Issue 3
JTAM, Sofia, vol. 7 Issue 3 (1976)

Free Convective Heat Transfer from the Outer Surface of an Unsteady Moving Vertical Circular Cylinder

Zapryan Zapryanov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences


An analysis of unsteady free convective flow of a viscous, incompressible fluid past a moving vertical circular cylinder is given. In particular the local Nusselt number is found. The problem has been solved by the method of regular asymptotic expansion.

JTAM, Sofia, vol. 7 Issue 3 pp. 009-014 (1976), [Full Article]

Problems of the Optimization of Thermomechanical Processes

Angel I. Baltov
Sofia, Institute of Mathematics and Mechanics with Computing, Centre, Bulgarian Academy of Sciences

This is a discussion of the basic problems related to the formulation of an optimization problem concerning a speed technologic al process of working metals by plastic deformation. The author has applied the theory of systems for describing the thermomechanical process. The limiting conditions and the optimization criterion have been explained, and a new fracture criterion has been proposed.

JTAM, Sofia, vol. 7 Issue 3 pp. 015-021 (1976)
Dynamic Stability of Semicock Cylindrical Shells

Marin Kozarov
Sofia, Higher Institute of Construction Engineering, 1 Hristo Smirnenski Blvd.

The paper examines the dynamic stability of semicock cylindrical shells, with particular reference to two cases of loading – axial-symmetric pressure and bending. The problem has been examined in its general form. Finally, the result is given for the particular case of static stability.

JTAM, Sofia, vol. 7 Issue 3 pp. 022-026 (1976)
Non-Isothermal Free Convection at High Prandtl Number

H. Takhar, M.H. Whitelaw

JTAM, Sofia, vol. 7 Issue 3 pp. 027-037 (1976), [Full Article]

Mechanics of the Gas Flows in Complex Pipelines

Georgi K. Nikolov, Radi V. Ivanov, Evgeni I. Yakovlev
The Geological Studies State Economic Association, 22 Georgi Dimitrov Blvd., Sofia

A method is proposed for solving the differential equations describing the movement of the gas in complex annular pipelines. The authors propose to replace the non-linear system of differential equations with a linear one having variable coefficients. The operational method of Laplace has been used, and the solutions are obtained in rapidly converging series. The formulae obtained can be used in the operative control of complex annular pipelines. They provide an opportunity to control the state of the main pipeline, to evaluate its accumulating capacity, and to determine the operations necessary for the rational exploitation of complex pipeline systems.

JTAM, Sofia, vol. 7 Issue 3 pp. 038-044 (1976)
Influence of the Irregularity of the Velocity Field on the Characteristics of the Unsteady Univariate Uniform Movement

Ivan Ivanov
Sofia, Institute of Mathematics and Mechanics with Computer Centre, Bulgarian Academy of Sciences

On the basis of the physicomathematical model of the univariate unstable uniform pressure movement the solution for a velocity field is obtained. For some particular cases of movement, the influence of the irregularity of the velocity field on the characteristics of the movement has been determined.

JTAM, Sofia, vol. 7 Issue 3 pp. 045-049 (1976)
Certain Relations in the Problem of an Oblique Shock with a Cone on a Flexible Membrane

S. Karapetrova
Higher Institute of Mechanical and Electrical Engineering – Durvenitsa, Sofia

The article gives the conditions under which three different cases occur in the problem involving an oblique shock with a cone on a flexible membrane: (i) propagation of the transverse wave only in the plane area of the membrane; (ii) propagation of the transverse wave only in the region of fitting of the membrane to the cone; and (iii) propagation of the transverse wave in both regions simultaneously. The graphs of the displacements of the particles have been shown for the first one of the cases, and a study has been made into their dependence on the normal and tangential components of the velocity of the shock.

JTAM, Sofia, vol. 7 Issue 3 pp. 050-059 (1976)
On the Elastic Constants of Nonhomogeneous Systems. II. Experiment

Konstantin Markov, Mitko Mihovski, Alexander Mechkov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences

Experimental data for a wide class of composites are given and are compared with the theoretical values, obtained in part I. It is shown that the theory yields qualitatively correct results.

JTAM, Sofia, vol. 7 Issue 3 pp. 060-069 (1976)
Heat Transfer from a Porous Sphere in a Stream of Small Reynolds Number

Zapryan Zapryanov, Ivan Bozdouganov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences

This is an investigation of the temperature distribution in a low Rey-nolds number flow past a porous sphere. It was established that the perme¬ability reduces the gradient of the temperature and the heat transfer from a sphere. The problem has been solved by the method of matched asymptotic expansions.

JTAM, Sofia, vol. 7 Issue 3 pp. 070-079 (1976), [Full Article]