Research on passive deformation and hydrodynamic performance of a biomimetic cownose ray in gliding motion through fluid-structure interaction analysis

This work explores the impact of passive deformation on the hydrodynamic performance of cownose rays gliding at various angles of attack (AoA) and pectoral fin stiffness. We employ a partitioned fluid-structure coupling scheme to resolve the dynamic interaction between the fluid and structure. Specifically, the incompressible Navier-Stokes equations are solved through the finite volume method, while structural deformation is addressed via the finite element method. A co-simulation engine is utilized for communication and coordination between the fluid and structural solver. Furthermore, an implicit coupling scheme is implemented to ensure numerical stability. Our results demonstrate that passive deformation of the pectoral fin would stabilize the gliding motion with increased drag and lift but reduced pitching moment. The lift-to-drag ratio is improved slightly at any angle of attack, with the maximum increase reached at an AoA of +/- 7.5(degrees). Pectoral fin stiffness can influence passive deformation significantly, and the minimal stiffness leads to the most evident impact on gliding lift enhancement and pitching moment reduction under the parameters considered in this work. This study may provide insight into the control strategy of optimal gliding angle of attack and the selection of material properties of flexible fins in the design of high-performance biomimetic underwater gliders.