Issue 2

JTAM, Sofia, vol. 20 Issue 2 (1989)

Existence Conditions for Parametric Resonance Rotating Oscillations in Machine Aggregates with Variable Mass Characteristics

N. Minchev, S. Kazandjiev
High. Inst. Mech. Elecir. Eng., Varna

The paper investigates rotating oscillations in machine aggregates with variable mass characteristics by using a suitable model. Henceforth, the method of basic main motions is applied. It is reduced in two coordinates. Existence conditions for parametric oscillations are obtained.

JTAM, Sofia, vol. 20 Issue 2 pp. 011-019 (1989)

Identification of Inertial and Dissipative Parameters of Industrial Robots

P. Genova
High. Inst. Mech. Electr. Eng., Sofia

The present paper consists of two parts. It is devoted to methods which identify generalized inertial and dissipative parameters when the experimental treatment is one and the same. The identification methods are based on the closed form of the differential equations that have been derived symbolically. The first part deals with the general treatment of a test motion scheme. The necessary number of experiments has been minimized. What is avoided is the configuration influence on dissipative characteristics. An illustration is made and the method is applied to a "Versatran" type regional system. The second part of the paper is devoted to concrete experimental schemes and computation treatment of "Etectrolux" and "Pickomatic" type manipulation systems.

JTAM, Sofia, vol. 20 Issue 2 pp. 020-026 (1989)

Technological Quality Criteria in the Synthesis of Clockwork Gears

S. Ganchev

The technological criteria characterize the quality of the gear tooth surface treatment, the simplicity and the realization quality of instrumental surfaces. They are components of the quality vector in optimization synthesis of clockwork gear tooth surfaces. The instrumental surfaces are included as well. Basic technological criteria and their limit values are defined in the paper. What is examined is the cutting geometry influence on quality criteria.

JTAM, Sofia, vol. 20 Issue 2 pp. 027-034 (1989)

On the Deformability of a Polymer Rod in a Liquid Medium

M. Todorov
A. Kanchev, High. Techn. Sch., Rousse

A critical literary review has been made on the subject. As a result of it, the differential equations are derived more strictly and in a more general treatment. They are necessary to examine deformability of a polymer rod in a liquid medium under special bending. Investigations show discreditation of the results that have been reviewed. Possibilities are proposed to eliminate some essential defects.

JTAM, Sofia, vol. 20 Issue 2 pp. 035-045 (1989)

Numerical Treatment of a Dynamic Viscoelastic Problem for 4-Parameter Media

E. Varbanova, S. Delin
High. Inst. Mech. Electr. Eng., Sofia

The linear dynamic viscoelastic problem is considered. What is used is the 4-parameter Burgers model which is described by a differential hyperbolic system. Both the Cauchy problem and the boundary value problem are discussed. The system has been solved numerically by a difference scheme. The stability itself has been examined by the method of harmonics. The numerical results of a test example show good agreement with the exact solution.

JTAM, Sofia, vol. 20 Issue 2 pp. 046-050 (1989), [Full Article]

Numerical Modelling of Hydrodynamic Interaction between an Erythrocyte and a Capillary Blood-Vessel

P. Shopov, I. Bajlekov
Inst. Mech. Biomech., Bulg. Acad. Sci., Block 4

What is solved numerically is the problem of hydrodynamic interaction between an erythrocyte and a capillary jet. The erythrocyte form has been defined experimentally. The numerical modelling itself is based on Stokes equations and on a finite element type method. Facts are listed in connection with current lines and velocity field. What is examined is the influence on flow hydrodynamics. It is resulted by the crack width between the erythrocyte and the blood vessel wall.

JTAM, Sofia, vol. 20 Issue 2 pp. 051-057 (1989)

Numerical Study of the Steady Flow Past Two Equal Elliptic Cylinders for Moderate Reynolds Numbers

Tz. Kotzev, Z. Zapryanov, E. Toshev
Inst. Mech. Biomech., Bulg. Acad. Sci., Block 4

What is considered in the steady flow for moderate Reynolds numbers is the hydrodynamic interaction between two equal elliptic cylinders in line. Two cases have been investigated when the major semiaxes are parallel or perpendicular to the flow direction. Drag coefficients and flow structure are found for different Reynolds numbers when the distance between thu bodies and their excentricity vary. The results are shown graphically. The method of "numerical matching of the solution" has been used. It is shown that complicated hydrodynamic problems can be solved by it. Comparisons are clone with the known results to check the algorithm accuracy.

JTAM, Sofia, vol. 20 Issue 2 pp. 058-070 (1989), [Full Article]

Application of the Finite Element Method to Solve Thermodispersion Problems in Porous Media

R. Petkov
Inst. Water Problems, Bulg. Acad. Sci., Block 1

The present paper develops a numerical method to a nonlinear differential system which is a model of nonsteady filtration thermodispersion in porous media. The treatment is three-dimensional. The numerical method combines the finite element method and the finite difference one. The numerical solution accounts for temperature and concentration influence on flow hydrodynamic parameters. What is found by the numerical experiment is the hydrodynamic parameter variations when they influence the filtration thermodispersion considerably.

JTAM, Sofia, vol. 20 Issue 2 pp. 071-077 (1989), [Full Article]

Control of Solidification Front Form in Monocrystal Formation from a Smelt

O. Lavrentieva

The crystallization process from a smelt is considered. The heat transfer in the liquid and in the solid phases is supposed to be based on thermoconductivity. The heat transfer regime is known at the liquid phase boundary. The problem is to find the heat transfer regime at the solid boundary. It assures a given behaviour of the phase transition front. A constructive method is proposed to solve the problem when the desired crystallization front form is flat and the motion velocity is constant. The process standard regime and its initial stage are examined when charging has been done before the solid phase.

JTAM, Sofia, vol. 20 Issue 2 pp. 078-084 (1989)

Numerical Solution of the Plain Contact Problem for Thermoelasticity of Strained Nonrectangular Blocks

O. Santurjian
Inst. Water Problems, Bulg. Acad. Sci., Block 1

It is considered a solution of the problem that has been described in the title. The Eri function is used for tensions. A numerical integration of defining equations is described as well. Its development and computer realization are due to the author. The finite difference method is used for a specific nonuniform orthogonal network with independent horizontal and vertical knot lines. Not all the knots of the inclined block contours are intersection points of the lines. Thus, most of the finite difference method defects have been eliminated for nonrectangular objects.

JTAM, Sofia, vol. 20 Issue 2 pp. 085-092 (1989)

Solving a Fixed Joint-Supported Beam under a Strained Scheme

K. Mladenov
High. Inst. Arch. Civ. Eng. 1 Hr. Smirnenski Bid., Sofia

A fixed joint-supported elastic beam with a constant stiffness is solved under a strained scheme. The stressed-strained state has been induced by an axial force, by translation and rotation of the fixing. Some formulae are obtained in the limit case. They are known in Mechanics of civil engineering and are deduced by the linear theory. A simple example is solved to compare the linear problem of frame stability. The results are shown graphically. Some conclusions are deduced as well. They concern the bifurcation point and the postcritical equilibrium curves.

JTAM, Sofia, vol. 20 Issue 2 pp. 093-101 (1989)

Creep Stability of Polymer Rods with Variable Cross Section

G. Mandichev
High. Inst. Mech. Electr. Eng., Sofia

Stability of polymer rods with constant cross section is studied quite well. The present work concerns rods with variable cross section. The minimal axial inertial moment is represented by an arbitrary degree function. The rods are supposed to be joint-supported at both ends. A physical law of deformation has been accepted according to Rjanitsin rheological model. Methods are described in details to define the constants in the model. The author has introduced a pseudo-periodic function which is used to derive the rod instant critical forces. The rod suspension is found in the form of a time function. Instant critical force, lasting critical force and the exploitation load P are found as well.

JTAM, Sofia, vol. 20 Issue 2 pp. 102- (1989)