Ph.D Student | Tulchinsky Arie |
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Subject | Dynamics of Thin Viscous Films Interacting with Slender Elastic Media |

Department | Department of Mechanical Engineering |

Supervisor | Professor Amir Gat |

Full Thesis text |

Deformation of an elastic medium bounded by viscous fluid transports the fluid and thus induces flow. The induced flow, in-turn, creates a pressure field which applies traction on the solid-fluid interface. This modifies the deformation-field of the elastic medium. In my doctoral studies I investigate the dynamics of a viscous fluid flowing in narrow passages bounded by elastic media.

Within the framework of the thesis we investigate four configurations. In chapter one we study the fluid-structure interaction occurring inside and around a frog’s toe pad, in the context of wet adhesion. Specifically, we focus on the relaxation dynamics of a toe pad initially compressed against a rigid, non-smooth surface. The viscous fluid, flowing from the outer region into the toe pad, yields a negative pressure-field and thus effectively creates an adhesion force. Initially, we illustrate the viscous-elastic adhesion mechanism by a simplified experimental apparatus. Next, we model the interaction of the toe pad with the fluid surrounding it and show the feasibility of the attachment mechanism.

In chapter two we investigate the transient dynamics of a lubrication film contained in a narrow gap between a rigid surface and a parallel elastic plate. The elastic plate is deformed due to an externally applied time-varying pressure-field. The analysis yields the pressure and deformation fields during and after application of external point forces. Furthermore, impact mitigation capabilities of the configuration are examined. The results reveal that order of magnitude reduction of liquid pressure compared with external pressure may be realized. In chapter three we study the steady-state oscillations of parallel elastic plates containing a thin liquid film in-between. The upper sheet is excited by a traveling pressure wave and the bottom sheet is supported by a linear spring array. Specifically, we focus on the effect of inertia (both solid and liquid) and the asymmetry of elasticity of the sheets on the response of the system.

The results exhibit the response dynamics of the configuration for a wide range of excitation parameters as well as reveal a new resonance frequency related to the interaction between parallel fluid flow and elastic transverse deformations. The results suggest fluid embedded structures may be utilized as protective surfaces and mechanical filters. In chapter four we study the heat induced dynamics and instabilities of a lubricated elastic plate due to thermal expansion effects. Heat is applied on the system creating plate deformation.

The expansion of the plate transports viscous fluid and thus creates bulk flow. In the limit of rapid heating, we examine the motion of an elastic-plated drop in transient temperature fields, and present self-similar solutions. For slower heating regimes, where liquid pressure is induced, we present series-type solutions describing deformation patterns due to application of localized heating. Finally, an instability is revealed, and an analysis is performed yielding a criterion for the stability of such configurations in the limit of small deformations.