arXiv subjects

Zhouping Xin

Publications and source records attributed to Zhouping Xin.

At least 19 recordsLinked to original sources

arXiv2026

Expanding solutions to the compressible Navier-Stokes equations with degenerate viscosities in spherical symmetry: global existence and inviscid limit

This paper is devoted to studying the strong solutions to the vacuum free boundary problem for the isentropic compressible Navier-Stokes equations with density-dependent viscosities under spherical symmetry, which models the motions of isentropic compressible viscous flows surrounded by vacuum. We construct a class of expanding global solutions when the initial data is a small perturbation of the expanding affine solutions for the adiabatic exponent $γ>1$ and the viscosity coefficients proportional to $ρ^γ$, with $ρ$ being the fluid density. In addition, when the viscosity coefficients tend to zero, the perturbed solutions are proved to converge to the solutions to the compressible Euler equations with an explicit converging rate of viscosity coefficients.

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arXiv2026

Shock formation for 3D steady supersonic flows with general short pulse data

This paper concerns the shock formation problem for the 3D steady supersonic potential equation of polytropic gases. The potential equation is described by a second order quasilinear wave equation $\displaystyle\sum_{i=1}^{3}\big[(\partial_iΦ)^2 - c^2(ρ)\big]\partial_i^2Φ+ 2\displaystyle\sum_{1\le i 1$), and $\partial_3Φ> c(ρ)$. For the short pulse boundary data $Φ|_{x^3=0} = δ^νΦ_0\big(\frac{r-1}δ,ω\big)$ and $\partial_3Φ|_{x^3=0}=q_0+δ^{ν-1}Φ_1\big(\frac{r-1}δ,ω\big)$ with $r=\sqrt{(x^1)^2+(x^2)^2}$, $ω=\big(\frac{x^1}{r},\frac{x^2}{r}\big)\in\mathbb{S}$, $1<ν<2$ and small $δ>0$, it is shown that a shock will be formed in a finite $x^3$-distance as long as the boundary data are supersonic and satisfy $(Φ_0,Φ_1)\not\equiv 0$. This coincides with physical phenomenon that strong compression of supersonic polytropic gases yields shocks. One of our main ingredients is to find a good unknown so that the previously imposed compatibility conditions on the short pulse initial data are removed as well as the required weighted energy estimates in the existing literatures are derived. It is expected that the method here will be applied to study the shock formation problem with general short pulse initial data for the 3D steady supersonic Euler equations of polytropic gases.

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arXiv2026

Enhanced stability and asymptotic limits to the non-isentropic compressible fluid-particle interaction model with thermal effects

In Einstein's seminal work [Ann. Physik, 17 (1905), 549-560], he pointed out that the temperature of a fluid influences the motion of suspended particles dramatically. To describe the effect of the temperature in this physical process more precisely, Boudin et al. [ESAIM Proc., 28 (2009), 195-210] introduced a new fluid-particle interaction model containing of the non-isentropic compressible Euler equations for the fluid and a nonlinear Vlasov-Fokker-Planck type equation for the particles. By adding some viscous and heat conductive terms to the fluid part of this model, Mu and Wang [Calc. Var. Partial Differential Equations, 59 (2020), Paper no. 110] established the global existence of classical solutions near an equilibrium state. In this paper, through establishing the uniform a priori estimates with respect to the viscosity and heat conductivity coefficients and taking the combined zero viscosity and heat conductivity limits, we show that the model introduced by Boudin et al. still admits a global classical solution and enjoys optimal decay rates thereby improving Mu and Wang's results and confirming Einstein's predications. Our work indicates that the presence of particles indeed emanates new dissipation effects on the non-isentropic compressible fluid-particle model via the differences between the macroscopic velocity of the particles and the fluid velocity, and the macroscopic temperature of the particles and the fluid temperature, which is significantly different from the case of pure non-isentropic compressible Euler equations. To achieve these goals, we have developed new ideas and techniques to surmount substantial obstacles caused by the absence of viscosity and heat conductivity, and the nonlinear interactions between the fluid and particles.

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arXiv2025

Asymptotic stability of the equilibrium for the free boundary problem of a compressible atmospheric primitive model with physical vacuum

This paper concerns the large time asymptotic behavior of solutions to the free boundary problem of the compressible primitive equations in atmospheric dynamics with physical vacuum. Up to second order of the perturbations of an equilibrium, we have introduced a model of the compressible primitive equations with a specific viscosity and shown that the physical vacuum free boundary problem for this model system has a global-in-time solution converging to an equilibrium exponentially, provided that the initial data is a small perturbation of the equilibrium. More precisely, we introduce a new coordinate system by choosing the enthalpy (the square of sound speed) as the vertical coordinate, and thanks to the hydrostatic balance, the degenerate density at the free boundary admits a representation with separation of variables in the new coordinates. Such a property allows us to establish horizontal derivative estimates without involving the singular vertical derivative of the density profile, which plays a key role in our analysis.

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arXiv2025

Global smooth solutions to 4D quasilinear wave equations with short pulse initial data

In this paper, we establish the global existence of smooth solutions to general 4D quasilinear wave equations satisfying the first null condition with the short pulse initial data. Although the global existence of small data solutions to 4D quasilinear wave equations holds true without any requirement of null conditions, yet for short pulse data, in general, it is sufficient and necessary to require the fulfillment of the first null condition to have global smooth solutions. It is noted that short pulse data are extensions of a class of spherically symmetric data, for which the smallness restrictions are imposed on angular directions and along the outgoing directional derivative $\partial_t+\partial_r$, but the largeness is kept for the incoming directional derivative $\partial_t-\partial_r$. We expect that here methods can be applied to study the global smooth solution or blowup problem with short pulse initial data for the general 2D and 3D quasilinear wave equations when the corresponding null conditions hold or not. On the other hand, as some direct applications of our main results, one can show that for the short pulse initial data, the smooth solutions to the 4D irrotational compressible Euler equations for Chaplygin gases, 4D nonlinear membrane equations and 4D relativistic membrane equations exist globally since their nonlinearities satisfy the first null condition; while the smooth solutions to the 4D irrotational compressible Euler equations for polytropic gases generally blow up in finite time since the corresponding first null condition does not hold.

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arXiv2025

Global well-posedness of the Cauchy problem for the modified Whitham equations

This paper aims to show global existence and modified scattering for the solutions of the Cauchy problem to the modified Whitham equations for small, smooth and localized initial data. The main difficulties come from slow decay and non-homogeneity of the Fourier multiplier $(\sqrt{\tanh ξ/ξ})ξ$, which will be overcome by introducing an interaction multiplier theorem and estimating the weighted norms in the frequency space. When estimating the weighted norms, due to loss of derivatives, the energy estimate will be performed in the frequency space, and the absence of time resonance will be effectively utilized by extracting some good terms arising from integration by parts in time before the energy estimate.

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arXiv2025

Refined regularity for nonlocal elliptic equations and applications

In this paper, we establish refined regularity estimates for nonnegative solutions to the fractional Poisson equation $$ (-Δ)^s u(x) =f(x),\,\, x\in B_1(0). $$ Specifically, we have derived Hölder, Schauder, and Ln-Lipschitz regularity estimates for any nonnegative solution $u,$ provided that only the local $L^\infty$ norm of $u$ is bounded. These estimates stand in sharp contrast to the existing results where the global $L^\infty$ norm of $u$ is required. Our findings indicate that the local values of the solution $u$ and $f$ are sufficient to control the local values of higher order derivatives of $u$. Notably, this makes it possible to establish a priori estimates in unbounded domains by using blowing up and re-scaling argument. As applications, we derive singularity and decay estimates for solutions to some super-linear nonlocal problems in unbounded domains, and in particular, we obtain a priori estimates for a family of fractional Lane-Emden type equations in $\mathbb{R}^n.$ This is achieved by adopting a different method using auxiliary functions, which is applicable to both local and nonlocal problems.

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arXiv2024

Some three dimensional smooth transonic flows for the steady Euler equations with an external force

We establish the existence and uniqueness of some smooth accelerating transonic flows governed by the three dimensional steady compressible Euler equations with an external force in cylinders with arbitrary cross sections, which include both irrotational flows and Beltrami flows with nonuniform proportionality factors. One of the key ingredients in the analysis of smooth transonic irrotational flows is the well-posedness theory of classical solutions in $H^4$ to a linear elliptic-hyperbolic mixed second order differential equation of Keldysh type in cylinders with mixed boundary conditions. This is achieved by extending the problem to an auxiliary linear elliptic-hyberbolic-elliptic mixed problem in a longer cylinder where the governing equation becomes elliptic at the exit of the new cylinder, so that one can use the multiplier method and the cut-off techniques to derive the $H^2$ and higher order estimates in transonic regions. It is further shown that the energy estimate can be closed in the $H^4$ framework. For smooth transonic Beltrami flows, we solve a transport equation for the proportionality factor and a type-changing enlarged deformation-curl system with mixed boundary conditions. The compatibility conditions for the $H^4$ estimate to the enlarged deformation-curl system near the intersection between the entrance and the cylinder wall play a crucial role in the analysis.

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arXiv2024

Global weak solutions with higher regularity to the compressible Navier-Stokes equations under Dirichlet boundary conditions

In this manuscript, we aim to establish global existence of weak solutions with higher regularity to the compressible Navier-Stokes equations under no-slip boundary conditions. Though Lions\cite{L1} and Feireisl\cite{F1} have established global weak solutions with finite energy under Dirichelet boundary conditions by making use of so called effective viscous flux and oscillation defect measure,Hoff has investigated global weak solutions with higher regularity in \cite{H1,Hof2} when the domain is either whole space or half space with Navier-slip boundary conditions, yet the existence theory of global weak solution with higher regularity under Dirichlet boundary conditions remains unknown. In this paper we prove that the system will admit at least one global weak solutions with higher regularity as long as the initial energy is suitably small when the domain is a 2D solid disc. This is achieved by exploiting the structure of the exact Green function of the disc to decompose the effective viscous flux into three parts, which corresponds to the pressure term, boundary term and the remaining term respectively. In order to control the boundary term, one of the key observations is to use the geometry of the domain which sucessfully to bound the integral of the effective viscous flux where $L^1$ norm is always unbounded.

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arXiv2024

Finite time blowup of strong solutions to the two dimensional MHD equations

Whether the smooth solution of the multi-dimensional viscous compressible fluids will blow-up in finite time has always been a chanllenging problem. In the recent work\cite{FM}, Merle et al. proved that there are smooth solutions to the 2D radially symmetric compressible Navier-Stokes equations which will inevitably form shell singularities in finite time.\\ \indent In this article, we first prove the existence of local strong solutions that allow vacuum for the two-dimensional viscous compressible MHD equations on bounded domains without magnetic diffusion. Furthermore, it is shown that if the initial data are radial symmetric and its vacuum set contains a ball centered at the origin where the total magnetic field is non-trivial, then the radial symmetric strong solution to the initial boundary value problem will definitely blow up in finite time. This is the first example for the formation of finite time singularity of strong solutions that allows interior vacuum of a viscous compressible fluid.

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arXiv2024

Global smooth solutions of 2D quasilinear wave equations with higher order null conditions and short pulse initial data

For the short pulse initial data with a first order outgoing constraint condition and optimal orders of smallness, we establish the global existence of smooth solutions to 2D quasilinear wave equations with higher order null conditions. Such kinds of wave equations include 2D relativistic membrane equations, 2D membrane equations, and some 2D quasilinear equations which come from the nonlinear Maxwell equations in electromagnetic theory or from the corresponding Lagrangian functionals as perturbations of the Lagrangian densities of linear wave operators. The main ingredients of the analysis here include looking for a new good unknown, finding some key identities based on the higher order null conditions and the resulting null frames, as well as overcoming the difficulties due to the slow decay of solutions to the 2-D wave equation, so that the solutions can be estimated precisely.

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arXiv2024

Well-posedness of regular solutions for 3-D full compressible Navier-Stokes equations with degenerate viscosities and heat conductivity

For the degenerate viscous and heat conductive compressible fluids, the momentum equations and the energy equation are degenerate both in the time evolution and spatial dissipation when vacuum appears, and then the physical entropy S behaves singularly, which make it challenging to study the corresponding well-posedness of regular solutions with high order regularities of S near the vacuum. In this paper, for the physically important case that the coefficients of viscosities and heat conductivity depend on the absolute temperature θin a power law of Chapman-Enskog, we identify a class of initial data admitting a local-in-time regular solution with far field vacuum to the Cauchy problem of the 3-D full CNS, and such a solution possesses the uniformly high order regularities for S near the vacuum. The key idea here is to study the vacuum problem in terms of the mass density ρ, velocity u and S instead of (ρ, u,θ), which makes it possible to compare the orders of the degeneracy of the time evolution and the spatial dissipations near the vacuum in terms of the powers of ρ. However, for heat conductive fluids, both a degenerate spatial dissipation and a source term related to \triangle ρ^{γ-1}, will appear in the time evolution equation for S, which makes it formidable to study the propagation of regularities of S. Fortunately, based on some elaborate analysis of the intrinsic degenerate-singular structures of the 3-D full CNS, we can choose proper weights to control the behaviors of (ρ, u,S) by introducing an enlarged reformulated system, which includes a singular parabolic system for u, and one degenerate-singular parabolic equation for S. Then one can carry out a series of weighted energy estimates carefully designed for this reformulated system, which provides an effective propagation mechanism for S's high order regularities near the vacuum.

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arXiv2024

On global smooth solutions to the 2D isentropic and irrotational Chaplygin gases with short pulse data

This paper establishes the global existence of smooth solutions to the 2D isentropic and irrotational Euler equations for Chaplygin gases with a general class of short pulse initial data, which, in particular, resolves in this special case, the Majda's conjecture on the non-formation of shock waves of solutions from smooth initial data for multi-dimensional nonlinear symmetric systems which are totally linearly degenerate. Comparing to the 4D case, the major difficulties in this paper are caused by the slower time decay and the largeness of the solutions to the 2D quasilinear wave equation, some new auxiliary energies and multipliers are introduced to overcome these difficulties.

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arXiv2024

Existence and stability of cylindrical transonic shock solutions under three dimensional perturbations

We establish the existence and stability of cylindrical transonic shock solutions under three dimensional perturbations of the incoming flows and the exit pressure without any further restrictions on the background transonic shock solutions. The strength and position of the perturbed transonic shock are completely free and uniquely determined by the incoming flows and the exit pressure. The optimal regularity is obtained for all physical quantities, and the velocity, the Bernoulli's quantity, the entropy and the pressure share the same regularity. The approach is based on the deformation-curl decomposition to the steady Euler system introduced by the authors to decouple the hyperbolic and elliptic modes effectively. However, one of the key elements in application of the deformation-curl decomposition is to find a decomposition of the Rankine-Hugoniot conditions, which shows the mechanism of determining the shock front uniquely by an algebraic equation and also gives an unusual second order differential boundary conditions on the shock front for the first order deformation-curl system. After homogenizing the curl system and introducing a potential function, this unusual condition on the shock front becomes the Poisson equation with homogeneous Neumann boundary condition on the intersection of the shock front and the cylinder walls from which an oblique boundary condition for the potential function can be uniquely derived.

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arXiv2023

Smooth transonic flows with nonzero vorticity to a quasi two dimensional steady Euler flow model

This paper concerns studies on smooth transonic flows with nonzero vorticity in De Laval nozzles for a quasi two dimensional steady Euler flow model which is a generalization of the classical quasi one dimensional model. First, the existence and uniqueness of smooth transonic flows to the quasi one-dimensional model, which start from a subsonic state at the entrance and accelerate to reach a sonic state at the throat and then become supersonic are proved by a reduction of degeneracy of the velocity near the sonic point and the implicit function theorem. These flows can have positive or zero acceleration at their sonic points and the degeneracy types near the sonic point are classified precisely. We then establish the structural stability of the smooth one dimensional transonic flow with positive acceleration at the sonic point for the quasi two dimensional steady Euler flow model under small perturbations of suitable boundary conditions, which yields the existence and uniqueness of a class of smooth transonic flows with nonzero vorticity and positive acceleration to the quasi two dimensional model. The positive acceleration of the one dimensional transonic solutions plays an important role in searching for an appropriate multiplier for the linearized second order mixed type equations. A deformation-curl decomposition for the quasi two dimensional model is utilized to deal with the transonic flows with nonzero vorticity.

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arXiv2023

A conservative hybrid physics-informed neural network method for Maxwell-Ampère-Nernst-Planck equations

Maxwell-Ampère-Nernst-Planck (MANP) equations were recently proposed to model the dynamics of charged particles. In this study, we enhance a numerical algorithm of this system with deep learning tools. The proposed hybrid algorithm provides an automated means to determine a proper approximation for the dummy variables, which can otherwise only be obtained through massive numerical tests. In addition, the original method is validated for 2-dimensional problems. However, when the spatial dimension is one, the original curl-free relaxation component is inapplicable, and the approximation formula for dummy variables, which works well in a 2-dimensional scenario, fails to provide a reasonable output in the 1-dimensional case. The proposed method can be readily generalised to cases with one spatial dimension. Experiments show numerical stability and good convergence to the steady-state solution obtained from Poisson-Boltzmann type equations in the 1-dimensional case. The experiments conducted in the 2-dimensional case indicate that the proposed method preserves the conservation properties.

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arXiv2023

Local Well-posedness of the Incompressible Current-Vortex Sheet Problems

We prove the local well-posedness of the incompressible current-vortex sheet problems in standard Sobolev spaces under the surface tension or the Syrovatskij condition, which shows that both capillary forces and large tangential magnetic fields can stabilize the motion of current-vortex sheets. Furthermore, under the Syrovatskij condition, the vanishing surface tension limit is established for the motion of current-vortex sheets. These results hold without assuming the interface separating the two plasmas being a graph.

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arXiv2023

On the Free Boundary Problems for the Ideal Incompressible MHD Equations

We investigate the general plasma-vacuum interface problems for the ideal incompressible MHD equations with or without surface tension and prove their nonlinear local well-posedness in standard Sobolev spaces under either non-zero surface tension or the stability condition that the magnetic fields are everywhere non-collinear on the interface. In particular, the results show that both capillary forces and tangential magnetic fields can stabilize the motion of the plasma-vacuum interfaces. Moreover, the vanishing surface tension limit results are established under the Rayleigh-Taylor sign condition or the non-collinearity condition. All these results hold with no graph assumption on the free interface.

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