Journal of Theoretical and Applied Mechanics
Volume 33, Number 2, 2003
Acad. G. Bonchev Str., Block 4, 1113
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
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
e-mail: firstname.lastname@example.org, email@example.com
Numerical verification of the Cassie’s EQUATION
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,
of Mathematics and Informatics,
G. Bonchev Str., Bl.4, 1113
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.
Institute of Mathematics and
Acad. G. Bonchev Str., Bl. 8, 1113
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.
Laboratory of Physical Chemical Mechanics,
Bonchev Str, Bl. 1, 1113
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,
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.