Issue 3

JTAM, Sofia, vol. 20 Issue 3 (1989)

Deformational and Amplitude-Frequency Analysis of Manipulative Systems

P. Genova1, E. Zahariev2
1High. Eng. Inst., Durvenitsa
2IMBM, Bulg. Acad. Sci.

In the work presented a software supplied method for deformational and amplitude frequency analysis of a structurally arbitrary manipulative system, including the one with an open-closed kinematic chain, is described. The FEM is applied and the frequences are obtained as roots of the equation for linearly vibrating system without dissipation. The theoretical statements are illustrated with the deformational and the amplitude-frequency analysis of the manipulative system of a robot for conture operations – type PAI TEP, with an open-closed structure. The results are analysed and physically useful conclusions are drawn for designers.

JTAM, Sofia, vol. 20 Issue 3 pp. 009-018 (1989)

A Quality Criterion for Tooth Gears in the Optimal Synthesis of Clock Engagements

S. Ganchev1, P. Parushev2
2IMBM, Bulg. Acad. Sci.

Clock engagements are non-conjugated tooth engagements. A satisfactory quality when transferring motion during exploitation is obtained by the use of optimization synthesis of the tooth surfaces of gears with clock profile. In the present work the influence of the variable geometric parameters of gears with clock profiles, on the value and the character of the kinematic criterions and the force transmission conditions, defining the geometric balance in mechanics, is illustrated.

JTAM, Sofia, vol. 20 Issue 3 pp. 019-028 (1989)

On the Deformability of a Polimer Rod in Fluid Medium in Some Private Cases

M. Todorov
High. Techn. School "A. Kuntchev", Rousse

The equations, obtained by the author in a previous work, for a polymer rod in fluid medium in a comparatively general statement, are applied for some private cases: centric extension and pressure, pure bending and stability of a polimer rod in fluid medium. On this basis a critical analysis of some works in this area is made.

JTAM, Sofia, vol. 20 Issue 3 pp. 029-038 (1989)

On the Validity of a Theoretical Model for Determination of Stresses in Covers in the Case of Big Displacements. Part I

Hr. Kouiumdjiev
High. Techn. School "A. Kuntchev", Rousse

In both parts of the work a theoretical problem, stated long ago in technical literature, is solved. Using the basic equations of the space problem (physically linear and geometrically nonlinear) of the elasticity theory, a theoretical model of the widely used specimen for determining the stress in covers, is checked. A criterion for applicability of the model and the relations drawn using this model, for testing practice, are proposed.

JTAM, Sofia, vol. 20 Issue 3 pp. 039-047 (1989)

On the Validity of a Theoretical Model for Determination of Stresses in Covers in the Case of Big Displacements. Part II

Hr. Kouiumdjiev
High. Techn. School "A. Kuntchev", Rousse

JTAM, Sofia, vol. 20 Issue 3 pp. 048-054 (1989)

Quasi One-Dimensional Model of Drawing of Glass Microcapillaries and Approximate Solutions

A.L. Yarin1, V.M. Rusinov2, P. Gospodinov2, S. Radev2
1Inst. Appl. Mech. USSR
2IMBM, Bulg. Acad. Sci.

A quasi one-dimensional model for the steady drawing of microcapillaries is proposed. Preformed glass tubes are used for the capillary production. A system of nonlinear ordinary differential equations is obtained from the motion and energy equations. The latter are written emloying a local coordinate system attached to the middle surface of the product. The obtained system of ordinary differential equations accounts for the effects of curvature and slope of the middle surface. A simplified numerical solution is obtained as a first step of the numerical treatment of the full quasi one-dimensional model.

JTAM, Sofia, vol. 20 Issue 3 pp. 055-062 (1989), [Full Article]

On the Mechanical Mathematical Modelling of Diffusion with Memory, Using FE

R. Blagoeva, N. Petrov
IMBM, Bulg. Acad. Sci.

The boundary problem for diffusion with decreasing memory is considered. The uniqueness of the solution and the restrictions on the memory function, following from the second thermodynamics principle, are investigated. An algorithm for numerical solution of the boundary problem is presented, discretization with respect to the space coordinates being performed using finite elements, and the one with respect to time-using finite differences. The stability of the difference scheme in time is considered, too. Numerical examples for two-dimensional area, performed using a program realization are given. A comparison is made with the corresponding analytical solutions.

JTAM, Sofia, vol. 20 Issue 3 pp. 063-072 (1989)

Mathematical Analysis of an Aortic Flow Rate Model with Concentrated Parameters

I. Iliev, V. Petrov
IMBM, Bulg. Acad. Sci.

An aortic flow rate model with concentrated parameters, derived in a previous authors, paper [1], is now investigated more precisely by an analytical method. Two cases of the model are considered: elastic reservoir approximation corresponding respectively, to partially and completely conjugated governing equations of the model. It is shown that for physiologically probable variations of the model parameters the transitions from the stable solutions of the system to the unstable ones arises. A comparison of the results with some haemodynamics effects is made.

JTAM, Sofia, vol. 20 Issue 3 pp. 073-081 (1989)

Carrying Capacity of Steel Beams at Thermal Actions

N. Bontcheva, St. Todorov
IMBM, Bulg. Acad. Sci.

The behaviour of steel beams subjected to strong thermal actions is considered. It turns out that beams designed for work at normal temperature conditions (200 C) loose carrying capacity due to strong temperature increase. An investigation is made of the carrying load capacity of different basic beam types at temperature increase. Some concrete examples are solved, the plastic displacements and the moment of carrying capacity loss are obtained.

JTAM, Sofia, vol. 20 Issue 3 pp. 082-094 (1989)

Critical Intensity Coefficiens of Stresses in Hereditary Statement

K. Popov, K. Hadjov, D. Dontchev
High Chem. Techn. Inst., Durvenitsa

In the present work, an equation describing the change of the critical intensity coefficient of stresses in time, on the basis of the hereditary theory of elasticity and the fracture mechanics, is drawn. An experimental confirmation of the theoretical results is obtained.

JTAM, Sofia, vol. 20 Issue 3 pp. 095-097 (1989)

A New Finite Element for Investigation of the Stability of Three-Layer Composite Material Beam

M. Kishkilov
High Inst. Arch. Civ. Engin., Sofia

The present work is an attempt to create methods for numerical solution of a three-layer beam filled with composite material with reonom properties. The numerical realization is performed on the basis of FEM in displacements, and the account of the reonom properties – on the basis of linear hereditary creep theory. New in the proposed work is the so-called new finite element (NFE) with six stages of liberty, built on the basis of an analytical solution [1]. The NFE is used for the first time by the author in work [2]. Here it is used to solve the stability problem for three-layer beam. The increment stiffness matrix is obtained. Its elements are quite more complicated than the ones when using eight liberty stages FE, which are widely applied in mechanics problems. It is built on the basis of the separated displacements [3]. Despite all that the NFE has one significant merit – decrease of the number of solving equations and ability for performing independent solutions in time and space.

JTAM, Sofia, vol. 20 Issue 3 pp. 098-108 (1989)

Development of the Methods for Determining the Dynamic Fracture Stability by the Use of Small Test Bodies

St. Vodenitcharov
Sci. Prod. Org “Metal Techn.”, Sofia

A problem survey of the methods for determining the dynamic fracture stability by the use of small test bodies is done in the work. In the works analysed results of the author and his collaborators are included.

JTAM, Sofia, vol. 20 Issue 3 pp. 109- (1989)