波流作用下新型立管大水槽试验研究

Experimental Investigation of Wave and Current Actions on a New Type of Riser in Large Wave Flume

针对一种新型自由站立式防台风隔水立管系统,在3种不同浮筒净浮力条件下,通过几何比尺1∶21的大水槽物理模型试验,研究了纯水流以及波流联合作用下隔水立管整体的涡激振动和运动轨迹情况,统计了不同测点顺流向位移的平均值和横流向位移的均方根,并对比了纯水流和波流联合工况下立管涡激响应的差异性.研究表明,浮筒净浮力对新型立管的固有频率和运动响应有较大影响,可以通过调整浮筒净浮力来避免立管自振频率与外界激励频率锁定,保证结构安全;纯水流工况下新式立管的涡激振动现象明显,同时通过分析立管不同位置的运动轨迹发现由于结构的复杂性和外部荷载的不稳定性会激发频率为固有频率偶数倍的非对称振动.在波流联合工况下,波浪在一定程度上抑制了隔水立管的涡激振动,使其整体偏移量减小;在横流向,波流联合工况下新式隔水立管的涡激振动相比于纯水流工况发生明显变化,波浪频率成为控制其振动响应的主导频率,此时立管位移的最大值未出现于顶端测点处,而是出现在距离表面波影响较小的测点处.

The vortex-induced vibration(VIV)of a new type of self-standing riser system against typhoons is studied under three different net buoyancy conditions by a physical model test with a length scale of 1∶21.The VIV and motion trace of riser under the only current and wave-current combined condition is studied;additionally,the average value of the displacements in the in-line direction and the root mean square of the displacements in the crossflow(CF)direction are calculated,and the difference is compared under different conditions.Buoyancy has a significant influence on the natural frequency and motion response of the new riser.The buoyancy of the buoy can be adjusted to avoid the lock-in between the natural frequency of the riser and the external excitation frequency to ensure structural safety.Under the only current condition,the VIV of the new riser is obvious.Simultaneously,analysis of the motion traces of different positions of the riser shows that because of the complexity of the structure and the instability of the external load,asymmetric vibrations with an even multiple of natural frequency will be excited.However,under the wave-current combined condition,the wave suppresses the VIV of the riser in a certain degree.Moreover,in the CF direction,the VIV of the new riser under the wave-current coupling condition is significantly different from that under the pure current condition.This time,the wave frequency becomes the dominant frequency to control the vibration response of the riser,and the maximum displacement of the riser appears at the place where the influence of surface wave is small,not at the top measuring point.