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

Sliding susceptibility of a rough cylinder on a rough inclined perturbed surface

A susceptibility function ${\chi}(L)$ is introduced to quantify some aspects of the intermittent stick-slip dynamics of a rough metallic cylinder of length $L$ on a rough metallic incline submitted to small controlled perturbations and maintained below the angle of repose. This problem is studied from the experimental point of view and the observed power-law behavior of ${\chi}(L)$ is justified through the use of a general class of scaling hypotheses.Comment: 14 pages including 5 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

Morphodynamic modeling of aeolian dunes: Review and future plans

Sand dunes are ubiquitous in deserts, on coasts, on the sea bottom, and on the surface of Mars, Venus and Titan. The quantitative understanding of dune dynamics is thus of relevance for a broad range of physical, geological and planetary sciences. A morphodynamic model for dunes, which combines an analytical description of the average turbulent wind field over the topography with a continuum saltation model, has proven successful to quantitatively reproduce the shape of aeolian dunes of different types. We present a short review on the physics of dune formation and the model development, as well as some future plans for further developments and applications

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Numerical modeling of wind-blown sand on Mars

Recent observation results show that sand ripples and dunes are movable like those on Earth under current Martian climate. And the aeolian process on Mars therefore is re-attracting the eyes of scientific researchers in different fields. In this paper, the spatial and temporal evolution of wind-blown sand on Mars is simulated by the large-eddy simulation method. The simulations are conducted under the conditions of both friction wind speed higher and lower than the “fluid threshold”, respectively. The fluid entrainment of the sand particles, the processes among saltation sand particles and sand bed, and the negative feedback of sand movement to flow field are considered. Our results show that the “overshoot” phenomenon also exists in the evolution of wind-blown sand on Mars both temporally and spatially; impact entrainment affects the sand transport rate on Mars when the wind speed is smaller or larger than the fluid threshold; and both the average saltation length and height are one order of magnitudes larger than those on Earth. Eventually, the formulas describing the sand transport rate, average saltation length and height on Mars are given, respectively