Issue 3

JTAM, Sofia, vol. 16 Issue 3 (1985)

Oscillations of a Heavy Solid Body with a Single Fixed Point

V. Sergeev
Comp. Centre, Ac. Sci. USSR, Moscow, USSR

The paper proves the existence of two families of solutions of the equation of motion of a solid body around a fixed point. However, Poincare's method is employed and solutions stand periodical with respect to Euler's angles. The heavy body under consideration is similar to Lagrange's gyroscope. Oscillations that have been found correspond to the non-degenerate oscillations involved in the undisturbed problem, with frequencies close to those of Lagrange's case.

JTAM, Sofia, vol. 16 Issue 3 pp. 011-015 (1985)

Non-Ideal Energy Impact on Pendulum Systems

T. Krasnopolskaya, A. Shvets
Inst. Mech., USSR Acad. Sci., Kiev, USSR

Dynamic phenomena occurring during high frequency parametric energy impact on a pendulum are analysed. However, power of energy is limited and the impact delay is taken into account.

JTAM, Sofia, vol. 16 Issue 3 pp. 016-018 (1985)

Approximate Calculation of the Eigen Frequencies of Torsion Oscillations

B. Cheshankov
High. Inst. Mech. Electr. Eng., Darvenitsa

An approximate method for the calculation of the first several eigen frequencies of torsion oscillations is proposed. Eigen forms, as well as corresponding knots are specified and Rayleigh's formula is employed. Several examples are given and comparison to results, obtained by employing other methods, is performed.

JTAM, Sofia, vol. 16 Issue 3 pp. 019-029 (1985)

Structure Creep Analysis Based on the Black Box Approach

Yu. Samarin, Yu. Eremin
Kuybishev Politechn. Inst., USSR

An approach to structure creep analysis based on the black box concept is proposed. However, structure elements are taken to be objects, undergoing external impacts and reacting properly. Such an approach allows for the introduction of new ideas in the structure aggregation. Moreover, it provides solution to the problem of prediction of product deformation properties.

JTAM, Sofia, vol. 16 Issue 3 pp. 030-042 (1985)

Rheology Models Composed of Parallel Connected Maxwellian and Bingham Elements

T. Balevski
Inst. Met. Res. Techn., Bulg. Acad. Sci.. Bl. 1

Structure equations of rheology models with the above characteristics are derived in the paper. Moreover, processes of deformation with constant strain rate, stress relaxation for constant total strain, as well as creep under constant stress, are analysed. Possibility to describe a complex of rheology properties of real metals and alloys is proved on the basis of multi-element model, composed of Bingham elementary structure units.

JTAM, Sofia, vol. 16 Issue 3 pp. 043-049 (1985)

Chain Solution Bifurcation of Offshore Scafffold Bridge Hydroelastic Problem

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

The paper presents solution of the problem of irradiating a group of arbitrary arranged parallel cylinders, by employing a plane wave. Moreover, the solution is modified for the case of impulse loading, whereas impulse loading of beams, which axes lie in one and the same plane, is analysed in detail. The scheme of the solution design and convergence are given.

JTAM, Sofia, vol. 16 Issue 3 pp. 050-058 (1985), [Full Article]

On the Correct Posing of the Method of Transfinite Interpolation for Solving Free-Boundary Problems of Fluid Flows

Chr. Christov1, P. Volkov2
1Department of Fluid Mechanics, Institute of Mechanics and Biomechanics, Bulgarian Academy of Sciences, P.O. Box 373, Sofia 1090
2Institute of Theoretical and Applied Mechanics, Siberian Branch of the Academy of Sciences of the USSR

The method of transfinite interpolation is employed to design mobile coordinate grids on a region with indefinite boundaries. This method allows to reduce the grid generation problem to the solution of a system of partial differential equations on this boundary. What is further shown is that the initial boundary value problem is correct, but the routine way of solving the system proves incorrect.

JTAM, Sofia, vol. 16 Issue 3 pp. 059-067 (1985), [Full Article]

On the Stability of Two-Layer Capillary Jet

S. Radev1, V. Shkadov2
1Institute of Mechanics and Biomechanics, Bulgarian Academy of Sciences, Sofia
2Lomonosov Moscow State University, Moscow, USSR

Stability of a two-laver jet is investigated by employing one-dimensional model. However, the jet is composed of a cylindric part surrorded by a concentric layer of another fluid. Both fluids are supposed to be incompressible and immiscible and the jet velocity profile is homogeneous and uniform. Two families of waves with growing amplitudes are specified. Some limit cases are studied and comparison to classical results for homogeneous jet stability is performed.

JTAM, Sofia, vol. 16 Issue 3 pp. 068-075 (1985)

On the Energetic Approach in Viscoplasticity

A. Baltov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

New model of a viscoplastic body is presented. It is built on the basis of microstructure energy approach while body undergoes dynamic impacts. The effect of plastic deformation, strain rate and temperature are taken into account and smooth transition to quasi dynamic impacts is provided. A simplified one-dimensional model is proposed and a method for the determination of the model material functions is designed. This method is applied to particular models.

JTAM, Sofia, vol. 16 Issue 3 pp. 076-087 (1985)

On the Response of a Single-floor Steel Frame with Screens and Undergoing Horisontal Seismic Impacts Part I. Experimental Study

B. Yanev
P. B. 1100, N. Y. C. 10023, USA

Typical results from the experimental study of the response of a single-floor frame with screens, undergoing simulated seismic impacts, are presented. General, as well as particular screen effects are specified.

JTAM, Sofia, vol. 16 Issue 3 pp. 088-094 (1985)

An Application of the Finite Element Method in General Form for Plates

P. Kolev
High. Inst. Arch. Civ. Eng., 1 Hr. Smirnenski Blvd., Sofia

The paper gives an application of a finite element model, involving plate displacements and loads. The Hellinger-Reissner variational principle is employed. However, the mixed variational principle provides good possibility to account for the equivalent stresses, as well as to reduce both the degree of discretization and computing time. Furthermore, accuracy is increased. Convenient application to physically nonlinear systems is illustrated by solving several numerical examples.

JTAM, Sofia, vol. 16 Issue 3 pp. 095-102 (1985)

Application of the Finite Element Method to the Study of Fracture of Anisotropically Hardening Materials

N. Boncheva, R. Yankov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8

The finite element method is applied to a model of elastoplastic and anisotropically hardening material, whereas a specific hybrid finite element is introduced. A computing programme is designed which is employed to perform numerical experiments, as well as to determine the plastic regions and crack propagation in notched specimens. However, the effect of the preliminary plastic deformation is studied as well.

JTAM, Sofia, vol. 16 Issue 3 pp. 103-117 (1985)