Propulsion experimental Research on the Structure of Swordfish’s Lunate Caudal Fin

Swordfish is the fastest fish in the world, which can reach a high speed of 110km/h. Depending on the swing of the caudal fin, swordfish gets the power of swimming. The caudal fin of the swordfish shows crescent and wide broadening which exceed the highest part of the body. The unique caudal fin of the swordfish and the way of swing are the main reasons for swimming fast. By testing and analyzing the structure of caudal fin of swordfish, it is built the parametric description of the geometric structure .R1 and R2 are radius of the two circles, and that R1＜R2, A is center distance of two circles. The two circles intersect to form the shape of crescent. This research choose the R1、R2 and A as parameters, then make a geometric shape description of crescent.The research optimizes the structure parameter of swordfish’s caudal fin by the method of experimental optimization. The experiment result shows that the smaller aspect ratio may have grater propulsion (R2 much bigger than R1, aspect ratio close to 2) when the swing frequency above the 2Hz and the increasing aspect ratio may enhance the propulsion when the swing frequency below the 2Hz.Keywords: Propulsion; Lunate Caudal Fin; Optimization; Swordfish