Liquid Filtration in an Unbounded Water‐Bearing Stratum with an Inclined Confining Bed

PolubarinovaKochina, Numerov, and other authors paid much attention to filtration problems of a heavy incompressible liquid in inclined waterbearing strata. In this work, therefore, classical schemes of liquid filtration on inclined confining beds are considered along with the general problem of filtration for arbitrary polygonal impermeable walls of a waterbearing stratum. In doing so, we also consider direct problems of physical and geometrical parameters of filtration flows.     

Pressure-hole errors—an alternative approach

A new analysis of the pressure-hole problem, which avoids some of the problems of the Higashitani-Pritchard (HP) analysis, is presented. The results are the same as those of the HP analysis for any fluid where the viscosity and the normal stress functions are multiples of one another. The relation of this result to experiments and computations is discussed.     

Container for Localization of an Explosion of a Compact High–Explosive Charge with an Inert Shell

Results of an experimental study of fragmentation effects in the explosion and the piercing power of the fragments of inert masses in the form of hemispherical aluminum and soft–steel shells enclosing the spherical charge of a high explosive under their action on flat steel, aluminum, steel–net, and claydite—concrete barriers are given. A design of the lightest spherical explosion–proof container with a load–carrying steel or glass–reinforced plastic shell protected by a splinter–proof layer capable of withstanding an explosion of a high–explosive charge (with a twofold safety factor) with an inert steel shell is proposed.     

Die Spaltströmung an geraden Schaufelgittern

Zusammenfassung In einem Wasserkanal wurde die Spaltströmung an geraden Schaufelgittern mit Druckanstieg untersucht. Es wird eine Methode zur Erzeugung von Schwebeteilchen in Wasser und ein stereographisches Meßverfahren beschrieben.Die Strömungsbilder zeigen, daß sich bei dünnen Schaufelprofilen und kleiner Spaltbreite die durch den Spalt fließende Flüssigkeit zu einem tütenförmigen Wirbel aufrollt. Wenn der Druckanstieg des Gitters größer ist als der Staudruck der Durchsatzgeschwindigkeit, so können die Spaltwirbel diesen Druckanstieg nicht überwinden und enden innerhalb des Gitters in einem Totwassergebiet.Die Untersuchung eines Schaufelgitters mit großer Spaltbreite ergab, daß der Spalt bei starkem Druckanstieg nicht durchströmt wird, daß vielmehr eine Kontraktion des Strömungsquerschnittes stattfindet ähnlich wie bei einer Luftschraube.Herrn Professor Dr. A. Betz, unter dessen Leitung die vorliegende Arbeit im Max-Planck-Institut für Strömungsforschung und in der Aerodynamischen Versuchsanstalt in Göttingen als Diplomarbeit durchgeführt wurde, danke ich für wertvolle Anregungen. Ferner möchte ich auch Herrn Dr. F. W. Riegels meinen Dank aussprechen.Aerodynamische Versuchsanstalt Göttingen.     

Delamination of an elastic film from an elastic–plastic substrate during adhesive contact loading and unloading

Adhesive contact between a rigid sphere and an elastic film on an elastic–perfectly plastic substrate was examined in the context of finite element simulation results. Surface adhesion was modeled by nonlinear springs obeying a force-displacement relationship governed by the Lennard–Jones potential. A bilinear cohesive zone law with prescribed cohesive strength and work of adhesion was used to simulate crack initiation and growth at the film/substrate interface. It is shown that the unloading response consists of five sequential stages: elastic recovery, interface damage (crack) initiation, damage evolution (delamination), film elastic bending, and abrupt surface separation (jump-out), with plastic deformation in the substrate occurring only during damage initiation. Substrate plasticity produces partial closure of the cohesive zone upon full unloading (jump-out), residual tensile stresses at the front of the crack tip, and irreversible downward bending of the elastic film. Finite element simulations illustrate the effects of minimum surface separation (i.e., maximum compressive surface force), work of adhesion and cohesive strength of the film/substrate interface, substrate yield strength, and initial crack size on the evolution of the surface force, residual deflection of the elastic film, film-substrate separation (debonding), crack-tip opening displacement, and contact instabilities (jump-in and jump-out) during a full load–unload cycle. The results of this study provide insight into the interdependence of contact instabilities and interfacial damage (cracking) encountered in layered media during adhesive contact loading and unloading.     

On the Buckling of an Infinite Beam of Finite Width Embedded in an Isotropic Elastic Solid∗

The present paper considers the problem of buckling of a beam of finite width that is embedded in bonded contact with an isotropic elastic solid. Analysis of the buckling problem is restricted to the class of slender beams of narrow width that exhibit flexure only in the longitudinal direction. The governing integral equations are solved in an approximate fashion. Numerical results presented indicate the manner in which the buckling load is influenced by the relative flexibility of the beam-elastic medium system.     

Viskositätsmessungen an Gußeisenschmelzen

Zusammenfassung Es wird ein Viskosimeter zur Messung von Gußeisenschmelzen bis zu 1400°C aus dem Rotationsviskosimeter Bauart MPA und der dazu erforderliche keramische Drehkörper bezüglich Form und Material entwickelt.Dieses Viskosimeter kann für Kontrollmessungen im Gießereibetrieb eingesetzt werden, da es durch die elektrische Fernanzeige möglich ist, die feinen Meßinstrumente in größerer Entfernung von der eigentlichen Meßstelle aufzubauen und sie vor den Einflüssen des rauhen Betriebes zu schützen.Es wird für diese Temperaturbereiche eine völlig neue Methode beschrieben, die sich von den bisherigen Messungen vonP. Oberhoffer undA. Wimmer (4) nach der Torsionsmethode und Messungen vonH. Thielmann undA. Wimmer (5) nach der Schwingtiegelmethode an weißem Gußeisen dadurch unterscheidet, daß während der Messung keine Temperaturkonstanz angestrebt zu werden braucht, da die einzelne Messung kein Zeitintervall erfordert und die dazugehörige Temperatur exakt bestimmt werden kann.Leider können die hier erhaltenen Ergebnisse nicht mit den Messungen vonOberhoffer undWimmer verglichen werden, da die Verfasser keine absoluten Werte angeben. Bei den Messungen vonThielmann undWimmer handelt es sich um weißes Gußeisen, das auf Grund unterschiedlicher Siliziumgehalte gegenüber Grauguß nicht vergleichbar mit den gefundenen Ergebnissen ist.     

Is vorticity-banding due to an elastic instability?

A possible mechanism for the vorticity-banding instability is proposed on the basis of experiments with colloidal rod-like particles that exhibit an isotropic–nematic phase transition. The proposed mechanism is similar to the well-known elastic instability for polymer systems that is due to nonuniform elastic deformation of polymer chains as a result of gradients in the local shear rate (the Weissenberg effect). However, the role of polymer chains is now played by inhomogeneities that exist in systems exhibiting vorticity banding. For the rod-like colloidal system investigated here, inhomogeneities are formed during the early stages of phase separation. Nonuniform deformation of these inhomogeneities are thus proposed to lead to hoop stresses which give rise to banded structures where there is secondary, weakly rolling flow within each of the bands. Many of the features found experimentally for the rod-like colloidal system can be understood on the basis of this proposed mechanism. For different types of systems that also show vorticity banding, inhomogeneities can be identified, which might lead to vorticity banding for the same reasons as for the rod-like colloidal systems studied here.     

Nonlinear Oscillation Analysis by an Orthogonal Function Method

ＮＯＮＬＩＮＥＡＲＯＳＣＩＬＩＡＴＩＯＮＡＮＡＬＹＳＩＳＢＹＡＮＯＲＴＨＯＧＯＮＡＬＦＵＮＣＴＩＯＮＭＥＴＨＯＤＳｕｎＰｉ，ｈｏｎｇ（孙丕忠）ＴａｎｇＰｉａｎｇａｎｇ（唐乾刚）ＳｕｎＳｈｉｘｉａｎ（孙世贤）（ＮａｔｉｏｎＵｎｉｖｅｒｓｉｔｙｏｆＤｅｆ...     

What does an ideal wall look like?

This paper deals with the interface between a solid and an ideal gas. The surface of the solid is considered to be an ideal wall, if the flux of entropy is continuous, i.e., if the interaction between wall and gas is non-dissipative. The concept of an ideal wall is discussed within the framework of kinetic theory. In particular it is shown that a non-dissipative wall must be adiabatic and does not exerts shear stresses to the gas, if the interaction of a gas atom with the wall is not influenced by the presence of other gas atoms. It follows that temperature jumps and slip will be observed at virtually all walls, although they will be negligibly small in the hydrodynamic regime (i.e., for small Knudsen numbers).     

Interface effects on elastic behavior of an edge dislocation in a core–shell nanowire embedded to an infinite matrix

The elastic behavior of an edge dislocation located inside the core of a core–shell nanowire which is embedded in an infinite matrix is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved exactly by using complex potential functions. An important parameter so-called interface characteristic parameter which has the dimension of length and is a combination of the interface moduli enters the formulations. The stress field of the dislocation, image force acting on the dislocation, and the dislocation strain energy is calculated by considering the interface effect. The introduced characteristic parameter allows the examination of the core–shell size on the image forces acting on the dislocation. The repelling and attracting effects of the interface parameter on the image force are discussed. The equilibrium position of the dislocation is also studied. The dislocation strain energy in the interface elasticity framework is only slightly different from that of traditional elasticity when the dislocation is placed in the central region of the core and reaches its maximum value when it is located near the core–shell interface.     

On the Cρ-Smoothness of an Invariant Torus of a Countable System of Difference Equations Defined on an m-Dimensional Torus

Using the method of truncation, we establish sufficient conditions of differentiability of order 2 with respect to the angular variable for an invariant torus of a countable system of difference equations with deviation of the discrete argument.     

Collective migrations in an epithelial–cancerous cell monolayer

Acta Mechanica Sinica - Collective cell migration is extensively observed in embryo development and cancer invasion. During these processes, the interactions between cells with distinct identities...     

Moderne Probleme der statischen Prüfverfahren an Faserstoffen

Ohne Zusammenfassung     

Buckling of an Axially Compressed Incompressible Half Space∗

Symmetric and nonsymmetric buckling solutions are obtained for an axially compressed half space. The half space is assumed to be made of a general in compressible isotropic elastic material. Solutions are made possible via the use of a direct approach that does not employ conventional Fourier-analysis calculations.     

Fuel injection model for Euler–Euler and Euler–Lagrange large-eddy simulations of an evaporating spray inside an aeronautical combustor

Large-Eddy Simulations (LES) of an evaporating two-phase flow in an experimental burner are investigated. Two different numerical approaches for the simulation of the dispersed phase are coupled to the same gaseous solver: a mesoscopic Eulerian method and a Lagrangian particle tracking technique. The spray is represented by a single droplet size owing to the locally monodisperse formulation of the employed mesoscopic Eulerian approach. Both approaches use the same drag and evaporation models. They do not take into account the atomization process and a simplified injection model is applied instead. The presented methodology, referred as FIM-UR (Fuel Injection Method by Upstream Reconstruction) defines injection profiles for the monodisperse spray produced by a pressure-swirl atomizer. It is designed so as to ensure similar spray characteristics for both approaches and allows for a direct comparison between them. After a validation of the purely gaseous flow in the burner, liquid-phase dynamics and droplet dispersion are qualitatively and quantitatively evaluated for the Eulerian and Lagrangian simulations. Results obtained for both approaches are in very good agreement and compare reasonably with experiments, indicating that simplified injection methods are appropriate for the simulation of realistic combustor geometries.     

Natural convection of an alumina-water nanofluid inside an inclined wavy-walled cavity with a non-uniform heating using Tiwari and Das’ nanofluid model

The present study is devoted to numerical analysis of natural convective heat transfer and fluid flow of alumina-water nanofluid in an inclined wavy-walled cavity under the effect of non-uniform heating. A single-phase nanofluid model with experimental correlations for the nanofluid viscosity and thermal conductivity has been included in the mathematical model. The considered governing equations formulated in dimensionless stream function, vorticity, and temperature have been solved by the finite difference method. The cavity inclination angle and irregular walls (wavy and undulation numbers) are very good control parameters for the heat transfer and fluid flow. Nowadays, optimal parameters are necessary for the heat transfer enhancement in different practical applications. The effects of the involved parameters on the streamlines and isotherms as well as on the average Nusselt number and nanofluid flow rate have been analyzed. It has been found that the heat transfer rate and fluid flow rate are non-monotonic functions of the cavity inclination angle and undulation number.     

Comparative study of in-cylinder tumble flows in an internal combustion engine using different piston shapes—an insight using particle image velocimetry

This paper deals with the experimental investigations of the in-cylinder tumble flows in a single-cylinder engine with five different piston crown shapes at an engine speed of 1,000 rev/min., during suction and compression strokes under motoring conditions using particle image velocimetry. Two-dimensional in-cylinder tumble flow measurements and analysis are carried out in combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze the tumble flow structure. Tumble ratio and average turbulent kinetic energy are evaluated and used to characterize the tumble flows. From results, it is found that at end of compression, pentroof-offset-bowl piston shows about 41 and 103% improvement in tumble ratio and average turbulent kinetic energy respectively, compared to that of flat piston. The present study will be useful in understanding effect of piston crown shapes on nature of the in-cylinder fluid tumble flows under real engine conditions.     

Die Potentialströmung mit Totwasser an einer geknickten Wand

Ohne ZusammenfassungBericht der Aerodynamischen Versuchsanstalt Göttingen.