Issue 2
JTAM, Sofia, vol. 8 Issue 2 (1977)

Fully Developed Visco-Noncontractible Fluid Flow in a Curved Pipe

Z. Zaprianov, H. Hristov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences, Bl. 8, Kv. Geo Milev


Steady laminar flow in a curved pipe of circular cross is investigated. It is assumed that the flow is fully developed, i.e. the flow is far enough from the entry and the exit, so that the velocity profile can be assumed to be similar in every cross section. The Navier-Stokes equations in stream-function vorticity form are solved numerically. Computer calculations are described and mechanical implications are discussed.

JTAM, Sofia, vol. 8 Issue 2 pp. 011-017 (1977)

Initial Transfer Functions of Spatial Kinematic Chains

M. Konstantinov, M. Markov
Sofia. Higher Institute of Mechanical and Electrical Engineering, Kv. Durvenitsa

The article gives a direct description of the initial transfer functions of monocontour spatial devices by means of geometrical characteristics and configurational functions. Algebraic but not differential operations are applied. The problem is based on the properties of kinematic speed screws with their displacements being infinitesimal. Thus kinematic definiteness of all tridimensional Grüblers chains is verified. A numerical crankschaft problem is solved.

JTAM, Sofia, vol. 8 Issue 2 pp. 018-023 (1977)
Analysis of Structural Gystems' Behavior with Changing their Basic Parameters

L. Cenov, H. Botcheva
Sofia. Institute of Ceophysics, Bulgarian Academy of Sciences, Kv. Geo Milev, Bl. 4

Designing of structures in seismic regions must consider large and controllable unelastic deformations, i.e. those structures must absorb and dissipate seismic energy when earthquakes take place. When deformations grow some structure parameters change. It is considered that unelastic deformations cultivate in vertical and horisontal directions in structures designed my means of vertical diaphragms. Thus every diaphragm is transformed into a group of disks, while unelastic deformations appear in yielding bonds between those disks. The article deals with the effect of those bonds of structure's deformation and on its eigenoscillation. That effect changes the basic parameters of the soil-structure system. Numerical criteria are formulated, defining the effectiveness of unelastic deformations' admission.

JTAM, Sofia, vol. 8 Issue 2 pp. 024-028 (1977)
Geometrically Nonlinear Problems in Plastic Shell's Theory

M. Mitov, M. Duszek
1Sofia. Institute of Mathematics and Mechanics with Commputing Centre, Bulgarian Academy of Sciences, Kv. Geo Milev, Bl, 8
2Warsaw, Institute of Fundamental Technological Research. Polish Academy of Sciences

Thin-rigid-plastic cylindrical shells are considered with different nonlinear kinematic relations applied. Some basic kinematic equations are analysed, considering shell's geometry-deflection relation. A short shells with large radial deflections and small tangential displacements example is given. It is numerically solved, diagrams are drawn. The inner forces field problem and the displacements field problem are solved in closed form. "Geometrical" hardening effect on loading-deflection relations is determined.

JTAM, Sofia, vol. 8 Issue 2 pp. 029-039 (1977)
Elastic Buckling of a Circular Cylindrical Stiffened Shell, Subjected to Axial Pressure

P. Kolev
Sofia. Higher Institute of Civil Engineering, 1 Hristo Smirnensky Blvd.

An elastic buckling of a circular cylindrical shell with stiffeners in longitudinal and circumferential directions, under uniform distributed axial pressure, is investigated. The governing equation is obtained by means of Reisner's variational principle. Using the criterion of initial imperfection, the formula for critical stress of the stiffened shell is obtained.

JTAM, Sofia, vol. 8 Issue 2 pp. 040-046 (1977)
Lieuville's Type Equations Variational Principles in Nonpotential Systems

T. Boiajiev
Shumen, 32 Jun Gagarin St.

An expanded space quantum description – statistic description analogy of a proper dynamical system is determined. Thus a variational principle in Lieuville's type equations is formulated.

JTAM, Sofia, vol. 8 Issue 2 pp. 047-057 (1977)
On a Nonholonomic Bonds – Variable Masses Machine Units Modelling

N. Mintchev
Varna, Higher Military Naval Academy "N. Y. Vaptsarov"

The article summarises Prof. Hieronimus' method for constant mass parameters – nonholonomic bonds machine units mathematical modelling. Thus an enriching of dynamical modelling (force reduction) method is proposed. That method dials with machine units' motion equations formulation while the units' mass parameters are variable.

JTAM, Sofia, vol. 8 Issue 2 pp. 058-066 (1977)
Dynamic Stability of Flexible Shafts, Running on Flexible Supports under Nonconservative Loading

V. Alexandrov
Sofia. Higher Institute of Civil Engineering, 1. Hristo Smirnenski Blvd.

This paper deals with the dynamic stability of a uniform shaft, rotating on flexible supports. The shaft is subjected to a follower torque and to dissipative forces. The shaft dynamical stability differential equations are defined by using Galiorkin's variational principle. The basic theoretical and numerical results are illustrated and discussed.

JTAM, Sofia, vol. 8 Issue 2 pp. 067-072 (1977)
Experimental Hypothesis of Stress Tensor Behavior in Steady Turbulent Flow with Semi-Empirical Modelling Applied

V. Mednikarov, V. Georgiev
Sofia. Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences, Kv. Geo Milev, Bl. 8

The authors suppose the nonlinear relation between turbulent tangential stress distribution in Prandtl's interpretation and flow's cross section. Furthermore, that stress distribution is similar to flow's total energy fall distribution. A semi empirical method is applied. Results are analysed with conclusions made.

JTAM, Sofia, vol. 8 Issue 2 pp. 073-077 (1977)
Cylinder Walls Elastic Deformation in Cylinder-Liquid System with Circular Waves Applied

G. Georgiev, V. Angelova
Sofia. Higher Institute of Mechanical and Electrical Engineering. Kv. Durvenitsa

The article deals with the above deformations definition. Numerical method is used in displacements determining.

JTAM, Sofia, vol. 8 Issue 2 pp. 078-083 (1977)
On a Gradient Elastic Model of a Composite Material

K. Markov
Sofia. Institute of Mathematics and Mechanics with Computing Centre, Bulgarian Academy of Sciences, Sofia, Kv. Geo Milev, Bl. 8

A phase interaction registering method is discussed when calculating elasticity modules of composite materials with globular impurities. This method is based on gradient-elastic model of deformable solids. Distortion and elastic nonhomogeneity problems are analysed in the first part of the article. Secondly, an algebraic system for defining Young's modul is formed. It summarises the selfcoordinated system of dispersal composites mechanics and treats some special cases.

JTAM, Sofia, vol. 8 Issue 2 pp. 084-090 (1977)