JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 28 Number 2 1998
                                                                    CONTENTS
 

GENERAL

MECHANICS
 

B. Belnikolovsky

Iv. Kralov
 

Technical University - Sofia

An Investigation of the Dynamic Loads in a Two-stage Spur Gear Machine Aggregate - Part I

A model of a two-stage spur gear machine aggregate with 12 degree of freedom is treated. The influence of the mass, elastic and damping parameters of the shafts, bearings, gear meshings and characteristics of the driving and driven machine on the dynamic loads in shafts, bearings and meshings is investigated in a wide frequency area, as well as the impact forces in teeth at beginning of contact out of the theoretical meshing line.



St. Batchvarov

V. Vassilev

V. Zlatanov
 

Technical University-Sofia

Higher Institute of Food and Flavour Industry - Plovdiv

Dinamical Analysis of One Type Manipulation System with a Closed Structure

In this paper is presented a manipulation system consisted of ideally rigid links with one degree of freedom which is driven by an asynchronous electrical motor. The differential equation of the motion is obtained by means of the Lagrange's method. The solution of the non-linear differential equation is obtained through a computer program for a numerical integration using fourth order Hamming's modified method. Fourth order Runge-Kutta method, suggested by Ralston, is used for computation of initial values. The changes of a reduced moment of the external forces and inertia are studied, as well the motion law of the co-ordinates.



CONTINUUM

MECHANICS

V. A. Dzhupanov
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Systematic Review on the Models of a Cantilevered Pipe Conveying Fluid and Lying on a Multiparametric Resisting Medium

As a rule the multitude of the control parameters in the problems on dynamic stability of the real structures is quite large and their mutual interactions in the process of the solution are quite cumbersome... This fact introduces great complications which persistently require periodically to systematize the knowledge of the problems in using some classifying statements. However, the present article is just such systematic and in high degree analytical and critical description of the dynamic models of cantilevered beams, (or beam-like cantilevered pipes conveying fluid) dynamically interacting with a resisting mediums. In the context of the present investigation the term model is understood as a sum of the governing equation and the boundary conditions of the mechanical system. The methodical systematization did provide new investigation aspects which are visibly shown to be objects of future investigations.



A. Feraidon

J.  Sejnoha

M.  Sejnoha
 

Iman Khomeini Higher Education Center, Tehran-IRAN
Czech Technical University, Faculty of Civil Engineering, Czech

Sensitivity Analysis of Flexible Laminated Plates

A method of design sensitivity analysis for a failure probability is presented and formulae are derived in such a form that a perturbation technique can be applied for a general reliability-based optimum design formulation of laminated plates. The resulting sensitivity coefficients contain only first order derivatives. Different failure criteria are considered and several examples are solved by means of a geometrically non-linear stochastic thin-plate finite element. The method described herein is applicable for general cases where the failure state can only be defined explicitly through a set of equations.



FLUID

MECHANICS

S. Slavtchev
 

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

Solutal Marangoni Instability in One- and Two- Liquid Systems

The onset of stationary Marangoni instability in one- or two-layered systems accompanied by solute transfer across the liquid interface is studied. The mass transfer is considered as a two-step process consisting bulk diffusion of the species to a very thin sublayer adjacent to the interface and transport of the solute inside the sublayer zone due to linear adsorption-desorption kinetics. The hydrodynamic stability theory is applied and the characteristic equation for the corresponding eigenvalue problem is derived in analytical form. The influence of the different transfer mechanisms as well as of the relative depth of the layers on the system instability is revealed.



H. Chamati

D. Danchev

N. Tonchev
 

Institute of Solid State Physics, Bulg. Ac. Sci., Sofia
Institute of Mechanics, Bulg. Ac. Sci., Sofia
Institute of Solid State Physics, Bulg. Ac. Sci., Sofia

Finite-size Scaling Properties and Casimir Forces in an Exactly Solvable Quantum Statistical-mechanical Model

A d-dimensional finite quantum model system confined to a general hypercubical geometry with linear spatial size L and ``temporal size'' 1/T (T - temperature of the system) is considered in the spherical approximation under periodic boundary conditions. Because of its close relation with the system of quantum rotors it represents an effective model for studying the low-temperature behaviour of quantum Heisenberg antiferromagnets. Close to the zero-temperature quantum critical point the ideas of finite-size scaling are used for studying the critical behaviour of the model. For a film geometry in different space dimensions s/2 < d < 3s/2, where 0 < s £ 2 controls the long-ranginess of the interactions, an analysis of the free energy and the Casimir forces is given.



SOLID

MECHANICS

A. Baltov

Chr. Kouyumdjiev

N. Stancheva

Iv. Ivanov
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

``A.Kanchev'' University of Rousse, Rousse

On the Modelling of the Sliding Friction Process Between Elastic Solids in the Presence of a Thin Contact Interlayer

In this work are studied some questions connected with the modelling of the process of sliding friction between two elastic solids. The case when on one solid is formed a thin contact layer with physical and mechanical properties different from these of the solid is considered.

Here is formulated a test example and solved by the Finite Element Method in nine variants where the geometrical, physical and mechanical parameters are modified. On the basis of the obtained results, basic simplifying assumptions are verified and numerical data are proposed for quantities, used in modelling of the process aiming at solving practical problems.



M. Datcheva
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Inelastic Behaviour of Anisotropic Loading Type Sensitive Materials

The aim of the present investigation is to construct in a general sense the constitutive equations for inelastic loading type sensible materials. Existing approaches and difficulties in mechanical theories for loading type sensitive materials are presented. The model suitable to create a common algorithm for both creep and plasticity and also to take into account the effects of the creep damaging. The methodology to identify the model parameters is presented and the basic experiments for their determination are chosen.


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