JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 30 Number 4 2000
                                                                    CONTENTS
 

M. D. Todorov, Z. T. Tcherneva.

Technical University of Sofia,
8, St. Kl. Ohridski Blvd., 1756 Sofia, Bulgaria,
e-mail: misho@aero.vmei.acad.bg

Investigation of the Vibration of a Counterbalanced Engine Driven Fork-Lift Truck with Half-Elastic Suspension of an Engine and Hydrodynamic Transmitter, Excited by the Engine

Abstract. In this paper a spatial model of a truck with a half-elastic suspension of an engine and hydrodynamic transmitter is presented. The vibrations are excited by the unbalanced inertia and gas forces and moments. The results for the truck with hoisting capacity 1600 kg are given.

Key words: mechanics, dynamics, vibrations. 



 G. Y. Vukov.

University of Forestry Engineering,
10, St. Kl. Ohridski Blvd., 1756 Sofia, Bulgaria,
e-mail: givukov@ltu.acad.bg

Effect of the Dynamic Unbalance of the Countershaft on the Loading of the Universal Joint

Abstract. The unbalance is one of the main sources of vibration, sound and dynamical loads in the rotating machinery. The machinery containing universal joint (Cardan joint) with countershaft unbalance are object of this study. The countershaft rotates unevenly even when the driving shaft rotates with constant angular velocity. As a result of this the dynamical loads are amplified.

Key words: dynamic unbalance, sources of vibration. 



P. Kalitzova-Kurteva, S. Slavtchev, I. Kurtev.
 

P. Kalitzova-Kurteva, S. Slavtchev
Institute of Mechanics, Bulgarian Academy of Sciences
Acad.G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: penka@imbm.bas.bg
I. Kurtev
Technical University of Sofia,
8, St. Kl. Ohridski Blvd., 1756 Sofia

Linear Instability in Liquid Layers on an Inclined, Non-Uniformly Heated Wall

Abstract. Linear stability analysis is performed to study the long-wave instability in a thin liquid layer flowing down an inclined, non-uniformly heated wall. Constant (positive or negative) temperature gradient is imposed along the wall surface. Due to non-uniform distribution of the free surface temperature, a surface tension gradient appears and induces a thermocapillary force acting along the interface. That force influences the surface wave instability induced by gravity. The solution of the stability problem is seeked in series in a small wavenumber. The first three approximations of the solution are found in analytical form and the neutral stability curves are calculated. It is shown that the critical values of the Reynolds number depend on the ratio of the Marangoni number to the Prandtl one.

Key words: falling liquid layer, non-uniformly heated wall, linear instability. 



S. D. Iliev.

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: stani@bgcict.acad.bg

Stick-Slip Behaviour of the Liquid Drops on an Inclined Plane: a Numerical Example

Abstract. A numerical modelling of the stick-slip effect of the contact line of a liquid droplet, located on a sloping plane is proposed. Our study is based on a continuum model of the contact angle hysteresis [6]. We assume the system to approach an equilibrium state following a specific path. A jerky change of the contact line is obtained in two cases: when the drop volume is increased and when the inclination of a sloping plane is changed.

Key words: stick-slip behaviour, liquid drops, contact line. 



N. D. Nikolov,  J. D. Nikolova.

University ``Prof. Dr. Assen Zlatarov'', Bourgas,
Kl. Ochridsky Str. 8, 1756 Sofia, Bulgaria
e-mail: n_n1001@hotmail.com

Pulse Backwashing in Ultrafiltration

Abstract. Ultrafiltration of model solution of dextran (molecular weight 40000 Da) was studied by using tubular cellulose membranes. Periodical pulsation backwashing was employed and membrane productivity was found to increase.

Key words: ultrafiltration, dextran, backwashing, pulsation.



S. Panev, Gerard Siarras, D. Kisselkov.

S. Panev
University of Chemical Technology and Metallurgy of Sofia,
6, St. Kl. Ohridski Blvd., 1756 Sofia, Bulgaria,
e-mail: pan@uctm.edu
Gerard Siarras
L'institut Nationalle des Sciences Appliqu'ees - Lion,
20, Albert Einstein Str., 69621 Villeurbanne Cedex,
e-mail: MGSiaras@insa-lion.fr
D.Kisselkov
Institute of Metal Science, Bulgarian Academy of Sciences,
67, Shipchenski prohod Str., 1574 Sofia, Bulgaria,
e-mail: dkisselkov@ims.acad.bg
 

About One Problem of Stability

Abstract. A monorail used in the mines is considered. Investigation of the stability problem of the wagon maintained by gyroscope and its control is proposed.The system consists of three solids: a wagon, a crankcase and gyroscope. An electric drive is mounted between the wagon and crankcase in such manner that the stator is coupled with the wagon and the rotor with the crankcase. The stator exercises the couple M12(t) on the rotor.The control law of M12(t) that permits Y (the angle between the frame fixed to the wagon and the frame absolute) to pass from value Y1 to the value Y2 = 0, for the time minimum, such that |M12(t)|£ \gb, must be determined. The convenient couple is a constant.

Key words: stabilization, control law, gyroscope, monorail.



A. Nedev, N. Nikolov.

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

A Numerical Simulation of Deep Drawing Process of Axisymmetrical Blanks

Abstract. An Approximate Discrete Method (ADM) of numerical simulating of deep drawing process is represented in work [1]. A theoretical basis for ADM enlargement with the possibility to take into account the strain rate and stress-state sensitivity is given in paper [2]. The reliability of the numerical results obtained by the ADM, before to be enlarged by above possibility, is determined in analysis based on them. In present paper in order to improve the reliability of the results obtained by ADM, comparison with the same ones obtained by Finite Element Method (FEM) is made. In two different cases, the results obtained for equivalent stresses and strains for ``draw force-punch displacement'' profiles are compared and some comments are given.

Key words: deep drawing process, elasto-plastic model, finite element method.



V. Apostolov, M. Djulgerova.

High Naval School ``N. J. Vaptsarov'', Varna, Bulgaria
Kl. Ochridsky Str. 8, 1756 Sofia, Bulgaria
e-mail: kish@vmei.acad.bg
M.Djulgerova
University `` Prof. As. Zlatarov'', Bourgas, Bulgaria,
e-mail: mag_djulgerova@hotmail.com

Coupled Effect of Two and More Random Processes upon Fatigue Safety Life of Structures

Abstract. A problem about destruction in cases of fatigue of structures when stresses are the sum total of several narrow-band spectrum processes is considered. The equations about the effective period of the summary process are obtained. The influence of the vibration stresses on safety life of ships is represent. The results obtained show that when two processes act simultaneously, besides the ratio of the amplitudes, the ratio of frequencies is also important.

Key words: random process, fatigue safety life, ship safety life.



V. Petrov, N. Valkov .

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad.G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: vgp@bgcict.acad.bg

Towards Constructing Kinetic Equation of Erythrocyte Aggregation

Abstract. The well-known S-shaped settling curve in the hematology is used as a basis to construct the kinetic equation of corresponding erythrocyte aggregation. For this purpose a main problem for reconstructing a second-order differential equation is formulated and solved by using an appropriate method of interpolation.

Key words: sedimentation process, aggregation kinetics.



N. Petrov.

Institute of Mechanics, Bulgarian Academy of Sciences,
G. Bonchev Str., Bl..4,  1113 Sofia, Bulgaria
e-mail: nikolapetrov@usa.net

Estimation of the Hydraulic Canalicular Radius in Cortical Bone

Abstract. The fact that osteocytes are not more than 0.1 to 0.2 mm from capillary strongly suggests for canalicular via by which osteocytes are nourished and rid themselves of waste products. As possible mechanisms appear to be diffusion and stress generated fluid flow. However it is not clear, what are the efficiency limits of these two ways to transport the species. Because of the presence of cell processes within the canaliculus, it is unknown, what part of the canalicular cross section is occupied and what is free for fluid flow or species diffusion. The objective of the present study is to answer the question: what is the order of the hydraulic canalicular radius? In the present study its value is estimated about 19 nm. In the present study for first time, in the literature, the hydraulic radius of the canaliculus is directly estimated by processing data of relaxation type experiments

Key words: bone, nikola petrov, biomechanics, stress, fluid, flow, streaming, potential, remodelling, osteon.



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