|Ph.D Student||Matia Yoav|
|Subject||Dynamics of Solid-Liquid Composite Beams|
|Department||Department of Mechanical Engineering||Supervisor||Professor Amir Gat|
|Full Thesis text|
In this work we analyze the transient dynamics of solid-fluid composite structures. This is an interdisciplinary research subject, which lies on the border between theoretical fluid mechanics, soft-robotics and composite-structures. We focus on an elastic beam embedded with fluid-filled cavities as an element representing many commonly used configurations. Beam deformation both creates, and is induced by internal viscous flow, where changes to cavities' volume are balanced by a change in axial flux. As a result, pressure gradients develop in the fluid, and stresses are induced at the solid-fluid interface. These, in turn, create local moments and normal forces acting at the solid-liquid interface, deforming the surrounding solid and vice versa.
In this work we derive three models, corresponding to different physical regimes. Initially we examine the dynamic regime where the fluidic viscous-elastic time scale is significantly shorter than the solid-inertial response, rendering viscosity effects negligible. We approximate the deformation of such structures, and relate the fluid pressure and geometry of the fluidic network to a continuous deformation-field function. We present a scheme to design channel networks to generate pre-defined deformation patterns in the presence of steady state and oscillatory external forces, and put it all in context and functionality of designing dynamic soft robotics and soft actuators.
Second, we further expand on the previous configuration, and focus on the introduction of viscous flow; extending the range of actuation modes enabled via viscosity. Under assumptions of creeping flow and small deflections, we obtain a fourth-order integro-differential equation governing the time-dependent deflection field. We show how leveraging viscosity allows to extend the capabilities of beam-shaped actuators, and create inertia-like standing and moving wave solutions in configurations with negligible inertia.
Last, we generalize the examined configuration to an elastic beam embedded with a set of fluid-filled cavities, similar to a honeycomb structure, and interconnected by an array of slender tubes. The configuration of the connecting tubes is arbitrary, and each tube may connect any two cavities. Applying concepts from poroelasticity, and leveraging Cosserat rod large-deformation models, we obtain a set of three coupled transient equations relating the fluidic pressure within the cavities to the large transverse and longitudinal displacements of the beam. We show that by changing the viscous resistance of the connecting tubes we are able to modify the amplitude of oscillatory deformation modes created due to external excitations on the structure. In addition, rearranging tube configuration in a given system is shown to add an additional degree of control, and generate varying mode shapes for the same external excitation.
The results of the presented research can be applied to define the required geometric and physical properties of solid-fluid structures in order to achieve specific responses to external excitations, thus allowing to leverage viscous-elastic dynamics to create novel soft-actuators and solid-fluid composite materials with unconventional mechanical properties.
Keywords: soft-smart metamaterials, actuators, energy harvesting, soft matter, fluid dynamics, fluid structure interaction, large deformation, two way coupling, dynamic modeling