Issue 3

JTAM, Sofia, vol. 22 Issue 3 (1991)

Theory of Lyapunov's Characteristic Exponents for Impulsive Differential Systems III. Regular Systems

P. Simeonov1, D. Bainov2
1Higher Military School, Pleven
2Blagoevgrad University

In the present paper the notion of regularity of a linear system of impulsive differential equations is introduced and the relation of this property to the properties of normality of the basis and reducibility is investigated.

JTAM, Sofia, vol. 22 Issue 3 pp. 008-014 (1991), [Full Article]

Condition for Retaining Equilibrium during the Motion of a Wheel-Chair

G. Boyadjiev1, D. Stefanov2
1Sofia University
2Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

The study considers the equilibrium conditions during the motion of a wheel-chair as an example of a biotechnical manipulation system. Criteria are derived to retain the motion equilibrium. Thus, a technical device has been developed to follow the equilibrium criteria and to cancel inexpedient commands of the operator, which could lead to the loss of equilibrium.

JTAM, Sofia, vol. 22 Issue 3 pp. 015-020 (1991), [Full Article]

Synthesis of Path Generation Mechanisms

V. Galabov
Technical University, Sofia

The structure of the path generation mechanisms is represented as a superposition of a provisionally open kinematic chain and function generator mechanisms connecting the links of the chain. This allows to accomplish the synthesis of the path generation mechanisms at separate stages: type-dimensional synthesis and dislocation of the provisionally open kinematic chain; determination of the transfer functions of the function generator mechanisms; type-dimensional synthesis of these mechanisms. This simplifies the preliminary introduction of various restrictions and allows easier algorithms for synthesis and control of path generation mechanisms. Three methods for synthesis of the path generation mechanisms are proposed: methods of differential geometry and differential calculus; matrix-geometric apparatus; methods of kinematic and analytic geometry. This makes possible the adaptivity of the subjective factor to choose the most suitable form of a mathematical model for synthesis of a concrete path generation mechanism, to duplicate and to control the synthesis results.

JTAM, Sofia, vol. 22 Issue 3 pp. 021-035 (1991), [Full Article]

Design of a Gear Drive for Minimal Crankshaft Reaction in Planar Linkages

I. Kochev
Kettelerstrasse 8, 6084 Gernsheim, Germany

This study offers an alternative design technics of a gear drive for minimal crankshaft reaction in planar linkages. It is supposed that the planar linkages are driven by a circular or a noncircular gearset. A nontrivial optimization problem has been formulated in case of a dominant variable and inertia forces.

JTAM, Sofia, vol. 22 Issue 3 pp. 036-041 (1991), [Full Article]

Concerning the Replacement of Steel Dies by Dies Made of Non-Ferrous Metals and Alloys

L. Drenchev
Institute of Metal Science and, Technology, Bulg. Acad. Sci., Sofia

The suggested article describes an algorithm, by means of which necessary calculations could be done to replace dies of one material by dies of another one keeping the major casting performance. This technological task has been solved by the heat transfer boundary value inverse problems. An example is given concerning the application of the algorithm to the replacement of a steel cylindrical die by an aluminium one. The algorithm can be generalised in the multidimensional case.

JTAM, Sofia, vol. 22 Issue 3 pp. 042-048 (1991), [Full Article]

A Study of the Nonlinear Behaviour of Reinforced Concrete Frame under Strong Ground Motions

E. Vasseva
Geophysical Institute, Bulg. Acad. Sci., Sofia

The main aim of this paper is to prc. sent the basic principles and the method procedure in nonlinear dynamic analysis of multistoried and multibayed frames under strong ground motions. The nonlinear deformations are taken into account according to the Takeda's hysteresis model. The effect of the seismic intensity on the structural system and its linear and nonlinear behaviour have been investigated. The results of the study show that the time-history analysis enables the determination of the structural and the local ductility factors. The analysis of the results leads to conclusions and recommendations for the design of seimic resistant R/C structures.

JTAM, Sofia, vol. 22 Issue 3 pp. 049-058 (1991), [Full Article]

Sensitivity Analysis for Shape Optimization by the BEM

J. Ivanova, P. Dineva, V. Valeva, L. Hadjikov
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

In this paper the shape optimization problem is examined in the inelastic case by a hybrid utilization of the BEM and the design sensitivity analysis. The method of Gourevich has been used to describe the inelastic behaviour of the solid. The problem to determine the optimal shape of the free boundary of a hole in a rectangular elastic or inelastic metal plate under static tension has been solved as a numerical example.

JTAM, Sofia, vol. 22 Issue 3 pp. 059-068 (1991), [Full Article]

The Rayleigh-Taylor instability of Two Viscoelastic Superposed Fluids

B. Sharma1, R. Sharma2
1College of Agriculture, 303 329 Jobner, India
2Simla University, Simla, India

This paper describes the numerical solution of the stability analysis separated by two viscoelastic fluids when the whole system is immersed in a uniform vertical magnetic field.

JTAM, Sofia, vol. 22 Issue 3 pp. 069-074 (1991), [Full Article]

Numerical Simulation of Separated Flaw Past Circular Cylinder by a Discrete-Vortex Method

J. Fraczak
Institute of Fluid-Flow Machinery, Pol. Acad. Sci., Poland

Separated flow oast a circular cylinder in a uniform stream of inviscid fluid impulsively started from the rest is numerically simulated by a discrete-vortex approximation. Viscosity effects are taken into account indirectly by the artificially fixed mean position of flow separation depending on the Reynolds number. The time dependence of the flow is followed by the initial formation of two symmetric vortices to subsequent asymmetry and eventual alternate shedding behind' the circular cylinder. The lift and drag coefficients and the Strouhal number are calculated and compared with experimental data.

JTAM, Sofia, vol. 22 Issue 3 pp. 075-088 (1991), [Full Article]

On the Basic Geometric Characteristics of Co-Axial Turbulent Jets

P. Stankov, Y. Dinkov, J. Denev
Technical University, Sofia

The basic geometric characteristics of the flow have been investigated by various velocity and area ratios at the nozzle outlet. A numerical procedure has been worked out by the authors to be used in the investigation. An assessment is made by comparing some of the numerical results with experimental data by different authors. The paper also discusses some regularities in the behaviour of the main geometric characteristics of the flow and the possibilities for their mathematical modelling.

JTAM, Sofia, vol. 22 Issue 3 pp. 089-096 (1991), [Full Article]

The Second Statistic Moment of the Compound Safety Margin

M. Grois, F. Svoboda
Technical University, Brno, Czechoslovakia

The content of this paper relates to the fatigue calculations for products, the functionality of which is connected with an exact securing of responsibly and entirely defined service course.

JTAM, Sofia, vol. 22 Issue 3 pp. 097-099 (1991), [Full Article]

Quasi-Static Modelling of Elastic Poly-Contour Manipulating Systems

P. Genova, E. Zakhariev
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

Mathematical modelling of manipulating systems is the basis of designing the mechanical structure, the control system and the strategies of motion. The present paper suggests a force-deformation-frequency model of the mechanical structure, which is used at the design stage. Methods and criteria are also suggested to evaluate force, energy and accuracy indices concerning the behaviour of the structure in all points of the working space. The resulting information has been used to design the motors, the transmission mechanisms, the mechanical structure, the control systems, etc.

JTAM, Sofia, vol. 22 Issue 3 pp. 100-106 (1991), [Full Article]

On the Optimal Third-Order Bounds on the Effective Conductivity of Random Dispersions of Spheres

K.Markov1, K. Zvyatkov2
1Sofia University
2Higher Pedagogical Institute, Schumen

The problem of obtaining the optimal third-order bounds on the effective conductivity of random dispersions of nonoverlapping spheres is considered in the paper. The optimality is understood here in the sense that the bounds should be the most restrictive ones that take into account the statistical information contained in the two and the three-point correlation dispersion functions. It is shown that the bounds due to Beran and Torquato are optimal to c2-order, here c is the volume fraction of the spheres.

JTAM, Sofia, vol. 22 Issue 3 pp. 107-116 (1991), [Full Article]