Studying the influence of moonpool on ship resistance to find effective measures to reduce the resistance has become one of the focuses of researchers. In this study, numerical simulations have been made for models with scale ratio λ=1:30 and λ=1:1 with and without moonpool by using a RANS approach. The influence of moonpool on ship resistance and the characteristics of resistance components with and without moonpool are discussed. The resistance predictions for model with scale ratio λ=1:1 based on different extrapolation methods and the results of CFD simulation for model with scale ratio λ=1:1 are compared, and the scale effect of the added resistance of moonpool is analyzed.
In order to meet the needs of underwater drilling operations and ensure the safety of operating equipment and operators, the moonpool structure is often arranged in the middle of the drilling ship, which vertically runs through the main body of the structure, and there is a free liquid surface. At the same time, the water inside the moonpool is connected with the outside sea water. During the movement of the drilling ship, to some extent, the hydrodynamic performance of it will be affected by the interaction of external and internal fluid. At present, many scholars at home and abroad have carried out many researches on moonpool, including the influence of the moonpool on the hull resistance and motion performance, the analysis of the hydrodynamic performance of the fluid in the moonpool and so on.
Many scholars have carried out researches to study the characteristics of the moonpool and analyze reasons for increasing resistance on ship affected by the moonpool. Aalbers et al. (1984) investigated the hydrodynamics of the moonpool and established the equations of motion of the fluid inside the moonpool in waves. Faltinsen (1993) studied the piston motion characteristics of the fluid in the two-dimensional moonpool, and obtained the natural period of the piston motion of the fluid in the moonpool. Cotteleer (2000) did two series of moonpool model tests at the Delft Ship Hydrodynamics Laboratory to study the oscillation pattern of the water in the moonpool and accumulated valuable experimental data. Hammargren et al. (2012) performed numerical simulations of the two-dimensional moonpool, analyzed the flow field characteristics, and carried out a feasibility study of three-dimensional moonpool resistance prediction based on the two-dimensional moonpool resistance. Liu et al. (2014) used the model test and the CFD method to study the resistance characteristics of the deep-water drilling ship with the moonpool. Huang et al. (2016) adopted FINE/Marine to calculate the resistance of the drilling ship when the moonpool was closed and opened at different speeds, then compared with the model test results to study the additional resistance of the moonpool. Yan et al. (2017) used CFD method, taking a salvage ship as the research object, to carry out the numerical simulation of ships with or without moonpools, calculate the increase in resistance due to moonpools, and study changes in wave making characteristics.