A Source Transfer Domain Decomposition Method for Helmholtz Equations in Unbounded Domain Part II: Extensions

In this paper we extend the source transfer domain decomposition method (STDDM) introduced by the authors to solve the Helmholtz problems in two-layered media, the Helmholtz scattering problems with bounded scatterer, and Helmholtz problems in 3D unbounded domains. The STDDM is based on the decomposition of the domain into non-overlapping layers and the idea of source transfer which transfers the sources equivalently layer by layer so that the solution in the final layer can be solved using a PML method defined locally outside the last two layers. The details of STDDM is given for each extension. Numerical results are presented to demonstrate the efficiency of STDDM as a preconditioner for solving the discretization problem of the Helmholtz problems considered in the paper.     

Stability of a cylindrical shell in a stratified flow

Analysis of the Kelvin stability of a horizontal plane flow of two fluid layers of different densities and one moving relative to the other is extended to the case of longitudinal coaxial flow of a two-layered fluid within a circular cylindrical shell. It is shown that the loss of stability of the whole system sets in for low velocities of the layer motion, one relative to the other. A comparison is made with classical flutter for which the flow is not stratified.     

Parametric Vibrations of a Three-Layer Conical Piezoshell

Based on the Kirchhoff-Love hypotheses and adequate supplementary hypotheses for the distribution of electric field quantities, a model for parametric vibrations of composite shells of revolution made of a passive (without a piezoeffect) middle layer and two active (with a piezoeffect) surface layers under the action of harmonic mechanical and electric loads is developed. The dissipative material properties are taken into account by linear viscoelastic models. Since the vibrations on the boundary of the main domain of dynamic instability (MDDI) are harmonic, the investigation of this domain, in a first approximation, is reduced to generalized eigenvalue problems, which are solved by the finite-element method. The problem on parametric vibrations of a three-layer conical shell under harmonic mechanical loading is considered. The influence of the shell thickness, dissipation, and electric boundary conditions on the MDDI is investigated. Two limiting cases of electric boundary conditions are considered, where the electrodes are short-circuited or not. The curves presented show a considerable influence of the electric boundary conditions on the characteristics of the MDDI, namely on its width and position on the frequency axis and on the critical parameter of excitation.     

Junction layer analysis in one-dimensional steady-state Euler-Poisson equations

We study the quasi-neutral limit in one-dimensional steady-state Euler-Poisson equations with junction layers. Typically, the junction layer phenomenon occurs in a ballistic diode of a semiconductor device where the doping profile is a discontinuous function. We derive the junction layer equations and prove the existence of their solutions which decay exponentially. Finally, we justify the quasi-neutral limit with junction layers by giving uniform error estimates.     

Subcritical Rossby Waves in Zonal Shear Flows with Nonlinear Critical Layers

It was shown by Benney and Bergeron [ 1 ] that singular neutral modes with nonlinear critical layers are mathematically possible in a variety of shear flows. These are usually subcritical modes; i.e., they occur at values of the flow parameters where their linear, viscous counterparts would be damped. One question raised then is how such modes might be generated.
This article treats the problem of Rossby waves propagating in a mixing layer with velocity profile ū = tanh y . The beta parameter, which is a measure of the stabilizing Coriolis force, is taken to be large enough so that linear instability cannot occur. First, computed dispersion curves are presented for singular modes with nonlinear critical layers. Then, full numerical simulations are employed to illustrate how these modes can be generated by resonant interaction with conventional nonsingular Rossby waves, even when the singular mode is absent initially.     

The solution of contact problems of creep theory for combined ageing foundations

Solutions are presented of certain plane and axisymmetric contact problems on the frictionless impression of a rigid stamp into a two-layered ageing viscoelastic foundation. It is assumed that the upper layer is thin relative to the contact domain, and inhomogeneously ageing. The rheological properties of the lower layer are described by the equations of linear creep theory for ageing materials. The layers are mutually rigidly adherent. The contact domain does not change with time. Depending on the relationships between the moduli of the instantaneous elastic strains of the layers, the mixed problems reduce to integral equations of the first or second kinds containing Fredholm and Volterra operators. An analytic method is proposed for solving such equations which enables an expansion to be obtained for the fundamental characteristics of the contact interaction for a force varying with time in an arbitrary manner and acting on the stamp. Cases are investigaged for the artificial and natural ageing of a two-layer foundation.     

The Stability of Flows in a Differentially Heated Rotating Fluid System with Rigid Bottom and Free Top

The stability of certain steady flows in a rotating system with rigid bottom and free top surfaces is investigated. The simplest flow states having the essential spatial variations of steady responses of a rotating fluid system to differential heating in the horizontal are studied, that is, those with a constant gradient temperature distribution with both horizontal and vertical components, and the accompanying Coriolis-balanced constant velocity shear (thermal wind). Ekman boundary layers and intermediate boundary layers are encountered in a systematic asymptotic analysis in two small parameters, the Ekman number and an inverse Richardson number. The resulting neutral stability curves indicate the possibility of instabilities above the inviscid stability criterion due to Eady, for some mean flow configurations. The estimate of the critical Taylor number is numerically close to the values obtained in the most nearly applicable experiments.     

Limiting Models for Josephson Junctions and Superconducting Weak Links

One of the broadest applications of superconductivity is the technology based on Josephson junction devices. These junction devices are formed by placing a thin layer of normal (nonsuperconducting) material between layers of superconducting material. We consider various limiting cases for models of the junction device based on the Ginzburg-Landau equations. Examples include a model for large values of the Ginzburg-Landau parameter, κ, in the high-field regime and a model for a thin normal layer. Convergence analysis for the simplified models is established and numerical simulations are presented.     

简单闭环路网交通流定常解

基于在分岔路口满足用户均衡原理的假定,研究了由三条路段和两个交叉路口组成的简单闭环路网的交通流定常解问题,发现定常解参数及其性态依赖于路网上的车流总数:当车流总数不大于第一个临界值,或不小于第二个临界值时,定常解在每一条路段上均为密度取常数的平凡解;否则,在瓶颈路口（上游最大流量大于下游最大流量的路口）的上游路段将产生激波间断,呈排队等候现象.对分岔路口和交汇路口为瓶颈的情况,分别给出了完整的解析结果     

Wave-field asymptotics in the problem of diffraction by a planar junction of thin layers and boundary-contact conditions

The problem of diffraction by a planar junction of thin layers covering a perfectly conducting substratum is considered, and its asymptotic solution is constructed. The wave field in the vicinity of the junction of the layers is described by a function of the boundary layer. Based on the asymptotics obtained, the generalized impedance boundary condition, which simulates thin layers, and the contact conditions are derived. The uniqueness of the solution of a model problem is discussed. Bibliography: 6 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 230, 1995, pp. 157–171. Original Translated by M. A. Lyalinov.     

Spatial Stability for Mixed Convection Boundary Layer over a Heated Horizontal Plate

The spatial stability properties of a mixed convection boundary layer developing over a heated horizontal plate is studied here under linear and quasi-parallel flow assumption. The main aim of the present work is to find out if there is a critical buoyancy parameter that would indicate the importance of heat transfer in destabilizing mixed convection boundary layers, when the buoyancy effect is given by Boussinesq approximation. The undisturbed flow used here is that given by the similarity solution of [ 1 ] that implies the wall temperature to vary as the inverse square root of the distance from the leading edge of the plate. The stability of this flow has been investigated by using the compound matrix method (CMM)—that allows finding all the modes in the chosen range in the complex wave number plane for spatial stability analysis. Presented neutral curves for mixed convection boundary layer show the existence of two types of disturbances present simultaneously, for large buoyancy parameter. One notices very unstable high-frequency mode when the buoyancy parameter exceeds the above-mentioned critical value. This unstable thermal mode is in addition to the hydrodynamic mode of isothermal flow given by corresponding similarity profile. The calculated critical buoyancy parameter is shown to qualitatively match with experimental results.     

Critical curves for the total normal curvature in surfaces of 3-dimensional space forms

A variational problem closely related to the bending energy of curves contained in surfaces of real 3-dimensional space forms is considered. We seek curves in a surface which are critical for the total normal curvature energy (and its generalizations). We start by deriving the first variation formula and the corresponding Euler–Lagrange equations of these energies and apply them to study critical special curves (geodesics, asymptotic lines, lines of curvature) on surfaces. Then, we show that a rotation surface in a real space form for which every parallel is a critical curve must be a special type of a linear Weingarten surface. Finally, we give some classification and existence results for this family of rotation surfaces.     

A mathematical model for solute coupled water transport in the production of aqueous humor

A simple mathematical model for the transport of solute and water in the production of aqueous humor by ciliary epithelium in the eye has been developed. The model introduces the intercellular channel, caped with a leaky (porous) tight junction between the layers of non-pigmented ciliary epithelium, as a bisectional channel which consists of two sections: one representing the tight junction which constitutes the blood-aqueous barrier and the other intercellular space with the active solute transport pumps on its lateral surfaces near the junction. The intercellular space and porous tight junction are modeled as electroneutral, uniform, semi-permeable channels of unequal cross-sectional area. Both the cylindrical pore- and rectangular-slit models for the transport through the channels are simultaneously introduced. The approximate analytical solutions to the governing non-linear coupled equations are obtained in normalized forms by employing Segal’s “Isotonic Convection Approximation”. The computational results for the scaled variables are presented through the graphs. The effects of important parameters on the flow/transport produced by (1) the hydrostatic pressure difference alone, (2) the concentration difference alone, and (3) the active transport alone, are examined and discussed. The results of the model may contribute to the present understanding of the mechanisms governing transport processes involved in the aqueous production.     

Algebraic criteria for global existence or blow-up for a boundary coupled system of nonlinear diffusion equations

This article deals with the critical curves for a degenerate parabolic system coupled via nonlinear boundary flux. By constructing the self-similar supersolution and subsolution, we obtain the critical global existence curve. The critical curve of Fujita type is conjectured with the aid of some new results.     

Minimal curves of constant torsion

The Griffiths formalism is applied to find constant torsion curves which are extremal for arclength with respect to variations preserving torsion, fixing the endpoints and the binormals at the endpoints. The critical curves are elastic rods of constant torsion, which are shown to not realize certain boundary conditions.

     

Line source and point source scattering of acoustic waves by the junction of transmissive and soft-hard half planes

Firstly, the analysis of [A. Büyükaksoy, G. Cinar, A.H. Serbest, Scattering of plane waves by the junction of transmissive and soft-hard half planes, ZAMP 55 (2004) 483-499] for the scattering of plane waves by the junction of transmissive and soft-hard half planes is extended to the case of a line source. The introduction of the line source changes the incident field and the method of solution requires a careful analysis in calculating the scattered field. The graphical results are presented using MATHEMATICA. We observe that the graphs of the plane wave situation [A. Büyükaksoy, G. Cinar, A.H. Serbest, Scattering of plane waves by the junction of transmissive and soft-hard half planes, ZAMP 55 (2004) 483-499] can be recovered by shifting the line source to a large distance. Subsequently, the problem is further extended to the case of scattering due to a point source using the results obtained for a line source excitation. The introduction of a point source (three dimensions) involves another variable which then requires the calculation of an additional integral appearing in the inverse transform.     

Hydromagnetic stability of plane Couette flow of an upper convected Maxwell fluid

Hydrodynamic stability of plane Couette flow of an upper convectedMaxwell fluid is investigated in presence of a transverse magneticfield assuming that the magnetic Prandtl number is sufficientlysmall. The resulting equation is a modified Orr–Sommerfeldequation. The equations of stability are solved numericallyusing Chebyshev collocation method with QZ algorithm. The criticalvalues of Reynolds number, wave number and wave speed are computedand the results are shown through the neutral curves. By increasingthe amount of elasticity to a certain value, it is shown that,as the Hartmann number increases, the minimum critical Reynoldsnumber decreases and it does not increase again in contrastto the Newtonian case.     

A simulated annealing based solution approach for the two-layered location registration and paging areas partitioning problem in cellular mobile networks

This paper presents a mathematical model and simulated annealing based solution approach for finding optimal location updates and paging area configuration for mobile communication networks. We use a two-layered zone-based location registration and paging scheme in which the costs of location updates and paging signaling traffic are reduced by introducing a two-step paging process. The location updates and paging procedures in a two-layered scheme are first described, and an approximation of the measure required for calculating the paging-related signaling volume is provided based on assumptions of cell shapes and mobile stations’ movement patterns. A simulated annealing (SA)-based solution method is devised along with a greedy heuristic, and computational experiments are conducted to illustrate the superiority of the proposed SA-based method over other solution methods.     

Value of games with two-layered hypergraphs

This paper studies cooperative games with restricted cooperation among players. We define situations in which a priori unions and hypergraphs coexist simultaneously and mutually depend on each other. We call such structures two-layered hypergraphs. Using a two-step approach, we define a value of the games with two-layered hypergraphs. The value is characterized by Owen’s coalitional value of hypergraph-restricted games and in terms of weighted Myerson value. Further, our value is axiomatically characterized by component efficiency and a coalition size normalized balanced contributions property.     

Hamiltonian identities for elliptic partial differential equations

New identities for elliptic partial differential equations are obtained. Several applications are discussed. In particular, Young's law for the contact angles in triple junction formation is proven rigorously. Structure of level curves of saddle solutions to Allen-Cahn equation are also carefully analyzed.