PUST, L.: Active control of damping of mechanical systems (Review paper) 157
NEMCEKOVA, M.: The gear equivalent loading correction based on experimental results (in Slovak) 167
SEMRAD, K., LAZAR, T.: Laser interferometry for experimental modal analysis of jet-engine blades 176
MORAVKA, S.: Elastic waves propagation in thick cylindrical semiinfinite elastic bars subjected to longitudinal impact solved by an exact three-dimensional theory. Part I (in Czech) 187
MURIN, J.: Beam element with varying cross section satisfying local and global equilibrium conditions (in Slovak) 208
Letter to the Editor
SLADKOVA, M.: Concise characteristics of some ISI databases (in Slovak) 224
Active control of damping of mechanical systems
An analysis of a two-degrees-of-freedom (2 DOF) mechanical system with damping controlled by a feedback loop is presented. The aim of the study carried out by means of analytic-numerical method is to show the possibility of minimizing the loss of energy by suitable control of damping coefficient according to the measured amplitude of vibration. The minimal or zero power loss is achieved in non-resonant zones. Sufficient damping guarantees the limitation of the amplitudes in resonances. A suitable dependence of damping force on amplitudes or velocities is proposed both for the linear and nonlinear systems.
The problem of fatigue life prediction is not new. However, there are not many published results about variable load tests of gears. The results of variable amplitude tests are, aside from studying the fatigue strength of components, suitable for examining the validity of cumulative damage theories by comparing the test results with those of corresponding theoretical life predictions. This comparison based on test results is presented in this paper.
K. SEMRAD, T. LAZAR
The paper deals with one of the possible optical methods for
measurement of mechanical vibrations, modal identification, and
modal testing of compressor and turbo-jet engines turbine blades
in laboratory conditions.
The vibration is optically scanned by a direct reflection of laser beam from a measured surface, and after interference with a reference beam in an interferometer, the optical signal is worked up by electronic equipment of interferometer and evaluated in a computer to make the modal analysis.
The results of an analytical solution of a longitudinal impact of thick cylindrical bars obtained by an exact three-dimensional theory are presented. Many valuable results made it possible to improve the hitherto knowledge of physical essence of the investigated problem. The paper brings some new information about waves propagation in the initial phase of the impact. The phenomena of concentration of the stress near the rod axis and propagation of the conical von Schmidt waves have been investigated. The Rayleigh waves in a thick bar have been searched for.
In this paper a stiffness matrix of the beam element satisfying local and global equilibrium is derived. Kinematical variables on the boundary and inside the element correspond to the results obtained from analytical solution for the linear truss theory. The calculated results are compared with the solution obtained by the Hermite beam element and also by bi-linear and bi-quadratic 2D plane stress elements.