Issue 1

JTAM, Sofia, vol. 30 Issue 1 (2000)

Rate Kinematics of a Hybrid Type Manipulation System

T. Tanev
Central Laboratory of Mechatronics and Instrumentation, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 01 (2000)

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

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

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 02 (2000)

Sliding Velocity Vectors Field in Case of Spatial Rack Mechanisms

V. Abadjiev, E. Abadjieva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 03 (2000)

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

Vl. Roussinov1, S. Stefanov1, V. Yanitskii2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G.Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria
2Computer Center, Russian Academy of Sciences, 40, Vavilova Str., 117967 Moscow, Russia

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 04 (2000)

Velocimetry and Displacements Measurement by One-Beam Digital Speckle Interferometry

Il. Roussev1, P. Koulev1, Evt. Toshev1, P. Bojanova1, T. Partalin2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad.G.Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria
2Faculty of Mathematics and Informatics, Sofia University ``St. Kl. Ochridski'', 5, J. Bourchier Str., 1164 Sofia, Bulgaria

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

JTAM, Sofia, vol. 30 Issue 1 pp. 05 (2000)

Nonlinear Behaviour of Reinforced Concrete Shear Wall Under Seismic Excitation

D. Stefanov
Central Laboratory for Seismic Mechanics and Earthquake Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.\ 3, 1113 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 06 (2000)

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

N. L. Piperov
Institute of Metal Science, Bulgarian Academy of Sciences, 67, Shipchenski Prohod Str., 1574 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 07 (2000)

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

T. Troufkin, V. Evlogieva
Institute of Metal Science, Bulgarian Academy of Sciences, 67, Shipchenski prohod Str., 1574 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 08 (2000)

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

S. I. Petkov
Technical University of Gabrovo

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.

JTAM, Sofia, vol. 30 Issue 1 pp. 09 (2000)