半潮堤前的反射形态与时均流速场分析

Reflective behaviors and period-averaged velocity fields by a low-crested breakwater

采用模型试验和数值模拟研究了不同水深工况下半潮堤前的反射形态及时均流速场。基于Hilbert变换建立了叠合波的时频分离技术,同时获取了入射波和反射波的波面过程及相位关系,通过试验数据证明其适用于不同反射程度的波浪信号分析。不同水深工况下,半潮堤前形成了部分立波系统,腹点和节点分别以四分之一波长的偶数倍和奇数倍交替增加。半潮堤前底床水质点水平速度包络图与波面包络图相差四分之一周期的相位,水平速度的极大值和极小值分别出现在波面包络图的节点和腹点,意味着节点处易形成冲刷,腹点处易形成淤积。3种工况的周期平均速度场均在迎浪基床上方的堤脚处存在一个小型环流系统,可能引起局部冲刷,此处需加强防护。淹没工况下,半潮堤前的周期平均速度场形成一个大型环流系统,表层水流向堤后,中下层水流向海侧,意味着底床悬起的泥沙很可能向离岸方向流失。

The reflective behaviors and period-averaged velocity fields by a low-crested breakwater at different water levels were studied through model tests and numerical simulations.A time-frequency separation technique was developed based on Hilbert transformation to simultaneously resolve the temporal surface profiles and phase relationship of incident and reflective waves.The application of this technique to wave signal analysis for various reflection effects was validated by experimental data.At different water levels,a typical partial standing wave system was formed on the weather side of the low-crested breakwater.Nodes and antinodes alternate spatially at x-locations at increments of even and odd times of one-quarter wavelengths,respectively.The envelope of the horizontal velocities of water particle on the weather-side bottom of the low-crested breakwater shows a phase difference by one-quarter wave periods from the envelope of wave profiles.The maximum and minimum horizontal velocities occur at the nodes and antinodes of the wave envelopes,respectively.This fact implies scouring-prone at nodes and accumulation-prone at antinodes.The period-averaged velocity fields for three cases show a small circulation system at the foot of the structure above the weather-side rubble mound,which may cause local scouring and requires enhanced protection.When the low-crested breakwater is fully immersed,a non-zero mean circulation is formed in the weather-side period-averaged velocity field.This large circulation causes the surface water to flow toward the leeside of the breakwater and the underlying water to flow seaward.The offshore loss of sediments stirred up from seabed can be expected.