Influence Of Moonpool On Hydrodynamic Performance Of Drillship

Nowdays,more and more offshore oil and gas resources are found in the deep sea.And drill vessel is a the key equipment to exploit deep-sea oil and gas.The moonpool is an opening in the hull which is necessary for drilling pipes and risers to operate.The moonpool can have different shapes varying from a clean rectangular moonpool to more advanced geometries with dampening devices installed.So,it is of great significance to analyse the influence of moonpool on drilling vessel.In this paper,the influence of lunar pool on the rapidity and seakeeping of drilling vessels is studied by combining model test with numerical calculation,and analyse the motion mode in moonpool.The model test was carried out in Haerbin Engineering University deepwater basin and towing tank.The main test content are free decay experiments in calm water,RAO test,the irregular wave test and the resistance test.The model test is used to measure the motion response of the drillship model under different conditions,different wave directions and different loading conditions and measure static water resistance of drilling ship model at different speed.Based on the basic theory of CFD,the resistance performance of drilling vessel is studied by using software STAR CCM+.Comparing the numerical results with the experimental results,the error is within a reasonable range.And the selection of computational domain and mesh generation in numerical computation are discussed.The influence of the moonpool on the total resistance of the drilling vessel is studied,including the opening and closing of the moonpool,the steps inside the moonpool,the slope angle inside the moonpool and the position of the moonpool.It is found that the resistance of the moonpool to the drilling vessel increases by 10%-20%.The existence of step and slope angle in the moonpool can reduce the resistance of the drilling vessel The position of the moonpool on the drilling vessel also affects the resistance of the drilling vessel,and the appropriate position will make the resistance of the drilling vessel smaller.Based on the three-dimensional potential flow theory,the frequency domain and time domain analysis of the drilling vessel in waves are carried out.The software AQWA is used to analyze the drilling vessel in frequency domain and time domain under different wave directions and loading conditions.The RAO(amplitude response operator)curves of the drilling vessel and the six-degree-of-freedom time history curves under different wave conditions are obtained.Comparing the influence of the opening and closing of the moonpool on the motion response of the drilling vessel,it is found that the existence of the moonpool will increase the amplitude of the roll motion and the heave motion of the drilling vessel,but has no obvious influence on the pitch motion of the drilling vessel.Based on the theory of CFD,the flow state of fluid in the moonpool is explored,and a two-dimensional numerical calculation model is constructed by using STAR CCM+software.The monitoring points are arranged in the interior of the moonpool to measure the variation of the wave heights under different wavelength-to-captain ratios.By comparing the flow of fluid in the rectangular moonpool with and without stepped structure at the same wavelength,it is concluded that the stepped structure can effectively reduce the oscillation of fluid in the rectangular moonpool.