Understanding damping properties is an essential part in design and operation of any system of structural mechanics. Damping is one of the key elements which determine the ultimate vibration response levels under external excitation, and consequently a lot of understanding of damping properties and damping elements has been gained in structural engineering. While for externally forced systems the damping in the system determines the resulting vibration levels, for self-excited systems the levels of damping in the system can actually determine, if the system yields self-excited large-amplitude vibrations or not. Especially near the stability boundaries, damping is known to play a decisive and intricate role. For complex structural systems composed of a number of elements and linkages, it has shown that that resulting self-excited vibrations are often irregular, i.e. not strictly periodic but recurrent, often aperiodic and sometimes chaotic. In self-excited vibrations, the irregularity of the resulting vibrations seems to stem from nonlinearities involved, often appearing directly on more than a single length and time scale, rendering the system in principle multi-scale.
The focus of the project is on the development of a method to analyse and characterise the influence and role of damping design elements and dissipation mechanisms in multi-component systems with self-excitation subject to complex system states and manifold load cases. While for regular dynamics, i.e. stationary periodic response or linear transients, damping elements and mechanisms can be described with standard techniques, for irregular dynamics it is a largely unsolved problem to identify sources and sinks of energy or even the flow of energy in structures. In addition, most technical systems contain a plethora of local nonlinearities and damping elements, e.g. the joints and contact interfaces of the system, and are subject to a multitude of different load cases. This causes a challenging scenario for the assessment of damping devices. In the irregular vibrational state the manifold energy sinks are in constant interaction. At the latest, the additional complexity caused by the manifold load cases makes the application of simple bottom-up physics-based damping or dissipation description for the assessment of damping devices impossible. Hence, new techniques to characterize damping design elements are required. In this context we propose developing methods for the thorough analysis of the vibration response as well as the structural, damping and load parameters. The first part will focus on developing the analysis and computational methods for studying damping devices in friction-excited systems subject to irregular vibrations and is restricted to computer modelling and data derived from numerical models. In this context methods from nonlinear time series analysis and multivariate statistics are employed and combined. The central element is the data matrix M which is filled with characteristic quantities from different classes for multiple load cases. The final result is a procedure for the assessment and optimization of damping devices and dissipation mechanisms in systems subject to irregular vibrations. The second part will strive to extend the approach to systems where data obtained from physical testing is included, and will thus serve as a validation element. The considered systems are a pin-on-disk system and an automotive friction brake. As almost always in validation, the ideal expectation for the outcome is that the approach developed earlier can be transferred to real and larger systems without further complications. However, we expect that the validation work that we propose to conduct here will also lead to new insights into how the approach itself has to be tailored or perhaps modified to reach robust and convincing results. The proposal strives to overcome existing boundaries between the domains of physics-based system modelling, data analysis and time-series analysis, as well as design. Thereby it has a highly visionary and ambitious tone.
Duration: 2019 – 2022
Within DFG priority program SPP 1897: Calm, Smooth and Smart - Novel Approaches for Influencing Vibrations by Means of Deliberately Introduced Dissipation