7,508 research outputs found
Particle hydrodynamics with tessellation techniques
Lagrangian smoothed particle hydrodynamics (SPH) is a well-established
approach to model fluids in astrophysical problems, thanks to its geometric
flexibility and ability to automatically adjust the spatial resolution to the
clumping of matter. However, a number of recent studies have emphasized
inaccuracies of SPH in the treatment of fluid instabilities. The origin of
these numerical problems can be traced back to spurious surface effects across
contact discontinuities, and to SPH's inherent prevention of mixing at the
particle level. We here investigate a new fluid particle model where the
density estimate is carried out with the help of an auxiliary mesh constructed
as the Voronoi tessellation of the simulation particles instead of an adaptive
smoothing kernel. This Voronoi-based approach improves the ability of the
scheme to represent sharp contact discontinuities. We show that this eliminates
spurious surface tension effects present in SPH and that play a role in
suppressing certain fluid instabilities. We find that the new `Voronoi Particle
Hydrodynamics' described here produces comparable results than SPH in shocks,
and better ones in turbulent regimes of pure hydrodynamical simulations. We
also discuss formulations of the artificial viscosity needed in this scheme and
how judiciously chosen correction forces can be derived in order to maintain a
high degree of particle order and hence a regular Voronoi mesh. This is
especially helpful in simulating self-gravitating fluids with existing gravity
solvers used for N-body simulations.Comment: 26 pages, 24 figures, currentversion is accepted by MNRA
Wind Forecasting Based on the HARMONIE Model and Adaptive Finite Elements
In this paper, we introduce a new method for wind
field forecasting over complex terrain. The main idea is to use the
predictions of the HARMONIE meso-scale model as the input data
for an adaptive finite element mass-consistent wind model. The
HARMONIE results (obtained with a maximum resolution of about
1 km) are refined in a local scale (about a few metres). An interface
between both models is implemented in such a way that the initial
wind field is obtained by a suitable interpolation of the HARMONIE results. Genetic algorithms are used to calibrate some
parameters of the local wind field model in accordance to the
HARMONIE data. In addition, measured data are considered to
improve the reliability of the simulations. An automatic tetrahedral
mesh generator, based on the meccano method, is applied to adapt
the discretization to complex terrains. The main characteristic of
the framework is a minimal user intervention. The final goal is to
validate our model in several realistic applications on Gran Canaria
island, Spain, with some experimental data obtained by the
AEMET in their meteorological stations.This work has been supported by the Spanish Government, ‘‘Ministerio de Ciencia e Innovación’’,
Grant Contracts: CGL2011-29396-C03-01 and CGL2011-29396-C03-02, and by ‘‘Junta de Castilla León’’, ‘‘ConsejerÃa de Educación’’, Grant Contract SA266A12-2
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