Publications
79 results found
Cantwell CD, Moxey D, Comerford A, et al., 2015, Nektar++: an open-source spectral/hp element framework, Computer Physics Communications, Vol: 192, Pages: 205-219, ISSN: 0010-4655
Nektar++ is an open-source software framework designed to support the development of high-performance scalable solvers for partial differential equations using the spectral/hphp element method. High-order methods are gaining prominence in several engineering and biomedical applications due to their improved accuracy over low-order techniques at reduced computational cost for a given number of degrees of freedom. However, their proliferation is often limited by their complexity, which makes these methods challenging to implement and use. Nektar++ is an initiative to overcome this limitation by encapsulating the mathematical complexities of the underlying method within an efficient C++ framework, making the techniques more accessible to the broader scientific and industrial communities. The software supports a variety of discretisation techniques and implementation strategies, supporting methods research as well as application-focused computation, and the multi-layered structure of the framework allows the user to embrace as much or as little of the complexity as they need. The libraries capture the mathematical constructs of spectral/hphp element methods, while the associated collection of pre-written PDE solvers provides out-of-the-box application-level functionality and a template for users who wish to develop solutions for addressing questions in their own scientific domains.
Claus S, Cantwell C, Phillips T, 2015, Spectral/hp element methods for plane Newtonian extrudate swell, Computers & Fluids, Vol: 116, Pages: 105-117, ISSN: 0045-7930
Spectral/hp element methods and an arbitrary Lagrangian–Eulerian (ALE) moving-boundary technique are used to investigate planar Newtonian extrudate swell. Newtonian extrudate swell arises when viscous liquids exit long die slits. The problem is characterised by a stress singularity at the end of the slit which is inherently difficult to capture and strongly influences the predicted swelling of the fluid. The impact of inertia (0⩽Re⩽100) and slip along the die wall on the free surface profile and the velocity and pressure values in the domain and around the singularity are investigated. The high order method is shown to provide high resolution of the steep pressure profile at the singularity. The swelling ratio and exit pressure loss are compared with existing results in the literature and the ability of high-order methods to capture these values using significantly fewer degrees of freedom is demonstrated.
Cohen J, Moxey D, Cantwell C, et al., 2015, POSITION PAPER: Ensuring an Effective User Experience when Managing and Running Scientific HPC Software, IEEE ACM 1st International Workshop on Software Engineering for High Performance Computing in Science (SE4HPCS), Publisher: IEEE, Pages: 56-59
Cohen J, Cantwell C, Moxey D, et al., 2015, TemPSS: A service providing software parameter templates and profiles for scientific HPC, IEEE International Conference On eScience, Publisher: IEEE, Pages: 78-87, ISSN: 2325-372X
Roney CH, Tzortzis KN, Cantwell CD, et al., 2015, A Technique for Visualising Three-Dimensional Left Atrial Cardiac Activation Data in Two Dimensions with Minimal Distance Distortion, 37th Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society (EMBC), Publisher: IEEE, Pages: 7296-7299, ISSN: 1557-170X
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- Citations: 6
Roney CH, Cantwell C, Siggers JH, et al., 2014, A Novel Method for Rotor Tracking Using Bipolar Electrogram Phase, Computing in Cardiology (CinC) 2014, Pages: 233-236
Assessing the location and stability of electrical rotors can help target ablation therapy for atrial fibrillation. Rotor cores can be tracked by identifying singularities in the phase of spatially distributed electrical recordings. This is routinely applied to unipolar electrogram and action potential data, but not to bipolar electrogram data, which contains local activation only. We developed and tested a technique to track phase singularities from simulated bipolar data. Bipolar electrogram phase was found to be as effective as action potential and as unipolar electrogram phase for rotor tip detection when using simulated data, suggesting that it may be used clinically as an alternative method to unipolar phase to locate rotor phase singularities in atrial fibrillation.
Roney CH, Cantwell C, Qureshi NA, et al., 2014, An Automated Algorithm for Determining Conduction Velocity, Wavefront Direction and Focal Source Location using a Multipolar Catheter, IEEE Engineering in Medicine and Biology Conference
Determining locations of focal arrhythmia sources and quantifying myocardial conduction velocity (CV) are two major challenges in clinical catheter ablation cases. CV, wavefront direction and focal source location can be estimated from multipolar catheter data, but currently available methods are time-consuming, limited to specific electrode configurations, and can be inaccurate. We developed automated algorithms to rapidly identify CV from multipolar catheter data with any arrangement of electrodes, whilst providing estimates of wavefront direction and focal source position, which can guide the catheter towards a focal arrhythmic source. We validated our methods using simulations on realistic human left atrial geometry. We subsequently applied them to clinically-acquired intracardiac electrogram data, where CV and wavefront direction were accurately determined in all cases, whilst focal source locations were correctly identified in 2/3 cases. Our novel automated algorithms can potentially be used to guide ablation of focal arrhythmias in real-time in cardiac catheter laboratories.
Cantwell C, Roney CH, Ali RL, et al., 2014, A Software Platform for the Comparative Analysis of Electroanatomic and Imaging Data including Conduction Velocity Mapping, IEEE Engineering in Medicine and Biology Conference
Electroanatomic mapping systems collect increasingly large quantities of spatially-distributed electrical data which may be potentially further scrutinized post-operatively to expose mechanistic properties which sustain and perpetuate atrial fibrillation. We describe a modular software platform, developed to post-process and rapidly analyse data exported from electroanatomic mapping systems using a range of existing and novel algorithms. Imaging data highlighting regions of scar can also be overlaid for comparison. In particular, we describe the conduction velocity mapping algorithm used to highlight wavefront behaviour. Conduction velocity was found to be particularly sensitive to the spatial distribution of the triangulation points and corresponding activation times. A set of geometric conditions were devised for selecting suitable triangulations of the electrogram set for generating CV maps.
Bolis A, Cantwell CD, Kirby RM, et al., 2014, From h to p efficiently: optimal implementation strategies for explicit time-dependent problems using the spectral/hp element method, International Journal for Numerical Methods in Fluids, Vol: 75, Pages: 591-607, ISSN: 1097-0363
We investigate the relative performance of a second-order Adams–Bashforth scheme and second-order andfourth-order Runge–Kutta schemes when time stepping a 2D linear advection problem discretised using aspectral/hp element technique for a range of different mesh sizes and polynomial orders. Numerical experimentsexplore the effects of short (two wavelengths) and long (32 wavelengths) time integration for sets ofuniform and non-uniform meshes. The choice of time-integration scheme and discretisation together fixes aCFL limit that imposes a restriction on the maximum time step, which can be taken to ensure numerical stability.The number of steps, together with the order of the scheme, affects not only the runtime but also theaccuracy of the solution. Through numerical experiments, we systematically highlight the relative effects ofspatial resolution and choice of time integration on performance and provide general guidelines on how bestto achieve the minimal execution time in order to obtain a prescribed solution accuracy. The significant roleplayed by higher polynomial orders in reducing CPU time while preserving accuracy becomes more evident,especially for uniform meshes, compared with what has been typically considered when studying this typeof problem.
, 2014, Simplifying the Development, Use and Sustainability of HPC Software, Journal of Open Research Software, Vol: 2, Pages: e16-e16, ISSN: 2049-9647
Cantwell CD, Yakovlev S, Kirby RM, et al., 2014, High-order spectral/hp element discretisation for reaction-diffusion problems on surfaces: application to cardiac electrophysiology, Journal of Computational Physics, Vol: 257, Pages: 813-829, ISSN: 0021-9991
We present a numerical discretisation of an embedded two-dimensional manifold using high-order continuous Galerkin spectral/hp elements, which provide exponential convergence of the solution with increasing polynomial order, while retaining geometric flexibility in the representation of the domain. Our work is motivated by applications in cardiac electrophysiology where sharp gradients in the solution benefit from the high-order discretisation, while the compu- tational cost of anatomically-realistic models can be reduced through the surface representation. We describe and validate our discretisation and provide a demonstration of its application to modeling electrochemical propagation across a human left atrium.
Ali RL, Cantwell CD, Roney CH, et al., 2014, A novel method for quantifying localised correlation of late-gadolinium intensity with conduction velocity, Computing in Cardiology (CinC) 2014, Pages: 193-196
Patient-specific computer models of the human atria have the potential to aid clinical intervention in the treatment of cardiac arrhythmias. However, quantifying and integrating the heterogeneous qualities of the myocardium through imaging is particularly challenging due to the unknown relationship between voxel intensity and tissue conductivities. We establish a method to determine the relationship between local conduction velocity and scar density, extracted through the analysis of late-gadolinium enhanced magnetic resonance imaging data.
Cantwell CD, Sherwin SJ, Moxey D, 2014, Nektar++
Nektar++ is a tensor product based finite element package designed to allow one to construct efficient classical low polynomial order h-type solvers (where h is the size of the finite element) as well as higher p-order piecewise polynomial order solvers.
Cohen J, Moxey D, Cantwell C, et al., 2013, Nekkloud: A Software Environment for High-order Finite Element Analysis on Clusters and Clouds, 2013 IEEE INTERNATIONAL CONFERENCE ON CLUSTER COMPUTING (CLUSTER), ISSN: 1552-5244
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- Citations: 2
Markall GR, Slemmer A, Ham DA, et al., 2012, Finite element assembly strategies on multi- and many-core architectures, International Journal for Numerical Methods in Fluids
Cantwell CD, Sherwin SJ, Kirby RM, et al., 2011, From h to p Efficiently: Selecting the Optimal Spectral/hp Discretisation in Three Dimensions, MATHEMATICAL MODELLING OF NATURAL PHENOMENA, Vol: 6, Pages: 84-96, ISSN: 0973-5348
Cantwell CD, Sherwin SJ, Kirby RM, et al., 2010, From h to p efficiently: Strategy selection for operator evaluation on hexahedral and tetrahedral elements, Computers and Fluids, Vol: 43, Pages: 23-28
Cantwell CD, Barkley D, 2010, Computational study of subcritical response in flow past a circular cylinder, Physical Review E, Vol: 82
Flow past a circular cylinder is investigated in the subcritical regime, below the onset of Bénard-von Kármánvortex shedding at Reynolds number Rec 47. The transient response of infinitesimal perturbations is computed.The domain requirements for obtaining converged results is discussed at length. It is shown that energyamplification occurs as low as Re=2.2. Throughout much of the subcritical regime the maximum energyamplification increases approximately exponentially in the square of Re reaching 6800 at Rec. The spatiotemporalstructure of the optimal transient dynamics is shown to be transitory Bénard-von Kármán vortex streets.At Re 42 the long-time structure switches from exponentially increasing downstream to exponentially decayingdownstream. Three-dimensional computations show that two-dimensional structures dominate the energygrowth except at short times.
Cantwell CD, Barkley D, Blackburn HM, 2010, Transient growth analysis of flow through a sudden expansion in a circular pipe, Physics of Fluids, Vol: 22
Results are presented from a numerical study of transient growth experienced by infinitesimal perturbations to flow in an axisymmetric pipe with a sudden 1–2 diametral expansion. First, the downstream reattachment point of the steady laminar flow is accurately determined as a function of Reynolds number and it is established that the flow is linearly stable at least up to Re = 1400. A direct method is used to calculate the optimal transient energy growth for specified time horizon τ, Re up to 1200, and low-order azimuthal wavenumber m. The critical Re for the onset of growth with different m is determined. At each Re the maximum growth is found in azimuthal mode m = 1 and this maximum is found to increase exponentially with Re. The time evolution of optimal perturbations is presented and shown to correspond to sinuous oscillations of the shear layer. Suboptimal perturbations are presented and discussed. Finally, direct numerical simulation in which the inflow is perturbed by Gaussian white noise confirms the presence of the structures determined by the transient growth analysis.
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