**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.

**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.

**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.

**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.

**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.

**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.

**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.

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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