Numercal Research On Fluid Motion In The Moonpool Of Deep-water Drilling Vessel

In order to become easy to lay cables,install riser,send and receive devices in the drilling ship,a deck will be set through the hull in the ship,whose bottom is connected to the sea and existing free surface moon pool structure inside the cavity.Reasonable form of the moon pool structure and its arrangement can shield external wave effect to some degree and ensure the safety of drilling ship's sailing in the sea and its operation safety.Fluid motion inside the moon pool has two kinds of ways: one is called the piston movement and its fluid vibrate up and down in the direction of moon pool's depth;another kind is called sloshing movement,which free surface of fluid rocks from side to side.There are two kinds of external incentives of moon pool: the navigational speed in the static water condition and no speed in the wave condition.Both two cases normally exist in the actual operation.Based on CFD theory and research of scholars,this paper do research on the motion of the fluid in the drilling ship moon pool under the above two excitation in the method of numerical simulation.This paper mainly analyzes the motion mechanism and pressure characteristics of the fluid in the moon pool and the main contents of the paper are as follows.First of all,the hydrostatic speed of the surface is equivalent to the external uniform flow excitation.This paper simplifies the drilling ship moon pool structure into a cavity-type calculation model,and create the two-dimensional monthly pool,three-dimensional square column pool and cylindrical pool by Ansys/Icem&Fluent.This paper simulate the motion of the fluid in the moon pool,when the moon pool is excited by the flow rate in the range 0.2m/ s ?v ?1.6m/ s,mainly analyze the origin of fluid movement in pool and its shear layer off situation.In the same time,the motion frequency,amplitude and wall pressure of different shapes of moon pool were compared.Research found that under the uniform flow excitation,the oscillating motion of the fluid in the moon pool comes from the excitation of the shear layer;When self-sustaining oscillation frequency close to the natural oscillation frequency of the fluid,significant piston oscillations appear;The amplitude of the piston movement and the sloshing motion of the prismatic pool are larger than that of the cylindrical lunar pool,and its free surface fluctuation is more intense.Secondly,situation of no speed in the wave condition is analyzed in this paper.Drilling ship model of 1:125 scale is set up by Ansys/Icem&Fluent,and regular waves are created by push plate in numerical wave tank based on the NS equation and the VOF method.This paper simulates internal movement of the fluid when the moon pool under different external different excitation wave periods and heights,and mainly analyzes the piston motion,sloshing motion and the pressure characteristics of moon pool.At the same time combining with dynamic grid technique,realize the drilling ship and wave coupling by given drilling ship pitching and heaving motion form.Research found that wave height of fluid in moon pool lags behind external wave due to the shielding of moon pool;Piston motion is obviously intense in the moon pool;The shape of the moon pool has little effect on the piston motion,but have bigger influence on the sloshing motion;The higher the wave height of the external excitation wave,the greater the amplitude of the fluid heave and sloshing in the moon pool;Coupled motions increase the range of motion of the fluid in a moon pool and the frequency of the fluid in the moon pool is only related to the external excitation wave and the natural frequency of the moon pool.Again,this paper analyzes the motion of fluid in moon pool that situations of the navigational speed in the static water condition and no speed in the wave condition occurred at the same time.Through the establishment of three-dimensional numerical basin,based on FLUENT software platform self-programming,this paper mainly analyzes the piston motion,sloshing motion and the pressure characteristics of moon pool when the moon pool under the loads of current and combined wave and current.Research found that the oscillation of the fluid in the moon pool is related to the Kc number,the variation trend of constant pressure and fluctuating pressure is similar in square and circle moon pool.Finally,the main work and research contents of this paper are summarized,and further research on the mechanism of fluid in moon pool is made,and some suggestions are put forward.