Peng-Nan Sun

Smoothed particle hydrodynamics (SPH) simulations of three-dimensional cavitating turbulent flows remain computationally demanding because high spatial resolution is required to resolve both cavity dynamics and turbulent structures. Since conventional adaptive particle refinement (APR) struggles with the extreme density and volume variations inherent to strong compressibility, in this work a multi-resolution SPH framework is developed by coupling APR with the volume adaptive scheme (VAS), extending APR to strongly compressible flows. Within this multi-resolution framework, the SPH cavitation model is further extended to three-dimensional simulations, achieving good computational efficiency while maintaining accuracy. Several benchmark cases, including a compressible piston problem, two-dimensional cavitating flows over a hydrofoil and a wedge, and three-dimensional cavitating flow past a sphere, are simulated to assess the accuracy, robustness, and efficiency of the method. The results show that the proposed APR-VAS SPH framework can reproduce the main features of unsteady cavitating flows while substantially reducing the particle number and computational cost compared with corresponding single-resolution simulations.

This paper presents SPHydroDRL, a mesh-free computational framework that couples quasi-Lagrangian Smoothed Particle Hydrodynamics (SPH) with Deep Reinforcement Learning (DRL) for solving Active Flow Control (AFC) problems. Built upon the previously developed SPHydro solver, the framework provides an SPH environment accelerated by graphics processing units and communicates with a DRL agent through a lightweight Python–C++ interface. Three hydrodynamic benchmark cases are considered to assess the numerical accuracy, robustness, and control performance of the coupled framework. The results demonstrate that the proposed SPH-DRL framework provides a practical particle-based route for long-duration AFC simulations involving free-surface flows and moving boundaries, while maintaining good global fluid-volume conservation.

This paper numerically investigates the vortex-induced vibration of flexible risers subjected to surge motion of floating platforms. The dynamic boundary condition associated with this degree of freedom is transformed into a superimposed flow composed of shear flow and sheared oscillatory flow. The effects of oscillation frequency and velocity ratio of the equivalent superimposed flow on riser vibration characteristics are examined across different Keulegan–Carpenter number ranges. Numerical results show that increasing the oscillation frequency of the superimposed flow strengthens the dominance of the dominant vibration mode, whereas increasing the velocity ratio enhances the contribution of higher-order modes. The vortex shedding mode at each riser section varies periodically, resulting in five distinct vortex shedding modes. Based on their evolution, mechanistic conclusions are drawn, indicating that the oscillation frequency of the superimposed flow influences the critical velocity governing transitions between high-frequency and low-frequency vortex shedding modes, while the velocity ratio has little effect on the magnitude of the critical velocity but alters its interval.