On semilinear Tricomi equations with critical exponents or in two space dimensions
This paper is a complement of our recent works on the semilinear Tricomi equations in [8] and[9].
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arXiv subjects
Huicheng Yin
Publications and source records attributed to Huicheng Yin.
Global smooth solutions of 3-D null-form wave equations in exterior domains with Neumann boundary conditions
The paper is devoted to investigating long time behavior of smooth small data solutions to 3-D quasilinear wave equations outside of compact convex obstacles with Neumann boundary conditions.
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On the global solution problem of semilinear generalized Tricomi equations, II
This paper is a continuation of our recent work in [9].
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On the steady non-Newtonian fluids in domains with noncompact boundaries
In this paper, we study non-Newtonian fluids in a class of unbounded domains with noncompact boundaries. With respect to the resulting mathematical problems, we establish the global existence of solutions with arbitrary large flux under some suitable conditions, and meanwhile, show the uniqueness of the solutions when the flux is sufficiently small. Our results are an extension or an improvement of those obtained in some previous references.
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Minimal regularity solutions of semilinear generalized Tricomi equations
We prove the local existence and uniqueness of minimal regularity solutions $u$ of the semilinear generalized Tricomi equation $\partial_t^2 u-t^m Δu =F(u)$ with initial data $(u(0,\cdot), \partial_t u(0,\cdot)) \in \dot{H^γ}(\mathbb R^n) \times \dot{H}^{γ-\frac2{m+2}}(\mathbb R^n)$ under the assumption that $|F(u)|\lesssim |u|^κ$ and $|F'(u)| \lesssim |u|^{κ-1}$ for some $κ>1$. Our results improve previous results of M. Beals [2] and of ourselves [15-17]. We establish Strichartz-type estimates for the linear generalized Tricomi operator $\partial_t^2 -t^m Δ$ from which the semilinear results are derived.
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On the global existence and blowup of smooth solutions to the multi-dimensional compressible Euler equations with time-depending damping
In this paper, we are concerned with the global existence and blowup of smooth solutions to the multi-dimensional compressible Euler equations with time-depending damping \begin{equation*} \partial_tρ+\operatorname{div}(ρu)=0, \quad \partial_t(ρu)+\operatorname{div}\left(ρu\otimes u+p\,I_d\right)=-α(t)ρu, \quad ρ(0,x)=\bar ρ+\varepsilonρ_0(x),\quad u(0,x)=\varepsilon u_0(x), \end{equation*} where $x=(x_1, \cdots, x_d)\in\Bbb R^d$ $(d=2,3)$, the frictional coefficient is $α(t)=\fracμ{(1+t)^λ}$ with $λ\ge0$ and $μ>0$, $\barρ>0$ is a constant, $ρ_0,u_0 \in C_0^\infty(\Bbb R^d)$, $(ρ_0,u_0)\not\equiv 0$, $ρ(0,x)>0$, and $\varepsilon>0$ is sufficiently small. One can totally divide the range of $λ\ge0$ and $μ>0$ into the following four cases: Case 1: $0\leλ<1$, $μ>0$ for $d=2,3$; Case 2: $λ=1$, $μ>3-d$ for $d=2,3$; Case 3: $λ=1$, $μ\le 3-d$ for $d=2$; Case 4: $λ>1$, $μ>0$ for $d=2,3$. \noindent We show that there exists a global $C^{\infty}-$smooth solution $(ρ, u)$ in Case 1, and Case 2 with $\operatorname{curl} u_0\equiv 0$, while in Case 3 and Case 4, in general, the solution $(ρ, u)$ blows up in finite time. Therefore, $λ=1$ and $μ=3-d$ appear to be the critical power and critical value, respectively, for the global existence of small amplitude smooth solution $(ρ, u)$ in $d-$dimensional compressible Euler equations with time-depending damping.
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On the global solution problem for semilinear generalized Tricomi equations, I
In this paper, we are concerned with the global Cauchy problem for the semilinear generalized Tricomi equation $\partial_t^2 u-t^m Δu=|u|^p$ with initial data $(u(0,\cdot), \partial_t u(0,\cdot))= (u_0, u_1)$, where $t\geq 0$, $x\in{\mathbb R}^n$ ($n\ge 3$), $m\in\mathbb N$, $p>1$, and $u_i\in C_0^{\infty}({\mathbb R}^n)$ ($i=0,1$). We show that there exists a critical exponent $p_{\text{crit}}(m,n)>1$ such that the solution $u$, in general, blows up in finite time when $1 p_{\text{crit}}(m,n)$ such that the solution $u$ exists globally when $p>p_{\text{conf}}(m,n)$ provided that the initial data is small enough. In case $p_{\text{crit}}(m,n)<p\leq p_{\text{conf}}(m,n)$, we will establish global existence of small data solutions $u$ in a subsequent paper.
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On the global existence and blowup of smooth solutions of 3-D compressible Euler equations with time-depending damping
In this paper, we are concerned with the global existence and blowup of smooth solutions of the 3-D compressible Euler equation with time-depending damping $$ \partial_tρ+\operatorname{div}(ρu)=0, \quad \partial_t(ρu)+\operatorname{div}\left(ρu\otimes u+p\,I_{3}\right)=-\,\fracμ{(1+t)^λ}\,ρu, \quad ρ(0,x)=\bar ρ+\varepsilonρ_0(x),\quad u(0,x)=\varepsilon u_0(x), $$ where $x\in\mathbb R^3$, $μ>0$, $λ\geq 0$, and $\barρ>0$ are constants, $ρ_0,\, u_0\in C_0^{\infty}(\mathbb R^3)$, $(ρ_0, u_0)\not\equiv 0$, $ρ(0,\cdot)>0$, and $\varepsilon>0$ is sufficiently small. For $0\leqλ\leq1$, we show that there exists a global smooth solution $(ρ, u)$ when $\operatorname{curl} u_0\equiv 0$, while for $λ>1$, in general, the solution $(ρ, u)$ will blow up in finite time. Therefore, $λ=1$ appears to be the critical value for the global existence of small amplitude smooth solutions.
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On the existence of low regularity solutions to semilinear generalized Tricomi equations in mixed type domains
In [19-20], we have established the existence and singularity structures of low regularity solutions to the semilinear generalized Tricomi equations in the degenerate hyperbolic regions and to the higher order degenerate hyperbolic equations, respectively. In the present paper, we shall be concerned with the low regularity solution problem for the semilinear mixed type equation $\p_t^2u-t^{2l-1}Δu= f(t,x,u)$ with an initial data $u(0,x)=φ(x)\in H^{s}(\Bbb R^n)$ ($0\le s<\f{n}{2}$), where $(t,x)\in\Bbb R \times\Bbb R^n$, $n\ge 2$, $l\in\Bbb N$, $f(t,x,u)$ is $C^1$ smooth in its arguments and has compact support with respect to the variable $x$. Under the assumption of the subcritical growth of $f(t,x,u)$ on $u$, we will show the existence and regularity of the considered solution in the mixed type domain $[-T_0, T_0] \times \R^n $ for some fixed constant $T_0>0$.
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Global multidimensional shock waves for 2-D and 3-D unsteady potential flow equations
Although local existence of multidimensional shock waves has been established in some fundamental references, there are few results on the global existence of those waves except the ones for the unsteady potential flow equations in n-dimensional spaces (n > 4) or in special unbounded space-time domains with non-physical boundary conditions. In this paper, we are concerned with both the local and global multidimensional conic shock wave problem for the unsteady potential flow equations when a pointed piston (i.e., the piston degenerates into a single point at the initial time) or an explosive wave expands fast in 2-D or 3-D static polytropic gas. It is shown that a multidimensional shock wave solution of such a class of quasilinear hyperbolic problems not only exists locally, but it also exists globally in the whole space-time and approaches a self-similar solution as t goes to infinity.
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The existence and singularity structure of low regularity solutions of higher-order degenerate hyperbolic equations
This paper is a continuation of our previous work [21], where we have established that, for the second-order degenerate hyperbolic equation (\p_t^2-t^mΔ_x)u=f(t,x,u), locally bounded, piecewise smooth solutions u(t,x) exist when the initial data (u,\p_t u)(0,x) belongs to suitable conormal classes. In the present paper, we will study low regularity solutions of higher-order degenerate hyperbolic equations in the category of discontinuous and even unbounded functions. More specifically, we are concerned with the local existence and singularity structure of low regularity solutions of the higher-order degenerate hyperbolic equations \p_t(\p_t^2-t^mΔ_x)u=f(t,x,u) and (\p_t^2-t^{m_1}Δ_x)(\p_t^2-t^{m_2}Δ_x)v=f(t,x,v) in \R_+\times\R^n with discontinuous initial data \p_t^iu(0,x)=ϕ_i(x) (0\le i\le 2) and \p_t^jv(0,x)=ψ_j(x) (0\le j\le 3), respectively; here m, m_1, m_2\in\N, m_1\neq m_2, x\in\R^n, n\ge 2, and f is C^\infty smooth in its arguments. When the ϕ_i and ψ_j are piecewise smooth with respect to the hyperplane \{x_1=0\} at t=0, we show that local solutions u(t,x), v(t,x)\in L^{\infty}((0,T)\times\R^n) exist which are C^\infty away from \G_0\cup \G_m^\pm and \G_{m_1}^\pm\cup\G_{m_2}^\pm in [0,T]\times\R^n, respectively; here \G_0=\{(t,x): t\ge 0, x_1=0\} and the Γ_k^\pm = \{(t,x): t\ge 0, x_1=\pm \f{2t^{(k+2)/2}}{k+2}\} are two characteristic surfaces forming a cusp. When the ϕ_i and ψ_j belong to C_0^\infty(\R^n\setminus\{0\}) and are homogeneous of degree zero close to x=0, then there exist local solutions u(t,x), v(t,x)\in L_{loc}^\infty((0,T]\times\R^n) which are C^\infty away from \G_m\cup l_0 and \G_{m_1}\cup\G_{m_2} in [0,T]\times\R^n, respectively; here Γ_k=\{(t,x): t\ge 0, |x|^2=\f{4t^{k+2}}{(k+2)^2}\} (k=m, m_1, m_2) is a cuspidal conic surface and l_0=\{(t,x): t\ge 0, |x|=0\} is a ray.
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Blowup of smooth solutions for general 2-D quasilinear wave equations with small initial data
For the 2-D quasilinear wave equation $\displaystyle \sum_{i,j=0}^2g_{ij}(\nabla u)\partial_{ij}u=0$ with coefficients independent of the solution $u$, a blowup result for small data solutions has been established in [1,2] provided that the null condition does not hold and a generic nondegeneracy condition on the initial data is fulfilled. In this paper, we are concerned with the more general 2-D quasilinear wave equation $\displaystyle \sum_{i,j=0}^2g_{ij}(u, \nabla u)\partial_{ij}u=0$ with coefficients that depend simultaneously on $u$ and $\nabla u$. When the null condition does not hold and a suitable nondegeneracy condition on the initial data is satisfied, we show that smooth small data solutions blow up in finite time. Furthermore, we derive an explicit expression for the lifespan and establish the blowup mechanism.
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Blowup of classical solutions for a class of 3-D quasilinear wave equations with small initial data
This paper is concerned with the small smooth data problem for the 3-D nonlinear wave equation $\partial_t^2u-\left (1+u+\p_t u\right)Δu=0$. This equation is prototypical of the more general equation $\dsize\sum_{i,j=0}^3g_{ij}(u, \nabla u)\partial_{ij}u=0$, where $x_0=t$ and $g_{ij}(u, \nabla u)=c_{ij}+d_{ij}u+\dsize\sum_{k=0}^3e_{ij}^k\partial_ku+O(|u|^2+|\nabla u|^2)$ are smooth functions of their arguments, with $c_{ij}, d_{ij}$ and $e_{ij}^k$ being constants, and $d_{ij}\neq0$ for some $(i,j)$; moreover, $\dsize\sum_{i,j,k=0}^3e_{ij}^k(\partial_ku)\p_{ij} u$ does not fulfill the null condition. For the 3-D nonlinear wave equations $\partial_t^2u-\left (1+u\right)Δu=0$ and $\partial_t^2u-\left (1+\partial_t u\right)Δu=0$, H. Lindblad, S. Alinhac, and F. John proved and disproved, respectively, the global existence of small smooth data solutions. For radial initial data, we show that the small smooth data solution of $\partial_t^2u-\left(1+u+\partial_t u\right)Δu=0$ blows up in finite time. The explicit expression of the asymptotic lifespan $T_{\varepsilon}$ as $\varepsilon\to0^+$ is also given.
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On the existence and cusp singularity of solutions to semilinear generalized Tricomi equations with discontinuous initial data
In this paper, we are concerned with the local existence and singularity structure of low regularity solutions to the semilinear generalized Tricomi equation $\p_t^2u-t^mΔu=f(t,x,u)$ with typical discontinuous initial data $(u(0,x), \p_tu(0,x))=(0, \vp(x))$; here $m\in\Bbb N$, $x=(x_1, ..., x_n)$, $n\ge 2$, and $f(t,x,u)$ is $C^{\infty}$ smooth in its arguments. When the initial data $\vp(x)$ is a homogeneous function of degree zero or a piecewise smooth function singular along the hyperplane ${t=x_1=0}$, it is shown that the local solution $u(t,x)\in L^{\infty}([0,T]\times\Bbb R^n)$ exists and is $C^{\infty}$ away from the forward cuspidal cone $Γ_0=\bigl{(t,x)\colon t>0, |x|^2=\ds\f{4t^{m+2}}{(m+2)^2}\bigr}$ and the characteristic cuspidal wedge $\G_1^{\pm}=\bigl{(t,x)\colon t>0, x_1=\pm \ds\f{2t^{\f{m}{2}+1}}{m+2}\bigr}$, respectively. On the other hand, for $n=2$ and piecewise smooth initial data $\vp(x)$ singular along the two straight lines ${t=x_1=0}$ and ${t=x_2=0}$, we establish the local existence of a solution $u(t,x)\in L^{\infty}([0,T]\times\Bbb R^2)\cap C([0, T], H^{\f{m+6}{2(m+2)}-}(\Bbb R^2))$ and show further that $u(t,x)\not\in C^2((0,T]\times\Bbb R^2\setminus(\G_0\cup\G_1^{\pm}\cup\G_2^{\pm}))$ in general due to the degenerate character of the equation under study; here $\G_2^{\pm}=\bigl{(t,x)\colon t>0, x_2=\pm\ds\f{2t^{\f{m}{2}+1}}{m+2}\bigr}$. This is an essential difference to the well-known result for solutions $v(t,x)\in C^{\infty}(\Bbb R^+\times\Bbb R^2\setminus (Σ_0\cupΣ_1^{\pm}\cup Σ_2^{\pm}))$ to the 2-D semilinear wave equation $\p_t^2v-Δv=f(t,x,v)$ with $(v(0,x), \p_tv(0,x))=(0, \vp(x))$, where $Σ_0={t=|x|}$, $Σ_1^{\pm}={t=\pm x_1}$, and $Σ_2^{\pm}={t=\pm x_2}$.
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On the lifespan of and the blowup mechanism for smooth solutions to a class of 2-D nonlinear wave equations with small initial data
This paper is concerned with the lifespan and the blowup mechanism for smooth solutions to the 2-D nonlinear wave equation $\p_t^2u-\ds\sum_{i=1}^2\p_i(c_i^2(u)\p_iu)$ $=0$, where $c_i(u)\in C^{\infty}(\Bbb R^n)$, $c_i(0)\neq 0$, and $(c_1'(0))^2+(c_2'(0))^2\neq 0$. This equation has an interesting physics background as it arises from the pressure-gradient model in compressible fluid dynamics and also in nonlinear variational wave equations. Under the initial condition $(u(0,x), \p_tu(0,x))=(\ve u_0(x), \ve u_1(x))$ with $u_0(x), u_1(x)\in C_0^{\infty}(\Bbb R^2)$, and $\ve>0$ is small, we will show that the classical solution $u(t,x)$ stops to be smooth at some finite time $T_{\ve}$. Moreover, blowup occurs due to the formation of a singularity of the first-order derivatives $\na_{t,x}u(t,x)$, while $u(t,x)$ itself is continuous up to the blowup time $T_{\ve}$.
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On the global existence and stability of a three-dimensional supersonic conic shock wave
We establish the global existence and stability of a three-dimensional supersonic conic shock wave for a perturbed steady supersonic flow past an infinitely long circular cone with a sharp angle. The flow is described by a 3-D steady potential equation, which is multi-dimensional, quasilinear, and hyperbolic with respect to the supersonic direction. Making use of the geometric properties of the pointed shock surface together with the Rankine-Hugoniot conditions on the conic shock surface and the boundary condition on the surface of the cone, we obtain a global uniform weighted energy estimate for the nonlinear problem by finding an appropriate multiplier and establishing a new Hardy-type inequality on the shock surface. Based on this, we prove that a multi-dimensional conic shock attached to the vertex of the cone exists globally when the Mach number of the incoming supersonic flow is sufficiently large. Moreover, the asymptotic behavior of the 3-D supersonic conic shock solution, that is shown to approach the corresponding background shock solution in the downstream domain for the uniform supersonic constant flow past the sharp cone, is also explicitly given.
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On the blowup and lifespan of smooth solutions to a class of 2-D nonlinear wave equations with small initial data
We are concerned with a class of two-dimensional nonlinear wave equations $\p_t^2u-÷(c^2(u)\na u)=0$ or $\p_t^2u-c(u)÷(c(u)\na u)=0$ with small initial data $(u(0,x),\p_tu(0,x))=(\ve u_0(x), \ve u_1(x))$, where $c(u)$ is a smooth function, $c(0)\not =0$, $x\in\Bbb R^2$, $u_0(x), u_1(x)\in C_0^{\infty}(\Bbb R^2)$ depend only on $r=\sqrt{x_1^2+x_2^2}$, and $\ve>0$ is sufficiently small. Such equations arise in a pressure-gradient model of fluid dynamics, also in a liquid crystal model or other variational wave equations. When $c'(0)\not= 0$ or $c'(0)=0$, $c"(0)\not= 0$, we establish blowup and determine the lifespan of smooth solutions.
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