Prof. Nejat Olgac (University of Connecticut, USA): Stability of LTI Systems with Multiple Delays, using the Bounds of Their Imaginary Root Crossings

Thu, 11/30/2017

Every one is warmly welcome to attend this seminar. We start at 10:00 at K14 seminar room. The estimated lenght is 60 minutes.


In this talk we will start with a review of the status on the quest of stability assessment for LTI systems with multiple rationally independent time delays and the cluster treatment of characteristic roots (CTCR) paradigm. For such dynamics any delay composition that results in an imaginary characteristic root lies either on a small number of kernel hypersurfaces (KH) or their infinitely many offspring hypersurfaces (OH). The complete (exhaustive and non-conservative) description of KH is the only prerequisite for the CTCR-based stability assessment procedure. As the number of delays increases, however, this step becomes prohibitive. Instead, we present a practical procedure to extract the 2-D cross-sections of the KH set in the domain of the two arbitrarily selected delays. For this we first determine the exact bounds of the imaginary spectra in this 2-D cross-section. We then use frequency sweeping methods to create the full knowledge of KH, which then triggers the CTCR paradigm to create the complete stability map in the domain of these two delays. We demonstrate the effectiveness of this methodology over an example case study.  Further, we bring forward some relevant industrial and present challenges, in particular on thermoacoustic instability in combustion.


Nejat Olgac, Dr. Eng. Sci. Columbia Univ. 1976, M.Sc. Technical Univ. of Istanbul, Turkey 1972 (summa-cum-laude), both in Mechanical Engineering.  He was engaged in manufacturing industry in Istanbul (1976-81).  Since 1981 he has been a professor with the Mechanical Engineering Department of the University of Connecticut.  His research interests are in robust nonlinear controls, active vibration absorption, time-delayed systems, micromanipulation in bio-engineering. Dr. Olgac holds four patents, three on the Delayed Resonator active vibration suppression technique (1995-1996-1999)  and a fourth one on anti-chatter concepts in simultaneous machining (2011).  He is the director of Advanced Laboratory for Robotics, Automation and Manufacturing (ALARM) at UConn. Dr. Olgac was Visiting Professor at INRIA (Sophia-Antipolis, France) 1988-89, SEW Eurodrive Fellow - Guest Professor at Technical Univ. of Munich, Germany in 1995-96, Visiting Professor at Harvard University 2002-03, and at Czech Tech. Univ. Prague 2017-18). He served on the editorial board of the ASME Trans. of Dynamic Systems, Measurement and Control (1996-2004), and the guest editor of the Special Issue of JDSMC on Time Delayed Systems (June, 2003), is presently on the Editorial Boards of  IEEE, Tran. Control System Technology, J. Vibration and Control, Int. J. of Mechatronics and Manufacturing Systems. He also served a member and later as the Chairman of the Executive Committee of the ASME Dynamic Systems and Control Division (2001-6). He was the General Chair of IFAC Time Delay Systems Workshop (TDS) 2012, and General Chairman of ASME Dynamic Systems and Controls Conference, DSCC 2013.  He was a member of the ASME Systems and Design Group Operating Board, he also served on the A2C2 (American Automatic Control Council) Board of Directors 2013-16. He is the recipient of a UCONN Research Excellence Award (2015) and ASME Distinguished Engineer of the Year, Hartford Chapter, CT (2015).  Prof. Olgac is a member of the Connecticut Academy of Science and Engineering (CASE), Fellow of ASME and Senior Member of IEEE.