Estimation and optimization of robotic fish design parameters for thrust velocity maximization

This paper proposes geometrical parameter design optimization for a novel robotic fish prototype. The developed model of the robot fish has a streamlined rigid anterior body, multi-link rear body with pectoral and dorsal fins and an oscillating lunate caudal fin. Earlier researches on fish design have focused on the relative link lengths optimization, particular fin geometries and the conventional motion parameters for its velocity maximization. In this work, a holistic design through optimization framework is presented. It is based on estimating airfoil geometries´ primary dimensions with corresponding constraints of buoyancy, physical constraints of components, their assembling as per the design rules, are imposed on the objective. NACA 4-digit series has been chosen as reference in our study which allows for symmetrical airfoil and associated relative ease in fabrication. The quasi-steady flow and fundamental airfoil theories are used to observe the hydrodynamic forces acting on the undulating links. A multi-objective optimization problem is formulated using two heuristic and two hybrid approaches. A hybrid approach of Genetic algorithm (GA) and Mini-Max algorithm is found to produce the best results. Further, a computational fluid dynamic (CFD) study for fluid-structure interaction (FSI) between fish model and surrounding fluid medium is also carried out to validate the results obtained.