毕业生知识库

水空跨介质航行器兼具水下潜行、空中飞行以及双向介质跨越等多种运动模式，突破了传统单介质无人系统作业限制，有效增强了其多环境适应能力，一直备受研究人员的关注。其中，水–空介质跨越是制约其发展的关键技术瓶颈。自然界中的水鸟、鱼类等为了觅食或避敌，进化出了优异的跨域运动能力，为研究跨介质航行器推进机理、结构设计等关键技术提供了仿生范例。生物鱼类，尤其是飞鱼，具备高速、高机动的水下运动能力和卓越的水空跨域运动能力。因此，本文以实现“游得更快”、“跃得更高”、“功能更强”为目标，围绕仿鱼摆尾式水下高速推进机理、水空跨域运动控制以及跨介质航行器设计等方面开展研究，主要内容如下：

一、针对柔性关节仿生机器鱼，提出了一种刚柔耦合的动力学建模方法，采用理论与实验相结合的方法探究了水下仿鱼柔性波动推进机制。首先，受鱼类柔性尾柄结构启发，提出了面向多关节仿生机器鱼的柔性被动关节设计方案。其次，基于Lagrange方法和流体动力学理论，提出了面向刚柔耦合机器鱼的建模方法，并采用融合数据驱动特性的参数辨识理论，解决了复杂外形结构下水动力参数难以确定的问题，实验验证了所构建模型的有效性。最后，探究了多关节机器鱼运动控制参数与柔性关节刚度对水下推进性能的影响，验证了柔性推进机制对提升机器鱼运动性能的有效性。

二、针对仿鱼高速游动问题，提出了基于高频摆动和柔性机制的仿生机器鱼系统设计方案，实现了其无缆线、爆发式的水下高速游动。首先，遵循小型化、轻量化准则，设计了胸鳍机构、高功率密度驱动系统、高效传动机构以及柔性尾关节等关键模块，搭建了机械系统和软硬件系统，完成了机器鱼样机的研制。其次，基于搭建的实验测试平台，完成了样机性能测试，实现了3.8倍体长每秒（Body Length Per Second，BL/s）的高速游动和439°/s的高机动俯仰运动，表明了柔性关节在高频驱动下对推进性能提升的有效性。最后，基于动力学模型探究了刚、柔关节下尾鳍推进力与速度、攻角等关键参量的变化规律，并进一步阐释了仿生机器鱼的高速游动机理，为高性能水下仿生推进系统设计与性能优化提供了重要参考。

三、针对仿鱼摆尾式跨介质运动，分别提出了机器鱼跨介质运动控制策略和推进性能优化方案。首先，通过简化流体动力学分析，构建了机器鱼竖直跃水运动模型，分析了速度、体长等关键参数对跨介质运动性能的影响。其次，提出了面向仿生机器鱼的自主跨介质运动控制策略，实现了仿鱼摆尾式竖直跃水运动，完成了跨介质仿生机器鱼设计的关键技术验证。再次，进一步开展了机器鱼驱动系统和结构参数的改进设计，研发了第二代仿生机器鱼样机。最后，实验探究了关节刚度在高频摆动下对机器鱼推进性能的影响，实现了机器鱼7.1 BL/s的游动速度和0.23 m的水空跨域高度。

四、以飞鱼为仿生对象，提出了一种具有变结构胸鳍的跨介质仿生机器飞鱼系统设计方案及其空中滑翔运动优化方法。首先，受启发于飞鱼翼鳍的双介质航行兼容性结构，提出了一种变结构胸鳍设计方案，通过整合爆发式水下仿鱼推进系统，完成了跨介质机器飞鱼游飞一体化设计与样机研制，实现了“鱼跃–展翼”式水空跨域运动。其次，针对基于可变结构胸鳍的滑翔运动，采用牛顿–欧拉建模方法和升阻力模型，构建了仿生机器飞鱼滑翔动力学模型，分析了其出水速度和出射角等关键参数对滑翔运动性能的影响。最后，构建了滑翔运动优化问题，提出了基于深度强化学习的滑翔距离优化控制策略，实现了基于变结构胸鳍的滑翔距离提升，仿真验证了所提方法的有效性。

本文探究了机器鱼柔性波动推进和高速游动机制，并搭建了样机，实现了机器鱼高速游动；在此基础上，开展了水空跨介质运动控制与性能优化研究，验证了仿鱼水空跨域运动可行性，实现了跨域高度提升；最后，为拓展机器鱼应用范围，研制出基于变结构胸鳍的跨介质机器飞鱼，完成了飞鱼式跨域运动的实验验证和基于模型仿真的滑翔性能优化控制。本文研究成果可为高性能水下仿生机器人与水空跨介质航行器的系统设计和性能优化提供理论基础和技术支撑。

The water-air cross-domain vehicle possesses the multimodal locomotion capabilities, such as underwater diving, air navigation, bidirectional medium crossing, and so on, which breaks through the operating limitations of traditional single-medium unmanned systems and enhances its adaptability in various environment effectively. Therefore, the cross-domain vehicle has been attracting the attention of researchers. Among these locomotion, the transition from water to air is the key technical bottleneck restricting its development. In nature, aquatic birds, fish, etc., have evolved excellent cross-domain capabilities for foraging or escaping from predators, which provide bionic paradigms for the key technologies research of cross-domain vehicle in propulsion mechanism, mechanical design, etc. Biological fish, especially flying fish, have excellent locomotion capabilities in high-speed, high-maneuvers swimming and agile water-air crossing. Therefore, with the goal of pursuing “swimming faster”, “leaping higher”, and “more functional”, this dissertation mainly focuses on the mechanism of underwater high-speed swimming, the control of cross-domain locomotion, and the design of a novel cross-domain vehicle. The technical contributions as summarized as follows:

First, aiming at the robot fish with compliant joints, a dynamic modeling method with rigid-flexible coupling is proposed, and the undulation propulsion mechanism of flexible structures is explored by combining theory and experiment. Inspired from the flexible tail of fish, a design scheme of compliant passive joint is proposed. A dynamic model with Lagrange method and hydrodynamics theory is established for a rigid-flexible coupling robotic fish. A parameter identification method with data-driven features is employed to overcome the difficulty in acquisition of hydrodynamic parameters of robotic fish with irregular geometric profiles. Extensive experiments have demonstrated the effectiveness of the proposed model. The effects of locomotion control parameters and compliant joint's stiffness on underwater propulsion performance of a multi-joint robotic fish are explored and the results validate the significance of flexible propulsion mechanism in swimming performance improvement.

Second, a design scheme of robotic fish with the combination of high-frequency oscillation and compliant passive mechanism is proposed, which ensures the untethered, explosive propulsion with high-speed swimming. Following the design principles of miniaturization and light weight, some key modules including pectoral fins, high-power-density actuation system, high-efficiency transmission mechanism, and compliant joint are designed. Both the mechanical system and control system are built, and the prototype of robotic fish is developed. The propulsion performance is tested, and the robotic fish achieves a high swimming speed of 3.8 body length per second (BL/s) and excellent pitch maneuvers with an average angular velocity of 439°/s, which verifies the effectiveness of compliant joint in the performance improvement under high-frequency oscillation. The variation of caudal fin's thrust with some key parameters, such as speed and angle of attack is explored with the dynamic model, and the high-speed swimming mechanism of robotic fish is further explained, which provides some significant insights into the design and performance optimization of underwater bionic propulsion system with high performance.

Third, in order to achieve the fish-like cross-domain motion, both a control strategy and a performance optimization scheme are proposed. The dynamic model of vertical leaping motion is constructed with simplified hydrodynamics and the influences of speed and body length on the leaping performance are analyzed. An autonomous cross-domain motion control strategy for a robotic fish is proposed, which helps realize the vertical leaping motion with fish-like propulsion. The results verify some key technologies of cross-domain system design. A second-generation robotic fish with the improved design in actuation system and structure parameters is developed and the effects of compliant joint's stiffness on swimming performance under high-frequency oscillation are explored via experiments. Finally, the robotic fish realizes a high swimming speed of 7.1 BL/s and a leaping height of 0.23 m.

Fourth, a design scheme of robotic flying fish with morphing structure of pectoral fins and an optimization method of aerial gliding motion are proposed. Inspired by the compatibility structure of flying fish's wing-like fins in the dual-media navigation, a pair of morphing pectoral fins is designed. By combining the robotic fish system with explosive propulsion, the design scheme of a cross-domain robotic flying fish is proposed, and the prototype is also developed. In addition, the "fish-like leaping and spread wings" motion is realized. The Newton-Euler method and the Lift-Drag model are used to establish the dynamic model of gliding motion with the morphing pectoral fins, and the influences of velocity and shooting angle on the gliding performance are analyzed. With regarding to the optimization problem of gliding motion, a control strategy with deep reinforcement learning method is proposed and the gliding distance is optimized with the control of morphing pectoral fins, which validates the effectiveness of proposed method.

This dissertation explores mechanisms of flexible undulation propulsion and high-speed swimming. A prototype of robotic fish is built and achieves high-speed swimming motion. Based on this, the control and performance optimization of water-air cross-domain locomotion are investigated, which validate the feasibility of fish-like cross-domain locomotion and realize the improvement of cross-domain height. Finally, for expanding the scope of applications, the robotic flying fish with morphing pectoral fins is developed and completes the demonstration of the flying fish-like cross-domain locomotion, as well as the gliding optimization control with dynamic model. The research results can provide theoretical foundation and technical support for the system design and performance optimization of high-performance underwater bionic robots and water-air cross-domain vehicles.