8,934 research outputs found
Event-based control of linear hyperbolic systems of conservation laws
International audienceIn this article, we introduce event-based boundary controls for 1-dimensional linear hyperbolic systems of conservation laws. Inspired by event-triggered controls developed for finite-dimensional systems, an extension to the infinite dimensional case by means of Lyapunov techniques, is studied. The main contribution of the paper lies in the definition of two event-triggering conditions, by which global exponential stability and well-posedness of the system under investigation is achieved. Some numerical simulations are performed for the control of a system describing traffic flow on a roundabout
Numerical simulation of conservation laws with moving grid nodes: Application to tsunami wave modelling
In the present article we describe a few simple and efficient finite volume
type schemes on moving grids in one spatial dimension combined with appropriate
predictor-corrector method to achieve higher resolution. The underlying finite
volume scheme is conservative and it is accurate up to the second order in
space. The main novelty consists in the motion of the grid. This new dynamic
aspect can be used to resolve better the areas with large solution gradients or
any other special features. No interpolation procedure is employed, thus
unnecessary solution smearing is avoided, and therefore, our method enjoys
excellent conservation properties. The resulting grid is completely
redistributed according the choice of the so-called monitor function. Several
more or less universal choices of the monitor function are provided. Finally,
the performance of the proposed algorithm is illustrated on several examples
stemming from the simple linear advection to the simulation of complex shallow
water waves. The exact well-balanced property is proven. We believe that the
techniques described in our paper can be beneficially used to model tsunami
wave propagation and run-up.Comment: 46 pages, 7 figures, 7 tables, 94 references. Accepted to
Geosciences. Other author's papers can be downloaded at
http://www.denys-dutykh.com
Wave and Dirac equations on manifolds
We review some recent results on geometric equations on Lorentzian manifolds
such as the wave and Dirac equations. This includes well-posedness and
stability for various initial value problems, as well as results on the
structure of these equations on black-hole spacetimes (in particular, on the
Kerr solution), the index theorem for hyperbolic Dirac operators and properties
of the class of Green-hyperbolic operators.Comment: 21 pages, 1 figur
Cumulative reports and publications through December 31, 1990
This document contains a complete list of ICASE reports. Since ICASE reports are intended to be preprints of articles that will appear in journals or conference proceedings, the published reference is included when it is available
Pointwise Asymptotic Behavior of Perturbed Viscous Shock Profiles
We consider the asymptotic behavior of perturbations of Lax and
overcompressive type viscous shock profiles arising in systems of regularized
conservation laws with strictly parabolic viscosity, and also in systems of
conservation laws with partially parabolic regularizations such as arise in the
case of the compressible Navier--Stokes equations and in the equations of
magnetohydrodynamics. Under the necessary conditions of spectral and hyperbolic
stability, together with transversality of the connecting profile, we establish
detailed pointwise estimates on perturbations from a sum of the viscous shock
profile under consideration and a family of diffusion waves which propagate
perturbation signals along outgoing characteristics. Our approach combines the
recent -space analysis of Raoofi [ Asympototic Behavior of Perturbed
Viscous Shock Profiles, to appear J. Hyperbolic Differential Equations] with a
straightforward bootstrapping argument that relies on a refined description of
nonlinear signal interactions, which we develop through convolution estimates
involving Green's functions for the linear evolutionary PDE that arises upon
linearization of the regularized conservation law about the distinguished
profile. Our estimates are similar to, though slightly weaker than, those
developed by Liu in his landmark result on the case of weak Lax type profiles
arising in the case of identity viscosity [Pointwise Convergence to Shock Waves
for Viscous Conservation Laws, Comm. Pure Appl. Math. 50 (1997) 1113--1182]
Event-triggered gain scheduling of reaction-diffusion PDEs
This paper deals with the problem of boundary stabilization of 1D
reaction-diffusion PDEs with a time- and space- varying reaction coefficient.
The boundary control design relies on the backstepping approach. The gains of
the boundary control are scheduled under two suitable event-triggered
mechanisms. More precisely, gains are computed/updated on events according to
two state-dependent event-triggering conditions: static-based and dynamic-based
conditions, under which, the Zeno behavior is avoided and well-posedness as
well as exponential stability of the closed-loop system are guaranteed.
Numerical simulations are presented to illustrate the results.Comment: 20 pages, 5 figures, submitted to SICO
Testing numerical relativity with the shifted gauge wave
Computational methods are essential to provide waveforms from coalescing
black holes, which are expected to produce strong signals for the gravitational
wave observatories being developed. Although partial simulations of the
coalescence have been reported, scientifically useful waveforms have so far not
been delivered. The goal of the AppleswithApples (AwA) Alliance is to design,
coordinate and document standardized code tests for comparing numerical
relativity codes. The first round of AwA tests have now being completed and the
results are being analyzed. These initial tests are based upon periodic
boundary conditions designed to isolate performance of the main evolution code.
Here we describe and carry out an additional test with periodic boundary
conditions which deals with an essential feature of the black hole excision
problem, namely a non-vanishing shift. The test is a shifted version of the
existing AwA gauge wave test. We show how a shift introduces an exponentially
growing instability which violates the constraints of a standard harmonic
formulation of Einstein's equations. We analyze the Cauchy problem in a
harmonic gauge and discuss particular options for suppressing instabilities in
the gauge wave tests. We implement these techniques in a finite difference
evolution algorithm and present test results. Although our application here is
limited to a model problem, the techniques should benefit the simulation of
black holes using harmonic evolution codes.Comment: Submitted to special numerical relativity issue of Classical and
Quantum Gravit
Lectures on Linear Stability of Rotating Black Holes
These lecture notes are concerned with linear stability of the non-extreme
Kerr geometry under perturbations of general spin. After a brief review of the
Kerr black hole and its symmetries, we describe these symmetries by Killing
fields and work out the connection to conservation laws. The Penrose process
and superradiance effects are discussed. Decay results on the long-time
behavior of Dirac waves are outlined. It is explained schematically how the
Maxwell equations and the equations for linearized gravitational waves can be
decoupled to obtain the Teukolsky equation. It is shown how the Teukolsky
equation can be fully separated to a system of coupled ordinary differential
equations. Linear stability of the non-extreme Kerr black hole is stated as a
pointwise decay result for solutions of the Cauchy problem for the Teukolsky
equation. The stability proof is outlined, with an emphasis on the underlying
ideas and methods.Comment: 25 pages, LaTeX, 3 figures, lectures given at first DOMOSCHOOL in
July 2018, minor improvements (published version
A Space-time Smooth Artificial Viscosity Method For Nonlinear Conservation Laws
We introduce a new methodology for adding localized, space-time smooth,
artificial viscosity to nonlinear systems of conservation laws which propagate
shock waves, rarefactions, and contact discontinuities, which we call the
-method. We shall focus our attention on the compressible Euler equations in
one space dimension. The novel feature of our approach involves the coupling of
a linear scalar reaction-diffusion equation to our system of conservation laws,
whose solution is the coefficient to an additional (and artificial)
term added to the flux, which determines the location, localization, and
strength of the artificial viscosity. Near shock discontinuities, is
large and localized, and transitions smoothly in space-time to zero away from
discontinuities. Our approach is a provably convergent, spacetime-regularized
variant of the original idea of Richtmeyer and Von Neumann, and is provided at
the level of the PDE, thus allowing a host of numerical discretization schemes
to be employed. We demonstrate the effectiveness of the -method with three
different numerical implementations and apply these to a collection of
classical problems: the Sod shock-tube, the Osher-Shu shock-tube, the
Woodward-Colella blast wave and the Leblanc shock-tube. First, we use a
classical continuous finite-element implementation using second-order
discretization in both space and time, FEM-C. Second, we use a simplified WENO
scheme within our -method framework, WENO-C. Third, we use WENO with the
Lax-Friedrichs flux together with the -equation, and call this WENO-LF-C.
All three schemes yield higher-order discretization strategies, which provide
sharp shock resolution with minimal overshoot and noise, and compare well with
higher-order WENO schemes that employ approximate Riemann solvers,
outperforming them for the difficult Leblanc shock tube experiment.Comment: 34 pages, 27 figure
A Parallel Mesh-Adaptive Framework for Hyperbolic Conservation Laws
We report on the development of a computational framework for the parallel,
mesh-adaptive solution of systems of hyperbolic conservation laws like the
time-dependent Euler equations in compressible gas dynamics or
Magneto-Hydrodynamics (MHD) and similar models in plasma physics. Local mesh
refinement is realized by the recursive bisection of grid blocks along each
spatial dimension, implemented numerical schemes include standard
finite-differences as well as shock-capturing central schemes, both in
connection with Runge-Kutta type integrators. Parallel execution is achieved
through a configurable hybrid of POSIX-multi-threading and MPI-distribution
with dynamic load balancing. One- two- and three-dimensional test computations
for the Euler equations have been carried out and show good parallel scaling
behavior. The Racoon framework is currently used to study the formation of
singularities in plasmas and fluids.Comment: late submissio
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