Issue 1

JTAM, Sofia, vol. 22 Issue 1 (1991)

On the Permanent Rotations of a Satellite-Gyrostat

V. Atanassov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

A permanent rotation of a satellite-gyrostat on a circular orbit is considered. Simultaneously with the orbital motion the satellite rotates with a constant angular velocity about an axis that has been orientated in the body arbitrarily and passing through its mass centre it keeps the orientation along the normal to the orbital plane during the motion. The present paper considers the problem to find the rotor motions which guarantee the realization of such a permanent rotation.

JTAM, Sofia, vol. 22 Issue 1 pp. 009-013 (1991), [Full Article]

Servocontrol of Manipulation Robots: Part II. Experimental Comparison via Numerical Simulation

S. Patarinski1, Sin En Cher2
1Inst. Mech. Biomech., Bulg. Acad. Sci., B1. 4
2Technical University, Sofia

The dynamic servocontrol of manipula¬tion robots (MR) is considered in the general motion on a continuous path. Using block schemes presentations the first part of the paper has reviewed the popular methods: feed-forward control, classical feedback control (with or without compensation), nonlinear feedback control (direct design, computed torque method, robust and adaptive methods). In the second part the methods are compared by a numerical simulation of an articulated robot model with two degrees of freedom which operates in a vertical plane.

JTAM, Sofia, vol. 22 Issue 1 pp. 014-021 (1991), [Full Article]

Dual Vector-Parameter in Manipulator Kinematics

C. Mladenova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

Solving the closed equations of a mani¬pulator in a prescribed motion one can ob¬tain the angular and the linear displacements of each manipulator joint. It is well known that the Denavit-Hartenberg formalism and the Rodrigues finite rotation formula are used for the purpose. In the present paper the above mentioned transformations are expressed by the "vector-parameter" notion, which has been used by the author in her previous works. Dual forms of the rotation and the Jacobian mat¬rices are obtained introducing dual numbers and a dual vector-parameter.

JTAM, Sofia, vol. 22 Issue 1 pp. 022-030 (1991), [Full Article]

Theory of Lyapunov's Characteristic Exponents for Impulsive Differential Systems: I. General Properties of the Characteristic Exponents

P. Simeonov1, D. Bainov2
1Higher Military School, Pleven
2University of Blagoevgrad

In the present paper the main properties of Lyapunov's characteristic exponents for linear impulsive differential systems are considered. Necessary and sufficient conditions for a normal basis of solutions are found.

JTAM, Sofia, vol. 22 Issue 1 pp. 031-037 (1991), [Full Article]

Redistribution of the Power Input of the Gear-Box with General Branching of Flow

M. Grois1, L. Dimitrov2
1VUT, Brno, Czechoslovakia
2Technical University, Sofia

An original construction of an aircraft gear-box satisfying the increased demands on aircraft mechanisms is proposed. Some defining parameters of the gearing and the gear teeth are examined.

JTAM, Sofia, vol. 22 Issue 1 pp. 038-041 (1991), [Full Article]

Molecular and Cellular Mechanics

G. Brankov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

The objective of this investigation is to reveal the mechanical motion of the biomolecules and biomembranes which is an integral part of the physical, chemical and more generally of the biological motion. On the basis of biophysical models we investigate biomechanical models of vibration, rotation and translation of proteins. We consider the geometry and the vibrations of the atoms in a single spiral and in a fragment of a double spiral of DNA and RNA. We investigate briefly the biomechanical model of the membrane shell theory and partly of moment shell theory.

JTAM, Sofia, vol. 22 Issue 1 pp. 042-046 (1991), [Full Article]

A Laplace Transform Aided Numerical Approach to Dynamic Unilateral Contact Problems

A. Liolios
Inst. Str. Mech., GR-67100 Xanthi, Greece

The paper presents a numerical approach to unilateral contact problems in structural dynamics using the Laplace transform. These problems have equalities as well as inequalities for governing conditions and so they are nonlinear. Their mathematical treatment can be done by the variational inequality concept. Here, the Laplace aided approach leads to a convolutional linear complementarity problem with a small number of unknowns. Finally, a numerical example verifying the applicability of the approach is presented.

JTAM, Sofia, vol. 22 Issue 1 pp. 047-052 (1991), [Full Article]

Some Remarks on the Fokker-Planck Equation in Velocity and Phase Space

M. Nichelatti
University of Bologna, Bologna, Italy

The possibility to find the distribution func¬tion by a reduction to the solution of a Fokker-Planck equation was pointed out in the mathematical procedure in a particular and in a more general case.

JTAM, Sofia, vol. 22 Issue 1 pp. 053-057 (1991), [Full Article]

On the Inverse Problems in Dynamics of Layered Systems

G. Karagiozova, L. Hadjikov, E. Manoach, V. Karagiozov
Inst. Mech. Biomech., Buig. Acad. Sci., Bl. 4

Some problems are considered in the paper to identify the material properties in layered system dynamics. A method is proposed to determine the unknown coefficients in the multilayered plate equations which depend on the material properties. This method is based on Fourier series expansions with spatial coordinates. A numerical example is presented too for a parametric determination of the visco-elastic covering of a three-layered plate under impulse loading and restricted suspending.

JTAM, Sofia, vol. 22 Issue 1 pp. 058-069 (1991), [Full Article]

Error Estimation of Direct Integration Process in Terms of Frequency Contents of Input Signal

Z. Petkov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 4

The error local discretization of an input with a continuous frequency spectrum is analysed in the paper. Convenient expressions are derived to examine forced oscillation accuracy in structural dynamics methods for direct integration. An error estimation is given by the proposed formulae when the Simeonov's method and the trapeze method are used.

JTAM, Sofia, vol. 22 Issue 1 pp. 070-075 (1991), [Full Article]

Identification of the Parameters of the Plated Element of the Netlike Medium

G. Wrobel

The paper shows the method and identifies plated element parameters of a netlike medium. Those elements along with the ones in papers [1, 2] constitute the basis of netlike model structure for stereomechanical analysis of elastic objects.

JTAM, Sofia, vol. 22 Issue 1 pp. 076-084 (1991), [Full Article]

A Personal Computer Program for the Elastoplastic Analysis of Frames

A. Avdelas
Aristotle University, Thessaloniki, Greece

The problem of the elasto-plastic analysis of plane frames can be expressed as a Linear Complementarity Problem. A direct quadratic programming algorithm is used in a computer program which finds the collapse load'load factor of framed structures taking account of unloading in the plastic range. The algorithm is characterized as a physical one in the sense that there is a direct relationship between the steps of the method and the successive equilibrium phases of the structure up to collapse. Furthermore, this paper should be considered as a contribution to the effort of providing the engineer with easy-to-use plastic analysis personal computer programs which are based on converging to the exact solution methods and easily cooperate with the existing elastic analysis programs.

JTAM, Sofia, vol. 22 Issue 1 pp. 085-099 (1991), [Full Article]

A Consistent Approach to the Nonlinear Analysis of Shells

G. Apostolidis, C. Karakostas, I. Sous, D. Talaslidis
Aristotle University, Thessaloniki, Greece

In this paper simple but effective formulations are presented which can be adapted to solve a broad class of nonlinear shell problems. To this aim modified versions of the Hu-Washizu principle serve as a basis for the discretization. Proper identification and decomposition of the deformational modes and the use of appropriate assumptions for the filed variables (displacements, strains and stresses) leads to consistent formulation of the corresponding energy terms. This approach is used to derive C0 and C1 quadrilateral and triangular elements and compatible beam elements which incorporate many attributes necessary to practical applications. Adaption to solve geometrically and materially nonlinear problems has been found to be straightforward. Concerning the geometrically nonlinear problem, the concept of small relative rotations is adopted. The elastoplastic analysis is based on von-Mises yield criterion and provides for hardening.

JTAM, Sofia, vol. 22 Issue 1 pp. 100-114 (1991), [Full Article]

Dynamic Fracture Toughness of Non-Alloyed Bainitic Ductile Irons

K. Mintchev1, K. Valkov2
1Inst. Met. Res. Techn., Bulg. Acad. Sci., BI. 1
2Inst. Met. Cast. Found. Equip.

The bainitic ductile iron behaviour under different exploitation conditions (loading velocity, temperature, etc.) is characterized by various mechanisms and parameters. While the static loading properties are comparatively well studied, the interest turns upon the behaviour under loading with raised velocities. The present paper examines the fracture toughness value changes under dynamic loading of bainitic ductile irons varying the parameters of the thermic treatment. Experimental data is presented which shows the L-ehaviour of ductile irons with silicium contents of 2.0% to 3.2%.

JTAM, Sofia, vol. 22 Issue 1 pp. 115-120 (1991), [Full Article]

Obituary: Professor M.S. Konstantinov

Editorial Board

JTAM, Sofia, vol. 22 Issue 1 pp. 121-122 (1991), [Full Article]