水下沙丘形态演化的数值模拟实验

水下沙丘在海洋、湖泊、河流等浅水砂质沉积区广泛分布。基于过程的数值实验方法探讨了沙丘形态演化问题,试图解释在沙丘形成过程中各因素的作用及它们之间的关系。模拟中考虑了以下的变量:水深、沉积物粒度、沉积层厚度以及台风作用。模拟结果显示,沙丘的空间分布控制了空间流场的参数k₂,沙丘波高受水深、沉积物粒度以及沉积层厚度等因素的影响,沉积层厚度决定了沙丘的形态是否饱满。在台风作用中,沙丘波峰的沉积物被侵蚀,高程降低,波高渐小;台风作用后,沉积物被重新输运至波峰,沙丘高度逐渐恢复。因此,沙丘的高度取决于台风作用的时间以及2次台风作用之间的间隔。沙丘形态和尺度在台风作用前后变化较小,但沙丘演化的速度却有所提高。根据台湾浅滩和北海南部地貌系统数据的验证,模拟具有较好的效果。

An evolution of subaqueous dune morphology: numerical experiments

Subaqueous dunes are widely distributed in shallow marine environments. The morphological characteristics and the evolution of these bed forms have been a focus for many studies.The evolution of sand dunes associated with tidal flows is discussed using a one-dimensional modeling approach, in an attempt to identify the role played by the various factors and their interrelationships. The variables considered in this model include a water depth,a sediment grain size, and the thickness of sediment layer,and a typhoon. The simulation results show that the dune morphology and the evolution time are influenced by these factors. The spatial distribution of sand dunes is controlled by the flow field parameter; the dune height is influenced by the water depth,the sediment grain size and the thickness of sediment layer while the shape of sand dune depends on the thickness of sediment layer. The evolution time to reach equilibrium is controlled by all of the above factors. During a typhoon, the sediment is washed away from the ridge of dunes and then the heights decrease. Following the storm event, the sediment is transported back to the crest and the heights increase, however, several years are required to recover. The simulation results are consistent with the data of sand dunes from the Taiwan Bank in the Taiwan Strait and the southern North Sea in Europe.