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The dynamic stability of the flow in a meander channel

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Science China(Technological Sciences) 2011年第4期54卷 931-940页

作者： bai yuchuan YANG YanHua Institute for Sedimentation River and Coastal Engineering Tianjin UniversityTianjin 300072China

The meander channel is one of the most common channel patterns in *** characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river *** transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent vortex in different flow conditions,the large-scale turbulent eddy structure adapted to a meander,*** this paper we study the laminar flow instability of the two-dimensional channel in a meander *** is essentially different from that in a straight channel:The neutral curve will move forward and the critical Reynolds number will *** flow is unstable in response to a wider range of the disturbance wave number,or the laminar flow instability can happen more *** above results could not be obtained in the traditional hydrodynamic stability theory so that our work in this paper would make up for the deficiency and blank in this aspect.

关键词： meander channel open-channel flow the dynamic stability of the flow

Stability characteristics of hyper-concentration flow in open channel

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Science China(Physics,Mechanics & Astronomy) 2008年第9期51卷 1316-1338页

作者： XU HaiJue bai yuchuan Institute for Sedimentation River and Coastal Engineering Tianjin UniversityTianjin 300072China

The flow instability is related to many engineering problems and belongs to a wide-ranging research field. When the problem on the transition from the laminar to the turbulence caused by the instability of the laminar is studied,the "neutral line" and the critical Reynolds number are always taken as the criterion to judge whether a certain kind of flow is stable,whose corresponding flow medium is the clear water,that is,the single-phase Newtonian fluid. And it is not studied in the traditional in-stability theory that the hyper-concentration flow widely exists in rivers. This shortage can be covered by this research. Study shows that the instability of non-Newtonian fluid such as hyper-concentration fluid,compared with Newtonian fluid such as clear water,is influenced by not only Reynolds number,the ratio of the inertia force and the viscous force,but also many other factors such as the sediment concentration,the concentration distribution,the grain size,the volu-metric weight of the sediment and so on,which make the mechanical principle even more complex. So the results of the research can supply the scientific basis for the explanations of "slurrying river",the turbulence intensity of the flow carrying sediment and the variance of the turbulence structure.

关键词： hyper-concentration stability turbulence mechanics of sediment motion

A study on the stability of laminar open-channel flow over a sandy rippled bed

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Science China(Technological Sciences) 2005年第1期48卷 83-103页

作者： bai yuchuan XU Haijue Institute for Sedimentation River and Coastal Engineering Tianjin University Tianjin 300072 China Institute for Sedimentation River and Coastal Engineering Tianjin University Tianjin 300072 China

The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become unstable as soon as the flow develops, thereby leading to the formation of sand ripples on the bed. In return, the formation of the sand ripples will modfy the instability path of the laminar flow passing over them. The wavy character of the bed will induce further instability of the flow, which is essentially different from that on a smooth bed: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily. The propagation speed of the sand ripples also affects the flow instability, since the stability of open channel flow over a movable bed is fundamentally different from that on a rigid bed. These instability effects are discussed in detail in this paper.

关键词： bed with sand ripples, open channel, flow instability.

Stability characteristics of the open channel flow above the asymmetrical irregular sand ripples

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Science China(Physics,Mechanics & Astronomy) 2010年第8期53卷 1515-1529页

作者： XU HaiJue bai yuchuan Institute for Sedimentation River and Coastal Engineering School of Civil EngineeringTianjin UniversityTianjin 300072China

Sandy bed cannot keep its original smoothness as the flows pass. With the increase of the flow intensity, the bed forms will appear as sand ripples and dune in turn. Among these morphologies, the sand ripple scale is the smallest, which is generally symmetrical when it just appears, but as time goes on, the asymmetrical form gradually develops. Just because of this sand ripples asymmetry, it manifests the influence of the flow on the bed morphology and also the impact on the laminar flow dynamical process, especially the stability characteristics. The stability features of laminar flow on open channels with the asymmetrical sand ripples are discussed, and also the results on the symmetrical sand ripples are compared in detail.

关键词： asymmetry open channel sand ripples stability

The nonlinear theory for sediment ripple dynamic process of straight river

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Science China(Technological Sciences) 2012年第3期55卷 753-771页

作者： XU HaiJue bai yuchuan State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China Institute for Sedimentation on River and Coastal Engineering Tianjin UniversityTianjin 300072China

There are various sand tipples in the natural world. The viewpoint of Yalin is that local disturbances result in laminar instability and in sand-tipple formation, namely, local disturbance^the instability of the laminar flow→the formation of sand ripples. Based on this viewpoint, a theoretical model of the resonant triad interaction and its nonlinear interaction with the sediment is established. The purpose of this model is to explain the formation and evolution of the sand-tipple and allow for analysis of the instability of open-channel flow caused by it and sand-tipple hydro-dynamic process. This model will not only pave a road to explore the mechanism of interaction between bed-form and turbulence, but also provide a good base for the study of aeolian sand-tipple formation.

关键词： straight river bed-forms symmetric sand-ripples perturbation method nonlinearity

Theoretical analyses on bed topography responses in large depth-to-width ratio river bends with constant curvatures

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Applied Mathematics and Mechanics(English Edition) 2018年第5期39卷 747-766页

作者： Shuxian GAO Haijue XU yuchuan bai Skate Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Tianjin Research Institute for Water Transport Engineering Ministry of Transport Institute for Sedimentation on River and Coastal Engineering Tianjin University

Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-width ratio, a theoretical model is established with the coupling of Navier-Stokes （N-S）~ sediment transport, and bed deformation equations. The flow characteristics and bed response of river are obtained with the perturbation method. The research results show that, under the effect of two- dimensional flow disturbance, the bars and pools present the regular response. For a given sinuousness, the amplitude of the bed response can be used as a criterion to judge the bedform stability. The effects of the Reynolds number, disturbance wavenumber, sinuousness, and bed morphology gradient on the bed response development are described.

关键词： meandering river large depth-to-width ratio channel disturbance wave,bed response

Applications of sediment sudden deposition model based on the third-generation numerical model for shallow water wave

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Acta Oceanologica Sinica 2007年第3期26卷 142-149页

作者： bai yuchuan ZHANG Yinqi ZHANG Bin Institute of Sediment on River and Coast Engineering Tianjin University Tianjin 300072 China China Communication Construction Corporation First Harbor Consultants Co. Ltd Tianjin 300222 China

The existing numerical models for nearshore waves are briefly introduced, and the third-generation numerical model for shallow water wave, which makes use of the most advanced productions of wave research and has been adapted well to be used in the environment of seacoast, lake and estuary area, is particularly discussed. The applied model realizes the significant wave height distribution at different wind directions. To integrate the model into the coastal area sediment, sudden deposition mechanism, the distribution of average silt content and the change of sediment sudden deposition thickness over time in the nearshore area are simulated. The academic productions can give some theoretical guidance to the applications of sediment sudden deposition mechanism for stormy waves in the coastal area. And the advancing directions of sediment sudden deposition model are prospected.

关键词： Boussinesq equation mild-slope equation third-generation numerical model for shallow water wave sedimentsudden deposition

A type of dynamic mechanism of river hydraulic geometry

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Science China(Technological Sciences) 2014年第4期57卷 847-855页

作者： bai yuchuan JI ZiQing ZHANG MingJin State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Tianjin Research Institute for Water Transport Engineering Key Laboratory of Engineering Sediment of Ministry of Transport

Large-sczde structure of river flow is the main driving force for bed erosion-deposition and bank delbrmation. The structure shapes and retains a corresponding hydraulic geometry form. Therefore, the most stable flow structure is the probable natural river plane formation. Natural coordinate transformation and perturbation methods were adapted to deform the governing equations of sine-generated river basic flow and disturbance flow independently. The stability and retention of perturbation waves were analyzed in our model to explain why meandering rivers followed a certain type of tqow path. Computation results showed that all types of perturbation waves in meandering rivers were most stable when the meandering wave number was about 0.39-0.41. We believe that this type of stable flow structure shaped a certain meandering river. The statistical average length-width ratios of Yalin, Habib and da Silva and Leopold and Wolman somewhat confirmed our most stable river mean- dering wave number. In some ways, meandering rivers always tend to diminish internal turbulence intensity.

关键词： meandering river stability coherent disturbance river optimization

On the mechanisms of the saltating motion of bedload

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International Journal of Sediment Research 2017年第1期32卷 53-59页

作者： Youhua Chen yuchuan bai Dong Xu State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Jinchang Water Conservancy Department

Saltation of sediment particles is an important pattern of bedload *** on force analysis for sediment particles,a Lagrangian model was proposed for the saltating motion of bedload in river flows,which was then solved with numerical *** results on the saltating trajectories neglecting particle rotation and turbulence effects compare fairly well with experimental *** mean values of the saltation parameters(saltation height,length and velocity) also agree well with the previous experimental *** on the numerical results,regression equations for the dimensionless saltation height,length and velocity were *** the numerically achieved characteristics of the sediment saltation,we also obtained mathematical expression for the sediment transport *** studies in this paper are significant for its contribution to mechanism of the bedload motion and the computation of sediment transport rate.

关键词： Bedload Saltation Numerical model Transport rate