Issue 1

JTAM, Sofia, vol. 20 Issue 1 (1989)

Investigation of the Practical Stability of the Solutions of Systems with Impulse Effect by the Help of the Comparison Method

G. Kulev, D. Bainov
University "P. Hilendarski", Plovdiv

The present paper applies the comparison method to investigate the practical stability of the solutions of differential systems with impulse effects. What are used are vector comparative equations and semi-continuous auxiliary functions which generalize Lyapunov's functions.

JTAM, Sofia, vol. 20 Issue 1 pp. 011-018 (1989), [Full Article]

On the Independent Dynamics Controllability of Manipulator Systems

P. Kiriazov, P. Marinov
Inst. Mech. Biornech., Bulg. Acad. Sci., Bl. 8

When the geometrical and inertial parametres of manipulators are specified some problems on the optimal design of their drive and control systems can be formulated. The subject of this work is the minimization of the inertial coupling coefficients, and further on the determination of the largest domain of the control inputs in which an independent joint controllability condition is satisfied. The design parametres are the gear ratios and the ratio of the control input bounds. The design procedure is applied to the complete dynamic model of a manipulator with two rotary joints. The procedure itself is in an analytical form. The proposed work is intended to improve robustness of many feedback control schemes and other manipulator performances in dynamic operations.

JTAM, Sofia, vol. 20 Issue 1 pp. 019-023 (1989), [Full Article]

Dynamics of a Manipulation Robot with Two Degrees of Freedom in the Case Resonance with a Root of the Characteristic Equation Which Is Equal to Zero

S. Butchvarov, P. Kolev
High Inst. Mech. Electr. Eng., Durvenitsa

The manipulation systems serve the fundamental production machines in the capacity of flexible system elements. The machines themselves cause vibrations which pass to the manipulation systems through the bearers with respect to the vibro-protection insurance. Thus, the dynamic investigation of manipulators and robots on close production conditions represents a pressing problem. What are proposed in the present work are dynamic investigations of a manipulation robot with two degrees of freedom accounting for one of the regional motion transmission and the construction elasticity. The differential equations of motion are introduced. The proper frequencies and the oscillation forms are determined. An analytic solution of the perturbated motion is constructed in asymptotic series using the Bogoliubov-Mitropolski method in the resonance case with a root of the characteristic equation which is equal to zero.

JTAM, Sofia, vol. 20 Issue 1 pp. 024-032 (1989)

An Indirect Electro-Mechanical Analogy Method for Investigating Machine Aggregates with Variable Masses and Positional Forces

N. Minchev, G. Grigorov, S. Kazandjiev
High Inst. Mech. Electr. Eng., Varna

Usually, the mass parametres and the forces which excite oscillations are positional functions. Then, the mathematical model which describes the machine aggregate motion represents a non-linear autonomous system of differential equations. Its integration is not possible in the general case. The paper proposes a scheme realization of a device for electric modelling of machine aggregates with variable masses and positional forces. This is done by electronic equivalents of inductions and condensers, i. e. by an indirect electro-mechanical analogy.

JTAM, Sofia, vol. 20 Issue 1 pp. 033-036 (1989)

Smooth Interpolation by an Effective Mechanical Model

H. Ganev, S. Bonev
Inst. of Water Problems, Bulg. Acad. Sci., Bl. 4

What is proposed in the present paper is a method for a specified smooth interpolation by an effective mechanical model that represents a flexible ruler (a beam) on an elastic pliable (Winkler's) foundation. Numerical examples are presented and they confirm the efficacy of the method. More exact formulae for function interpolation, differentiation in any point of the interval [0,1], integration, solving differential, integral and integro-differential equations can be obtained by the proposed method.

JTAM, Sofia, vol. 20 Issue 1 pp. 037-044 (1989)

On the Method of the Conditional Instant Fields

K. Hadjov
High Inst. of Chem. Eng., Durvenitsa

The physical sense of the existing restriction in the connection equation is explained in the present investigation, when the method of the conditional elastic fields has been applied to heredity boundary-value problems. It is shown the way to remove the restriction. The stress strain fields have been divided into spherical and deviation fields for the purpose. Respectively, the boundary value conditions have been divided into vector-pressure (dilatation) and vector-deviation stress (deformation), too.

JTAM, Sofia, vol. 20 Issue 1 pp. 045-049 (1989)

Stability Examination of Thick-walled Welded Bounds under Frail Fracture

P. Bochev1, K. Minchev2
1Inst. of Heavy Mech. Eng., Radomir
2IMTM, Bulg. Acad. Scl., Bl. 1

The paper presents some stability examination results of steel welded bonds under frail fracture. The welded bonds have been obtained by the electro-slag welding method and the protection-gas narrow space welding method. The dynamic loading method for the test body with a falling load has been used to determine welded bond stability under frail fracture. Some conclusions are made. They are related to the efficacy of the welding methods that have been applied. The critical fragility temperature and the fracture diagram of Pelini-Pyusak are used.

JTAM, Sofia, vol. 20 Issue 1 pp. 050-054 (1989)

Examination of the Possibilities to Influence Capillary Jet Flowings

P. Gospodinov, S. Radev
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

It is considered a capillary jet flowing in a boundary layer approximation. A near-wall jet flowing and one-layered jet flowing have been deduced in particular cases. What are examined numerically are the flowing initial value influence, the nozzle finite length and the internal body role or the viscous kernel role on the flowing development along the jet. The results give a possibility to evaluate the significance of the different effects when solving mass and energy transport problems.

JTAM, Sofia, vol. 20 Issue 1 pp. 055-063 (1989)

Photo-Absorptive Thermocapillary Convection in Viscous Liquid Thin Layer. II. Temperature and Dynamic Field

S. Slavchev
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

The paper solves the problem of photo-absorptive thermocapillary convection of a semi-transparent viscous incompressible fluid in a thin layer which covers a horizontal surface. What is assumed is a space-periodic radiation from above. The cases of small and great time intervals are considered from the moment that the light has been switched on. The flowing development regime is examined. Its stabilization is examined, too. The deformation on the fluid free surface has been taken into consideration for the purpose. What is investigated is the determination parametre influence on the fluid system reaction and the layer convection intensity.

JTAM, Sofia, vol. 20 Issue 1 pp. 064-069 (1989)

On the Determination of Air Friction Factor during the Spinning of Polymer Melts

J. Mishinev, H. Bechev
IMTM, Bulg. Acad. Sci., Bl. 1

A determination method for the air friction factor during polymer melt spinning is considered when the different filaments influence each other strongly. The filaments are parts of the yarn which is formed by the nozzle. The force balance during the melt spinning has been adapted to multi-filamented yarns for the purpose. An average air friction factor is introduced and it is dependent on the filament number and the filament disposition in the bundle. The factor is calculated as the limit of a function which has been determined by several equations. The construction of the equations uses the changes in the filament bundle geometry. Technics is proposed to realize the method practically.

JTAM, Sofia, vol. 20 Issue 1 pp. 070-074 (1989), [Full Article]

A Family of Finite Elements for the Analysis of Box Bridge Decks

L. Boswell

A family of one-dimensional sub-parametric elements is presented in this paper. In addition to the truss and beam elements the family includes a general thin-walled box beam element which may be curved in space and may have a variable cross-section. Sufficient degrees of freedom are included to account for the warping and distortional effects which occur in box beams. The design and analysis of a variety of bridge decks may be undertaken using the family of elements. In this paper particular attention is given to the general thin-walled element. The appropriateness of this element and the accuracy of the results obtained are demonstrated by comparison with the results of experiments. Three-dimensional finite element analyses were also carried out for comparison.

JTAM, Sofia, vol. 20 Issue 1 pp. 075-089 (1989), [Full Article]

Basic Differential Equations for the Displacements of the Thin Elastic Shells of Revolution

H. Hristov
Lenin Sq. 6, Sofia

What are obtained for a thin elastic shell of revolution and its static behaviour in too general linear formulation are the basic system of the differential equations of displacement and some formulae for the internal force determination. The corresponding equations have been simplified and specific relations for the shell singular central pole have been obtained. The external forces and the unknown functions are presented in Fourier series with a circumferential direction. Many features have been taken into consideration; arbitrary smooth shape of the shell meridian and a variable thickness in meridian direction; arbitrary distributed external loadings (forces and temperatures); a generalized elastic Winkler's foundation along the shell local directions, etc.

JTAM, Sofia, vol. 20 Issue 1 pp. 090-101 (1989)

On the Problem of Determining the Stress-Strain State of a Multi-Layered Specimen under Dynamic Loading

I. Nicolova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

A method for the stress-strain state determination of a multi-layered specimen is proposed in the present work. The multi-layered specimen is subjected to dynamic loading and is considered to be made of a "fictitious" substitutive material. This material reflects the energy dissipation identically due to the traversion across the layers. Maxwell's visco-elastic model is used for the purpose. Its viscosity coefficient is assumed to be dependent on the specimen layer number only. The relation between the viscosity coefficient and the layer number is derived.

JTAM, Sofia, vol. 20 Issue 1 pp. 102-106 (1989), [Full Article]

Jd-integral for Two-Dimensional Cracks in a Non-Elastic Deformable Solid

S. Vodenicharov, A. Baltov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

A new J1-integral definition for non-elastic deformable plane solids is proposed using the dynamic invariant integral definition in fracture linear mechanics. Partial dJd-integral summation is applied within the incremental theory framework. A theoretic experimental way to Jd-integral determination is proposed by means of Sharpy hammer. The dynamic problem is solved numerically by the finite-element method.

JTAM, Sofia, vol. 20 Issue 1 pp. 107-115 (1989)