Theory of nonsteady propellant combustion. Combustion in the presence of harmonically varying pressure

It is shown that in order to construct a theory of nonsteady propellant combustion it is necessary to know the steady-state dependences of the burning rate u₀ °, surface temperature T_s °, and flame temperature T_F ° on the external parameters and the initial temperature of the propellant. The combustion processes in an unbounded space, when one of the external parameters varies according to a harmonic law, are examined within the framework of such a theory.Translated from Zhumal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 60–69, September–October, 1971.     

Frequency at which vapor bubbles form during boiling

An expression is found for the frequency at which vapor bubbles form; the familiar empirical dependences follow from this expression as particular cases. The theoretical results are in satisfactory agreement with experiment.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 143–146, September–October, 1970.     

One dimensional lattice gases with rapidly decreasing interaction

We consider the pressure and the correlation functions of a one dimensional lattice gas in which the mutual interaction decreases as r exp-n ^t, (r, t>0), when the interparticle distance n. We prove that such a system cannot show phase transitions of order k1 in the sense that the pressure and the correlation functions are infinitely differentiable with respect to any relevant parameter (such as the temperature or the chemical potential).     

Stress concentrations in tensile strips with large circular holes

The purpose of this investigation was to determine more accurately the stress concentrations in tensile strips having large circular holes where the ratio of the hole diameter to strip width is greater than 0.5 Results of numerical elasticity analyses are presented for ratios of hole diameter to bar width ranging from 0.10 to 0.99, and photoelastic data are presented for the range from 0.40 to 0.94. Both numerical results and photoelastic data indicate that the stress-concentration factor based on net area approaches a value of one as the ratio of hole diameter to bar width approaches a value of one.     

Zum zeitlichen Verlauf des Kriechens von Zementstein und Beton

Zusammenfassung Es wird eine Kriechfunktion abgeleitet, die die bekannten, empirisch bestimmten Kriechfunktionen als Spezialfälle enthält. Für die relative Endkriechverformung ergibt sich sowohl aus der exakten Lösung als auch aus den Näherungen der Wert 2/E. Für die Halbwertszeit, nach der die Hälfte des Endkriechmaßes erreicht wird, bekommt mann = 2l RZ , E. R ist eine Größe, die der inneren Reibung proportional ist. Es wird eine Beziehung angegeben, dieR mit der AktivierungsenergieQ verknüpft. Mit den aus Kriechkurven zu entnehmenden Werten fürR ist damit auchQ bekannt.

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Summary A formula for creep deformation as a function of time has been derived. It has been shown, that the empirical functions previously used by several authors are special cases of this more general function. The final creep deformation is found to be 2/E. Half of the final creep deformation is reached after a time ofn=21RZ/qE. R is a value, which is proportional to internal friction. There exists a relation betweenR and the activation energy. The activation energy can be calculated ifR is evaluated from creep data.

     

Hydrodynamical modeling of the development of non-homogeneous oil reservoirs

Results of mathematical modeling of two-phase flow in non-homogeneous (layered) reservoirs are reported. Characteristic patterns of flow in reservoirs with high layer permeability contrast are investigated. It is shown that in such reservoirs crossflow between layers must be taken into account. Specific features of the use of hydrodynamic methods of improving oil recovery in such reservoirs based upon flow pattern control are studied. The possibility of using rational flow management to improve oil recovery partially blocking the reservoir in the neighborhood of the wells is demonstrated.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 87–94, November–December, 1995.     

Rising vortex ring in a viscous fluid

Most theoretical results for thermals, whose motion is determined by the complex interaction between dynamics and buoyancy, have been obtained numerically [1–4]. The analytic solutions for a convection element have been limited to consideration of the self-similar regime [5]. At the same time, the preself-similar stage of development of a vortex ring of dynamic origin has been described analytically [6]. This approach is now extended to a rising vortex ring. In this case a modification of the traditional formulation of the problem makes it possible to obtain an analytic solution of the problem of a weak thermal in the form of unsteady temperature, vorticity and stream function fields that tend in the limit to the self-similar regime. The rate of ascent of the convective vortex ring is found. A solution is obtained for the two-dimensional analog of the problem.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 42–48, May–June, 1989.     

Turbulent flow of dilute emulsions

An equation is obtained to determine the coefficient of hydraulic drag of dilute emulsions by using the turbulent viscosity concept and the phenomenon of quenching turbulent pulsations. The results of the theory are compared with experiment.     

Burnett simulation of flow and heat transfer in micro Couette flow using second-order slip conditions

The conventional Burnett equations with second-order velocity slip and temperature jump conditions were applied to the steady-state micro Couette flow of a Maxwellian monatomic gas. An analytical approach as well as a relaxation method was used to determine the velocity slip and temperature jump at the wall. Convergent solutions to the Burnett equations were obtained on arbitrary fine numerical grids for all Knudsen numbers (Kn) up to the limit of the equations’ validity. The Burnett equations with second-order slip conditions indicate a much better agreement with DSMC data over the first-order slip conditions at high Kn. The convergent Burnett solutions were obtained in orders of magnitude quicker than that with the corresponding DSMC simulation. The augmented Burnett equations were also introduced to model the flow but no obvious improvement in the results was found.     

Dependence of the yield stresses of certain materials on loading rate

The dependence of the dynamic yield stresses of certain metals and alloys on loading rate has been investigated at temperatures of +20 and –196°C. In the experiments the loading rate remained constant up to the appearance of plastic strains, i.e., , where . The yield stresses of the materials and the time to the appearance of plastic strains were determined from the oscillograms representing the strain and load as functions of time.