The steam turbine blades of low pressure stages are endangerd by the high-cyclic fatigue due to the combined loading of dynamic stresses by the steam time-variant pressure and the pre-stress from centrifugal forces. Therefore, the importance of their experimental dynamic analysis in the design stage is critical. For laboratory tests of the blades, the piezo actuators placed on the blades, unlike electromagnets placed in the stationary space, give a possibility to excite the flexural vibration of the blades within the bladed disk by time continuous forces independently of the rotor revolutions. In addition, the piezo actuators can be also used to control the vibrations of the blade. Therefore, several dynamic experiments of the clamped model blade equipped with PVDF films were performed for the force description of the piezo foils and their behavior as actuators of the blade vibration. The numerical beam models were used for numerical analysis of the vibration suppression effects both by additional parametric excitation and by active damping. The optimal phase shift of piezo actuator voltage supply was ascertained both for amplitude amplification and suppression. The results contribute to the knowledge of the actuation and active damping of blade vibration by the piezo elements
The parametric anti-resonance phenomenon as an active damping tool for suppression of externally excited resonant vibration is numerically studied herein. It is well known fact that the anti-resonance phenomenon, i.e. the stiffness periodic variation by subtractive, combination resonance frequency, brings stabilization and cancelling into self-excited vibrations. But this paper aims at a new possibility of its application, namely a damping of externally excited resonant vibration. For estimation of its effect we come both from a characteristic exponent of the analytical solution and numerical solution of forced vibration of 2DOF linear system with additional parametric excitation. The amplitude suppression owing to the parametric anti-resonance is studied on several parameters of the system: a depth of parametric excitation, mass ratio, damping coefficient and small frequency deviations from the parametric anti-resonance.
The aim of this study was to design and test an adjustable hydro-pneumatic damper for cab suspension. The goal was to make a simple and cheap solution for a damper, which is intended to be placed between the hydraulic cylinder and accumulator. Damping behaviour of different terrain types had to be taken into consideration. Terrain type varies from field to road driving and damping should react rapidly to varying conditions. In this study, the semi-active damper has been built with a hydraulic direct acting cartridge type 2/2-way proportional flow control valve. Flow-pressure curves and dynamic tests were carried out in the laboratory. The dynamic test with forced vibration focused on stability in damping frequencies and step response between different states. Also, total damping force was measured in different damping states and the proportional valve’s precise step responses and stability were investigated in a closed hydraulic system. As a result, this research gave a lot of new information about the proportional valve’s applicability to work as a semi-active damper and information about damping behaviour. Research showed that a proportional valve can work in a cab suspension damper as well as a multi-fixed orifice damper. Bi-directional flow in the proportional valve was found to remain stable in cab suspension working conditions. The proportional valve also has the ability to work as a continuous state damper, which could lead to better damping results with the appropriate control system.