Issue 3

JTAM, Sofia, vol. 17 Issue 3 (1986)

Science in the Light of the Decisions of the Bulgarian Communist Party XIII Congress

Editorial Board

JTAM, Sofia, vol. 17 Issue 3 pp. 009-010 (1986)

Mechanism Synthesis by an Automatic Iteration Approximation

L. Gel'man
Textile Inst.

A general convergent approximation synthesis of a mechanism class is developed. when the initial point is near the wanted minimum of the purpose function. Based on the Newton-Rafson optimization method this synthesis is of interpolation kind with mean-quadratic and uniform functional approximation. The procedure of one-dimensional minimization is eliminated to obtain a good first approximation. The Newton-Rafson method becomes iterative one and the purpose function matrix can be calculated using partial derivatives of first order. Some singularities of the synthesis that has been developed are considered as well. They are connected with stability of the solution.

JTAM, Sofia, vol. 17 Issue 3 pp. 011-018 (1986)

Dynamics and Control of a Robot with an Elastic Arm

M. Weber, U. Walendy, B. Heimann
Academy of Sciences, GDR

In this paper an alternative control concept is proposed that refers to a more realistic flexible multi-body model. It provides a better disturbance behaviour because not only the servo motor position but also the arm deflection are considered in a closed-loop algorithm. The paper is divided into three parts: 1. Derivation of a minimal order system. 2. Design of a control law that can be implemented on convential IR-hardware. 3. Numerical and experimental investigations. The results show that in the case of ptp-control a good performance quality can be achieved by using a control concept based on a realistic elastic robot model.

JTAM, Sofia, vol. 17 Issue 3 pp. 019-029 (1986)

Dispersion Equations of the Roundcylindrical Shell-Tank Hydroelasticity Problem. Part II

V. Dzhupanov, E. Gavrilova, A. Golovkina, V. Vassilev
lnst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

What is investigated is a construction of the dispersion equations of hydroelasticity problems connected with a roundcylindrical and linearly elastic shell. Two cases are considered. A constant liquid level is assumed in the first one although the ideal compressible liquid moves parallely to the shell generatrix at a transport velocity. The shell motion forms have been accepted as known. The general solution includes the qum of three velocity potentials, the one describing the stationary motion at a given transport velocity and the others being two acoustical potentials. The acoustical potentials satisfy boundary value conditions following the radial and the longitudinal coordinate, respectively. The analytic solution is given in most general terms because of considerable difficulties. What is assumed in the second case is a flowing of the ideal compressible liquid subjected to a given law of level diminuation. A dispersion equation has been constructed using the time dependence of the longitudinal wave numbers. This equation is in fact a necessary and sufficient condition for variable separation. Its strong non-linearity is quite natural. Some problems concerning the complicated dynamic shell-liquid interaction remain out of the investigation.

JTAM, Sofia, vol. 17 Issue 3 pp. 030-041 (1986), [Full Article]

A Method to Solve Boundary Value Problems in the Plane by Means of Non-Uniform and Non-Orthogonal Ne

O. Santurjian, I. Etimova
Inst. of Water Problems, Bulg. Acad. Sci., Bl. 1

A modified co-location method using an arbitrary discretization net has been developed. It serves to determine plane fields that are described by second order partial differential equations in irregular domains. The wanted function is approximated in a net knot neighbourhood by means of a fourth order partial polynomial with nine members. Specially selected this polynomial has been represented with respect to function values in the knot itself and the eight surrounding points. Further, the solution follows the co-location method principles. What is examined is the accuracy and the convergence of the method in the case of arbitrary and uniform nets. The method is applied to stationary heat-conductivity problem with two dimensions. The results are compared to the solution that is obtained by the finite element method. The net density of the polygonal body is supposed to be one and the same. When solving specific problems of technics some advantages are gained over the finite element method.

JTAM, Sofia, vol. 17 Issue 3 pp. 042-050 (1986)

Integral Equations of Motion of a Viscous Free Boundary Liquid in a Two-Connected Domain

L. Antonovsky
Inst. Hydrodyn., Acad. Sci., USSR

The Stokes equations of slow two-dimensional flows of a free boundary viscous fluid in a two-connected domain have been reduced to a system of two one-dimensional integral equations. The paper proposes a method for this reduction. One of the integral equations is of second order Fredhoim type. The advantages are in the comparatively simpler numerical solution.

JTAM, Sofia, vol. 17 Issue 3 pp. 051-058 (1986)

Boundary Layer Growth on a Rotating Circular Cylinder in a Planar Stagnation Flow

Z. Zapryanov, I. Lambova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

This paper presents an analytical solution to the Navier-Stokes equations by using the inner and outer expansion method for the case of a flow streaming past a rotating cylinder in the neighbourhood of a solid plane. The flow and the cylinder velocities vary as certain powers of time. This solution holds for slightly viscous fluids and small times compared to the initial time of boundary layer detachment. The special case of boundary layer overlapping around the body and the plane wall has not been considered. We have studied the influence of the rotatory motion upon flow behaviour which is illustrated graphically in Figures 1-5.

JTAM, Sofia, vol. 17 Issue 3 pp. 059-068 (1986), [Full Article]

Mechano-Mathematical Modelling for the Determination of Initial Tensions in Galvanic Coatings

H. Koujumdjiev
High Techn. Sch. 'A. Kanchev'. Rousse

The paper reviews the dependences from (2, 4, 6, 8) that deal with initial tension determination in galvanic coating deposition on an elastic tape cathode bender. What is examined in a three-plate model is the development of the theoretical model from (3), The argumentation from (6) has been examined as well. The dependences that have been obtained are compared to the dependences from (2, 4, 8).

JTAM, Sofia, vol. 17 Issue 3 pp. 069-075 (1986)

On Some Friability and Fracture Regularities under Creep Condition

R. Aroutunian
University of Leningrad, USSR

What is observed in experimental investigations of metal creep and its friability hidden phase is the essential part of pore and crack formation in micro-level damage accumulation. A unified fracture criterion has been formulated when taking into consideration the results of the experimental investigations and the mass preservation law. The criterion is valid both for great and small tensions. It coincides with the known condition of Hoff's elastic fracture in the case of incompressible material and great tensions. Near small tensions the new fragile fracture criterion serves as an asymtote. Durability curves have been constructed as well. It is shown that friability consideration is necessary to prognosticate correctly structure material efficiency, while the incompressibility assumption leads to unjustified durability reinsuring.

JTAM, Sofia, vol. 17 Issue 3 pp. 076-079 (1986)