Integrated-plane photoelastic method—Application of photoelastic isodynes

It has been shown by Pindera and Mazurkiewicz that a new type of scattered-light modulation in the plane of a two-dimensional photoelastic object can be obtained when the stationary integrated photoelastic method developed by Pindera and Straka is applied in a scanning mode and when the transfer function of the photoelastic system satisfies certain conditions. The new type of light modulation, called field of isodynes by the authors, carries information on stress components normal to the direction of propagation of primary beam, and on corresponding total-force component. The points where this stress component is equal to zero can be easily determined. The classical scattered-light modulation along a chosen line represents a cross section of a corresponding isodynes field. It is shown that these features of the method of isodynes make it possible to easily determine the distribution and values of normal stress components at any arbitrary rectilinear cross section, and to check immediately the accuracy of measurements. The experimental determination of contact stresses and contact regions using the method of isodynes is especially simple and elegant.     

Dynamics of milling processes with variable time delays

A milling-process model with a variable time delay associated with each cutting tooth is presented in this article. The source of this variable time delay is the feed rate. The effect of the feed motion on the entry cutting angle, the exit cutting angle, and the amplitude of feed mark is also discussed. Loss-of-contact effects are also considered. The system dynamics is described by a set of delay differential equations with periodic coefficients and variable time delays. A semi-discretization scheme is presented for analyzing the stability of periodic orbits of this system. The analysis provides evidence of period-doubling bifurcations and secondary Hopf bifurcations. Good agreement is found between the numerical results obtained from this work and the results of related experimental studies.     

Compensation of External Perturbations under Uncertainty

The issue of compensating external perturbations by the appropriate choice of the feedback matrix is studied for a controlled linear stationary system with uncertainty. The task is to minimize the norm of the controller matrix on the condition that H -norm of the transfer matrix, which determines the effect of the external perturbations, does not exceed a given value. An algorithm based on linear matrix inequalities is proposed for synthesis of suboptimal controllers. Examples are given to appraise its efficiency.     

An investigation of interior ballistics ignition phase

An axisymmetric viscous two-phase model is presented which describes the transient combustion of granular propellants during the ignition phase of a ballistic charge. Details of the model are presented along with computational results for a low-pressure ballistic simulator. Predicted pressure time evolutions are compared with experimental data of a real test-firing in which an unexpected pressure excursion occurred. Gun propellant breakup effects, due to bed compaction, are taken into consideration to explain the discrepancies between the numerical and experimental results. Finally, a discussion is presented of the mechanisms by which the behavior of pressure waves can be strongly influenced and thus controlled by the manner in which the propelling charge is ignited.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

A study of internal heat transfer in nonuniform porous structures

The results of theoretical and experimental studies of heat transfer and pressure drop in nonuniform porous materials and systems are presented. In experiments, measurements were made of the air flow rate, inlet and outlet air pressures, and air and porous sample temperatures. Experimental determination of the heat transfer coefficient in porous structures is associated with certain difficulties. The problem of determining a temperature difference between coolant and porous skeleton is the most complex. As a rule, under laboratory conditions this difference is small and cannot be found with sufficient accuracy. In the present work, the method of determination of the internal heat transfer coefficient is based on solving the inverse unsteady heat transfer problem for porous structures. Using this approach, the heat transfer coefficient is calculated indirectly or on the basis of the porous material temperature variation over time.     

A Cosserat shell model for interphases in elastic media

This study is concerned with the modeling of interphases in elastic media in general, and in composite materials in particular. The aim is to replace a boundary value problem consisting of a three-phase configuration, say that of fiber-interphase-matrix, by a simpler problem which involves the fiber and matrix only, plus certain matching conditions which simulate the interphase. The simplest of such known representations replaces a thin interphase by a “perfect contact interface” (a single surface) across which the displacements and tractions are assumed to be continuous. Another classical model replaces a thin and soft interphase by a “spring-type interface”, across which the tractions are continuous, but the displacement field undergoes a discontinuity. In the present paper, a Cosserat shell model of the interphase is derived which successfully models the original interphase in a unified manner, for the full range of its material parameters relative to those of the neighboring media. The model is derived in the setting of three-dimensional linear elasticity with small deformations and displacements. Comparisons with an existing exact solution of a coated fiber in an infinite matrix show that it performs extremely well even for moderately thick interphases.     

Rotation of a sphere in an unbounded gas

The problem of the slow rotation of a sphere in an unbounded gas is solved at arbitrary Knudsen numbers. The kinetic equation with collision integral in the form of the Bhatnagar-Gross-Krook model (BGK-model) describing the state of the surrounding medium is solved by the Lees method, all the moments of the distribution function which ensure the asymptotic passage of the distribution function into the Chapman-Enskog distribution function at large distances from the sphere being taken into account. In the particular case of moderately large spherical particles a value of the isothermal slip coefficient similar to the exact value is obtained. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 165–171, January–February, 1997.     

Experimental investigation of horizontal two-phase flow by an electrodiffusion method

The results of an experimental investigation of the local mean and fluctuating friction at the wall of a horizontal tube are presented for the case where a gas-liquid stream flows in the tube with a wide range of regime parameters. The electrodiffusion method is used for measuring the friction. Curves of the tangential stresses along the perimeter of the tube as well as along its length are constructed, permitting an objective determination of certain flow regimes. The experimental results are compared with those of the existing computational methods.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 101–108, March–April, 1973.