Coupled Hydrodynamic Performance Of The Deep Towed System's Mother Ship With Moonpool

As the study of the ocean gradually enters the deep sea,it is particularly important to deep-draft the mother ship as an important part of deep diving technology.The deep towed mother ship has functions such as retracting,maintaining and remote control of the deep sea submersible.In order to adapt to the towing and retracting and underwater operation,the deep towing mother ship is equipped with moonpool in the ship,and the movement of the fluid in the moonpool is complicated and will be related to the external environment.As well as the coupling of the movement of the hull,the towing body will be coupled with the tow body during the retracting operation,which may affect the retracting operation of the tow body and the safe driving of the mother ship.Therefore,it is necessary to study the coupling motion of the fluid in the moonpool.In this paper,a combination of model test and numerical simulation is used to study the coupling kinetics of a fluid in a deep-drafted mother ship with a moonpool opening.Firstly,the resonance period of the fluid in the moonpool under different theories is obtained by theoretical analysis.The resonance period of the fluid motion in the moonpool is calculated by CFD method.The fluid characteristics of the fluid in the moonpool are analyzed.It is found that the moonpool has a shielding effect on the wave.The wave rise in the moon pool lags behind the ambient wave,and the form of fluid movement is mainly piston movement,and the amplitude of the sloshing movement is small.Through the regular wave test,the pitch and heave RAO of the hull in the forward wave state,and the wave rising in the front,middle and back of the moon pool and the rolling RAO of the hull in the transverse wave state and the front and middle of the moonpool are obtained.The three-point wave rises to verify the accuracy of the monthly pool CFD calculation and the accuracy of the natural period of fluid motion in the moon pool.Through the combination of CFD and model test,the fluid motion characteristics in the moon pool are studied and analyzed.The effects of wave height variation and hull heave and pitch motion on fluid motion in the moon pool are studied respectively.The results show that the wave height increases linearly and the wave height increases in the moon pool.The amount of decline,the hull heave motion and the pitch motion will stimulate the fluid movement in the moon pool.The pitch motion will stimulate the high-order motion of the fluid.The heave motion mainly stimulates the piston movement of the fluid,and then studies the hull heave and the sway in the still water.The effect of harmonic motion on the fluid in the moonpool is found to be the largest in the moon pool when the pitching motion is 0.75 Hz and the heave motion is 1.04 Hz.Aiming at the longitudinal displacement of the tow body near the water surface during the towing and retracting process in the wave environment and the movement characteristics of the fluid in the moon pool when the tow body is near the water surface,the results show that the movement amplitude of the tow body is different when there is a moon pool under different periodic waves.When the wave period is less than 5 s,the movement amplitude of the tow body is greater than the wave period of 5 s,and the wave depth of the fluid in the moon pool is the largest when the wave period is 5 s.The displacement of the tow body and the fluid in the moon pool when the wave height is increased The motions are all characterized by strong nonlinearity,which exhibits nonlinear characteristics as a function of linear increase in wave height.Therefore,in the towing and retracting operation,the environment with a large wave height should be avoided as much as possible.If the wave period is close to the natural period of the fluid movement in the moon pool,it can be avoided by changing the angle.