Issue 2

JTAM, Sofia, vol. 12 Issue 2 (1981)

A Quick Action Synthesis of Stress Step Regulators

P. Genova
High. Inst. on Mech. and Electr. Eng., Durvenitsa

There is proposed a method for synthesis of stress step regulators (SSR) with respect to the maximum quick action. The problem is treated as a variational one. There are discussed several types of functionals referring to the maximum quick action. The transfer functions of the mechanisms are considered unknown. There is made a variation of the geometry and mass parameters of the SSR mechanisms. Thus, a coincidence between the transfer functions found according to the maximum quick action condition and those, characterising the mechanisms concerned, is looked for.

JTAM, Sofia, vol. 12 Issue 2 pp. 011-016 (1981)

On the Geometry of Spiroid Gear Screw Surfaces

V. Abadjiev, K. Minkov-Petrov
Inst. on Mech. Biomech., Bulg. Acad. Sci., Bl. 8 Geo Milev

There are derived the equations of various spiroid surfaces located on conic initial surfaces of spiroid worms. It is started from the most general case of a linear convolute helicoid and thus the special case of Archimedean and involute surfaces is obtained. The equations are valid in spiroid gear technology and production control.

JTAM, Sofia, vol. 12 Issue 2 pp. 017-027 (1981)

On the Existence of a P, Q, R, γ-variable Solution of the Euler – Poisson's System

S. Popov
Dept. of Mathematics, Univ. of Sofia, 6 A. Ivanov Blvd.

The paper treats a rigid body motion around a fixed point. It looks for a new first solution of the body's equation of motion and proves that there does not exist such a solution, which would depend on four variables, the three components of the body's angular speed among them. Taking into account the paper's results and those of prof. Arhangelski [1] there is obtained a corollary. It states that in cases different from the classical ones, the newly obtained first solution depends only on five variables, the angular speed's three components among them in any case.

JTAM, Sofia, vol. 12 Issue 2 pp. 028-033 (1981)

On the Calculation of Plane Supersonic Fields of Flows

K. Kozel, J. Polaček, M. Wawčinkowa

The paper investigates plane supersonic fields of flows and calculations concerning them.

JTAM, Sofia, vol. 12 Issue 2 pp. 034-043 (1981)

Unsteady Motion of Gas in Round Tube Systems

G. Nikolov
Geological Inv., 6 Oporska reka Str., Sofia

There is investigated the motion of gas in the systems mentioned. Some simplifications are made. Corresponding formulas are obtained.

JTAM, Sofia, vol. 12 Issue 2 pp. 044-048 (1981)

Hydrodynamics of Emultion-type Systems. I. The Approach of a Solid Sphere Towards a Tangentially Free Interface

E. Mileva, B. Radoev
University of Sofia

The motion of a solid sphere towards a flat interface between two viscous media of infinite extent is studied. The following assumptions are used: 1) the distance between the sphere and the interface (1) is smaller than the radius (R), i.e. a thin liquid film is formed; 2) there is a creeping flow in the fluids near the sphere; 3) the flat interface is undeformable; 4) the system is free of surface active Impurities. The problem is brought to the solution of an integral equation, determining the tangential velocity along the flat interface (U). In dimensionless form U depends on two parameters γ=√(2I/R) and β=γ(μ*/μ), where μ and μ* are the dynamic viscosites of the medium where the sphere moves, and that of the adjasent phases. Asymptotic expressions for β > I and β < I are derived. The results show that the flow in the phase, adjasent to the thin liquid film, has an isotropic distribution drawn to a scale of √2RI.

JTAM, Sofia, vol. 12 Issue 2 pp. 049-055 (1981)

Differential Equations of Dynamic Interaction between Sea Wave and Vertical Breakwater Taking into Account the Air Gripper Effect

V. Dzhupanov, J. Marinski
Inst. on Mech., Biomech., Bulg. Acad. Sci. Bl. 8 Geo Milev

The problem is formulated analytically. There is obtained a nonlinear system of differential equations which describe the evolution of the main flow and of the small disturbances on the surface between water and air. It is performed a qualitative analysis of the differential equations obtained. It is illustrated that the instability of the main flow is of physical character.

JTAM, Sofia, vol. 12 Issue 2 pp. 056-066 (1981)

Stress and Strain State of Tubes Made by Visco-plastic Material with Couple Stresses

N. Bontcheva
Inst. Mech. Bioniech., Bulg. Acad. Sci., Bl. 8 Geo Milev

It is analysed the problem of axisyminetric plane stress state of rigid visco-plastic continuum with couple stresses. Yield conditions of Mises type are assumed. There is solved an example of an infinite tube of such a material, which inner layer is of rigid-plastic material. Diagrams of stress and velocity distribution are given taking into account different values of the material constants. There is made a comparison between the solution obtained and the one concerning the same tube, made of material without couple stresses.

JTAM, Sofia, vol. 12 Issue 2 pp. 067-076 (1981)

Numerical Analysis of Creep of Statically Determined Combined Fero-Ferroconcrete Beam

D. Partov1, V. Tchernogorov2
1KNIPITIS, 135 Tsar Boris Str.
2Inst. Mech. Biornech., Bulg. Acad. Sci., Bl. 8 Geo Milev

Using the theory of visco-elastic body which determines the stress state of statically determined combined ferro-ferroconcrete beam in time t = ∞, the Volterra integral equations are derived. There is proposed a numerical method for solving the problem of heredity creep which is highly exact. The convergence of the method is illustrated by an exapmle.

JTAM, Sofia, vol. 12 Issue 2 pp. 077-080 (1981)

Buckling of Cylindrical Shell Taking into Account the Imperfection by Means of Ficticious External Loading

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

A critical loading for simple supported circular cylindrical shell under axial compression is obtained in the present paper. The solution is based on the linear theory of thin shells. The initial imperfection is taken into account by means of ficticious hydrostatic pressure. The investigation is carried out by the use of the variational principle of Hellinger-Reissner and the criterion of the initial imperfection. There are made numerical comparisons between the results of the present investigation and the available solutions.

JTAM, Sofia, vol. 12 Issue 2 pp. 081-086 (1981)

On the Eigen Forms in Beck's Problem

K. Mladenov
High. Inst. for Arch. and Civ. Eng., 1 Hr. Smirnenski Blvd., Sofia

The paper aims to give a method for the satisfaction of given initial expression in Beck's problem. The solving of this problem is relevant to the eigen (non orthogonal) forms of the Beck's problem by means of a full system of orthogonal functions. As a result of the satisfaction of some initial conditions it is obtained that the amplitude of the oscillations of points along the bar axis increases significantly as compared to the initial values. This fact may be inadmissible for some structures. The author's opinion is that this structure's state may be considered form of instability. There is performed a number of numerical investigations. The results are given in tables and on graphs.

JTAM, Sofia, vol. 12 Issue 2 pp. 087-096 (1981)

The Effect of Structure Length on the Design Seismic Loading

L. Tsenov
Inst. on Geophys., Bulg. Acad. Sci

The paper treats the problem of the effect of the structure length on the value of the design seismic loading. It is taken into account that the loading is applied perpendicularly to the structure longitudinal, axis. The investigations performed are based upon the supposition that the most effective influence on the structure is that of the seismic wave (a component of the complex earthquake motion of the foundation), which frequency coincides with the structure eigen frequency. On the ground of that supposition it is noted that the seismic impact does not reach its maximum amplitude value simultaneously at all the points along the axis of a long structure system. There are proposed expressions which more precisely give an account of the behaviour of such structures seismic loading.

JTAM, Sofia, vol. 12 Issue 2 pp. 097- (1981)