| Water spreads very widely on the surface of the earth, the area of rivers, lakesand seas accounts for about three-quarters of the earth’s surface, when thethe temperature drops in winter, the surface water in high latitudes always freezes. Ingeneral, global ice problems can be divided into sea ice and river ice, a large numberof residents living along rivers makes the river ice problems even more prominent.When rivers freeze in winter, the solid ice cover on the water surface canincrease the wetted perimeter of cross section, reduce the hydraulic radius and changethe flow pattern, which have some impacts, including loss of hydroelectric powerproduction, congestion of shipping lines, reduction of navigation period, damage ofhydraulic structures in the river, or even form the ice jam, the ice dam and result invarious ice disasters, flood farms and houses, bring serious damage to the safety ofpeople‘s life and property. There are different levels of ice problems in most rivers innorthern China, especially the lower reach of Yellow River which is a world-famous "suspend river", the channel is wide in top and narrow in bottom, flows fromlow latitude to high latitude, the difference between north and south latitude is3°, theriver ice in winter is very complicated and frequently causes serious disasters.Therefore, it‘s very important to do research on the formation, evolution and transportof river ice in the lower Yellow River for disaster prevention.This paper analyses the evolution process and types of river ice in winter, furtherexplores the characters, reasons, formation conditions and changing process of icejams and ice dams in lower Yellow River. The water depth formulas are set up whenthe river with whole ice cover, partial ice cover and without ice cover. Based on theforce analysis of the floating ice before and under the ice cover, the paper derives thecritical velocities of the ice go down to the beneath of the ice cover and keep moveingbelow the ice cover respectively.Physical experiments for velocity profiles of ice covered flow were carried outunder various conditions such as different velocities, water depth, ice cover types androughness. The results by analysing the measurements are as follows:(1) The velocity distribution along vertical direction blow the ice cover lookslike letter U‘which is smaller at both ends and bigger in the middle, the depth ofwater in the model with smooth ice cover is greater than which in free flow at thesame discharge.The velocity near the bed in the model with smooth ice cover isslightly larger than which in free flow at the position, and they will get closer with theincreasing experiment depth.The maximum velocity in the model with smooth icecover is greater than the velocity at the same position in free flow when the dischargeis the same.(2) The maximum velocity in the model with rough ice cover increases with theice cover roughness, and it‘s closer to the bed which is smoother. At different water depthes conditions, the distance between the maximum velocity point and beddecreases with the increasing ice cover-bed roughness ratio, and present linearrelationship between them.(3) The water depth of open area in the boder ice model is larger than which infree flow. The velocity in the former condition is greater than the latter one, andincreases with the width of the border ice. The water depth under the boder ice issmaller than which in free flow at the same condition.The two dimensional ice dynamic numerical method used to simulate the processof ice movement and jamming in complicated channels is improved, the Eulerianfinite element method is used for the hydrodynamic simulations, a Lagrangiandiscrete parcel method based on the smoothed particle hydrodynamics is applied tosimulate the transport of surface ice, and this paper develops a two dimensionalnumerical model to calculate the river ice movement in the lower Yellow River.To verify the accuracy of the improved two dimensional ice dynamic numericalmodel by carrying out experiments in the lab, made the input conditions the same aswhich in the numerical model, the comparison between observations and simulationsof the ice concenreation in the study region and the water depths at the typicalsections indicates the model simulated the process of ice movement successfully.Setting up the user interface, and its aim is for the convenience of users.Firstly, input the collected meteorological and channel data to the model and theice dam occurred in Xu Zhuang of the lower Yellow River on January1970. Thecomparision between the observations and simulations of the dam length, thicknessand water depth shows that the model simulated the process of ice dam formation anddevelopment successfully.Secondly, taking the reach between Bei Dianzi and LuoKou hydrologic station of Yellow River as study region which is narrow and winding,the changes of ice thickness in the study region in winter of2010is simulated bysetting ice island as border ice. The results indicate that the strong wind acting on iceplayed a major role in ice moving, and the border ice narrowed the width of open areawhich stimulated the formation of ice cover behind it.Then the ice movoment in thestudy region on January2013is simulated, it turned out that ice jamming didn‘thappen and the observations and simulations of ice concentration at the Luo Kouhydrologic station are relatively consistent. Installing an ice boom in front of the LuoKou hydrologic station in the river is proposed to promote the formation of stable icecover and prolong the service time of the Luo Kou floating bridge. Use the same inputdata as the former case to simulate the ice movement after setting up the ice boom, itshows that the ice parcels tiled behind the boom and formed an ice cover gradually,and extended to upstream of the river.For ease of operation, an ice dynamic simulation system of the lower YellowRiver is developed, and the users can get the clear and direct output results from theinterface. |
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