It is well known that tuna fish in the ocean can dynamically morph their median fins to achieve optimal hydrodynamic performance, e.g. linear acceleration and maneuverability. In this study, based on the previous studies about the median fin's hydrodynamic effects focusing on tethered conditions, we continue to explore the hydrodynamic function of tuna morphing dorsal fin in free swimming conditions for better approaching real-life situations.Here, we developed a tuna-inspired robotic fish platform that can swim independently in three dimensions, equipped with a biomimetic morphing dorsal fin magnetically attached to the robotic fish. Based on the free-swimming robotic fish platform, we investigated how the erected dorsal fin affects the speed, cost of transport (COT), and robotic fish's yaw angle at different frequencies and amplitudes. The erected dorsal fin plays a positive role in improving the yaw stability of robotic fish. However, it shows little influence on the speed and COT in our test. This remains to be further investigated in the future.

翻译：众所周知，海洋中的金枪鱼能够动态变形其正中鳍以实现最佳的流体动力学性能，例如线性加速和机动性。本研究基于以往主要聚焦于系泊条件下正中鳍流体动力学效应的研究成果，进一步探索金枪鱼变形背鳍在更贴近现实情境的自由游泳状态下的流体动力学功能。我们开发了一种能独立进行三维游动的金枪鱼仿生机器人平台，该平台配备通过磁吸方式固定的仿生变形背鳍。基于自由游泳机器人平台，我们研究了在不同频率和振幅下，竖立背鳍对游速、运输成本（COT）以及机器人偏航角的影响。实验表明，竖立背鳍对提升机器人的偏航稳定性具有积极作用，但在测试中对游速和运输成本的影响较小。这一现象有待未来进一步研究。