SUMMARYFree-surface flows occur in several problems in hydrodynamics, such as fuel or water sloshing in tanks, waves breaking in ships, offshore platforms, harbours and coastal areas. The computation of such highly nonlinear flows is challenging since free-surfaces commonly present merging, fragmentation and breaking parts, leading to the use of interface-capturing Eulerian approaches. In such methods the surface between two fluids is captured by the use of a marking function which is transported in a flow field. In this work we present a three-dimensional parallel edge-based incompressible SUPG/PSPG finite element method to cope with free-surface problems with volume-of-fluid (VOF) extensions to track the evolving free surface. The pure advection equation for the scalar marking function was solved by a fully implicit parallel edge-based SUPG finite element formulation. We studied variants of this formulation, considering the effects of discontinuity capturing and a particular tangent transformation designed to increase interface sharpness. Global mass conservation is enforced adding or removing mass proportionally to the absolute value of the normal velocity of the interface. We introduce a parallel dynamic deactivation algorithm to solve the marking function equation only in a small region around the interface. The implementation is targeted to distributed memory systems with cache-based processors. The performance and accuracy of the proposed solution method were tested with several validation problems.

One of the main advantages of using a scientific workflow management system (SWfMS) to orchestrate data flows among scientific activities is to control and register the whole workflow execution. The execution of activities within a workflow with high performance computing (HPC) presents challenges in SWfMS execution control. Current solutions leave the scheduling to the HPC queue system. Since the workflow execution engine does not run on remote clusters, SWfMS are not aware of the parallel strategy of the workflow execution. Consequently, remote execution control and provenance registry of the parallel activities is very limited from the SWfMS side. This work presents a set of components to be included on the workflow specification of any SWMfS to control parallelization of activities as MTC. In addition, these components can gather provenance data during remote workflow execution. Through these MTC components, the parallelization strategy can be registered and reused, and provenance data can be uniformly queried. We have evaluated our approach by performing parameter sweep parallelization in solving the incompressible 3D Navier-Stokes equations. Experimental results show the performance gains with the additional benefits of distributed provenance support.

SUMMARYSeveral performance improvements for finite-element edge-based sparse matrix-vector multiplication algorithms on unstructured grids are presented and tested. Edge data structures for tetrahedral meshes and triangular interface elements are treated, focusing on nodal and edges renumbering strategies for improving processor and memory hierarchy use. Benchmark computations on Intel Itanium 2 and Pentium IV processors are performed. The results show performance improvements in CPU time ranging from 2 to 3.

A parallel edge-based solution of three dimensional viscoplastic flows governed by the steady Navier-Stokes equations is presented. The governing partial differential equations are discretized using the SUPG/PSPG stabilized finite element method on unstructured grids. The highly nonlinear algebraic system arising from the convective and material effects is solved by an inexact Newton-Krylov method. The locally linear Newton equations are solved by GMRES with nodal block diagonal preconditioner. Matrix-vector products within GMRES are computed edge-by-edge (EDE), diminishing flop counts and memory requirements. A comparison between EDE and element-by-element data structures is presented. The parallel computations were based in a message passing interface standard. Performance tests were carried out in representative three dimensional problems, the sudden expansion for power-law fluids and the flow of Bingham fluids in a lid-driven cavity. Results have shown that edge based schemes requires less CPU time and memory than elementbased solutions.

In this work we apply the residual-based variational multiscale method (RB-VMS) to the volume-of-fluid (VOF) formulation of free-surface flows. Using this technique we are able to solve such problems in a Large Eddy Simulation framework. This is a natural extension of our Navier-Stokes solver, which uses the RB-VMS finite element formulation, edge-based data structures, adaptive time step control, inexact Newton solvers and supports several parallel programming paradigms. The VOF interface capturing variable is advected using the computed coarse and fine scales velocity field. Thus, the RB-VMS technique can be readily applied to the free-surface solver with minor modifications on the implementation. We apply this technique to the solution of two problems where available data indicate complex free-surface behavior. Results are compared with numerical and experimental data and show that the present formulation can achieve good accuracy with minor impacts on computational efficiency.Keywords Variational multiscale method · Edge-based computations · Volume of fluid · Free surface flows

SUMMARYA distance field is a representation of the closest distance from a point to a given surface. Distance fields are widely used in applications ranging from computer vision, physics and computer graphics and have been the subject of research of many authors in the last decade. Most of the methods for computing distance fields are devoted to Cartesian grids while little attention has been paid to unstructured grids. Finite element methods are well known for their ability to deal with partial differential equations in unstructured grids. Therefore, we propose an extension of the fast marching method for computing a distance field in a finite element context employing the element interpolation to hold the Eikonal property ( ∇ = 1). A simple algorithm to develop the computations is also presented and its efficiency demonstrated through various unstructured grid examples. We observed that the presented algorithm has processing times proportional to the number of mesh nodes.

SUMMARYModeling of gravity current flows is important in many problems of science and engineering. Gravity currents are primarily horizontal flows driven by a density difference of few per cents. This phenomenon occurs in many scales in nature, such as ocean and marine flows, sea breeze formation, avalanches, turbidite flows, etc. Most of the gravity current simulations employ structured grid or spectral methods. In this work, we simulate gravity-driven flows by a parallel stabilized edge-based finite element code with particular emphasis on the simulation of the lock-exchange problem for planar and cylindrical configurations. Our results are validated against other highly resolved numerical simulations and experiments.

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