| The marine riser system is the key element to the offshore oil and gas exploration & development platform system. As a necessary equipment of the riser system, affiliated risers not only could do the basic production functions, but also could change the flow field around the riser to inhibit VIV. Based on this mentality, affiliated riser can be taken as a vortex induced vibration suppression device with varying the arrangement. The final aim is to obtain an optimized scheme for future reference.According to the relevant theories, this article simplified the riser system to a two-dimensional scale model. To focus on the key dynamic factors about the drag force, lift force and the Strouhal number by using wind tunnel experiments, water tunnel experiment and numerical simulation methods. Then the research of flow control for VIV on marine riser by affiliated risers was completed in the sub-critical flow region. Specifically, a single riser's flow results were obtained by three ways firstly, and then compared them with classic results. A good agreement of each other was achieved. At last, through the comparison of the additional suppression devices, the feasibility of wind tunnel experiments and accuracy of numerical simulation do been proven.The further research conclusions show that: different layouts and the size of affiliated risers can lead to different effects remarkably; the subsidiary riser should be used in pairs; in this paper, the affiliated risers can reduce the drag and lift reduction can up to 40% and 85 %. In view of the change of the flow direction of current, the model of affiliated riser number, N =8 is the best choice. In that case, the time-averaged drag coefficient and fluctuating lift coefficient can be reduced more than 30 percent and 70 percent, respectively. The regular changes of drag and lift have disappeared, and the possibility of VIV was greatly reduced... |
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