3D dynamic Green’s functions in a multilayered poroelastic half-space

The complete 3D dynamic Green’s functions in the multilayered poroelastic media are presented in this study. A method of potentials in cylindrical coordinate system is applied first to decouple the Biot’s wave equations into four scalar Helmholtz equations, and then, general solutions to 3D wave propagation problems are obtained. After that, a three vector base and the propagator matrix method are introduced to treat 3D wave propagation problems in the stratified poroelastic half-space disturbed by buried sources. It is known that the original propagator algorithm has the loss-of-precision problem when the waves become evanescent. At present, an orthogonalization procedure is inserted into the matrix propagation loop to avoid the numerical difficulty of the original propagator algorithm. At last, the validity of the present approach for accurate and efficient calculating 3D dynamic Green’s functions of a multilayered poroelastic half-space is confirmed by comparing the numerical results with the known exact analytical solutions of a uniform poroelastic half-space.     

基于TOPSIS的属性关联直觉模糊多属性决策方法

针对属性值为直觉模糊数,已知部分属性偏好关系及属性交互类型的属性关联多属性决策问题给出决策方法.首先定义方案到正(负)理想方案的距离及各方案与正理想方案相对贴近度.然后以极大化各方案与相对贴近度为目标建立优化模型,确定出属性集的模糊测度.进而基于直觉模糊Choquet积分算子计算各方案的直觉模糊综合评价值,再根据直觉模糊数的得分值及精确度得到方案的排序.最后通过实例验证了方法的有效可行性.     

Vertical vibration of a circular stamp on an elastic-porous half-space with saturation fluid

A specific problem concerning the vertical vibrating response of a composite layer (elastic-porous and saturation fluid) under rigid circular stamp is studied. The motion of the medium is governed byBiot’s dynamic potential equations and the problem is solved by the method of Fourier-Bessel transformation. Formulae are obtained for the vertical displacement of the rigid phase. Graphs are presented for the amplitude of vibration.     

Unique solvability of a linear problem with perturbed periodic boundary values

We investigate the problem with perturbed periodic boundary values

基于方案偏好值的属性关联区间多属性决策

针对属性值为区间数,属性权重完全未知,但给出方案的主观偏好值,部分属性偏好关系以及属性交互类型的属性关联多属性决策问题给出决策方法.首先建立期望值目标规划模型,确定出属性集的M(o|¨)bius表达式以及属性权重,然后利用扩展的区间Choquet积分算子对决策信息进行集结,计算出各方案的区间模糊综合评价值,再利用比较区间数的期望值方法,从而得到方案的最终排序.最后给出了分析实例以说明所提出方法的有效可行性.     

某些带变换的边值问题和奇异积分方程

本文主要考虑某些带变换的奇异积分方程。尽管用经典的正则化方法可以求解，我们还是给出一种新的分区跳跃方法，使它们化为较简单的可以系统地求解并可迅即讨论的Ｆｒｅｄｈｏｌｍ积分方程。     

Mean value property and a Berezin-type transform on the half-space

Let B be the open unit ball in Rn. Liu (2007) [6] has shown that if then the iterates of a Berezin-type transform of f converge to the Poisson extension of the boundary values of f, as k→∞. In this paper, we extend this to the half-space setting. First, we obtain the mean value property for harmonic functions on the half-space H. Based on this property, we define a Berezin-type transform BH and investigate the limit of the iterates of BH.     

Constant-Sign Solutions of a System of Fredholm Integral Equations

We consider the following system of Fredholm intergral equations u _i (t)=₀ ¹ g _i (t,s)f _i (s,u ₁(s),u ₂(s),...,u _n (s)) ds, t[0,1], 1in. Criteria are offered for the existence of single, double and multiple solutions of the system that are of constant signs. The generality of the results obtained is illustrated through applications to several well known boundary value problems. We also extend the above system of Fredholm intergral equations to that on the half-line [0,) u _i (t)=₀ g _i (t,s)f _i (s,u ₁(s),u ₂(s),...,u _n (s)) ds, t[0,), 1in and investigate the existence of constant-sign solutions.     

Regularized Solutions of a Nonlinear Convolution Equation on the Euclidean Group

In this paper we apply Fourier analysis on the two and three dimensional Euclidean motion groups to the solution of a nonlinear convolution equation. First, we review the theory of the irreducible unitary representations of the motion group and discuss the corresponding Fourier transform of functions on the motion group. The main reasons why exact solutions of this convolution equation do not exist in many cases are discussed. Techniques for regularization of the problem and numerical methods for finding approximate solutions are presented. Examples are considered and approximate solutions are found.     

Dynamics of a rotating layer of an ideal electrically conducting incompressible fluid

A system of nonlinear partial differential equations is considered that models perturbations in a layer of an ideal electrically conducting rotating fluid bounded by spatially and temporally varying surfaces with allowance for inertial forces. The system is reduced to a scalar equation. The solvability of initial boundary value problems arising in the theory of waves in conducting rotating fluids can be established by analyzing this equation. Solutions to the scalar equation are constructed that describe small-amplitude wave propagation in an infinite horizontal layer and a long narrow channel.     

A Contact Problem of the Interaction of a Semi-Finite Inclusion with a Plate

A piece wise-homogeneous plane made up of twodifferent materials and reinforced by an elastic unclusion is considered on a semi-finite section where the different materials join. Vertical and horizontal forces are applied to the inclusion which haz a variable thichness and a variable elasticity modulus.Under certain conditions the problem is reduced to integrodifferential equations of third order. The solution is constructed effectively by applying the methods of theory of analytic functions to a boundary value problem of the Carleman type for a strip. Asymptotic estimates of normal contact stress are obtained.     

A multilevel decoupled method for a mixed Stokes/Darcy model

This paper studies decoupled numerical methods for a mixed Stokes/Darcy model for coupling fluid and porous media flows. A two-level algorithm is proposed and analyzed in Mu and Xu (2007) [10]. We generalize the two-level algorithm to a multilevel algorithm in this paper and present numerical analysis on the error estimates for the multilevel algorithm. The multilevel algorithm solves the mixed Stokes/Darcy system by applying efficient legacy code for single model solvers to solve two decoupled Stokes and Darcy subproblems on all the subsequently refined meshes, except for a much smaller global problem only on a very coarse initial mesh. Numerical experiments are conducted for both the two-level and multilevel algorithms to illustrate their effectiveness and efficiency, and validate the related theoretical analysis.     

An exact solution of start-up flow for the fractional generalized Burgers’ fluid in a porous half-space

Modified Darcy’s law for fractional generalized Burgers’ fluid in a porous medium is introduced. The flow near a wall suddenly set in motion for a fractional generalized Burgers’ fluid in a porous half-space is investigated. The velocity of the flow is described by fractional partial differential equations. By using the Fourier sine transform and the fractional Laplace transform, an exact solution of the velocity distribution is obtained. Some previous and classical results can be recovered from our results, such as the velocity solutions of the Stokes’ first problem for viscous Newtonian, second grade, Maxwell, Oldroyd-B or Burgers’ fluids.     

一类对偶积分方程组正则化为Cauchy奇异积分方程组解法

本文基于Mellin变换法求解复杂更一般形式的对偶积分方程组．通过积分变换，由实数域化成复数域上的方程组，引入未知函数的积分变换，移动积分路径，应用Cauchy积分定理，实现退耦正则化为Cauchy奇异积分方程组，由此给出一般性解，并严格证明了对偶积分方程组退耦正则化为Cauchy奇异积分方程组与原对偶积分方程组等价性，以及对偶积分方程组解的存在性和唯一性．给出的解法和理论解，作为求解复杂对偶积分方程组一种有效解法，可供求解复杂的数学、物理、力学中的混合边值问题应用．     

Numerical solution to a two-dimensional hypersingular integral equation and sound propagation in urban areas

A mathematical model of sound propagation from a noise source in urban areas is constructed. The exterior Neumann problem for the scalar Helmholtz equation is reduced to a system of hypersingular integral equations. A numerical method for solving the system of integral equations is described. The convergence of the quadrature formulas underlying the numerical method is estimated. Numerical results are presented for particular applications.     

Boundary integral approximation of a heat-diffusion problem in time-harmonic regime

In this paper we propose and analyse numerical methods for the approximation of the solution of Helmholtz transmission problems in the half plane. The problems we deal with arise from the study of some models in photothermal science. The solutions to the problem are represented as single layer potentials and an equivalent system of boundary integral equations is derived. We then give abstract necessary and sufficient conditions for convergence of Petrov–Galerkin discretizations of the boundary integral system and show for three different cases that these conditions are satisfied. We extend the results to other situations not related to thermal science and to non-smooth interfaces. Finally, we propose a simple full discretization of a Petrov–Galerkin scheme with periodic spline spaces and show some numerical experiments.     

一类多节对偶积分方程组正则化为超(强)奇异积分方程组求解法

基于Mellin变换法,首先方程组进行Mellin变换,然后,通过引入新的未知函数的Mellin变换代换原来未知函数的Mellin变换,使对偶积分方程组退耦正则化为超(强)奇异积分方程组．将未知函数分解并表示成未知函数和已知幂函数的乘积,幂指数(a_i,v_i)需使超(强)奇异积分方程组中的超(强)奇异积分,在端点(a_i,b_i)有界或可积奇异,求解超(强)奇异积分方程组可以使用有限部分积分式．将未知函数展成任意完备函数系(?)_n*(u)的级数,将超(强)奇异积分方程组,化成线性代数方程组,通过求解级数中的各项系数,由此给出对偶积分方程组的一般性解．并严格证明了对偶积分方程组和由它化成的超(强)奇异积分方程组的等价性,解的存在性和解的表示形式不唯一性．本文给出的理论解和解法,可供求解数学,物理,力学中的混合边值问题应用．     

Inversion of a logarithmic operator defined on a regular set of arcs lying on a circle

The theory of singular integral equations is used to derive simple inversion formulas for a logarithmic operator defined on a contour consisting of an arbitrary number of identical arcs lying on a circle at an equal angular spacing. The action of the inverse operator on trigonometric functions is calculated, and the moments of the inverse operator with trigonometric functions are found. Even simpler formulas are derived in the approximation of small arcs.