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Effects of logjams on river hydrodynamics under inundation conditions

Journal of Hydrodynamics 2024年第4期36卷 757-771页

作者： Huai-jian Bao Ping Wang Wei-jie Wang Yu-yan Liu Tian-jiao Feng School of Soil and water Conservation Beijing Forestry UniversityBeijing100091China State key Laboratory of Simulation and Regulation of water Cycle in River Basin China Institute of Water Resources and Hydropower ResearchBeijing100048China

Large wood in rivers can lead to accumulations in the river channel, affecting local flow structures, aquatic habitats, and the river’s topography. This plays a crucial role in the ecological restoration of the river. This paper presents flow field measurements downstream of six types of logjams at different flow velocities using acoustic Doppler velocimetry (ADV) for artificially designed engineered logjams. The results indicate that the presence of logjams reduces the flow velocity and increases the turbulent kinetic energy in the wake region, and as the distance downstream increases, the flow velocity and turbulence intensity in the wake region gradually return to the upstream level. The minimum values of normalized flow velocity under different conditions are located in the region of the bottommost logs. The differences in normalized flow velocity at various flow rates are not significant. Jets are less likely to be generated in logjams with larger and more concentrated projection areas, but the strength of the jet is influenced by the physical structure of the logjam (projection area, gap ratio). The flow distribution behind the logjam is primarily influenced by the proportion of the projected area in different regions. Changes in the vertical physical structure of the logjam have minimal effect on the lateral flow distribution. Flow velocity in the gap area (b0) at the bottom of different logjams is influenced by their physical structure. The larger the overall blockage area of the logjams, the larger the flow velocity in the bottom gap area will be. The flow velocity in the bottom gap area of a densely placed logjam is mainly influenced by the gap ratio. The velocity of flow in the gap area can impact the initiation and deposition of sediment near the logjam. However, the internal structure complexity of the logjam does not significantly affect river energy dissipation and flow attenuation. This study broadens the applicability of certain theoretical models a

关键词： Open channel flow engineered logjams nonuniform logs flow structure river ecological restoration

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Flow regime and head loss in a drip emitter equipped with a labyrinth channel

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Journal of Hydrodynamics 2016年第4期28卷 610-616页

作者：张林吴普特朱德兰郑超 Institute of Soil and water Conservation Northwest A&F University College of water Resources and Architectural Engineering Northwest A&F University

Labyrinth channels are widely adopted in emitter designs to regulate the water *** flow regime and the head loss of labyrinth channels have significant impacts on the hydraulic performance of *** this study,the flow behavior of water passing through an emitter channel is observed using the micro particle image velocimetry（PIV）,and the head loss during the flow is analyzed for an emitter with a triangular labyrinth *** results show that the flow regime is consistent with the classical theory of hydraulics governing straight channels,even when the cross-sectional area is very small（as small as 0.5 mm×0.5 mm）.The critical Reynolds number from laminar to turbulent flows in a labyrinth channel is approximately in a range between 43 and *** local head loss factor decreases as the Reynolds number increases for labyrinth channels with smaller cross-sectional areas,such as 0.5 mm×0.5 mm and 1.0 mm×1.0 *** local head loss factor is not related to the Reynolds number and is only a function of the boundary conditions of the labyrinth channel when the Reynolds number exceeds approximately 1 000（for cross-sectional areas of 1.5 mm×1.5 mm and 2.0 mm×2.0 mm）.The ratio of the local head loss to the total head loss total（ /）j fh h first increases and then remains nearly constant as the Reynolds number increases in the labyrinth *** head loss in the labyrinth channel is almost equal to the local head loss,and total（ h_j/h_（ftctal））is approximately 0.95 for cross-sectional areas of greater than 1.0 mm×1.0 *** results can be used for optimizing the design of emitter channels.

关键词： Reynolds emitter turbulent laminar straight sectional regime hydraulic passing beads

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Crack status analysis for concrete dams based on measured entropy

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Science China(Technological Sciences) 2016年第5期59卷 777-782页

作者： WU Bang Bin WU Zhong Ru CHEN Bo SU Huai Zhi BAO Teng Fei WANG Shao Wei State key Laboratory of Hydrology-water Resources and Hydraulic Engineering Hohai University College of water Conservancy and Hydropower Engineering Hohai University

The integrity and safety of concrete darns are seriously affected by the existing cracks in dam bodies, and some serious cracks may cause dam failure or disaster. The propagation of cracks in concrete dams is accompanied by changes in energy distribution, which can be represented by changes in the structure＇s system entropy. Therefore, the entropy theory can be used in analyzing the behavior of dam cracks. Due to the randomness and locality of crack propagation, it is difficult to predict the loca- tion of cracks by traditional monitoring methods. To solve this problem, the influence of spatial positions of monitoring points on inspection zones is represented by a weight index, and the weight index is determined by the distance measure method proposed in this paper. Through the weighted linear fusion method, the entropy of multiple monitoring points is obtained for analyzing the behavior of dam cracks in the selected zones. Meanwhile, the catastrophe theory is used as the variation criterion of an entropy sequence in order to predict the instability time of dam cracks. Case studies are put forward on a high arch darn, and the fusion entropy is calculated according to the monitoring data from strain gauges. Results show that the proposed method can effectively predict the occurrence time and location of dam cracks regardless of the layout of monitoring instruments, and it is a new way to analyze the occurrence and propagation of dam cracks.

关键词： energy measured data entropy changes multiple monitoring points fusion concrete dam

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Numerical Simulation of Breaking Wave Generated Sediment Suspension and Transport Process Based on CLSVOF Algorithm

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China Ocean Engineering 2014年第5期28卷 701-712页

作者：卢新华张小峰陆俊卿董炳江 State key Laboratory of water Resources and Hydropower Engineering Science Wuhan University State key Laboratory of Hydrology-water Resources and Hydraulic Engineering Hohai University State key Laboratory of Simulation and Regulation of water Cycle in River Basin China Institute of Water Resources and Hydropower Research South China Institute of Environmental Science Ministry of Environmental Protection Hydrology Bureau Yangtze River Water Resource Commission

The sediment suspension and transport process under complex breaking wave situation is investigated using large eddy simulation (abbreviated as LES hereafter) method. The coupled level set (LS) and volume of fluid (VOF) method is used to accurately capture the evolution of air-water interface. The wall effect at the bottom is modeled based on the wave friction term while the complicate bottom boundary condition for sediment is tackled using Chou and Fringer's sediment erosion and deposition flux method. A simulation is carried out to study the sediment suspension and transport process under periodic plunging breaking waves. The comparison between the results by CLSVOF method and those obtained by the LS method is given. It shows that the latter performs as well as the CLSVOF method in the pre-breaking weak-surface deformation situation. However, a serious mass conservation problem in the later stages of wave breaking makes it inappropriate for this study by use of the LS method and thus the CLSVOF method is suggested. The flow field and the distribution of suspended sediment concentration are then analyzed in detail. At the early stage of breaking, the sediment is mainly concentrated near the bottom area. During the wave breaking process, when the entrapped large-scale air bubble travels downward to approach the bottom, strong shear is induced and the sediment is highly entrained.

关键词： sediment suspension wave breaking subgrid-scale model CLSVOF level set

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Uncertainty and Sensitivity Analyses of the Simulated Seawater—Freshwater Mixing Zones in Steady-State Coastal Aquifers

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China Ocean Engineering 2015年第4期29卷 489-502页

作者：赵忠伟赵坚辛沛华国芬金光球 State key Laboratory of Hydrology-water Resources and Hydraulic Engineering Hohai University College of water Conservancy and Hydropower Engineering Hohai University

The uncertainty and sensitivity of predicted positions and thicknesses of seawater-freshwater mixing zones with respect to uncertainties of saturated hydraulic conductivity, porosity, molecular diffusivity, longitudinal and transverse dispersivities were investigated in both head-control and flux-control inland boundary systems. It shows that uncertainties and sensitivities of predicted results vary in different boundary systems. With the same designed matrix of uncertain factors in simulation experiments, the variance of predicted positions and thickness in the flux-control system is much larger than that predicted in the head-control system. In a head-control system, the most sensitive factors for the predicted position of the mixing zone are inland freshwater head and transverse dispersivity. However, the predicted position of the mixing zone is more sensitive to saturated hydraulic conductivity in a flux-control system. In a head-control system, the most sensitive factors for the predicted thickness of the mixing zone include transverse dispersivity, molecular diffusivity, porosity, and longitudinal dispersivity, but the predicted thickness is more sensitive to the saturated hydraulic conductivity in a flux-control system. These findings improve our understandings for the development of seawater-freshwater mixing zone during seawater intrusion processes, and give technical support for groundwater resource management in coastal aquifers.

关键词： seawater intrusion mixing zone uncertainty analysis fractional factorial design Morris "s OAT design coastal aquifer

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Effects of patchy distributed Artemisia capillaris on overland flow hydrodynamic characteristics

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International Soil and water Conservation Research 2019年第1期7卷 81-88页

作者： Guanhua Zhang Jiajun Hu Soil and water Conservation Department Changjiang River Scientific Research InstituteChina Research Center on Mountain Torrent&Geologic Disaster Prevention of Ministry of water Resources China Changjiang water Resources Commission of the Ministry of water Resources Wuhan 430010China

Laboratory-simulated rainfall experiments were conducted to quantify the effects of patchy distributed Artemisia capillaris on overland flow *** intensities of 60,90,120,and 150 mm h-1 were applied on a bare plot (Ck) and four different patched patterns:a checkerboard pattern (CP),a banded pattern perpendicular to slope direction (BP),a single long strip parallel to slope direction (LP),and a pattern with small patches distributed like the letter'X'(XP).Each patterned plot underwent two sets of experiments,intact plant and root (the above-ground parts were removed),*** showed that flow velocity increased with rainfall intensity,and the lower slope velocity was higher than the upper *** removal of grass shoots significantly increased flow *** contributions of grass shoots and roots to the reductions in flow velocity under different rainfall intensities were *** shoots made greater contribution of 53-97% at 60 and 90 mm h-1,and the roots contributed more (51-81%) at 120 and 150 mm *** flow depth increased with rainfall intensity and it declined after the aboveground parts were *** numbers (Re) in this study were 25-80,indicating a laminar flow in the *** numbers (Fr) were ≥ 1 for Ck and ked in the order of Ck < LP < BP/CP/XP with values of grass sections being higher than the bare sections and upper slope higher than the lower slope,and both decreased after removing the grass ***,CP,and XP performed more effectively than LP in retarding flow velocity and increasing hydraulic roughness.

关键词： Overland flow Vegetation pattern Hydrodynamics Soil erosion rate Simulated rainfall

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Experimental and numerical analysis of flow over a rectangular full-width sharp-crested weir

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water Science and Engineering 2018年第1期11卷 75-80页

作者： Ghorban Mahtabi Hadi Arvanaghi Department of water Engineering Faculty of Agriculture University of Zanjan Department of water Engineering Faculty of Agriculture University of Tabriz

Weirs are a type of hydraulic structure, used for water level adjustment, flow measurement, and diversion of water in irrigation systems. In this study, experiments were conducted on sharp-crested weirs under free-flow conditions and an optimization method was used to determine the best form of the discharge coefficient equation based on the coefficient of determination （R2） and root mean square error （RMSE）. The ability of the numerical method to simulate the flow over the weir was also investigated using Fluent software. Results showed that, with an increase of the ratio of the head over the weir crest to the weir height （h/P）, the discharge coefficient decreased nonlinearly and reached a constant value of 0.7 for hiP 〉 0.6. The best form of the discharge coefficient equation predicted the discharge coefficient well and percent errors were within a ±5% error limit. Numerical results of the discharge coefficient showed strong agreement with the experimental data. Variation of the discharge coefficient with Reynolds numbers showed that the discharge coefficient reached a constant value of 0.7 when hiP 〉 0.6 and Re 〉 20000.

关键词： Discharge coefficient Measurement Numerical model Sharp-crested weir Weir height

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Effect of temperature on anoxic metabolism of nitrites to nitrous oxide by polyphosphate accumulating organisms

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Journal of Environmental Sciences 2014年第2期26卷 264-273页

作者： Zhijia Miao Wei Zeng Shuying Wang Yongzhen Peng Guihua Cao Dongchen Weng Guisong Xue Qing Yang key Laboratory of Beijing for water Quality Science and water Environment Recovery Engineering Engineering Research Center of Beijing Beijing University of Technology

Temperature is an important physical factor, which strongly influences biomass and metabolic activity. In this study, the effects of temperature on the anoxic metabolism of nitrite （NO2） to nitrous oxide （N2O） by polyphosphate accumulating organisms, and the process of the accumulation of N2O （during nitrite reduction）, which acts as an electron acceptor, were investigated using 91% ：e 4% Candidatus Accumulibacterphosphatis sludge. The results showed that N2O is accumulated when Accumulibacter first utilize nitrite instead of oxygen as the sole electron acceptor during the denitrifying phosphorus removal process. Properties such as nitrite reduction rate, phosphorus uptake rate, N2O reduction rate, and polyhydroxyalkanoate degradation rate were all influenced by temperature variation （over the range from 10 to 30℃ reaching maximum values at 25℃）. The reduction rate of N2O by N2O reductase was more sensitive to temperature when N2O was utilized as the sole electron acceptor instead of NO2, and the N2O reduction rates, ranging from 0.48 to 3.53 N2O-N/（hr.g VSS）, increased to 1.45 to 8.60 mg N2O-N/（hr·g VSS）. The kinetics processes for temperature variation of 10 to 30℃ were （01 = 1.140-1.216 and θ2 = 1.139-1.167）. In the range of 10℃ to 30℃, almost all of the anoxic stoichiometry was sensitive to temperature changes. In addition, a rise in N2O reduction activity leading to a decrease in N2O accumulation in long term operations at the optimal temperature （27℃ calculated by the Arrhenius model）.

关键词： polyphosphate accumulating organisms temperature nitrite denitrifying phosphorus removal N2O kinetics stoichiometry

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Mixing of A Non-Circular Jet into A Counterflow

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China Ocean Engineering 2015年第1期29卷 91-104页

作者：李志伟肖洋唐洪武 State key Laboratory of Hydrology-water Resources and Hydraulic Engineering Hohai University College of water Conservancy and Hydropower Engineering Hohai University

An elliptic jet and a square jet flowing into a counterflow with different jet-to-current velocity ratios are investigated by using realizable Ice model. Some computed mean velocity and scalar features agree reasonably well with experimental measurements, and more features are obtained by analyzing the computed results. After fluid issues from a nozzle, it entrains ambient fluid, and its velocity and concentration on the centerline decay with the distance downstream from the potential core （10）. The decay ratio increases with the decreasing jet-to-current velocity ratio a. For an elliptic jet, the evolution of the excess velocity half-width b and the concentration half-width be merely remains constant near the jet exit on major-axis plane while they increase linearly on the minor-axis plane. However, the half-widths on the major-axis and minor-axis plane become proportional to the axial distance downstream after equaling each other. For a square jet, b and bc increase linearly with the distance downstream from the jet exit, but the spread ratio is larger on the middle plane than that on the diagonal plane before they equal each other. The radial extent of the dividing streamline r~ or the mixing boundary rs~ increases linearly downstream, and decreases exponentially after reaching a peak at Xb. The ratio on the minor-axis plane is larger than that on the major-axis plane for an elliptic jet. The characteristics are the same for the square jet. b, be, rs, and rsc on two corresponding planes become equal to each other more rapidly for the square jet than for the elliptic jet, because the sharp comer of the square nozzle induces secondary structures that are more intense. The distributions of the excess axial velocity and scalar concentration exhibit self-similarity for either the elliptic jet or square jet in the region of 10 〈 x 〈 xb. On the cross section, four counter-rotating pairs of vortices, which enhance the entrainment between the jet and counterflow, form at

关键词： counterflow excess velocity scalar concentration penetration length radial extent

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Quantitative comparison of semi- and fully-distributed hydrologic models in simulating flood hydrographs on a mountain watershed in southwest China

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Journal of Hydrodynamics 2013年第6期25卷 877-885页

作者：张会兰王玉杰王云琦李丹勋王兴奎 key Laboratory of Soil and water Conservation and Desertification Combating Ministry of EducationDepartment of Soil and Water ConservationBeijing Forestry University State key Laboratory of Hydroscience and Engineering Tsinghua University key Laboratory of Soil and water Conservation and Desertification Combating Ministry of EducationSchool of Soil and Water ConservationBeijing Forestry University

To investigate the performance of fully- and semi-distributed hydrologic models in simulating the process of transformation from rainfall to runoff in mountain areas, the fully-distributed models Basin Pollution Calculation Center （BPCC） and HEC- HMS are calibrated for the Zhenjiangguan watershed located in the upper stream of Minjiang River Southwest China using streamflow observations at the basin outlet. Semi-automatical optimization method is implemented to both models to improve simulated resuits by removing artificial errors. Based on the consistency of the simulated hydrographs with the observed ones, the statistical coefficients such as the relative error, the probability distribution and the correlation coefficient, are further introduced to evaluate quantitatively the performance of the two models. Analyses indicate that the hydrographs simulated by the BPCC are relatively closer to the observed ones than those simulated by the HEC-HMS in view of the spatial heterogeneity in terrain, soil texture, land cover and meteorological conditions in mountain areas.

关键词： Basin Pollution Calculation Center (BPCC) HEC-HMS hydrologic modeling mountain area semi-automaticallyoptimization

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