# Numerical Analysis of Load Reduction in the Gliding Process Achieved by the Bionic Swan’s Webbed-Foot Structures

## TL;DR

This study uses computational methods to analyze how swans' webbed feet reduce impact during water landing, offering insights for designing better water-entry systems in vehicles.

## Contribution

The study introduces a CFD-based analysis of swan webbed-foot gliding entry, revealing phase-specific dynamics and optimal angles for stability.

## Key findings

- The gliding water-entry process consists of two phases: stable skipping and surface gliding.
- An optimal pitch angle of 20° maximizes glide-skip stability, while angles beyond 25° or below 15° cause instability.
- Higher water-entry velocity increases impact loads and skipping frequency, while higher angles intensify load magnitude.

## Abstract

Webbed-foot gliding water entry is a characteristic water-landing strategy employed by swans and other large waterfowls, demonstrating exceptional low-impact loading and remarkable motion stability. These distinctive biomechanical features offer significant potential for informing the design of cross-medium vehicles’ (CMVs’) water-entry systems. To analyze the hydrodynamic mechanisms and flow characteristics during swan webbed-foot gliding entry, the three-dimensional bionic webbed-foot water-entry process was investigated through a computational fluid dynamics (CFD) method coupled with global motion mesh (GMM) technology, with a particular emphasis on elucidating the regulatory effects of entry parameters on dynamic performance. The results demonstrated that the gliding water-entry process can be divided into two distinct phases: stable skipping and surface gliding. During the stable skipping phase, the motion trajectory exhibits quasi-sinusoidal periodic fluctuations, accompanied by multiple water-impact events and significant load variations. In the surface-gliding phase, the kinetic energy of the bionic webbed foot progressively decreases while maintaining relatively stable load characteristics. Increasing the water-entry velocity will enhance impact loads while simultaneously increasing the skipping frequency and distance. Increasing the water-entry angle will primarily intensify the impact load magnitude while slightly reducing the skipping frequency and distance. An optimal pitch angle of 20° provides maximum glide-skip stability for the bio-inspired webbed foot, with angles exceeding 25° or below 15° leading to motion instability. This study on webbed-foot gliding entry behavior provided insights for developing novel bio-inspired entry strategies for cross-medium vehicles, while simultaneously advancing the optimization of impact-mitigation designs in gliding water-entry systems.