Bending stresses in out-of-round uni- and multi-axial internally pressurized strength specimens

A derivation is presented for the bending stresses in internally pressurized slightly elliptical tubular or ring specimens used in the testing of uni- and multiaxial strength. The solution obtained shows that the bending stresses are directly proportional to Young's modulus of elasticity of the material being tested. A numerical example applicable to strength testing of aluminum oxide demonstrates, that a slight out-of-round-ness can result in bending stresses which are an appreciable percentage of the observed values of the fracture strength. It is concluded that strength testing by means of the internal pressurization of tubular or ring specimens requires close dimensional control in specimen manufacture.     

Nonlinear instability during the isothermal draw of optical fibers

The nonlinear instability of the isothermal draw of optical fibers from cylindric preforms is studied. The unsteady model of the process is solved numerically, accounting for the effects of inertia, gravity and surface forces. The effect of viscosity and gravity on the nonlinear stability of the process is studied. The possibility of draw resonance occurring is shown for a rate ratio much lower than the critical one, obtained when solving the simplified model. The proposed solution can be used to study technological stability and to model the draw of fibers of other materials which behave as Newtonian fluids.     

On the stability of generalized hill''s equation with three independent parameters

This paper presents a stability criterion of a generalized Hill's equation with three independent parameters, examined by means of an asymptotic method. The theory has been applied to a special form of Hill's equation and the region of stability, has been graphically illustrated. The separatrix between bounded and unbounded solutions yields in parametric space the contour of a ‘stabilitatskörper’ in which the solution is always stable.     

Untersuchungen an Bogenkathoden

Zusammenfassung Der Kathodenfall in Hg- und Xe-Hochdruckentladungen zwischen Wo-Elektroden ist bei Stromstärken unterhalb 10 A für niedrige Drucke beträchtlich grösser als für höhere. Er nimmt mit zunehmender Stromstärke ab und erreicht bei etwa 20 A einen vom Druck unabhängigen Endwert (Xe: 6,5 V; Hg: 9,5 V). Der Anodenfall beträgt ziemlich unabhängig von Druck und Stromstärke 1 V. Die kathodischen Stromdichten sind bei höheren Belastungen nur wenig von der Stromstärke abhängig. Sie nehmen mit dem Druck zu. Der Strom im Kathodenfallgebiet, das eine Ausdehnung von einigen 10^–6 cm hat, wird vorwiegend durch Elektronen getragen. In einem anschliessenden Ionisationsgebiet mit einer Ausdehnung von rund 10^–2 cm erfolgt der übergang zum thermischen Gas des stark kontrahierten Säulenendes. Die hohen kathodischen Stromdichten werden durch Glühemission der Kathode, die wegen der hohen elektrischen Feldstärke um mehr als eine Zehnerpotenz gegenüber der feldfreien Thermoemission angehoben ist, erzielt.     

A physically based correlation for the effects of power law rheology and inclination on slug bubble rise velocity

A study has been made of the motion of long bubbles in inclined pipes containing viscous Newtonian and non-Newtonian liquids. A semi-theoretical expression for the rise velocity of air bubbles in water is derived on the hypothesis that the dominant factor is the momentum exchange of the bubble underflow, i.e. the bubble nose shape. The correlation calls on empirical inputs from established literature on bubble rise speeds at high Reynolds number. The effects of increasing Newtonian viscosity are analysed with reference to the momentum exchange and it is shown how viscosity reduces the inclination dependence of the bubble Froude number. Results from an experimental survey in seven different non-Newtonian liquids in three different diameter pipes are presented. These data are correlated so as to decouple the effects of surface tension and viscosity. An empirical relation is proposed for the effective shear rate in the fluid travelling around the bubble nose. Our correlation is compared to literature data from a broad range of Reynolds numbers with excellent agreement except at shallow angles.     

Unsteady aerodynamic characteristics of a three-dimensional plate cascade in a subsonic gas flow

M. A. Lavrent'ev Institute of Hydrodynamics of the Siberian Division of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 45–55, March–April, 1995.     

Some features of the flow of gas that occurs as a result of the interaction between a shock-wave and a cloud of particles

Institute of Theoretical and Applied Mechanics, Siberian Division of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 8–18, March–April, 1995     

Optimum conditions of turbulence reduction with screens

The results of an experimental investigation of the conditions of flow turbulence suppression with a set of screens, each of which operates in the optimum regime, are presented. Recommendations are made concerning the choice of the number of screens in the set, their geometric parameters and their location in the flow which guarantee the most efficient reduction of free-stream turbulence.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.1, pp. 181–191, January–February, 1993.     

Extended glare point velocimetry and sizing for bubbly flows

A novel measuring technique for bubbly flows, named glare point velocimetry and sizing (GPVS), was developed in order to measure both bubble size and velocity with high accuracy in a 2D plane. This is accomplished by observing glare points in-focus under an observation angle of 96°. When a second laser-sheet is added, even higher accuracies are obtained and the relative refractive index of the bubble can be measured. It also allows non-spherical bubbles to be rejected and arbitrary angles to be used (e.g. 90°). The accuracy of the size and refractive index measurements was found to be within 1.3%.