MechE PhD Prospectus Defense - Alexandros Oratis

  • Starts: 10:00 am on Wednesday, December 5, 2018
  • Ends: 12:00 pm on Wednesday, December 5, 2018
TITLE: NON-LINEAR DYNAMICS OF RODS, BEAMS AND BUBBLES. COMMITTEE: Prof. James Bird (ME/MSE) (Advisor) Prof. Douglas Holmes (ME/MSE) Prof. Paul Barbone (ME/MSE) Prof. C. Eugene Wayne (Math & Stats) ABSTRACT: Rods and beams are ubiquitous in our everyday life and can be found in a variety of length scales, from large supports of buildings to carbon nano- tubes. Similarly, the presence of bubbles can also span a variety of scales, from a glass of soda to the tiny bubbles formed by waves in the ocean. Yet, the behavior of beams and bubbles can occur so fast that the dynamics go unnoticed. The deformation of beams is governed by its elasticity while that of bubbles is typically governed by capillarity. In this prospectus we aim to explore the dynamics beams and bubbles under various external conditions. In the first part of this prospectus we aim to combine capillarity with elas- ticity to study the torsion of a flexible rod. Capillary forces are able to align particles with discrete wettabilities – or Janus particles – at liquid interfaces. Their amphiphilic properties enable Janus particles to orient themselves at liq- uid interfaces such that both of their surfaces are facing their preferred fluid. Here we extend ideas of elasto-capillarity to modulate rotational alignment by connecting amphiphilic Janus cylinders in an antisymmetric configuration. As the Janus cylinders rotate they cause a twisting deformation of rod. We develop both a mathematical model and a physical macroscale setup to relate the angle of twist to the elastic and interfacial properties, which can be used to tune the extent of alignment of Janus particles at air-water interfaces. We proceed by analyzing the retraction of a stretched rubber band. When a cut elastic strip is stretched from its end and suddenly released, the dynamics depend on a balance of stretching and inertia. However when a rubber band is stretched, a region of high-curvature is created and it is unclear how this curvature affects the dynamics. Here, we demonstrate that during the retraction of a circular rubber band, a wavelength develops at the rear which increases in size as time progresses. Through a combination of experiments and modeling, we investigate the speed at which the back of the elastic retracts and observe a self-similar shape that depends on stretching, inertia, and bending. Finally, we study the interaction of bubbles with slippery surfaces. When a bubble comes into contact with a lubricated surface it begins to spread. How- ever, it is unknown how the surface’s film affects the spreading dynamics. Our preliminary results indicate an unexpected non-monotonic spreading response with the film’s viscosity. With a better understanding of the interaction between a bubble and a slippery surface, we can hopefully gain better insight on how slippery surfaces are so effective in battling biofoul
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