Force distribution within a barchan dune

Abstract

Barchan dunes, or simply barchans, are crescent-shaped dunes found in diverse environments such as the bottom of rivers, Earth's deserts and the surface of Mars. In a recent paper [Phys. Rev. E 101, 012905 (2020)], we investigated the evolution of subaqueous barchans by using computational fluid dynamics - discrete element method (CFD-DEM), and our simulations captured well the evolution of an initial pile toward a barchan dune in both the bedform and grain scales. The numerical method having shown to be adequate, we obtain now the forces acting on each grain, isolate the contact interactions, and investigate how forces are distributed and transmitted in a barchan dune. We present force maps and probability density functions (PDFs) for values in the streamwise and spanwise directions, and show that stronger forces are experienced by grains at neither the crest nor leading edge of the barchan, but in positions just upstream the dune centroid on the periphery of the dune. We show also that a great part of grains undergo longitudinal forces of the order of 10$^{-7}$ N, with negative values around the crest, resulting in decelerations and grain deposition in that region. These data show that the force distribution tends to route a great part of grains toward the crest and horns of subaqueous barchans, being fundamental to comprehend their morphodynamics. However, to the best of the authors' knowledge, they are not accessible from current experiments, making of our results an important step toward understanding the behavior of barchan dunes.