On Local Nonreflecting Boundary Conditions for Time Dependent Wave Propagation

The simulation of wave phenomena in unbounded domains generally requires an artificial boundary to truncate the unbounded exterior and limit the computation to a finite region. At the artificial boundary a boundary condition is then needed, which allows the propagating waves to exit the computational domain without spurious reflection. In 1977, Engquist and Majda proposed the first hierarchy of absorbing boundary conditions, which allows a systematic reduction of spurious reflection without moving the artificial boundary farther away from the scatterer. Their pioneering work, which initiated an entire research area, is reviewed here from a modern perspective. Recent developments such as high-order local conditions and their extension to multiple scattering are also presented. Finally, the accuracy of high-order local conditions is demonstrated through numerical experiments.     

On $L^2$-Stability Analysis of Time-Domain Acoustic Scattering Problems with Exact Nonreflecting Boundary Conditions

This paper is devoted to stability analysis of the acoustic wave equation exterior to a bounded scatterer, where the unbounded computational domain is truncated by the exact time-domain circular/spherical nonreflecting boundary condition (NRBC). Different from the usual energy method, we adopt an argument that leads to $L^2$-a priori estimates with minimum regularity requirement for the initial data and source term. This needs some delicate analysis of the involved NRBC. These results play an essential role in the error analysis of the interior solvers (e.g., finite-element/spectral- element/spectral methods) for the reduced scattering problems. We also apply the technique to analyze a time-domain waveguide problem.     

具非线性边界条件的泛函微分方程边值问题奇摄动(英文)

研究一类具非线性边界条件的泛函微分方程边值问题εx″( t) =f ( t,x( t) ,x( t-τ) ,x′( t) ,ε) ,　 t∈ ( 0 ,1 ) ,x( t) =φ( t,ε) ,　 t∈ [-τ,0 ],　 h( x( 1 ) ,x′( 1 ) ,ε) =A(ε) .我们利用微分不等式理论证明了边值问题解的存在性 ,并给出了解的一致有效渐近展开式     

具非线性边界条件的半线性时滞微分方程边值问题奇摄动

利用微分不等式理论研究了一类具非线性边界条件的半线性时滞微分方程边值问题.采用新的方法构造上下解,得到了此边值问题解的存在性的充分条件,并给出了解的一致有效渐近展开式.     

带跳跃非线性边界的p-Laplacian问题(英文)

利用Fadell与Rabinowitz提出的同调指标理论,研究了一类带不定权非线性边界的p-Laplacian特征值问题;更进一步,利用环绕定理,证明了一类带跳跃非线性边界的p-Laplacian问题非平凡解的存在性.     

非线性边界条件下抛物问题解的爆破

本文讨论在在非线性边界条件下反应-扩散方程解的爆破.当非线性项f,g满足一定的条件时,我们得到其解在有限时间内爆破.     

Existence and Non-Existence Results for Quasilinear Elliptic Exterior Problems with Nonlinear Boundary Conditions

Existence and non-existence results are established for quasilinear elliptic problems with nonlinear boundary conditions and lack of compactness. The proofs combine variational methods with the geometrical feature, due to the competition between the different growths of the nonlinearities.     

带非线性边界条件的非线性抛物型方程组

本文讨论带非线性边界条件的抛物型方程组ｕｔ＝Δｕｍ，ｖｔ＝Δｖｍ，ｘ∈Ω，ｔ＞０，ｕｎ＝ｖｐ，ｖｎ＝ｕｑ，ｘ∈Ω，ｔ＞０，ｕ（ｘ，０）＝ｕ０（ｘ）δ＞０，ｖ（ｘ，０）＝ｖ０（ｘ）δ＞０，ｘ∈Ω（Ｉ）解的整体存在性和在有限时刻爆破问题．其中ｍ，ｐ，ｑ＞０，ΩＩＲＮ是有界光滑区域，δ＞０可以充分小．     

具非线性边界条件的Volterra型时滞微分方程边值问题奇摄动

该文研究一类时滞微分方程边值问题〖JB({〗εx″(t)=f(t,x(t),x(t-τ(t)),\[Tx\](t),x′(t),ε),t∈(0,1),\=x(t)=φ(t,ε),t∈\[-τ,0\],h(x(1),x′(1),ε)=A(ε),[JB)]其中ε>0为小参数，τ(t)≥τ\-0>0,τ=\%\{max\}\%[DD(X]t∈\[0,1\][DD)]τ(t)<1,\[Tx\](t)=ψ(t)+∫\+t\-0k(t,x)x(s）ds为Volterra型算子。利用微分不等式理论证明了边值问题解的存在性，并给出了解的一 致有效渐近展开式。     

The Obstacle Problems for Second Order Fully Nonlinear Elliptic Equations with Neumann Boundary Conditions

In this paper we prove the existence theorem of the strong solutions to the obstacle problems for second order fully nonlinear elliptic equations with the Neumann boundary conditions F(x, u, Du, D²u) ≥ 0, x ∈ Ω u ≤ g, x ∈ Ω (u - g)F(x, u, Du, D²u) = 0, x ∈ Ω D_vu = φ(x, u), x ∈ ∂Ω where F(x, z, p, r) satisfies the natural structure conditions and is concave with respect to r, p, and φ(x, z) is nondecreasing in z, and g(x) satisfies the consistency condition.     

微分包含的非线性边值问题

基于 Marteli 定理^[8], 该文得到了一个新的不动点定理,利用这一结果,作者给出了在Banach空间中的多值微分包含的非线性边值问题的解的存在性的充分条件.     

Boundary Value Problems with Compatible Boundary Conditions

If Y is a subset of the space ℝⁿ × ℝⁿ, we call a pair of continuous functions U, V Y-compatible, if they map the space ℝⁿ into itself and satisfy Ux · Vy ≥ 0, for all (x, y) ∈ Y with x · y ≥ 0. (Dot denotes inner product.) In this paper a nonlinear two point boundary value problem for a second order ordinary differential n-dimensional system is investigated, provided the boundary conditions are given via a pair of compatible mappings. By using a truncation of the initial equation and restrictions of its domain, Brouwer's fixed point theorem is applied to the composition of the consequent mapping with some projections and a one-parameter family of fixed points P _δ is obtained. Then passing to the limits as δ tends to zero the so-obtained accumulation points are solutions of the problem.     

n阶非线性微分方程的非线性三点边值问题

本文利用广义对接方法,建立了n阶非线性微分方程y(n)=f(x,y,y',…, y(n-1))满足非线性三点边界条件的非线性三点边值问题解的存在性与唯一性定理,所得结果将已有的很多相应结果作为特例.     

多孔固体充满黏性流体时的边界条件

基于物理学基本原理和能量守恒定律的精确检查,导出充满黏性流体多孔固体边界呈连续性要求的边界条件.当孔隙流体具有黏性时,多孔弹性固体就是一个耗散的充满黏性流体的多空固体.孔隙流体的黏性造成的耗散应力准确地表达了边界条件.边界上两种固体连接的不完全,导致孔隙流体的流出,多孔骨料两边微粒运动的不平衡.导出多孔.多孔固体界面孔隙局部连接时的数学模型.在该界面上,滑移的松.紧,以及孔隙开.合,能造成一部分应变能的耗散.数值结果表明,在水和饱和油砂岩之间的界面上,修正的边界条件将影响各向同性多孔介质中折射波的能量.     

n阶非线性常微分方程的非线性两点边值问题

本文利用打靶法,给出了ｎ阶非线性常微分方程具有非线性两点边界条件的边值问题存在解与存在唯一解的一般性结果,并将所得结果应用于Ｌｉｐｓｃｈｉｔｚ方程的两点过值问题,给出了存在解与存在唯一解的具体的充分条件。     

非线性波方程的初边值问题

本文利用Leray-Schauder不动点定理证明了非线性波方程utt-[a0 a2(ux)^β]uxx-a1uxxtt=f(x,t,ux,ut,uxt)的初边值问题广义解的存在唯一性。     

Energy Methods for Problems with Nonhomogeneous Boundary Conditions

This paper employs the weighted energy method to derive estimates for the dynamic behavior of solutions to boundary and initial boundary value problems with nonhomogeneous boundary conditions. In particular, the method is applied to the heat and Laplace equations in a bounded or unbounded region. Extensions to related equations are also studied. Similar estimates but for the spatial behavior is obtained for the heat equation and the backward in time heat equation. Results for blow-up in finite time of solutions to certain nonlinear equations are generalized to include nonhomogeneous boundary conditions, while solutions that vanish on part of the boundary are briefly discussed in the final section.