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Heyns J.A.,Advanced Computational Methods Research Group | Malan A.G.,Advanced Computational Methods Research Group | Harms T.M.,Stellenbosch University | Oxtoby O.F.,Advanced Computational Methods Research Group
International Journal for Numerical Methods in Fluids | Year: 2013

With the aim of accurately modelling free-surface flow of two immiscible fluids, this study presents the development of a new volume-of-fluid free-surface capturing formulation. By building on existing volume-of-fluid approaches, the new formulation combines a blended higher resolution scheme with the addition of an artificial compressive term to the volume-of-fluid equation. This reduces the numerical smearingof the interface associated with explicit higher resolution schemes while limiting the contribution of the artificial compressive term to ensure the integrity of the interface shape is maintained. Furthermore, the computational efficiency of the the higher resolution scheme is improved through the reformulation of the normalised variable approach and the implementation of a new higher resolution blending function. The volume-of-fluid equation is discretised via an unstructured vertex-centred finite volume method and solved via a Jacobian-type dual time-stepping approach. © 2012 John Wiley & Sons, Ltd.

Malan A.G.,Advanced Computational Methods Research Group | Oxtoby O.F.,Advanced Computational Methods Research Group
Computer Methods in Applied Mechanics and Engineering | Year: 2013

In this paper we propose a fast, parallel 3D, fully-coupled partitioned hybrid-unstructured finite volume fluid-structure-interaction (FSI) scheme. Spatial discretisation is effected via a vertex-centred finite volume method, where a hybrid nodal-elemental strain procedure is employed for the solid in the interest of accuracy. For the incompressible fluid, a split-step algorithm is presented which allows the entire fluid-solid system to be solved in a fully-implicit yet matrix-free manner. The algorithm combines a preconditioned GMRES solver for implicit integration of pressures with dual-timestepping on the momentum equations, thereby allowing strong coupling of the system to occur through the inner solver iterations. Further acceleration is provided at little additional cost by applying LU-SGS relaxation to the viscous and advective terms. The solver is parallelised for distributed-memory systems using MPI and its scaling efficiency evaluated. The developed modelling technology is evaluated by application to two 3D FSI problems. The advanced matrix-free solvers achieve reductions in overall CPU time of up to 50 times, while preserving close to linear parallel computing scaling using up to 128 CPUs for the problems considered. © 2012 Elsevier B.V.

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