A fluid-structure interaction study of soft robotic swimmer using a fictitious domain/active-strain method

Biological swimmers often exhibit rich physics due to the hydrodynamic coupling between the fluid flow and the immersed deforming body. Complexity and nonlinearity of their behaviors have imposed significant challenges in design and analysis of robots that mimick biological swimming motions. Inspired by the recent experimental studies of soft robotic swimmers, we develop a fictitious domain/active strain method to numerically study the swimming motion of thin, light-weight robots composed of smart materials that can actively undergo reversible large deformations (e.g., liquid crystal elastomer). We assume the elastic material to be neo-Hookean, and behave like an artificial "muscle" which, when stimulated, generates a principal stretch of contraction. We adopt an active strain approach to impose contractive strains to drive elastic deformation following a multiplicative decomposition of the deformation gradient tensor. The hydrodynamic coupling between the fluid and the solid is then resolved by using the fictitious domain method where the induced flow field is virtually extended into the solid domain. Pseudo body forces are employed to enforce the interior fictitious fluid motion to be the same as the solid structure dynamics. Using the fictitious domain/active strain method, we perform a series of numerical explorations for soft robotic swimmers with both 2D and 3D geometries. We demonstrate that these robot prototypes can effectively perform undulatory swimming and jet-propulsion when active strains are appropriately distributed on the elastica. (C) 2018 Elsevier Inc. All rights reserved.