A Modified Muskingum Flow Routing Model for Flood Wave Propagation during River Ice Thawing-Breakup Period

During the period of river ice thawing and breakup process (termed as “ice cover thawing-breakup”), vast amount of water stored in ice-covered river reach will be released comparing to that under open flow condition. The flow routing process during river ice thawing-breakup period will be different from that under open flow condition, since water stored in and channel from ice thawing-breakup process and flow routing process are very complicated. If the flow routing process during river ice thawing-breakup period can be predicted, it will very important for flood protection in the downstream river reach. In present study, water released from ice cover thawing process is considered as the lateral inflow to the channel flow during propagation process of flood wave from upstream to downstream. A model for the flood routing process during river ice thawing-breakup period has been developed based on the Muskingum hydrologic method. Using the modified Muskingum model, the routed outflow hydrograph has been determined along the Baotou Reach of the Yellow River during river ice thawing-breakup period. Results showed that the simulated hydrographs using developed model agree well with those of field measurements.

     

Simulation and analysis of ice processes in an artificial open channel

The Middle Route Project for South-to-North Water Transfer, which consists of a long artificial open channel and various hydraulic constructions, is a big water conveyance system. A numerical modeling of water conveyance in the ice period for such large-scale and long distance water transfer project is developed based on the integration of a river ice model and an unsteady flow model with complex inner boundaries. A simplified method to obtain the same flow discharge in the upstream and downstream of the structure by neglecting the storage effect is proposed for dealing with the inner boundaries. According to the measured and design data in winter-spring period, the whole ice process, which includes the formation of the ice cover, its development, the melting and the breaking up as well as the ice-water dynamic response during the gate operation for the middle route, is simulated. The ice characteristics and the water conveyance capacity are both analyzed and thus the hydraulic control conditions for a safety regulation are obtained. At last, the uncertainties of some parameters related to the ice model are discussed.     

武开河的边界约束判别准则

根据封冻河道春季冰盖破裂机理,采用弯曲河道边界约束概念,提出可用于预测武开河发生的判别准则,并对其适用性进行了论证。应用黄河河曲段1985~1994年的原型观测资料对该判别准则进行验证,结果表明该准则可以较好地用于河道武开河的判别。     

Comprehensive two-dimensional river ice model based on boundary-fitted coordinate transformation method简

River ice is a natural phenomenon in cold regions, influenced by meteorology, geomorphology, and hydraulic conditions. River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal processes, and they are also influenced by weather and hydrologic conditions. Because natural rivers are serpentine, with bends, narrows, and straight reaches, the commonly-used one-dimensional river ice models and two-dimensional models based on the rectangular Cartesian coordinates are incapable of simulating the physical phenomena accurately. In order to accurately simulate the complicated river geometry and overcome the difficulties of numerical simulation resulting from both complex boundaries and differences between length and width scales, a two-dimensional river ice numerical model based on a boundary-fitted coordinate transformation method was developed. The presented model considers the influence of the frazil ice accumulation under ice cover and the shape of the leading edge of ice cover during the freezing process. The model is capable of determining the velocity field, the distribution of water temperature, the concentration distribution of frazil ice, the transport of floating ice, the progression, stability, and thawing of ice cover, and the transport, accumulation, and erosion of ice under ice cover. A MacCormack scheme was used to solve the equations numerically. The model was validated with field observations from the Hequ Reach of the Yellow River. Comparison of simulation results with field data indicates that the model is capable of simulating the river ice process with high accuracy.     

黄河头道拐段冰输移及堆积过程数值模拟

头道拐河段因其特殊的河道形态及地理位置而成为黄河内蒙古段最易形成冰坝的河段,研究该河段河冰输移及堆积过程是理解内蒙古段河冰过程及卡冰结坝作用机理的关键。本文基于耦合的二维有限元水动力学模型和DPM(Discrete Parcel Method)河冰动力学模型,模拟了黄河头道拐河段2020—2021年冬季封河过程并进行了验证,讨论了不同水力条件、上游流凌密集度及河道形态对封河过程的影响。结果表明：相比于官牛犋弯道,河道弯曲率大、束窄程度高的什四份子弯道更易形成卡冰,且流量越小,卡冰作用越明显,冰盖向上游发展速度越快。河道流凌密集度小于0.4时,各种流量下研究河段未发生卡冰;流凌密集度增大至0.4,表面流冰首先在弯曲率系数较大的什四份子弯道处形成卡冰,随着流凌密集度和流量的进一步增大,下潜并输移到下游的流凌也会在官牛犋弯道形成卡冰,因此,头道拐河段形成卡冰的流凌密集度临界条件为0.4。应用冰水耦合二维动力学模型可以很好地模拟天然河道河冰输移、堆积过程中河道的水力特性、冰厚增长及封河形态,揭示了影响河冰过程的相关因素及作用机理,为黄河内蒙古段防凌减灾工作提供技术支撑。     

河冰水力学研究进展

近几十年来,随着经济的发展,河流冰情灾害引起的损失越来越大,因此很多专家、学者投入到河冰问题的研究,使得河冰水力学得到了很大的发展。分别从天然河道、水库、人工输水渠道等原型观测研究,新型冰情观测仪器的研发和使用,冰塞演变机理、冰盖下的流速分布和泥沙输移等实验研究,冬季河道冰情发展演变过程、冰塞的形成、冰塞溃决时的洪水波等河冰动力学数值模拟研究,以及基于神经网络技术的冰情预报等方面,综述了国内外学者在冰情研究中最新的研究进展,重点介绍了其中一些具有代表性的成果,并对目前河冰工程研究中仍未解决的问题和以后需要进行的工作进行了尝试性地分析。     

融冰洪水演进的马斯京根模型

为解决参数率定过程复杂的问题,将河段内的融冰产生的流量视为河段下断面出流的一部分,构建出适用于文开河融冰时期洪水演进的马斯京根模型,并将优化算法应用到模型参数率定的过程中。以黄河宁蒙河段为例,采用试错法、非线性规划法和智能算法中的遗传算法这3种方法对所构建的模型参数进行率定。模拟结果表明:3种方法所模拟的出流过程线均合格;整体上,非线性规划法模拟的精度最高,其洪水的确定性系数D_c为0.980,过程平均相对误差RE为4.840%;而试错法模拟的洪峰流量更为准确,且冰期模拟精度高于无冰期。本研究为融冰洪水演进的模拟提供了一种新方法。     

基于神经网络理论的开河期冰坝预报研究

在北方高寒地区的天然河道,开河期冰坝形成和导致凌汛的机理复杂,目前的冰水动力学模型难以模拟和预报其发生、发展和溃决的过程,可用的冰坝预报多采用传统的统计学方法和经验判别式法,为应对严重的防凌形势,迫切需要找到冰坝预报的新方法。本文在对开河期冰坝成因及机理研究的基础上,建立了基于神经网络理论的冰坝预报模型,并将其应用到黑龙江上游凌汛灾害频发的漠河江段冰坝预报中。通过神经网络聚类法预报冰坝是否发生,神经网络聚类法预报精度为85%,高于传统统计学的几率分析法62%的预报精度。通过预报开河日期实现了对冰坝发生时间的预报,开河日期预报平均预见期为10天,最大误差2天,预报合格率100%。该模型提前准确预报2017年黑龙江漠河江段开河冰坝发生情况。及时、准确的冰坝预报能为提前制订主动防凌方案和采取必要防凌措施提供重要的依据。     

长距离输水渠道冰期运行控制研究

高纬度地区的渠道在冬季往往采用冰盖下输水,保证冰盖的稳定性是渠道冬季安全输水的前提条件。目前,渠道在冬季的运行控制多依靠经验,开展长距离渠道冰期运行控制研究对实现冰期安全输水是十分重要的。利用数值模拟的方法分析了长距离输水渠道的冰情和水情的变化过程,根据渠道内的冰情演变特性,提出冬季渠道应采用闸前常水位方式运行。鉴于气象预报以及冰情预报可能存在的不确定性,提出采用水位-流量串级的反馈控制算法,建立了渠道冰期运行控制模型,并在控制器内加入解耦环节,以提高渠道的控制效果。并通过南水北调中线干渠的数值模拟实验,对渠道冰期运行控制模型的控制效果进行了验证。结果表明,该冰期运行控制模型可以实现渠道冬季安全、适时、适量的供水目标。     

大型串联渠系冰塞-水力响应特性分析

为了定性定量描述南水北调中线工程冰塞特征与水力响应特性之间的耦合关系,采用数值模拟方法,建立了串联渠系冰塞事件-水力响应-闸门操作耦合响应模型,通过多工况对比揭示冰塞体范围、厚度和输水流量及闸门群应对方式等造成的渠系水力响应规律。研究结果表明：闸门群耦合响应下,发生冰塞事件的渠池仅影响其上游渠池的水力过程,对于发生冰塞事件的渠池,其冰塞体上游段水位壅高,下游段水位降低,而该渠池上游所有渠池水位整体降低;闸门群无响应时,冰塞可造成渠系放空风险,而PI控制器作用下的闸门群调度可明显改善渠系应对冰塞事件的水力响应,水位波动幅度随冰塞体和输水流量的增大而不断增大,在模拟工况下,闸前最大水位偏差达0.5 m,输水目标恢复时间约20 h,在冰塞体足够大时,渠系面临漫堤风险。做好渠池风险评估和优化冰塞事件应对控制器是下一步研究的重点。     

冰盖生长和消融的实验研究与数值模拟

为研究冰盖生长和消融的规律,在实验室内设计了水体结冰实验.通过实验得到冰盖厚度、水温和冰内温度随时间的变化过程.根据对水体结冰和融化物理过程的分析,建立水温与冰盖生长、消融相互作用的耦合模型.采用耦合模型来模拟水体结冰和融化过程,通过对模拟结果与实测结果的对比,发现冰厚和水温的计算值与实测值基本吻合.此结果为研究高海拔、高纬度地区封冻水库的结冰机制及冰盖下的水温时空分布提供重要理论基础.     

融冰期加厚冰盖糙率物理模型试验研究

流凌期输水能力可能成为制约输水工程冰期输水能力的瓶颈,而流凌期允许冰凌下潜,采用加厚冰盖下输水方式运行可以有效提高工程输水能力。加厚冰盖糙率的合理选择直接影响加厚冰盖形成后渠道水位和过流能力计算的正确性,但是加厚冰盖的糙率受到多种因素的影响,见刊的实测资料中,其糙率分布范围很宽。现以冻结模型冰为试验材料,以南水北调中线工程总干渠为原型,通过物理模型试验研究得到:输水渠道融冰期加厚冰盖形成初期糙率约为0.029,以供南水北调中线工程冰期输水调度和冰害防治提供参考。试验研究同时表明:水力加厚冰盖底面的最大水流弗劳德数取值0.09是合适的;力学加厚冰盖前缘都是水力加厚类型的,其长度大约与水面宽度相近;力学加厚冰盖形成和发展的过程是这样的一个循环:前缘发展→推挤增厚→前缘发展。     

凌汛期堤防漫顶溃口破坏规律断面模型试验Ⅰ:黏性土堤

凌汛期河道存在大量冰凌,导致河流壅塞、水位上涨,对堤防安全造成了严重隐患。为了探究凌汛期黏性土堤的漫顶溃口破坏规律,建立了室内水槽物理模型,模拟了冰凌条件下的堤防漫顶破坏,通过改变堤身含水率和河道流量,分析了冰凌条件下溃堤时的溃口破坏形式、溃口发展过程和水位变化过程。结果表明:溃堤过程中冰凌挤压对堤体的破坏作用明显,堤身含水率和河道流量对溃堤过程有显著的影响;与洪水条件相比,冰凌条件下溃堤时溃口前期发展较为缓慢,而中、后期较为强烈;冰凌条件下的堤前水位峰值要高于洪水条件。     

斜向进水消力井水力特性模拟研究

水利水电工程中的泄水建筑物出口往往正冲河道,圆形消力井可以很好地适应山区峡谷地形条件的变化,使下泄水流平顺归河。针对一定纵坡条件下,尾水出口与泄槽轴线呈非对称正交的圆形消力井内复杂的水力特性问题,采用有限域数值模拟计算的方法对比验证并补充了物理模型试验成果,进一步开展了沿空间射流方向的相关水力要素机理分析。研究表明:消力井内水流流态依次呈平面横向紊动扩散自由射流、主流动力自相似淹没射流和冲击射流、近壁面附着扩散旋滚水跃3个临界雷诺数分区演变过程;沿程最大流速变化符合试验半经验公式拟合规律且近似呈平面扩散分布;水体压强结构特征可分解为水平轴对称及竖直变幅下的叠加分布。     

弯曲冰块在顺直河段中的输移条件

针对弯曲冰块在顺直河段中的输移条件,以春季封冻河道的冰盖破裂机理为基础,根据水动力学、热力学、固体力学及气象水文等学科理论,综合考虑水力、热力、河势及地貌特征等影响因素,引入顺直河道固体边壁的约束条件,建立力学分析模型,进而提出了弯曲冰块在顺直河道中输移所需最小流量即临界流量的判别准则,并对其适用性及相关参数进行了研究分析。应用黄河河曲段的原型观测资料对该准则及相关参数进行了率定及验证,结果表明提出的针对弯曲冰块在顺直河段输移的临界流量计算值与实测值较为接近,可以认为该输移判别准则能够较好地用于判别弯曲冰块在顺直河段中的输移情况。此外,根据实测资料提出了反映热力消融对冰盖体厚度减小、强度降低等的综合系数表达式,可用于没有开河历史观测资料河道的冰情研究。     

冰期河流弯道冰水动力学行为研究

以黄河什四份子弯道为研究对象,基于2019-2020年度的凌情监测影像及现场试验数据,分析了河流弯道冰水动力学行为特征。结果表明:上宽下窄的河道形态是造成弯道卡冰的主要原因,流凌-封河阶段,弯顶节点工程对水流的顶托作用促进了上游回流区的形成;受弯道离心力作用,河冰聚集于河道凹岸一侧,并在回流区堆积形成冰桥,从而缩小了断面过冰面积,河道逐渐封冻;弯顶下游流速大且来冰量少,形成清沟,主流向河中发展;冰塞堆积于弯顶上游凹岸主河槽内,水流被挤压至凸岸非冰塞区,弯道主流易位;在稳封期,河道冰水动力特征基本不再变化,在解冻开河期,凸岸非冰塞区流速较大,主流区冰盖优先解冻且沿主流输移,回流区冰盖最后消融,河道主流逐渐恢复至畅流阶段,整体呈复归式。     

适用于明渠流及冰盖流的统一泥沙颗粒起动流速公式

为得到冰盖流条件下的非黏性泥沙起动公式,揭示冰期河道断面强烈冲淤变化的机理,基于Einstein假定,推导得到了同时适用于明渠流及冰盖流的统一的非黏性泥沙颗粒起动流速公式,所得公式与已有冰下泥沙起动流速试验数据符合良好.当冰盖糙率为0时,冰盖流泥沙颗粒起动流速公式即化为明渠流泥沙颗粒起动流速公式.应用所得公式,比较了明...     

Revisit submergence of ice blocks in front of ice cover–an experimental study

The present paper studies the stabilities of ice blocks in front of an ice cover based on experiments carried out in laboratory by using four types of ice blocks with different dimensions. The forces acting on the ice blocks in front of the ice cover are analyzed. The critical criteria for the entrainment of ice blocks in front of the ice cover are established by considering the drag force caused by the flowing water, the collision force, and the hydraulic pressure force. Formula for determining whether or not an ice block will be entrained under the ice cover is derived. All three dimensions of the ice block are considered in the proposed formula. The velocities calculated by using the developed formula are compared with those of calculated by other formulas proposed by other researchers, as well as the measured flow velocities for the entrainment of ice blocks in laboratory. The fitting values obtained by using the derived formula agree well with the experimental results.     

黄河大柳树河段河床演变的三维数值模拟

针对河岸冲刷、河床演变显著的河流,建立考虑河岸变形的三维水沙数值模型,对黄河大柳树河段的河势演变进行数值模拟分析研究。模型中利用三角形网格和局部网格移动及局部加密技术,采用有限体积法离散控制方程,以及基于非结构化同位网格中的SIMPLE算法进行数值求解。依据2011年11月至2012年10月黄河大柳树河段典型断面实测资料对数值模拟结果进行验证,模拟结果与实测结果吻合较好。结果表明该模型能够较好地模拟黄河大柳树河段的水流运动和河床演变,模型中提出的河岸修正技术和局部网格加密技术可有效提高模拟计算精度和效率。     

南水北调中线工程冬季输水冰情的数值模拟

南水北调中线工程总干渠是由明渠和各种过水建筑物组成的树状系统,特点是线路长、过水建筑物类型多、冰水动力学响应过程复杂。本文将冰情发展模型与树状明渠系统复杂内边界条件下的渠道非恒定流模型进行集成耦合,开发了大型长距离调水工程冬季输水冰情数值模拟平台,提出了树状明渠系统复杂内边界条件的等效变换方法和计算冰盖前缘动态发展的虚拟流动法。根据实测的沿线气象资料和设计资料,利用该平台系统模拟了在寒冷气温条件下总干渠初冰、冰盖形成、发展和消融过程。分析了冬季输水的冰情特性及冰期输水能力,提出了冰期安全运行的水力控制条件,通过对典型年总干渠敞流期、冰盖形成期、稳封期、调度期以及开河全过程的模拟,给出了安全运行输水调度方案及建议。