平面动力问题的理论求解

通过对平面动力问题控制方程的分析,研究了相应的应力函数，得出了关于应力函数的基本方程。     

波动方程系数反问题的求解方法

讨论了一维波动方程系数反演的一种求解方法,将解进行一阶渐进展开,得到相应的反问题,将其转化为第二类Volttera型积分方程组,证明了反问题解的存在唯一性.     

扩散方程系数的半逆问题水

一般地,扩散方程的系数q(x)与p(x)是由两组谱或者一组谱及其标准常数唯一确定的.运用Hochstadt与Lieberman的方法证明了:(a)如果给定区间[π/2,π]上的p(x)及区阿[0,π]上的q(x),则扩散方程的一组谱可唯一确定另一半区间[0,π/2]上系数p(x);(b)如果给定区间[π/2,π]上的g(x)及区间[0,π]上的p(x),则扩散方程的一组谱可唯一确定另一半区间[0,π/2]上系数q(x).     

一个变系数的波动方程的Cauchy问题之解

在[1]中,曾研究过具有最大对称性的物理时空,现在命之为(?)_k,其中K代表曲率。进一步的问题自然是要研究这些时空的波动方程的解。当K=0,这是熟知的经典的常系数的波动方程,它的讨论在数学物理微分方程的书中都有的。当K≠0时,(?)_K中的波动方程是变系数的,它的Cauchy问题的解的具体表达式还未见到过。由于K>0与     

饱水孔隙介质的质量耦合波动问题

本文按照混合物理论严格地推导出了饱和孔隙介质的一般波传播理论.该理论的重要性在于包含了质量耦合作用,并为研究该问题提供了理性基础和实用方程.本文对所得方程中的系数的物理意义和热力学限制进行了讨论.通过比较认为本文的理论和Biot古典理论基本上一致.本文还对完全透水、完全不透水和具有刚性固体骨架的介质的无边界条件下的波传播问题进行了研究,得到了一些有意义的结论.     

变系数波动方程的边界镇定

应用Riemann几何方法和乘子方法,得到一定条件下变系数波动方程在线性边界反馈下能量的指数衰减性.     

用映射动力无穷元求解地基中的三维波动问题

本文从三维粘弹性波动方程出发,利用Garlerkin加权余量法,导出了三维粘弹性波动方程的离散形式。然后提出了一种三维映射动力无穷元,同时阐述了这类无穷元的基本原理和构造方法。文中所提出的无穷元极易与有限元耦合,并保持着适应复杂介质条件和边界条件以及大量缩减系统自由度的优点。文中通过算例验证了这类无穷元具有良好的计算精度。最后对弹性半空间上基础板的弹性对板中动力柔度系数的影响进行了研究。计算结果表明,只有当基础板与地基弹模比E_F/E_R≥10⁴—10⁵时,才能简化为刚性基础板来处理。     

求解2—D波动方程系数反问题的迭代方法及收敛性

本文针对地震勘探中提出一类重要的２－Ｄ波动方程反演问题，通过定义一个新的非线性算子将２－Ｄ波动方程的反演问题归结为一个新的非线性算子方程，详细讨论了非线性算子的性质，给出了求解反问题的迭代方法，并证明了这种迭代方法的收敛性。     

一类变系数线性波动方程初值问题的求解

本文讨论了一类变系数线性波动方程初值问题的求解，获得较为理想的结果．     

一类变系数线性波动方程初值问题的求解

本讨论了一类变系数线性波动方程初值问题的求解，获得较为理想的结果。     

Transformation Operators in the Problems of Controllability for the Degenerate Wave Equation with Variable Coefficients

Ukrainian Mathematical Journal - We study a control system $$ {w}_{tt}=frac{1}{rho }{left(k{w}_xright)}_x+gamma w,wleft(0,tright)=u(t),xin left(0,lright),tin left(0,Tright), $$ in...     

入水冲击问题变分原理及其它

首先建立入水前后两个衔接阶段的较为严密的场方程.再得到与之对应的各类变分原理,界限定理,第二阶段问题的边界积分方程.证明了解的存在性并提供了求解实施方案.最后以船舶兴波阻力问题的算例,论证了第二阶段问题的一种特殊应用及其正确性.从而为求取较为精确的入水冲击问题基本方程的变分有限元及边界元方法奠定了严密的理论基础.     

Uniqueness of Solutions of Initial-Boundary Value Problems for Parabolic Systems with Dini-Continuous Coefficients in Domains on the Plane

Doklady Mathematics - The first and second initial-boundary value problems for Petrovskii parabolic systems of the second order with coefficients satisfying the Dini condition in plane domains with...     

Blow Up of Solutions to One Dimensional Initial-boundary Value Problems for Semilinear Wave Equations with Variable Coefficients

This paper is devoted to studying the following initial-boundary value problemfor one-dimensional semilinearwave equationswith variable coefficients andwith subcritical exponent: $u_{tt}-∂_x(a(x)∂_xu)=|u|^p, x > 0, t > 0, n=1,$ where $u=u(x,t)$ is a real-valued scalar unknown function in $[0,+∞)×[0,+∞)$, here a(x) is a smooth real-valued function of the variable $x∈(0,+∞)$. The exponents p satisfies $1 < p < +∞$ in (0.1). It is well-known that the number $p_c(1)=+∞$ is the critical exponent of the semilinear wave equation (0.1) in one space dimension (see for e.g., [1]). We will establish a blowup result for the above initial-boundary value problem, it is proved that there can be no global solutions no matter how small the initial data are, and also we give the lifespan estimate of solutions for above problem.     

Hydrodynamic Theory of Sound Wave Propagation

We formulate the limits of applicability of the hydrodynamic equations and prove the necessity of introducing a correction to the potential energy transfer in the heat conductivity equation, which allows developing the hydrodynamic theory of the propagation of sound waves with small amplitudes. We show that this correction affects almost all predictions of the standard hydrodynamic theory. In particular, this correction allows extending the applicability domain of the hydrodynamic theory to the case of an arbitrarily viscous liquid. Moreover, in total accordance with the experimental data, the theory predicts that the sound speed and the damping rate remain finite at all frequencies up to frequencies of the order of 10^-12 sec^-1, while the hydrodynamic equations make no sense at higher frequencies and sound wave propagation in the medium consequently becomes impossible. We show that the dimensionless dispersion equation contains only one material parameter. We predict the existence of the highly damped second sound.     

Strichartz Estimates for Wave Equations with Coefficients of Sobolev Regularity

Wave packet techniques provide an effective method for proving Strichartz estimates on solutions to wave equations whose coefficients are not smooth. We use such methods to show that the existing results for C ^{1, 1} and C ^{1, α} coefficients can be improved when the coefficients of the wave operator lie in a Sobolev space of sufficiently high order.     

Condition Number Bounds for Problems with Integer Coefficients

An explicit a priori bound for the condition number associated to each of the following problems is given: general linear equation solving, least squares, nonsymmetric eigenvalue problems, solving univariate polynomials, and solving systems of multivariate polynomials. It is assumed that the input has integer coefficients and is not on the degeneracy locus of the respective problem (i.e., the condition number is finite). Our bounds are stated in terms of the dimension and of the bit-size of the input.  In the same setting, bounds are given for the speed of convergence of the following iterative algorithms: QR iteration without shift for the symmetric eigenvalue problem and Graeffe iteration for univariate polynomials.     

Calculation of Transmission Coefficients for Generalized Propagation Problems

Generalized wave propagation takes place through a homogeneousslab governed by a differential equation of arbitrary even order,the elementary physical case being given when this order istwo. Approximation procedures are investigated whereby the transmissioncoefficient is calculated for highly overdense slabs, in sucha way that a correction term can be specified for the unit valueof the modulus of the reflection coefficient.