Gastvortrag 22.05.2018 - 16.00 - M 0526

„The Shoelace Catastrophe (or a Knotty Problem on a Shoestring)“

Professor Oliver M. O'Reilly
Department of Mechanical Engineering
University of California at Berkeley

The accidental untying of a shoelace while walking often occurs without warning. Modeling and simulating the untying is an exceptionally difficult task in part because of the wide range of length scales, time scales and parameters. Finding external funding to examine the problem is arguably an even harder problem.

In this talk, we present a set of hypotheses for the series of events that lead to a shoelace knot becoming untied. First, the repeated impact of the shoe on the floor during walking serves to loosen the knot. Then, the whipping motions of the free ends of the laces caused by the leg swing produce slipping of the laces. This leads to eventual runaway untangling of the knot. As demonstrated using slow-motion video footage and a series of experiments, the failure of the knot happens in a matter of seconds, often without warning, and is catastrophic. The controlled experiments showed that increasing inertial effects of the swinging laces leads to increased rate of knot untying, that the directions of the impact and swing influence the rate of failure, and that the knot structure has a profound influence on a knot's tendency to untie under cyclic impact loading. The research was conducted over a period of three years on weekends and spare time using borrow equipment and laboratory space.

This talk is based on a paper, coauthored with Christopher Daily-Diamond and Christine Gregg, published last year in the Proceedings of the Royal Society: which captured widespread media attention.

Brief Biosketch: Oliver M. O’Reilly is a professor in the Department of Mechanical Engineering at the University of California at Berkeley. His research and teaching feature a wide range of problems in the dynamics of mechanical systems.  He received his B.E. in Mechanical Engineering from the National University of Ireland, Galway (NUIG). Subsequently, he received his M.S. and Ph.D. degrees in Theoretical and Applied Mechanics from Cornell University.  O’Reilly has received multiple teaching awards, including the Distinguished Teaching Award from U.C. Berkeley, published over 90 archival journal articles, written three textbooks and is a co-inventor on two patents. His latest book, coauthored with Alyssa Novelia and Khalid Jawed is a Primer on the Kinematics of Discrete Elastic Rods (Springer, 2018).

Gastvortrag 23.05.2018 - 14.00 - M 0526

A New Geometric Explanation for Gimbal Lock in the Apollo Moon Landing Program and Related Problems

Professor Oliver M. O'Reilly
Department of Mechanical Engineering
University of California at Berkeley

Coordinate singularities and gimbal lock are two phenomena that present themselves in models for the dynamics of mechanical systems. The former phenomenon pertains to the coordinates used to parameterize the configuration manifold of the system, while the latter phenomenon has a distinctive physical manifestation and rose to prominence in the Apollo Moon landing program. In the Apollo program a platform was mounted on two gimbals to save weight but this lead to locking of the gimbals and failure of the platform as a navigation aid in certain circumstances. To avoid locking, three gimbals could be used but this option was discarded in the interests of conserving weight. In this talk, we use tools from differential geometry to show how gimbal lock is intimately associated with an orthogonality condition on the applied forces and moments which act on the system. This condition is equivalent to a generalized applied force being normal to the configuration manifold of the system. Numerous examples, including the classic bead on a rotating hoop example and a gimbaled rigid body, are used to illuminate the orthogonality condition. These examples help to offer a new explanation for the elimination of gimbal lock by the addition of gimbals and demonstrate how integrable constraints alter the configuration manifold and may consequently eliminate coordinate singularities. This talk is based on the recent paper in Multibody System Dynamics coauthored with Evan Hemingway:

Gastvortrag 19.12.2017: „Towards vibro-impact energy harvesting“

Daniil Yurchenko
Dr. Sc., Ph.D
Associate Professor

Department of Mechanical Engineering
Heriot-Watt University, UK

Energy harvesting (EH) remains an attractive field of interests due to the needs for powering low-energy-consumption industrial sensor networks, wearable sensors or wireless sensors that required power but placed in hard-to reach locations, like tires. Efforts undertaken by the scientists all over the world have resulted in a high number of publications and significant advances achieved in understanding various types of mechanical energy conversion. Among many possible ways of converting mechanical energy of vibrations one may consider a vibro-impact (VI) interaction, which potentially has a number of benefits like high kinetic energy at impacts, possible low frequency impact motion and others. Some ideas have been proposed and investigated on how to incorporate the VI dynamics into EH process. The focus of this talk is on the application of the VI dynamics in a combination with dielectric elastomers (DE) used as a material for membranes subjected to the impacts. The design details, the EH principle, VI dynamics of the device and its applications will be discussed.

Zeit:   Dienstag, 19. Dezember  2017, 13:00 Uhr

Ort:    TUHH, Gebäude M, Eißendorfer Straße 42, Raum 2589

Zu diesem Vortrag lade ich herzlich ein.

R. Seifried