient strong scaling a key requirement for numerical algorithms. In order to achieve efficient scalability on massively parallel systems scientific software must evolve across the entire stack to exploit the multiple levels of parallelism exposed in modern architectures. In this paper we demonstrate the use of hybrid MPI/OpenMP parallelisation to optimise parallel sparse matrix-vector multiplication in PETSc, a widely used scientific library for the scalable solution of partial differential equations. Using large matrices generated by Fluidity, an open source CFD application code which uses PETSc as its linear solver engine, we evaluate the effect of explicit communication overlap using task-based parallelism and show how to further improve performance by explicitly load balancing threads within MPI processes. We demonstrate a significant speedup over the pure-MPI mode and efficient strong scaling of sparse matrix-vector multiplication on Fujitsu PRIMEHPC FX10 and Cray XE6 systems. © 2013 Springer-Verlag.

  • JOURNAL ARTICLE
    Latham J-P, Anastasaki E, Xiang J, Latham J-P, Anastasaki E, Xiang J, Latham J-P, Anastasaki E, Xiang Jet al., 2013,

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

    , COASTAL ENGINEERING, Vol: 77, Pages: 151-166, ISSN: 0378-3839

    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

  • CONFERENCE PAPER
    Latham J-P, Xiang J, Baird B, Latham J-P, Xiang Jet al., 2013,

    A NUMERICAL INVESTIGATION OF THE INFLUENCE OF FRICTION AND VIBRATION ON LABORATORY SCALE ARMOUR UNIT LAYERS

    , 6th International Conference on Coastal Structures, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 849-860
  • JOURNAL ARTICLE
    Latham J-P, Xiang J, Belayneh M, Nick HM, Tsang C-F, Blunt MJ, Latham J-P, Xiang J, Belayneh M, Nick HM, Tsang C-F, Blunt MJ, Latham JP, Xiang J, Belayneh M, Nick HM, Tsang C, Blunt MJet al., 2013,

    Modelling stress-dependent permeability in fractured rock including effects of propagating and bending fractures

    , INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, Vol: 57, Pages: 100-112, ISSN: 1365-1609
  • JOURNAL ARTICLE
    Legler B, Johnson HD, Hampson GJ, Massart BYG, Jackson CA-L, Jackson MD, El-Barkooky A, Ravnas R, Legler B, Johnson HD, Hampson GJ, Massart BYG, Jackson CAL, Jackson MD, El-Barkooky A, Ravnas R, Legler B, Johnson HD, Hampson GJ, Massart BYG, Jackson CA-L, Jackson MD, El-Barkooky A, Ravnas R, Legler B, Johnson HD, Hampson GJ, Massart BYG, Jackson CAL, 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

    Existing facies models of tide-dominated deltas largely omit fine-grained, mud-rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well-preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non-channelized tidal bars and tidal channels. Non-channelized tidal bars comprise coarsening-upward sandbodies, including large, downcurrent-dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single-storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward-facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically-accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along-strike variability defines a similar large-scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence-set top, and flanked by stacked, non-channelized tidal bars and smaller channelized bodies. The tide-dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net-progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary ch

  • CONFERENCE PAPER
    Markall GR, Rathgeber F, Mitchell L, Loriant N, Bertolli C, Ham DA, Kelly PHJ, 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. © 2013 Springer-Verlag.

  • JOURNAL ARTICLE
    Merton SR, Buchan AG, Pain CC, Smedley-Stevenson RP, 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
    Miljkovic K, Collins GS, Mannick S, Bland PA, Miljković K, Collins GS, Mannick S, Bland PA, Miljković K, Collins GS, Mannick S, Bland PA, Miljković K, Collins GS, Mannick S, Bland PAet al., 2013,

    Morphology and population of binary asteroid impact craters

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 363, Pages: 121-132, ISSN: 0012-821X

    Observational data show that in the Near Earth Asteroid (NEA) region 15% of asteroids are binary. However, the observed number of plausible doublet craters is 2-4% on Earth and 2-3% on Mars. This discrepancy between the percentage of binary asteroids and doublets on Earth and Mars may imply that not all binary systems form a clearly distinguishable doublet crater owing to insufficient separation between the binary components at the point of impact. We simulate the crater morphology formed in close binary asteroid impacts in a planetary environment and the range of possible crater morphologies includes: single (circular or elliptical) craters, overlapping (tear-drop or peanut shaped) craters, as well as clearly distinct, doublet craters. While the majority of binary asteroids impacting Earth or Mars should form a single, circular crater, about one in four are expected to form elongated or overlapping impact craters and one in six are expected to be doublets. This implies that doublets are formed in approximately 2% of all asteroid impacts on Earth and that elongated or overlapping binary impact craters are under-represented in the terrestrial crater record. The classification of a complete range of binary asteroid impact crater structures provides a template for binary asteroid impact crater morphologies, which can help in identifying planetary surface features observed by remote sensing. © 2013 Elsevier B.V.

  • CONFERENCE PAPER
    Milthaler FFM, Pavlidis D, Xiang J, Latham J-P, Pain CC, Vire A, Piggott MD, Farrell PE, Milthaler F, Xiang J, Pavlidis D, Latham J-P, Pain CC, Vire A, Piggott MDet al., 2013,

    THE IMMERSED BODY METHOD COMBINED WITH MESH ADAPTIVITY FOR FLUID-SOLID COUPLING

    , 6th International Conference on Coastal Structures, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 277-283
  • JOURNAL ARTICLE
    Oishi Y, Piggott MD, Maeda T, Kramer SC, Collins GS, Tsushima H, Furumura T, Oishi Y, Piggott MD, Maeda T, Kramer SC, Collins GS, Tsushima H, Furumura T, Oishi Y, Piggott MD, Maeda T, Kramer SC, Collins GS, Tsushima H, Furumura T, Oishi Y, Piggott MD, Maeda T, Kramer SC, Collins GS, Tsushima H, Furumura Tet 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

    Large-scale tsunami propagation simulations from the fault region to the coast are conducted using a three-dimensional (3-D) parallel unstructured mesh finite element code (Fluidity-ICOM). Unlike conventional 2-D approximation models, our tsunami model solves the full 3-D incompressible Navier-Stokes (NS) equations. The model is tested against analytical solutions to simple dispersive wave propagation problems. Comparisons of our 3-D NS model results with those from linear shallow water and linear dispersive wave models demonstrate that the 3-D NS model simulates the dispersion of very short wavelength components more accurately than the 2-D models. This improved accuracy is achieved using only a small number (three to five) of vertical layers in the mesh. The numerical error in the wave velocity compared with the linear wave theory is less than 3% up to kH = 40, where k is the wave number and H is the sea depth. The same 2-D and 3-D models are also used to simulate two earthquake-generated tsunamis off the coast of Japan: the 2004 off Kii peninsula and the 2011 off Tohoku tsunamis. The linear dispersive and NS models showed good agreement in the leading waves but differed especially in their near-source, short wavelength dispersive wave components. This is consistent with the results from earlier tests, suggesting that the 3-D NS simulations are more accurate. The computational performance on a parallel computer showed good scalability up to 512 cores. By using a combination of unstructured meshes and high-performance computers, highly accurate 3-D tsunami simulations can be conducted in a practical timescale. Key Points describe a highly accurate 3-D model of near-field tsunami propagation. We demonstrate advantages of the present 3-D model over conventional 2-D models. We apply the model to the 2011 Tohoku tsunami and compare with observations. ©2013. American Geophysical Union. All Rights Reserved.

  • BOOK CHAPTER
    Piggott MD, Pain CC, Gorman GJ, Marshall DP, Killworth PD, Piggott MD, Pain CC, Gorman GJ, Piggott MD, Pain CC, Gorman GJ, Marshall DP, Killworth PDet al., 2013,

    Unstructured Adaptive Meshes for Ocean Modeling

    , Ocean Modeling in an Eddying Regime, Editors: Hecht, Hasumi, Hecht, Hasumi, Publisher: Amer Geophysical Union, Pages: 383-408, ISBN: 9781118666432

    © 2008 by the American Geophysical Union. This article presents an overview of unstructured and adaptive mesh methods for numerical ocean modeling. These methods are able to simultaneously resolve coupled dynamics at both the small and large scale, while smoothly varying resolution and conforming to complex geometries. The finite element method is the favored discretization method to be used with unstructured meshes here; other options include the finite volume and spectral element methods, but are not covered in the interest of brevity. Many of the techniques employed derive from the computational fluid dynamics literature, but there exist significant challenges when applying them to the oceanographic regime. Some of the topics discussed include: unstructured mesh generation and data structures; background to the finite element method including weak forms of the underlying equations and assembly procedures; error measures and anisotropy; and the stability of finite element discretizations, especially for advection dominated flows and in the context of balance in strongly stratified rapidly rotating regimes. Numerical examples conducted with a three-dimensional nonhydrostatic adaptive unstructured mesh ocean model are also presented.

  • JOURNAL ARTICLE
    Piotrowski M, McGilvary GA, Sloan TM, Mewissen M, Lloyd AD, Forster T, Mitchell L, Ghazal P, Hill J, Piotrowski M, McGilvary GA, Sloan TM, Mewissen M, Lloyd AD, Forster T, Mitchell L, Ghazal P, Hill J, Piotrowski M, McGilvary GA, Sloan TM, Mewissen M, Lloyd AD, Forster T, Mitchell L, Ghazal P, Hill J, Piotrowski M, McGilvary GA, Sloan TM, Mewissen M, Lloyd AD, Forster T, Mitchell L, Ghazal P, Hill J, Piotrowski M, McGilvary GA, Sloan TM, Mewissen M, Lloyd AD, Forster T, Mitchell L, Ghazal P, Hill J, Piotrowski M, McGilvary G, Sloan T, Mewissen M, Lloyd A, Forster T, Mitchell L, Ghazal P, Hill Jet al., 2013,

    Exploiting Parallel R in the Cloud with SPRINT

    , METHODS OF INFORMATION IN MEDICINE, Vol: 52, Pages: 80-90, ISSN: 0026-1270

    BACKGROUND: Advances in DNA Microarray devices and next-generation massively parallel DNA sequencing platforms have led to an exponential growth in data availability but the arising opportunities require adequate computing resources. High Performance Computing (HPC) in the Cloud offers an affordable way of meeting this need. OBJECTIVES: Bioconductor, a popular tool for high-throughput genomic data analysis, is distributed as add-on modules for the R statistical programming language but R has no native capabilities for exploiting multi-processor architectures. SPRINT is an R package that enables easy access to HPC for genomics researchers. This paper investigates: setting up and running SPRINT-enabled genomic analyses on Amazon's Elastic Compute Cloud (EC2), the advantages of submitting applications to EC2 from different parts of the world and, if resource underutilization can improve application performance. METHODS: The SPRINT parallel implementations of correlation, permutation testing, partitioning around medoids and the multi-purpose papply have been benchmarked on data sets of various size on Amazon EC2. Jobs have been submitted from both the UK and Thailand to investigate monetary differences. RESULTS: It is possible to obtain good, scalable performance but the level of improvement is dependent upon the nature of the algorithm. Resource underutilization can further improve the time to result. End-user's location impacts on costs due to factors such as local taxation. CONCLUSIONS: Although not designed to satisfy HPC requirements, Amazon EC2 and cloud computing in general provides an interesting alternative and provides new possibilities for smaller organisations with limited funds.

  • JOURNAL ARTICLE
    Potter RWK, Collins GS, Potter RWK, Collins GS, Potter RWK, Collins GS, Potter RWK, Collins GSet al., 2013,

    Numerical modeling of asteroid survivability and possible scenarios for the Morokweng crater-forming impact

    , METEORITICS & PLANETARY SCIENCE, Vol: 48, Pages: 744-757, ISSN: 1086-9379

    The fate of the impactor is an important aspect of the impact-cratering process. Defining impactor material as surviving if it remains solid (i.e., does not melt or vaporize) during crater formation, previous numerical modeling and experiments have shown that survivability decreases with increasing impact velocity, impact angle (with respect to the horizontal), and target density. Here, we show that in addition to these, impactor survivability depends on the porosity and shape of the impactor. Increasing impactor porosity decreases impactor survivability, while prolate-shaped (polar axis > equatorial axis) impactors survive impact more so than spherical and oblate-shaped (polar axis < equatorial axis) impactors. These results are used to produce a relatively simple equation, which can be used to estimate the impactor fraction shocked to a given pressure as a function of these parameters. By applying our findings to the Morokweng crater-forming impact, we suggest impact scenarios that explain the high meteoritic content and presence of unmolten fossil meteorites within the Morokweng crater. In addition to previous suggestions of a low-velocity and/or high-angled impact, this work suggests that an elongated and/or low porosity impactor may also help explain the anomalously high survivability of the Morokweng impactor. © The Meteoritical Society, 2013.

  • JOURNAL ARTICLE
    Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJ, Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJ, Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJ, Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJet al., 2013,

    Numerical modeling of the formation and structure of the Orientale impact basin

    , JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 118, Pages: 963-979, ISSN: 2169-9097

    The Orientale impact basin is the youngest and best-preserved lunar multi-ring basin and has, thus, been the focus of studies investigating basin-forming processes and final structures. A consensus about how multi-ring basins form, however, remains elusive. Here we numerically model the Orientale basin-forming impact with the aim of resolving some of the uncertainties associated with this basin. By using two thermal profiles estimating lunar conditions at the time of Orientale's formation and constraining the numerical models with crustal structures inferred from gravity data, we provide estimates for Orientale's impact energy (2-9 × 10 25 J), impactor size (50-80 km diameter), transient crater size (∼320-480 km), excavation depth (40-55 km), and impact melt volume (∼10 6 km 3 ). We also analyze the distribution and deformation of target material and compare our model results and Orientale observations with the Chicxulub crater to investigate similarities between these two impact structures. Key PointsNumerical models of the Orientale basin-forming impact undertakenOrientale basin attributes, including impact energy and melt volume, estimatedModel results and Orientale observations are compared with the Chicxulub crater ©2013. American Geophysical Union. All Rights Reserved.

  • 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, Štekl I, Guasch L, Win C, Conroy G, Bertrand A, Warner M, Ratcliffe A, Nangoo T, Morgan J, Umpleby A, Shah N, Vinje V, Štekl I, Guasch L, Win C, Conroy G, Bertrand A, 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, ISSN: 0016-8033

    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 moreintense 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. © 2013 Society of Exploration Geophysicists.

  • CONFERENCE PAPER
    Xiang J, Latham J-P, Zimmer D, Baird B, Fons M, Xiang J, Latham J-P, Zimmer D, Baird WFet al., 2013,

    MODELLING BREAKWATER ARMOUR LAYERS AND THE DYNAMIC RESPONSE OF ARMOUR UNITS

    , 6th International Conference on Coastal Structures, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 318-329
  • JOURNAL ARTICLE
    Xiao D, Fang F, Du J, Pain CC, Navon IM, Buchan AG, ElSheikh AH, Hu G, Xiao D, Fang F, Du J, Pain CC, Navon IM, Buchan AG, ElSheikh AH, Hu G, 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
    Baker CMJ, Buchan AG, Pain CC, Tollit B, Eaton MD, Warner P, Baker CMJ, Buchan AG, Pain CC, Tollit B, Eaton MD, Warner P, Baker CMJ, Buchan AG, Pain CC, Tollit B, Eaton MD, Warner Pet al., 2012,

    Quadratic inner element subgrid scale discretisation of the Boltzmann transport equation

    , ANNALS OF NUCLEAR ENERGY, Vol: 45, Pages: 124-137, ISSN: 0306-4549

    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.

  • CONFERENCE PAPER
    Barker DJ, Neethling SJ, Parameswaran G, 2012,

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

    , CFD 2012
  • JOURNAL ARTICLE
    Bray VJ, Schenk PM, Melosh HJ, Morgan JV, Collins GS, Bray VJ, Schenk PM, Jay Melosh H, Morgan JV, Collins GS, Bray VJ, Schenk PM, Jay Melosh H, Morgan JV, Collins GS, Bray VJ, Schenk PM, Melosh HJ, Morgan JV, Collins GSet al., 2012,

    Ganymede crater dimensions - Implications for central peak and central pit formation and development

    , ICARUS, Vol: 217, Pages: 115-129, ISSN: 0019-1035

    The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures. © 2011 Elsevier Inc.

  • JOURNAL ARTICLE
    Brito-Parada PR, Cilliers JJ, Brito-Parada PR, Cilliers JJ, Brito-Parada PR, Cilliers JJ, Brito-Parada PR, Cilliers JJet al., 2012,

    Experimental and numerical studies of launder configurations in a two-phase flotation system

    , MINERALS ENGINEERING, Vol: 36-38, Pages: 119-125, ISSN: 0892-6875

    Studying the effect that different tank configurations have on operating variables in a flotation system is of interest in order to better understand the phenomena taking place in the froth phase. In this work a laboratory scale flotation tank was used to carry out experiments for different launder layouts using a two-phase system that resembles a flotation froth. Stagnant foam zones were observed during the experiments and were linked to specific tank configurations. In addition, recently developed three-dimensional, Computational Fluid Dynamics (CFD) models for the gas and liquid in flotation froths have allowed modelling the behaviour of these phases on non-symmetric tanks. These models are relevant to the study of flotation cells in which the configuration of the overflowing lips or the geometry of the tank result in a flow that cannot be represented in two dimensions due to the lack of symmetry. Simulations were performed for the different launder layouts making use of experimental data, reproducing some of the observed phenomena and making it possible to study aspects of the process that are difficult, if not impossible, to be analysed by other means. It is shown that the configuration of the overflows in the cell has an impact on air recovery and liquid overflow rate, and thus important implications for flotation cell design. © 2012 Elsevier Ltd. All rights reserved.

  • JOURNAL ARTICLE
    Brito-Parada PR, Kramer SC, Wilson CR, Pain CC, Neethling SJ, Cilliers JJ, Brito-Parada PR, Kramer SC, Wilson CR, Pain CC, Neethling SJ, Cilliers JJ, Brito-Parada PR, Kramer SC, Wilson CR, Pain CC, Neethling SJ, Cilliers JJ, Brito-Parada PR, Kramer SC, Wilson CR, Pain CC, Neethling SJ, Cilliers JJet al., 2012,

    A finite element formulation to model the flow of flotation foams

    , CHEMICAL ENGINEERING SCIENCE, Vol: 69, Pages: 279-286, ISSN: 0009-2509

    In this paper, a numerical model for the flow of foams in flotation cells in up to three dimensions is described. By using finite elements to solve Laplace's equation for a potential scalar, the flow pattern and velocity of the foam can be obtained. This has allowed, for the first time, the carrying out of numerical investigations of foam flow patterns regardless of the symmetry of the system. The numerical model has been implemented in Fluidity, a general purpose finite element method code that allows simulations to be carried out on anisotropic unstructured meshes. Such a model is of particular interest since other phenomena occurring in flotation depend on the foam velocity. Convergence tests that verify the numerical model are presented, and simulation results that showcase important features of the present implementation are discussed. © 2011 Elsevier Ltd.

  • JOURNAL ARTICLE
    Brito-Parada PR, Neethling SJ, Cilliers JJ, 2012,

    CFD study of liquid drainage in flotation foams

    , Computer Aided Chemical Engineering
  • CONFERENCE PAPER
    Brito-Parada PR, Neethling SJ, Cilliers JJ, 2012,

    Forced drainage simulations in 2D and 3D foams

    , 9th European Conference on Foams and Emulsions
  • CONFERENCE PAPER
    Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJet al., 2012,

    CFD study of liquid drainage in flotation foams

    , 22nd European Symposium on Computer Aided Process Engineering (ESCAPE), Publisher: ELSEVIER SCIENCE BV, Pages: 1143-1147, ISSN: 1570-7946

    Froth flotation is a separation process used in a number of applications worldwide. Recycled paper deinking, water purification, bitumen recovery from oil sands and, in particular, mineral separation, benefit from this industrial operation. The complex phenomena occurring within the froth phase of a flotation cell, however, are not entirely understood. The flow patterns of the froth, the drainage of liquid within the system and the behaviour of solid particles, represent a challenge for both experimental and numerical studies.State of the art Computational Fluid Dynamics (CFD) techniques can be used to assess the performance of flotation tanks in order to achieve better equipment design and enhanced operations. This work makes use of mathematical models for foam flow and liquid drainage in two-phase foams implemented in Fluidity, a finite element code which incorporates anisotropic adaptive remeshing. Adaptivity is an important feature for improving the computational cost of modelling these systems, as there are boundary layers present in the process whose size is independent of the scale of the flotation tank being modelled.Potential flow theory, previously shown to adequately represent the flow of froths in flotation tanks, has been used to obtain the velocity and trajectory of the foam, whilst the equations for liquid drainage in foams have been extended to consider transient simulations in up to three dimensions. In addition, the flexibility offered by the Finite Element Method in terms of the selection of the element types has been exploited, and mixed elements are employed to accurately represent the fields of interest.This work presents results from numerical investigations of a large laboratory scale flotation tank and discusses important aspects of the model that make it suitable for studying industrial processes involving the drainage of liquid through flowing foams. © 2012 Elsevier B.V.

  • JOURNAL ARTICLE
    Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJ, Brito-Parada PR, Neethling SJ, Cilliers JJet al., 2012,

    The advantages of using mesh adaptivity when modelling the drainage of liquid in froths

    , MINERALS ENGINEERING, Vol: 33, Pages: 80-86, ISSN: 0892-6875

    A key factor in most computational fluid dynamics (CFD) techniques is the grid that contains the representation and connectivity of the elements into which the domain has been subdivided. Unstructured anisotropic meshes present benefits due to the fact that they are more easily adapted and allow higher resolution to be focused only where it is required, so the mesh can be optimised to adequately resolve local features occurring during the solution of the physical problem. This paper examines how transient simulations of the drainage of liquid in flotation froths can be benefited from using adaptive remeshing. Fluidity, a general purpose finite element method code capable of using anisotropic mesh adaptivity, is used to accurately resolve the boundary layers present at the liquid-foam interface as well as other strong gradients that can develop during the drainage process. © 2011 Elsevier Ltd. All rights reserved.

  • JOURNAL ARTICLE
    Buchan AG, Pain CC, Goddard AJH, Eaton MD, Gomes JLMA, Gorman GJ, Cooling CM, Tollit BS, Nygaard ET, Glenn DE, Angelo PL, Buchan AG, Pain CC, Goddard AJH, Eaton MD, Gomes JLMA, Gorman GJ, Cooling CM, Tollit BS, Nygaard ET, Glenn DE, Angelo PL, Buchan AG, Pain CC, Goddard AJH, Eaton MD, Gomes JLMA, Gorman GJ, Cooling CM, Tollit BS, Nygaard ET, Glenn DE, Angelo PL, 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, ISSN: 0306-4549

    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. &cop

  • JOURNAL ARTICLE
    Buchan AG, Pain CC, Umpleby AP, Smedley-Stevenson RP, Buchan AG, Pain CC, Umpleby AP, Smedley-Stevenson RP, 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

    This article describes a new element agglomeration multigrid method for solving partial differential equations discretised through a sub-grid scale finite element formulation. The sub-grid scale discretisation resolves solution variables through their separate coarse and fine scales, and these are mapped between the multigrid levels using a dual set of transfer operators. The sub-grid scale multigrid method forms coarse linear systems, possessing the same sub-grid scale structure as the original discretisation, that can be resolved without them being stored in memory. This is necessary for the application of this article in resolving the Boltzmann transport equation as the linear systems become extremely large. The novelty of this article is therefore a matrix-free multigrid scheme that is integrated within its own sub-grid scale discretisation using dual transfer operators and applied to the Boltzmann transport equation. The numerical examples presented are designed to show the method's preconditioning capabilities for a Krylov space-based solver. The problems range in difficulty, geometry and discretisation type, and comparisons made with established methods show this new approach to perform consistently well. Smoothing operators are also analysed and this includes using the generalized minimal residual method. Here, it is shown that an adaptation to the preconditioned Krylov space is necessary for it to work efficiently. © 2012 John Wiley & Sons, Ltd.

  • JOURNAL ARTICLE
    Cole KE, Brito-Parada PR, Xu C, Neethling SJ, Cilliers JJ, Cole KE, Brito-Parada PR, Xu C, Neethling SJ, Cilliers JJ, Cole KE, Brito-Parada PR, Xu C, Neethling SJ, Cilliers JJ, Cole KE, Brito-Parada PR, Xu C, Neethling SJ, Cilliers JJet al., 2012,

    Experimental studies and numerical model validation of overflowing 2D foam to test flotation cell crowder designs

    , CHEMICAL ENGINEERING RESEARCH & DESIGN, Vol: 90, Pages: 2196-2201, ISSN: 0263-8762

    A computational fluid dynamics model of froth motion has been developed to assess different flotation cell designs. This work presents an implementation of the model in a 2D case, to compare the simulated bubble velocity distribution and streamlines to an experimental foaming system. The model uses finite elements to solve Laplace's equation for a potential function from which the foam velocity can be obtained. It requires the air recovery, or the amount of air that overflows a flotation cell as unburst bubbles, as an input parameter to calculate the foam velocity distribution and bubble streamlines. The air recovery was obtained by image analysis from a vertical, overflowing monolayer of foam (2D) created in a Hele-Shaw column, which mimicked important flowing properties of flotation froths such as coalescence. Inserts were included in the foam column to represent potential crowder designs for industrial flotation cells. Three different designs were chosen to compare the effect of insert depth and shape, including rectangles and a triangle. The effect of the insert design on the overflowing foam is obvious from visual assessment of the bubble streamlines and velocity distribution, which were closely agreed by both the experiment and model. © 2012 The Institution of Chemical Engineers.

  • JOURNAL ARTICLE
    Collins GS, Collins GS, Collins GS, Collins GS, Collins GS, Collins GSet al., 2012,

    Moonstruck Magnetism

    , SCIENCE, Vol: 335, Pages: 1176-1177, ISSN: 0036-8075

    Do magnetic anomalies on the Moon indicate the remains of a giant asteroid impact?

  • JOURNAL ARTICLE
    Collins GS, Melosh HJ, Osinski GR, Collins GS, Melosh HJ, Osinski GR, Collins GS, Melosh HJ, Osinski GRet al., 2012,

    The Impact-Cratering Process

    , ELEMENTS, Vol: 8, Pages: 25-30, ISSN: 1811-5209

    Impact cratering is an important and unique geologic process. The high speeds, forces and temperatures involved are quite unlike conventional endogenic processes, and the environmental consequences can be catastrophic. Kilometre-scale craters are excavated and collapse in minutes, in some cases distributing debris around the globe and exhuming deeply buried strata. In the process, rocks are deformed, broken, heated and transformed in unique ways. Elevated temperatures in the crust may persist for millennia, and important chemical reactions are promoted by the extreme environment of the impact plume. Released gases may cause long-term perturbations to the climate, and impact-related phosphorus reduction may have played a role in the origin of life on Earth.

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