47,819 research outputs found
Probing turbulent superstructures in Rayleigh-B\'{e}nard convection by Lagrangian trajectory clusters
We analyze large-scale patterns in three-dimensional turbulent convection in
a horizontally extended square convection cell by Lagrangian particle
trajectories calculated in direct numerical simulations. A simulation run at a
Prandtl number Pr , a Rayleigh number Ra , and an aspect ratio
is therefore considered. These large-scale structures, which are
denoted as turbulent superstructures of convection, are detected by the
spectrum of the graph Laplacian matrix. Our investigation, which follows
Hadjighasem {\it et al.}, Phys. Rev. E {\bf 93}, 063107 (2016), builds a
weighted and undirected graph from the trajectory points of Lagrangian
particles. Weights at the edges of the graph are determined by a mean dynamical
distance between different particle trajectories. It is demonstrated that the
resulting trajectory clusters, which are obtained by a subsequent -means
clustering, coincide with the superstructures in the Eulerian frame of
reference. Furthermore, the characteristic times and lengths
of the superstructures in the Lagrangian frame of reference agree
very well with their Eulerian counterparts, and ,
respectively. This trajectory-based clustering is found to work for times
. Longer time periods require a
change of the analysis method to a density-based trajectory clustering by means
of time-averaged Lagrangian pseudo-trajectories, which is applied in this
context for the first time. A small coherent subset of the pseudo-trajectories
is obtained in this way consisting of those Lagrangian particles that are
trapped for long times in the core of the superstructure circulation rolls and
are thus not subject to ongoing turbulent dispersion.Comment: 12 pages, 7 downsized figures, to appear in Phys. Rev. Fluid
Real-time lattice boltzmann shallow waters method for breaking wave simulations
We present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.Peer ReviewedPostprint (author's final draft
Large-scale lattice Boltzmann simulations of complex fluids: advances through the advent of computational grids
During the last two years the RealityGrid project has allowed us to be one of
the few scientific groups involved in the development of computational grids.
Since smoothly working production grids are not yet available, we have been
able to substantially influence the direction of software development and grid
deployment within the project. In this paper we review our results from large
scale three-dimensional lattice Boltzmann simulations performed over the last
two years. We describe how the proactive use of computational steering and
advanced job migration and visualization techniques enabled us to do our
scientific work more efficiently. The projects reported on in this paper are
studies of complex fluid flows under shear or in porous media, as well as
large-scale parameter searches, and studies of the self-organisation of liquid
cubic mesophases.
Movies are available at
http://www.ica1.uni-stuttgart.de/~jens/pub/05/05-PhilTransReview.htmlComment: 18 pages, 9 figures, 4 movies available, accepted for publication in
Phil. Trans. R. Soc. London Series
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