Bio-inspired forward and backward swimming gaits resulting from fluid-structure interactions

Biological undulatory swimmers display a wide range of gaits and are adept at swimming in different directions. This study explores the impact of passive dynamics as a result of fluid-structure interaction on the gaits of a model swimmer through computational simulations. Inspired by slender-bodied natural aquatic swimmers, the model consists of a flexible body and a rigid head. Systematically varying body stiffness and head pitching, the research replicates various swimming patterns observed in nature (both forward and backward). Optimal forward gaits, akin to anguilliforms and carangiforms, result from low to high bending rigidity and small pitching amplitudes. Conversely, low bending rigidity with high pitching amplitude produces backward swimming (tail-first), similar to mosquito larvae, exhibiting unique flow-field features and generating backward propulsion forces. The study underscores the significant role of passive dynamics in undulatory swimming and the potential for diverse gait generation through tailored structural and kinematic design in bio-inspired devices.

Methods
Data is collected by simulation using an in-house fluid-structure interaction solver. The raw data from the simulations are further processed using MATLAB. All the details about the script file are mentioned in the respective folders.

生物摆动式游泳生物展现出丰富多样的游动步态，且能够灵活实现多方向游动。本研究通过计算仿真手段，探究了流固耦合（fluid-structure interaction）产生的被动动力学特性对模型游动生物步态的影响。
本研究受细长体型自然水生游泳生物的启发，所构建的模型由柔性躯体与刚性头部组成。通过系统性调节躯体刚度与头部俯仰运动，本研究复现了自然界中观测到的多种游动模式（包括正向与反向游动）。
对应从中到高的弯曲刚度与较小的头部俯仰幅值时，可得到类似鳗形游动和鲹形游动的最优正向步态。反之，当弯曲刚度较低且头部俯仰幅值较高时，则会产生尾先行的反向游动，该模式类似蚊幼虫游动，展现出独特的流场特征并可产生向后的推进力。本研究强调了被动动力学在摆动式游动中的关键作用，以及通过定制化结构与运动学设计在仿生装置中实现多样化步态生成的潜力。

研究方法
本研究通过自研流固耦合求解器开展仿真以采集数据。仿真所得的原始数据将通过MATLAB进行后续处理。脚本文件的全部细节均在对应文件夹中予以说明。