Issue 4
JTAM, Sofia, vol. 7 Issue 4 (1976)

The Flow Field Induced by an Oscillating Fluid Drop Immersed in Another Fluid

Z. Zapryanov, S. Stoyanova
Sofia 1113, Institute of Mathematics and Mechanics with a Computer Center, Acad. G. Bonchev street, block VIII. Bulgarian Academy of Sciences


The flow field induced by a translatory oscillating spherical drop immersed in another fluid is considered. It is examined the case when the amplitude of oscillation and the frequency parameter are small. Of particular interest is the steady streaming induced both inside and outside of the drop. The problem has been solved on the basis of the Navier-Stokes equations by the method of matched asymptotic expansions.

JTAM, Sofia, vol. 7 Issue 4 pp. 009-015 (1976), [Full Article]

Unsteady Free Convection of a Viscous Fluid with Taking Account of Energy Dissipation

S.G. Slavchev
Sofia 1113, Institute of Mathematics and Mechanics with a Computer Center, Bulgarian Academy of Sciences, Acad. G. Bonchev street, block VIII

The unsteady laminar free convection of a viscous fluid on a heated cylindrical or axisymmetric body is investigated. The difference between the body and the fluid temperature is given as a multiplication of a power function of the time and an arbitrary function of the longitudinal coordinate. For small times the thermal boundary layer equations which include the dissipation term, are solved by the method of successive approximations. Two approximations to the fluid velocity and the temperature are analytically obtained. The skin friction and the heat flux from the wall are calculated. The free convection of the fluid on a circular cylinder and a sphere is studied. The influence of the energy dissipation on the average Nusselt number is determined.

JTAM, Sofia, vol. 7 Issue 4 pp. 016-024 (1976)
Improvement of the Method of Testing of Cylindrical Rock Specimens on Shear with Compression

G.E. Andreev
Sofia 1113, Institute of Geology, Bulgarian Academy of Sciences, Acad. G. Bonchev street, block II

A new method of testing of cylindrical rock specimens on shear with compression is proposed. Experiments have been carried out and the obtained results are graphically presented.

JTAM, Sofia, vol. 7 Issue 4 pp. 025-035 (1976)
Eigen Frequencies of Vibration of Ring-Line Plates with a Motionless and a Free Outline

A.A. Jondjorov, G.I. Venkov
Sofia – Dărvenica, Higher Institute of Mechanical and Electrical Engineering

In this paper after the presentation of an analytical solution it is considered an algorithm of numerical determination the eigenvalues and eigenfunctions of vibration of ring-line plates with a motionless and a free outline. Numerical results are also presented.

JTAM, Sofia, vol. 7 Issue 4 pp. 036-039 (1976)
Forced and Parametrically Excited Nonlinear Vibrations of Thin Elastic Plates with Initial Imperfections

S.D. Kisliakov
Sofia, boul. H. Stnirnenski 1, Higher Institute of Civil Engineering

Vibrations of a thin elastic plate with initial imperfection under a periodical loading, uniformly distributed along the edges and at deflections, comparable with the plate thickness, are considered. The nonsteady-state and the steady-state vibrations are investigated and a criterion about the existence of "double-sided" vibrations is obtained. Further, a new analytical method is proposed, enabling to obtain the output for an arbitrary loading frequency. The carried out analog computer studies are in good agreement with the proposed analytical solutions and demonstrate some interesting features of the problem.

JTAM, Sofia, vol. 7 Issue 4 pp. 040-050 (1976), [Full Article]

On the Rheology of Porous Bodies

K.Z. Markov
Sofia, 1113. Institute of Mathematics and Mechanics with a Computer Center, Bulgarian Academy of Sciences, Acad. G. Bonchev street, block VIII

Basing on the self-consistent theory of the composite and on Volterra principle, the rheological behaviour of a linear viscoelastic porous matrix is investigated. Considered are numerical and approximate methods of establishing the defects of the elastic moduli. Approximate rheological relations for description of the porous medium are presented in the case when the matrix is a standard nonelastic Zener's body.

JTAM, Sofia, vol. 7 Issue 4 pp. 051-058 (1976)
On the Stability of Tubes, Subjected to Axial Compression or Torsion under Creep Conditions

K. Marinova, L. Hadjikov
Sofia 1113, Institute of Mathematics and Mechanics with a Computer Center, Bulgarian Academy of Sciences, Acad. G. Bonchev street, block VIII

Basing on experimental data, the rheological coefficients of the residual deformation at axial compression or torsion in the non-linear generalized Maxwell Gurevich-Rabinovich equation are determined. Ascertained are the theoretical relations between these coefficients. Further, the stability of cylindrical tubes, subjected to compression or torsion under creep conditions at “critical times" is investigated by the already determined rheological coefficients and the non-linear generalized Maxwell-Gurevich-Rabinovich equation. These theoretical results are compared with the experimentally obtained critical times.

JTAM, Sofia, vol. 7 Issue 4 pp. 059-065 (1976)
Parametric Oscillations of Dynamical Systems under the Influence of Non-linear Frictions

Nghuen Van Dao
SR Vietnam, Hanoi, Polytechnical Institute

The differential equation describing parametric oscillations of dynamical systems under the influence of non-linear frictions is studied. The influence of the frictions is graphically illustrated.

JTAM, Sofia, vol. 7 Issue 4 pp. 066-075 (1976), [Full Article]

The Problem of the Cross-sections and the Computing Moments Correspondency in Two-span Metal Bars

A.V. Maljuk, N. Draganov
Sofia, boul. H. Smirnenski 1, Higher Institute of Civil Engineering

The problem of the equal-strength correspondency between the cross-sections and the computing moments in two-span metal bars at forcing the zone above the middle support is considered.

JTAM, Sofia, vol. 7 Issue 4 pp. 076-082 (1976)
An Axisymmetric Finite Element with Improved Qualities

D. Hristov
Russe-7004, VIMMESS, 8, Komsomolska street

The basic relations of the finite element method for a circumferential finite element, applicable at the solution of the plane axisymmetric problem of the theory of elasticity are obtained. The possibilities of the element are tested on three examples.

JTAM, Sofia, vol. 7 Issue 4 pp. 083-089 (1976)
Stability at Creep of Metal Cylindrical Shells under Pure Bending

L. Hadjikov1, A.A. Nikishin2, V.P. Fomin2
1Sofia 1113, Institute of Mathematics and Mechanics with a Computer Center, Bulgarian Academy of Sciences, Acad. G. Bonchev street. block VIII
2MADI, Moscow, USSR

A solution for testing the stability at creep of metal circumferential cylindrical shells under pure bending is presented. The investigation is carried out on the basis of the non-linear generalized Maxwell-Gurevich-Rabinovich equation. A system of non-linear differential equations, accounting the creep strain is obtained. Numerical solutions are carried out. The obtained results are compared with experimental data.

JTAM, Sofia, vol. 7 Issue 4 pp. 090-099 (1976)