Cancelling self-excited vibrations by parametric excitation

So-called "self-excited" (also named self-sustained) vibrations may just cause unpleasant noise but can also be dangerous for machines, plants and structures if the vibration level is almost unbounded. Such vibrations can be reduced or even be cancelled by applying counteracting vibrations. This project is dedicated to the study of this recently discovered phenomenon. Self-excited vibrations represent a major problem in several engineering disciplines. Such vibrations are frequently characterised by high vibration amplitudes. They can lead to loud and continuous noise, e.g. squeaking noise of brakes, or to violent oscillations of wires and cables which are exposed to strong winds, to give another example. There has been even an incident where a bridge collapsed, due to self-excited vibrations. Therefore, it is mandatory to consider such vibrations at the design stage of certain machines and structures and take appropriate measures against them. In this research project a new method dedicated to cancel self-excited vibrations is developed and investigated. The main idea of this method is to periodically change a certain parameter of the structure. If frequency and amplitude of this parametric excitation are chosen correctly, then the undesirable self-excited vibrations can be cancelled completely. There are several possibilities of putting this parametric excitation into practice, ranging from a simple mechanical design to mechatronic actuators. In this project investigations will be carried out analytically, computationally by numerical simulation and also experimentally with a test stand to be designed in the course of this project. One can think of applications of this new method in several areas of civil or mechanical engineering. Possibilities of realisation are investigated and discussed as part of the project. Flow-induced vibrations of rotors and turbine blades could be suppressed by this method. Also oscillations of machine-foundation systems and friction-induced vibrations of structures are possible areas of application.

Bothering mechanical oscillations, annoying acoustical noise, dangerously increasing vibrations in machines and structures can be reduced or cancelled by a specific manipulation of certain system parameters. Since this direct intervention usually causes vibrations on its own, one can say that one kind of vibrations is used to kill another one. Vibrations, especially so-called "self-excited" (also named self-sustained) vibrations may just cause unpleasant noise but can also be dangerous for machines, plants and structures. Self-excited vibrations represent a major problem in several engineering disciplines. Such vibrations are frequently characterised by high vibration amplitudes. They can lead to loud and continuous noise, e.g. squeaking noise of brakes, or to violent oscillations of wires and cables which are exposed to strong winds, to give another example. There has been even an incident where a bridge collapsed, due to self-excited vibrations. Therefore, it is mandatory to consider such vibrations at the design stage of certain machines and structures and take appropriate measures against them. In this research project a new method dedicated to cancel self-excited vibrations was developed, investigated and tested. The main idea of this method is to periodically change a certain parameter of the structure. If frequency and amplitude of this parametric excitation are chosen correctly, then the undesirable self-excited vibrations can be cancelled completely. There are several possibilities of putting this parametric excitation into practice, ranging from a simple mechanical design to mechatronic actuators. In this project investigations were carried out analytically, computationally by numerical simulation and also experimentally on a test stand, designed exclusively for this project. One can think of applications of this new method in several areas of civil or mechanical engineering. Possibilities of realisation have been investigated and discussed as part of the project. Flow-induced vibrations of rotors and turbine blades could be suppressed by this method. Also oscillations of machine-foundation systems and friction- induced vibrations of structures are possible areas of application.