The stiffness of flapping wings significantly influences the aerodynamic characteristics and structural response of insects in forward flight. While numerous studies have focused on the fluid-structure interaction of small insect wings, research on butterflies, characterized by large wing areas and low aspect ratios, remains relatively scarce. To investigate the effects of different flexibility distributions on the fluid-structure interaction characteristics of butterfly-like flapping wings in forward flight, a geometric model and kinematic equations were established based on the morphology and motion patterns of Chilasa clytia. A fluid-structure interaction solver combining the lattice Boltzmann method (LBM) and the finite element method (FEM) was developed and validated with benchmark cases. The developed method was then employed to systematically compare the aerodynamic performance and structural responses among isotropic flexible, anisotropic flexible, and rigid butterfly wings during flapping. The results indicate that the isotropic flexible wing exhibits significantly enhanced flight performance compared to the anisotropic and rigid wings. The flapping of the isotropic flexible wing generates more complex vortex structures, including the wingtip secondary flow vortex (WSFV) and the hindwing tip vortex (HTV). These vortices create an additional low-pressure region, thereby improving the aerodynamic performance. This study provides new insights into the vortex dynamics associated with lift enhancement mechanisms in flapping flight and offers valuable references for the design of novel bio-inspired micro flapping-wing aerial vehicles.

This study presents a Fluid-Structure Interaction (FSI) model to analyze the water landing characteristics of a reentry capsule equipped with airbag cushioning. The model employs the Arbitrary Lagrangian-Eulerian (ALE) method to simulate the capsule’s impact with water, while the control volume method is used to model the airbag cushioning process. Additionally, both regular and irregular heading waves are incorporated to simulate the landing dynamics of the capsule-airbag system under various sea conditions. The developed FSI model is utilized to investigate the effects of initial velocity, attitude angle, and wave phase on the water landing characteristics of the capsule-airbag system under calm water, regular and irregular wave conditions. Key parameters, such as the impact force on the capsule, as well as the pressure, mass flow rate, and stress distribution within the airbags, are analyzed. The insights gained from this study provide valuable guidance for minimizing damage to personnel and equipment during maritime recovery operations.

The inflation process of a parachute involves complex fluid-structure interaction (FSI) phenomena. The immersed boundary (IB) method, as a boundary non-conforming approach, is suitable for addressing such nonlinear large-deformation FSI problems. By integrating the sharp-interface IB method proposed by Mittal et al. with large eddy simulation (LES), the flow around a parachute at medium to high Reynolds numbers (Re) was simulated. On this basis, a nonlinear finite element method was incorporated to develop an FSI approach based on the dynamic Vreman subgrid-scale (Vreman SGS) model, which was suitable for complex geometries and non-uniform turbulence, to simulate the parachute inflation process. Finally, the accuracy of the developed LES/IB method was validated by a classic cylinder flow case (Re = 3900). The results demonstrate that the LES/IB method achieves good agreement with direct numerical simulation (DNS), LES, and experimental data in terms of the mean drag coefficient ( ${\overline{C}}_D$), mean base pressure coefficient at the rear stagnation point ( $-{\overline{C}}_{p,\mathrm{b}}$), and Strouhal number (St), with errors all below 8%. Furthermore, the developed Vreman SGS model was employed to analyze the aerodynamic performance and structural response during the inflation of typical round and cruciform parachutes, and the results were compared with Smagorinsky SGS model. During the breathing phase of parachute inflation, the results of the drag coefficient and projected area calculated by both methods show good agreement, with relative errors within 5%, thereby validating the reliability of the proposed FSI method.

In order to study the ability of the harbor seal whisker system to precisely perceive and identify the wakes of objects, the hydrodynamic characteristics of the whisker in the wake of different objects are analyzed: in this paper, a geometric model of seal whisker was developed based on a general geometric shape parameter equation. Subsequently, numerical simulations were conducted for the whisker model exposed to the wakes of cylindrical, square, and diamond-shaped objects at a Reynolds number of 300. The vortex-induced vibration characteristics of the whisker model and the associated flow field structures are studied in depth, focusing on the dynamic responses of the model under different wakes. The results demonstrate that the primary frequency of the cross-flow vibration of the whisker model is consistent with the vortex shedding frequency of the upstream obstacle, irrespective of the wake type. Furthermore, there are notable disparities among different wakes regarding the flow patterns between the upstream object and the downstream whisker model and the vibration features of the latter, underscoring the intricate mechanism of the harbor seal whisker to perceive and identify objects according to different wake properties.