Dynamics of a flutter-excited articulated ichthyoid propulsor

A concept of an ichthyoid propulsor mimicking the undulating motion of a swimming fish is proposed and verified. The propulsor consists of an articulated fluid-conveying pipe with a triangular fin attached to its free end. A sufficiently high flow velocity in the propulsor leads to the instability of the system and the possible appearance of snake-like flutter vibrations. A dynamical model of the system is proposed. It is based on classical Benjamin’s model of the dynamics of an articulated fluid-conveying pipe and Lighthill’s elongated body theory, which quantifies hydrodynamic forces generated by the swimming fish. Parameters of the system for which the propulsor is subject to dynamic loss of stability, leading to the appearance of periodic flutter vibrations, are identified. Methods of bifurcation analysis, supported by numerical simulations, prove that the system can undergo a supercritical Hopf bifurcation. This soft self-excitation yields a stable limit cycle of the system, for which the thrust and lateral forces generated by the propulsor are calculated. It is shown that the mean value of the thrust is positive for a range of swimming speeds. The performance of the propulsor is assessed in relation to the swimming speed. The research may broaden knowledge about articulated pipes conveying fluid and support possible applications of the proposed propulsor.