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Rapid Onset Impulsive Loading: Three Dynamical Case Studies

  • Author(s): Daily-Diamond, Christopher Albert
  • Advisor(s): O'Reilly, Oliver M
  • et al.
Abstract

In this dissertation I present research undertaken on three dynamical systems, which I

term ‘case-studies’. The most interesting dynamics in these systems were largely precipitated

by abbreviated periods where impulsive loading dominated.

The first case-study features an impulsively-loaded wave energy converter (WEC) for

which mass modulation schemes have been proposed which take advantage of the ambient

water motion. Experimental results for a pair of passively and impulsively initiated

schemes are presented and one of them is shown to be effective in increasing the energy

harvesting potential of a WEC; numerical analysis of the model also shows the potential

benefits of the mass-modulation scheme and, moreover, validates the benefits of harnessing

impulsively applied fluid pressures which are often neglected in the design of a WEC.

The second case-study examines the accidental untying of a shoelace while walking. In

this case-study, I discuss the series of events that lead to a shoelace knot becoming untied.

Slow-motion video footage and a series of experiments show the failure of the knot happens

in a matter of seconds, often without warning, and is catastrophic. Controlled experiments

show 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 final case-study concerns the ground-up development of prototyping techniques for

a soft-robot modeled after the common caterpillar. I sought to suggest an analysis path for

rapid prototyping of a SMA based, caterpillar inspired soft-robot to undergo undulatory

motion. Analysis of the kinematics and dynamics of the caterpillar are structured through

simple models which yield estimates of forces and energetics that would be extremely

difficult to determine directly, in addition to suggestions for open-loop motion patterns.

Simultaneously, simple experiments and optical tracking of SMA segments were performed

to yield properties input directly into a robust numerical solver used to simulate a prototype

soft-robot’s undulatory motion and reveal facets leading to the success or failure of its

motion.

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