In this study, the dynamics of the symmetric oscillation and turning characteristics of a flexible fin underwater robot propelled by two fins were studied. First, a three-dimensional model of a robot was established using three-dimensional software. Then, a fluid simulation experiment was conducted and a dynamic model of a flexible fin was established. The deformation of the flexible fin during symmetric undulations was studied. A motion equation for the wave track of the outer edge of the fin surface was also established. This motion equation was simulated and verified. Finally, an experimental prototype was fabricated to verify the simulation results. The results show that if the robot fish oscillates symmetrically using bilateral flexible pectoral fins, it can stay suspended, float vertically, or dive in the water. Its average turning speed can reach 0.8 rad/s. Because a turn made by the robot fish is only driven by its pectoral fins, it can turn in situ in this case. The results show that the flexible fin underwater robot provides more abundant turning methods, better maneuverability, and higher turning efficiency. This research into the motion of the robot body for different wave parameters when the two fins move together provides a theoretical basis for the cooperative motion of two fins.

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Polarization rotation of a probe pulse by the target is observed with the Faraday rotation method in the interaction of an intense laser pulse with a solid target. The rotation of the polarization plane of the probe pulse may result from a combined action of fused silica and diffused electrons. After the irradiation of the main pulse, the rotation angle changed significantly and lasted ∼2 ps. These phenomena may imply a persistent magnetic field inside the target. An analytical model is developed to explain the experimental observation. The model indicates that a strong toroidal magnetic field is induced by an energetic electron beam. Meanwhile, an ionization channel is observed in the shadowgraph and extends at the speed of light after the irradiation of the main beam. The formation of this ionization channel is complex, and a simple explanation is given.

In this research, the sinusoidal actuation of a flexible fin for median and/or paired fin propulsion is studied. A prototype of an underwater robot is built, and the computer-aided engineering simulation method is used for the transmission system of the flexible fin. The fin ray at the end of the trajectory and the crankshaft drive the parameters as a function of the fin ray output parameters. Given the fin and the fin surface motion for the coupled simulation analysis, the flexible fin surface and the fin sinusoidal oscillation are studied. The deformation of the fin surface is established outside the edge wave trajectory equation of motion. The equations of motion are verified by simulation. The single fin wave model is solved with the computational fluid dynamics method, and the hydrodynamic performance of the fin surface is obtained. Using the dynamic mesh technique, the complex large fluctuation motion of the fin surface is solved. With different amplitudes and periods of the fin wave as the input parameters, a simulation of the fin wave propulsion is conducted, and the relationship between the fin wave propulsion force and the fin wave resistance is calculated. The correctness of the simulation results of the sinusoidal fixed wave of the fin surface is verified by a fin wave ink experiment.