Xiaodong Cao

Die Übertragungsfunktion eines mechanischen Systems ist eine der wichtigsten Messgrößen in der Schwingungsanalyse. Um die Übertragungsfunktion möglichst breitbandig bestimmen zu können, wird eine breitbandige Anregung benötigt, welche z.B. durch eine Plasmaanregung realisiert werden kann. Allerdings stellt die Bestimmung des Spektrums einer solchen Plasmaanregung, welche für die Ermittlung der Übertragungsfunktion notwendig ist, zurzeit noch eine Herausforderung in der Forschung dar. In diesem Beitrag bestimmen wir das Anregungsspektrum durch ein Simulationsmodell und vergleichen das Ergebnis mit dem Resultat einer bisher typischerweise eingesetzten experimentellen Schätzmethode. Der vorgestellte Ansatz benötigt einen deutlich geringeren Aufwand und stellt damit für praktische Anwendungen eine gute Alternative zum aktuellen Stand der Technik dar. The frequency response function (FRF) of a mechanical system is one of the most important measured characteristics in vibration analysis. To determine the FRF as broadband as possible, a broadband excitation, such as plasma excitation, is required. However, determination of the spectrum of the plasma excitation, which is necessary for the determination of FRF, is still a challenge to research. In this paper we determine the excitation spectrum by a simulation model and compare the result with the outcome of a typical experimental approach. The presented method requires significantly less effort and is therefore a good alternative to the state of the art for practical applications.

Scanning laser–Doppler vibrometry (SLDV) can localize and visualize damages in mechanical structures. In order to enable scanning, it is necessary to repeat the vibration. Therefore, this technique is not suited to detect emerging hazards in working machinery that change the vibration behavior. A common technique for such cases is monitoring the vibration excited by machine operation with accelerometers. This technique requires mechanical coupling between sensors and the measurement object, which influences the high-frequency vibration responses. However, in the low-frequency range, local damages do not shift resonances or distort operational deflection shapes (ODS) significantly. These alterations in the vibration behavior are tiny and hard to detect. This paper shows that multipoint laservibrometry (MPV) with laser excitation can measure these effects efficiently, and it further demonstrates that damages influence ODSs at frequencies above 20 kHz much stronger than at frequencies below 20 kHz. In addition, ODS-based damage indices are discussed; these are highly sensitive to minute visible changes of the ODSs. In order to enhance the sensitivity of hazard detection, the response vector assurance criterion value is computed and evaluated during operation. The capabilities and limitations of the methodology on the example of a cantilever with manually emerging damage are demonstrated.