Issue 2

JTAM, Sofia, vol. 17 Issue 2 (1986)

On a Mathematical Model of the Optimal Reliability Theory and Some Mechanical Applications

Nguyen Van Pho

JTAM, Sofia, vol. 17 Issue 2 pp. (1986)

Kinetostatic lnvestigations on a Manipulator Gripper

P. Gradinarov
High. Inst. Mech. Electr. Eng., Varna

What is used to study the kinetostatics of a plane gripper is the method proposed by I. B. Chelpanov and S. N. Kolpashnikov. A domain of the object stationary fixing in the gripper mouth has been defined in the space of the force factors applied to the manipulated object. This domain is constructed for a symmetric gripper when accounting or not for friction between the gripper mouth and the object. Some optimization problems are considered and they show evident possibilities of the method in question.

JTAM, Sofia, vol. 17 Issue 2 pp. 011-019 (1986)

On the Constructive Relative Kinematics of the Lever Mechanism

L. Gel'man
Textile Inst. "A. N. Kossigin", Moscow

A general method for a plane ]ever mechanism is developed to calculate the kinematic functions and their partial derivatives. The method is based on mechanism topology which is used in iteration synthesis. The coordinates of fixed boundary points from the mechanism vector covering net are chosen as parametres. The projections of several vectors in the mechanism initial location are chosen as parametres, too. All of them are measured in the same units. The positions of the vectors are determined with respect to the initial locations.

JTAM, Sofia, vol. 17 Issue 2 pp. 020-029 (1986)

Vibrations of Rigid Bodies in the Visco-Elastic Model

Nguyen Van Dao

The paper deals with rigid body auto-oscillations which are due to friction. The friction itself depends on the velocity third power ("negative friction"). Forced oscillations excited by external harmonic forces are considered, too. What is examined in details is the effect of the oscillation damping which is carried out by means of a dynamic damper.

JTAM, Sofia, vol. 17 Issue 2 pp. 030-035 (1986), [Full Article]

A Method for Optimal Heating of Asymmetric Bimetal Plates

P. Kiriazov, P. Marinov
Inst. Mech. Biomech., Bulg. Acad. Sci., BI. 8

The solution of the problem for bilateral heating of a bimetal plate is analyzed. Propositions about the distribution of the characteristic roots and the convergence order of the series are proved. The problem of time optimum heating is formulated when control temperature impacts are specified by step values. This formulation is expedient in practice. The optimal solution is found with respect to the commutation moments. The numerical realization of the method proposed is carried out in case of a steel-brass bimetal plate.

JTAM, Sofia, vol. 17 Issue 2 pp. 036-042 (1986)

Generation of Accelerograms or Industrial Zones

I. Pascaleva, G. Georgiev
Bulg. Acad. Sci., Bl. 3

The Bulgarian territory is characterized as high seismic. Most of the industrial zones are built in high seismic and unfavourable conditions. A seismic rise is noted and terrestrial motions provoked by human activities are registrated in various industrial zones. The important equipment of such zones is not always examined for seismic impact. Defining and generating the most probable seismic impact seem to be necessary in many cases of investigating the structure and the equipment of the zone. In the present paper is shown a procedure to find the characteristics of synthetic accelerograms. The Fourier amplitude spectrum has been used in accelerogram generation.

JTAM, Sofia, vol. 17 Issue 2 pp. 043-049 (1986)

Dispersion Equations of the Round-Cylindrical Shell-Tank Hydroelasticity Problem (Part 1)

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

The dispersion equations of different hydroelasticity problems have been examined. They concern the linear elastic round-cylindrical shell-tank which is partially filled up by an ideal acoustic fluid. The idea is to show the use of the dispersion equation analysis to the choice of acoustic potential. The potential itself describes the corresponding fluid motion. The case of incompressible fluid with a constant level (forced and free oscillations) as well as the case of compressible fluid with constant level, too, (forced and free oscillations) have been analyzed. The problem is assumed to be axisymmetric with vanishing symmetry, i.e. it does not depend on the polar coordinate. The cases examined are with proper technological sense. Moreover, they are considered as preparatory to the problem of compressible fluid flowing to the tank bottom through a central opening. This problem is the subject of the second part of the paper.

JTAM, Sofia, vol. 17 Issue 2 pp. 050-062 (1986), [Full Article]

Mathematical Simulation of the Processes of Heat and Mass Transfer in a Boiler of an Accumulating Type

G. Georgiev, J. Popov, S. Boushev, B. Zlatev, V. Kovachev, T. Stoichev
IMTM, Bulg. Acad. Sci. Bl. 1

We propose a complete mathematical model of the processes of heat and mass transfer in the form of a closed system of differential and functional equations. At a preset rate of consumption and temperature of the consumed water as functions of time, the thermodynamical state of the system is described. The heat transfer through the pipes in the boiler and the installations, depending of the hydrodynamical state of the flow, is accounted for. Some experimental results concerning the testing of the model are included.

JTAM, Sofia, vol. 17 Issue 2 pp. 063-070 (1986)

Solid-Liquid Isothermal Phase Transition in Two-Dimensional Lennard-Jones System

V. Bedanov1, G. Gadiak1, S. Radev
1Institute of Theoretical and Applied Mechanics, Novosibirsk, USSR
2Inst. Mech. Biomech. Bulg. Acad. Sci., Bl. 8

Solid-liquid phase transition in two-dimensional Lennard-Jones system is studied by the molecular dynamics method. The isotherm is considered. It is shown that the melting o' this system is the first order transition with metastable overheated solid and solid-liquid coexistence phase. Intermediated liquid-crystal phase is not found contrary to the recent experiment on Xe monolayer on graf oil.

JTAM, Sofia, vol. 17 Issue 2 pp. 071-075 (1986)

An Equation Describing the Evolution of Non-Stationary Geometrically Thin Accretion Disc

L. Philipov
Central Lab. Space Reserch, Bulg. Acad. Sci.

The author shows how a model equation of "diffusion" type can be obtained. He uses a more generalized form of the plasm laws for viscosity and transparency in a geometrically thin accretion disc. The equation obtained appears to be a generalization of past model equations. What is specified by the author about the application of this equation is a qualitative description of the processes in non-stationary accretion discs.

JTAM, Sofia, vol. 17 Issue 2 pp. 076-080 (1986), [Full Article]

On the Determination of Residual Tensions in Galvanic Coating

H. Koujoumdjiev
High. Techn. Sch. "A. Kanchev", Rousse

The dependences for distribution determination of residual tensions in the cross-section of galvanic coating has been reviewed. The coating itself is deposited on a bending elastic tape cathode. The solutions obtained by means of the approximate algorithms [3, 4, 6, 8] are compared under suitable testing conditions.

JTAM, Sofia, vol. 17 Issue 2 pp. 081-090 (1986)

Investigations on the Behaviour of Highly Orientated Polycaproamide under Static Tensile Conditions

H. Bechev, R. Mladenov, E. Denev
Higher Inst. Chem. Technology

The tension relaxation under constant strain of highly orientated polycaproamide (polyamide rayon) has been investigated. The results obtained have been treated by constructing a discrete spectrum of relaxation time. The aim is to forecast the behaviour of the materials that have been examined. It is shown that time-temperature superposition principle is impossible to be applied because of structural metastability of the highly orientated polycaproamide.

JTAM, Sofia, vol. 17 Issue 2 pp. 091-099 (1986), [Full Article]

On a Mathematical Model of the Optimal Reliability Theory and Some Mechanical Applications

Nguyen Van Pho
Hanoi University, Viet Nam

What is constructed in the paper is a mathematical model of the reliability theory for general and optimal systems. The problem of reliability and the motion of optimal systems are defined. A general scheme is proposed to calculate the reliability of optimal systems. The determination of system probability resistance to boundary forces has been discussed as an application.

JTAM, Sofia, vol. 17 Issue 2 pp. 100-106 (1986), [Full Article]

Cracking of Metal Sheets Undergoing Cold Rolling

K. Lilova1, L. Stanev1, R. Kazandjiev
1Inst. Mech. Biomech., Bulg. Acad. Sci
2Inst. Metal. Res. Techn., Bulg. Acad. Sci.

The paper presents the mechanical characteristics of the process of cold rolling of metal sheets. A criterion for the stability of such a process of plastic deformation is presented as well. What is derived is a criterion for fractureless rolling and, moreover, experiments are performed to prove the criterion validity. Good agreement between theoretical results and experimental evidence is obtained.

JTAM, Sofia, vol. 17 Issue 2 pp. 107-116 (1986)