Hydrodynamic model of the beaver-like bendable webbed foot and paddling characteristics under different flow velocities

Abstract

Bionic robots usually move forward in water with the swinging or paddling propulsion. Amphibious robots generally use webbed feet to paddle forward. Thus, the webbed foot is a key part to propel the body and numerously has multiple joints. The flippers interact with water to generate propulsive forces in propulsion phase, while the resistance is generated during the recovery phase. Therefore, the research on hydrodynamics of the webbed foot contributes to reveal the mechanism of the interaction between the paddling webbed foot and water and improve the paddling ability. At present, the feet of amphibious robots mostly adopt non-bending structure, which have great resistance in the retracting stage. At the same time, the existing hydrodynamic model does not take into account the changes in the flow velocity caused by the paddling, which results in the low performance of the bionic flippers and the inaccurate calculation of the hydrodynamic theory. In addition, at present there is no specific standard to measure the paddling ability of flippers, so the paddling performance cannot be accurately evaluated.In this paper, the beaver is used as a bionic object, and a platform of the beaver-like bendable webbed foot was constructed through the analysis of the structure and motion trajectories of beaver's flexible webbed foot. A hydrodynamic model of the beaver-like bendable webbed foot was established. Then three parameters, namely the paddling force factor, maximum flow velocity and compound paddling force factor were proposed as indicators to quantify the paddling performance of beaver-like webbed foot. Through the theoretical calculation and computational fluid dynamics simulation, the results verify that the proposed hydrodynamic calculation model is more accurate compared with the existing methods in different paddling trajectories of the beaver-like webbed foot under various flow velocities. Through hydrodynamic simulations of non-bending and bendable webbed foot under different flow velocities, it is found that the bendable webbed foot can effectively reduce the resistance of webbed foot in the recovery stage. Different trajectories and bending degrees of the webbed foot have different effects on the resistance of paddling. The webbed foot's paddling performance is quantitatively analyzed and clearly evaluated by calculating the paddling force factor, maximum flow velocity and compound paddling force factor under six trajectories of beaver-like webbed foot. It provides theoretical support for the trajectory planning of the webbed foot. On this basis, an improved motion trajectory is proposed by adding a pause process after the paddling propulsion stage of the beaver-like webbed foot, which can reduce the resistance generated by the water flow and improve the paddling performance. The hydrodynamic modeling of the beaver-like webbed foot and the study of the paddling characteristics under different flow velocities can provide a new method for the hydrodynamic research of underwater webbed bionic robots, and offer a quantifiable standard for the analysis of the paddling performance of the webbed foot, further promote the development of underwater bionic robot in hydrodynamic theory and motion performance study.