The paper describes a bioinspired propulsion system for a robotic fish model. The system is based on a combination of an elastic chord with a tail fin fixed on it. The tail fin is connected to a servomotor by two symmetric movable thrusts simulating muscle contractions. The propulsion system provides the oscillatory tail movement with controllable amplitude and frequency. Tail oscillations translate into the movement of the robotic fish implementing the thunniform principle of locomotion. The shape of the body and the tail fin of the robotic fish were designed using a computational model simulating a virtual body in an aquatic medium. A prototype of a robotic fish was constructed and tested in experimental conditions. Dependencies of fish velocity on the dynamic characteristics of tail oscillations were analyzed. In particular, it was found that the robot’s speed increased as the frequency of tail fin oscillations grew. We also found that for fixed frequencies, an increase in the oscillation amplitude lead to an increase in the swimming speed only up to a certain threshold. Further growth of the oscillation amplitude lead to a weak increase in speed at higher energy costs.
The article describes a method for active reduction of magnetic noise generated by a magnetic field that exists in the airgap of an induction motor. In this article a mathematical model of the process of magnetic noise excitation in a stators is presented. The model take into account that magnetic field waves, radial magnetic force waves (so-called Maxwell forces) and stator deformation waves (magnetic noise) are characterized by their own values of amplitude, mode number, frequency and phase shift. By comparing the equations for calculating the stator mechanical impedance, the amplitude of the radial magnetic force and the simplified magnetic noise equation, the relationships between these variables were established. The method of active reduction of magnetic noise proposed in the article is based on the use of these relationships. The novelty of the proposed method lies in the use of the filtered spectrum of output signal of the accelerometer installed on the stator to determine the most intense harmonics of the magnetic field in the motor airgap in order to further suppress them. The compensation signal generated by a special device adapts not only in frequency, but also in phase and amplitude of each vibration-disturbing harmonic.
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