This contribution supplements the series of work oriented on active reduction of unacceptable vibrations by means of parametric excitation fulfilling certain conditions. Paper deals with the suppression of undesirable vibration using special parametric excitation fulfilling certain conditions. It is shown that this phenomenon can be used not ony for suppressing the self-excited vibrations or parametric resonances arising outside the region of main resonances in the vicinity of eigenfrequencies as are subharmonic resonances. and Obsahuje seznam literatury
A model with two masses is considered where the upper mass is self-excited due to the negative linear damping component and the lower mass represents the damped foundation subsystem. The passive means represents the positive linear damping of foundation subsystem and the active one the linear parametric excitation due to the periodic changing of the foundation mounts stiffness. In the case when only passive means are used the optimal tuning can be reached when stability limits for both vibration modes merge together. The condition for such tuning of the system in question is formulated. But when the stability condition is not met then this tuning of the system is not suitable for using in addition the active means in the form of parametric excitation. and Obsahuje seznam literatury
The methodology of modelling and of qualitative analysis of large rotating systems with gear and bearing couplings is presented. The emphasis is laid on the modelling of nonlinear gear and bearing couplings and on their influence on the dynamic system response to the internal kinematic excitation in gearing and to parametric excitation caused by the time-varying meshing stiffness. The aim is to introduce a method of investigation the beahviour of the rotating system influenced by the mentioned excitation and to examine the influence of chosen operational parameters. The methodology of modelling and of qualitative dynamic behaviour analysis is tested on a two-stage gearbox. and Obsahuje seznam literatury
Mechanical systems with parametric excitation have been investigated more frequently during the last years. New findings on the system behavior when excited at a parametric combination resonance frequency have triggered this increasing interest in such systems. Almost all studies, however, have been carried out analytically or numerically, so that there is a need for experimental work to prove the theoretical results. Partly the reason for this lack of experimental studies is found in several design problems that one faces when this task is tackled. In this contribution, a review of test facilities known from the literature is presented. Typical solutions suitable for experimental work and recent developments are discussed. and Obsahuje seznam literatury
A new application of the parametric anti-resonance is discussed. This phenomenon can be used not only for suppressing self-excited vibration or to reduce the externally excited vibration but also to suppressing self-excited vibration or to reduce the externally excited vibration but also to suppress the parametric resonance when certain conditions are met. Another aim is to stimulate further investigations and the practical applications. and Obsahuje seznam literatury
In the paper there are deduced differential equations of the vibroisolation system of the ambulance couch. The kinematic excitation is realized in three directions: the vertical translation and the rotations around the both horizontal axes of the car. The suspension of the ambulance couch corresponds to this presumption and is made by the parallelogram; on the upper base there is a double level Cardan suspension.
The linearised system of the motion equations is stated and the preliminary analysis of the dependency of all the three natural frequencies on the selected parameters is made. By vertical kinematics excitation numerical simulation of the excited oscillations is made. and Obsahuje seznam literatury