1,410 research outputs found
Geometrically-exact time-integration mesh-free schemes for advection-diffusion problems derived from optimal transportation theory and their connection with particle methods
We develop an Optimal Transportation Meshfree (OTM) particle method for
advection-diffusion in which the concentration or density of the diffusive
species is approximated by Dirac measures. We resort to an incremental
variational principle for purposes of time discretization of the diffusive
step. This principle characterizes the evolution of the density as a
competition between the Wasserstein distance between two consecutive densities
and entropy. Exploiting the structure of the Euler-Lagrange equations, we
approximate the density as a collection of Diracs. The interpolation of the
incremental transport map is effected through mesh-free max-ent interpolation.
Remarkably, the resulting update is geometrically exact with respect to
advection and volume. We present three-dimensional examples of application that
illustrate the scope and robustness of the method.Comment: 19 pages, 8 figure
Anti-selfdual Lagrangians: Variational resolutions of non self-adjoint equations and dissipative evolutions
We develop the concept and the calculus of anti-self dual (ASD) Lagrangians
which seems inherent to many questions in mathematical physics, geometry, and
differential equations. They are natural extensions of gradients of convex
functions --hence of self-adjoint positive operators-- which usually drive
dissipative systems, but also rich enough to provide representations for the
superposition of such gradients with skew-symmetric operators which normally
generate unitary flows. They yield variational formulations and resolutions for
large classes of non-potential boundary value problems and initial-value
parabolic equations. Solutions are minima of functionals of the form (resp. )
where is an anti-self dual Lagrangian and where are
essentially skew-adjoint operators. However, and just like the self (and
antiself) dual equations of quantum field theory (e.g. Yang-Mills) the
equations associated to such minima are not derived from the fact they are
critical points of the functional , but because they are also zeroes of the
Lagrangian itself.Comment: 50 pages. For the most updated version of this paper, please visit
http://www.pims.math.ca/~nassif/pims_papers.htm
Variational Data Assimilation via Sparse Regularization
This paper studies the role of sparse regularization in a properly chosen
basis for variational data assimilation (VDA) problems. Specifically, it
focuses on data assimilation of noisy and down-sampled observations while the
state variable of interest exhibits sparsity in the real or transformed domain.
We show that in the presence of sparsity, the -norm regularization
produces more accurate and stable solutions than the classic data assimilation
methods. To motivate further developments of the proposed methodology,
assimilation experiments are conducted in the wavelet and spectral domain using
the linear advection-diffusion equation
A variational approach to Navier-Stokes
We present a variational resolution of the incompressible Navier-Stokes
system by means of stabilized Weighted-Inertia-Dissipation-Energy (WIDE)
functionals. The minimization of these parameter-dependent functionals
corresponds to an elliptic-in-time regularization of the system. By passing to
the limit in the regularization parameter along subsequences of WIDE minimizers
one recovers a classical Leray-Hopf weak solution
Space-modulated Stability and Averaged Dynamics
In this brief note we give a brief overview of the comprehensive theory,
recently obtained by the author jointly with Johnson, Noble and Zumbrun, that
describes the nonlinear dynamics about spectrally stable periodic waves of
parabolic systems and announce parallel results for the linearized dynamics
near cnoidal waves of the Korteweg-de Vries equation. The latter are expected
to contribute to the development of a dispersive theory, still to come.Comment: Proceedings of the "Journ\'ees \'Equations aux d\'eriv\'ees
partielles", Roscoff 201
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