Determination of the stress distribution in assemblies of photoelastic particles

An optical measuring method and a calculation procedure for determining the distribution of the stress tensor in a plane-strained three-dimensional assembly of random-shaped photoelastic particles are described. The stress tensor at an arbitrary point of the model is determined by an integration procedure, based on the equations of equilibrium of stresses. The distribution of the principal-stress direction and the relative principal-stress difference and at least two normal stresses in a plane have to be known to perform the integration. The distribution of the principal-stress directions and their difference are measured optically by scanning the model with an optical filter system with a single rotating polarizer.     

Onset of oscillatory thermocapillary convection in systems with a deformable interface

Oscillatory interfacial instability is investigated with allowance for the deformation of the interface. The possibility of two types of oscillations being excited is established. One of these is similar to the well-known type in systems with a plane interface, while the other is determined by the oscillations of the deformable surface.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 11–16, July–August, 1991.     

Elastic properties of obliquely wound composites with a damaged matrix

Special Design and Technological Office, Institute of Mechanics, Academy of Sciences of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 25, No. 2, pp. 82–89, February, 1989.     

The effect of “creep acceleration” in the theory of viscoelasticity

A particular case of constitutive relations in the Pobedrya nonlinear theory of viscoelasticity is considered. It is shown that these relations can be used in the problem of describing the material softening under pulsed loading.     

On the finite deformation of a sector plate

Summary In this paper an investigation is given into the behaviour of the stress singularity which occurs in the linear theory of elasticity at the deformation of a sector plate, if finite deformations are considered. It is assumed that for very small deformations Hooke's law is valid, and only in the neighbourhood of the singularity Hooke's law has to be extended. This extension is not unique. It is shown that for two different strain-energy functions, which have the same asymptotic expansion for infinitesimal deformations, the behaviour of the solutions is quite different. One of the strain-energy functions leads to a bounded solution, while the solution, obtained from the other one becomes singular for the case of contraction. As it cannot be expected that it will be possible to decide on an experimental basis about the right extension, an assertion about the difference in smoothness of solutions to problems in linear and non-linear theory cannot be given. An open question is raised: whether or not the requirement of regularity for this kind of problems in non-linear theory can be posed as a restriction on the admissible energy functions.     

Theory of Disappearance of the Electric Signal Induced by an Aircraft Jet Engine in the Afterburner Regime

Electrical aspects of aircraft jet engine operation are considered. A phenomenon previously observed experimentally, namely, the disappearance of the engine current and alternating electric signal induced by the engine jet in the afterburner regime, is explained. It is shown that this phenomenon results from the detachment of electrons from negative ions when the gas temperature in the afterburner increases. This leads to an increase in the effective conductivity of the gas. As a result, the engine current circuit is closed on the internal duct walls and engine charging becomes insignificant.A physico-mathematical model of the electrical processes in the afterburner is formulated and model problems are solved.     

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.     

Interaction of pressure waves with a wet foam

Brest. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 5, pp. 78–83, September–October, 1994.     

Flow structure in a flat vortex chamber

We investigate a flow in a flat vortex chamber in which the distance between the end walls is smaller than the radius of the chamber. The study was mainly performed by optical methods: a Töpler device was employed, with the Foucault knife replaced by a diaphragm. It is shown that the flow in the chamber has a complicated spatial structure. In addition to the basic helical flow, an intense “transverse” rotation of the type of Taylor-Görtler vortices occurs. In contrast to previously studied flows, where these vortices were observed near a concave surface, in the motion considered transverse vortices occur in the entire working volume of the chamber. In this case, four parallel vortex filaments are formed. The high intensity of the vortices has allowed one to visualize them by the Töpler method and by “tinting” the flow by highly disperse particles. Quantitative dependences of the dimensions of the vortex cells on the flow regime, i.e., on the pressure of gas deceleration, were obtained.     

Deep field noise in holographic particle image velocimetry (HPIV): numerical and experimental particle image field modelling

 Holographic recording overcomes the limits in 2-D particle image velocimetry (PIV) to cover a 3-D flow field volume. Interrogation by focusing on single planes in a reconstructed particle field is disturbed by noise from out-of-focus particles. A numerical simulation models image reconstruction and shows how validation rates depend on aperture and volume depth. An experimental model environment of scattering particles in moveable plastic slices gives support to the numerical results. Simulations and tests are carried out for interrogation by autocorrelation and crosscorrelation techniques and furnish guidelines for system design. Received: 27 December 1996 / Accepted: 14 August 1997