Issue 1
JTAM, Sofia, vol. 8 Issue 1 (1977)

60th Anniversary of Academician Jurii Alexeevich Mitropolski the Editorial Board

Editorial Board


JTAM, Sofia, vol. 8 Issue 1 pp. 009-010 (1977)

Flow Field Induced by an Oscillating Porous Sphere

Z. Zapryanov, S. Stoyanova
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgaria Academy of Sciences

This paper deals theoretically with the flow field induced by a porous sphere oscillating along a diameter in a viscous fluid which is otherwise at rest. The case when the amplitude of oscillation and the frequency parameter M are small is examined. Of particular interest is the effect of permeability on the steady streaming induced both inside and outside of the sphere. The solution is obtained by the method of matched asymptotic expansions.

JTAM, Sofia, vol. 8 Issue 1 pp. 011-018 (1977), [Full Article]

On a Fracture Model of Solids

G. Zahariev, A. Baltov
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgarian Academy of Sciences

A model of the process of fracture of solids, accounting reversible and irreversible effects is proposed. Basing on the results obtained for the one-dimensional steady tension, some of the possibilities of generalizing the fracture model in the case of a three-dimensional stressed state are considered.

JTAM, Sofia, vol. 8 Issue 1 pp. 019-025 (1977)
Parametrically Excited Vibrations of a Shallow Cylindrical Panel

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

In this paper the nonlinear vibrations of a shallow cylindrical panel under periodic longitudinal loading are investigated. The periodical solution at parametric resonance is sought in the form of a power series with a nonlinear generating system. The existence of a nonlinear parametric resonance is established for the case when the initial amplitude is in the decreasing-restoring-force range and the excitation frequency is edual to twice the nonlinear free vibration frequency. The theoretical results are in good agreement with the analog computer studies carried out.

JTAM, Sofia, vol. 8 Issue 1 pp. 026-034 (1977)
Effect of Outflow Velocity and Physico-Chemical Properties on the Stability of a Cylindrical Jet in a Liquid-Liquid System

A. Asenov1, I. Penchev1, S. Radev2
1Sofia, Darvenica, Higher Institute of Chemical Engineering
2Sofia 1113, Institute of Mathematics and Mechanics with Computer Center. Bulgarian Academy of Sciences

The classical Tomotika results are expanded on the stability of a liquid cylindrical jet, flowing into immovable liquid. Considered is the most general case of stability of a liquid jet when both the inertial and viscous effects are taken into account.

JTAM, Sofia, vol. 8 Issue 1 pp. 035-040 (1977), [Full Article]

On the Creep Stability of Elliptic Cylindrical Shells under Complex Load

M. Kozarov, P. Kolev
Sofia, boul. H. Smiruenski 1, Higher Institute of Civil Engineering

In the present paper the stability of a thin, isotropic cylindrical shell with average length and elliptic cross-section is investigated at creep and when externally loaded by uniform and normal on the surface pressure and uniform tangential torsion.

JTAM, Sofia, vol. 8 Issue 1 pp. 041-049 (1977)
Thermo-Viscoelasticity of Two Continua under Small Deformations Field

P. Marinov
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgarian Academy of Sciences

The thermo-viscoelastic behaviour of two continua under small deformations is investigated. The stress tensor, the internal forces of interaction, the couple stress tensor and the entropy density under an arbitrary varying temperature could be obtained by a free energy potential function. It is shown that under nonisothermal conditions the behaviour of an isotropic visco-elastic medium of two continua depends on six relaxation functions.

JTAM, Sofia, vol. 8 Issue 1 pp. 050-058 (1977), [Full Article]

Path Independent Integral for Large-Scale Yielding in the Bending Problem of a Cracked Plate

I.M. Mihovsky
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgarian Academy of Sciences. Acad. G. Bonchev Str. block 8

In this paper an approximate large-scale yielding range estimate of the energy release rate is obtained for the bending problem of a cracked plate. The analysis is based on the application of a certain path independent integral to a simple perfectly plastic crack model of Dugdale type.

JTAM, Sofia, vol. 8 Issue 1 pp. 059-063 (1977)
On the Motion from Rest of a Class of Cylinders. Elliptic Cylinder Case

G. Simeonov
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. block 9

The motion from rest following a power law of a class of cylinders is discussed on the basis of the Navier-Stokes equations by the method of matched asymptotic expansions. The acceleration law includes the case of an impulsive started and that of an uniformly accelerated body. The fluid is supposed to be incompressible and the Reynolds number to be large. The second order solutions are obtained. Their relation with the respective boundary layer solutions is noted. The elliptic cylinder case is considered in details. Other special cases are pointed out.

JTAM, Sofia, vol. 8 Issue 1 pp. 064-075 (1977), [Full Article]

Solution of the Heat-Transfer Problem at Unsteady Temperature Regime of Reinforced Concrete Slabs

S. Sivrieva-Zlatarova
Sofia, complex Mladost-1, block 97 "A"

A new method of determination the temperature fields at an unsteady temperature regime is considered. The method of Hartree and Womersky is applied for solving the Fourier heat-transfer differential equations. According to this method the second partial derivative is presented as a finite difference. This leads to the solution of a system of differential equations to which the Runge-Kutta method is applied. This method is applicable to one- and multi-layer structures at one- and two-dimensional cases at given initial temperatures and given temperature changes on the boundaries. An example is given for determining the time at which the limit temperature (450°C) of the reinforcement of the slab is reached.

JTAM, Sofia, vol. 8 Issue 1 pp. 076-082 (1977)