基于离散元方法与水动力学耦合的河冰动力学模型

流凌和冰坝是我国北方冬季比较常见的河冰现象,尤其冰坝,可导致严重的凌洪灾害,是河冰研究中的重要部分。本文将离散单元方法与二维水动力学相耦合,建立河冰的动力学数值模型,以模拟河冰输移、聚集、堆积,以及冰坝形成的动力过程。针对河道中大量密集且几何形状随机的流冰现象,采用扩展多面体单元对冰块进行构造,并通过离散元接触模型表征河冰输移和冰坝形成过程中冰块间的相互作用。河流水动力部分则采用考虑河冰影响的二维非定常浅水方程进行描述,并采用有限元方法进行数值计算。冰水耦合中的计算参数由河冰离散单元与其所在水动力学有限元网格节点的位置插值计算得到。通过对冰盖封河造成水位抬高过程的数值模拟,并将计算结果与理论分析结果以及DynaRICE河冰模型的模拟结果进行对比,以验证模型的有效性。在此基础上,对规则河道中河冰输移、堆积和形成冰坝的过程进行数值模拟和结果分析。通过以上河冰离散元与水动力学的耦合方法及其对河冰动力过程的数值模拟,对河冰动力过程从细观角度进行新的认识并为河冰动力过程研究提供一种有效的数值方法。

A river ice dynamic model based on coupling of discrete element method and hydrodynamics

Dynamic transport and jamming of surface ice is a common phenomenon for river in cold re-gion,and the ice flooding disaster caused by ice jams is a focus of academic research. To simulate the dy-namic process of ice transport, accumulation, ice jam formation and release, a river ice dynamic model coupled discrete element method (DEM) and two-dimensional hydrodynamics is established. The dilated polyhedron is employed in ice simulation to represent the granular characteristics of the large number of dense,thick,hard and discrete ice blocks formed by river ice dynamic break-up. The contact force model of DEM is applied to characterize the complex and random process of river ice interaction during ice trans-port and ice jam. The two-dimensional unsteady shallow water governing equation considering surface ice is used for the hydrodynamic component, and is solved by the finite element method. The ice-water coupling is done by the interpolation calculation based on the location of the river ice discrete element and the fi-nite element mesh. To validate the model, simulation of stage increase process in rectangular channel from open water to ice covering is modeled. The results are compared with the results from DynaRICE and theo-retical analysis. Furthermore,the process of ice transport,accumulation and ice jam formation in river chan-nels is simulated and analyzed. Through the establishment of the model and the simulation of the river ice processes, a new understanding of mechanism of river ice processes is obtained, which provides a new method for the study of river ice.