Swimming Dynamics of Bottlenose Dolphins: a Koopman Modeling Approach

Marine mammals rely on their flukes for propulsion. However, the forces generated by their foil-like flukes can not be measured directly due to the complexities of the marine environment. This study presents a data-driven modeling framework to investigate propulsive hydrodynamic forces during swimming. First, synthetic data was generated using a low-order simulation based on prior research to generate training data for model identification. The simulation models the two-dimensional translational motion (longitudinal and vertical) of the animal and approximates its fluking gait as a multi-linkage system. The propulsion force acting on the fluke is simulated using the principles of unsteady hydrodynamics and hydroelasticity. Subsequently, extended dynamic mode decomposition identifies a nonlinear model by lifting the original state-space into a higher-order nonlinear representation. The results demonstrate that the proposed method accurately estimates both the motion of the animal and the hydrodynamic forces exerted on it.