ANSYS Simulation of Loads Experienced by the Peduncle of a Design of Robotic Fish

Aims: This article aims at simulating the forces and dynamic load that the peduncle of a robotic fish using vulcanized natural rubber for its joint and plywood for its tail fin will experience.
Methodology: Using standard strength of material equations and constitutive equation that fits the selected natural rubber, the loads that will be encountered in a water with density 990kg/m3 were calculated. The result was then used in ANSYS multiphysics environment to setup the simulation of the response of the peduncle to the calculated loads. Autodesk Inventor 7 was used for the geometrical drawings and calculations such as area and centroid of the non standard shape. Furthermore, the Payne effect for the rubber joint was found experimentally as its result will guide in the threshold of tail oscillation frequency allowed.
Results: von Mises stress within the components of the peduncle due to the drag load was found to be 0.03kN/m2 to 4.64kN/m2 for the rubber and 0.03kN/m2 to 41.48kN/m2 for the plywood fin. Stress experienced by the peduncle under its own weight shows that for the rubber component, the maximum von Mises stress experienced by the rubber is 4.9kN/m2 and for the plywood material, it is 1.087kN/m2. Test for warping/ bending of the peduncle shows a straight isoline pattern. Tensile stress within the epoxy bonded joints shows a uniform bond pattern. The dynamic torque experienced by the peduncle increases with frequency of oscillation and even more rapidly as the angle of swing increases though at a fixed ratio to each other. Frequency induced softening (Payne effect) shows that the rubber will become soft as the frequency reaches 25Hz.
Conclusion: The use of plywood material for the fin and vulcanized natural rubber for the joint and using epoxy glue for the designed peduncle of the robotic fish will be capable of withstanding the stresses that will be developed in real life scenario.