Numerical method for computing two-dimensional unsteady rarefied gas flows in arbitrarily shaped domains

A high-order accurate method for analyzing two-dimensional rarefied gas flows is proposed on the basis of a nonstationary kinetic equation in arbitrarily shaped regions. The basic idea behind the method is the use of hybrid unstructured meshes in physical space. Special attention is given to the performance of the method in a wide range of Knudsen numbers and to accurate approximations of boundary conditions. Examples calculations are provided.     

The Gaussian primes contain arbitrarily shaped constellations

We show that the Gaussian primesP[i] ? ?[i] contain infinitely constellations of any prescribed shape and orientation. More precisely, we show that given any distinct Gaussian integersv ₀,…,v _k?1, there are infinitely many sets {a+rv ₀,…,rv _k?1}, witha ∈?[i] andr ∈?{0}, all of whose elements are Gaussian primes. The proof is modeled on that in [9] and requires three ingredients. The first is a hypergraph removal lemma of Gowers and Rödl-Skokan or, more precisely, a slight strenghthening of this lemma which can be found in [22]; this hypergraph removal lemma can be thought of as a generalization of the Szemerédi-Furstenberg-Katznelson theorem concerning multidimensional arithmetic progressions. The second ingredient is the transference argument from [9], which allows one to extend this hypergraph removal lemma to a relative version, weighted by a pseudorandom measure. The third ingredient is a Goldston-Yildirim type analysis for the Gaussian integers, similar to that in [9], which yields a pseudorandom measure. which is concentrated on Gaussian “almost primes”.     

Analysis of arbitrarily shaped planar cracks in two-dimensional hexagonal quasicrystals with thermal effects. Part II: Numerical solutions

The extended displacement discontinuity (EDD) boundary element method is developed to analyze an arbitrarily shaped planar crack in two-dimensional (2D) hexagonal quasicrystals (QCs) with thermal effects. The EDDs include the phonon and phason displacement discontinuities and the temperature discontinuity on the crack face. Green's functions for uniformly distributed EDDs over triangular and rectangular elements for 2D hexagonal QCs are derived. Employing the proposed EDD boundary element method, a rectangular crack is analyzed to verify the Green's functions by discretizing the crack with rectangular and triangular elements. Furthermore, the elliptical crack problem for 2D hexagonal QCs is investigated. Normal, tangential, and thermal loads are applied on the crack face, and the numerical results are presented graphically.     

On magnetoelastic problems of a plane with an arbitrarily shaped hole under stress and displacement boundary conditions

An analytical method for the static plane problem of magnetoelasticityis developed for an infinite plane containing a hole of arbitraryshape under stress and displacement boundary conditions in aprimary uniform magnetic field. The magnetic field influencesthe elastic field by introducing a body force called the Lorentzponderomotive force in the equilibrium equations. The body forcecan be further described in a form relating with the electromagneticstress tensor. The complex variable method in conjunction withthe rational mapping function technique is used in the analysisfor both magnetic field and mechanical field. Governing equationsand boundary conditions are expressed in terms of complex functions.Complex magnetic potential and stress functions are obtainedusing Cauchy integrals for the paramagnetic and soft ferromagneticmaterials, respectively. The distributions of magnetic fieldand the stress components are shown for certain directions ofprimary magnetic fields in an infinite plane with a square hole,as an example. It is found that the stress distributions forthe two types of materials are identical despite the differenceof magnetic fields. The extreme cases of a free and a fixedhole reduced to a crack and a rigid fibre, respectively, arealso investigated. The stress intensity factors at the tipsof crack and rigid fibre are computed, and their variation forcertain directions of primary magnetic field is shown.     

Two arbitrarily located normal forces and a penny‐shaped crack: a complete solution

The following problem is considered: a penny‐shaped crack is located in the plane z=0 of a transversely isotropic elastic space and interacts with two equal and opposite normal forces, which are located arbitrarily, but symmetrically with respect to the plane of the crack. An exact closed‐form solution is obtained and expressed in terms of elementary functions for the fields of stresses and displacements in the whole space. This kind of problem deemed to be intractable by the methods of contemporary mathematical analysis, and has never been attempted before, even in the case of an isotropic body. Copyright © 1999 John Wiley & Sons, Ltd.     

A coupled stress and energy failure model for crack initiation in arbitrarily shaped adhesive lap joints

In this work, crack initiation in adhesive lap joints of arbitrary joint configuration is studied by means of a finite fracture mechanics approach. The analysis is based on a general stress solution for adhesive joints combined with a coupled stress and energy criterion. The instantaneous formation of a crack of finite size is predicted if a stress and energy criterion are satisfied simultaneously. The closed-form analytical solution of the stress field allows for an efficient evaluation of the crack initiation load and corresponding finite crack length. A comparison to experimental results from literature and to numerical results obtained with a cohesive zone model approach shows a good agreement. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of arbitrarily shaped planar cracks in two-dimensional hexagonal quasicrystals with thermal effects. Part I: Theoretical solutions

An extended displacement discontinuity (EDD) boundary integral equation method is proposed for analysis of arbitrarily shaped planar cracks in two-dimensional (2D) hexagonal quasicrystals (QCs) with thermal effects. The EDDs include the phonon and phason displacement discontinuities and the temperature discontinuity on the crack surface. Green's functions for unit point EDDs in an infinite three-dimensional medium of 2D hexagonal QC are derived using the Hankel transform method. Based on the Green's functions and the superposition theorem, the EDD boundary integral equations for an arbitrarily shaped planar crack in an infinite 2D hexagonal QC body are established. Using the EDD boundary integral equation method, the asymptotic behavior along the crack front is studied and the classical singular index of 1/2 is obtained at the crack edge. The extended stress intensity factors are expressed in terms of the EDDs across crack surfaces. Finally, the energy release rate is obtained using the definitions of the stress intensity factors.     

Numerical simulation of Casson fluid flow through differently shaped arterial stenoses

The present investigation deals with a mathematical model of blood flow through an asymmetric (about its narrowest point) arterial constriction obtained from casting of a mildly stenosed artery. The flowing blood is represented as the suspension of all red cells (erythrocytes) in plasma assumed to be Casson fluid, while the arterial wall is considered to be rigid having differently shaped stenoses in its lumen arising from various types of abnormal growth or plaque formation. The governing equations of motion accompanied by the appropriate choice of the boundary conditions are solved numerically by Marker and Cell method in order to compute the physiologically significant quantities with desired degree of accuracy. The necessary checking for numerical stability has been incorporated in the algorithm for better precision of the results computed. The quantitative analyses have been carried out finally with the inclusion of the respective profiles of the flow field over the entire arterial segment as well. The key factors such as the wall shear stress, the pressure drop and the velocity profiles are exhibited graphically and examined thoroughly for qualitative insight into blood flow phenomena through arterial stenosis.     

Thermal stresses in an elastic half-space associated with an arbitrarily distributed moving heat source

Zusammenfassung Es wird das thermoelastische Spannungsfeld in einem Halbraum erhalten, erzeugt durch eine willkürlich verteilte, sich längs des Randes gleichförmig rasch bewegenden Wärmequelle. Dabei wird angenommen, dass Wärme aus dem elastischen Halbraum durch Konvektion abgeleitet wird. Es wird die zweidimensionale entkoppelte Theorie verwendet. Als Beispiel wird ein Problem der elasto-hydrodynamischen Schmierung betrachtet.

---

---

This work was sponsored by the Office of Naval Research, U.S. Navy.     

Numerical solution by LMMs of stiff delay differential systems modelling an immune response

Summary. We consider the application of linear multistep methods (LMMs) for the numerical solution of initial value problem for stiff delay differential equations (DDEs) with several constant delays, which are used in mathematical modelling of immune response. For the approximation of delayed variables the Nordsieck's interpolation technique, providing an interpolation procedure consistent with the underlying linear multistep formula, is used. An analysis of the convergence for a variable-stepsize and structure of the asymptotic expansion of global error for a fixed-stepsize is presented. Some absolute stability characteristics of the method are examined. Implementation details of the code DIFSUB-DDE, being a modification of the Gear's DIFSUB, are given. Finally, an efficiency of the code developed for solution of stiff DDEs over a wide range of tolerances is illustrated on biomedical application model. Received March 23, 1994 / Revised version received March 13, 1995     

On an application of forms of arbitrarily high degree as the Lyapunov functions

In the paper a method of studying forms of odd degree in some cone of a domain of the space is given,which allows us to use as functions the Lyapunov forms of arbitrarily high degree. It is shown that anapplication of such forms gives a possibility of obtaining conditions on monotonic stability of one modelsystem with a polynomial right-hand side of a special form. With the help of forms of high degree we modifythe known theorem on an exponential stability, and also the possibility of using them as components of avector Lyapunov function in the study of stability of complex systems is shown.Translated from Dinamicheskie Sistemy, No. 7, pp. 89–95, 1988.     

Numerical determination of heat exchanger response

In this paper there is presented approximative calculation of the temperature of fluid in fixed point of heat exchanger and in fixed time. In presented method are used Newton-Cotes formulas. Moreover there is evaluated the error which is made during determination of heat exchanger response. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical solution of the dynamic problem of the elasticity theory in arbitrary shaped plane domain

The numerical method for solving the dynamical problems of the theory of elasticity in two-dimensional arbitrary shaped regions is proposed. The developed method consists of two main stages. The first one deals with the numerical grid generation. The method for creating the regular two dimensional grids based on equations of longitudinal plate deformation is presented. The last problem is solved numerically by means of finite difference method with the posterior using of the iteration process. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Integral trees of arbitrarily large diameters

In this paper, we construct trees having only integer eigenvalues with arbitrarily large diameters. In fact, we prove that for every finite set S of positive integers there exists a tree whose positive eigenvalues are exactly the elements of S. If the set S is different from the set {1} then the constructed tree will have diameter 2|S|.