JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 30 Number 1  2000
                                                                    CONTENTS
 

T. Tanev

Central Laboratory of Mechatronics and Instrumentation,
Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria,
e-mail: tanio@bgcict.acad.bg

Rate Kinematics of a Hybrid Type Manipulation System

Abstract. The paper presents an approach to solving the inverse velocity problem for a hybrid manipulation system. The
proposed approach offers an efficient alternative to using the inverse Jacobian. The considered manipulation system consists of
two variable-geometry modules, which are serially connected. An numerical example and a simulation of the kinematic solutions
derived in this paper have been performed.

Key words: hybrid manupulation system, kinematics.



P. Raikov, N. Valchkova, D. Denev.

Central Laboratory of Mechatronics and Instrumentation,
Bulgarian Academy of Sciences,
Acad.G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria,
e-mail: raykov@bgcict.acad.bg

An Investigation of the Robot Service Coefficient During the Manipulation System Calibration

Abstract. An approach for calibration of the joint-axes orientation of the robots by calculating of the service coefficient is
proposed. The computational scheme uses a ``grid-based'' numerical method for estimation of the working area of multilink
mechanisms.

The proposed approach is applied using the geometrical parameters of two commercially available in Bulgaria robots and the
results of these computations are presented.

Key words: robot, manipulator, optimisation, service coefficient.


V. Abadjiev, E. Abadjieva

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: abadjiev@imbm.imech.bas.bg

Sliding Velocity Vectors Field in Case of Spatial Rack Mechanisms

Abstract. This work studies spatial rack mechanisms transforming rotation into translation. The transformation is realized by the
theoretically conjugate surfaces. The created mathematical model describes the sliding velocity vectors field and the axoids of
the rack sets. The defined kinematic characteristics have a direct application to the synthesis of these mechanisms.

Key words: spatial rack mechanism, mathematical model, vector field, sliding velocity.



Vl. Roussinov, S. Stefanov, V. Yanitskii.

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G.Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: stefanov@imbm.bas.bg
V. Yanitskii
Computer Center,  Russian Academy of Sciences,
40, Vavilova Str., 117967 Moscow, Russia,
e-mail: yanit@ccas.ru
 

Chaotic Spatio-Temporal Structures in the Rayleigh-Benard Flow of a Rarefied Gas

Abstract. A permanent non-stationary and nonperiodical finite difference solution (known as ''strange attractor'') of the  Rayleigh-Bénard problem of a rarefied gas has been found out for Knudsen number Kn = 0.001, Froude number Fr = 1.0  and temperature ratio Tc/Th = 0.1. The continuum model is based on the full Navier-Stokes equations for compressible viscous gas with viscosity and heat-transfer coefficients obtained from the first order Chapmen-Enskog approximation of the Boltzmann kinetic equation for low Knudsen number.

Key words: rayleigh-Bénard problem, rarefied gas, compressible viscous gas, finite difference method.



 Il. Roussev, P. Koulev, Evt. Toshev, P. Bojanova, T. Partalin.

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad.G.Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: ilia@imbm.bas.bg
T. Partalin
Faculty of Mathematics and Informatics, Sofia University ``St. Kl. Ochridski'',
5, J. Bourchier Str., 1164 Sofia, Bulgaria

Velocimetry and Displacements Measurement by One-Beam Digital Speckle Interferometry

Abstract. The hardware and the software parts of a method for One-Beam Digital Speckle-Interferometry have been
developed. The possibilities of the technique are experimentally confirmed in the cases of: digital translation of synthesised
speckle pattern, real rigid body translation and rotation, rubber-plate deformation and two-dimensional sedimentation in
Hele-Show cell of marble-sendand quartz-send particles suspension in mineral oil

Key words: Fast Fourier Transformation (FFT) based algotithm, Digital Speckle Photography, sedimentation.



D. Stefanov.

Central Laboratory for Seismic Mechanics and Earthquake
Engineering,
Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl.\ 3, 1113 Sofia, Bulgaria,
e-mail: seismech@geophys.bas.bg
 

Nonlinear Behaviour of Reinforced Concrete Shear Wall Under Seismic Excitation
 

Abstract. The reinforced concrete shear walls are the primary bearing elements in building structures in nuclear power plants.
This paper investigates the nonlinear behaviour of a shear wall, experimentally tested on shaking table. The applied loading
permits to comprehend the response at levels ranging from the elastic state to the elasto-plastic ultimate state. A finite element
model is used, taking into account the nonlinear behaviour of the materials - concrete and steel. Comparisons between
analytical and experimental results are made.

Key words: reinforced concrete shear wall, nonlinear behaviour of a shear wall.



 N. L. Piperov.

Institute of Metal Science, Bulgarian Academy of Sciences,
67, Shipchenski Prohod Str., 1574 Sofia, Bulgaria,
e-mail: s.popov@ims.bas.bg

Examination of the Structure and Mechanical Behaviour of Constructional Foamed and Recycled Thermoplastic Composites (CFRTC)

Abstract. Some structural and constructional-technological peculiarities of the recycling and the re-use of composite foamed
thermoplastic products are studied in this paper. The experimental and theoretical analysis carried out of structure forming
under the conditions of the method of gas counter-pressure injection moulding, of the zones with plastic leaking at the
boundaries of dispersed particles and gas bubbles, of the formation and accumulation of defects in the interphase marginal
zones of CFRTC enables the search for correlation with the technological and constructional parameters of the system
``thermoplastic matrix-dispersed filler-gas phase'' by predicting its functional fitness and possibilities over a wide
composite-technological and operating range.

Key words: constructional foamed recycled thermoplastics, moulding under gas counter pressure, structure-forming, structural
model, products.



T. Troufkin, V. Evlogieva.

Institute of Metal Science, Bulgarian Academy of Sciences,
67, Shipchenski prohod Str., 1574 Sofia, Bulgaria
e-mail: dors@bgcict.acad.bg

Modelling the Temperature Condition in the Ends of Long Cylindrical Forgings during Hot Plastic Deformation in a Radial Forging Machine

Abstract. Well-known analytical formulae of relative dimensionless temperatures in infinite cylinder and infinite plate the
intersection of which forms a cylinder of finite dimensions are used. In the computer calculation the method of consecutive
intervals is applied and it is operated with weighted average values for the radii, the thickness of the two half plates and the
coefficients of thermal conductivity and heat transfer of the hot metal. A calculation experiment is carried out by means of the
computer model developed. The difference in the cooling of the ends in comparison with the central part of the forging is
quantitatively determined.

Key words: temperature field, hot plastic deformation, radial forging machine, modelling and simulation.



S. I. Petkov.

Technical University of Gabrovo,
e-mail: symo@tugab.bg

Investigation of the Mechanical and Nuclear Magnetic Resonance Properties of Human Vascular Walls in Vitro

Abstract. The purpose of the present study is to find a correlation between the visco-elastic and proton nuclear magnetic
resonance (H1 NMR) properties aiming to characterise the stress state of the vascular wall by non-invasive method. In order to
obtain quantitative relationships between mechanical characteristics of large human vascular walls of different anatomic
localisation both static and dynamic methods were applied. The results obtained were compared with data from H1 NMR
measurements at 4 MHz and 60 MHz. Typical changes of line-shape have been observed by hystologicaly controlled selective
lysis for identification of collagen protons: the fast component of the signal disappears after collagen extract. On limited number
of samples from normal and aneurysmal aorta the technique was applied and significant correlation between the line-shape
second moment and mechanical characteristics was obtained.

Key words:arteries, vascular wall, mechanical properties, nuclear magnetic resonance, correlation.


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