849 research outputs found
Advanced Automatic Code Generation for Multiple Relaxation-Time Lattice Boltzmann Methods
The scientific code generation package lbmpy supports the automated design
and the efficient implementation of lattice Boltzmann methods (LBMs) through
metaprogramming. It is based on a new, concise calculus for describing multiple
relaxation-time LBMs, including techniques that enable the numerically
advantageous subtraction of the constant background component from the
populations. These techniques are generalized to a wide range of collision
spaces and equilibrium distributions. The article contains an overview of
lbmpy's front-end and its code generation pipeline, which implements the new
LBM calculus by means of symbolic formula manipulation tools and
object-oriented programming. The generated codes have only a minimal number of
arithmetic operations. Their automatic derivation rests on two novel Chimera
transforms that have been specifically developed for efficiently computing raw
and central moments. Information contained in the symbolic representation of
the methods is further exploited in a customized sequence of algebraic
simplifications, further reducing computational cost. When combined, these
algebraic transformations lead to concise and compact numerical kernels.
Specifically, with these optimizations, the advanced central moment- and
cumulant-based methods can be realized with only little additional cost as when
compared with the simple BGK method. The effectiveness and flexibility of the
new lbmpy code generation system is demonstrated in simulating Taylor-Green
vortex decay and the automatic derivation of an LBM algorithm to solve the
shallow water equations.Comment: 23 pages, 6 figure
Steering in computational science: mesoscale modelling and simulation
This paper outlines the benefits of computational steering for high
performance computing applications. Lattice-Boltzmann mesoscale fluid
simulations of binary and ternary amphiphilic fluids in two and three
dimensions are used to illustrate the substantial improvements which
computational steering offers in terms of resource efficiency and time to
discover new physics. We discuss details of our current steering
implementations and describe their future outlook with the advent of
computational grids.Comment: 40 pages, 11 figures. Accepted for publication in Contemporary
Physic
Comparison of free-surface and conservative Allen-Cahn phase-field lattice Boltzmann method
This study compares the free-surface lattice Boltzmann method (FSLBM) with
the conservative Allen-Cahn phase-field lattice Boltzmann method (PFLBM) in
their ability to model two-phase flows in which the behavior of the system is
dominated by the heavy phase. Both models are introduced and their individual
properties, strengths and weaknesses are thoroughly discussed. Six numerical
benchmark cases were simulated with both models, including (i) a standing
gravity and (ii) capillary wave, (iii) an unconfined rising gas bubble in
liquid, (iv) a Taylor bubble in a cylindrical tube, and (v) the vertical and
(vi) oblique impact of a drop into a pool of liquid. Comparing the simulation
results with either analytical models or experimental data from the literature,
four major observations were made. Firstly, the PFLBM selected was able to
simulate flows purely governed by surface tension with reasonable accuracy.
Secondly, the FSLBM, a sharp interface model, generally requires a lower
resolution than the PFLBM, a diffuse interface model. However, in the limit
case of a standing wave, this was not observed. Thirdly, in simulations of a
bubble moving in a liquid, the FSLBM accurately predicted the bubble's shape
and rise velocity with low computational resolution. Finally, the PFLBM's
accuracy is found to be sensitive to the choice of the model's mobility
parameter and interface width
A next-generation CFD tool for large-eddy simulations on the desktop
Dive deep into the fascinating world of real-time computational fluid dynam-
ics. We present details of our GPU-accelerated flow solver for the simulation of non-linear
violent flows in marine and coastal engineering. The solver, the efficient lattice boltzmann
environment elbe, is accelerated with recent NVIDIA graphics hardware and allows for
three-dimensional simulations of complex flows in or near real-time. Details of the very ef-
ficient numerical back end, the pre- and postprocessing tools and the integrated OpenGL visualizer
tool will be discussed. Moreover, several applications with marine relevance demonstrate
that elbe can be considered as prototype for next-generation CFD tools for
simulation-based design (SBD) and interactive flow field monitoring on commodity
hardware
High performance cluster computing with 3-D nonlinear diffusion filters
This paper deals with parallelisation and implementation aspects of PDE-based image processing models for large cluster environments with distributed memory. As an example we focus on nonlinear diffusion filtering which we discretise by means of an additive operator splitting (AOS). We start by decomposing the algorithm into small modules that shall be parallelised separately. For this purpose image partitioning strategies are discussed and their impact on the communication pattern and volume is analysed. Based on the results we develop an algorithmic implementation with excellent scaling properties on massively connected low latency networks. Test runs on a high-end Myrinet cluster yield almost linear speedup factors up to 209 for 256 processors. This results in typical denoising times of 0.5 seconds for five iterations on a 256 x 256 x 128 data cube
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