28,891 research outputs found
Enhanced goal-oriented error assessment and computational strategies in adaptive reduced basis solver for stochastic problems
This work focuses on providing accurate low-cost approximations of stochastic Âżnite elements simulations in the framework of linear elasticity. In a previous work, an adaptive strategy was introduced as an improved Monte-Carlo method for multi-dimensional large stochastic problems. We provide here a complete analysis of the method including a new enhanced goal-oriented error estimator and estimates of CPU (computational processing unit) cost gain. Technical insights of these two topics are presented in details, and numerical examples show the interest of these new developments.Postprint (author's final draft
Feedback control of inertial microfluidics using axial control forces
Inertial microfluidics is a promising tool for many lab-on-a-chip
applications. Particles in channel flows with Reynolds numbers above one
undergo cross-streamline migration to a discrete set of equilibrium positions
in square and rectangular channel cross sections. This effect has been used
extensively for particle sorting and the analysis of particle properties. Using
the lattice Boltzmann method, we determine equilibrium positions in square and
rectangular cross sections and classify their types of stability for different
Reynolds numbers, particle sizes, and channel aspect ratios. Our findings
thereby help to design microfluidic channels for particle sorting. Furthermore,
we demonstrate how an axial control force, which slows down the particles,
shifts the stable equilibrium position towards the channel center. Ultimately,
the particles then stay on the centerline for forces exceeding a threshold
value. This effect is sensitive to particle size and channel Reynolds number
and therefore suggests an efficient method for particle separation. In
combination with a hysteretic feedback scheme, we can even increase particle
throughput
One machine, one minute, three billion tetrahedra
This paper presents a new scalable parallelization scheme to generate the 3D
Delaunay triangulation of a given set of points. Our first contribution is an
efficient serial implementation of the incremental Delaunay insertion
algorithm. A simple dedicated data structure, an efficient sorting of the
points and the optimization of the insertion algorithm have permitted to
accelerate reference implementations by a factor three. Our second contribution
is a multi-threaded version of the Delaunay kernel that is able to concurrently
insert vertices. Moore curve coordinates are used to partition the point set,
avoiding heavy synchronization overheads. Conflicts are managed by modifying
the partitions with a simple rescaling of the space-filling curve. The
performances of our implementation have been measured on three different
processors, an Intel core-i7, an Intel Xeon Phi and an AMD EPYC, on which we
have been able to compute 3 billion tetrahedra in 53 seconds. This corresponds
to a generation rate of over 55 million tetrahedra per second. We finally show
how this very efficient parallel Delaunay triangulation can be integrated in a
Delaunay refinement mesh generator which takes as input the triangulated
surface boundary of the volume to mesh
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