A unified three-dimensional smoothed particle hydrodynamics framework with an improved boundary treatment for fluid-flexible-structure interaction: Application to kite dynamics

A self-developed, fully Lagrangian three-dimensional Smoothed Particle Hydrodynamics (SPH) model is presented for fluid-flexible-structure interaction (FFSI) involving thin flexible structures, with both the fluid and structural governing equations solved consistently within a unified SPH framework. The shell model with single-layer particles is used to simulate the thin flexible structure. To resolve the support-domain truncation issue associated with the single-layer boundary while preserving the physical discontinuity across the interface, an improved boundary treatment strategy is used, consisting of a normal-flux correction to eliminate truncation-induced errors and an improved partitioned computational framework to maintain the physical discontinuity, thereby ensuring an accurate SPH approximation near the interface. To address the intensive computational demands of three-dimensional simulations, a dual-Graphics Processing Unit (GPU) parallelization strategy is implemented via Message Passing Interface. The dual-GPU implementation achieves approximately 70% performance improvement compared to the single-GPU setup. The proposed SPH method for three-dimensional FFSI problems is validated through hydrostatic and flag flutter simulations, demonstrating the accuracy and numerical stability of the proposed method. The flow around the three-dimensional kite is simulated by the proposed method to study its fluid–structure interaction. Results reveal that appropriately increasing the ribbon tail length can suppress the vibrations of the kite body by up to 62% through vortex attenuation. However, excessive tail length may induce complex deformations and asymmetrical motion.