分流河道淤积与洞庭湖萎缩对长江洪灾的影响

1998年长江流域的特大洪水灾害表明，目前长江流域防洪体系在面临特大洪水时仍然显得比较脆弱．以长江中下游荆江洞庭湖地区为背景，运用有限体积计算方法建立了一维河道和二维湖泊交错的复杂水系洪水演进数值模型，细致分析了由于分流河道淤积以及洞庭湖萎缩对长江洪灾的影响．得出长江分流河道和洞庭湖由于泥沙淤积产生的萎缩将造成长江干流河道洪水期间水位抬升，从而加重长江的洪水灾害．其结论可为长江中下游地区的洪水治理提出建设性意见．     

Optimal control of drainage basin considering moving boundary

The purpose of this article is to present a technique to optimally control river flood using a drainage basin considering a moving boundary. The main theme of this article is to obtain outflow discharge from the drainage basin that maintains the water level at a downstream point and empties the drainage basin as soon as possible. The water flow phenomenon inside the drainage basin when a river flood occurs is considered. This phenomenon can be analysed by the finite element method considering a moving boundary. The optimal control theory can be implemented to obtain the optimal control discharge. The finite element analysis with a moving boundary is introduced in the optimal control theory. A new boundary condition on the downstream side of the river is proposed. This condition is formulated by the solitary wave condition based on the basic water level being capable of representing natural water surface. As a numerical study, optimal control of shallow water flow is carried out for the Tsurumi River and its drainage basin model.     

Vortices and wall shear stresses in asymmetric and symmetric channels with sinusoidal wavy walls for pulsatile flow at low Reynolds numbers

Numerical simulation and flow visualization were performed to study the dynamical behavior of vortices generated in channels with two different geometries, i.e., a periodically converging–diverging channel and serpentine channel, both having sinusoidal wavy walls. This system for pulsatile flow is used to enhance heat and mass transfer in very viscous liquids. The numerical results predict well the dynamical behavior of vortices and agree with the flow visualizations. For both channels, the vortex expands in each furrow of the channel walls during the deceleration phase and shrinks during the acceleration phase, which leads to fluid exchange between the vortex and the mainstream. The time-averaged vortex strength and wall shear stresses increase, as the frequency of fluid oscillation increases under a fixed oscillatory fraction of the flow rate. However, above a certain value of the frequency, they reversely decrease due to viscous effects. This frequency for the serpentine channel is smaller than that for the converging–diverging channel. The channel geometries are found to have an important effect of the flow characteristics.     

Study on resistance coefficient in compound channels

This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility (SERC-FCF). And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods can not assess correctly the conveyance capacity of compound channels is also analyzed in this paper.The project supported by the National Natural Science Foundation of China (50279024), the National Key Basic Research and Development Program of China (973 Program) (2003CB415202) and the Specialized Research Fund for the Doctoral Program of Higher Education (20030610039)The English text was polished by Ron Marshall     

复杂含水条件下滑坡的稳定性分析及治理措施

成渝铁路K492滑坡为一大型堆积层老滑坡,自1998年开始变形以来,每年雨季出现线路外移、下沉和地面开裂现象,且日趋加大。随着地下水位和前缘长江水位的变化,该滑坡呈阶段性滑动变形,它的形成与发展以孔隙水压力为主。确定了该滑坡在不同水位条件下的安全系数,在特大洪水位下处于不稳定状态。同时提出根据水位的变化、裂隙的发育情况及裂隙水位计算其安全系数,对复杂含水的堆积层滑坡应以支挡和排水综合治理。     

梯级溃坝洪水洪峰增强机制

我国在多条河流上修建了大量梯级水库, 梯级坝溃决诱发洪水大大超过单坝溃决洪水洪峰, 因此亟需加深对梯级坝溃决洪水洪峰增强机制的认识. 本文建立了梯级坝溃决洪水演进过程的一维浅水动力学模型, 发展了一套能捕捉激波、干湿边界和保平衡结构的数值求解方法, 通过大量算例, 系统研究了梯级坝溃决洪水演进过程的质量转化和能量转化机制. 研究结果表明, 梯级溃决中, 上游溃决诱发的洪水大大增大下游水库的质量和动量, 形成一个带动量的水塔, 同时在尾部残留一个动量较大的射流, 不断补充下游坝体溃决后水塔的质量和动量, 持续维持洪峰高度. 根据该射流-水塔机制, 建立了梯级坝溃决洪水演进过程对应的射流-水塔单坝溃决洪水过程等效模型, 该等效模型基本反映了梯级坝溃决诱发洪水的洪峰过程, 并成功预测了多个坝间距为百公里量级的梯级坝溃决洪水洪峰高程和流量, 可望为流域防洪和梯级坝设计提供理论依据.      

A non-horizontal multi-layer numerical model for the flow in natural rivers

A non-horizontal multi-layer element model is developed for the simulation for the flow in natural rivers. Either Cartesian coordinates or sigma coordinates will experience difficulties in dealing with the water surface and irregular bed topography of natural rivers. To create the surface-fitting and non-deformed cells, the newly developed model divides the water column into several layers with non-horizontal interfaces which are nearly parallel to the water surface. The irregular bed topography is also represented by the layered integration between non-horizontal interfaces. Two case studies for the flow in a straight channel and the flow in an S-shaped meander channel are conducted with good agreement between the numerical predictions and the analytical or experimental results. The model is further applied for the investigation of the flow in a 12-km-long and 3.46-m-drop reach of the Yangtze River with the water surface evaluation and the stream-wise velocity satisfactory accordance with the observed data.     

Flow division at a channel crossing with subcritical or supercritical flow

The passage of an extreme storm over an urban area can lead to the flooding of the streets if the rainfall intensity exceeds the design value and/or the drainage system is not functional. The study of flow distribution in street networks thus is important for the design of flood protection measures. The flow distribution is affected by the junction flow characteristics, inflow discharges and downstream water depths. To reduce the degree of empiricism, a 3D Reynolds‐averaged Navier–Stokes equations model has been implemented in this study to investigate the flow phenomena in a cross junction. The Spalart–Allmaras model is used for turbulence closure. The numerical model utilizes the split‐operator approach, in which the advection, diffusion and pressure propagations are solved separately. The numerical model predicts accurately the flow distribution in a channel crossing under different subcritical flow conditions, for which experimental data are available. Recirculation zones exist at both the downstream channels and the associated contraction coefficient varies linearly with the ratio of the discharges at the two inlets. Secondary currents are apparent for the flow with strong asymmetric outlet conditions. Under supercritical inflow conditions, the model reproduces the hydraulic jump and hydraulic drop phenomena and predicts accurately the relationship between the input power ratio and the outflow discharge ratio of the street crossing. Copyright © 2009 John Wiley & Sons, Ltd.     

STUDY ON DEBONDING FAILURE MODEL OF POLYUREA-BASED COATING WITH HIGH VELOCITY WATER FLOW BASED ON COHESIVE ZONE MODEL

冲磨和空蚀破坏是水利水电设施最为常见的病害之一,严重影响水利水电设施的安全运行和效益发挥. 泄洪建筑物通常喷涂聚脲基涂层来提高抗冲耐磨性能,但在泄洪高速水流速度作用下抗冲磨聚脲基涂层的剥离破坏机理的研究尚属空白. 本文基于高速水流的流态形式,提出了高速水流对泄洪建筑物的力学作用模型,水流作用对泄洪建筑物的载荷主要包括拖曳力、冲击力、脉动力和上浮力;采用内聚力模型表征聚脲基涂层与泄洪建筑物防护体界面的剥离破坏过程,建立了高速水流聚脲涂层的剥离破坏模型, 给出了模型的有限元形式方程、本构关系以及损伤起始原则、演化原则和接触碰撞模型. 通过聚脲涂层与混凝土基底的剥离破坏试验,分析了不同剥离倾角下界面剥离破坏的拉应力与倾角之间的变化规律,得到了聚脲涂层剥离破坏过程中应力-$\!$-位移变化关系. 根据剥离破坏试验计算了界面剥离破坏断裂模型参数,采用数值方法对模型进行了验证,试验结果与模型计算结果吻合良好,为泄洪建筑物的抗冲耐磨设计提供理论依据.     

Micron-scale channel formation by the release and bond-back of pre-stressed thin films: A finite element analysis

Buckling of thin films on a rigid substrate during use or fabrication is a well-known but unwanted phenomenon. However, this phenomenon can also be exploited to generate well-controlled patterns at the micro and nano-scale. These patterned surfaces find various technological applications such as optical gratings or micro/nano-fluidic channels. In this article, we present a numerical model that accounts for the buckling-up of pre-strained thin films by a reduction of the interface toughness and the subsequent bond-back. Channels are formed whose dimensions can be controlled by tuning the film dimensions, film thickness and stiffness, the eigenstrain in the film and the cohesive interface energy between the film and the substrate. We will show how the buckling-up and draping back processes can be captured in terms of a limited set of dimensionless parameters, providing quantitative insight on how these parameters should be tuned to generate a specified channel geometry.     

基于内聚力模型的高速水流聚脲基涂层剥离破坏模型研究

冲磨和空蚀破坏是水利水电设施最为常见的病害之一,严重影响水利水电设施的安全运行和效益发挥. 泄洪建筑物通常喷涂聚脲基涂层来提高抗冲耐磨性能,但在泄洪高速水流速度作用下抗冲磨聚脲基涂层的剥离破坏机理的研究尚属空白. 本文基于高速水流的流态形式,提出了高速水流对泄洪建筑物的力学作用模型,水流作用对泄洪建筑物的载荷主要包括拖曳力、冲击力、脉动力和上浮力;采用内聚力模型表征聚脲基涂层与泄洪建筑物防护体界面的剥离破坏过程,建立了高速水流聚脲涂层的剥离破坏模型, 给出了模型的有限元形式方程、本构关系以及损伤起始原则、演化原则和接触碰撞模型. 通过聚脲涂层与混凝土基底的剥离破坏试验,分析了不同剥离倾角下界面剥离破坏的拉应力与倾角之间的变化规律,得到了聚脲涂层剥离破坏过程中应力-$\!$-位移变化关系. 根据剥离破坏试验计算了界面剥离破坏断裂模型参数,采用数值方法对模型进行了验证,试验结果与模型计算结果吻合良好,为泄洪建筑物的抗冲耐磨设计提供理论依据.      

Steady suspension flows into two-dimensional horizontal and inclined channels

In this study a model which was developed previously is used to theoretically investigate the steady flow of a particulate suspension into two-dimensional horizontal and inclined channels. The continuity equation for the fluid and the simplified two-dimensional Navier-Stokes equations are then solved together with a particle concentration equation. This latter equation is formulated by considering the balance between the particle flux due to gravity with the corresponding particle fluxes due to convection and shear-induced diffusion. The resulting coupled system of equations is solved numerically using a specialised finite-difference method. It is found, for the parameter range for flows of proppants in hydraulic fractures, that when the suspension enters the channel with a uniform velocity profile it almost instantaneously becomes parabolic. In addition, the effects of particle sedimentation are most dominant in the entrance region, but further downstream such effects are balanced as shear-induced particle diffusion becomes more important. It is also shown that the suspension flow depends critically on the choice of the parameters used, e.g. the ratio of the particle radius to the height of the channel.     

A POD-based reduced-order model for uncertainty analyses in shallow water flows

ABSTRACT

This work presents an intrusive reduced-order model (IROM) for uncertainty propagation analyses for flood flows. The 2D shallow water equations are reduced using Galerkin’s projection onto bases obtained from the snapshot-based proper orthogonal decomposition technique. To speed up the computations, the non-polynomial and nonlinear momentum and friction terms are judiciously approximated and the time accuracy issues are addressed using the principal interval decomposition technique. The performance of the IROM is investigated in some test cases. Also, this model is applied to the study of uncertainty propagation for a hypothetical flood in a real river, to derive a probabilistic flood map. The upstream discharge and the Manning roughness coefficient are considered as the uncertain parameters. For relatively small variations around the mean of the inputs, the comparisons of the statistical moments (mean and standard deviation) of the water depth show errors, between the reduced and full models, less than 0.72%. These simulations were completed at up to 50 times faster using the proposed reduced model.     

Developing laminar convection in a vertical double-passage channel

 The effect of the presence of a thin, perfectly conductive baffle on the development of laminar convection in a vertical channel has been investigated numerically. The channel has different constant wall temperatures which are higher than those at the entrance. Velocity and temperature profiles have been presented. The effect of the different parameters on heat transfer in the channel has been discussed. The occurrence of flow reversal has been observed in some cases but examination of this phenomenon has been considered to be beyond the scope of the present work. For long channels, the numerical solutions approach the fully developed flow analytical solution. Finally, the results showed that higher values of Nu_h can be obtained when the baffle is near the hot wall. Received on 23 May 2000     

Concurrent use of finite element and finite volume methods for shallow water flows in locally 1‐D channel networks

A numerical model is developed for shallow water equation in locally 1‐D channel networks. The model concurrently uses the standard Galerkin finite element method for the continuity equation and the finite volume method with an upwind scheme for the momentum equation. The surface gradient method is consistently employed. A minimum treatment is given for channel junctions so that application to multiply connected channels do not require any special consideration The model is capable of computing different types of transcritical flows, wet and dry flows, and flows with complex source terms. Standardized test problems and laboratory experimental data are used for verifying the model. Applicability of the models is validated in a multiply connected channel network draining hydromorphic farmlands located in a West African savanna, and Manning's roughness coefficient is identified, so that the steady solution is consistent with field observations. Unsteady simulation demonstrates that the model is capable of stably reproducing shifts of hydraulic jumps in flows of sub‐millimeter water depths. Copyright © 2011 John Wiley & Sons, Ltd.     

Entrance effects in the channels of the parallel plate stack in oscillatory flow conditions

This paper considers an entrance flow into the channels formed by a stack of parallel plates, placed in an acoustic resonator that provides oscillatory flow forcing. Interesting complex flow phenomena around the extremity of the stack are observed, essentially due to the introduction of cross-sectional discontinuities: vortex formation and shedding during the fluid ejection from the channels and development of an entrance flow during the suction phase, when the fluid enters the channels from outside. It is the latter that is of particular interest in this study. Particle image velocimetry (PIV) is used to investigate the flow structures in the “entrance region”. Velocity profiles are measured as a function of phase angle within an oscillation period and the distance from the stack end into the channel. Using the data obtained, an “entrance length” defined by analogy with existing fluid mechanical definitions, is estimated. The experiments are supplemented by CFD calculations to improve the understanding of such entrance flows.     

Numerical analysis of pressure drop oscillations in parallel channels

In this study pressure drop oscillations in two parallel channels are analyzed taking into account the thermal capacity of the pipes. A different limit cycle than the one that takes place in a single channel system is found. During the instability one channel always follows the typical pressure drop oscillations limit cycle while the other channel oscillates always in the superheated vapor region. This behavior leads to very high wall temperatures at the outlet of the heated pipe. This undesirable situation with one channel operating in the superheated vapor region takes place also for the maldistributed stable solutions.     

Influences of the fish-mouth project and the groins on the flow and sediment ratio of the Yangtze River waterway

A depth-integrated two-dimensional numerical model of current, salinity andsediment transport was proposed and calibrated by the observation data in the Yangtze RiverEstuary. It was then applied to investigate the flow and sediment ratio of the navigationchannel, i. e. the North Channel of the Yangtze River Estuary, before and after the firstphase waterway project is implemented. Particularly, the influences of groin length and theorientation of the submerged dam on the flow ratio and sediment load discharging into theNorth Channel were discussed. The numerical results demonstrate that less sediment loaddischarges into the navigation channel, which unburdens the waterway dredging, but in themeantime the flow ratio is also decreased. The flow and sediment ratio can be adjusted bychanging layout and dimensions of the hydro-structures, such as the groin length, the topheight, etc. The effect of the orientation of the submerged dam is more obvious than thegroin lengh.     

金沙江美姑河牛牛坝水电站库区泥石流对工程影响分析

金沙江美姑河牛牛坝水电站库区泥石流沟分布面积广、发生频率高;调查表明库区现有不同类型泥石流沟31条,其中属于高度危险的泥石流沟4条,中度危险的泥石流沟15条;这些泥石流不会造成严重的堵河问题。在施工期泥石流对水电站工程的影响突出,特别是靠近库首的泥石流对工程的安全构成威胁。水库蓄水后,库区泥石流对水电站工程影响有所降低,但位于大坝下游区的泥石流对水电站正常运行仍有较大的影响。     

Prediction of liquid level distribution in horizontal gas-liquid stratified flows with interfacial level gradient

A one-dimensional momentum equation has been derived based on a two-fluid model and used to predict the axial distribution of liquid level or void fraction in steady, cocurrent, gas-liquid stratified flows in horizontal circular pipes and rectangular channels. The equation is carefully formulated to incorporate the effect of interfacial level gradient. Two different critical liquid levels are found from the momentum equation and are adopted as a boundary condition to calculate the liquid level or void fraction distribution upstream of the channel exit. The predicted void fraction distributions are compared with the experimental data obtained in a rectangular channel in this work and other data reported for large-diameter pipes. Good agreement is shown for air-kerosene, air-water and stream-water stratified flows with a smooth gas-liquid interface.