Uncertainty of measurement of eigenfrequency using a dynamically directed vibroexciter

Measurement of eigenfrequency using a dynamically directed vibroexciter is investigated. Lyapunov indicators are calculated for various values of parameters of the system. It is shown that when the frequency of excitation coincides with the eigenfrequency there is a positive Lyapunov indicator. Thus chaotic motion takes place and causes uncertainty in the measurement of eigenfrequency

Measurement of vibrations of a pipe system

The two dimensional system of pipes is investigated. The model of a pipe system consisting from two dimensional beams by taking the inertia of fluid filling the pipes into account is used and the eigenmodes are determined. The places of the pipe with small amplitudes of vibrations and with large amplitudes of vibrations for the eigenmodes are determined. Then the places where the amplitudes for several first eigenmodes are large are determined. In those places it is recommended to perform measurements of vibrations of the pipe system

Selection of number of gaps in superimposed moiré measurements

Plane vibrations of a two dimensional elastic structure are investigated in this paper. Vibrations taking place according to the eigenmode are represented by using the method of stroboscopic geometric moiré. Selection of number of gaps when using the superimposed moiré technique is investigated and recommendations for choosing of their number are provided

Measurement of plane vibrations of a two dimensional elastic structure

Plane vibrations of a two dimensional elastic structure are analyzed in this paper. The vibrations taking place according to the eigenmode are represented by using the method of stroboscopic geometric moiré. This requires to perform the investigation for two mutually perpendicular directions of moiré fringes. Here the superimposed moiré technique is proposed to represent both images at the same time

Transverse vibrations of a two-dimensional pipe system

Transverse vibrations of the two dimensional system of pipes are investigated. The model of transverse vibrations of a two dimensional pipe system consisting from beams by taking the inertia of fluid filling the pipes into account is used and the eigenmodes are determined. Then the places of the pipes with small amplitudes of vibrations and with large amplitudes of vibrations for the eigenmodes are determined. After this the places where the amplitudes for several first eigenmodes are large are indicated. In those places it is recommended to perform measurements of transverse vibrations of the pipe system

Measurement of stresses in a vibrating polymeric film

One dimensional model for the investigation of longitudinal vibrations of polymeric film is investigated. Comparison of stroboscopic and time averaged intensities in the photo-elastic images is performed. Results about the required number of images for performing time averaging are provided. Recommendations for simultaneous application of both stroboscopic and time averaged photo-elasticity for measurement of stresses are given. One dimensional model for the investigation of vibrations of polymeric film having two nodal degrees of freedom (longitudinal displacement and displacement of the upper surface, assuming that displacement of the lower surface is of the same value but in the opposite direction) is investigated. This model is applied for the interpretation of results of thermo-elastic analysis. Recommendations for the interpretation of the stress field by using photo-elastic and thermo-elastic methods are provided

Investigation of stresses during dynamic behavior of polymeric films used for Braille

In recent years publications for the blind people using Braille writing began to be produced on polymeric films. This has the advantage with respect to previous technologies, because such publications have longer time period till the time when their quality degrades and they become unacceptable for use. Plotting isoclinics for bending vibrations of a polymeric film using photo-elastic coatings is analyzed. The numerical procedure is based on the technique of conjugate approximation with smoothing. Improved smoothing procedure for two dimensional Lagrange quadratic elements is proposed. Composite isoclinic patterns with isoclinics for various directions of the vector of polarization in a plane polariscope are obtained. A single Braille element of the polymeric film on the basis of the plane strain problem is investigated. Nodal stresses are calculated by using the procedure of conjugate approximation. Equivalent stresses are represented by intensity of the image. Special experimental setup was created. Three samples were investigated: the first two samples were made from transparent polymeric film with Braille elements, the third sample was made from transparent polymeric film with Braille elements formed by the method of thermal shaping. The level of stresses is estimated in the static status of the sample and after rotations by various angles. For precise estimation of the stress fields photo-elastic images for a number of different values of the angle of rotation are required. Thus in this paper stresses in transparent polymeric films and Braille elements in them are investigated. The obtained results are used in the process of forming Braille elements in polymeric films

Measurement of vibrations of a wing

In the paper vibrations of a wing are investigated experimentally by using the method of time averaged projection moiré. Experimental setup is developed and the results obtained by using the experimental procedure are analyzed. Interpretation of projection moiré images on a shallow surface is more complicated than on a plane surface. For this purpose, a special simplified two-dimensional numerical model is developed and used in hybrid experimental – numerical procedures of investigation of vibrations of a wing

Measurement of stability of a pipe system with flowing fluid

The two dimensional system of coupled vibrating pipes is investigated. The model of a pipe system consisting from two dimensional beams is employed. The problem of stability because of the reduction of stiffness caused by the flow of fluid is solved and the stability eigenmodes are determined. The places where the deflections of the stability eigenmodes are large are recommended for the location of measurement devices

Investigation of elliptical approximation in the model of the force of dry friction

In the numerical procedures involving the force of dry friction some type of numerical approximation for this investigated phenomenon is used in the process of calculations. Elliptic approximations for the local transition region are proposed, and numerical results are presented in this paper. The smoothness and continuity of this approximation is demonstrated by several computational experiments