Study On Hydrodynamic Response Of Riser In Moonpool Of Drilling Ship

China is a country centered on economic construction.The demand is increasing for all kinds of energy sources,especially the oil and gas resources,which is an important energy material which is related to the national construction.However,the exploitation of deepwater oil and gas resources requires not only drilling ship,platforms,etc.,but also the riser system is one of the key equipment.The riser is placed into the sea through the moonpool.The riser system is an important part of ocean engineering and one of the weakest components of ocean engineering.The riser is the conduit connecting the floating device on the surface and the submarine equipment located on the seabed.It is equipped with various pipelines,and it is the extremely important connecting channel from the offshore platform to the bottom of sea.Based on Fine/Marine software,the riser in the moonpool of drilling ship is studied,and the fluid movement in the moonpool without riser and with riser is compared,which explains the necessity of studying riser.The wave height,pressure and other monitoring points are arranged in the moonpool of the drilling ship,and the hydrodynamic response of the drilling ship and the riser under different conditions is analyzed.The main research work and the analysis results are as follows:Firstly,based on the mooring module of Fine/Marine software,a set of spring oscillator system is established to simulate the motion response of riser under wave-current load in moonpool.The horizontal force of the riser is solved numerically according to Morison equation and verified by CFD.The displacement of riser in the moonpool is obtained by static analysis of pipe59 element in ANSYS,so as to combine the distribution of cables in spring oscillator system.The initial tension and stiffness of the system are obtained.Thus a set of effective simulation system for riser motion response is established.Secondly,by comparing and analyzing the wave height and pressure in the moonpool without riser and with riser,the riser is in a static state.Four layers monitoring points are setting up,they’re located at the static surface,one meter below the static surface,two layers above the static surface,and the interval is 1m.Through monitoring the wave height and pressure,this paper studies the drilling ship at different wave angles and different wave periods,thus it is clear that the riser has an obvious effect on the fluid movement in the moonpool.When T=10s,the increase ratio in the shallow water area and side area is small,the increase ratio in the deep water area and the guiding edge is large,and the increase ratio is about 30%.The results show that riser has a great influence on the wave climbing.Then,the spring oscillator system is added,and the degrees of freedom of pitch,surge and sway are released.The state of the drilling ship is set to two kinds of working conditions: one is static,the other is to release its pitch and heave degrees of freedom based on the drilling ship’s own coordinate system.By analyzing the horizontal force,displacement and pitch of the riser under different motion state,and at the same time monitoring the change of wave height and pressure in the moonpool,the influence of the moonpool on the pipe is studied.Finally,the spectrum analysis of the riser under various working conditions is carried out,and the spectrum diagram of the riser response is obtained by Fourier transform,so that the coupling motion between the drilling ship and the riser under the wave-current load can be clearly expressed.At the same time,combining with other literatures,the movement trajectory of riser in coupling state is analyzed.In this paper,the dynamic response of marine riser under various loads is studied,and the influence of wave-current load on the riser is analyzed.Through theoretical analysis and CFD simulation,the theoretical basis for the parameter design,optimal design and safe use of riser is provided,at the same time,it also provides a valuable reference for the safe application of riser in marine engineering in the future.Therefore,the analysis of marine riser system plays an important role in preventing fatigue damage and optimizing drilling parameters.The response analysis of riser under external load is an important problem in the research of offshore oil engineering.It is of great significance to the development of offshore oil and gas.