**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.

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.

**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.

**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.

**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.

**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.

**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.

**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.

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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