JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 28 Number 4 1998
                                                                    CONTENTS
 
 
 
 

GENERAL

MECHANICS
 

V. Galabov

I. Avramov
 

Technical University of Sofia

Synthesis of Open Kinematics chains for Robot Mechanisms by Using Relative Conditions for Position Input-output Synchronization. Part 1 - Model Based on Vectorial-projection Equations

Generalized mathematical models are presented that facilitate the solution of problems for dimensional synthesis of conditionally or unconditionally open planar kinematics chains with R kinematics pairs. The synthesis is performed in accordance with previously defined relative conditions for synchronization of the finite linear and angular displacements of the end-effector link with the finite relative rotations of the links. The setting of mathematical models for structural- dimensional synthesis of robotics mechanisms is the basic stage in the design of specialized robots. A generalized mathematical model for dimensional synthesis of open kinematics chains, based on vectorial-projectional equations, is presented in part one of this work.



D. Chakarov
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Optimization Synthesis of Parallel Manipulators with Desired Stiffness

The paper presents an investigation of parallel manipulators with redundant actuation being able to specify a desired stiffness, needed for the successful performance of contact tasks which are linked with manipulation against kinematic and dynamic disturbances. A procedure for the synthesis of the stiffness is created in the paper. The stiffness in the driving joints and the basic geometric parameters are considered to be optimization parameters. This procedure enables one to solve problems both of manipulator design and manipulator control. Based on this procedure, computer experiments have been performed. The stiffness of manipulator with 14 driving joints is synthesized, and the results are presented graphically.



P. Georgieva

K. Ishtev
 

Institute of Control and System Research, Bulg. Ac. Sci., Sofia,
Technical University of Sofia

Robust Control Design of Aerial System

An approach to obtaining performance robustness in an H-inf sense for an aerial system is presented. The suitability of the robust optimizing feedback is demonstrated on a simplified MIMO aerial model in the frequency domain where robustness to several parameter variations is investigated.
The paper also discusses ongoing efforts to obtain the Linear Fractional Transformation (LFT) of the starting plant model, by which the parametric uncertainty is included in a non-conservative structured way.
The results show that this approach leads to controller that exhibits robust stability and performance.



CONTINUUM

MECHANICS

D. Kisliakov
 

University of Architecture, Civil Engineering and Geodesy, Sofia

Earthquake-Induced Motion of a High-Pressure Pipeline on Tall Frictional Supports

A multiple-supported high-pressure pipeline on tall support columns under seismic excitation is analysed. The frictional pipe support devices are located on the tops of the columns, allowing only axial displacement of the pipe. Transversal horizontal seismic excitation is considered which is represented by acceleration and displacement time histories. In a previous work by the author a method has been developed for the analysis of such pipeline supported on columns of equal height. In the present paper the more general case with support columns of different height is investigated. The method previously developed is used for the analysis of this case, but the influence of the adjacent pipeline spans on the one considered is also analysed. Numerical example with real data sets is solved.



FLUID

MECHANICS

M. Kartalev
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Diffusion of the Interplanetary Magnetic Field into the Planetosphere of Venus

A new model approach is proposed for explaining the penetration of the interplanetary magnetic field inside the Venusian planetosphere. A new type of magnetic field diffusion is introduced in a single- fluid mass-loaded gasdynamic model describing the planetosphere of the nonmagnetic planet. The photoionization in the oxygen corona is supposed to be responsible for the creation of the ionized substance in the planetosphere. The finite time duration of the new ions assimilation is taken into account by introduction of additional currents and charges, caused by non - picked up new ions in the frame of small time and length scales. The magnetic field is not ``frozen in'' in this approach. There is a component of the magnetic field diffusion against the flow of the background neutral particles. This phenomenon can explain the penetration of he IMF through the planetopause.



P. Kalitzova-Kurteva

S. Slavtchev

I. Kurtev
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Technical University of Sofia

Marangoni Instability in a Liquid Layer with Deformable Free Surface at Temperature-Dependent Viscosity

The onset of Marangoni instability in a horizontal liquid layer induced by variations of the surface tension with temperature is studied. The layer is heated from below, and both conducting and insulating bottom walls are considered. The upper free surface of the layer is allowed to deform. The viscosity of the liquid is assumed to depend exponentially on temperature. The linear stability analysis is applied and the solution of the eigenvalue problem is obtained in analitical form. The influence of the variable viscosity and the deformability of the free surface on the onset of stationary and oscillatory convections is analised.



SOLID

MECHANICS

St. Grigorov

D. Tzanev

N. Dicheva

St. Tasev

M. Mateev
 

Institute of Water Problems, Bulg. Ac. Sci., Sofia
University of Architecture, Civil Engineering and Geodesy

Thick Shell Analysis by Finite Elements with Combined Approximation of the Displacements 

Thick-shells with elastic theory equations as basic physics mathematical model are considered. The unique simple assumption is that a rectilinear shell element, which is normal to the middle surface, remains rectilinear after the deformation, but it is possible to be extensible and not normal.

The problem is solved by the finite element method using a rarely found in the practice isoparametric finite element with combined approximation of the displacements: linear to the thickness and quadratic - to the other two directions of the shell.

The results of the displacements, the stresses and the natural frequencies of a construction -an arch dam with combined sections, are represented graphically as an illustration of the suggested method.



Ch. Kouyumdjiev

Iv. Ivanov
 

``Angel Kanchev'' University of Rousse

Determination of the Average Residual Stress in Orthotropic Elastic Coating by the Bending Strip Method
The average residual stress in a cross section of the coating is the most frequently determined by using the bending strip method. The existing relationship for its calculation for isotropic coating is generalized in the present paper for the case of orthotropic coating. The influence of the anisotropy on stress values is investigated.



Al. Ishtev
 

Technical University - Sofia

An Aerial Control System Analysis

A system including a tower, an aerial support, and an aerial control system is analyzed in this paper. Block diagrams are derived from the initial finite element models of the tower and aerial support. They are transformed then to transfer functions and frequency response functions. On the base of them the control system parameters are determined. Computer simulation (using MATLAB/SIMULINK) have been carried out for the whole system.



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