Research On Flow Patten In Moonpool Of Drill Ship And Numerical Prediction Method And Regression Of Its Resistance

Moonpools mainly setting in the midship of drill ships are necessary holes for drilling operation, but the large holes have a bad inpact on vessels’ resistance performance. However, internal research on additional resistance due to moonpool is still in progress. Therefore, by combining numerical and experimental method, research on resistance performance of drill ships is carried out in this paper, with the support from national research project “Research on key technology in design and construction of 3000 m deepwater drillship and its industrilization”.Firstly, both steady and unsteady CFD methods for viscous field simulation of drill ships are studied. Steady CFD simulations for one drill ship with four different moonpool are carried out, and results show that the steady CFD method is valid for resistance prediction when water motion is moderate in low transit speed. Unsteady CFD simulations for the vessel with vertical and stepped moonpool are carried out respectively, and results show that inpact of unsteady flow in moonpool on the resistance can be considered in the unsteady method, so it seems more accurate in high transit speed. Furthermore, based on the above-mentioned study, generation of additional moonpool resistance is studied.Secondly, experimental study on additional moonpool resistance is carried out. The model tests are carried out in the circulating water tunnel of Shanghai Jiao Tong University, the relationship between additional resistance and moonpool shap, dimensions, draft. Results show that different oscillation mode may appear in different transit speed, but “sloshing” mode can be expected when draft/length ratio is lower than 0.4. In different oscillation mode, the additional resistance is found to increase linearly with the oscillation amplitude respectively. The oscillation frequency will sustained a same value over a large speed regime due to the phase locking phenomenon.Then, based on the model test results, regression analysis to additional moonpool resistance is carried out and a simplified calculation method is constructed for “sloshing” oscillation mode.Finally, studies on two methods to reduce the additional resistance, steped moonpool and grid of flaps, are carried out. A new resistance reduction device in grid of flaps type is developed, and declared patent protection.