Issue 4

JTAM, Sofia, vol. 8 Issue 4 (1977)

Corresponding member Georgi Delchev Bradistilov – Obituary

Editorial Board

JTAM, Sofia, vol. 8 Issue 4 pp. 011-014 (1977)

On the Equilibrium Orientation of a Satellite-Gyrostat

At. Anchev
Sofia 1113, Institute of Mathematics and Miechanics with Computer Center, bl. 8, POB 373

In the present paper it is shown that in circular orbit any orientation of a satellite can be the position of the relative equilibrium. The force moments acting on the rotor and securing the equilibrium of the hull in this orientation with respect to the orbital system are presented.

JTAM, Sofia, vol. 8 Issue 4 pp. 015-023 (1977)

An Exact Solution of the Problem of Unsteady Fully Developed Viscous Flow in a Slightly Curved Porous Tube

Z. Zapryanov, V. Matakiev
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, bl. POB 373

The fully developed flow in a pipe of circular cross-section which is coiled in a circle is studied, the pressure gradient along the pipe varying sinusoidally in time with frequency ω. The nature of curved tube viscous fluid motion, as compared with simple straight tube parabolic flow, causes higher critical Reynolds number for transition to turbulent flow, relatively high average heat-transfer and mass-transfer rates per unit axial pressure drop and significant peripheral distributions of the transport rates. In order to simplify the problem the radius of the pipe curvature is assumed large in relation to its own radius. The secondary flow generated by the centrifugal effects acting in every plane of the cross-section of the pipe is of special interest. A closed form analytic solution is derived for arbitrary values of the frequency parameter a. The secondary flow is found to consist of a steady component and a component oscillatory at frequency 2ω.

JTAM, Sofia, vol. 8 Issue 4 pp. 024-036 (1977), [Full Article]

On the Thermomechanical Process in Adiabatic Band at Rectangular Metal Cutting

A. Baltov, M. Mitov, T. Dueheva
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, bl. 8, POB 373

A subject of consideration is the case of a rectangular metal cutting at which a thin zone of a concentrated visco-plastic strain is formed with occurring in it adiabatic process. The thermomechanical process occurring in the adiabatic band is qualitatively investigated by determining the stress, the strain and the temperature and their changes during the process. A numerical example of aluminum cutting is presented.

JTAM, Sofia, vol. 8 Issue 4 pp. 037-041 (1977)

The Influence of Boundary Conditions on the Stress Singularities in a Biwedge

P.S. Theocaris, E.E. Gdoutos
Department of Theoretical and Applied Mechanics, The National Technical University, Athens (625), Greece

The singular stress field developed at the vertex of a biwedge under homogeneous stress, displacement and mixed-boundary conditions was studied by the complex variable technique. The characteristic equations for the calculation of the order of the elastic stress singularity for the above three different boundary conditions were determined in terms of the mechanical properties and the local geometry of the biwedge. Two different particular geometrical configurations were studied in detail: the equal angle biwedge and the elastic plane indenter acting on a half-plane. Numerical results for these two different geometries of the biwedge were given. Interesting laws for the dependence of the order of singularity on the geometry, mechanical properties and the boundary conditions for the above two different geometric configurations of the biwedge were established.

JTAM, Sofia, vol. 8 Issue 4 pp. 042-051 (1977), [Full Article]

Thermodynamic Description of Hydrodynamics

G. Lebon
Institute of Mathematics, Liege University, av. des Tilleuls, 15, B 4000 Liège, Belgium

We consider the rather general problem of the flow of a mutticomponent viscous compressible and isotropic fluid with r constituents between which there is diffusion and amongst which a chemical reaction is possible. The temperature and all the other properties of the systems are supposed to vary in time and space. A thermodynamical approach to describe the flow of the fluid in consideration is applied.

JTAM, Sofia, vol. 8 Issue 4 pp. 052-058 (1977), [Full Article]

Method of Testing the Material Heredity Using Plane Samples

Y. Miastkowski
IPPT – PAN, ul. Świgtokrzyska 21, Warszawa, Poland

Method of testing the effect of the preliminary plastic strain on the behaviour of materials is described. For the purpose plane samples are used from which tensile samples are cut afterwards under different angles.

JTAM, Sofia, vol. 8 Issue 4 pp. 059-069 (1977)

Effects of Hall Currents on the Hydromagnetic Flow Past an Accelerated Porous Flat Plate

I. Pop1, V.M. Soundalgekar2
1Faculty of Mathematics, University of Cluj, R-3400 Cluj, Romania
2Department of Mathematics, I. I. P., Powai, Bombay-76, India

We study the effects of hall currents on the motion of a viscous, electrically conducting incompressible fluid past an accelerated, porous, infinite, flat plate with time-dependent suction. The magnetic field is assumed to be applied uniformly and transverse to the direction of the flow.

JTAM, Sofia, vol. 8 Issue 4 pp. 070-073 (1977), [Full Article]

Ultrasonic Wave Motion of a Fluid in a Circular Cylinder-Shaped Container with a Complex Shape

V. Djupanov, P. Dineva
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, bl. 8, POB 373

The motion of an ideal compressible fluid in a complex region bounded between two coaxial cylinders with flat bottoms is studied. The motion is perturbed by ultrasonic oscillations at the bottom of the outer cylinder. The perturbed fluid motion is supposed to be potential. A boundary problem for determining the velocity potential is solved by the method of dividing the complex region into subregions. The infinite algebraic system of the integrated constants, obtained at the solution of the boundary problem is investigated and it is proved to be quasi-regular and permits solution by the reduction method. The fluid acoustic pressure is determined for the whole complex region.

JTAM, Sofia, vol. 8 Issue 4 pp. 074-081 (1977)

Reinforced Structures

S. Drenowski, W. Marks
IPPS – PAN, ul. Swietokrzyska 21, Warszawa, Poland

The usage of unforced cables in the compressible zone of structure elements and the reinforcement gives the possibility of avoiding large structure spans or of decrease in the structure height. The idea and the technical possibilities of the application of the enforcement and of the strength conditions which have to be observed at the reinforced-unforced structures are presented in the paper. The cases when the carrying capacity of the beams can be increased by applying unforcement are also considered.

JTAM, Sofia, vol. 8 Issue 4 pp. 082-089 (1977)

Positional Identification of Spatial Kinematic Chains

M.S. Konstantinov, M.D. Markov
VMEI "Lenin" department “TMM", Sofia

A numerical method for displacement analysis of spatial kinematic chains is proposed, based on the algebraic algorithmization of the first and second transfer functions by help of screw methods. Having appropriately chosen the initial position of the mechanism, the displacement functions are numerically deciphered step by step by using Taylor expansions of finite increments without applying iteration methods.

JTAM, Sofia, vol. 8 Issue 4 pp. 090-095 (1977)

On the Problem of the Parametric Oscillations of Visco-Elastic Cylindrical Shells

L. Hadjikov, K.M. Simeonova
Sofia 1113. Institute of Mathematics and Mechanics with Computer Center, bl. 8, POB 373

The equation of the parametric oscillations of visco-elastic cylindrical shells is derived in the paper. The equations of motion refer to a shell in strained state. Assumptions of the semimoment theory are applied at the derivation of the equations. The equation is derived on the basis of Maxwell-Gurevich-Rabinovich generalized nonlinear equation. The obtained equation can be used at the solution of different problems of the circular-cylindrical shell dynamics.

JTAM, Sofia, vol. 8 Issue 4 pp. 096-105 (1977)

Linear Control System with Integral Quadratic Effectiveness Criterion

T. R. Gichev
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, bl. 8, POB 373

Subject of consideration in the present communication are the cases when the linear problem for optimal control with integral quadratic effectiveness criterion and free right bound can be solved and cases when it cannot be solved. The numerous solutions are proved to be in semicontinuous from above dependence on the initial state and parameter.

JTAM, Sofia, vol. 8 Issue 4 pp. 106-111 (1977)