浮力筒自由涡激运动的模型试验研究

摘要

The vortex-induced motion(VIM) responses of a free vibration buoyancy can were studied experimently.The buoyancy can was put vertically, with a diameter of 150 mm and a length of 700 mm.By the model test, 6-DOF motion parameters were measured under different working conditions and the motion responses were analysed in the cross-flow, in-line and yaw directions.The results indicate that the in-line motion frequency is twice as high as that of the cross-flow motion and the trajectory of the cylinder is obviously in "8"shape when the reduced velocity becomes large.The yaw motion is of single frequency under a small reduced velocity and when the reduced velocity got larger, two frequencies appear and both increase as the reduced velocity increases,where the higher yaw motion frequency is equal to the cross-flow (CF) frequency.So, the CF motion and yaw motion come from a same excitation source, namely there is coupling effect.It is also found that the mean drag coefficient of VIM is about 100% more than that of the diffraction flow round the circular cylinder.%对外径150mm,长700mm垂直放置的浮力筒模型开展了自由涡激运动试验研究,测量了浮力筒在不同试验工况下六个自由度的运动参数,并着重对浮力筒顺流向、横向和艏摇运动的运动特性进行了分析.试验中发现,当约化速度较小时浮力筒主要发生顺流向运动而横向和艏摇运动较小且不规则;当约化速度增大到一定程度后,顺流向运动频率是横向运动频率的2倍,此时艏摇运动出现了两个主要运动频率,其中较大的艏摇运动频率等于横向运动频率,因此认为横向运动和艏摇运动的激励力来源相同,即二者存在耦合作用,而且浮力筒的运动轨迹呈现明显的"8"字形.试验中还发现,浮力筒涡激运动的平均拖曳力系数比圆柱绕流的阻力系数增大了约100%.