**GENERAL**

**MECHANICS**

**V. Konoplev**

**A. Cheremensky**

Institute for Problems of
Mechanical Engineering, Russ. Ac. Sci., St. Petersburg

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

Linear Space of Equipollent Systems of Forces

This paper explores the mathematical
nature of force systems in the multibody system mechanics. It yields computer-aided
tools for using equipollent systems of forces.

**V. Ivanova**

IPF-Sliven

Synthesis and Optimization of Precise Planer Cam Mechanisms

In this paper are proposed
the polynomial-harmonious motion laws with continuous 3rd and 4th transfer
functions.

The planer cam mechanisms
are systematized in eight varieties. General equations are worked out for
their synthesis, based on the envelope theory. The synthesis of the cam
profile is done with a precision up to the 4-th derivative of the motion
law. To achieve this, we have derived the recurrent dependencies for calculation
of the n-th derivative of the cam curve.An error analysis of the motion
law and its derivatives up to the 2nd have been performed. There are two
approaches suggested to increase the precision of the motion laws, realized
by the cam.The optimization criteria of the basic parameters of cam mechanisms
are complex and refer to the Efficiency Coefficient, the distortion, the
stress and the size.

**Al. Vatzkitchev**

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

On the Using of Matrix Transformations in the Force and Deformation Analysis of Manipulation Systems with Built-in Force-Torque Sensors

This paper presents the development
of some ideas about force/deformation analysis using force/torque sensors.
It is based on matrix transformations between the robot links. The difference
between the real loads and the sensor measurement is due to the different
position of the contact zone and the sensor. The question of interdependence
between the real parameters of load and the data from the sensor is posed.
The formalisation of the tasks in force and deformation analysis matrices
permits to simplify their decision. We can determine exactly the influence
of each factor (joint coordinates, dimensions, gravitation and inertia)
on the accorded analysed parameters. The use of such matrices decreases
in great degree the calculation time for decision of the described tasks.

**D. Petrova**

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

On the Singularity of Skew-Axes Gears with Straight-line Contact Between the Tooth Surfaces

What are considered are skew-axes
gears generated in accordance with the second Oliver's principle and a
straight-line contact between the tooth flanks. For this class of gears
it is of essential interest the problem for non-existence of ordinary nodes
and points of undercutting in the region of mesh. The scientific research
is a basis of the computer test for a singularity. Thus the elimination
of the undesired singular points is performed before the expensive technological
design of the gear sets.

**S. G. Nikolov**

**I. Edissonov**

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

Reconstruction of Polynomial Right-hand Sides of Two-dimensional Dynamical System on Given Integral Curve

In this paper is solved the
problem for reconstruction of unknown right-hand sides of two-dimensional
dynamical system on given integral curve. A method for determination of
dynamical system with polynamial right-hand sides (with integral curve
given parametrically) is elaborated. The proposed method is applied to
concrete two-dimensional dynamical system.

**MECHANICS**

**V. H. Vassilev**

**R. Flores-Berrones**

Institute of Water Problems,
Bulg. Ac. Sci., Sofia

Mexican Institute of Water
Technology, Mexico

Finite Element Method Modelling of Seismic Wave Propagation Effects on Buried Segmented Pipelines

Finite Element Method in
two-dimensional formulation is used to investigate the dynamic behaviour
of buried pipeline. Quasi-static analysis is adopted for assessment of
the pipeline response. Buried pipeline is presented as a series of segmented
elastic beams, connected longitudinally with joints. Soil is assumed to
be homogeneous(or unhomogeneous) isotropic(or transversal isotropic) elastic
media in plane strain conditions. Seismic forces at the each finite element
are determined as mass forces depending on the ground acceleration. The
possibility of slippage at the surface between the pipe and the soil is
evaluated as well when the seismic ground strain becomes large. A computer
program called SPLAN is developed under the above considerations including
pre-processing and post- processing mechanisms and numerical experiments
were done to study the influence of the geological and soil conditions
on the stress strain state of the pipeline.

**O. Santurjian**

**I. Etimova**

**L. Kolarov**

Institute of Water Problems, Bulg. Ac. Sci., Sofia

Three-Dimensional Modelling of Thermal Regime and Stresses in Mass Concrete Structures - PC Program Thermostress

Studies of the thermal regime and the development of the thermal stresses in design are necessary for prevention of the blocks and other massive elements of mass concrete structures from crack formation. An important tool for such studies is the PC program ``Thermostress 5''. The program enables the numerical modelling of three-dimensional temperature and stress fields in concrete blocks during construction and operation and thus supports the thermal analyses of mass concrete structures as dams, foundations, thick walls etc. In the article are described the main features of the program, its logic and possibilities for solving of different problems and other information relevant for such scientific products.

**St. Stoytchev**

**A. Rachev**

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

Mechanical Criteria for Design and Use of Deformable Synthetic Grafts

Mathematical model of a graft/artery system is presented. Two criteria for mechanical compatibility, based on a minimization of the distance which represent a) the flow induced shear stress at the inner surface of the host artery and the graft, and b) compliamces of both vessels over a relevant physiological pressure range, are formulated. Numerical study was performed in the case of human common iliac and femoral arteries, replaced by fibrous polyurethane or Dacron grafts. The analysis of the results shows that the shear stress criterion provides better similarity of the pressure-radius curves of the host artery and the graft than the compliance criterion. We propose to select initial graft diameter and thickness by means of shear stress criterion.

**SOLID**

**MECHANICS**

**I. Kolarov**

**V. Valeva**

High Military Transport School,
Sofia

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

On the Possibility for a Determination of the Stress State in Real Constructions of Press-fit Joints

The aim of the present paper is to investigate the possibility for a practical prediction of the mechanical stress concentrations in real constructions of the press-fit joints by the use both the numerical (BEM) and experimental (ultrasonic) methods.

Technical University - Sofia

Simple Error Estimators for Dimensional-Adaptivity: Applications for Beams

In this paper problems of dimensional adaptivity are studied. Possible transitions from a beam model to higher models and possible disturbances, that make the beam solution inaccurate, are presented. Several a-posteriori error estimators, which have a physically interpretation, for the model error of the 2D bending beam are proposed. All error estimators can be computed with a very small computational effort and with a little additional information from the solution of the beam model. The application of the error estimators to different examples shows the very good behaviour of the energy-based error estimators. The presented work can be used as a basis for the development of other error estimators for different disturbances and other models.

**K. Tushtev**

Technical University - Sofia

Variant of Plasticity for Cast Iron

A material model for the elastoplastic deformation of cast iron is presented. It accounts for the different strength in tension and compression and the nonelastic volume change which is typical for cast iron.

The governing equations for the elastoplastic deformation, based on an non-associated flow rule, are derived. They are based on anisotropic hardening and hardening parameter determined by a modified plastic work. The hardening parameter is defined by a function dependent on the mean stress. The plastic potential is a function of the first invariant of the stress tensor and the second invariant of deviator tensor.

A non-linear procedure for
the numerical implementation of the model for 2D proportional loading is
presented. The agreement with experimental data is good.

**MECHANICS**

**L. Zolochevskaya**

Kharkov State University, Ukraine

Anisotropic Creep Theory for Materials with Different Damage in Tension and Compression

A continuum damage mechanics
model for creep response of initially transversely isotropic materials
with parallel planar microcracks is presented. A complete polynomial expansion
of the equivalent stress in the creep potential with respect to the unilateral
damage is developed, and the general form of the creep constitutive equation
for an initially transversely isotropic materials with parallel disk-like
microcracks is derived. This model describes simultaneously initial anisotropy,
damage induced anisotropy, different damage development in tension and
compression, and different creep properties in tension and compression.

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