27 research outputs found
Calculation of the separation streamlines of barchans and transverse dunes
We use FLUENT to calculate the wind profile over barchans and transverse
dunes. The form of the streamlines of flow separation at the lee side of the
dunes is determined for a symmetric barchan dune in three dimensions, and for
the height profile of a measured transverse dune field in the Len\c{c}\'ois
Maranhenses.Comment: 6 pages including 5 figures. Proceedings of PSIS 200
Nontrivial temporal scaling in a Galilean stick-slip dynamics
We examine the stick-slip fluctuating response of a rough massive
non-rotating cylinder moving on a rough inclined groove which is submitted to
weak external perturbations and which is maintained well below the angle of
repose. The experiments presented here, which are reminiscent of the Galileo's
works with rolling objects on inclines, have brought in the last years
important new insights into the friction between surfaces in relative motion
and are of relevance for earthquakes, differing from classical block-spring
models by the mechanism of energy input in the system. Robust nontrivial
temporal scaling laws appearing in the dynamics of this system are reported,
and it is shown that the time-support where dissipation occurs approaches a
statistical fractal set with a fixed value of dimension. The distribution of
periods of inactivity in the intermittent motion of the cylinder is also
studied and found to be closely related to the lacunarity of a random version
of the classic triadic Cantor set on the line.Comment: 7 pages including 6 figure
Vegetation and induration as sand dunes stabilizators
Sand dunes are found in a variety of shapes in deserts and coasts and also on the planet Mars. The basic mechanisms of dune formation could be incorporated into a continuum saltation model, which successfully reproduced the shape of the barchan dunes and has been also applied to calculate interaction of barchans in a field. We have recently extended our dune model to investigate other dune shapes observed in nature. Here, we present the first numerical simulation of the transformation of barchan dunes, under the influence of vegetation, into parabolic dunes, which appear frequently on coasts. Further, we apply our model to reproduce the shape of barchan dunes observed on Mars, and we find that an interesting property related to the martian saltation is relevant to predict the scale of dunes on Mars. Our model can also reproduce unusual dune shapes of the Martian north polar region, like rounded barchans and elongated linear dunes. Our results support the hypothesis that these dunes are indurated