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Cambridge, United Kingdom

Braithwaite M.,Laboratory for Scientific Computing
Performance of Explosives and New Developments: Workshop Hosted by FRAGBLAST 10 - The 10th International Symposium on Rock Fragmentation by Blasting | Year: 2013

A review of ideal detonation theory, thermochemical computer codes for calculation of ideal detonation behavior and applications of these to blasting engineering is presented. This paper provides background for a first stage analysis of the ideal detonation process in an explosive composition and estimation of detonation parameters such as velocity of detonation and energy. Both these are critical parameters in design of blasts. Source


Blakely P.M.,Laboratory for Scientific Computing | Nikiforakis N.,Laboratory for Scientific Computing | Henshaw W.D.,Rensselaer Polytechnic Institute
Astronomy and Astrophysics | Year: 2015

Aims. We investigate the use of some high-resolution shock-capturing schemes on curvilinear grids in the context of general relativistic hydrodynamics (GRHD). We aim to demonstrate that these can be used to evolve accurately fluid flow onto a black hole. Methods. We describe a numerical scheme which applies high-resolution shock-capturing schemes and the curvilinear overlapping grids methodology to the evolution of the equations of GRHD. Results. We apply our scheme to the problem of Bondi-Hoyle-Lyttleton accretion onto a black hole. We validate our approach against an exact solution of the problem and against previous numerical results. Our approach allows for the incident wind to be at any angle to the spin-axis of the Kerr black hole, and also allows the flow density to be perturbed upstream. We give an illustration of the effects of these perturbations on the resulting flow-field. © ESO, 2015. Source


Blakely P.M.,Laboratory for Scientific Computing | Nikiforakis N.,Laboratory for Scientific Computing | Henshaw W.D.,Rensselaer Polytechnic Institute
Astronomy and Astrophysics | Year: 2015

Aims. We evaluate some approximations for solving the equations of special relativistic hydrodynamics within complex geometries. In particular, we assess the following schemes: the Generalized FORCE (GFORCE) and MUlti STAge (MUSTA) approaches which are used as the basis for a second-order-accurate Slope-LImited-Centred (SLIC) method. These do not require detailed knowledge of the characteristic structure of the system, but have the potential to be nearly as accurate as more expensive schemes which do require this knowledge. Methods. In order to treat complex geometries, we use multiple overlapping grids which allow the capturing of complex geometries while retaining the efficiencies associated with structured grids. Results. The schemes are evaluated using a suite of one dimensional problems some of which have known exact solutions, and it is shown that the schemes can be used at CFL numbers close to the theoretical stability limit. We compare the effects of the MUSTA approach when applied to two different schemes. The scheme is further validated on a number of problems involving complex geometries with overlapping grids. © ESO, 2015. Source


Blakely P.M.,Laboratory for Scientific Computing | Nikiforakis N.,Laboratory for Scientific Computing
Astronomy and Astrophysics | Year: 2015

We investigate Bondi-Hoyle-Lyttleton accretion onto a black hole for ultra-relativistic flows, and how flow features are affected by density perturbations, upstream fluid velocity, and black hole spin. Methods. We use high-resolution shock-capturing (HRSC) schemes solved on curvilinear overlapping grids as demonstrated in a previous publication. Results. We demonstrate the quantitative dependence of the shock-angle and mass accretion rate on black hole spin, upstream fluid velocity, and density perturbations. We also demonstrate the qualitative dependence of the accretion region and flow features on the same parameters. Conclusions. We find that the mass accretion rate does not depend strongly on these parameters, and most of the difference in flow is seen in the shock angle and general flow patterns close to the black-hole, as previously predicted by lower-dimensional simulations. Moreover, we demonstrate independence of initial conditions in that a steady flow around a non-spinning black-hole which suddenly starts to spin will converge to the same flow pattern as if the black-hole had been spinning initially. © 2015 ESO. Source

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