Alexander F. Vakakis, University of Illinois at Urbana-Champaign, US
Topic: Non-reciprocal nonlinear energy transfers in dynamics and acoustics
Abstract: We explore passive energy management through non-reciprocal energy transfers in dynamical and acoustical systems based on the synergy of intentional implementation of strong nonlinearity, asymmetry, and internal scale hierarchy. Central to this concept is the inducement of irreversible nonlinear energy transfers from large-to-small scales that break classical reciprocity in controlled and predictable ways. Then, broadband or narrowband input energy is either directed in preferential paths/modes, dissipated locally/globally, or harvested at a priori designated sites in a system through predictable design. These non-reciprocal energy transfers mimic analogous energy cascades that occur often in Nature (e.g., in turbulent flows or granular media), and, as such, benefit from the well-known robust and enhanced dissipative features exhibited by these natural phenomena. Our approach dictates advanced theoretical modeling and analysis, but also nonlinear system identification and reduced-order modeling to characterize the experimental realizations that validate the theoretical predictions. In specific applications, we’ll discuss non-reciprocal energy transfers in fluid-structure interactions, as well as, new approaches for designing, analyzing, characterizing and experimentally testing non-reciprocal lattice materials incorporating internal hierarchical scales. The aim is to translate these materials to new technologies and devices that exploit and showcase acoustic non-reciprocity.
Biographical Sketch: Alexander F. Vakakis received a Ph.D. from Caltech (1990), an M.Sc. from Imperial College, London (1985), and a Diploma in Mechanical Engineering from the University of Patras, Greece (1984). He is the Donald Biggar Willett Professor of the College of Engineering of the University of Illinois where he co-directs the Linear and Nonlinear Dynamics and Vibrations Laboratory (http://lndvl.mechse.illinois.edu/). In the recent past he was the Edmond J. Safra Visiting Professor at Technion, Israel (2020). Among other awards, he is the recipient of an Alexander von Humboldt Research Award (2019), and the ASME Thomas K. Caughey Award in nonlinear dynamics (2014). He has published over 300 archival journal publications, holds two patents, and has authored or edited 6 technical texts and monographs. Many of his PhD students are faculty and members of R&D Laboratories, and his research interests center on nonlinear dynamics, vibrations and acoustics.
Dongxu Li, NUDT, China
Biographical Sketch: Dongxu Li is an academician of Chinese Academy of Sciences. She is an expert on structural dynamics and vibration control. She has received her bachelor degree and doctoral degree both in solid mechanics from National University of Defense Technology (NUDT). She is currently a professor and a doctoral supervisor of aerospace science and technology in the College of Aerospace Science and Engineering, NUDT, P. R. China. She has been engaged in the fields of structural dynamics, vibration control, smart materials and smart structures, etc. for more than thirty years. She has published more than 200 refereed papers and 7 scientific writings, and has been authorized 62 invention patents. She has received a number of awards for her contributions to scientific and technological progress in China, such as the National Technological Invention Award, National Prize for Progress in Science and Technology, and so on. Also, she is now the principal investigator of many important research projects, such as National Natural Science Foundation, National Key Project, etc.
Huajiang Ouyang, University of Liverpool, UK
Topic: Friction-induced vibration and viro-impact in triboelectric energy harvesting
Abstract: Electrostatic energy harvesting (EEH) is a distinct means of energy harvesting. Although it is not as widely used and studied as piezoelectric energy harvesting (PEH) and electromagnetic energy harvesting (EMEH), it has several advantages. Triboelectric energy harvesting (THE) is a special kind of EEH and has attracted much attention in recent years, advocated and largely advanced by Prof Zhonglin Wang's group at Georgia Tech in their work on triboelectric nanogenerators (TENGs) in recent years. The majority of research work on TEH is on material science, manufacturing and electric circuit design. There is a lack of research into friction-induced vibration and vibro-impact that are essential in TEH, which we think has hindered the improvement in harvesting efficiency and wide use of this new kind of energy harvesters. This talk introduces the concepts of TEH and discusses several challenging research issues concerning TEH. It presents numerical results of friction-induced vibration and vibro-impact, and electric outputs from simulations conducted by the Dynamics and Control Group at the University of Liverpool. It also covers some experimental results.
Biographical Sketch: Huajiang Ouyang received BEng and MSc in Engineering Mechanics in 1982 and 1985, respectively, and PhD in Structural Engineering in 1989, at Dalian University of Technology, China. He is a full Professor at the School of Engineering at the University of Liverpool and Head of the Dynamics and Control Research Group. Dr Ouyang is a Fellow of Institute of Physics and a Fellow of Higher Education Academy. He was a Royal Academy of Engineering and Leverhulme Trust Senior Research Fellow in 2009-2010. He is also a Changjiang Chair Professor. He is a Deputy Editor-in-Chief of Journal of Sound and Vibration, European Editor of International Journal of Vehicle Nosie and Vibration and on the editorial boards of Applied Sciences and Chinese Journal of Computational Mechanics. He has published 255 journal papers and 112 conference papers. His main search areas are structural dynamics and control, and structural identification. He is particularly interested in friction-induce vibration, moving-load dynamics and inverse structural modifications, and in the last few years, vibration-based energy harvesting.
Janko Slavič, University of Ljubljana, Slovenia
Topic: Recent advances in vibration fatigue research
Abstract: Vibration fatigue describes the fatigue of flexible structures where the frequency range of the excitation forces is overlapping with the natural dynamics of the excited structure. The goal of vibration fatigue is to understand the mechanics of failure and to estimate the fatigue life. If classical fatigue is focused into time-domain fatigue life estimation, the vibration fatigue is focused into frequency-domain fatigue life estimation. Initially, the fatigue load counting methods in the frequency‑domain have been researched; however, recent years have seen a significant progress in the field of structural-dynamics-based fatigue research.
Biographical Sketch: Janko Slavič, is the first author of the Elsevier book Vibration Fatigue by Spectral Methods (Sep 2020), he is a full professor of Mechanics at the University of Ljubljana, Faculty of Mechanical Engineering. He authored close to 80 SCI scientific articles, most of them in Q1 journals, his h-index is 17. He supervised 13 finished PhD projects and is currently supervising 6. His research interest are in signal processing, vibration fatigue, optical structural identification methods, and smart 3D printed structures. He is a member of the Editorial board of Mechanical Systems and Signal Processing. Prof. Slavič is also a regular contributor to open-source scientific packages; recently, he co-authored a Nature Methods publication which received close to 300 WoS citations in the first 6 months since publication.
Scott D. Sommerfeldt, Brigham Young University, US
Topic: Active structural acoustic control using the weighted sum of spatial gradients method
Abstract: A number of noise control applications involve noise being radiated from vibrating structures. For low frequency noise, an active control solution for such applications can be attractive. However, the approach of simply attenuating the structural vibration is typically inefficient and ineffective, both because it is difficult to achieve global attenuation of the vibration and not all vibration results in efficient acoustic radiation. Thus, a desirable approach would be to just attenuate the vibration response that is responsible for the acoustic radiation. In an effort to achieve this desired outcome, an approach referred to as the Weighted Sum of Spatial Gradients method has been developed. This approach, which has its basis in acoustic radiation modes, utilizes a compact array of vibration sensors to obtain four minimization terms that loosely correspond to the lowest four radiation modes. The method has been implemented to reduce the radiation from flat plates, as well as from finite cylindrical structures. Results will be shown that indicate this method is capable of attenuating the radiated sound power to near optimal levels at low frequencies where the number of contributing radiation modes is limited.
Biographical Sketch: Scott D. Sommerfeldt holds the rank of Professor in the Department of Physics & Astronomy at Brigham Young University. He received his PhD in Acoustics from The Pennsylvania State University, in 1989. Prior to coming to BYU, Sommerfeldt held the joint positions of Research Associate in the Applied Research Laboratory and Assistant Professor of Acoustics at Penn State University, from 1989-1995. He has been a faculty member at BYU since 1995. Sommerfeldt is a fellow of the Acoustical Society of America and a member of the Institute of Noise Control Engineering (INCE).