As a Lagrangian mesh-free method, the moving particle semi-implicit (MPS) method can easily handle complex incompressible flow with a free surface. However, some deficiencies of the MPS method, such as inaccurate results, unphysical pressure oscillation, and particle thrust near the free surface, still need to be further resolved. Here, we propose a modified MPS method that uses the following techniques: (1) a modified MPS scheme with a split-pressure Poisson equation is proposed to reproduce hydrostatic pressure stably; (2) a new virtual particle technique is developed to ensure the symmetrical distribution of particles on the free surface; (3) a Laplacian operator that is consistent with the original gradient operator is introduced to replace the original Laplacian operator. In addition, a two-judgment technique for distinguishing free surface particles is introduced in the proposed MPS method. Four free surface flows were adopted to verify the proposed MPS method, including two hydrostatic problems, a dam-breaking problem, and a violent sloshing problem. The enhancement of accuracy and stability by these improvements was demonstrated. Moreover, the numerical results of the proposed MPS method showed good agreement with analytical solutions and experimental results.

The moving particle semi-implicit (MPS) method is employed to investigate the dynamic response of a wave energy converter (WEC) buoy subjected to dam-break flows. The buoy is connected to a hydraulic power take-off (PTO) system equipped with an accumulator, enabling it to capture wave energy. First, the MPS method is validated by comparison with experimental results, demonstrating its accuracy in simulating violent interactions between dam-break flows and the buoy. Subsequently, numerical simulations are conducted to analyze the influence of different PTO forces and buoy positions on the heave motion, fluid forces and captured power of the buoy. The results indicate that PTO force exerts a significant influence on heave motion, captured power and vertical fluid force while having a relatively minor effect on the horizontal fluid force. In addition, the maximum power that the buoy can capture increases as its distance from the wall decreases. Notably, the maximum average captured power of the buoy located near a wall can be five times higher than that of a buoy far away from the wall, indicating that a vertical wall can significantly increase the efficiency of nearshore WEC devices. These findings could provide valuable insights for the design, optimization and operation of nearshore WEC devices.