Issue 1-2
JTAM, Sofia, vol. 25 Issue 1-2 (1995)

Equation of Motion of a Gig with Hydraulic Operating

L. Kandov, N.Yoncheva
University of Mining and Geology, Sofia


In the ascending motion of a lifting machine with a hydraulic system, when the efficiency of the oil pumps is constant and the oil fosses are a constant function of time, the motion itself can be described without the need of solving differential equations. On the contrary when the jib is lowered (descending motion) the velocity depends on a number of regulable elements of the system and on the hydraulic resistance in the liquid consumption. In this connection the motion law of the system can be determined only as a result of the integration of essential non-linear differential equations. The paper indicates the way for solving a general system driven by hydraulic cylinders. Enclosed is the example of a hydraulic jack the motion of which is controlled by a simple four-link mechanism. The example shows that the method for working out and integrating the motion equations can be applied to mechanisms of a general type, such as multi- cylinder excavators and support systems for longwall coal mining.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 017-021 (1994)

Equation of Motion of a Gig with Hydraulic Operating

L. Kandov, N.Yoncheva
University of Mining and Geology, Sofia

In the ascending motion of a lifting machine with a hydraulic system, when the efficiency of the oil pumps is constant and the oil fosses are a constant function of time, the motion itself can be described without the need of solving differential equations. On the contrary when the jib is lowered (descending motion) the velocity depends on a number of regulable elements of the system and on the hydraulic resistance in the liquid consumption. In this connection the motion law of the system can be determined only as a result of the integration of essential non-linear differential equations. The paper indicates the way for solving a general system driven by hydraulic cylinders. Enclosed is the example of a hydraulic jack the motion of which is controlled by a simple four-link mechanism. The example shows that the method for working out and integrating the motion equations can be applied to mechanisms of a general type, such as multi- cylinder excavators and support systems for longwall coal mining.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 017-021 (1995), [Full Article]

Variants of Structure of Double-Stage One-Row Planetary Gears

J. SÅ­pak, M. Grois
Technical University, Brno

The paper presents variants of structure of double-stage one-row planetary gears. Some of the variants have not been realized yet. Thus, the paper completes the theory of planetary gears only partially.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 022-026 (1994)
Variants of Structure of Double-Stage One-Row Planetary Gears

J. SÅ­pak, M. Grois
Technical University, Brno

The paper presents variants of structure of double-stage one-row planetary gears. Some of the variants have not been realized yet. Thus, the paper completes the theory of planetary gears only partially.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 022-026 (1995), [Full Article]

Vibrations of Circular Plates on Elastic Foundation with In-Plane Loading

R. Kurktchiev, I. Vaisilov
Higher Institute of Architecture and Civil Engineering, Sofia

The paper considers the free linear transversal vibrations of circular plate resting on Winkler elastic foundation. The plate is acted upon with constant radial loading distributed along the end. The natural frequencies of the plate as a function of the load parameter and the Winkler constant are obtained solving numerically the characteristic equation. The existence of a new additional frequency which depends only on the Winkler constant is determined.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 027-033 (1995), [Full Article]

A Theoretical Study on Vertical Vibrations of an Internal Combustion Engine

St. Bachvarov, St. Poulev, L. Kunchev
Technical University, Sofia

In this work the vertical vibrations of one cylinder four-stroke internal combustion engine are investigated. It is assumed that the vertical vibrations are small, the body elements of engine are not elastic and the support elasticity and damping characteristics of foundation are linear. For the mechanical model with two degrees of freedom is obtained the non-linear system of differential equations of motion. The solution of motion equations is found with asymptotical methods. The same equations are also numerically solved for concrete mechanical system.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 034-039 (1995), [Full Article]

Free Three-Dimensional Vibrations Carriage Waggon. Natural Frequencies

I. Angelov1, An. Ivanov2
1Technical University, Sofia
2High Military Transport School, Sofia

In this paper are studied the free three-dimensional vibrations of a high-speed and light carriage waggon in conjunction with the useful load - passengers and luggage. The authors take into account concretely existing connection for transferring of energy from ones generalized coordinates to others as well as asymmetrical mass, inertia and geometrical properties of the waggon with the intent - dynamic synthesis of the high-speed and light railway vehicles with a view to minimum vibrations. The presented theory and methods give us possibility to formulate the differential equations of the free three dimensional vibrations of an high-speed and light carriage waggon in conjunction with arbitrary placed on the vehicle useful load - passengers and luggage. The dimensions of the elastic elements are taken into account. The mass and elastic matrix of the vehicle, the natural frequencies, the modal vectors and modal matrix are determined.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 040-052 (1995), [Full Article]

Mechatronic Approach to Analysis and Synthesis of Gear-Linkages Mechanisms for Automation and Robotics

I. Avramov1, V. Galabov1, V. Michajlov2
1Technical University, Sofia
2Institute of Mechanics, Bulg. Acad. Sci., Sofia

This paper specifies essential stages from the realization of the mechatronic approach to the tasks of structural and metrical analysis and synthesis to a new class hybrid (gear-linkage) mechanisms. Gear-linkage mechanisms are considered in this paper as planar mechanisms with one or two kinematic degrees of freedom. The results shown the paper illustrate the structural and metrical synthesis of mechanisms with possible output long stay and constant input.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 053-058 (1995), [Full Article]

Stationary Motion Dynamics of an Open Periodical Structure Transport System

P. Kolev
High Military Transport School, Sofia

The Mechanical and mathematical modelling of a typical railway transport mechanical system has been made in the research work "Mathematical modelling of a system with consistent open dynamic structure driven on both ends", which was reported at the National seminar on mechanical systern dynamics Varna'92. The system is modelled as a plain periodical structure. One of the coordinates describes the global movement of the system, and the other ones describe the relative horizontal and absolute vertical and angular vibrations. The natural frequencies and forms of the system are determined in the present work. A single frequency asymptotical solution of the disturbed system according to Bogoljubov-Mitropolski's method has been constructed. An analysis of the interaction between macro- and micromotions has been carried out.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 059-064 (1995), [Full Article]

Planning of Smooth Collision-Free Paths for Manipulation Robots

V. Balavessov
Institute of Mechanics, Bulg. Acad. Sci., Sofia

The problem of generating smooth collision-free paths arises as an intermediate problem between shortest path planning and path finding, on the one hand, and time optimal trajectory planning, on the other hand. The objective of the report is an optimization approach to obstacle-free path planning that provides smooth paths at low computational costs through the choice of an appropriate criterion. It is based on a method for optimum path finding, that ensures obtaining of a local minimum. Planning is performed in the configuration space, although a task space formulation is also possible.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 065-074 (1995), [Full Article]

Six-Component Force-Torque Sensor

T. Tonchev, V. Michajlov
Institute of Mechanics, Bulg. Acad. Sci., Sofia

The six-component force-torque sensor is destined for the ARO robot. This type of sensor allows for fulfillment of precise assembly operations with control of the contact forces. Similar sensors are used for force control in world coordinates. An user friendly interface program is realized in MS Windows. The sensor is to be mounted at the robot wrist. The robot is designed at the Department of Robotics and Mechatronics, Institute of Mechanics, Bulgarian Academy of Sciences.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 075-081 (1995), [Full Article]

Dynamic Modelling and Design of Adaptive Effectors for Manipulation Robots

Kr. Georgiev
Institute of Mechanics, Bulg. Acad. Sci., Sofia

This paper is concerned with the dynamic modelling and design of adaptive effectors for manipulation robots. Dynamic models of the action are derived and analytical solutions obtained. Based on the dynamic investigation a methodology and interactive procedure for design of such moduls are developed. The main results obtained in graphical form are shown and discussed.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 082-089 (1995), [Full Article]

Hydrodynamic Flow in Thin Liquid Films of Surfactant Solutions Containing Polydisperse Micelles

C. Dushkin, I. Ivanov
Faculty of Chemistry, University of Sofia

A theory for the thinning of liquid films containing surfactant monomers and aggregates (micelles) is proposed. Based on the Raynolds approximation asymptotic equations for the bulk concentration, the surface velocity and the velocity of film thinning are derived. The micelles are assumed of polydisperse Gaussian size distribution. Due to the concentration gradients the micelles are stressed to diffuse and release monomers in order to restore the equilibrium with the free monomers. Hence, the micelles play a role of additional carriers and sources of material facilitating the supply of the adsorption layer with monomers. As a result the tangential mobility of the film surfaces increases which can increase in turn the velocity of film thinning.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 090-095 (1995), [Full Article]

Analysis of Consentration Distribution Characteristics in Dispersed Liquid Jet

M. Angelov, I. Antonov, L. Elenkov
Technical University, Sofia

This study makes an analysis of concentration distribution characteristics (intensity and sprinkling) in the field of dispersed flat jet. The stream is created in a space interaction of two or three cylinder liquid jets flowing out at an angle one against the other in one plain. Depending on the angle of jet's arrangement, a dispersed jet can be realized, having an alternating configuration with a vertical section looking like an elongated ellipsis. The angle increase between the jets leads to plain widening increase, that is perpendicular to that of the flowing out. The flat jet character of the stream can be proved by means of photo visual observations and by means of a constant intensity of sprinkling, as well.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 096-101 (1995), [Full Article]

Filtration in Channel with Elliptic Cross-Section

C. Vassilieff
Faculty of Chemistry, University of Sofia

An analytical equation is derived describing the filtration of pure solvent in a channel with elliptic cross-section. It generalizes existing results for simpler channel geometries. Such analytical formulae for cross-flow filtration of one-component liquids describe the case of very low concentration of a second component, which is rejected by the filter. They represent limiting cases of more general self-consistent theoretical models, which require the application of computational methods.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 102-109 (1995), [Full Article]

Vortical Interaction of a Jet in a Crossflow

Y. Dinkov
Technical University, Sofia

This paper makes another attempt to analyze the jet-crossflow interaction in terms of the already published experimental data, the Reynolds-averaged Navier-Stokes equations, and calculations by the K – ε turbulence model. A discussion is given concerning the arguments supporting the existence of a multiple vortex system which determines the flow behaviour. Mechanisms are mentioned, which ensure the required conditions for occurrence and development of the multiple vortex system.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 110-126 (1995), [Full Article]

Numerical Method for Identification of the Parameters in System of Nonlinear Ordinary Differential Equations

G. Georgiev
Institute of Metal Science, Bulg. Acad. Sci., Sofia

It is proposed an universal method for numerical treating of the problem for identification parameters in system of nonlinear ordinary differential equations, supposing the existence of effective algorithm for solving the treated system of equations and combined with a variant of the methods of local minimization of many dimensional functions and functionals, known as methods with variable metric. The possibilities of the method are illustrated by means of the concrete model treating the thermodynamically processes in "Quick-cup" sensors (used in express melt's analysis).

JTAM, Sofia, vol. 25 Issue 1-2 pp. 127-134 (1995), [Full Article]

On Determination of Dynamic Bending Moment in a Ship Due to

V. Apostolov1, M. Todorov2
1Shipbuilding Institute, Varna
2Technical University, Rousse

A place is destined for this problem also in a literary source quoted in the present work, in which the author obtains the dynamic bending moment in a ship in the form of an infinit divergent series and in this connection he draws the pessimistic conclusion "Very often it is indispensable to encounter divergence or very bad convergence of series at transient loads and until now there is no an effective method for solving of similar problems". An approach is grounded in the paper, which, in the case considered, leads to an effective, practically suitable solution.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 135-147 (1995), [Full Article]

Blood Viscosity Measurements in the Detection of Early Cerebrovascular Disease

R. Whittington1, N. Antonova2
1King's College Hospital, London
2Institute of Mechanics, Bulg. Acad. Sci., Sofia

A group of patients with cerebrovascular disease of ischemic origin was investigated. The group included the patients with latent, transient and chronic disturbances of the cerebral circulation. The apparent viscosity of whole blood (determined by means of a rotational viscometer Couette LS 30 Contraves at a steady flow) were estimated in all patients and the results were compared to a control group of healthy persons. The present work studies use of the rigidity number "h", defined by the "Tokyo" expression of the R. Whittington et al, which itself incorporates both absolute and relative viscosities, as well as some examination of the plasma viscosity. The rigidity number "h" is defined as (Y-X), where Y and X are determined by the parameters of the expression. The results are presented in a domain of the parameters, suitable for indicating the difference between viscous and elastic forces which constitutes, we assume, the "effective rigidity". The larger number of patients, diagnosed as being positive for cerebrovascular disease were confirmed by a tentative criterion, including viscosity and rigidity number "h".

JTAM, Sofia, vol. 25 Issue 1-2 pp. 148-154 (1995), [Full Article]

Method of Analytical Prolongation in Certain Plane Problems from the Nonlinear Theory of Elasticity

L. Dobrodjginidze1, R. Raev2
1Technical University of Tbilisi, Georgia
2Technical University, Rousse

The present paper conserning certain plane problems from nonlinear theory of elasticity for materials of harmonic type. A modified method of analytical prolongation is used enabling to represent the field of elastic elements through one piece-wise analytical function of complex argument.

JTAM, Sofia, vol. 25 Issue 1-2 pp. 155-160 (1995), [Full Article]