Issue 4

JTAM, Sofia, vol. 21 Issue 4 (1990)

The Problem of the Rectilinear Frictional Brahistohrone in a Gravitational Centrifugal Field

V. Vitliemov
High. Techn. Sch. "A. Kanchev", Rousse

The extreme speed displacement of a material point is examined along an inclined withstanding line that rotates round a fixed vertical axis. It is assumed that t he horizontal distance is given and the friction is dry. The results that have been obtained can be applied to ground the constructive parameters of different centrifugal apparatuses with an increased performance due to their greater efficiency.

JTAM, Sofia, vol. 21 Issue 4 pp. 011-015 (1990)

Servocontrol of Manipulation Robots: Part I. The State-of-the-Art

S. Patarinski1, Sin En Cher2
1Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4
2High. Inst. Mech. Electr. Eng., Sofia, Durvenitsa

The dynamic servocontrol of manipulation robots is discussed in the general case of continuous path motion. The state-of-the-art is reviewed in the first part of the paper and the most popular methods: feedforward control, classical feedback control (with or without compensation), nonlinear feedback control (direct design and computed torque, robust and adaptive methods), are presented by block schemes.

JTAM, Sofia, vol. 21 Issue 4 pp. 016-023 (1990), [Full Article]

Bifurcation and Stability of the Relative Equilibrium of a Satellite-Gyrostate System

V. Roubanovski

What are examined in the case of a rotating axis which is not on the main planes of the central three-axial inertial ellipsoid are the bifurcation and the stability and the relative equilibrium of asatellite-gyrostate system. The results are presented in a bifurcation diagram, where the distribution of the instability degrees satisfies the general relations in the bifurcation theory. The gyrostate moment of rotation has been considered to be a bifurcation parameter.

JTAM, Sofia, vol. 21 Issue 4 pp. 024-030 (1990)

Natural Frequencies of a Parallelepiped Resonator with an Elastic Window

E. Gavrilova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

The walls of a parallelepiped box-like construction are assumed to be absolutely rigid. A rectangular window has been cut out in one of them and a thin elactic plate has been walled in. The cavity that has been obtained has been filled by and ideal compressible liquid. Together with the plate it forms an uniform mechanical system which is called to be "hydroelastic" (HES). The aim of the paper is to determine its proper frequency spectrum. What is proposed is an improved analytical method which is based on the integration of: (i) the Levi integration method to describe the plate vibrations by the corresponding differential equation; (ii) the Leibenson method to take into account the interaction between the plate and the liquid.

JTAM, Sofia, vol. 21 Issue 4 pp. 031-034 (1990), [Full Article]

Influence of Some Basic Parameters on the Earthquake-Induced Motion of an Open High-Pressure Pipe-Line

D. Kisliakov
High. Inst. Arch. Civ. Eng., 1 Hr. Smirnenski Bld., Sofia

The problem of the dynamic interaction between an open high-pressure pipeline and the inside flowing has been solved by the author in a previous work after a thorough kinematic analysis by a two-staged application of the Coriolis theorem. In result the partial differential equation of the earthquake-induced motion of an open high-pressure pipe-line with an inside flowing has been obtained. The actual seismic input has been assumed to be horizontal and it has been involved by real earthquake records. The aim of the present paper is to trace the influence of the basic pipe-line parameters on the earthquake-induced motion. The investigation has been performed by the numerical solutions of different real examples and the results have been analysed. Some conclusions are made to take into account the influence of the seismic input data.

JTAM, Sofia, vol. 21 Issue 4 pp. 035-042 (1990), [Full Article]

Analytical and Numerical Investigations on the Hydroelasticity of One-Span Pipings in Their Parametric Space

D. Dermendjian, V. Dzhupanov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl.4

What are considered are five schemes of one-span pipings which convey ideal compressible and heavy liquids. The schemes differ from each other by the supportings. The purpose is to obtain the stability domains of each of them. The Bubnov – Galerkin variational method has been applied to solve the problem. A good result is obtained in the third approximation. The stability domains of each one-span piping is obtained in the space (L, U, σ) as well, where L is the span length, U is the flow velocity and σ is the piping proper frequency. A new case has been recorded. It concerns a non-conservative system which represents a duplex clamped beam with a Q-apparatus on the one end.

JTAM, Sofia, vol. 21 Issue 4 pp. 043-049 (1990), [Full Article]

An Algorithm for Numerical Solution of a Class of Inverse Problems for Diffusion with Memory

R. Blagoeva, N. Petrov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

A class of inverse diffusion problems for materials with memory is considered to determine the model parameters during a concrete moisture-transfer isothermic process. A numerical algorithm and a program have been developed for an automatic evaluation of the model parameters. The mass change of the samples has been taken into account. The program has been tested in the case of cement stone drying.

JTAM, Sofia, vol. 21 Issue 4 pp. 050-052 (1990), [Full Article]

Vapour Condensation on Spirally Corrugated Tubes for Horizontal Condensers – Heat-Transfer Coefficient

V. Zimparov, N. Vulchanov
High. Inst. Mech. Electr. Eng. Gabrovo

What is examined experimentally is the influence of the groove form on the heat-transfer coefficient during vapour condensation on 25 spirally corrugated tubes. The results have been described in a general way. The change of the nondimensional heat-transfer parameter h+0 is shown, taking into account the dependence on the Reynolds number for each tube. The groove form itself has been presented by several geometric parameters of the surface-tension and the tube drain capacities. The groove form influence is considered. A correlation for the degree of the heat-transfer intensification is proposed, accounting for the Weber number and the helix angle. The correlation is in good agreement with the present experimental results and the results that have been obtained by other authors.

JTAM, Sofia, vol. 21 Issue 4 pp. 053-058 (1990), [Full Article]

A Numerical Solution of the Problem for the Cylindric Shell Behaviour under Dynamic Loading

A. Netrebko

What is considered by the net method is a numerical solution of the problem for the cylindric shell behaviour under dynamic loading. A modification of the numerical scheme is proposed to increase its stability. A simplification of the initial Tymoshenko type system of equations is performed by the solution that has been obtained. The results are finally compared.

JTAM, Sofia, vol. 21 Issue 4 pp. 059-064 (1990)

Basic Relations in the Plasticity Theory of II-jushin: A Generalization of the Case of Big Plastic Deformations

P. Trousov, O. Doudar

Most of the models in the geometric nonlinear plasticity theory are based on different generalizations of the plastic flow theory in the case of big displacement gradients. According to the geometric linear plasticity the relations in the plastic flow theory describe plastic flow processes along small curve trajectories only and the accuracy is sufficient. The relations in the elasticity theory of Iljushin can describe processes that have been subjected to a complex loading. The accuracy is sufficient, The aim of the paper is to generalize these relations in the case of big plastic 'deformations.

JTAM, Sofia, vol. 21 Issue 4 pp. 065-072 (1990)

On Some Equivalence of the Method of Large Fragments (MLF) and the Boundary Elements Method (BEM), Providing Generalization and Enlargement of the BEM

Hr. Ganev
Inst. of Water Problems, Bulg. Acad. Sci., Bl. 1

The mathematical domain under consideration has been presented as a closed N-gonal, on the boundary of which the unknown parameters are distributed. It is possible to receive the necessary system of linear algebraic equations using the Lagrange principle of virtual displacements and the Legandre functions. As illustration is proposed by a typical example.

JTAM, Sofia, vol. 21 Issue 4 pp. 073-083 (1990), [Full Article]

A Methodology to Determine the Crack Stability of Metals under Cyclic Loadings

Yu. Davidov, St. Vodenicharov
NPO "Technology of metals", Sofia

The potentiometric method is considered to determine the growing crack dimensions. Some advantages and some defects are established when this method is used to determine the lengths of growing and fatigue cracks. In this connection a methodology and the corresponding realization devices are developed to record real criteria that have been introduced in fracture mechanics to describe material behaviour under cyclic loadings. Investigations are performed in the small cyclic loading domain and the dependence of the J-integral on the length of the fatigue crack is determined. What is established in addition is a 12% difference between the J-integral real value and the value which has been determined by a conventional device realization of the potential difference method. The use of the methodology increases the precision and the accuracy of the experiment.

JTAM, Sofia, vol. 21 Issue 4 pp. 084- (1990)