595 research outputs found
A "well-balanced" finite volume scheme for blood flow simulation
We are interested in simulating blood flow in arteries with a one dimensional
model. Thanks to recent developments in the analysis of hyperbolic system of
conservation laws (in the Saint-Venant/ shallow water equations context) we
will perform a simple finite volume scheme. We focus on conservation properties
of this scheme which were not previously considered. To emphasize the necessity
of this scheme, we present how a too simple numerical scheme may induce
spurious flows when the basic static shape of the radius changes. On contrary,
the proposed scheme is "well-balanced": it preserves equilibria of Q = 0. Then
examples of analytical or linearized solutions with and without viscous damping
are presented to validate the calculations. The influence of abrupt change of
basic radius is emphasized in the case of an aneurism.Comment: 36 page
FullSWOF: A free software package for the simulation of shallow water flows
Numerical simulations of flows are required for numerous applications, and
are usually carried out using shallow water equations. We describe the FullSWOF
software which is based on up-to-date finite volume methods and well-balanced
schemes to solve this kind of equations. It consists of a set of open source
C++ codes, freely available to the community, easy to use, and open for further
development. Several features make FullSWOF particularly suitable for
applications in hydrology: small water heights and wet-dry transitions are
robustly handled, rainfall and infiltration are incorporated, and data from
grid-based digital topographies can be used directly. A detailed mathematical
description is given here, and the capabilities of FullSWOF are illustrated
based on analytic solutions and datasets of real cases. The codes, available in
1D and 2D versions, have been validated on a large set of benchmark cases,
which are available together with the download information and documentation at
http://www.univ-orleans.fr/mapmo/soft/FullSWOF/.Comment: 38 page
SWASHES: a compilation of Shallow Water Analytic Solutions for Hydraulic and Environmental Studies
Numerous codes are being developed to solve Shallow Water equations. Because
there are used in hydraulic and environmental studies, their capability to
simulate properly flow dynamics is critical to guarantee infrastructure and
human safety. While validating these codes is an important issue, code
validations are currently restricted because analytic solutions to the Shallow
Water equations are rare and have been published on an individual basis over a
period of more than five decades. This article aims at making analytic
solutions to the Shallow Water equations easily available to code developers
and users. It compiles a significant number of analytic solutions to the
Shallow Water equations that are currently scattered through the literature of
various scientific disciplines. The analytic solutions are described in a
unified formalism to make a consistent set of test cases. These analytic
solutions encompass a wide variety of flow conditions (supercritical,
subcritical, shock, etc.), in 1 or 2 space dimensions, with or without rain and
soil friction, for transitory flow or steady state. The corresponding source
codes are made available to the community
(http://www.univ-orleans.fr/mapmo/soft/SWASHES), so that users of Shallow
Water-based models can easily find an adaptable benchmark library to validate
their numerical methods.Comment: 40 pages There are some errors in the published version. This is a
corrected versio
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
Uncertainty quantification in littoral erosion
International audienceWe aim at quantifying the impact of flow state uncertainties in lit-toral erosion to provide confidence bounds on deterministic predictions of bottom morphodynamics. Two constructions of the bathymetry standard deviation are discussed. The first construction involves directional quantile-based extreme scenarios using what is known on the flow state Probability Density Function (PDF) from on site observations. We compare this construction to a second cumulative one using the gradient by adjoint of a functional involving the energy of the system. These ingredients are illustrated for two models for the interaction between a soft bed and a flow in a shallow domain. Our aim is to keep the computational complexity comparable to the deterministic simulations taking advantage of what already available in our simulation toolbox
Beyond Shallow Water: appraisal of a numerical approach to hydraulic jumps based upon the Boundary Layer Theory
International audienceWe study the flow of a thin layer of fluid over a flat surface. Commonly, the 1-D Shallow-water or Saint-Venant set of equations are used to compute the solution of such flows. These simplified equations may be obtained through the integration of the Navier-Stokes equations over the depth of the fluid, but their solution requires the introduction of constitutive relations based on strict hypothesis on the flow régime. Here, we present an approach based on a kind of boundary layer system with hydrostatic pressure. This relaxes the need for closure relations which are instead obtained as solutions of the computation. It is then demonstrated that the corresponding closures are very dependent on the type of flow considered, for example laminar viscous slumps or hydraulic jumps. This has important practical consequences as far as the applicability of standard closures is concerned
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