Issue 2

JTAM, Sofia, vol. 21 Issue 2 (1990)

Elements of the Measurement Group Theory

V. Ivanov

A group theory approach is proposed to solve synthesis and analysis problems for measuring operations in the case of incomplete information. Some basic properties of groups have been considered together with their physical measurement connection. What are systematized are some basic problems of the theoretical metrology which can be solved by the proposed method.

JTAM, Sofia, vol. 21 Issue 2 pp. 010-019 (1990)

Dynamics of a Plane Locomotion Robot Model in the Nonresonance Case for the Walk Phase. Initial Conditions

M. Peikova
High Inst. Mech. Electr. Eng., Durvenitsa

The paper considers dynamics of a plane antropomorphic robot model for nonresonance cases in the walk phase. The law of motion has been derived in a vector form accounting for the Poincare initial conditions that concern periodic solution existence. These conditions are used when the differential equations of motion have been solved approximately. They connect the initial conditions for the generalized coordinates and the generalized velocities that have been obtained after applying the Poincare theorem. The robot motion itself has been realized by the action of chosen drive control moments. The motion law expressions are suitable to computers because the Poincare initial conditions guarantee the computing procedure convergence. According to the author's practice this is not possible under arbitrary choice of the initial conditions.

JTAM, Sofia, vol. 21 Issue 2 pp. 020-023 (1990), [Full Article]

Two-Dimensional Inverse Analysis of Nature Measurements in Tunnels under Face Influence

V. Vassilev
Inst. of Water Problems, Bulg. Acad. Sci., Bl. 1

What is proposed in the paper is a method to inverse analysis of nature measured displacements in tunnels. It is based on the finite element method and gives a possibility to account for the rock massif elastic deformations that have been realized before the measuring instrument installation. Thus, the accuracy increases in estimating the rock massif physico-mechanical characteristics. Afterwards, the characteristics themselves become input data in underground equipment tension and deformation investigations. A numerical example has been solved.

JTAM, Sofia, vol. 21 Issue 2 pp. 024-028 (1990)

On a Generalization of Solving Methods for Plastic Solids Using the Finite Element Method

N. Boncheva, St. Todorov, R. Yankov
Inst. Mech. Biomech., Bulg. Acad. Sci., BI. 4

The paper gives an unified recording of the basic dependences that appear when the finite element method has been used to solve plastic solids by two different methods. Also, there are given dependences which concern an elastic solid. What are shown are the links between the first two methods and the differences to which they lead. All the dependences enable the construction of an unified computing program that applies one of the three methods according to user's desire.

JTAM, Sofia, vol. 21 Issue 2 pp. 029-038 (1990)

On Some Actual Problems for Structure Materials and Elements in Fracture Mechanics

V. Panassyuk

Some new results are examined to solve fracture mechanical problems for deformable solids with narrow pole-crack defect type. The macro crack generation at the top of the tension concentrator has been analyzed too.

JTAM, Sofia, vol. 21 Issue 2 pp. 039-050 (1990)

Axisymmetric Flow Examination of a Viscous Fluid with Gas Bubbles in a Circular Cross Cylindric Tube

P. Veinstein, O. Ganiev, I. Jeleva

The paper considers a viscous fluid flow in a circular cross cylindric tube under gas bubble injection along the axis. What is assumed by studying such a multiphase medium is a small volume of the gas. The gas phase itself has been modelled by a continuum without any proper pressure. The interphase interaction accounts for the viscous friction (according to the Stokes law) and the joining mass force. The bubble trajectories have been estimated. What are examined are the solutions that have been obtained.

JTAM, Sofia, vol. 21 Issue 2 pp. 051-055 (1990)

Turbulent Hydraulic Friction in Spirally Corrugated Tubes for Condenser Applications

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

What are analyzed to determine some geometric characteristics of the cold-rolled turbulence promoter and the influence on the hydraulic friction coefficient are the hydraulic characteristics of 25 spirally corrugated tubes (SCT) which have been obtained experimentally. A new geometric complex is introduced to characterize the physical nature and the intensity of the flow between two adjacent promoters. A correlation curve is obtained on the base of 150 experimental points. It describes the momentum transfer over rough surfaces in certain argument ranges. A dependence is shown to calculate the friction coefficient during a fluid flow in SCT. The correlation results are compared to the friction coefficient values that have been measured experimentally. The relative discrepancy is less than ± 10%.

JTAM, Sofia, vol. 21 Issue 2 pp. 056-061 (1990), [Full Article]

Estimation of Structure Steel Behaviour by Temperature Transition Characteristics

K. Minchev, V. Miladinova, G. Stoimenov
Inst. Met. Res. Techn., Bulg. Acad. Sci., Bl. 1

The total energy of a test body destruction can be divided into two parts using dynamic test diagrams. The first part is the crack initiation energy while the second one is the propagation energy. Thus, investigating the temperature dependences a possibility appears to specify the fragility critical temperature of structure steels. The paper presents some results about different steel thermo-treatments. What is established is a sharp change of the propagation energy when the fragility critical temperature has been reached.

JTAM, Sofia, vol. 21 Issue 2 pp. 062-065 (1990)

On the Application of the Finite Element Method to the Plane Elastic Theory Problem

G. Gospodinov, P. Drakaliev
High Inst. Arch. Civ. Eng., 1 Hr. Smirnenski Bld., Sofia

A complete solution of the plane elastic theory problem is obtained in the paper. The finite element method has been applied. What are admissible for the domain under investigation are multiconnection, an arbitrary contour and an arbitrary loading which includes concentrated forces. A methodology, an algorithm and a program on the base of a linear finite element are developed. All of them give possibilities to divide the object into subdomains with different elastic and geometric characteristics. Some difficulties appear in the angular points. By the so called "incompatible elements" the difficulties have been overcome simply and with a satisfactory accuracy. The numerical results show high efficiency and accuracy of the method.

JTAM, Sofia, vol. 21 Issue 2 pp. 066-073 (1990)

The Finite Element Method in the Investigation of Connected Thermo-Visco-Elastic Effects in a Three-Layered Beam under Long Vibrational Loading

M. Kishkilov
High. Inst. Arch. Civ. Eng., 1 Hr. Smirnenski Bld., Sofia

What is examined by the finite element method is the thermomechanical behaviour of a three-layered beam under long vibrational loading. The two outer layers of the beam are elastic while the middle one is perfectly visco-elastic and temperature depending. The application of the finite element method uses a new finite element that has been constructed by the "separated suspension" method with eight degrees of freedom. At last, a numerical example has been enclosed.

JTAM, Sofia, vol. 21 Issue 2 pp. 074-080 (1990)

A Geometric Interpretation of Strength Energetic Criterion in Hereditary Mechanics

D. Donchev
High Inst. Chem. Eng., Durvenitsa

The present paper examines the three Urwin coefficient changes of the tension intensity in hereditary materials. A geometric interpretation of the fracture energetic criterion in c hereditary treatment is proposed.

JTAM, Sofia, vol. 21 Issue 2 pp. 081- (1990)