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Zhifei Zhang

Publications and source records attributed to Zhifei Zhang.

At least 199 records · Page 11Linked to original sources
arXiv2015

Local well-posedness and break-down criterion of the incompressible Euler equations with free boundary

In this paper, we prove the local well-posedness of the free boundary problem for the incompressible Euler equations in low regularity Sobolev spaces, in which the velocity is a Lipschtiz function and the free surface belongs to $C^{\f32+\varepsilon}$. Moreover, we also present a Beale-Kato-Majda type break-down criterion of smooth solution in terms of the mean curvature of the free surface, the gradient of the velocity and Taylor sign condition.

math.AP↗
arXiv2015

From the Q-tensor flow for the liquid crystal to the Harmonic map flow

In this paper, we consider the solutions of the relaxed Q-tensor flow in $\R^3$ with small parameter $ε$. Firstly, we show that the limiting map is the so called harmonic map flow; Secondly, we also present a new proof for the global existence of weak solution for the harmonic map flow in three dimensions as in \cite{struwe88} and \cite{keller}, where Ginzburg-Landau approximation approach was used.

math.AP↗
arXiv2015

Integral Control on Lie Groups

In this paper, we extend the popular integral control technique to systems evolving on Lie groups. More explicitly, we provide an alternative definition of "integral action" for proportional(-derivative)-controlled systems whose configuration evolves on a nonlinear space, where configuration errors cannot be simply added up to compute a definite integral. We then prove that the proposed integral control allows to cancel the drift induced by a constant bias in both first order (velocity) and second order (torque) control inputs for fully actuated systems evolving on abstract Lie groups. We illustrate the approach by 3-dimensional motion control applications.

eess.SY↗
arXiv2014

Dynamics of the Nematic-Isotropic sharp interface for the liquid crystal

In this paper, we derive the sharp interface model of the nematic-isotropic phase transition from the Landau-de Gennes theory by using the matched asymptotic expansion method. The model includes the evolution equation of the velocity and director field of the liquid crystal, the sharp interface and Young-Laplace jump condition on the interface.

math.AP↗
arXiv2014

Long time well-posdness of Prandtl system with small and analytic initial data

In this paper, we investigate the long time existence and uniqueness of small solution to $d,$ for $d=2,3,$ dimensional Prandtl system with small initial data which is analytic in the horizontal variables. In particular, we prove that $d$ dimensional Prandtl system has a unique solution with the life-span of which is greater than $\e^{-\f43}$ if both the initial data and the value on the boundary of the tangential velocity of the outflow are of size $\e.$ We mention that the tool developed in \cite{Ch04, CGP} to make the analytical type estimates and the special structure of the nonlinear terms to this system play an essential role in the proof of this result.

math.AP↗
arXiv2014

Global well-posedness of 3-D inhomogeneous Navier-Stokes equations with ill-prepared initial data

In this paper, we investigate the global well-posedness of 3-D incompressible inhomogeneous Navier-Stokes equations with ill-prepared large initial data which are slowly varying in one space variable, that is, initial data of the form $\bigl(1+\e^{\be}a_0(x_{\rm h},\e x_3),(\ve^{1-\al} v^{\rm h}_0, \ve^{-\al}v_0^3)(x_{\rm h},\e x_3)\bigr)$ for any $\al\in ]0,1/3[,$ $\be>2\al,$ and $\ve$ being sufficiently small. We remark that initial data of this type do not satisfy the smallness conditions in \cite{c-p-z,HPZ3} no matter how small $\e$ is. In particular, this result greatly improves the global well-posedness result in \cite{PZZ3} with the so-called well-prepared initial data.

math.AP↗
arXiv2013

On the ill-posedness of the compressible Navier-Stokes equations in the critical Besov spaces

We prove the ill-posedness of the 3-D baratropic Navier-Stokes equation for the initial density and velocity belonging to the critical Besov space $(\dot{B}^{\f 3p}_{p,1}+\barρ,\,\dot{B}^{\f 3p-1}_{p,1})$ for $p>6$ in the sense that a ``norm inflation" happens in finite time, here $\barρ$ is a positive constant. Our argument also shows that the compressible viscous heat-conductive flows is ill-posed for the initial density, velocity and temperature belonging to the critical Besov space $(\dot{B}^{\f 3p}_{p,1}+\barρ,\,\dot{B}^{\f 3p-1}_{p,1},\,\dot{B}^{\f 3p-2}_{p,1})$ for $p>3$. These results shows that the compressible Navier-Stokes equations are ill-posed in the smaller critical spaces compared with the incompressible Navier-Stokes equations.

math.AP↗
arXiv2013

Break-down criterion for the water-wave equation

We study the break-down mechanism of smooth solution for the gravity water-wave equation of infinite depth. It is proved that if the mean curvature $κ$ of the free surface $Σ_t$, the trace $(V,B)$ of the velocity at the free surface, and the outer normal derivative $\frac {\pa P} {\pa \textbf{n}}$ of the pressure $P$ satisfy \beno &&\displaystyle\sup_{t\in [0,T]}\|κ(t)\|_{L^p\cap L^2}+\int_0^T\|(\na V, \na B)(t)\|_{L^\infty}^6dt<+\infty, &\displaystyle\inf_{(t,x,y)\in [0,T]\times Σ_t}-\frac {\pa P} {\pa \textbf{n}}(t,x,y)\ge c_0, \eeno for some $p>2d$ and $c_0>0$, then the solution can be extended after $t=T$.

math.AP↗
arXiv2013

Global unique solvability of inhomogeneous Navier-Stokes equations with bounded density

In this paper, we prove the global existence and uniqueness of solution to d-dimensional (for $d=2,3$) incompressible inhomogeneous Navier-Stokes equations with initial density being bounded from above and below by some positive constants, and with initial velocity $u_0\in H^s(\R^2)$ for $s>0$ in 2-D, or $u_0\in H^1(\R^3)$ satisfying $|u_0|_{L^2}|\na u_0|_{L^2}$ being sufficiently small in 3-D. This in particular improves the most recent well-posedness result in [10], which requires the initial velocity $u_0\in H^2(\R^d)$ for the local well-posedness result, and a smallness condition on the fluctuation of the initial density for the global well-posedness result.

math.AP↗
arXiv2012

The 2D incompressible Boussinesq equations with general critical dissipation

This paper aims at the global regularity problem concerning the 2D incompressible Boussinesq equations with general critical dissipation. The critical dissipation refers to $α+β=1$ when $Λ^α\equiv (-Δ)^{\fracα{2}}$ and $Λ^β$ represent the fractional Laplacian dissipation in the velocity and the temperature equations, respectively. We establish the global regularity for the general case with $α+β=1$ and $0.9132\approx α_0<α<1$. The cases when $α=1$ and when $α=0$ were previously resolved by Hmidi, Keraani and Rousset \cite{HKR1,HKR2}. The global existence and uniqueness is achieved here by exploiting the global regularity of a generalized critical surface quasi-gesotrophic equation as well as the regularity of a combined quantity of the vorticity and the temperature.

math.AP↗
arXiv2012

Well-posedness of the Ericksen-Leslie system

In this paper, we prove the local well-posedness of the Ericksen-Leslie system, and the global well-posednss for small initial data under the physical constrain condition on the Leslie coefficients, which ensures that the energy of the system is dissipated. Instead of the Ginzburg-Landau approximation, we construct an approximate system with the dissipated energy based on a new formulation of the system.

math.AP↗
arXiv2012

The small Deborah number limit of the Doi-Onsager equation to the Ericksen-Leslie equation

We present a rigorous derivation of the Ericksen-Leslie equation starting from the Doi-Onsager equation. As in the fluid dynamic limit of the Boltzmann equation, we first make the Hilbert expansion for the solution of the Doi-Onsager equation. The existence of the Hilbert expansion is connected to an open question whether the energy of the Ericksen-Leslie equation is dissipated. We show that the energy is dissipated for the Ericksen-Leslie equation derived from the Doi-Onsager equation. The most difficult step is to prove a uniform bound for the remainder in the Hilbert expansion. This question is connected to the spectral stability of the linearized Doi-Onsager operator around a critical point. By introducing two important auxiliary operators, the detailed spectral information is obtained for the linearized operator around all critical points. However, these are not enough to justify the small Deborah number limit for the inhomogeneous Doi-Onsager equation, since the elastic stress in the velocity equation is also strongly singular. For this, we need to establish a precise lower bound for a bilinear form associated with the linearized operator. In the bilinear form, the interactions between the part inside the kernel and the part outside the kernel of the linearized operator are very complicated. We find a coordinate transform and introduce a five dimensional space called the Maier-Saupe space such that the interactions between two parts can been seen explicitly by a delicate argument of completing the square. However, the lower bound is very weak for the part inside the Maier-Saupe space. In order to apply them to the error estimates, we have to analyze the structure of the singular terms and introduce a suitable energy functional.

math.AP↗
arXiv2012

Well-posedness of Hydrodynamics on the Moving Elastic Surface

The dynamics of a membrane is a coupled system comprising a moving elastic surface and an incompressible membrane fluid. We will consider a reduced elastic surface model, which involves the evolution equations of the moving surface, the dynamic equations of the two-dimensional fluid, and the incompressible equation, all of which operate within a curved geometry. In this paper, we prove the local existence and uniqueness of the solution to the reduced elastic surface model by reformulating the model into a new system in the isothermal coordinates. One major difficulty is that of constructing an appropriate iterative scheme such that the limit system is consistent with the original system.

math.AP↗
arXiv2012

On the interior regularity criterion and the number of singular points to the Navier-Stokes equations

We establish some interior regularity criterions of suitable weak solutions for the 3-D Navier-Stokes equations, which allow the vertical part of the velocity to be large under the local scaling invariant norm. As an application, we improve Ladyzhenskaya-Prodi-Serrin's criterion and Escauriza-Seregin-Šverák's criterion. We also show that if weak solution $u$ satisfies $$ \|u(\cdot,t)\|_{L^p}\leq C(-t)^{\frac {3-p}{2p}} $$ for some $3<p<\infty$, then the number of singular points is finite.

math.AP↗