Journal of
Theoretical and Applied Mechanics
Volume 33, Number 2, 2003
Acad. G. Bonchev Str., Block 4, 1113
e-mail: alex_kazakoff@yahoo.co.uk
RESONANT FREQUENCIES OF ELECTRICAL STATORS
AS AFFECTED BY TEETH, FRAME AND
LAMINATIONS
Abstract. This paper deals with
modal analysis of electrical stators, prediction of the natural frequencies and mode
shapes of different vibration modes as affected by teeth, frame and laminations. The
problems associated with thick cylindrical shells are of considerable engineering
importance in numerous applications. One important application of such shells is the
stator of electrical machines, where the thick stator-core with teeth and windings is
encased by a thin frame. In order to design a quiet electrical machine, the accurate
determination of resonant frequencies and vibration characteristics of the stator is
essential. The vibration properties of an induction motor are investigated in this paper
using a Finite Element (FE) method. The influence of teeth, frame and laminations on the
overall vibration response of the stator is evaluated and a suitable modeling approach is
suggested. The results presented should help design-engineers to determine resonant
frequencies and natural response of stators accurately by proper incorporation of effects
of teeth, frame and laminations. Also, the physical interpretations of the results, given
in the paper, would help in acquiring a better understanding of the vibration behaviour of
stators in relation to the problem of electromagnetic acoustic noise in electrical
machines.
Key words: electrical stators, natural frequency
prediction, noise and vibration, modal analysis
Acad. G. Bonchev Str., Bl. 4, 1113
e-mail: boicho_marinoff@yahoo.co.uk
BEHAVIOUR
INVESTIGATION OF POWER TRANSMISSION LINES IN VEHICLES IN CASE OF SIMULTANEOUS ACTION OF
TORSIONAL AND LONGITUDINAL VIBRATION EXCITATION
Abstract.
In this paper a theory is developed for sizing the shafts of a power transmission line.
The behaviour of the line is investigated when the torsional and longitudinal vibrations
act simultaneously. The angular velocity of the shafts varies in working mode and the
system passes through different resonance zones. The purpose of this investigation is to
establish the resonance zones provoked by the first two natural frequencies from the
torsional and longitudinal vibrations, and to choose suitable values of the linear
characteristics, so that the stresses of the power transmission line are smaller than the
permissible values. This study is a base for the investigation of the complex dynamic
loads generated by the joint action of torsional, bending and longitudinal vibrations in
resonance and non-resonance modes.
Key
words: shafts,
sizing, frequency, vibrations, angular velocity, dynamic loads.
N. Pesheva, S. Iliev
Acad.
e-mail: nina@imbm.bas.bg,
stani@imbm.bas.bg
Numerical verification of the
Cassie’s EQUATION
for well-defined
heterogeneous substrates with “
Abstract. The wetting properties of model heterogeneous flat
substrates are studied numerically. In the framework of the classical capillary theory the
shapes of three-dimensional liquid drops in equilibrium with such substrates are obtained.
The numerical method used is based on the local variations approach. It has been extended
here to treat chemically heterogeneous substrates with “mesa” defects, i.e. sharp
boundaries between surface patches with different surface tensions. We discuss the
implications for the Cassie’s equation.
Key words: Cassie’s
law, contact angles, heterogeneous substrates, liquid drops.
Ts.
P. Ivanov,
Faculty
of Mathematics and Informatics,
5,
e-mail:
tsoloiv@fmi.uni-sofia.bg
R.
Savova
Acad.
G. Bonchev Str., Bl.4, 1113
e-mail:
radianka@imech.imbm.bas.bg
Motion
and Stability of an Elastic and Asymmetric Heavy Top
Abstract.
Motion and stability of an elastic top with stress-free surface and a fixed point moving
in a gravitational field is considered. The investigation is based on a direct approach in
the energy momentum method split into two steps. The deformation of the top due to the
gravitation and an arbitrary rotation is considered first and after that - the motion of
the deformed top as a rigid one. This separation is possible since the elastic deformation
is assumed static during the motion, which leads to relative equilibrium state of the top.
It is stable if the top is in a stable state with respect to both of them - the
deformation and the motion. The Koiter's
definition for non-linear stability with respect to the deformation and the usual Lagrange
definition for stability of the motion of the deformed top as a rigid one are adopted.
Relative equilibrium states are determined and criteria for stability are proved.
Key words:
top, elasticity, relative equilibrium, energy momentum methods, stability.
Tsviatko Rangelov
Institute of Mathematics and
Informatics,
Acad. G. Bonchev Str., Bl. 8, 1113
e-mail: rangelov@math.bas.bg
Abstract. Scattering problem in
cracked elasto-anisotropic plane is studied. A representation of the scattering field due
to time-harmonic wave motion in the exterior of an arc crack is derived. Using Radon
transform a fundamental solution in the frequency domain is obtained. In the case of a
line crack an inverse problem for determining the crack opening area and stress intensity
factors is presented. Numerical examples for solution of the direct and inverse scattering
problem in orthotropic plane are given.
Key words: cracked elasto-anisotropic plane, direct and
inverse problems, BIEM.
Central
Laboratory of Physical Chemical Mechanics,
Acad. G.
Bonchev Str, Bl. 1, 1113
e-mail: krastev@clphchm.bas.bg
Mechanical
properties and ratios of GF/POM under three
test regimes
Key
words: loading regime, mechanical loading, lifetime prediction, GF/POM.
1, Christo Smirnenski”
Blvd., 1046 Sofia,
Bulgaria,
e-mail: lilkova_fhe@uacg.bg
Influence of Variable Middle
Elastic Support to the Dynamic Stability of a Cantilevered Fluid Conveying Pipe with Two
Additional Elastic Supports
Key words: pipe, elastic supports, fluid flow, critical
velocity, dynamic stability.