Explicit solutions of the problems of elastostatics for an elastic circle with double porosity

In this paper the Aifantis linear theory of consolidation with double porosity is considered. The boundary value problems (BVPs) of elastostatics for an elastic circle are formulated and the uniqueness theorems for regular (classical) solutions are proved. The explicit solutions of these BVPs are constructed by means of absolutely and uniformly convergent series.     

Dimension Reduction in the Context of Structured Deformations

In the present paper the basic boundary value problems (BVPs) of the full coupled linear theory of elasticity for triple porosity materials are investigated by means of the potential method (boundary integral equation method) and some basic results of the classical theory of elasticity are generalized. In particular, the Green’s identities and the formula of Somigliana type integral representation of regular vector and regular (classical) solutions are presented. The representation of Galerkin type solution is obtained and the completeness of this solution is established. The uniqueness theorems for classical solutions of the internal and external BVPs are proved. The surface (single-layer and double-layer) and volume potentials are constructed and their basic properties are established. Finally, the existence theorems for classical solutions of the BVPs are proved by means of the potential method and the theory of singular integral equations.     

Uniqueness theorems in the theory of thermoelasticity for solids with double porosity

In this paper the coupled linear theory of thermoelasticity for solids with double porosity is considered. The governing system of field equations of this theory is based on motion equations, conservation of fluid mass, constitutive equations, extended Darcy’s law for materials with double porosity and Fourier’s law for heat conduction. A wide class of the basic internal and external boundary value problems (BVPs) of steady vibrations is formulated and uniqueness theorems for regular (classical) solutions of these BVPs are proved.     

Potential Method in the Linear Theory of Viscoelastic Materials with Voids

In the present paper the linear theory of viscoelasticity for Kelvin–Voigt materials with voids is considered and some basic results of the classical theory of elasticity are generalized. Indeed, the basic properties of plane harmonic waves are established. The explicit expression of fundamental solution of the system of equations of steady vibrations is constructed by means of elementary functions. The Green’s formulas in the considered theory are obtained. The uniqueness theorems of the internal and external basic boundary value problems (BVPs) are proved. The representation of Galerkin type solution is obtained and the completeness of this solution is established. The formulas of integral representations of Somigliana type of regular vector and regular (classical) solution are obtained. The Sommerfeld-Kupradze type radiation conditions are established. The basic properties of elastopotentials and singular integral operators are given. Finally, the existence theorems for classical solutions of the internal and external basic BVPs of steady vibrations are proved by using of the potential method (boundary integral method) and the theory of singular integral equations.     

A practical implementation of spectral methods resistant to the generation of spurious eigenvalues

This work describes a practical way of constructing a spectral representation of linear boundary value problems (BVPs) using a tau method. All BVPs are treated as first-order systems, unlike most implementations which tend to view the problem in terms of a single high-order differential equation. For most applications this formulation will adhere more closely to the natural derivation of the original equations from, for example, a series of conservation laws. The technique is exemplified for Chebyshev polynomials in a variety of real applications, although detailed results are provided for any polynomial basis.     

Peristaltic motion of third grade fluid in curved channel

＂ Analysis is performed to study the slip effects on the peristaltic flow of non-Newtonian fluid in a curved channel with wall properties. The resulting nonlinear partial differential equations are transformed to a single ordinary differential equation in a stream function by using the assumptions of long wavelength and low Reynolds number. This differential equation is solved numerically by employing the built-in routine for solving nonlinear boundary value problems （BVPs） through the software Mathematica. In addition, the analytic solutions for small Deborah number are computed with a regular perturbation technique. It is noticed that the symmetry of bolus is destroyed in a curved channel. An intensification in the slip effect results in a larger magnitude of axial velocity. Further, the size and circulation of the trapped boluses increase with an increase in the slip parameter. Different from the case of planar channel, the axial velocity profiles are tilted towards the lower part of the channel. A comparative study between analytic and numerical solutions shows excellent agreement.     

常微分方程技术及其在固体力学计算中的应用

常微分方程(ODE——Ordinary Differential Equation)边值问题的最新计算求解技术的迅速发展推出了一批高质高效的通用软件,而工程中大量的ODE问题并非呈现为这些求解器(Solver)所接受的标准形式。然而,运用一些简单的ODE变换技巧可以将大量的不同类型的特殊问题转化为标准形式。本文列举了若干常用的变换技巧,并广泛地应用于各种固体力学问题的计算中,使大量的ODE问题在形式上得到统一,得以用标准的ODE Solver方便有效地求解。     

Thermoelastostatic equilibrium of a spatial quadrant: Green’s function and solution in integrals

In this study, a new Green??s function and a new Green-type integral formula for a 3D boundary value problem (BVP) in thermoelastostatics for a quarter-space are derived in closed form. On the boundary half-planes, twice mixed homogeneous mechanical boundary conditions are given. One boundary half-plane is free of loadings and the normal displacements and the tangential stresses are zero on the other one. The thermoelastic displacements are subjected by a heat source applied in the inner points of the quarter-space and by mixed non-homogeneous boundary heat conditions. On one of the boundary half-plane, the temperature is prescribed and the heat flux is given on the other one. When the thermoelastic Green??s function is derived, the thermoelastic displacements are generated by an inner unit point heat source, described by ??-Dirac??s function. All results are obtained in elementary functions that are formulated in a special theorem. As a particular case, when one of the boundary half-plane of the quarter-space is placed at infinity, we obtain the respective results for half-space. Exact solutions in elementary functions for two particular BVPs for a thermoelastic quarter-space and their graphical presentations are included. They demonstrate how to apply the obtained Green-type integral formula as well as the derived influence functions of an inner unit point body force on volume dilatation to solve particular BVPs of thermoelasticity. In addition, advantages of the obtained results and possibilities of the proposed method to derive new Green??s functions and new Green-type integral formulae not for quarter-space only, but also for any canonical Cartesian domain are also discussed.     

Solution for dissimilar elastic inclusions in a finite plate using boundary integral equation method

This paper studies the boundary value problem for a finite plate containing two dissimilar inclusions. The matrix and the two inclusions have different elastic properties. The loadings applied along the outer boundary are in equilibrium. The mentioned problem is decomposed into three boundary value problems (BVPs). Two of them are interior BVP for the elastic inclusions, while the other is a BVP for the triply-connected region. Three problems are connected together through the common displacements and tractions along the interface boundaries. Explicit form for the complex variable boundary integral equation (CVBIE) is derived. After discretization of relevant BIEs, the solutions are evaluated numerically. Three numerical examples for different elastic constant combinations are provided.     

The history of community genetics: the contribution of the haemoglobin disorders

The emerging possibilities of applying new diagnostic technologies for genetic diagnosis and screening point to the need for a discipline of community genetics. Genetic population screening for haemoglobin disorders (thalassaemias and sickle cell disorders) has been practised on a large scale for over 20 years, and basic concepts and methods of community genetics have been developed within this framework, under the auspices of the WHO. Genetic population screening is a public health activity. It involves many disciplines, and planning depends on reliable and regularly updated information. Basic methods for describing genetic epidemiology in terms of service needs, and for regular service audit have been developed, and IT-based approaches for making simple, accurate and diagnosis-specific information accessible to the public and health professionals are being explored.     

分段常微分方程边值问题的改进COLSYS算法

对分段定义的常微分方程边值问题的 COLSYS算法进行了改进 ,提高了其计算效率及数值稳定性 ,并且可以节省内存 ,这些优势随着分段数的增加而迅速加大。     

DOUBLE HIGH ORDER S－BREAKING BIFURCATION POINTS AND THEIR NUMERICAL DETERMINATION

ＤＯＵＢＬＥＨＩＧＨＯＲＤＥＲＳ－ＢＲＥＡＫＩＮＧＢＩＦＵＲＣＡＴＩＯＮＰＯＩＮＴＳＡＮＤＴＨＥＩＲＮＵＭＥＲＩＣＡＬＤＥＴＥＲＭＩＮＡＴＩＯＮ￥(杨忠华，叶瑞松)ＹａｎｇＺｈｏｎｇｈｕａ；（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓ，Ｓｈａｎｇｈ...     

PRINCIPLE AND APPLICATION OF STIFFNESS-DISTRIBUTION DIAGRAM MULTIPLICATION METHOD1)

在结构力学中,当采用常规图乘法计算变截面梁结构的位移时,通常会面临弯矩图分块面积多、图乘次数多、计算量大、计算效率低等困难。针对这些问题,从结构刚度的角度出发,提出变截面梁结构位移计算的刚度分配图乘法,推导了该方法的基本公式并建立其使用的基本操作原则。该方法概念清晰,容易理解,充分发挥了图乘法的优势。 算例的应用与比较表明,采用该方法进行位移图乘计算简便合理,计算量非常小,计算效率高,值得推广。     

Determination of the deformed position of a thin shell from surface strains and height function

This paper focuses on the following problem: given the strain tensor of a deformed reference surface of a thin shell and the distances of the points on this surface from some arbitrarily fixed reference plane (the so-called height function) find the position of this reference surface. Two alternative procedures supplying the solution are developed. The first one follows from the ideas developed by Darboux (Leçons sur la Théorie Général des Surfaces, Troisiéme Partie, Gauthier-Villars, Paris, 1894), whereas the second one is based on the polar decomposition theorem and techniques developed in continuum mechanics. These procedures are purely kinematic, valid for arbitrary surface geometry and for unrestricted surface strains. Szwabowicz (Deformable surfaces and almost inextensional deflections of thin shells, Habilitation Thesis, 1999) proposed a relatively simple non-linear boundary-value problem (BVP) for thin elastic shells, which was expressed in three surface strains and the height function as basic independent field variables. The results of this paper suggest that this approach to the non-linear problems of thin shells may be an attractive alternative to other BVPs developed in the literature.     

Plane Elastic Boundary Value Problem Posed by Displacement and Force Orientations on a Closed Contour

A boundary value problem (BVP) of the plane elasticity posed in terms of the orientations of forces and displacements is considered. The main aim of the present paper is to investigate the solvability of BVPs of this kind. Firstly, analysis of two cases is performed: the case of a circle with special orientations of force and displacement vectors on the circumference and the case of an arbitrary contour with coaxial orientations of these vectors. The solutions obtained indicate that the problem can have a certain number of solutions or be unsolvable. Then the BVP is reduced to a boundary integral equation and its solvability is investigated for the general case of a smooth simple-connected closed contour. As a result, the number of linearly independent solutions is determined. This number only depends upon the angle between the force and displacement vectors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Second-gradient homogenized model for wave propagation in heterogeneous periodic media

The paper is focused on a homogenization procedure for the analysis of wave propagation in materials with periodic microstructure. By a reformulation of the variational-asymptotic homogenization technique recently proposed by Bacigalupo and Gambarotta (2012a), a second-gradient continuum model is derived, which provides a sufficiently accurate approximation of the lowest (acoustic) branch of the dispersion curves obtained by the Floquet–Bloch theory and may be a useful tool for the wave propagation analysis in bounded domains. The multi-scale kinematics is described through micro-fluctuation functions of the displacement field, which are derived by the solution of a recurrent sequence of cell BVPs and obtained as the superposition of a static and dynamic contribution. The latters are proportional to the even powers of the phase velocity and consequently the micro-fluctuation functions also depend on the direction of propagation. Therefore, both the higher order elastic moduli and the inertial terms result to depend by the dynamic correctors. This approach is applied to the study of wave propagation in layered bi-materials with orthotropic phases, having an axis of orthotropy parallel to the direction of layering, in which case, the overall elastic and inertial constants can be determined analytically. The reliability of the proposed procedure is analysed by comparing the obtained dispersion functions with those derived by the Floquet–Bloch theory.     

具有待定形函数的有限元线法

有限元线法是一种优良的半解析法，但其解函数存在解析方向和离散方向上的精度不相称的问题。本文提出了一种基于有限元线法的双向解析法——具有待定形函数的有限元线法。该方法设形函数为未知待定并借助能量原理对形函数进行解析性求解，使解函数在两个方向上的精度达到相称，从而大幅度提升了解答的整体质量和精度。文中，以二维Poisson方程问题为例，具体给出了待定形函数的有限元线法的算法和算例，用以表明本法的可行性和有效性。     

Adjoint Pairs of Differential-Algebraic Equations and Their Lyapunov Exponents

This paper is devoted to the analysis of adjoint pairs of regular differential-algebraic equations with arbitrarily high tractability index. We consider both standard form DAEs and DAEs with properly involved derivative. We introduce the notion of factorization-adjoint pairs and show their common structure including index and characteristic values. We precisely describe the relations between the so-called inherent explicit regular ODE (IERODE) and the essential underlying ODEs (EUODEs) of a regular DAE. We prove that among the EUODEs of an adjoint pair of regular DAEs there are always those which are adjoint to each other. Moreover, we extend the Lyapunov exponent theory to DAEs with arbitrarily high index and establish the general class of DAEs being regular in Lyapunov’s sense. The Perron identity which is well known in the ODE theory does not hold in general for adjoint pairs of Lyapunov regular DAEs. We establish criteria for the Perron identity to be valid. Examples are also given for illustrating the new results.     

Experimental investigation of the interaction between an electrically charged liquid-drop dispersed phase and a turbulent air-steam jet

The interaction of an electrically charged liquid-drop dispersed phase with a turbulent air-steam jet in a "water drop generator (capillary)-jettarget" system is investigated. The experimental conditions were as follows: volume flow of water through the capillary 0.01 cm³/s. capillary inside diameter 0.8 mm, electric potential applied to the capillary 20 kV. When the electric field is absent, condensation does not develop in the jet despite the existence of oversaturation zones. Two regimes of interaction between the charged dispersed phase and the jet are detected. The first regime (for ϕ<8 kV) is characterized by the regular launching of fairly large charged drops (0.5<r<2 mm) from the capillary and the absence of condensation in thejet. As the potential ϕ increases, the drop size decreases, whereas the drop charge increases. This regime made it possible to model the motion of individual charged clusters of different charge and size in aircraft engine jets. The second regime (ϕ>8 kV) is characterized by the irregular launching of drops from the capillary, drop dispersion with respect to size, a sharp increase in the target current, and the sudden appearance of condensation in the air-steam jet. The possible electrohydrodynamic and heterophase processes are qualitatively analyzed. Moscow, e-mail: vatazhin@ciam.ru.likhter@ciam.ru. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 102–114, July–August, 2000. The work received financial support from the Russian Foundation for Basic Research (project No. 99-01-00983).     

Analytical Model for The Capillary Pressure Gradient in Oil–Water–Rock System

A simplified analytical expression for the capillary pressure gradient in homogeneous porous media is proposed. Basic assumptions are: (1) the three phase contact angle between two fluids and porous rock is finite, (2) the surface area of contact between two fluids is small in comparison with contact surface areas between each fluid and porous rock in the unit volume of the system under consideration, (3) the model corresponds to conditions when both phases are continuous.