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    Developing complex network perspectives as an alternative view on nonlinear dynamics in large multi-component mechanical structures - Towards a better understanding of engineering vibrations
    This project aims at integrating methods from the field of complex networks into the analysis of large multi-component mechanical structures and their dynamics. Complex network analysis is a growing field of research that is applied throughout many different disciplines such as medicine, earth sciences or fluid dynamics. We propose a novel way of approaching current challenges in mechanical systems analysis by complementing the classical view of a geometric structure with a functional network perspective: The structure is represented as a network of individual components, and hence one can study the dynamic interplay, driving agents and component roles in the overall system dynamics better than with traditional methods. With the tools of network analysis, current challenges in nonlinear engineering dynamics can be handled in new and simpler ways. Particularly, the outcome of this project will allow for (i) visualization of dynamical phenomena hidden in the high dimensionality of the system; (ii) identification of emergent phenomena arising from collective behavior; (iii) analysis and design of mechanical system improved by network analysis tools. A network-based view on structural dynamics will enable us to identify and predict qualitative changes in the systems behavior, such as bifurcations, and emergent phenomena. Functional network representations of the complex dynamical system will provide a more intuitive understanding of the system dynamics, its governing nonlinearities and dynamic relationships between the components and sub-assemblies. This viewpoint will be expedient in the development of new multi-component mechanical systems, as resources can be focused on the dynamically most relevant parts during the design process. The methods obtained throughout this project will be of use for manufacturing and and quality management, when defining manufacturing tolerances or assessing fault impacts. Early warning methods for transitions and rare events can be established based on the proposed complex network analysis, which are of special interest in predictive maintenance. Thus, all phases of a products life cycle can profit from a complex network perspective on the systems dynamics rendered accessible through this project.
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    Excitability of Ocean Rogue Waves – Numerical Prediction and Early Warning by combining Wave Physics, Numerical Simulation and Data Driven Methods
    Achieving short-term predictions of rogue waves on the ocean is widely considered an important objective for offshore operations and shipping. At present none of the approaches and methods published or used today can be considered satisfying. Prediction times at present are on the order of a minute or less. Probably the most important reason for this is the inability to integrate the wave amplitude dependent dispersion effects properly into a computating and simulation environment that is numerically efficient enough to have real-time capability. Furthermore, also small errors in the initial conditions extracted from the data sources grow quickly during the prediction, which is unavoidable with a view to the usually chaotic or even weakly turbulent wave dynamics under consideration. The present state-of-the-art is thus far below what is needed, and it is far below what our knowledge on nonlinear wave physics suggests is possible, which ranges in the order of five to fifteen minutes, or even beyond. Two key obstacles still need to be overcome: First, from the available wave-state measurement data, initial or initial-boundary conditions have to be identified for the subsequent prediction process. At present this identification process forms the weakest part in the process chain. Second, the prediction processes themselves need to reach a substantially higher quality and numerical efficiency, if real-time capability is intended. At present three related research fields of (i) understanding the physics of rogue ocean waves, (ii) predicting the short-term occurrence of rogue ocean waves by numerical simulation, and (iii) employing data driven methods in the context of rogue ocean waves, are largely disconnected. We propose to integrate the three fields of knowledge and methods to develop novel hybrid approaches. The vision is to predict the sea state evolution and the occurrence of rogue wave events up to the limit given by the theoretical horizon of predictability of the specific chaotic sea state. This proposal aims at studying optimised combinations of all three fields mentioned to push the boundary of how one can achieve predictions closer to the theoretically possible horizon of predictability. We strive to overcome the present limitations by a combination of exploiting wave physics, advanced numerical simulation, and data driven methods. It is our aim to reach prediction times of 5 to 10 minutes. This implies a sufficient accuracy in terms of amplitude and phase error of the prediction within the desired time frame. The objective is to keep both amplitude and phase errors within an error bound of +/- 10 % within the prediction period. We expect such a method to subsequently find wide applicability in many fields, like sea-keeping, ship routing, early warning to evacuate dangerous zones on ships or platforms, construction of offshore wind plants, ocean energy devices, etc.
      75
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    Nonlinear Vibration Localization in Cyclic Structures
    Many mechanical structures in engineering and technology, like rotors, turbines, compressors etc, are cyclically assembled in the form of nearly identical components. The operational loads are often unsteady and lead to vibrations that determine or limit the function or lifetime of the systems. Often vibrations result that are not homomogeneously spread out over the whole system, but are confined to certain spatial zones only: localized vibrations. In the context of linear system models, slight inhomogeneities or perturbations of the symmetry explain localization very well. Rather recently, however, it has become more obvious that such cyclic systems also bear marked nonlinear properties. Which bring along novel nonlinear vibration phenomena. One class of such nonlinear vibrations are nonlinearly localized vibrations, which is the topic of the present project. From nonlinear dynamics in general it is well known that there are certain mechanisms that may lead to nonlinearly localized dynamics. While for many fields in science such nonlinear localization has been studied for a long time, and its relevance is widely acknowledged, for nonlinear mechanical vibrations the understanding is still comparatively limited. In nonlinear vibrations, the amplitude-dependent frequency shifts of single nonlinear oscillators may lead to a reduced coupling to neighbouring oscillators, which under certain conditions may result in full spatial localization of the vibration. In the present project the starting point will be the so-called discrete breathers. Conceptual, numerical, and experimental studies, based on a model system, are to be conducted to characterize and quantify the phenomena related with nonlinear vibration localization. We will aim at answering, under what system and loading conditions nonlinear vibration localization appears, and how robust or stable it is. Further topics of the study are the emergence of extended domains of localized vibration, the transition regeion between zones of strong and weak or no vibration, and the interplay between linear and nonlinear localization mechanisms.
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    Understanding and improving energy dissipation and vibration damping in structures subject to self-excited irregular vibrations – linking data driven approaches with modelling
    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.
      98
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      747
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    Calm, Smooth and Smart - Novel Approaches for Influencing Vibrations by Means of Deliberately Introduced Dissipation
    Die besondere Aktualität und Neuheit des Themas dieses Schwerpunktprogramms stammt aus den geänderten Rahmenbedingungen, die die wissenschaftliche Forschung der letzten Jahre, der Gesetzgeber sowie der Verbraucher vorgegeben haben. Der zunehmende Leichtbau hat zwar zu leichteren Strukturen geführt, diese jedoch auch weitaus schwingungsanfälliger gemacht. Gleichzeitig fordern strengere gesetzliche Regelungen an vielen Stellen eine deutliche Reduktion solcher Schwingungen. Dieser Konflikt ist somit erst in den letzten Jahren zu einem dringenden Problem geworden und erfordert deshalb nun große Forschungsanstrengungen. Die Forschungsförderung muss sich hierauf einstellen und die vorhandenen Forschungskapazitäten interdisziplinär bündeln und zielgerecht einsetzen. So müssen neben den bereits vorhandenen Kompetenzen aktuelle sowie neue Entwicklungen in Mechanik, Mathematik, Tribologie und Materialwissenschaften zu einem wesentlich besseren Verständnis von bedarfsgerecht eingesetzter Dissipation und Dämpfung führen. Diesen Anforderungen soll mit dem beantragten SPP Rechnung getragen werden, dessen Ziel es demnach ist, dass aus NVH – Noise, Vibration, Harshness für Automobile in Zukunft CSS – Calm, Smooth and Smart für die Technik im Allgemeinen wird. „Calm“ bedeutet dabei, dass unerwünschte Geräusche oder Lärm vermieden werden und auch durch neuartige Wege der Schwingungsbeeinflussung nicht eingebracht werden dürfen. „Smooth“ kennzeichnet ein angenehmes, gleichmäßiges Verhalten, bei dem die Schwingungen in einer natürlichen Weise beeinflusst werden und ein ruckelfreies Verhalten erzielt wird. „Smart“ ist ein intelligentes Verhalten, bei dem Dämpfungselemente auch strukturtragende Aufgaben übernehmen und eine äußere und innere aktiv steuerbare Beeinflussung von Schwingungen ermöglichen. Der Schlüssel zu „Calm, Smooth and Smart“ liegt in der Schwingungsbeeinflussung durch zeitlich und örtlich gezielt eingesetzte Dissipation, bei der die Schwingungsenergie in Wärme oder andere Energieformen umgewandelt wird. Dabei können dissipative Einflüsse das Schwingungsverhalten nicht nur quantitativ beeinflussen durch Veränderung der Schwingungsamplitude, sondern auch das grundsätzliche qualitative Verhalten ändern und damit entscheidend für das Funktionieren oder Versagen technischer Strukturen sein. Viele physikalische Phänomene und Wirkmechanismen der Dämpfung bzw. der Dissipation sind bis zum heutigen Zeitpunkt jedoch nur in einem nicht ausreichenden Maße verstanden und werden deshalb in der Technik nicht eingesetzt. In der Ingenieurspraxis war und ist es daher üblich, dissipative Einflüsse entweder ganz zu vernachlässigen oder nur vereinfacht abzubilden, so dass eine intensive Begleitung durch aufwändige Versuche nach wie vor notwendig ist. Die korrekte Berücksichtigung dissipativer Effekte beim Entwurf, der Modellierung und der Simulation ist somit heute die zentrale Herausforderung des SPP, die es zu bewältigen gilt, um im Maschinenbau das Ziel von Schwingungssimulationen mit prädiktivem Charakter zu erreichen. Es ist daher das besondere Anliegen des SPP, die Grundlagen für die gezielte und nicht allein auf Experimenten beruhende Nutzbarmachung und Auslegung dissipativer Mechanismen zu schaffen, die eine Entwicklung von Fahrzeugen, Maschinen und Anlagen ermöglichen, die energieeffizient und leicht, aber gleichzeitig von ihren Schwingungseigenschaften her „calm, smooth and smart“ sind. Zu diesem Zweck gilt es in diesem SPP folgende Aufgaben zu lösen: - Systematische Erforschung von Dissipationsmechanismen und Erarbeitung von mathematischen Modellen zu deren Beschreibung und Parametrierung. - Beschreibung, Untersuchung und Validierung neuartiger Dämpfungselemente und deren schwingungstechnischer Wirkung. - Entwicklung von Methoden für die Beschreibung von Dissipation und Dämpfungselementen in ingenieurkonformen Berechnungsumgebungen. - Integration der Modelle von Dämpfungselementen in Gesamtmodelle der Fahrzeuge, Maschinen oder Anlagen und deren Modellreduktion. - Experimentelle Untersuchung der dynamischen Parameter bezüglich der gewünschten Eigenschaften im Gesamtsystem.
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    Excitability of Peregrine Type Rogue Water Waves on Irregular Background
    In the project Peregrine wave groups are to be excited on irregular wave carrier. As medium deep water with surface water waves is considered. The work is both experimental and numerical. Water wave flumes at Technische Universitat Hamburg and computational facilities and methods are available. The aim of the project is to reach an improved understanding of the excitability of Peregrine breather type water waves on irregular background and a statistical characterisation of their excitability.
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