| 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.This paper considers engineering practice,using numerical simulation and experimental method to study the effect of moonpool resistance,the hydrodynamic characteristics and the anti-wave device in the pond,and the main contents are as follows:(1)Explaining the background of the study,combined with the characteristics of drilling vessel and moonpool,analyzing the significance of the study,introducing the basic theory and method of numerical calculation and experimental research,and clarifing the main contents and innovations of this paper.(2)Through combinating umerical simulation and model experiment,the influence of moonpool on drilling at different speed is discussed.And the law of moonpool resistance growth is summarized.Taking the ladder pool as the main research object,based on the CFD numerical calculation theory,two kinds of 3D drilling ship models were created in the closed and open state of moonpool.The fine/marine software was used to analyze the resistance of the drilling vessel at 8kn~14kn.At the same time,the model experiment method was used to produce the experimental drilling vessel model with moonpool closed or open.And the rapid experiment series of the drilling vessel was completed in the towing pool of Jiangsu University of Science and Technology,including the experiment of propeller open water,drilling tank resistance experiment and self-propelled experiment.The numerical results are compared with the experimental results.It is found that the resistance of the drilling vessel reduces 25% ~ 30% when the pool is closed.The higher the speed,the greater the resistence.Accurate estimation of the hull resistance of the drilling vessel helps to determine the propeller and host configuration.(3)The experimental method is used to study the fluid motion law in the moonpool and the ladder-shaped moonpool under the rule wave.Based on the rectangular and stepped moonpool,the self-designed moonpool-hull experiment model was used to study the 20 kinds of rules wave in each cycle pool experiment of Yangzhou University.It is found that the pond has a shielding effect on the external waves,and the fluid motion in the moonpool lags behind the external wave motion.The amplitude of the fluid motion in the pool is larger than that of the external excitation when wave resonance cycle.Y-sloshing is weak at rectangular moonpool,and x-sloshing is based.Ladder-shaped pool,the "waterfall" causes y-sloshing aggravated,is less than x-sloshing value,but still can not be ignored,and should be important research components.(4)According to the law of fluid movement in rectangle and stepped moonpool,the new anti-wave device is designed independently,and the effect of suppression is improved by model experiment.Based on the law of fluid movement in rectangular and stepped lunar pool,four kinds of anti-wave device in moonpool are designed,four sets of anti-wave device in the rectangular moonpool,including the positive baffle type anti-wave device,the reverse baffle type anti-wave device,dichotomous anti-wave device and grid-type anti-wave device.Three sets of anti-wave device in the ladder-type moonpool,including the positive baffle type anti-wave device,the reverse baffle type anti-wave device and grid-type anti-wave device.The The moonpool model,the anti-wave device model and the hull model are independent of each other and are freely combined for experiments.The experiment was carried out in a circulating water tank,including seven experimental models×20 operating conditions=140 operating conditions.It is found that the baffle type anti-wave device suppresses the formation of the partition between the fluid and the external wave in the pool,which enhances the effect of the moonpool,and the fluid response in the pool lags behind the external excitation wave.The inclined plate structure in the deflector plate easly couses whirlpool,destructing fluid self-oscillation in moonpool.Under small cycle and wavelet high wave effecting,the dichotomous anti-wave device caused the pool of fluid "dislocation" phenomenon,the pool forword and backword of the fluid movement phase is always at different half a cycle.Grille plate in Grid-type anti-wave device cuts fluid in moonpool,causing the wave surface crushed,effectively prevent the pool of fluid along the moon wall up or down,destructing original self-support movemence in moonpool.At the same time the ladder on the platform above the grid plate,the formation of "weir" to improve the "waterfall" drop height,change the "waterfall" point of view,the impact of fluid in moonpool,causing fluid movement intensified.(5)Summarize the main work and research contents of this paper,make further suggestions on the three factors of drilling vessel drag reduction measures,influencing factors of hydrodynamic characteristics in moonpool and the optimization of the anti-wave device.In summary,this paper puts forward reasonable numerical calculation and model experiment scheme from three aspects: the resistance effect of moonpool,the hydrodynamic characteristics of the moonpool and fluid suppression device in moonpool.Exploring the moon pool resistance effect,predicting performance of drilling ship under the influence of moonpool,analysising significance of study the performance of the research on the performance of the drilling vessel under the influence of the moon pool,which has a very good engineering significance.Based on the study of the hydrodynamic characteristics of the pond in the pond,get the conclusion of innovation.the proposed method is proposed to provide a theoretical basis and technical support for the mastering of the key technology of the drilling vessel. |
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