A perturbation technique for solving boundary value problems arising in the electrodynamics of conducting bodies

The electrodynamics of wave reflection from conducting media lead to difficult mathematical problems because of the matching conditions which must be met at the interface between conductors and nonconductors. Simplified boundary conditions have been proposed by Leontovitch and others which considerably simplify certain of the mathematical problems. We discuss the Leontovitch condition together with certain of its shortcomings and present a new method which overcomes some of the difficulties of the Leontovitch condition. The new method is a perturbation away from infinite conductivity which allows the solution of electrodynamics problems to be calculated to any order of accuracy in the quantity (ωε/σ)^1/2 for some important cases. An instance in which the perturbation method fails is also discussed.     

Hopf bifurcation for a ecological mathematical model on microbe populations

1　ＭｏｄｅｌａｎｄＢａｃｋｇｒｏｕｎｄＩｎｍｉｃｒｏｂｅｂｉｏｃｈｅｍｉｃａｌｒｅａｃｔｉｏｎｓｔｈｅｒｅａｒｅｃｏｍｐｌｅｘｍｅｔａｂｏｌｉｓｍｐｒｏｃｅｓｓｅｓａｎｄｕｓｕａｌｌｙｍａｎｙｐｏｐｕｌａｔｉｏｎｓ[1].Ａｍｏｎｇｔｈｅｓｅｐｏｐｕｌａｔｉｏｎｓｔｈｅｒｅｍａｙｂｅａｒｅｌａｔｉｏｎｔｈａｔｔｈｅｍｅｔａｂｏｌａｔｅｉｎｔｈｅｆｉｒｓｔｐｒｏｃｅｓｓｃｏｎｓｔｒｕｃｔｔｈｅｎｕｔｒｉｍｅｎｔｏｆｔｈｅｓｅｃｏｎｄｐｒｏｃｅｓｓ.Ｎｏｗｗｅｃｏｎｓｉｄｅｒｏｎｌｙｔｗｏｉｍｐｏｒｔａ…     

Surface activity and bubble motion

This paper reviews recent progress in the theories of the surface boundary conditions of adsorbed solutes in liquids, and of the effects of those solutes on the steady motion of a bubble or drop in the liquid. Both singular perturbation theory and numerical solutions have useful roles in this problem, and their relationship is explored. In addition, analytical solutions are given to two problems concerning a spherical bubble rising steadily at low Reynolds number in a viscous fluid. One of these is displacement of the internal vortex centre from its position in the absence of surface activity when there is a small stagnant cap of surfactant at the rear. The results agree with experimental data in the direction of that displacement but give only about half its amount. The other problem is the velocity perturbation all round the surface caused by a very dilute solution of a weak surfactant at high Péclet number. This compares quite well with the numerical solution for a Péclet number of 60, having relative errors of order (60)^–1/2 as would be expected.     

On the electroelastic interaction of a piezoelectric screw dislocation with an elliptical inclusion in piezoelectric materials

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｉｎｔｅｒａｃｔｉｏｎｏｆｄｉｓｌｏｃａｔｉｏｎｓｗｉｔｈｉｎｃｌｕｓｉｏｎｓｉｓｏｆｃｏｎｓｉｄｅｒａｂｌｅｉｍｐｏｒｔａｎｃｅｆｏｒｕｎｄｅｒｓｔａｎｄｉｎｇｔｈｅｐｈｙｓｉｃａｌｂｅｈａｖｉｏｒｏｆｍａｔｅｒｉａｌｓ.Ｓｕｃｈｓｔｕｄｉｅｓｃａｎｐｒｏｖｉｄｅｄｉｎｆｏｒｍａｔｉｏｎｃｏｎｃｅｒｎｉｎｇｃｅｒｔａｉｎｓｔｒｅｎｇｔｈｅｎｉｎｇｏｒｈａｒｄｅｎｉｎｇｍｅｃｈａｎｉｓｍｓｉｎｎｕｍｂｅｒｏｆｔｒａｄｉｔｉｏｎａｌａｎｄｃｏｍｐｏｓｉｔｅｍａｔｅｒｉ…     

Analysis of a screw dislocation inside an elliptical inhomogeneity in piezoelectric solids

This paper formulates and examines the electro-elastic coupling effects resulting from the presence of a screw dislocation inside an elliptical piezoelectric inhomogeneity embedded in an infinite piezoelectric matrix. The general solution to this problem is obtained by conformal mapping and Laurent series expansion of the corresponding complex potentials. The appropriate expressions of the field potentials and the field components are given explicitly in both the inhomogeneity and the surrounding matrix using a perturbation technique. The internal energy and the force on the dislocation are computed and several specific examples are provided to illustrate the validity and versatility of the developed formulations.     

THE PROBLEMS OF THE NONLINEAR UNSYMMETRICAL BENDING FOR CYLINDRICALLY ORTHOTROPIC CIRCULAR PLATE（II）

ＴＨＥＰＲＯＢＬＥＭＳＯＦＴＨＥＮＯＮＬＩＮＥＡＲＵＮＳＹＭＭＥＴＲＩＣＡＬ．ＢＥＮＤＩＮＧＦＯＲＣＹＬＩＮＤＲＩＣＡＬＬＹＯＲＴＨＯＴＲＯＰＩＣＣＩＲＣＵＬＡＲＰＬＡＴＥ（ＩＩ）ＨｕａｎｇＪｉａｙｉｎ（黄家寅）;ＱｉｎＳｈｅｎｇｌｉ（秦圣立）;Ｘｉ...     

Asymptotic analysis of perforated plates and membranes. Part 2: Static and dynamic problems for large holes

Static and dynamic problems for the elastic plates and membranes periodically perforated by holes of different shapes are solved using the combination of the singular perturbation technique and the multi-scale asymptotic homogenization method. The problems of bending and vibration of perforated plates are considered. Using the asymptotic homogenization method the original boundary-value problems are reduced to the combination of two types of problems. First one is a recurrent system of unit cell problems with the conditions of periodic continuation. And the second problem is a homogenized boundary-value problem for the entire domain, characterized by the constant effective coefficients obtained from the solution of the unit cell problems. In the present paper the perforated plates with large holes are considered, and the singular perturbation method is used to solve the pertinent unit cell problems. Matching of limiting solutions for small and large holes using the two-point Padé approximants is also accomplished, and the analytical expressions for the effective stiffnesses of perforated plates with holes of arbitrary sizes are obtained.     

Bifurcation and stability analysis for liquid surfaces

A more comprehensive discussion on the bifurcation problems for the shape of liquid surfaces is made in this paper. The necessary conditions for bifurcation are given, and the bifurcating solutions near bifurcation points can be obtained by perturbation technique. Finally the stability of the bifurcating states is analyzed by means of the principle of minimum potential energy.     

Asymptotic analysis of perforated plates and membranes. Part 1: Static problems for small holes

Static problems for the elastic plates and rods periodically perforated by small holes of different shapes are solved using the asymptotic approach based on the combination of the asymptotic technique and the multi-scale homogenization method. Using the asymptotic homogenization method the original boundary-value problem is reduced to the combination of two types of problems. First one is a recurrent system of unit cell problems with the conditions of periodic continuation. And the second problem is a homogenized boundary-value problem for the entire domain, characterized by the constant effective coefficients obtained from the solution of the unit cell problems. The combination of the perturbation method and the technique of successive approximations is applied for the solution of the unit cell problems. Taking into the account small size of holes the method of perturbation of the shape of the boundary and the Schwarz alternating method are used. The problems of torsion of a rod with perforated cross-section; deflection of the perforated membrane loaded by a normal load; and bending of perforated plates with circular and square holes are considered consecutively. The error of the applied asymptotic techniques is estimated and the high accuracy of the obtained solutions is demonstrated.     

Antiplane interaction of line crack with an arbitrarily located elliptical inclusion

The antiplane problem of the interaction between a main crack and an arbitrarily located elastic elliptical inclusion near its tip is addressed in the current study. The analysis is based on the use of the complex potentials for the antiplane problem, Laurent series expansion method and an appropriate superposition scheme. The stress intensity factor at the main crack is obtained in a general series form. Explicit asymptotic solutions are also derived by using a perturbation technique and retaining the leading order terms in series expansion. The present solutions are shown to coincide with the Taylor expansion of exact solutions for special cases available in the literature. Discussed are changes in the crack tip stress intensity which can be enhanced or suppressed depending on the location of the elliptical inclusion. The explicit solutions provided herein are well suited for the further quantitative analysis of toughening mechanisms in ceramic composite materials.     

A Perturbation Argument for a Monge–Ampère Type Equation Arising in Optimal Transportation

We prove some interior regularity results for potential functions of optimal transportation problems with power costs. The main point is that our problem is equivalent to a new optimal transportation problem whose cost function is a sufficiently small perturbation of the quadratic cost, but it does not satisfy the well known condition (A.3) guaranteeing regularity. The proof consists in a perturbation argument from the standard Monge–Ampère equation in order to obtain, first, interior C^1,1 estimates for the potential and, second, interior Hölder estimates for second derivatives. In particular, we take a close look at the geometry of optimal transportation when the cost function is close to quadratic in order to understand how the equation degenerates near the boundary.     

Singular perturbation for the weakly nonlinear reaction diffusion equation with boundary perturbation

In this paper, a class of nonlinear singularly perturbed initial boundary value problems for reaction diffusion equations with boundary perturbation are considered under suitable conditions. Firstly, by dint of the regular perturbation method, the outer solution of the original problem is obtained. Secondly, by using the stretched variable and the expansion theory of power series the initial layer of the solution is constructed. And then, by using the theory of differential inequalities, the asymptotic behavior of the solution for the initial boundary value problems is studied. Finally, using some relational inequalities the existence and uniqueness of solution for the original problem and the uniformly valid asymptotic estimation are discussed.     

NONLINEAR THREE-DIMENSIONAL ANALYSIS OF COMPOSITELAMINATED PLATES

ＮＯＮＬＩＮＥＡＲＴＨＲＥＥ－ＤＩＭＥＮＳＩＯＮＡＬＡＮＡＬＹＳＩＳＯＦＣＯＭＰＯＳＩＴＥＬＡＭＩＮＡＴＥＤＰＬＡＴＥＳ￥(江晓禹，张相周，陈百屏)ＪｉａｎｇＸｉａｏｙｕ；（ＳｏｕｔｈｗｅｓｔｅｒｎＪｉａｏｔｏｎｇＵｎｉｖｅｒｓｉｔｙ，Ｃｈｅｎｇｄｕ６...     

Stability conditions for brittle-plastic symmetric thick-walled shell structures

Starting with the damage surface perturbation formulation (DSPF) for stability problems of brittle-plastic structures, this paper investigates the stability conditions of brittle-plastic symmetric thick.- walled shell structures by means of the fixed loading criteria derived from the DSPF. The results obtained are discussed.     

Nonlinear three-dimension analysis for axially symmetrical circular plates and multilayered plates

Analytic nonlinear three-dimension solutions are presented for axially symmetrical homogeneous isotropic circular plates and multilayered plates with rigidly clamped boundary conditions and under transverse load.The geometric nonlinearily from a moderately large deflection is considered.A developmental perturbation method is used to solve the complicated nonlinear three-dimension differential equations of equilibrium.The basic idea of this perturbation method is using the two-dimension solutions as a basic form of the corresponding three-dimension solutions,and then processing the perturbation procedure to obtain the three-dimension perturbation solutions.The nonlinear three-dimension results in analytic expressions and in numerical forms for ordinary plates and multilayered plates are presented.All of the plate stresses are shown in figures.The results show that this perturbation method used to analyse nonlinear three-dimension problems of plates is effective.     

复合材料层合板的三维研究

本文提出了固支复合材料各向异性层合圆板受均布横向载荷作用下的满足三维弹性力学基本微分方程和边界条件的解析解答。文中采用一种发展的摄动方法进行求解，板中的每个应力和位移都展开为无量纲厚度参数ε的摄动级数，并采用二维板理论解答作为其相应三维摄动解答的一个基本解的形式，通过摄动方法逐级求解而获得完整的三维解答。文中以解析形式和数值形式给出了高精确度的三维应力和位移结果，结果表明，本文求解三维问题的解析方法是合理有效的。     

Flow of viscoelastic fluids through a porous channel—I

The flow of viscoelastic fluids through a porous channel with one impermeable wall is computed. The flow is characterized by a boundary value problem in which the order of the differential equation exceeds the number of boundary conditions. Three solutions are developed: (i) an exact numerical solution, (ii) a perturbation solution for small R, the cross-flow Reynold's number and (iii) an asymptotic solution for large R. The results from exact numerical integration reveal that the solutions for a non-Newtonian fluid are possible only up to a critical value of the viscoelastic fluid parameter, which decreases with an increase in R. It is further demonstrated that the perturbation solution gives acceptable results only if the viscoelastic fluid parameter is also small. Two more related problems are considered: fluid dynamics of a long porous slider, and injection of fluid through one side of a long vertical porous channel. For both the problems, exact numerical and other solutions are derived and appropriate conclusions drawn.     

Application of the perturbation method in mechanics of deformable solids

Although the solutions of the classical problems of continuum mechanics have been studied sufficiently well, the smallest deviations, for example, of the body boundary or of the material characteristics from the traditional values prevent one from obtaining exact solutions of these problems. In this case, one has to use approximate methods, the most common of which is the perturbation method. The problems studied in [1–6] belong to classical problems in which the perturbation method is used to study the behavior of deformable bodies. A wide survey of studies analyzing the perturbations of the body boundary shape caused by variations in its stress-strain state is given in [5, 6]. In numerous studies, it was noted that the problem on the convergence of approximate solutions and hence the studies of the continuous dependence of the solution of the original problem on the characteristics of perturbations (“imperfections”) play an important role. In the present paper, we analyze the forms of mathematical models of deformable bodies by studying whether the solution of the original problem continuously depends on the characteristics of the perturbed shape of the body boundary on which the boundary conditions are posed in terms of stresses and on the characteristics of the material properties. We use the results of this analysis to conclude that, when using the perturbation method, one should state the boundary conditions in terms of stresses on the boundary of the real body in stressed state.     

Analysis of superposed fluids by the finite element method: Linear stability and flow development

A Galerkin finite element method is described for studying the stability of two superposed immiscible Newtonian fluids in plane Poiseuille flow. The formulation results in an algebraic eigenvalue problem of the form Aλ² + Bλ + C = 0 which, after transforming to a standard generalized eigenvalue problem, is solved by the QR algorithm. The numerical results are in good agreement with previous asymptotic results. Additional results show that the finite element method is ideally suited for studying linear stability of superposed fluids when parameters characterizing the flow fall outside the range amenable to perturbation methods. The applicability of the finite element method to similar eigenvalue problems is demonstrated by analysing the steady-state spatial development of two superposed fluids in a channel.     

Well Adapted Normal Linearization in Singular Perturbation Problems

We provide smooth local normal forms near singularities that appear in planar singular perturbation problems after application of the well-known family blow up technique. The local normal forms preserve the structure that is provided by the blow-up transformation. In a similar context, C ^k -structure-preserving normal forms were shown to exist, for any finite k. In this paper, we improve the smoothness by showing the existence of a C ^∞ normalizing transformation, or in other cases by showing the existence of a single normalizing transformation that is C ^k for each k, provided one restricts the singular parameter ε to a (k-dependent) sufficiently small neighborhood of the origin.