A biomimetic underwater vehicle, which is propelled by two undulating long-fins, is introduced in this paper. The undulating or oscillating movements of symmetrical long-fins cause the complex locomotion of biomimetic underwater vehicle. For convenience, three motion modes are proposed and considered firstly. Then an inertial unit is installed for collection of accelerations and angular velocity. The underwater vehicle's MIMO model is reduced into a SISO model by some simplifications. A sine wave function deduced from the long-fin's time-varying membrane is proposed and used as the input of the biomimetic underwater vehicle ARMA model, and velocity or angular velocity is considered as the model output. The algorithms based on recursive weighted least squares are applied for model parameter identification. Experiments carried out with a long-fin propelled underwater vehicle. The experimental results show that the proposed methods can build valid locomotion models for three motion modes efficiently.
