Experiment Research On Flow Noise And Hydrodynamics Character Of Moonpool

With the further study of the ocean exploitation, in order to place equipments and the dial, lay cables, and fit the pipes, etc, more and more engineering vessels such as vessels of scientific research, of artesian well, of laying cables, of offing engineering supplement, collocate moonpool which goes through the vessel's body vertically, connects the ocean, and having free surface in it. For the water in the moon pool, there exists tow inherent oscillation-- Piston, which generates from the extension of the free surface, and Sloshing, which results from the shaking from side to side of the free surface。The frequency of both oscillation have bearing on the structure, size and draft in the moonpool, and when the flow interrupts frequency and keep correspondence with it, resonance of the water in the moon pool then comes out. In addition, on the condition of even flow, flow noise generates at the opening of moon pool. All of these take disadvantage to normal work of the vessel's body. In consequence, it is a necessity to make a study of the hydrodynamics of the moon pool, and the features of flow noises as well, so as to provide valuable information to the design of moon pool.The innovating merits of the experiment model decomposition are that we can get the intrinsic model function which is in correspondence with certain physical sense, and analyze the complicated experiment data. As a result, the article does the research about the flow noise and features of hydrodynamics under the circumstances of circle moon pool and the square one by adopting the method of the EMD and contrasting. The coming flow should be the combination of even flow, waves and wave-flow condition.Through the analysis of the experiment, the article is in its belief that on the condition of even flow, the shear layer self sustains oscillation is the stirring source of water piston vibration. And the frequency of the shear layer self sustains oscillation is relevant to the speed of flow, and raise with its increase. When it comes to being close to the piston oscillation frequency in the moon pool, the phenomenon of resonance and the piston phenomenon arise. Besides, the article considers that the "lock-in" phenomenon should exist in the piston phenomenon of the moon pool as well. The thesis regards the phenomenon of piston oscillation in the moon pool as a mass-spring vibration system, calculate the piston frequency under certain hypothesis, and get a result well-matched with the value of the experiment.When there is wave and wave-flow, the water in the moon pool gets inspiration from the waves, which is difference from that coming from self sustain oscillation of shear layer when it is the even flow. Thus, the oscillation features of the water in the moon pool differ a lot comparing with the condition of even flow. And on the condition of waves and wave-flow respectively, the water has distinguished characteristics in different wave periods, which mainly exist in whether the water in the moon pool can oscillation basing on the nature frequency of piston oscillation or on the frequency of waves or wave-flow. Through the research, the thesis gives the assumption of certain critical data, and explains it thoroughly.The experiment still discovers that resonance comes out when the waves cycle is 2 seconds, and the encountering frequency is similar to the nature frequency of the piston oscillation in the moon pool; if the encountering frequency is inferior to the inherent frequency of the piston vibration, the vibration of the water in the moon pool presents a characteristic of "tap"; and when the encountering frequency is a little superior to the inherent frequency of the piston vibration, the phenomenon of "tap" will not appear, and it is as well with the square moon pool with a 0 degree between the rotundity and the attack angle, no matter whether wave-flow inspiration is superior or inferior to the nature frequency of the piston oscillation.