2017年4月26日下午，英国阿伯丁大学工程学院应用动力学研究中心Marian Wiercigroch教授来我院作了题为“Grazing Induced Bifurcations: Innocent or Sinister?”的学术报告。
In this lecture I will examine nature of subtle phenomenon such grazing bifurcations occurring in non-smooth systems. I will start with linear oscillators undergoing impacts with secondary elastic supports, which have been studied experimentally and analytically for near-grazing conditions . We discovered a narrow band of chaos close to the grazing condition and this phenomenon was observed experimentally for a range of system parameters. Through stability analysis, we argue that this abrupt onset to chaos is caused by a dangerous bifurcation in which two unstable period-3 orbits, created at "invisible" grazing collide .
The experimentally observed bifurcations are explained theoretically using mapping solutions between locally smooth subspaces. Smooth as well as non-smooth bifurcations are observed, and the resulting bifurcations are often as an interplay between them. In order to understand the observed bifurcation scenarios, a global analysis has been undertaken to investigate the influence of stable and unstable orbits which are born in distant bifurcations but become important at the near-grazing conditions . A good degree of correspondence between the experiment and theory fully justifies the adopted modelling approach.
Similar phenomena were observed for a rotor system with bearing clearances, which was analysed numerically and experimentally . To gain further insight into the system dynamics we have used a path following method to unveil complex bifurcation structures often featuring dangerous co-existing attractors.
Marian Wiercigroch - Brief Bio
Professor Marian Wiercigroch educated in Poland, UK and US holds a prestigious Sixth Century Chair at the University of Aberdeen. He is a founding director of the internationally renowned Centre for Applied Dynamics Research and a Director of Internationalizationfor the College of Physical Sciences at the University of Aberdeen.
His area of research is theoretical and experimental nonlinear dynamics, which he applies to various engineering problems such as oil & gas drilling, rotor systems, underwater acoustics, fatigue and vibration isolation and renewable energy harvesting. Professor Wiercigroch has published extensively (over 350 journal and conference papers) and sits on some eight editorial boards of peer review journals. He is an editor of ActaMechanicaSinica and an Editor-In-Chief of International Journal of Mechanical Sciences. He is a frequent keynote and plenary speaker at major international conferences.
He has received many awards and distinctions including a Senior Fulbright Scholarship in 1994. In 2009 for his contribution to engineering and mathematicshe was elected a Fellow of the Royal Society of Edinburgh, the Scotland national academy and in 2013 he was awarded an honorary doctorate, DSc honoris causa, by the Lodz University of Technology, the best Polish University for mechanical engineering.