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APPliCATION OF MULTIGRID METHOD IN 2-D MATHE-MATICAL MODEL IN OPEN CHANNELS

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Journal of Hydrodynamics 2000年第3期12卷 59-67页

作者： Cao, Zhifang li, yitian Zhao, Mingdeng Wuhan Univ of Hydraulic and Electric Engineering Wuhan China

In 2-D mathematical model, one of important problems is to improve computational speed. The multigrid method is a new rapid iteration method developed in the recent 20 years, and it has been widely used in many fields, but in sediment mathematical model it has been rarely used, especially in plane mathematical model with large scale computational scope. In this paper, the multigrid method was introduced and expected to be used widely in this field. And it is verified that the more layers are adopted, the higher convergent speed will be reached in computation.

关键词： Flow of water Sediment transport Mathematical models Iterative methods Numerical methods Computational fluid dynamics

Relationship between the equilibrium morphology of river islands and flow-sediment dynamics based on the theory of minimum energy dissipation

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International Journal of Sediment Research 2022年第4期37卷 514-521页

作者： Xuhai Yang Zhaohua Sun Jinyun Deng Dongfeng li yitian li State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Department of Geography National University of Singapore

River islands are vital geomorphic units in alluvial rivers, and the variation of their morphology and position plays a significant role in regulating flow-sediment transport and channel stability. Based on the theories of minimum energy dissipation theory of fluid movement and river morphodynamics, this study uses the river islands in anabranching channels to analyze the relationship between the shape coefficient of river island and the flow-sediment dynamics under stable equilibrium conditions. Results indicate that the river islands could adjust their lengths and widths to reach an appropriate allocation of flow diversion ratio and sediment separation ratio in the two anabranching channels to ensure flow-sediment being smoothly transported downstream and achieve the minimum energy dissipation. Under the minimum energy dissipation condition of flow-sediment transport balance, the ratio of “sediment separation ratio” to “flow diversion ratio” in short and straight branching channels is between 1 and *** the proportion of flow-sediment transport reaches its maximum, the steady island morphology coefficient is approximately 0.2; that is, the island length is five times the width. We verify the steady island morphology coefficients using two typical islands in the middle and lower reaches of the Yangtze River and find the relative error is within ±3%.

关键词： Equilibrium morphology of islands Flow-sediment dynamics Minimum energy dissipation theory Sediment separation ratio Flow diversion ratio

Flow resistance in the channel-bar landscape of large alluvial rivers

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Frontiers of Earth Science 2024年第2期18卷 412-421页

作者： Yong HU Congcong liU Jinyun DENG Wei ZHANG yitian li State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072China CCCC Second Harbor Engineering Company Ltd Wuhan 430040China Key Laboratory of Large-span Bridge Construction Technology Wuhan 430040China Research and Development Center of Transport Industry of Intelligent Manufacturing Technologies of Transport Infrastructure Wuhan 430040China CCCC Highway Bridge National Engineering Research Centre Co.Ltd Wuhan 430040China

Accurate approaches for estimating flow resistance in large alluvial rivers are fundamental for simulating discharge,sediment transport,and flood ***,methods for estimating riverbed resistance and additional resistance in the channel-bar landscapes remain poorly *** this study,we used in situ river bathymetry,sediment,and hydraulic data from the Shashi Reach in the Yangtze River to develop a semi-empirical approach for calculating flow *** method quantitatively separates flow resistance into riverbed resistance and additional resistance and shows high accuracy in terms of deviation ratio(~20%),root-mean-square error(~0.008),and geometric standard deviation(~3).Additional resistance plays a dominant role under low-flow conditions but a secondary role under high flows,primarily due to the reduction in momentum exchange in channel-bar regions as discharge *** resistance first decreases and then increases,which might be attributed to bedform changes in the lower and transitional flow regimes as flow velocity ***,our findings further the understanding of dynamic changes in flow resistance in the channel-bar landscapes of large river systems and have important implications for riverine ecology and flood management.

关键词： flow resistance channel-bar landscape interaction region large river bedform

On Newton-like Methods for Solving Nonlinear Equations

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Geo-Spatial Information Science 2006年第1期9卷 76-78页

作者： KOU Jisheng liU Dingyou li yitian HE Julin State Key Laboratory of Water Resources and Hydropower Engineering Sciences Wuhan University 8 South Donghu Road Wuhan 430072 China

In this paper, we present a family of general New to n-like methods with a parametric function for finding a zero of a univariate fu nction, permitting f′(x)=0 in some points. The case of multiple roots is n ot treated. The methods are proved to be quadratically convergent provided the w eak condition. Thus the methods remove the severe condition f′(x)≠0. Based on the general form of the Newton-like methods, a family of new iterative meth ods with a variable parameter are developed.

关键词： Newton method Newton-like method nonlinear equations iteration method

Water level variation characteristics under the impacts of extreme drought and the operation of the Three Gorges Dam

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Frontiers of Earth Science 2019年第3期13卷 510-522页

作者： Yuanfang CHAI yitian li Yunping YANG Sixuan li Wei ZHANG Jinqiu REN Haibin XIONG State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072China Key Laboratory of Engineering Sediment Tianjin Research Institute for Water Transport EngineeringMinistry of TransportTianjin 300000China

Under the influence of a climate of extreme drought and the Three Gorges Dam (TGD) operation, the water levels in the middle and lower reaches of the Yangtze River in 2006 and 2011 changed significantly compared with those in the extreme drought years of 1978 and 1986. To quantitatively analyze the characteristics of water level variations in 2006 and 2011, a new calculation method was proposed, and the daily water level and discharge from 1955-2016 were collected in this study. The findings are as follows: in 2006 and 2011, the water level in the dry season significantly increased, but that in the flood season obviously decreased compared with the levels in 1978 and 1986. Here, we described this phenomenon as “no low-water-level in dry season, no high-water-level in flood season”. Based on the calculation method, the contributions of climate variability and the Three Gorges Dam operation to water level variations in the middle and lower reaches of the Yangtze River were calculated, and the contributions indicated that climate variability was the main reason for the phenomenon of “no low-water-level in diy season, no high-water-level in flood season” instead of flood peak reduction in the flood season and drought runoff implementation in the dry season, which are both induced by TGD.

关键词： water level extreme drought climate the Three Gorges Dam the Yangtze River Basin

Flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam

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Journal of Geographical Sciences 2022年第10期32卷 2013-2035页

作者： HU Yong DENG Jinyun li yitian liU Congcong HE Zican State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072China CCCC Second Harbour Engineering Co Ltd Wuhan 430040China

Since the Three Gorges Dam(TGD)was put into operation,the flood water level at an identical discharge rate has not displayed a decreasing trend along the middle reaches of the Yangtze River(MYR).The flow resistance variations of the channel and bars in response to the operation of the TGD remain poorly understood,despite the importance of understanding these for water disaster mitigation and water environment ***,the impacts of the TGD on the downstream flow resistance of the channel and bars in the MYR were analyzed using systematic surveys of hydrological datasets,cross-sectional profiles,sediment datasets,and remote sensing images,during different *** the actual natural conditions in the MYR,a modified semi-empirical formula,which considered the grain,dune resistance,as well as the topographic features of the riverbed,was proposed to predict the channel ***,the effect of various dam-control flow and sediment elements on the variation in different flow resistance components,and the corresponding relationships among them were *** showed a decline in the comprehensive,channel,and bar resistances as the discharge increased,whereas there was a slight increase when reaching the bank-full ***,the bar resistance occupied 65%,while the channel resistance,in which dune resistance was much larger than grain resistance,contributed 35%to the comprehensive *** addition,while flow resistance rose over time,there was a decline as the distance from the TGD *** conclusion,the increased dune and bar resistances,interpreted by the fluctuated channel longitudinal profile and growing vegetated area on bars,were the dominant factors preventing the flood water level from dropping.

关键词： flow resistance water level channel geomorphology bar Three Gorges Dam Middle Yangtze River

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Erosion-deposition patterns and depo-center movements in branching channels at the near-estuary reach of the Yangtze River

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Frontiers of Earth Science 2020年第3期14卷 537-552页

作者： Boyuan Zhu Jinyun Deng Jinwu Tang Wenjun Yu Alistair G.L.Borthwick Yuanfang Chai Zhaohua Sun yitian li School of Hydraulic Engineering Changsha University of Science&TechnologyChangsha410114China Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province Changsha410114China State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan430072China Changjiang Institute of Survey PlanningDesign and ResearchWuhan430010China Changjiang Waterway Institute of Planning Design&ResearchWuhan430040China School of Engineering The University of EdinburghThe King’s BuildingsEdinburghEH93JLUK Department of Earth Sciences Vrije Universiteit AmsterdamBoelelaan 10851081 HVAmsterdamThe Netherlands

Channel evolution and depo-center migrations in braided reaches are significantly influenced by variations in *** study examines the effect of runoff variations on the erosion-deposition patterns and depocenter movements within branching channels of the near-estuary reach of the Yangtze *** assume that variations in annual mean duration days of runoff discharges,ebb partition ratios in branching channels,and the erosional/depositional rates of entire channels and sub-reaches are representative of variations in runoff intensity,flow dynamics in branching channels,and morphological features in the *** results show that the north region of Fujiangsha Waterway,the liuhaisha branch of Rugaosha Waterway,the west branch of Tongzhousha Waterway,and the west branch of Langshansha Waterway experience deposition or reduced erosion under low runoff intensity,and erosion or reduced deposition under high runoff intensity,with the depocenters moving upstream and downstream,*** waterway branches undergo opposite trends in erosion-deposition patterns and depo-center movements as the runoff *** morphological changes may be associated with trends in ebb partition ratio as the runoff discharge rises and *** flattening the intra-annual distribution of runoff discharge,dam construction in the Yangtze Basin has altered the ebb partition ratios in waterway branches,affecting their erosion-deposition patterns and depo-center *** trends are likely to continue into the future due to the succession of large cascade dams under construction along the upper Yangtze and ongoing climate change.

关键词： near-estuary reach Yangtze River runoff discharge ebb partition ratio erosion-deposition pattern depo-center movement

Suspended sediment load in the turbidity maximum zone at the Yangtze River Estuary： The trends and causes

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Journal of Geographical Sciences 2014年第1期24卷 129-142页

作者： YANG Yunping li yitian SUN Zhaohua FAN Yongyang State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Wuhan430072 China

Based on the analysis of suspended sediment elements at estuaries, influence of human activities and estuarine regulation projects on the turbidity maximum zone was studied according to the measurement data between 1959 and 2011. It was found that human activi- ties had little effect on the seaward water while the sharp decrease of sediment volume and concentration in runoff led to the sharp decrease of turbidity maximum zone in the estuary. The concentration at outside sea and Hangzhou Bay did not change, and that along the Subei coast also decreased a little, which had no influence on the turbidity maximum zone. Com- pared with the concentration between 1959 and 1999, the peak of concentration moved up- stream in the estuary, and the concentration in 2000-2009 decreased by about 24.73% with a narrower variation range along the river to the sea. The suspended sediment concentration in North Passage was low in upstream and downstream because of the decrease of seaward sediment and coarsening of bed material, while it was relatively high in the middle due to the influence of sediment cross the north jetty.

关键词： turbidity maximum zone (TMZ) suspended sediment concentration trends and causes Yangtze Riverestuary

A STUDY ON THE EQUIliBRIUM PROFILE FOR THE LUOSHAN-HANKOU REACH IN THE MIDDLE YANGTZE RIVER

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International Journal of Sediment Research 2003年第2期18卷 107-114页

作者： Jinyun DENG ,yitian li Wuhan University Key Lab of Water and Sediment Sciences Ministry of Education 430072 Wuhan

Based on the morphology of the Luoshan-Hankou reach in the middle Yangtze River, the one dimensional (1-D), unsteady flow and sediment transport model was applied to study the river channel equilibrium profile. Meanwhile, a simple theoretical model relating the equilibrium profile and the incoming flow and sediment from the upper reach was developed. The numerical simulation results of the 1-D model were compared with the corresponding results of the theoretical model with reasonable agreement found between the two models. Finally, the equilibrium slope variations and their effects on flood control in response to the changes in the sediment transport process because of the Three Gorges Reservoir were analyzed using the 1-D model.

关键词： Equilibrium profile Incoming flow and sediment Slope Flood level 1-D mathematical model