Issue 3

JTAM, Sofia, vol. 25 Issue 3 (1995)

Computation of Pneumatic Type Tension Sensors for Magnetic Storage Devices

Iv. Sarafov
Institute of Mechatronics, Bulg. Acad. Sci. Sofia

Pneumatic sensors build in externally pressurized tape bearings are discussed in this article. Theoretical research, based on experimental data and dependences, is made. Basic parameters of the sensors by joint action with tape bearings are determined. An algorithm to computation the boundary gaps under the tape, corresponding to maximum and minimum of tension force is given. A choice of the pressure to voltage piezoresistive transducer used in 12.7 mm cartridge tape drive is made.

JTAM, Sofia, vol. 25 Issue 3 pp. 013-021 (1995), [Full Article]

Synthesis of a Four-Hinged Mechanism

N. loncheva
University of Mining and Geology, Sofia

An original method is suggested applying a particular type of functions, called transmission functions. With given first and second transmission functions, respectively angular velocities and angular accelerations of the links of a four-link mechanism, the mechanism itself is synthesized. Its motion is defined by three moving vectors which are searched. These vectors connect the hinges of the mechanism. Formulae are derived, for finding the position of the mechanism defined by the given velocities and accelerations of its links. The method can be applied for the synthesis of a wide range of mechanisms.

JTAM, Sofia, vol. 25 Issue 3 pp. 022-025 (1995), [Full Article]

Optimal Dynamic Synthesis for the Design of a Mechanism with Single Stage Spur Gear

B. Abuid1, I. Jordanov2, B. Belnikolovski2
1Basrah University, Iraq
2Technical University, Sofia

In this work a dynamic synthesis for the design of a single stage spur gears machine aggregate with optimal parameters is made. The aggregate is considered as a six degree of freedom vibrational model. The inertial and the elastic characteristics are considered as basic design parameters of the optimization, while the objective functions are the dynamic load factors excited in gear teeth, shafts and supports. The problem is solved as a single-criterion optimization case which includes a general and a super criteria with weight coefficients of importance as well. The optimization is carried out using an efficient technique to obtain the optimal design parameters.

JTAM, Sofia, vol. 25 Issue 3 pp. 026-034 (1995), [Full Article]

Forced Oscillations and Harmonic Balance Method in Systems for Control with Delay

D. Tsvetkov
University of Veliko Turnovo

In this paper periodic modes in systems for control with delay are considered. Sufficient conditions are obtained for existence of forced periodic oscillations and for applicability of the harmonic balance method for their approximate construction.

JTAM, Sofia, vol. 25 Issue 3 pp. 035-043 (1995), [Full Article]

Non-Linear Many-Dimensional Vibrations of a Motorcar under Disturbance from the Engine and the Road

I. Angelov, M. Georgiev
Technical University, Sofia

The non-linear three-dimensional vibrations of a motorcar with a driver and charge, and the connected with them angular vibrations in the transmission are treated in this paper. The many-dimensional vibrations are excited from the engine (ICE), and the road. In the composed dynamical model the motorcar is represented as a multibody system-driver, charge, body, engine, transmission, with elastic and damped connections. The mass, elasticity, damping, kinematics, geometry and power properties of the system elements are taken into account. The transmission circuit is branched by an automotive differential, and closed by the wheels and the road. The differential equations, describing the non-linear many-dimensional vibrations in matrix form are composed. The results give an opportunity to make a dynamical computer synthesis of motorcars.

JTAM, Sofia, vol. 25 Issue 3 pp. 044-051 (1995), [Full Article]

Computer Aided Optimal Design of Elastic Suspended Presses

B. Belnikolovski, I. Jordanov, N. Nikolov
Technical University, Sofia

Presses are considered as elastic suspended rigid body with six degree of freedom. Parameters describing inertial and elastic characteristics of the presses are under optimization. Objective functions of the optimization defined dynamic loading of presses parts and the impact loading transmitted to the basement. The optimization problem is treated as a single-criterion one and the designed optimal parameters are obtained.

JTAM, Sofia, vol. 25 Issue 3 pp. 052-061 (1995), [Full Article]

Path to Chaos for Flow-Induced Vibrations in Tubes Conveying Fluid

Gr. Makrides
Intercollege, Nicosia, Cyprus

The full nonlinear system of equations governing the oscillations of a cautilevered tube conveying fluid in the presence of motion-limiting constraints is solved numerically by the finite element method. This study shows a new path to chaos as the motion constraints are allowed to vary along the tube.

JTAM, Sofia, vol. 25 Issue 3 pp. 062-069 (1995), [Full Article]

Analysis of Simultaneous Propagation, Sedimentation and Resuspension Contaminants by Integral Transform Methods

M. Slawomirski1, I. Barbieri2, P. Pettazzoni2, G. Pallotti2, W. Yang3
1Division of Applied Numerical Modelling, Krakow, Poland
2University of Bologna, Italy
3University of Michigan, USA

The paper analyses propagation of contaminants in air and its sedimentation on the earth surface. It is assumed that diffusion effects are small in comparison with advection and that the sedimentation process is accompanied by resuspension. Two primary parameters are employed to describe the propagation and sedimentation processes of pollution: pollutant concentration in air and on the earth surface which are function of location and time. Exact solutions are obtained by means of the double Carson-Laplace transformation method. The mathematical model and its results can be applied to chemical contaminants as well as radiaoctive pollutants.

JTAM, Sofia, vol. 25 Issue 3 pp. 070-076 (1995), [Full Article]

Fundamentals of Coarse Dispersion Flow

Yu. Buyevich, Sh. Kapbasov
Urals State University, Ekaterinburg, Russia

A mathematical model is worked out to treat random small-scale pulsations of particles and a fluid in a macroscopically uniform mixture. The particles are assumed to be large enough to ensure the interparticle exchange of momentum and energy to be effected through direct collisions, so that the particle pulsations are nearly isotropic. The model provides for closure of conservation equations governing flow of both the mixture phases.

JTAM, Sofia, vol. 25 Issue 3 pp. 077-081 (1995), [Full Article]

On the Effective Viscosity of Blood Flowing through an Artery

K. Dey1, H. Mazumdar2
1College for Women, Calcutta, India
2Indian Statistical Institute, Calcutta, India

In this paper, we investigate the profiles of effective viscosity in blood flowing through the arterial tube for different values of hematocrit percentage. The model consists of two layers of fluide, e.g. a cell free plasma layer near the wall and a core layer comprising of red cells in plasma. The results obtained are computed and discussed.

JTAM, Sofia, vol. 25 Issue 3 pp. 082-088 (1995), [Full Article]

Plasticity Theory for Materials with Different Behaviour in Tension and Compression

A. Zolochevsky
Polytechnic Institute, Kharkov, Ukraine

A new increment plasticity theory of isotropic materials based on three invariants of stress tensor is presented in the paper. It is shown how the different parameters in the constitutive equations offered can be determined from a series of basic experiments. Specific physical relations with smaller number of material constants and invariants are formulated. For example, the description of plastic compressibility of filled polyethylene with a different behaviour in tension and compression is discussed. Finally, the advantages and limitations of the appropriate constitutive equations are investigated.

JTAM, Sofia, vol. 25 Issue 3 pp. 089-097 (1995), [Full Article]

Influence of Friction on Density Distribution in Porous Metals during Compaction processes

R. lankov
Institute of Mechanics, Bulg. Acad. Sci., Sofia

Compaction processes of porous metals are considered. A rigid-plastic mechanical model taking into account volumetric changes is assumed. A friction law is proposed describing the dependence of the friction factor on density. Numerical calculations based on the Finite Element Method are performed and the distribution of the relative density in the billet for different mechanical and geometrical parameters is found.

JTAM, Sofia, vol. 25 Issue 3 pp. 098-109 (1995), [Full Article]

An Approach to the Synthesis of Structural Elements Made of Composite Materials by Using of a Constant Magnetic Field

K. Delchev, E. Manoach
Institute of Mechanics, Bulg Acad. Sci., Sofia

The problem of the synthesis of structural elements made of composite material, consisting of an elastic non-ferromagnetic matrix and a ferromagnetic filler is considered. The orientation of the filler (short fibres) is controlled by an external magnetic field, generated in such a way as to satisfy preliminary given mechanical properties of the structures. Two different criteria – maximal principal stresses and maximal displacements are used, for the reinforcement of plane structures (panels). The boundary conditions for the magnetic field equations are obtained so that optimum reinforcement of the structure to be fulfilled.

JTAM, Sofia, vol. 25 Issue 3 pp. 110-118 (1995), [Full Article]