The mixed oil and gas including water and sand are extracted from well to offshore structure. This mixed fluid must be separated for subsequent processes by using wash tanks or separators. To design such a system, a proper numerical‐prediction tool for multiphase fluids is required. In this regard, a new moving particle simulation (MPS) method is developed to simulate multiliquid‐layer sloshing problems. The new MPS method for multifluid system includes extra search methods for interface particles, boundary conditions for interfaces, buoyancy‐correction model, and surface‐tension model for interface particles. The new particle interaction models are verified through comparisons with published numerical and experimental data. In particular, the multiliquid MPS method is verified against Molin et al’s (2012) experiment with three liquid layers. In case of excitation frequency close to one of the internal‐layer resonances, the internal interface motions can be much greater than top free‐surface motions. The verified multiliquid MPS program is subsequently used for more nonlinear cases including multichromatic multimodal motions with larger amplitudes, from which various nonlinear features, such as internal breaking and more particle detachment, can be observed. For the nonlinear case, the differences between with and without buoyancy‐correction and surface‐tension models are also demonstrated.

The mesh-free particle method is the latest method in the computational fluid dynamics field. It has become well-known due to its application for simulating any kind of interface deformation and fragmentation, including large disturbance on the interface. In this study, the moving particle semi-implicit (MPS) method has been developed for multi-phase to simulate mobile (erodible)-bed under violent flows such as a dam break. In order to develop the MPS method, multi-phase particle interaction models including self-buoyancy and surface tension models were employed. All of the newly adopted particle interaction models were modified by the author. When fluids collide with the soil bed, the erodible bed can be liquefied. In this regard, polyethylene oxide (PEO) solution was used as a mobile bed. The water column captured by the gate collapsed after opening the gate, and it then propagated over a mobile bed. The mobile bed has various thicknesses based on corresponding experiments. Moreover, the dam break on an inclined tank was also simulated to investigate the swash uprush problem. The maximum velocity and height of mixed flows were measured at a certain point, which aligned with the corresponding experiment. All of the simulation results were compared with those obtained from some experimental work.

For oil/gas production/processing platforms, multiple liquid layers can exist and their respective sloshing motions can also affect operational effectiveness or platform performance. To numerically simulate those problems, a new multiliquid moving particle simulation (MPS) method is developed. In particular, to better simulate the relevant physics, robust self-buoyancy model, interface searching model, and surface-tension model are developed. The developed multiliquid MPS method is validated by comparisons against experiment in which three-liquid-sloshing experiment and the corresponding linear potential theory are given. The validated multiliquid MPS program is subsequently coupled with a vessel-motion program in time domain to investigate their dynamic-coupling effects. In case of multiple liquid layers, there exists a variety of sloshing natural frequencies for respective interfaces, so the relevant physics can be much more complicated compared with the single-liquid-tank case. The simulation program can also reproduce the detailed small-scale interface phenomenon called Kelvin–Helmholtz instability. The numerical simulations also show that properly designed liquid cargo tank can also function as a beneficial antirolling device.