A unified SPH framework for shell-related interactions

A unified Smoothed Particle Hydrodynamics (SPH) framework is proposed to simulate interaction dynamics involving thin shells modeled by a reduced-dimensional, single-layer particle discretization, as opposed to full-dimensional SPH solids. The framework encompasses one-sided fluid-shell interactions, with the fluid present on only one side of the shell, as well as solid-shell, shell-shell, and shell-self interactions The study introduces a novel concept of imaginary shell contact particles, generated by projecting real shell particles along the local normal direction within the cut-off radius of the fluid particle, thereby mapping this reduced-dimensional shell model into a full-dimensional representation. With the volume of the imaginary particles defined based on the local shell curvature, the projection preserves kernel completeness for fluid-shell interactions while leaving the fluid-structure interaction (FSI) dynamics unchanged, such that the fluid-shell coupling algorithm is the same as in standard fluid-solid coupling. In addition, a particle-to-particle contact model for solid-solid interactions is developed by analogy to fluid dynamics: a contact density is computed using a fluid-style density initialization, and the resulting contact forces follow a momentum-equation-inspired formulation. Combined with the projection strategy, this contact formulation is directly extended to efficiently handle shell-related contact problems. The proposed method is validated using a series of benchmark tests, demonstrating stable and accurate performance across diverse interaction scenarios.