Issue 1

JTAM, Sofia, vol. 15 Issue 1 (1984)

Synthesis of Time-Optimal Control for Manipulator Dynamics

P.A. Marinov, P.K. Kiriazov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Geo Milev, Sofia

In the paper a general method for synthesis of time-optimal control for manipulator dynamics in handling operations is developed. Sequential starting of joint motions is supposed. The joint constraints on the general coordinates are satisfied and the signs of the general velocities do not change during the time of the manipulator motion. Numerical verification of the method is performed on a model of VERSATRAN type manipulator.

JTAM, Sofia, vol. 15 Issue 1 pp. 013-019 (1984), [Full Article]

On the Stabilization of Linear Systems Defined Over a Ring of Entire Functions

A. Tcheremenskii
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Geo Milev, Sofia

Basing on the concept of the configuration space the general linear model of the problem of optimal synthesis of systems stabilization is investigated when stochastic perturbations are presented. Matrix equations are considered with coefficients which are entire functions of the Laplace transformation variable. A concrete definition of the duality principle is presented and thus the properties of the system are cleared out in connection with the time inversion. The relation is shown to the problem of modal control and observation. The necessary and sufficient conditions for modal control and observation are given.

JTAM, Sofia, vol. 15 Issue 1 pp. 020-029 (1984)

Optimal Control of Motion of Machine Aggregates

M. Kolovskii

The paper has been presented at the Fourth National Congress of Theoretical and Applied Mechanics, Varna, September 1981.

JTAM, Sofia, vol. 15 Issue 1 pp. 030-034 (1984)

Hypersingularities and Cracks in Plane and Three-Dimensional Elasticity

N.I. Ioakimidis
Greece, Patras, P. O. Box 120

Crack problems in plane elasticity are often interpreted as edge dislocation arrays. Singular stress fields, like those due to concentrated forces, dislocations and centres of rotation and dilation prove often useful in the interpretation and/or solution of elasticity problems. Here a new kind of singular stress fields, called hypersingularities (since they are straightforwardly related to hyperintegrals in mathematics), is introduced. The stress components of hypersingularities are seen to tend to infinity more rapidly than in other singular stress fields. The hypersingul ari ties considered here are related to simple crack problems in plane and three-dimensional elasticity. Generalizations and further applications of the present results are quite possible.

JTAM, Sofia, vol. 15 Issue 1 pp. 035-040 (1984), [Full Article]

An Application of Volterra-Wiener Series in Mechanics of Composite Materials

K. Markov
Sofia University, Dept. Math. Mechanics, A. Ivanov 6, 1126 Sofia

It is suggested in the paper the Volterra-Wiener series to be employed when predicting the effective properties for composite materials. As an illustration of the proposed method the problem of calculating the effective thermal conductivity for a two-phase material is detailed. For dilute concentration, an integrodifferential equation for the kernel of the first-order Volterra-Wiener operator is derived, making use of which the influence of inclusion clustering upon effective conductivity is investigated.

JTAM, Sofia, vol. 15 Issue 1 pp. 041-050 (1984), [Full Article]

Investigation of the Influence of the Bending and Shear Deformations on the Dynamic Parameters of a Console Beam

T. Karamansky, M. Zefirov
Inst. Civil Engn., Chr. Smirnensky 1, Sofia

A given problem of the structure dynamics is investigated in the paper. The aim of the analysis is to define, basing on the model adopted, the changes in the first eigen frequency and the first eigen form caused by different deformabilities due to bending and shear. The numerical computations show that for a given deformability ratio both the first eigen frequency and the first eigen form are easy to be obtained with a sufficient accuracy provided these same quantities are known for the two limit cases of deformability due to bending and shear only. The results of the analysis imply possibilities for a more effective design with an account for the specific deformability of the structure in pure bending and shear conditions.

JTAM, Sofia, vol. 15 Issue 1 pp. 051-057 (1984)

On the Solution of the Direct and the Inverse Problem of the Engineering Seismology with Account for the Attenuation Within the Earth

K. Ishtchev, F. Filipov, P. Dineva, L. Hadjikov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Geo Milev, Sofia

A method is proposed in the paper for the solution of the direct and the inverse problem of the engineering seismology which accounts for the two basic types of attenuation within the earth. These are the geometrical attenuation and the attenuation due to the energy dissipation within the earth layers. A combined model is constructed for the description of the dynamical behaviour of the earth basis. For this purpose the structural approach of the systems theory is applied. The model is based on the known models of Gurvitch and Napetvaridze. The ranges of applicability of the two latter models are estimated. Certain specificities and advantages of the model proposed are considered.

JTAM, Sofia, vol. 15 Issue 1 pp. 058-064 (1984)

Effect of Rotation on Rayleigh-Taylor Instability in the Presence of a General Oblique Magnetic Field

B. Sharma
College of Agriculture, 303 329 Jobner, India

The investigation of the hydromagnetic effects of the dispersion relations is of a great importance for the development of the instabilities in the sense of Rayleigh-Taylor. The equilibrium state of a nonviscous incompressible fluid of variating density was first considered by Rayleigh. The combined effect of a horizontal and a vertical magnetic field over the Rayleigh-Taylor instability was first studied by Ariel. The present work concerns the effect of the rotation, including the effect of a general oblique magnetic field, on the development of the Rayleigh-Taylor instability.

JTAM, Sofia, vol. 15 Issue 1 pp. 065-068 (1984), [Full Article]

Global Stability of Cylindrical Ortho tropic Shells with Linear Memory under Pressure

I. Ivanova
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Geo Milev, Sofia

Basing on the generalized variational principle A the postcritical deformations are studied for the class of the shells considered. The viscous properties of the material are of the type of an exponential kernel with attenuating memory. The form of the shell edges is obtained in the vicinity of the low critical load. The latter is determined as well for a large variety of elastic and viscous parameters. The numerical results obtained are presented graphically.

JTAM, Sofia, vol. 15 Issue 1 pp. 069-076 (1984)

Global Stability of Cylindrical Ortho tropic Shells with Linear Memory under Pressure

I. Ivanova

JTAM, Sofia, vol. 15 Issue 1 pp. 069-076 (1984)

Determination of the Temperature Depending Dynamic Fracture Resistance

K. Mintchev, St. Vodenitcharov
Inst. of Met. Techn., Tchapaev 53, Sofia

The essential sensibility of the mechanical properties of the low-carbon and low-alloy materials to the loading velocity and the operating temperature define the ranges of their applicability. With the aid of the linear and the linear-plastic mechanics one may enlarge the limits of determination of the dynamic fracture resistance, i.e. the dynamic fracture toughness Kld. In the paper different cases of determination of Kld over different ranges within the interval tGY < t < tDY are considered. Experimental results are shown which are obtained by means of an impact device furnished with force-time and force-deflection recorders.

JTAM, Sofia, vol. 15 Issue 1 pp. 077-082 (1984)

Dynamic Investigation of the Stress State of a Plane Structure by Means of the Enlarged Fragments Method

Chr. Ganev, K. Georgiev, T. Dimitrov
Inst. Water Problems, Bulg. Acad. Sci., Bl. 4, Sofia

The stress and strain state of plane, plane stressed structures of complicated configurations and variable thicknesses under dynamic loading is investigated. The problem is stated in a variational sense. The Lagrange's principle of virtual displacements is applied which serves as a basis for the mathematical model of the method of the enlarged fragments. Numerical results are obtained for the eigen values and the eigen functions of a section of a massive-gravitational wall. The results are compared with those obtained by means of the finite elements method. This comparison proves the high efficiency and accuracy of the method considered.

JTAM, Sofia, vol. 15 Issue 1 pp. 083-089 (1984)

On the Determination of the Critical Loads for Hinged at Both Ends Beams of Variable Cross-Section

G. Manditchev
High. Inst. Mech. Electr. Engn., Darvenitza, Sofia

A hinged at both its ends beam is considered in the paper. The inertial moment of the beam in the plane of stability loss changes according to an arbitrary power law. A simple relation is obtained for the critical force.

JTAM, Sofia, vol. 15 Issue 1 pp. 090-094 (1984)