Dynamic coupling between ship motion and three-layer-liquid separator by using MPS (Moving Particle Simulation)
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The initial separation of mixed oil/gas and water from risers is done by wash tanks inside FPSO/FLNG hull. As vessel size increases, larger size separators/wash-tanks and storage tanks are considered. The performance of separators/wash-tank is in general affected by vessel motions and the vessel motion itself is also influenced by multi-layer-liquid sloshing motions inside wash tanks. MPS (Moving Particle Simulation) method has shown that it is adequate in predicting violent sloshing pattern and the corresponding impact loading on tank walls in case of single-phase-liquid problems. However, the application of the MPS method to multi-layer-liquid system has been very rare in the open literature. In the case of multi-phase-fluid system, a proper buoyancy model including surface tension has to be included to more accurately simulate the behavior among different-density particle members. Another important factor of multi-phase-liquid problem is a reasonable treatment of tracing multiple interfaces and imposing proper kinematic and dynamic boundary conditions at the interfaces. The newly developed MPS method for multiple liquid layers is validated through comparisons against linear potential theory (in the case when interfacial amplitudes are small) and some available experimental results. The multi-phase-liquid MPS sloshing program is also coupled in time domain with a ship-motion program to assess their interactions in a typical operational sea environment. The generation of interfacial sloshing waves depending on excitation wave period is clearly demonstrated and the internal waves are in several cases much greater than free-surface waves. Since various interfacial sloshing motions of different frequencies can be generated at the respective interfaces, the influence of large separators on vessel motion can be more complicated than the single-liquid tank. Copyright 2013 by the International Society of Offshore and Polar Engineers (ISOPE).