Research On Fluid Characteristics In The Moonpools Of The Ships With Speed

The fluid movement in the moonpool is very violent during the ship sailing.The piston motion,sloshing motion,shear layer oscillation and complex mixing of water and gas have seriously deteriorated the fluid environment in the moonpool.This phenomenon directly threatens or even damages the working equipment in the moonpool.Therefore,it is of great significance to study the motion characteristics of fluid,shear layer oscillation and water and gas characteristics in the moonpool during the ship sailing for the maintenance and the design of equipment related to the moonpool.By investigating the research status of the fluid motion characteristics in the moonpool,it is found that there are still great difficulties and challenges in the study of fluid motion characteristics and water vapor mixing characteristics,the influence rules of disturbed models on shear layer oscillation characteristics,the influence rules of slow down fluid motion measures on the fluid motion characteristics,especially in the study of bubbles motion characteristics in the moonpool.To solve above problems,this paper firstly established a numerical model of fluid motion in the moonpool based on FLUENT software,and studied the pressure distribution and water vapor distribution characteristics of the fluid in the moonpool with the sonar model.Then,on the basis of numerical study,the towing test of ship model was designed,and the design principle,scheme and flow of the experiment were discussed.According to the test results,the oscillation characteristics of the shear layer in the moonpool were analyzed.Based on the empirical mode decomposition method,the oscillation frequency of the bottom shear layer was extracted and the influence of sonar model on shear layer oscillation was studied.By means of high-speed camera video,the motion characteristics of free surface in the moonpool with disturbed models were studied.Finally,the effect of the sailing speed of ship model on water vapor mixing characteristics was analyzed qualitatively.On the basis of the above experimental research,three schemes for slowing down the fluid movement in the moonpool were proposed:guide appendage,bubble shunt and grid.The fluid characteristics of these three schemes in the moonpool were analyzed experimentally,and the effectiveness of the three schemes in slowing down the fluid movement was verified.To solve the problem of bubbles movement inside and beneath the moonpool,a water tunnel model experiment was designed and the methods to deal with the bubbles are proposed.On the one hand,the bubbles characteristics and free surface motion characteristics of the moonpool with disturbed models were studied.Based on TEMA software,the movement of a single bubble in the moonpool was tracked to obtain the movement mode of the bubble.Then,the trajectory,velocity and acceleration of bubbles in the whole region were obtained by using the polynomial particle tracking method,and the bubbles distribution characteristics under different bubble radius,bubble quantity change law and gas spectrum were studied.Finally,the relationship between the free surface movement and the variation of bubble quantity was summarized.On the other hand,the phenomenon of bubbles releasing from the bottom of the moonpool was studied.Based on the analysis of the trajectory,velocity,acceleration and gas spectrum of the bubbles beneath the moonpool,the fluid dynamic characteristics and the bubbles distribution characteristics of the bubbles were studied by using PIV method.Finally,the effects of velocity,shape and scale on the quantity of bubbles in and at the bottom of the moonpool were given.