On the similarity solutions of magnetohydrodynamic flows of power-law fluids over a stretching sheet

A rigorous mathematical analysis is given for a magnetohydrodynamics boundary layer problem, which arises in the two-dimensional steady laminar boundary layer flow for an incompressible electrically conducting power-law fluid along a stretching flat sheet in the presence of an exterior magnetic field orthogonal to the flow. In the self-similar case, the problem is transformed into a third-order nonlinear ordinary differential equation with certain boundary conditions, which is proved to be equivalent to a singular initial value problem for an integro-differential equation of first order. With the aid of the singular initial value problem, the uniqueness and existence results for (generalized) normal solutions are established and some properties of these solutions are explored.     

MHD power-law fluid flow and heat transfer over a non-isothermal stretching sheet

This article presents a numerical solution for the magnetohydrodynamic (MHD) non-Newtonian power-law fluid flow over a semi-infinite non-isothermal stretching sheet with internal heat generation/absorption. The flow is caused by linear stretching of a sheet from an impermeable wall. Thermal conductivity is assumed to vary linearly with temperature. The governing partial differential equations of momentum and energy are converted into ordinary differential equations by using a classical similarity transformation along with appropriate boundary conditions. The intricate coupled non-linear boundary value problem has been solved by Keller box method. It is important to note that the momentum and thermal boundary layer thickness decrease with increase in the power-law index in presence/absence of variable thermal conductivity.     

Eigenvalue analysis for a crack in a power-law material

A nonlinear eigenvalue problem related to determining the stress and strain fields near the tip of a transverse crack in a power-law material is studied. The eigenvalues are found by a perturbation method based on representations of an eigenvalue, the corresponding eigenfunction, and the material nonlinearity parameter in the form of series expansions in powers of a small parameter equal to the difference between the eigenvalues in the linear and nonlinear problems. The resulting eigenvalues are compared with the accurate numerical solution of the nonlinear eigenvalue problem.     

Time-harmonic acoustic propagation in the presence of a shear flow

This work deals with the numerical simulation, by means of a finite element method, of the time-harmonic propagation of acoustic waves in a moving fluid, using the Galbrun equation instead of the classical linearized Euler equations. This work extends a previous study in the case of a uniform flow to the case of a shear flow. The additional difficulty comes from the interaction between the propagation of acoustic waves and the convection of vortices by the fluid. We have developed a numerical method based on the regularization of the equation which takes these two phenomena into account. Since it leads to a partially full matrix, we use an iterative algorithm to solve the linear system.     

Non-continuation of the periodic oscillations of a forced pendulum in the presence of friction

A well known theorem says that the forced pendulum equation has periodic solutions if there is no friction and the external force has mean value zero. In this paper we show that this result cannot be extended to the case of linear friction.

     

Computed oscillations of a confined submerged liquid jet

The jet oscillation observed in thin slab continuous casting is studied numerically by modelling the flow of liquid injected through a submerged entry nozzle and into a cavity. The oscillation relies on the exchange of fluid between recirculation cells on each side of the jet via a cross-flow through the gap between the nozzle shaft and the broad face of the cavity wall. Features of the oscillating jet are investigated by varying the resistance to cross-flow. This resistance occurs naturally since the nozzle obstructs cross-flow. The predicted oscillation can be manipulated by altering the cross-flow (through the use of an effective resistance force in the model) or stopped altogether to form a static asymmetrical flow pattern. Flow calculations are performed using a transient, two-dimensional, turbulent, fluid flow model.     

On small oscillations of a compressible stratified liquid

We study the structure of the spectrum and the completeness and basis property of a system of eigenvectors. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 12, pp. 1614–1623, December, 2006.     

Nonlinear oscillations of a variable composition liquid in a cylindrical vessel

The problem of wave motions of an ideal liquid of variable composition in a cylindrical vessel is reduced to an infinite system of nonlinear differential equations. It is shown that in the case of axisymmetric oscillations the equations obtained refine the linear analog of the problem, even if the vessel filling depth is significantly greater than the amplitude of the liquid free surface oscillations.Donetsk. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 20, pp. 104–107, 1989.     

Forced oscillations in a rotating liquid (I)

Zusammenfassung Der vorliegenden Analyse liegen die linearisierten Gleichungen für die achsensymmetrischen Störungen einer gleichförmig rotierenden Flüssigkeit zugrunde. Dabei wird aber keine Annahme hinsichtlich einer Zeitabhängigkeit der erzwungenen Bewegungen gemacht und die Entwicklung der Störungen vom Beginn der erzwungenen Bewegung an studiert. Ungeachtet der sich zeigenden analytischen Schwierigkeiten können über die allgemeinen Störbewegungen Aussagen gemacht werden.Für die relativ schnellen harmonischen Schwingungen (mit einer Störfrequenz grösser als die doppelte Rotationsfrequenz) findet man, nachdem die Einwirkung zeitlich genügend dauerte, dass die Bewegung der Flüssigkeit und jene des erzwungenen Mechanismus — wie in den früheren Arbeiten angenommen — überall phasengleich ist. Demgegenüber wird für Schwingungen mit kleinerer Relativfrequenz ein System fortschreitender Wellen vorausgesagt. Spezielle Aufmerksamkeit wird hier dem früheren Falle geschenkt; mit Hilfe einer Ähnlichkeitsbetrachtung kann die Analyse einer breiten Klasse der durch kleine harmonische Schwingungen erregten Bewegungen auf ein Problem der Potentialtheorie reduziert werden. Als Beispiele werden die axial schwingende und die radial pulsierende Kugel kurz erörtert.     

Finite element modeling of the nonlinear oscillations in axisymmetric acoustic resonators

Oscillation of a gas in closed resonators has gained considerable interest in the past years. In this paper, the nonlinear equations governing the behavior of the gas oscillations inside the resonator are formulated in a weak form and then modeled using the finite element method. The pressure ratios, predicted by the proposed model, are in close agreement with the exact solutions available for simple geometries such as cylindrical, exponential and linearly varying area resonators. The presented comparisons validate the accuracy of the finite element model and emphasize its potential for predicting the performance or resonators of more complex geometries which are necessary for generating high pressures from the standing waves. Also, gas flow through the boundaries of the resonator is implemented in the proposed model. The presented finite element model presents an invaluable tool for designing a new class of acoustic compressors which can be used, for example, in refrigeration and vibration control applications.     

Non-linear oscillations of a non-viscous cylindrical liquid system in weightlessness condition

For an immiscible cylindrical liquid system in a circular cylindrical container and a liquid layer around a rigid center core consisting of incompressible and non-viscous liquid the natural non-linear frequencies are determined, if the system is in a zero-gravity environment. The frequencies are determined as a function of the surface elevation and are presented as backbone curves.It was found, that the immiscible liquid system shows hardening effect depending on the length-to-diameter ratio of the column, the density ratio and the diameter ratio. This means that with increasing interface amplitude the natural frequency increases above the linearized frequency. Decreasing density ratio (inner to outer density), increasing diameter ratio and decreasing aspect ratio yield stronger hardening effects. For a liquid layer around a rigid center core the system shows stronger effects, but exhibits softening behavior, i.e. lower natural frequencies for increasing liquid surface amplitude. Decreasing aspect ratio and decreasing layer thickness show stronger softening effects, as do increasing mode numbers. Close to the Rayleigh instability the liquid system shows extreme non-linear effects.

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Zusammenfassung Es werden die nichtlinearen Frequenzen eines nichtmischbaren Flüssigkeitssystems in einem Kreiszylinderbehälter und einer Flüssigkeitsschicht um einen Zylinder im schwerelosen Zustand bestimmt. Die Frequenzen werden als Funktion der Oberflächenauslenkung dargestellt.Es wurde festgestellt, da\ die Trennflächenfrequenzen des nichtmischbaren Systems überlinear sind, wobei die Stärke der Nichtlinearität vom Streckungs-, Dichte- und Durchmesserverhältnis abhängt. Ein kleiner werdendes Dichteverhältnis (innerer zu äu\erer Dichte), grö\er werdendes Durchmesserverhältnis und kleineres Streckungsverhältnis ergeben stärkere Überlinearität. Für eine Flüssigkeitsschicht um einen Zylinder konnte unterlineares Verhalten festgestellt werden. Kleiner werdendes Streckungs- und Dickenverhältnis sowie höhere Schwingungsformen ergeben stärkere Unterlinearität. In der Nähe der Rayleigh-Instabilität zeigt das Flüssigkeilssystem extreme Nichtlinearitäten.

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List of symbols a radius of container wall or rigid center core - b radius of interfacial or free liquid surface (see Fig. 1) - L length of liquid column - m,n angular mode number of liquid, axial mode number - I _m,K _m modified Besselfunctions of first and second kind andmth order - r,,z polar coordinates - R ₁,R ₂ radii of curvature - t time - ₁, ₂ velocity potential of liquid outside and inside - (, z, t) free liquid- or interfacial elevation - _1;2 liquid densities - liquid surface tension (or interface tension) - _mn ⁽⁰⁾ linear natural frequency of liquid - frequency of liquid (non-linear)     

Weak oscillations of a gas bubble in a spherical volume of compressible liquid

The following spherically symmetric problem is considered: a single gas bubble at the centre of a spherical flask filled with a compressible liquid is oscillating in response to forced radial excitation of the flask walls. In the long-wave approximation at low Mach numbers, one obtains a system of differential-difference equations generalizing the Rayleigh-Lamb-Plesseth equation. This system takes into account the compressibility of the liquid and is suitable for describing both free and forced oscillations of the bubble. It includes an ordinary differential equation analogous to the Herring-Flinn-Gilmore equation describing the evolution of the bubble radius, and a delay equation relating the pressure at the flask walls to the variation of the bubble radius. The solutions of this system of differential-difference equations are analysed in the linear approximation and numerical analysis is used to study various modes of weak but non-linear oscillations of the bubble, for different laws governing the variation of the pressure or velocity of the liquid at the flask wall. These solutions are compared with numerical solutions of the complete system of partial differential equations for the radial motion of the compressible liquid around the bubble.     

The stability of a column of liquid to torsional oscillations

Résumé On fait appel à la théorie linéaire de stabilité pour démontrer que des perturbations axisymétriques d'une colonne infinie de fluide en rotation continue et entourée d'un autre fluide noncompressible peuvent être représentées comme la somme des oscillations méridionales et des oscillations de torsion, pourvu que les nombres de Reynolds soient petits. Dans ce cas, le composant de torsion ne peut conduire à des instabilités.     

Geostatistical computing of acoustic maps in the presence of barriers

Acoustic maps are the main diagnostic tools used by authorities for addressing the growing problem of urban acoustic contamination. Geostatistics models phenomena with spatial variation, but restricted to homogeneous prediction regions. The presence of barriers such as buildings introduces discontinuities in prediction areas. In this paper we investigate how to incorporate information of a geographical nature into the process of geostatistical prediction. In addition, we study the use of a Cost-Based distance to quantify the correlation between locations.     

The motion of a submerged sphere in a liquid under an ice sheet

The solution of the linear steady problem of the flow of an inviscid, incompressible and infinitely deep liquid around a sphere under an ice sheet, which is modelled by a thin elastic stressed plate of constant thickness is constructed. Special cases of this problem are the motion of a submerged sphere under broken ice, a membrane, and also under the free surface both in the presence and absence of capillary effects. The method of multipole expansions is used in the framework of the linear potential wave theory. The hydrodynamic loads (the wave drag and the buoyancy) acting on the body and also the distribution of the deflections of the ice sheet are calculated as a function of the body velocity, the ice thickness and the value of the compressing or stretching forces. It is shown that all the flow characteristics depend considerably on the ratio of the body velocity and the critical velocity of flexural-gravitational waves.     

A mathematical analysis of the elasto-plastic plane stress problem of a power-law material

In this paper a generic study on the plane stress problem ofa power-law material undergoing infinitesimal deformations iscarried out, and a general solution for the stress and strainfields is derived using a stress function method and analyticfunction theory. Hencky's deformation theory and von Mises'yield criterion are used, and a differential transformationis invoked in the analysis. As an example, the closed-form solutionof the pure bending problem of a thin beam of power-law materialis obtained by applying the general solution directly.     

On initial value problems for the flow in a thin sheet of viscous liquid

Résumé Une couche mince d'un liquide visqueux coule sur un plan horizontal. On établit l'équation différentielle, qui est non-linéaire pour ce mouvement. Pour le cas d'une concentration initiale du liquide à l'origine, nous calculons le développement de la forme de la surface libre. En outre, une solution de similitude est determinée.