Undulation locomotion analysis of fish in cruising swimming

The locomotion of fish swimming is an important topic in the bio- and bio-inspired mechanics. The study of this locomotion provides a fundamental knowledge about how a fish interacts with ambient fluid and utilizes the flow vortex. Cruising swimming is a most common way adopted by fish in moving. In this study, we measured the undulation locomotion of fish in cruising swimming. Proper Orthogonal Decomposition is adopted to analyze the measured data. We found that in the cruising swimming, the first two proper orthogonal modes capture the major features of the total motion. Two approaching methods are given to depict the undulation locomotion approximately with only six parameters. Comparing with the traditional methods depicting the swimming of a fish, they are less complicated than directly using measured swimming data and they are more physical than using an artificial assumed swimming locomotion. The undulation locomotion analysis using Proper Orthogonal Decomposition proposed here provides a quantitative way to depict the motion and its major locomotion modes.