Adaptive and sensory machines : active foam and swimming rheometers
- Passive adaptation and sensing are exceptionally useful attributes, enabling robustness and redundancy in the design of functional machines. We see this for example in biological tissues and in hierarchical network infrastructures. In this dissertation we discuss two specific examples of fully-synthetic engineered systems that display these attributes of passive adaptation and sensing: active foam  and swimming rheometers . First, in the context of studying the self-assembly of programmable soft matter, we discuss the response of 2D air-liquid foam to cyclical inflation and deflation of an embedded "active" bubble. Experimental and numerical results suggest that such volume oscillations can be used to train foam to achieve local structural properties, communicate long-range mechanical signals through the CW/CCW motion of vertex trajectories, and may be used to actively probe properties of the surrounding network structure. We will also discuss the statistical influence of microstructural yielding events ("T1 transitions") within the material, and the role of disorder on the mechanical response. In the next example, we will discuss how an untethered robot is capable of self-propulsion at low Reynolds number only when submerged in an elastic fluid. Based on prior theoretical results, this robot consists of two counter-rotating rotationally-symmetric objects, and propels itself in the direction of the larger "head" object. By controlling the relative rotation rate of this device while recording motility, the robot acts as rheological sensor of the surrounding elastic fluid, with remarkable sensitivity (at strain rates < 1 Hz). We will discuss our experimental discovery of a non-inertial, viscoelastic jet structure responsible for propulsion, and the specific rheological properties that can be inferred by observation of the device. Fundamentally, these examples demonstrate how adaptive and sensory machines can be used in engineering to enable exceptional redundancy and robustness in real-world environments.  Kroo, Laurel A., Matthew Storm Bull, and Manu Prakash. "Active Foam: The Adaptive Mechanics of 2D Air-Liquid Foam under Cyclic Inflation." arXiv preprint arXiv:2204.00937 (2022).  Kroo, L. A., et al. "A freely suspended robotic swimmer propelled by viscoelastic normal stresses." Journal of Fluid Mechanics 944 (2022).
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Kroo, Laurel Anne
|Santiago, Juan G
|Degree committee member
|Santiago, Juan G
|Stanford University, Department of Mechanical Engineering
|Statement of responsibility
|Laurel A. Kroo.
|Submitted to the Department of Mechanical Engineering.
|Thesis Ph.D. Stanford University 2022.
- © 2022 by Laurel Anne Kroo
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