487 research outputs found
A model for Faraday pilot waves over variable topography
Couder and Fort discovered that droplets walking on a vibrating bath possess
certain features previously thought to be exclusive to quantum systems. These
millimetric droplets synchronize with their Faraday wavefield, creating a
macroscopic pilot-wave system. In this paper we exploit the fact that the waves
generated are nearly monochromatic and propose a hydrodynamic model capable of
quantitatively capturing the interaction between bouncing drops and a variable
topography. We show that our reduced model is able to reproduce some important
experiments involving the drop-topography interaction, such as non-specular
reflection and single-slit diffraction
Harmonic density interpolation methods for high-order evaluation of Laplace layer potentials in 2D and 3D
We present an effective harmonic density interpolation method for the
numerical evaluation of singular and nearly singular Laplace boundary integral
operators and layer potentials in two and three spatial dimensions. The method
relies on the use of Green's third identity and local Taylor-like
interpolations of density functions in terms of harmonic polynomials. The
proposed technique effectively regularizes the singularities present in
boundary integral operators and layer potentials, and recasts the latter in
terms of integrands that are bounded or even more regular, depending on the
order of the density interpolation. The resulting boundary integrals can then
be easily, accurately, and inexpensively evaluated by means of standard
quadrature rules. A variety of numerical examples demonstrate the effectiveness
of the technique when used in conjunction with the classical trapezoidal rule
(to integrate over smooth curves) in two-dimensions, and with a Chebyshev-type
quadrature rule (to integrate over surfaces given as unions of non-overlapping
quadrilateral patches) in three-dimensions
Theory of weakly nonlinear self sustained detonations
We propose a theory of weakly nonlinear multi-dimensional self sustained
detonations based on asymptotic analysis of the reactive compressible
Navier-Stokes equations. We show that these equations can be reduced to a model
consisting of a forced, unsteady, small disturbance, transonic equation and a
rate equation for the heat release. In one spatial dimension, the model
simplifies to a forced Burgers equation. Through analysis, numerical
calculations and comparison with the reactive Euler equations, the model is
demonstrated to capture such essential dynamical characteristics of detonations
as the steady-state structure, the linear stability spectrum, the
period-doubling sequence of bifurcations and chaos in one-dimensional
detonations and cellular structures in multi- dimensional detonations
Theory of weakly nonlinear self-sustained detonations
We propose a theory of weakly nonlinear multidimensional self-sustained detonations based on asymptotic analysis of the reactive compressible Navier-Stokes equations. We show that these equations can be reduced to a model consisting of a forced unsteady small-disturbance transonic equation and a rate equation for the heat release. In one spatial dimension, the model simplifies to a forced Burgers equation. Through analysis, numerical calculations and comparison with the reactive Euler equations, the model is demonstrated to capture such essential dynamical characteristics of detonations as the steady-state structure, the linear stability spectrum, the period-doubling sequence of bifurcations and chaos in one-dimensional detonations and cellular structures in multidimensional detonations
General-purpose kernel regularization of boundary integral equations via density interpolation
This paper presents a general high-order kernel regularization technique
applicable to all four integral operators of Calder\'on calculus associated
with linear elliptic PDEs in two and three spatial dimensions. Like previous
density interpolation methods, the proposed technique relies on interpolating
the density function around the kernel singularity in terms of solutions of the
underlying homogeneous PDE, so as to recast singular and nearly singular
integrals in terms of bounded (or more regular) integrands. We present here a
simple interpolation strategy which, unlike previous approaches, does not
entail explicit computation of high-order derivatives of the density function
along the surface. Furthermore, the proposed approach is kernel- and
dimension-independent in the sense that the sought density interpolant is
constructed as a linear combination of point-source fields, given by the same
Green's function used in the integral equation formulation, thus making the
procedure applicable, in principle, to any PDE with known Green's function. For
the sake of definiteness, we focus here on Nystr\"om methods for the (scalar)
Laplace and Helmholtz equations and the (vector) elastostatic and time-harmonic
elastodynamic equations. The method's accuracy, flexibility, efficiency, and
compatibility with fast solvers are demonstrated by means of a variety of
large-scale three-dimensional numerical examples
Influence of chemistry on the steady solutions of hydrogen gaseous detonations with friction losses
Agence Nationale de la Recherche | Ref. FASTD ANR-20-CE05-0011-0
A complex-scaled boundary integral equation for time-harmonic water waves
This paper presents a novel boundary integral equation (BIE) formulation for
the two-dimensional time-harmonic water-waves problem. It utilizes a
complex-scaled Laplace's free-space Green's function, resulting in a BIE posed
on the infinite boundaries of the domain. The perfectly matched layer (PML)
coordinate stretching that is used to render propagating waves exponentially
decaying, allows for the effective truncation and discretization of the BIE
unbounded domain. We show through a variety of numerical examples that, despite
the logarithmic growth of the complex-scaled Laplace's free-space Green's
function, the truncation errors are exponentially small with respect to the
truncation length. Our formulation uses only simple function evaluations (e.g.
complex logarithms and square roots), hence avoiding the need to compute the
involved water-wave Green's function. Finally, we show that the proposed
approach can also be used to find complex resonances through a \emph{linear}
eigenvalue problem since the Green's function is frequency-independent
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