“尼罗河魔鬼”长背鳍波动包络线的提取算法

"尼罗河魔鬼"采用长背鳍波动推进方式,属于典型的奇鳍/对鳍推进鱼类.在已有的理论模型中,细长体理论(Elongated-body theory)较为适合于分析该类游动方式的推进性能.长背鳍的波动包络线方程是细长体理论的必要参数.拍摄实验样本(MPC-I)的自由游动视频,从中选取多组平稳运动图像序列,经旋转校正、零点配准、尺度归一、小波去噪等预处理后,提取了柔性长背鳍波动推进时的顶端边缘轮廓样本曲线簇,进而给出了波动包络曲线的多项式拟合方程.实验结果表明长背鳍波动包络线提取算法是有效的,根据算法所提取的长背鳍波动包络线方程为后续的推进力及推进效率的分析奠定了基础.

A Contour-detecting Algorithm for Undulation by the Long-based Dorsal Fin of Gymnarchus Niloticus

Gymnarchus niloticus,propelled by undulations of a long-based dorsal fin,is a typical representative of median and/or paired fin(MPF) fishes.Elongated-body theory(EBT) is one of the most effective theoretical models which can be applied to analyze the swimming performance of MPF fishes.This paper proposes an algorithm to detect the contour curve of undulations by the long-based dorsal fin, and furthermore the contour function is indeed a key factor in EBT.In this study,some videos are recorded when the specimen(which we name MPC-I) is freely swimming.We preprocess each frame of several selected video segments with a series of operations including rotation-calibrating,origin-matching,scale-regularizing as well as noise-reducing.Finally,the contour curve is fitted with a polynomial expression which is determined by a cluster of preprocessed undulation curve samples.The experimental results show that this algorithm is effective, and moreover the detected contour function is a good preparation for further analyses on the dorsal fin propulsion thrust and efficiency.