412 research outputs found
Selection of dune shapes and velocities. Part 2: A two-dimensional modelling
We present in this paper a simplification of the dune model proposed by
Sauermann et al. which keeps the basic mechanisms but allows analytical and
parametric studies. Two kinds of purely propagative two dimensional solutions
are exhibited: dunes and domes, which, by contrast to the former, do not show
avalanche slip face. Their shape and velocity can be predicted as a function of
their size. We recover in particular that dune profiles are not scale invariant
(small dunes are flatter than the large ones), and that the inverse of the
velocity grows almost linearly with the dune size. We furthermore get the
existence of a critical mass below which no stable dune exists. However, the
linear stability analysis of a flat sand sheet shows that it is unstable at
large wavelengths and suggests a mechanism of dune initiation.Comment: submitted to Eur. Phys. J. B, 13 pages, 17 figure
Numerical stress response functions of static granular layers
We investigate the stress response function of a layer of grains, i.e. the
stress profile in response to a localized overload. The shape of the profile is
very sensitive to the packing arrangement, and is thus a good signature of the
preparation procedure of the layer. This study has been done by the use of
molecular dynamics numerical simulations. Here, for a given rain-like
preparation, we present the scaling properties of the response function, and in
particular the influence of the thickness of the layer, and the importance of
the location of the overload and measurement points (at the boundaries, in the
bulk).Comment: 6 pages, 4 figures, to appear in the proceedings of the "Traffic and
Granular Flow 2003" conferenc
Selection of dune shapes and velocities. Part 1: Dynamics of sand, wind and barchans
Almost fifty years of investigations of barchan dunes morphology and dynamics
is reviewed, with emphasis on the physical understanding of these objects. The
characteristics measured on the field (shape, size, velocity) and the physical
problems they rise are presented. Then, we review the dynamical mechanisms
explaining the formation and the propagation of dunes. In particular a complete
and original approach of the sand transport over a flat sand bed is proposed
and discussed. We conclude on open problems by outlining future research
directions.Comment: submitted to Eur. Phys. J. B, 20 pages, 20 figure
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