Issue 1
JTAM, Sofia, vol. 29 Issue 1 (1999)

Application of Condensation Techniques for Modelling of a Group of Mechanical Systems

K. Istev1, A. Ianakiev2, F. Filipov3
1Faculty of Automation, Technical University of Sofia, 8, St.Kl.Ohridski Str., 1000 Sofia, Bulgaria
2Faculty of Mechanical Engineering, Technical University of Sofia, 8, St.Kl.Ohridski Str., 1000 Sofia, Bulgaria
3Central Laboratory for Seismic Mechanics and Earthquake Engineering, Bulgarian Academy of Science, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgar


The current trend to analyze more and more complex finite element models of mechanical systems increases the size of the corresponding matrices, which impose obstacles for synthesis and simulation of control. The paper presents a possible approach to overcome the problem by employing models based on transfer functions between the Laplace operators of the signals at specified points and the inputs. Apart from being more compact the transfer functions in these models provide an easy approach for reduction of the models, keeping at the same time the necessary level of accuracy for the required frequency range. The introduction and eventually the correction of the damping is a simple task in the above models.

JTAM, Sofia, vol. 29 Issue 1 pp. 01 (1999)

Synthesis of Open Kinematics Chains for Robot Mechanisms by Using Relative Conditions for Position Input-Output Synchronization, Part 2 - Models Based on System of Vectorial-Matrix Equations

V. B. Galabov, I. I. Avramov
Technical University of Sofia, 8, St.Kl.Ohridski Str., 1000 Sofia, Bulgaria

The generalized mathematical model for dimensional synthesis of open kinematics chains for specialized robots in this part is built on the base of vectorial-matrix equations. The synthesis of such a chain is performed using the same relative conditions for synchronization of the finite linear and angular displacements of the output link with the finite relative rotations of its links, as shown in part one of the paper. A computer programme, incorporating the two types of generalized mathematical models discussed, is used for the design of the open kinematics chain of the GRIPMAT specialized robot. This robot is used for serving of horizontal presses for casting under pressure. The two types of generalized models are compared and analysed with respect to linearity and non-linearity.

JTAM, Sofia, vol. 29 Issue 1 pp. 02 (1999)
An Investigation of the Dynamic Loads in a Two-Stage Spur Gear Machine Aggregate - Part II

B. Belnikolovsky, Iv. Kralov
Technical University of Sofia, 8, St.Kl.Ohridski Str., 1000 Sofia, Bulgaria

A model of a two-stage spur gear machine aggregate with 12 degree of freedom is treated. The influence of the gear meshing parameters: the elasticity of the meshing, period of the meshing, gear modulus number of teeth, gear wheels width and the distribution of the gear ratio on the dynamic loads in shafts, bearings and meshings is investigated in a wide frequency area, as well as the impact forces in teeth at beginning of contact out of the theoretical meshing line.A model of a two-stage spur gear machine aggregate with 12 degree of freedom is treated in this paper. The model, the differential equations, parameters nomenclature and constant values of the parameters are the same as in part I. The aim is investigation of the following gear meshing parameters: the elasticity and period of meshing and the distribution of gear ratio upon dynamic loads in a two-stage spur gear machine aggregate.

JTAM, Sofia, vol. 29 Issue 1 pp. 03 (1999)
Particle Size Distribution Effect on a Solid Carryover of Particles in a Fluidized Bed

A. M'chirgui1, L. Tadrist1, St. Radev2
1Institut Universitaire des systemes Thermiques Industriels (IUSTI),CNRS - UMR 6595 Technopole de Chateau Gombert, 13453 Marseille Cedex 13 France
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

The effect of particle size distribution (PSD) on the carryover of solid phase from a gaz-solid fluidized bed has been investigated. Solid entrainment rate and carried solids size measurements have been performed. The variation laws of the solids entrainment rate and the mean diameter of the entrained solids with the gas velocity were found to depend strongly on the breadth of the PSD. The wider the PSD function of fluidized material, the more progressive the transition from weak to sharp removal of solids. An analytic approach based on the single particle model has been developed. This approach gives formula to predict the PSD of the entrained solids in a reasonable agreement with experiments.

JTAM, Sofia, vol. 29 Issue 1 pp. 04 (1999)
On the Numerical Modelling of the Venus Planetosphere/Mantle

V. Nikolova, M. Kartalev
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

A scheme for modelling the interaction of solar wind with nonmagnetic planet is proposed. The creation of the ionized gas, forming the planetosphere, is supposed to be only due to the ionization processes in the existing neutral exosphere of the planet. A self - consistent consideration of the planetosheath and the planetopause (planetosheth boundary) is performed in gasdynamic approach, supposing decoupling of the MHD system of equations. Mass- loading process in both regions is taken into account. The pressure balance is establishing the shape and position of the planetopause, determined in the solution. A grid characteristic numerical scheme is applied. The results are demonstrating quite satisfactory coincidence with some Pioneer Venus Orbiter measurements around Venus. Modelling of the solar wind interaction with nonmagnetic planets chronologically follows the ideas, arising in considering in the literature the analogical problem for the magnetic planets.

JTAM, Sofia, vol. 29 Issue 1 pp. 05 (1999)
Mechanical Behaviour of Amorphous Materials on the Basis of a Micro-Structural Mode

V. Iliev, M. Popova
Department of Applied Mechanics, University of Chemical Technology and Metallurgy 8, St.Kl. Ohridski Str., 1756 Sofia, Bulgaria

To model the transition micro-macro for the case of amorphous materials, the present article proposes a procedure for computer simulation of the mechanical material behaviour based on a simplified micro-structural model. The main idea of the model proposed is to substitute the discrete structural unit for a modelling homogeneous triangular finite element having equivalent mechanical behaviour. To further simplify the problem, we construct the model in a pseudo three-dimensional domain, based on the hypothesis that a qualitative insight of the stress-strain state of the representative bulk of material can be obtained by analyzing a finite number of plane sections. The simplified geometrical micro-structural model can be considered as composed of two types of finite elements: triangular, modelling the structural units; and triangular or quadrilateral, modelling the stiffness of the rings formed by bonding the structural units. The stiffness matrix of the elements is derived from a radial-symmetric potential of the central forces of the Lenard-Johnes type. The following summary of a stress distribution analysis for tension and shear within the micro-structure of the pilot material is to demonstrate how the procedure for computer simulation of the material mechanical behaviour at micro level works. The values obtained have been compared with those obtained by other methods.

JTAM, Sofia, vol. 29 Issue 1 pp. 06 (1999)
On the Application of a New Mixed Finite Element Model to In-Plane Problems

P. T. Kolev
University of Architecture, Civil Engineering and Geodesy, 1, Hr. Smirnenski Str., 1421 Sofia, Bulgaria

The present paper has a practical purpose and seeks to show some of possibilities of one new mixed model in the finite element method to in-plane problem in the theory of elasticity. Bilinear approximating functions for description of the fields of the stresses and displacements, spread over the whole area of the finite element, are proposed. The new model is applied for an in-plane problem (wall beam) with non-symmetrical holes. The results obtained are compared with those obtained by the program SAP'90 and a frame model representing the plane problem as a frame construction.

JTAM, Sofia, vol. 29 Issue 1 pp. 07 (1999)
Wave Mechanisms Using Biomechanical Principles of Locomotion of Some Terrestrial Animals

A. I. Dobrolyubov, A. A. Kolesnik, S. K. Shumak
Institute of Engineering Cybernetics of Academy of Sciences of Belarus 6, Surganov Str., Minsk, Belarus, 220012

Investigations of transport capability of travelling deformation waves on elongated deformable bodies have led to new explanations of some methods of locomotion of such a living creature as a caterpillar, an earthworm, a terrestrial snake. This enables to create new engineering mechanisms and instruments using these biomechanical wave methods of locomotion. The information about the new linear wave mechanisms and transport devices without driving wheels is given. The kinematic analysis of the travelling deformation waves running along an elongate deformable body (a flexible filament) is also given.

JTAM, Sofia, vol. 29 Issue 1 pp. 08 (1999)