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Fazel Hadadifard

Publications and source records attributed to Fazel Hadadifard.

9 recordsLinked to original sources
arXiv2025

Horizontally periodic generalized surface quasigeostrophic patches and layers

We study solutions to the $\alpha$-SQG equations, which interpolate between the incompressible Euler and surface quasi-geostrophic equations. We extend prior results on existence of bounded patches, proving propagation of $H^k$-regularity of the patch boundary, $k \ge 3$, for finite time for patches that are periodic in one spatial dimension. Such periodic patches also encompass layers, or two-sided fronts. As the authors have treated the Euler case in prior work, we now primarily focus on the range of $\alpha$ for which $\alpha$-SQG lies strictly between the Euler and SQG equations.

math.AP↗
arXiv2022

Contour dynamics and global regularity for periodic vortex patches and layers

We study vortex patches for the 2D incompressible Euler equations. Prior works on this problem take the support of the vorticity (i.e., the vortex patch) to be a bounded region. We instead consider the horizontally periodic setting. This includes both the case of a periodic array of bounded vortex patches and the case of vertically bounded vortex layers. We develop the contour dynamics equation for the boundary of the patch in this horizontally periodic setting, and demonstrate global $C^{1,ε}$ regularity of this patch boundary. In the process of formulating the problem, we consider different notions of periodic solutions of the 2D incompressible Euler equations, and demonstrate equivalence of these.

math.AP↗
arXiv2021

A class of Finite difference Methods for solving inhomogeneous damped wave equations

In this paper, a class of finite difference numerical techniques is presented to solve the second-order linear inhomogeneous damped wave equation. The consistency, stability, and convergences of these numerical schemes are discussed. The results obtained are compared to the exact solution, ordinary explicit, implicit finite difference methods, and the fourth-order compact method (FOCM). The general idea of these methods is developed by using the C0-semigroups operator theory. We also showed that the stability region for the explicit finite difference scheme depends on the damping coefficient.

math.NA↗
arXiv2020

Well-posedness and asymptotics of a coordinate-free model of flame fronts

We investigate a coordinate-free model of flame fronts introduced by Frankel and Sivashinsky; this model has a parameter $α$ which relates to how unstable the front might be. We first prove short-time well-posedness of the coordinate-free model, for any value of $α>0.$ We then argue that near the threshold $α\approx 1,$ the solution stays arbitrarily close to the solution of the weakly nonlinear Kuramoto--Sivashinsky (KS) equation, as long as the initial values are close.

math.AP↗
arXiv2020

Mass-in-Mass Lattices with Small Internal Resonators

We consider the mass-in-mass (MiM) lattice when the internal resonators are very small. When there are no internal resonators the lattice reduces to a standard Fermi-Pasta-Ulam-Tsingou (FPUT) system. We show that the solution of the MiM system, with suitable initial data, shadows the FPUT system for long periods of time. Using some classical oscillatory integral estimates we can conclude that the error of the approximation is (in some settings) higher than one may expect.

math.AP↗
arXiv2020

On the forced surface quasi-geostrophic equation: Existence of steady states and sharp relaxation rates

We consider the asymptotic behavior of the surface quasi-geostrophic equation, subject to a small external force. Under suitable assumptions on the forcing, we first construct the steady states and we provide a number of useful a posteriori estimates for them. Importantly, to do so, we only impose minimal cancellation conditions on the forcing function. Our main result is that all $L^1\cap L^\infty$ localized initial data produces global solutions of the forced SQG, which converge to the steady states in $L^p(\mathbf R^2), 1<p\leq 2$ as time goes to infinity. This establishes that the steady states serve as one point attracting set. Moreover, by employing the method of scaling variables, we compute the sharp relaxation rates, by requiring slightly more localized initial data.

math.AP↗
arXiv2019

Sharp relaxation rates for plane waves of reaction-diffusion systems

It is well-known and classical result that spectrally stable traveling waves of a general reaction-diffusion system in one spatial dimension are asymptotically stable with exponential relaxation rates. In a series of works in the 1990's, the authors have considered plane traveling waves for such systems and they have succeeded in showing asymptotic stability for such objects. Interestingly, the (estimates for the) relaxation rates that they have exhibited, are all algebraic and dimension dependent. It was heuristically argued that as the spectral gap closes in dimensions $n\geq 2$, algebraic rates are the best possible. In this paper, we revisit this issue. We rigorously calculate the sharp relaxation rates in $L^\infty$ based spaces, both for the asymptotic phase and the radiation terms. These turn out to be are indeed algebraic, but about twice better than the best ones obtained in these early works, although this can be mostly attributed to the inefficiencies of using Sobolev embeddings to control $L^\infty$ norms by high order $L^2$ based Sobolev space norms. Finally, we explicitly construct the leading order profiles, both for the phase and the radiation terms. Our approach relies on the method of scaling variables, which provides sharp relaxation rates in a class of weighted $L^2$ spaces as well.

math.AP↗
arXiv2016

On the global regularity of the 2D critical Boussinesq system with $α>2/3$

This paper examines the question for global regularity for the Boussinesq equation with critical fractional dissipation. The main result states that the system admits global regular solutions for all (reasonably) smooth and decaying data, as long as $\al>2/3$. This significantly improves upon some recent works. The main new idea is the introduction of a new, second generation Hmidi-Keraani-Rousset type, change of variables, which further improves the linear derivative in temperature term in the vorticity equation. This approach is then complemented by new set of commutator estimates, which may be of independent interest.

math.AP↗