Abstract: Soft robots, as a modern gateway to unlocking the mysteries of underwater realms, present new complexities. Modeling their behavior when in contact with external forces, whether point-based or distributed, is a primary challenge due to the nature of soft bodies. To obtain a holistic view of the system’s behavior determining the governing dynamics is deemed necessary. This paper proposes a new technique to simulate the dynamic lateral undulation of a soft robotic fish with a cable-driven soft tail. By integrating the rigid finite element method with rigid-body robotics, the model represents the undulation of a finite number of rigid elements connected through a set of torsional spring and damper. Instead of directly modeling external forces, we substitute equivalent joint torques into the system dynamics, allowing us to consider external effects without complicating the model. The resulting model yields valuable insights into the system’s behavior, including propulsive and lateral forces. A comparison with experimental results shows strong agreement, with a tip amplitude error of 10% at 0.8 Hz, 5.25% at 1.6 Hz and 2.54% at 2.2 Hz flapping frequency. These findings illuminate the influence of lateral undulation on the overall dynamics, paving the way for fully autonomous robotic fish.

Key words: Dynamic modeling, Soft robotic fish, Lateral motion prediction, Rigid finite element method, Propulsiveforce, Lateral force')">Dynamic modeling, Soft robotic fish, Lateral motion prediction, Rigid finite element method, Propulsiveforce, Lateral force