Please note that the list below only shows forthcoming events, which may not include regular events that have not yet been entered for the forthcoming term. Please see the past events page for a list of all seminar series that the department has on offer.

 

Past events in this series


Thu, 30 May 2024

12:00 - 13:00
L3

Patterned illumination for complex spatio-temporal morphing of LCE sheets

John Biggins
(University of Cambridge)

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Further Information

Biography

John Biggins read natural sciences at Cambridge University. He specialized in experimental and theoretical physics, and was the top ranked student in his cohort. He then did a PhD in the theory of condensed matter group under the supervision of Prof Mark Warner FRS, working on the exotic elasticity of a new phase of soft matter known as a liquid crystal elastomer (LCE). During his PhD he made an extended visit to Caltech to work with Prof Kaushik Bhattacharya on analogies between LCEs and shape memory alloys.

After his PhD, John won an 1851 Royal Commission Fellowship and traveled to Harvard to work with Prof L. Mahadevan on instabilities in soft solids and biological tissues, including creasing, fingering and brain folding. He then returned to Cambridge, first as Walter Scott Research Fellow at Trinity Hall and then as an early career lecturer in the tcm group at the Cavendish Laboratory. During this time, he explained the viral youtube phenomena of the chain fountain, and explored how surface tension can sculpt soft solids, leading to a solid analogue of the Plateau–Rayleigh instability. He also taught first year oscillations, and a third year course "theoretical physics 1."

In 2017, John was appointed to an Assistant Professorship of applied mechanics in Cambridge Engineering Department, where he teaches mechanics and variational methods. In 2019 he won a UKRI Future Leaders Fellowship on "Liquid Crystal Elastomers, from new materials via new mechanics to new machines." This grant added an exciting experimental component to the group, and underpins our current focus on using LCEs as artificial muscles in soft mechanical devices.

 

from http://www.eng.cam.ac.uk/profiles/jsb56 

Abstract

Liquid crystal elastomers are rubbery solids containing molecular LC rods that align along a common director. On heating, the alignment is disrupted, leading to a substantial (~50%) contraction along the director.  In recent years, there has been a great deal of interest in fabrication LCE sheets with a bespoke alignment pattern. On heating, these patterns generate  corresponding patterns of contraction that can morph a sheet into a bespoke curved surface such as a cone or face. Moreover, LCEs can also be activated by light, either photothermally or photochemically, leading to similarly large contractions. Stimulation by light also introduces an important new possibility: using spatio-temporal patterns of illumination to morph a single LCE sample into a range of different surfaces. Such stimulation can enable non-reciprocal actuation for viscous swimming or pumping, and control over the whole path taken by the sheet through shape-space rather than just the final destination. In this talk, I will start by with an experimental example of a spatio-temporal pattern of illumination being used to actuate an LCE peristaltic pump. I will then introduce a second set of experiments, in which a monodomain sheet morphs first into a cone, an anti-cone and then an array of cones upon exposure to different patterns of illumination. Finally, I will then discuss the general problem of how to choose a pattern of illumination to morph a director-patterned sheet into an arbitrary surface, first analytically for axisymmetric cases, then numerically for low symmetry cases. This last study exceeds our current experimental capacity, but highlights how, with full spatio-temporal control over the stimulation magnitude, one can choreograph an LCE sheet to undergo almost any pattern of morphing.

Thu, 06 Jun 2024

12:00 - 13:00
L3

Isolating internal waves using on-the-fly Lagrangian filtering in numerical simulations

Lois Baker
(University of Edinburgh, School of Mathematics)

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Further Information

Dr Lois Baker is the Flora Philip Fellow and EPSRC National Fellow in Fluid Dynamicsa in the School of Mathematics at the University of Edinburgh. Her research involves using mathematical and numerical models to understand oceanic fluid dynamics. Baker is particularly interested in the interactions of internal waves and submesoscale vortices that are generated in the deep and upper ocean.

Abstract

 

In geophysical and astrophysical flows, we are often interested in understanding the impact of internal waves on the non-wavelike flow. For example, oceanic internal waves generated at the surface and the seafloor transfer energy from the large scale flow to dissipative scales, thereby influencing the global ocean state. A primary challenge in the study of wave-flow interactions is how to separate these processes – since waves and non-wavelike flows can vary on similar spatial and temporal scales in the Eulerian frame. However, in a Lagrangian flow-following frame, temporal filtering offers a convenient way to isolate waves. Here, I will discuss a recently developed method for evolving Lagrangian mean fields alongside the governing equations in a numerical simulation, and extend this theory to allow effective filtering of waves from non-wavelike processes.

 

Thu, 13 Jun 2024

12:00 - 13:00
L3

The mechanics of physical knots: from shoelaces to surgical sutures

Pedro M. Reis
(EPFL)

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Further Information

 

Pedro M. Reis

Flexible Structures Laboratory, 

Institute of Mechanical Engineering,

Ecole Polytechnique Fédérale de Lausanne (EPFL), 

Pedro Miguel Reis is a Professor of Mechanical Engineering at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. Prof. Reis received a B.Sc. in Physics from the University of Manchester, UK (1999), a Certificate of Advanced Studies in Mathematics (Part III Maths) from St. John’s College and DAMTP, University of Cambridge (2000), and a Ph.D. in physics from the University of Manchester (2004). He was a postdoc at the City College of New York (2004-2005) and at the CNRS/ESPCI in Paris (2005-2007). He joined MIT in 2007 as an Instructor in Applied Mathematics. In 2010, he moved to MIT’s School of Engineering, with dual appointments in Mechanical Engineering and Civil & Environmental Engineering, first as the Esther and Harold E. Edgerton Assistant Professor and, after 2014, as Gilbert W. Winslow Associate Professor. In October 2013, the Popular Science magazine named Prof. Reis to its 2013 “Brilliant 10” list of young stars in Science and Technology. In 2021, he was the President of the Society of Engineering Science (SES). Prof. Reis has also received the 2014 CAREER Award (NSF), the 2016 Thomas J.R. Hughes Young Investigator Award (Applied Mechanics Division of the ASME), the 2016 GSOFT Early Career Award for Soft Matter Research (APS), and he is a Fellow of the American Physical Society (APS).

Abstract

Even though most of us tie our shoelaces "wrongly," knots in ropes and filaments have been used as functional structures for millennia, from sailing and climbing to dewing and surgery. However, knowledge of the mechanics of physical knots is largely empirical, and there is much need for physics-based predictive models. Tight knots exhibit highly nonlinear and coupled behavior due to their intricate 3D geometry, large deformations, self-contact, friction, and even elasto-plasticity. Additionally, tight knots do not show separation of the relevant length scales, preventing the use of centerline-based rod models. In this talk, I will present an overview of recent work from our research group, combining precision experiments, Finite Element simulations, and theoretical analyses. First, we study the mechanics of two elastic fibers in frictional contact. Second, we explore several different knotted structures, including the overhand, figure-8, clove-hitch, and bowline knots. These knots serve various functions in practical settings, from shoelaces to climbing and sailing. Lastly, we focus on surgical knots, with a particularly high risk of failure in clinical settingsincluding complications such as massive bleeding or the unraveling of high-tension closures. Our research reveals a striking and robust power law, with a general exponent, between the mechanical strength of surgical knots, the applied pre-tension, and the number of throws, providing new insights into their operational and safety limits. These findings could have potential applications in the training of surgeons and enhanced control of robotic-assisted surgical devices.