Fringe projection technique for the instantaneous three-dimensional shape measurement of fin

Abstract

Tail fin is an important part of the fish to produce thrust in swimming. A three-dimensional (3D) analysis is necessary to understanding the function of tail fin. A precise test method for 3D tail fin profile is critical to study the tail fin kinematics. This paper describes the 3D shape measurement of swimming fish fin by a non-contact optical method based on the fringe projection technique. Sinusoidal fringes are projected onto fish during steady swimming by a slide projector. It will produce the deformed fringe patterns containing 3D information. These time-sequence deformed fringe pattern images are captured by a high speed camera (1000 frames per second). By 2D Fourier transform, filter, inverse Fourier transform and unwrap phases in 3D phase space frame-by-frame, the instantaneous 3D shape is obtained and the continuous variety profiles of tail fin are reconstructed. This paper displays parting the profiles in a quarter of a beat cycle, the steady swimming speed with 0.5Ls^-1(where the L is fish body length). The present study provides a new method to quantify the analysis of kinematic characteristic of the tail fin during steady swimming.