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Predicting submerged vegetation drag with a machine learning-based method

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Journal of Hydrodynamics 2024年第3期36卷 534-545页

作者： Meng-yang Liu hong-wu tang Sai-yu Yuan Jing Yan College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing210098China Key Laboratory of Hydrologic-Cycle and Hydrodynamic-System of Ministry of Water Resources Hohai UniversityNanjing210098China

Accurate estimation of the drag forces generated by vegetation stems is crucial for the comprehensive assessment of the impact of aquatic vegetation on hydrodynamic processes in aquatic *** coupling relationship between vegetation layer flow velocity and vegetation drag makes precise prediction of submerged vegetation drag forces particularly *** present study utilized published data on submerged vegetation drag force measurements and employed a genetic programming(GP)algorithm,a machine learning technique,to establish the connection between submerged vegetation drag forces and flow and vegetation *** using the bulk velocity,U,as the reference velocity scale to define the drag coefficient,C_(d),and stem Reynolds number,the GP runs revealed that the drag coefficient of submerged vegetation is related to submergence ratio(H^(*)),aspect ratio(d^(*)),blockage ratio(ψ^(*)),and vegetation density(λ).The relation between vegetation stem drag forces and flow velocity is implicitly embedded in the definition of C_(d).Comparisons with experimental drag force measurements indicate that using the bulk velocity as the reference velocity,as opposed to using the vegetation layer average velocity,U_(v),eliminates the need for complex iterative processes to estimate U_(v)and avoids introducing additional errors associated with U_(v)*** approach significantly enhances the model’s predictive capabilities and results in a simpler and more user-friendly formula expression.

关键词： Drag coefficient genetic programming algorithm submerged vegetation flow resistance cylinder array

The dynamics of river confluences and their effects on the ecology of aquatic environment:A review

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Journal of Hydrodynamics 2022年第1期34卷 1-14页

作者： Sai-yu Yuan Lei Xu hong-wu tang Yang Xiao Carlo Gualtieri State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai UniversityNanjing210024China Yangtze Institute for Conservation and Development Nanjing210024China Department of Structures for Engineering and Architecture University of Napoli Federico IINapoliItaly

Confluences act as critical nodes in a river *** affect hydrodynamics,sediment transport,bed morphology,and eco-hydraulics of the river *** of streams produces the complex mechanism of flow momentum and mass mixing which may affect the aquatic environment locally and even lasting for a long distance *** confluence creates a hotspot for the river system’s ecological change,which usually leads to changes in water temperature,suspended-sediment load,bed material,nutrient concentrations,water chemistry,and organic-matter ***,the dynamics of river confluences are very complex and have critical effects on river system’s water environment and *** this reason,a review summarizing turbulent flow,sediment transport,morphological-dynamics,mixing processes,and their effects on the ecology of the aquatic environment at river confluences is in order.A future research agenda and opportunities pertinent to river confluence are vitally emphasized as a multidisciplinary research topic.

关键词： River confluence hydrodynamics sediment transport morpho dynamics water environment water ecology

Multi-approach analysis of maximum riverbed scour depth above subway tunnel

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Water Science and Engineering 2010年第4期3卷 431-442页

作者： Jun CHEN hong-wu tang Zui-sen LI Wen-hong DAI State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University Nanjing 210098 P. R. China National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety Hohai University Nanjing 210098 P. R. China

When subway tunnels are routed underneath rivers, riverbed scour may expose the structure, with potentially severe consequences. Thus, it is important to identify the maximum scour depth to ensure that the designed buried depth is adequate. There are a range of methods that may be applied to this problem, including the fluvial process analysis method, geological structure analysis method, scour formula method, scour model experiment method, and numerical simulation method. However, the application ranges and forecasting precision of these methods vary considerably. In order to quantitatively analyze the characteristics of the different methods, a subway tunnel passing underneath a river was selected, and the aforementioned five methods were used to forecast the maximum scour depth. The fluvial process analysis method was used to characterize the river regime and evolution trend, which were the baseline for examination of the scour depth of the riverbed. The results obtained from the scour model experiment and the numerical simulation methods are reliable; these two methods are suitable for application to tunnel projects passing underneath rivers. The scour formula method was less accurate than the scour model experiment method; it is suitable for application to lower risk projects such as pipelines. The results of the geological structure analysis had low precision; the method is suitable for use as a secondary method to assist other research methods. To forecast the maximum scour depth of the riverbed above the subway tunnel, a combination of methods is suggested, and the appropriate analysis method should be chosen with respect to the local conditions.

关键词： high flow subway tunnel, scour depth scour model, numerical simulation

Scalar transport by propagation of an internal solitary wave over a slope-shelf

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Journal of Hydrodynamics 2019年第2期31卷 317-325页

作者： Jin Xu Ling-ling Wang hong-wu tang Zhu Hai John James Reginald Williams State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hobai UniversityNanjing 210098China College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China School of Engineering and Materials Science Queen Mary University of LondonLondonUK

Internal solitary waves(ISWs)of depression are commonly found in the coastal environment and are believed to re-suspend sediments in coastal regions where the waves *** this research,the direct numerical simulation is used to study the scalar transport induced by the ISWs of depression propagating over a slope-shelf *** scalar in this paper is considered to represent the concentrations of very fine suspended solids or *** are observed from the numerical results at the bottom boundary layer on the slope during the ISW shoaling process,resulting in a scalar *** in cident ISWs of depression are observed to produce a waveform inversion on the *** scalar transport from a slope to a shelf is the consequence of the combined vortices at the bottom boundary layer and the overturning of the ISWs of depression,and the latter was commonly ignored in previous *** study shows that the ISW-induced scalar transport consists of the following four stages:the slip transport,the wash transport,the vortex transport,and the secondary transport.A dimensionless time scales of the four stages are calculated,and the beginning times of the wash transport and the secondary transport are found to be uncorrelated with the slope gradients,taking values of 1.26,4,respectively.

关键词： Internal solitary waves slope-shelf scalar transport wave inversion dimensionless time scale

Critical velocities for local scour around twin piers in tandem

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Journal of Hydrodynamics 2018年第6期30卷 1165-1173页

作者： Quan-shuai Liu hong-wu tang Hao Wang Jian-feng Xiao State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University Nanjing 210098 China Huaihe River Commission of the Ministry of Water Resource Bengbu 233001 China

Experiments of the local scour around twin piers are carried out under steady clear-water conditions, including 95 tests to observe the influence of the pier spacing and the flow velocity on the local scour characteristics of the twin piers. It is shown that the start of the transition region is synchronous with the sediment transport from the upstream scour hole to the downstream one. The equations for the critical velocities are derived to quantify the velocity range of each of four different scour regions. Finally, a prediction formula of the downstream pier scour depth in the radical-deviation region is established.

关键词： Local scour clear-water scour twin piers critical velocity experiment

Incipient motion of sediment in presence of submerged flexible vegetation

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Water Science and Engineering 2015年第1期8卷 63-67页

作者： Hao Wang hong-wu tang Han-qing Zhao Xuan-yu Zhao Sheng-qi Lü State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University

The presence of submerged vegetation on river beds can change the water flow structure and alter the state of sediment motion. In this study, the incipient motion of sediment in the presence of submerged flexible vegetation in open channels was investigated in a laboratory experiment. The vegetation was simulated with flexible rubber cylinders arranged in parallel arrays. The effect of the vegetation density, water depth, and sediment grain size on the incipient motion was investigated. The experimental results indicate that the incipient motion velocity of sediment increases as the vegetation density decreases and the water depth and sediment grain size increase. With flexible plants, the incipient motion velocity of sediment is lower than it is without vegetation, and is larger than it is with rigid vegetation. A general incipient motion velocity equation was derived, which can be applied to both flexible and rigid vegetation conditions.

关键词： Sediment incipient motion Submerged flexible vegetation Open channel Experimentation Sediment grain size Water depth

Experimental study on influence of boundary on location of maximum velocity in open channel flows

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Water Science and Engineering 2011年第2期4卷 185-191页

作者： Jing YAN hong-wu tang Yang XIAO Kai-jie LI Zhi-Jun TIAN State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University Nanjing 210098 P. R. China National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety Nanjing 210098 P. R. China College of Water Conservancy and Hydropowe. Hohai University Nanjing 210098 P. R. China

The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.

关键词： velocity dip open channel flow location of maximum velocity sidewall effect aspect ratio

Hydrodynamic characteristics and particle tracking of 90° lateral intakes at an inclined river slope

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Water Science and Engineering 2024年第2期17卷 197-208页

作者： Wei He Si-yuan Feng Jian Zhang hong-wu tang Yang Xiao Sheng Chen Chun-sheng Liu College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China State Key Laboratory of Hydrology Water Resources and Hydraulic Engineering Hohai UniversityNanjing 210098China Collaborative Innovation Center on Water Safety and Water Science Hohai UniversityNanjing 210098China

Lateral intakes are common in *** pump effciency and sediment deposition are determined by the local hydrodynamic characteristics and mainstream division *** hydraulic characteristics of lateral withdrawal from inclined river slopes at different intake elevations should be ***,the division width exhibits significant vertical non-uniformity at an inclined river slope,which should be ***,a three-dimensional(3-D)hydrodynamic and particle-tracking model was developed with the Open Source Field Operation and Manipulation(Open FOAM),and the model was validated with physical model tests for 90°lateral withdrawal from an inclined side *** flow fields,withdrawal sources,and division widths were investigated with different intake bottom elevations,withdrawal discharges,and main channel *** study showed that under inclined side bank conditions,water entered the intake at an oblique angle,causing significant 3-D spiral flows in the intake rather than two-dimensional closed recirculation.A lower withdrawal discharge,a lower bottom elevation of the intake,or a higher main channel velocity could further strengthen this *** average division width and turbulent kinetic energy were smaller under inclined side bank conditions than under vertical bank *** a low intake bottom elevation,a low withdrawal discharge,or a high main channel velocity,the sources of lateral withdrawal were in similar ranges near the local inclined bank in the vertical *** inclined slope conditions,sediment deposition near the intake entrance could be reduced,compared to that under vertical slope *** results provide hydrodynamic and sediment references for engineering designs for natural rivers with inclined terrains.

关键词： Lateral withdrawal Hydrodynamic characteristics Particle tracking Inclined river slope Bottom elevation of intake OpenFOAM

On the Rational Spline Functions

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数学研究与评论 1984年第2期 31-36页

作者： Wang Ren-hong wu Shun-tang(Jilin University) (Zhenjiang Nomarl College)

Since Schoenberg’s fundamental paper was published in 1946, the theory of polynomial spline functions developed rapldly and was rich in contents. Spline functions have wide range of applications to numerical *** to certain functions, for example, to the function with singular points, the interpolation by polynomial spline is not always efficient and reasonable. Since 1973 some authors have investigated the rational spline functions, and abtained a lot of results. But

关键词： Rational Spline interpolation polynomial spline rational partition preserving algebraic singular