| With the rapid development of society, human beings have made great progress both in science and technology and economy. Oil and gas exploitation at shallow water have failed to meet human's ever-growing demand for energy. Offshore oil and gas industry, thus, are striding forward to deep sea. Particularly, more and more pivotal components of the circular cylinder shape represented by marine risers are widely used in the offshore platform and subsea pipeline systems, therefore it's of great practical significance to carry out research on forced oscillation and vortex-induced vibration(VIV) of circular cylinder. Currently, hydrodynamic coefficients of vortex-induced vibration are obtained by experiments, the rapid development in numerical methods and hardware performance, however, have resulted in advanced computer facilities which allow the more extensive studies of numerical simulations of the fluid-structure interaction. This paper presents a numerical simulation of a rigid cylinder's vortex-induced vibration with the application of the widely used commercial computational fluid software FLUENT, presenting the subcritical Reynolds numbers 10000. The experiment analyse at length of the rigid cylinder's vortex-induced vibration when it's still and the hydrodynamics of lock-in phenomenon when it's oscillating. The relative error between lift coefficient and resistant coefficient is within 20% when compare the calculation result with the experimental data, and then try to analyse the reason of error if there be.The development of deep-sea aquaculture, on the other hand of marine resource exploitation, has drawn more and more concern from our country and the rest of world. Aiming to seeking the better aquaculture environment as well as the high quality aquaculture products, people have driven the net cages to the deep sea. Deep sea cage aquaculture,hence, was brought into being. Attribute to the fact that deep sea cage is bulky and frequently tested by the more adverse environment at deep sea, thus its hydrodynamics has always been the hot spot in marine engineering. Whereas, although net cage is bulky, its components such as floating frame and webbing are small flexible floating structures when compared with large marine structure. The principle development of such structures'interaction with wave and current is awaited. As for the floating frame, the research simplifies it as a two-dimensional model with circular cross section, resolving its hydrodynamics under the conditions when it's still and vertically vibrating from the horizontal plane. As for the cylindrical viscous flow field with free surface, the free surface is dealt with the method of VOF(Volume of Fluid), and the turbulence model as well as parameters are settled through large numbers of trails.The two main purposes of this research are: One is the numerical simulation of vortex-induced vibration of circular cylinder in marine engineering. Above all, the forecast for the hydrodynamics of vortex-induced vibration with the method of experiment is widely used and relatively precise; the cost, yet, is high. The using of software CFD, on the contrary, is low in both cost and precision. This paper strives to calculate the relative error intuitively through one of the simulations of the vortex-induced vibration to lay a foundation for the following numerical simulations.The other is the numerical forecast for the hydrodynamics of deep sea fishery. As for the preparation for experiment is complicated and time-consuming, and a precise forecast is significant to the experiment processing smoothly and the collection of data. Hence this paper tries to find hydrodynamics solutions to the simplified floating frame of sea cage with the use of the software FLUENT.
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