【作者】 阮雪景；

【导师】 拾兵；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2013， 博士

【摘要】 水在地球表面的分布范围非常广，江河、湖泊和海洋等水体约占地球表面积的3/4，而高纬度地区的表面水体在冬季温度下降时经常会发生结冰现象。全球冰问题总体来说可分为海冰问题和河冰问题，由于河流沿岸区域居住着大量居民，使河冰问题显得尤为突出。冬季河流封冻后，水体表面出现固体冰盖，使得过水断面的湿周增大，水力半径减小，从而导致了水流形态的变化，带来的影响包括水力发电产量的损失，航运线路阻塞、航期缩短，河流中的水利结构破坏，严重时形成冰塞、冰坝并导致凌洪灾害，淹没农田房屋，危害人民生命和财产安全。我国北方多数河流都存在不同程度的冰情问题，尤其是黄河下游河道是举世闻名的地上悬河，河道上宽下窄，流向由低纬度向高纬度，南北纬度相差3°，冰情现象十分复杂，河冰灾害发生频繁且破坏力巨大。因此，对黄河下游河冰的形成、演变和输移过程进行系统、深入的研究对提前制定防灾措施具有重大意义。本文分析了冬季河冰结冰期、封冻期和解冻期的演变过程及河冰类型。进一步探究黄河下游冰塞和冰坝现象的特点、形成条件和变化过程，并总结了黄河下游开河时容易形成冰坝的原因。推导了河流无冰盖、部分被冰盖覆盖和完全被冰盖覆盖情况下的水深公式。通过对冰盖上游漂浮冰块和潜入冰盖下的冰块进行受力分析，得到了冰盖前冰块下潜的临界流速和下潜冰块在冰盖下继续向下游输移的临界流速。开展物理模型试验对不同流速、水深、冰盖类型和冰盖糙率等条件下冰盖流垂线流速进行观测和分析，得到的主要结论包括：（1）冰盖下的垂线流速呈现两头小中间大的U字形态，光滑冰盖模型的水深大于同流量明流水深。床面区光滑冰盖流的流速比同位置的明流流速稍大，但随着水深增加两者越来越接近。流量相等时光滑冰盖流的最大流速大于相同位置的明流流速。（2）粗糙冰盖流垂线最大流速值随冰盖糙率的增大而增大，最大流速点更靠近光滑的床面一侧。在不同水深情况下，最大流速点与床面之间的距离随着冰盖与床面糙率比的增大而减小，基本呈现出线性变化规律。（3）岸冰河流中心开敞区水深大于明流，垂线流速分布形式与明流相同，但相同深度上的流速比明流大，并且流速随着岸冰冰盖宽度的增加而增大。岸冰冰盖流在两岸冰盖处的水深小于相同情况的明流水深，垂线流速分布形态呈现出中间小两端大的形式。对用于模拟复杂河道地形中冰运动和阻塞过程的二维冰动力学数值方法进行改进，使用欧拉有限元法进行水动力模拟，冰运动模拟使用基于光滑粒子流体动力学（SPH）的拉格朗日离散元法（DPM），建立计算黄河下游河冰输移过程的二维数值模型。通过开展物理模型试验以验证二维冰动力学改进模型的准确性。也就是控制入口处的输入条件与数学模型相同，对比河道内冰密集度和典型断面水深的数模结果和实测结果，分析表明：模型能较好地模拟出了河道内的冰输移过程，且两者水深值比较吻合。首先将收集的地形、水深和气象等数据输入模型，模拟了黄河下游济南市徐庄处1970年1月发生的冰坝现象。通过对比模拟河段内冰坝长度、厚度和水深的实测值与模拟值，表明该模型较准确地模拟了冰坝形成和发展的过程。其次，以河道狭窄弯曲、易发生冰塞、冰坝的黄河下游北店子水文站至泺口水文站河段为模拟区域，通过冰岛的设定模拟了2010年冬季岸冰存在情况下该河段冰厚度变化。结果表明水流量较小时较强的风力作用对冰的拖曳力起到主导作用，且岸冰的存在缩小了开敞河道宽度，阻碍大块表面冰顺利通过；而在岸冰后平铺形成冰盖并向上游延伸。模拟了2013年1月该河段的流凌情况，可以发现流冰下泄比较顺畅，未发生冰阻塞，且泺口水文站冰密集度的数模值与实测值比较一致。由于模拟河段S型弯的地形易发生冰堆积，为促进河道内稳定冰盖的生成，并延长泺口浮桥的使用时间，提出在泺口水文站前河道内设置拦冰栅，使用2013年1月的输入条件，模拟该河段增加拦冰栅后的冰运动情况，结果显示表面冰在拦冰栅后平铺并逐渐形成稳定冰盖，并不断向上游延伸。为便于操作，本文建立了黄河下游冰动力模拟系统，使用户在界面上可得到清晰直观的输出结果。更多还原

【Abstract】 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.更多还原