571 research outputs found
Nonlinear Kinetic Dynamics of Magnetized Weibel Instability
Kinetic numerical simulations of the evolution of the Weibel instability
during the full nonlinear regime are presented. The formation of strong
distortions in the electron distribution function resulting in formation of
strong peaks in it and their influence on the resulting electrostatic waves are
shown.Comment: 6 pages, 4 figure
2D granular flows with the rheology and side walls friction: a well balanced multilayer discretization
We present here numerical modelling of granular flows with the
rheology in confined channels. The contribution is twofold: (i) a model to
approximate the Navier-Stokes equations with the rheology through an
asymptotic analysis. Under the hypothesis of a one-dimensional flow, this model
takes into account side walls friction; (ii) a multilayer discretization
following Fern\'andez-Nieto et al. (J. Fluid Mech., vol. 798, 2016, pp.
643-681). In this new numerical scheme, we propose an appropriate treatment of
the rheological terms through a hydrostatic reconstruction which allows this
scheme to be well-balanced and therefore to deal with dry areas. Based on
academic tests, we first evaluate the influence of the width of the channel on
the normal profiles of the downslope velocity thanks to the multilayer approach
that is intrinsically able to describe changes from Bagnold to S-shaped (and
vice versa) velocity profiles. We also check the well balance property of the
proposed numerical scheme. We show that approximating side walls friction using
single-layer models may lead to strong errors. Secondly, we compare the
numerical results with experimental data on granular collapses. We show that
the proposed scheme allows us to qualitatively reproduce the deposit in the
case of a rigid bed (i. e. dry area) and that the error made by replacing the
dry area by a small layer of material may be large if this layer is not thin
enough. The proposed model is also able to reproduce the time evolution of the
free surface and of the flow/no-flow interface. In addition, it reproduces the
effect of erosion for granular flows over initially static material lying on
the bed. This is possible when using a variable friction coefficient
but not with a constant friction coefficient
Flow rule, self-channelization and levees in unconfined granular flows
Unconfined granular flows along an inclined plane are investigated
experimentally. During a long transient, the flow gets confined by quasistatic
banks but still spreads laterally towards a well-defined asymptotic state
following a nontrivial process. Far enough from the banks a scaling for the
depth averaged velocity is obtained, which extends the one obtained for
homogeneous steady flows. Close to jamming it exhibits a crossover towards a
nonlocal rheology. We show that the levees, commonly observed along the sides
of the deposit upon interruption of the flow, disappear for long flow
durations. We demonstrate that the morphology of the deposit builds up during
the flow, in the form of an underlying static layer, which can be deduced from
surface velocity profiles, by imposing the same flow rule everywhere in the
flow.Comment: 4 pages, 5 figure
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