Quasi-Static Continuum Model with Fluid–Structure Interaction of an Octopus-Like Soft Robotic Arm Underwater Actuated by Twisted and Coiled Artificial Muscles

This study presents a qualitative investigation into the use of twisted and coiled artificial muscles (TCAMs) for actuating and replicating the bending motion of an octopus-like soft robotic arm underwater. The “extended” Cosserat theory of rods, alongside continuum mechanics principles, is employed to develop a strain-based model for the quasi-static motion of the soft arm, incorporating fluid–structure interaction through hydrostatic and dynamic forces from fluid flow. In the proposed model, the cross-section of the arm not only undergoes rigid rotation but also deforms within its plane, a feature that aligns with the biomechanical behavior of octopus arms, where local stiffness arises from the incompressibility of tissue. TCAMs, as lightweight and low-cost actuators, offer high power-to-weight ratios and can produce tensile forces up to 12,600 times their own weight, approaching the functionality of biological muscles. To support the modeling framework, a constitutive model is also developed to describe the characteristic material behavior of the soft octopus-like arm.