Through computational fluid dynamics (CFD) simulations of a model manta ray body, the hydrodynamic role of manta-like bioinspired flapping is investigated. The manta ray model motion is reconstructed from synchronized high-resolution videos of manta ray swimming. Rotation angles of the model skeletal joints are altered to scale the pitching and bending, resulting in eight models with different pectoral fin pitching and bending ratios. Simulations are performed using an in-house developed immersed boundary method-based numerical solver. Pectoral fin pitching ratio (PR) is found to have significant implications in the thrust and efficiency of the manta model. This occurs due to more optimal vortex formation and shedding caused by the lower pitching ratio. Leading edge vortexes (LEVs) formed on the bottom of the fin, a characteristic of the higher PR cases, produced parasitic low pressure that hinders thrust force. Lowering the PR reduces the influence of this vortex while another LEV that forms on the top surface of the fin strengthens it. A moderately high bending ratio (BR) can slightly reduce power consumption. Finally, by combining a moderately high BR = 0.83 with PR = 0.67, further performance improvements can be made. This enhanced understanding of manta-inspired propulsive mechanics fills a gap in our understanding of the manta-like mobuliform locomotion. This motivates a new generation of manta-inspired robots that can mimic the high speed and efficiency of their biological counterpart.

This paper numerically studies the flow dynamics of aerial undulation of a snake-like model, which is adapted from the kinematics of the flying snake (Chrysopelea) undergoing a gliding process. The model applies aerial undulation periodically in a horizontal plane where a range of angle of attack (AOA) is assigned to model the real gliding motion. The flow is simulated using an immersed-boundary-method-based incompressible flow solver. Local mesh refinement mesh blocks are implemented to ensure the grid resolutions around the moving body. Results show that the undulating body produces the maximum lift at 45° of AOA. Vortex dynamics analysis has revealed a series of vortex structures including leading-edge vortices (LEV), trailing-edge vortices, and tip vortices around the body. Changes in other key parameters including the undulation frequency and Reynolds number are also found to affect the aerodynamics of the studied snake-like model, where increasing of undulation frequency enhances vortex steadiness and increasing of Reynolds number enhances lift production due to the strengthened LEVs. This study represents the first study of both the aerodynamics of the whole body of the snake as well as its undulatory motion, providing a new basis for investigating the mechanics of elongated flexible flyers.

Environmental stressors such as hypoxia challenge the balance between individual physiological performance and the coordination required for collective behaviors like schooling. Here, we investigate how glass catfish ( Kryptopterus vitreolus ) modulate locomotor and group-level behavior across a gradient of oxygen saturation (95%–20%) while swimming steadily at a constant cruising speed. We found that tailbeat frequency decreased significantly with declining oxygen ( p < 0.0001), alongside reductions in wave speed ( p = 0.007). Tailbeat amplitude, by contrast, increased significantly under hypoxia ( p < 0.0001), and posterior segment angles showed a slight, non-significant increase, consistent with modestly greater tail bending. Despite these changes, the Strouhal number remained fairly constant, and waveform topology was conserved. School structure, including nearest-neighbor distance and distance to the center of the school, remained stable across oxygen treatments, but with significant variation across individual schools. A clear behavioral threshold was observed below 25% oxygen saturation, beyond which coordinated schooling deteriorated. These findings demonstrate that glass catfish employ internally coordinated, energetically economical kinematic adjustments to preserve group cohesion under metabolic constraint. This strategy highlights a decentralized mechanism for sustaining collective behavior near physiological limits and offers biologically-grounded insights relevant to energy-aware coordination in bioinspired swarms.

This paper presents a numerical investigation into the aerodynamic characteristics and fluid dynamics of a flying snake-like model employing vertical bending locomotion during aerial undulation in steady gliding. In addition to its typical horizontal undulation, the modeled kinematics incorporates vertical undulations and dorsal-to-ventral bending movements while in motion. Using a computational approach with an incompressible flow solver based on the immersed-boundary method, this study employs topological local mesh refinement mesh blocks to ensure the high resolution of the grid around the moving body. Initially, we applied a vertical wave undulation to a snake model undulating horizontally, investigating the effects of vertical wave amplitudes ( ψ m ). The vortex dynamics analysis unveiled alterations in leading-edge vortices formation within the midplane due to changes in the effective angle of attack resulting from vertical bending, directly influencing lift generation. Our findings highlighted peak lift production at ψ m = 2.5 ∘ and the highest lift-to-drag ratio (L/D) at ψ m = 5 ∘ , with aerodynamic performance declining beyond this threshold. Subsequently, we studied the effects of the dorsal–ventral bending amplitude ( ψ DV ), showing that the tail-up/down body posture can result in different fore-aft body interactions. Compared to the baseline configuration, the lift generation is observed to increase by 17.3% at ψ DV = 5°, while a preferable L/D is found at ψ DV = −5°. This study explains the flow dynamics associated with vertical bending and uncovers fundamental mechanisms governing body–body interaction, contributing to the enhancement of lift production and efficiency of aerial undulation in snake-inspired gliding.

During gliding, flying snakes flatten their ribs to create an airfoil-like cross-section and adopt S-shape postures, allowing upstream body segments to generate wake structures that affect the aerodynamic performance of downstream segments. This study investigates these interactions using numerical simulations of two-dimensional snake cross-sectional airfoils. By employing an immersed-boundary-method-based incompressible flow solver with tree topological local mesh refinement, various foil positions and movements were analyzed. The results show that aligning the downstream foil with the upstream foil reduces lift production by 86.5% and drag by 96.3%, leading to a 3.77-fold increase in the lift-to-drag ratio compared to a single airfoil. This improvement is attributed to the vortex–wedge interaction between the upstream vortex and the following foil’s leading edge (wedge), which enhances the gliding efficiency of the posterior body. Furthermore, integrating specific pitching motions with coordinated vortex shedding could further optimize its lift production. These findings provide valuable insights into the aerodynamics of tandem flying snake airfoils, offering guidance for configuring optimal body postures for improving gliding efficiency.