October 2
@
12:00 PM
–
1:00 PM
The Mechanics Seminar Series is a weekly seminar given by campus and visiting speakers on topics across the spectrum of mechanics research (solids, fluids, and dynamics). Professor Alex Vakakis is a professor at the University of Illinois Urbana-Champaign.
Title: Quantifying Energy Dissipation in Mechanical Systems
Abstract: The quantification of the inherent dissipative capacity and the rate of energy dissipation in mechanical systems is of importance in engineering design. Energy dissipation in a system is affected by diverse, multi-scale effects, such as, its damping distribution, possible time-varying and nonlinear effects, interfacial effects at the boundaries and/or internal attachments, interactions with its environment (e.g., fluid-structure interactions), etc. This dictates the development of reliable dissipative measures capable of accurately accounting for such diverse effects. To address this need an analytical and data-driven numerical framework is developed based on the generalization of the concepts of bandwidth – BW (in frequency), time constant or energy storage time – EST (in time), and time bandwidth product – TBP (in frequency-time), typically only defined for single-DOF, linear, time-invariant oscillators. The aim is to derive physically meaningful dissipative measures that are applicable to general classes of linear/nonlinear, time-invariant/variant, single-/multi-DOF models of practical systems. A first example of application of these measures is given for a model airplane with imperfectly attached stores generating strong nonlinearities (in the form of vibro-impacts). We quantify the effects of vibro-impacts on the global dissipative capacity and rate of energy dissipation of the entire plane though computational and experimental studies. A second example of application is the study of the limits of energy dissipation in linear multi-DOF mechanical models with classical viscous damping distribution. Interestingly enough, it appears to be an optimal design for this class of systems, corresponding to a global minimum of their TBP, which seems to be invariant to system topology and mass/stiffness distribution, and depends only of the number of DOF. Finally, some possible paths forward are discussed.
Bio: Alexander F. Vakakis received his Ph.D. from Caltech (1990 – T.K. Caughey advisor), M.Sc. from Imperial College, London, UK (1985 – D.J. Ewins advisor), and Diploma in Mechanical Engineering from the University of Patras, Greece (1984 – S.A. Paipetis advisor). Currently he is the Donald Biggar Willett Professor of the College of Engineering at the University of Illinois at Urbana – Champaign (UIUC) where he co-directs the Linear and Nonlinear Dynamics and Vibrations Laboratory (http://lndvl.mechse.illinois.edu/); moreover, he is co-affiliate faculty at the University of Stuttgart, Germany. Recipient of the Tau Beta Pi Daniel C. Drucker Eminent Faculty Award from the UIUC College of Engineering (2023), the best paper award of the journal Nonlinear Dynamics (2023), an Alexander von Humboldt Research Award (2019), the Edmond J. Safra Visiting Professorship from Technion (2019), and the ASME Thomas K. Caughey Award in nonlinear dynamics (2014). He has published a volume of archival journal publications, holds four patents (with two more pending), and has authored/edited 6 technical texts and monographs. Many of his PhD students and postdoctoral fellows are faculty members in US and International Universities and researchers in National Laboratories and R&D Centres. His research interests include nonlinear dynamics, vibrations and acoustics, passive energy management and targeted energy transfer across scales, phononics and acoustic metamaterials, system identification and reduced order modelling, non-smooth dynamics and vibration energy harvesting.