Issue 1
JTAM, Sofia, vol. 17 Issue 1 (1986)

On the Numerical Calculation of Periodic Rotational Vibrations in Driving Systems in Non-uniformly Transmitting Mechanisms

Nguen Van Khang


The dynamic equations of motion for the driving systems in non-uniformly transmitting mechanisms are described in the paper. The dynamically stable parameters of periodic rotational vibrations in these systems are numerically calculated. An example is given.

JTAM, Sofia, vol. 17 Issue 1 pp. 011-017 (1986)

Some Properties of the First Integrals of Nonholonomic System

Il. Iliev
Plovdiv, 47 As. Halachev Str.

Nonholonomic mechanical systems subjected to links of Tchataev's type are considered. First integral is defined by means of Ferrers equations. The definition differs from the usual one. Some connections between the existence of first integrals of the nonholonomic system and the existence of first integrals of the system without the links are established. Some examples are given.

JTAM, Sofia, vol. 17 Issue 1 pp. 018-025 (1986)
History of Hydroelasticity in the Institute of Mechanics and Biomechanics with the Bulgarian Academy of Sciences

V. Dzhupanov
Inst. Mech. Biomech., Bulg. Acad. Sci.. Bl. 8

An adapted variation of a more detailed manuscript on the history of hydroelasticity in Bulgaria is proposed. Geometric schemes of the hydroenergetic equipment which is the subject of hydroelastic investigation are shortly described. The means for exciting oscillations and the was of dynamic interaction in the constructive elements are listed. A general historical aspect of hydroelasticity is followed. The most characteristic investigations in hydroelasticity carried out up to nowadays in the Institute of Mechanics and Biomechanics with the Bulgarian Academy of Sciences and the results of these investigations are listed in a descriptive form.

JTAM, Sofia, vol. 17 Issue 1 pp. 026-032 (1986)
A Study on the Influence of Lubricant Inertial Forces and Small Deformations of the Limiting Surfaces over the Stability of Neck Motion in Hydrodynamic Bearings of Finite Length

V. Alexandrov
High. Inst. Arch. Civ. Eng., 1 Hr. Smirnenski Blvd.

The influence of the rubbing surface elastic deformations over the lubricant dynamic properties is studied. The local inertial members of the equation of lubricant motion are recognized as well. The movements of the neck center and the deformations of the elastic coating are assumed to be small compared to the lubricant layer thickness. Thus, the differential equations of the hydrodynamic pressure distributions are reduced to linear ones using the method of small perturbations. Results show that the recognized factors extend the stability domain of the neck motion.

JTAM, Sofia, vol. 17 Issue 1 pp. 033-039 (1986)
The Axisymmetric Boussinesq Problem for a Thick Elastic Plate under a Punch of Arbitrary Profile

M. Lal
India, Jabalpur 482001, R. D. Univ.

In this paper the axisymmetric Boussinesq's problem for a thick elastic plate under a punch of arbitrary profile has been analyzed. Particular results are obtained for parabolic and conical concave punches. The expre-ssions are derived for normal displacements and stresses for both cases.

JTAM, Sofia, vol. 17 Issue 1 pp. 040-044 (1986), [Full Article]

Lateral Instability of Two-Layer Liquid Capillary Jet

St. Radev
Inst. Mech. Biochem., Bulg. Acad. Sci., Bl. 8

The problem of lateral (asymmetric) stability lost of a complex liquid jet is considered in a nonviscous treatment. The dispersion equation of lateral perturbations in the jet axis is deduced. This equation is assymptotically and numerically analyzed for different nondimensional parameters. It is shown in the general case that two-wave families with increasing amplitude propagate in the jet. The control of a kernel stability is possible by means of suitable parameters of the concentric layer.

JTAM, Sofia, vol. 17 Issue 1 pp. 045-054 (1986)
Boundary Layer Growth on a Rotating Circular Cylinder in an Infinite Fluid

Z. Zapryanov, I. Lambova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

Here we present an approximate solution to the problem of the boundary layer growth on a rotating circular cylinder in an infinite viscous incompressible fluid. The assumptions are large Reynolds and Strouhal num-bers and small times compared to the initial detachment time. The full Navier-Stokes equations are solved by using the method of inner and outer expansions. Analytic zeroth and first approximation solutions to the stream functions of the boundary layer and the outer flow are obtained, hence the uniformly valid composite solution. We supply the flow patterns from which boundary layer detachment and eddy formation are discernible. Both the movement of the detachment points along the surface of the cylinder and the torque dependence on certain parameters are shown graphically.

JTAM, Sofia, vol. 17 Issue 1 pp. 055-066 (1986), [Full Article]

Normal Impingement of an Axisymmetric Air Jet onto a Flat Wall

H. Ennoji1, R. Rakadjiev2, T. Asanuma2, St. Radev2
1Japan, Tokai University
2Bulgaria, Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

The flow characteristics of an axisymmetric jet impinging normally onto a flat wall are calculated numerically by means of the inviscid flow equations. The numerical results are compared with experimental data obtained by the authors. The validity of the mathematical model used is discussed.

JTAM, Sofia, vol. 17 Issue 1 pp. 067-078 (1986)
The Dynamic Theory of Shakedown of Elasto-plastic Structures

Nghuen Van Pho
SR Vietnam, University of Hanoi

The problem of shakedown of elasto-plastic structures is of great importance for planning in elasto-plastic systems subjected to time variant loading and temperature. An extended theorem for dynamic shakedown is formulated and proved in the paper. Two problems for shakedown of structures are formulated as well. A method for approximate determination of the domain of residual tensions is proposed.

JTAM, Sofia, vol. 17 Issue 1 pp. 079-085 (1986), [Full Article]

Theoretical Models Connected with Determination of Means Tensions in Galvanic Coating

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

The dependences for determination of the so called means tensions in the cross-section of a galvanic coating deposited on elastically complient tape cathode (1) are reviewed in the paper. The progress of mechano-mathematical modelling and the corresponding dependences from [7], [10] which are well-grounded in [9] is followed. The most frequently used dependences from [1-6], [14, 15] are discussed and compared with those from [7,10].

JTAM, Sofia, vol. 17 Issue 1 pp. 086-095 (1986)
Shock-Loading Influence over Mechanical Characteristics of Low-Tempered Steel

K. Minchev, S. Vodenicharov, G. Stoimenov
IMTM, Bulg. Acad. Sci., 53 Chapaev Str.

The shock-loading influence over mechanical behaviour of low-tempered steel is studied by means of Sharpy's hammer. An experimental method is described and results are provided. Thus, conclusions for the qualities of the steel under consideration are deduced on condition of dynamic deformation.

JTAM, Sofia, vol. 17 Issue 1 pp. 096-100 (1986)