[Objective]The construction of weirs changes the hydraulic characteristics of rivers and affects the structure of phytoplankton communities and the health of aquatic ecosystems in the river.This study aims to explore ...[Objective]The construction of weirs changes the hydraulic characteristics of rivers and affects the structure of phytoplankton communities and the health of aquatic ecosystems in the river.This study aims to explore the nonlinear response relationship between phytoplankton community structure and its driving factors in spring and autumn in Furong Creek under the construction of cascade weirs.[Methods]The structure of phytoplankton communities and related environmental factors were investigated in Furong Creek from 2023 to 2024.This study focused on the analysis of the changes of nutrient concentrations and biomass of phytoplankton in autumn and spring within the same dry season in Furong Creek.Redundancy analysis was used to identify the key factors influencing the structure of phytoplankton communities.The MIKE 11 model was employed to simulate the hydrodynamic changes in the river.Combined with total nitrogen and permanganate index,a GAM model of phytoplankton diversity index and hydrodynamic factors was developed,and the change of phytoplankton diversity after the optimized layout of the cascade weirs was fitted.[Results]The result showed that the annual average value of Shannon-Wiener diversity index of phytoplankton in Furong Creek was 2.79,which was in a state of mild pollution.A total of 239 species from 95 genera in 8 phyla were identified.Among the phytoplankton,Chlorophyta was the dominant group throughout the year in Furong Creek,followed by Bacillariophyta and Cyanophyta.The cell abundance of phytoplankton ranged from 3.11 to 20.64 mg/L and from 0.23 to 6.31 mg/L in spring and autumn,which indicated a clear seasonal succession of phytoplankton community structure.Compared with autumn,the relative abundance of Cyanophyta significantly decreased in spring across the whole river section,while Chrysophyta and Dinophyta showed significant increase at some monitoring sites,leading to water bloom phenomenon and a noticeable decline in the diversity of phytoplankton.The dominant species in the water bodies throughout the year were Cyclotella catenata,Chlorella vulgaris,Scenedesmus bijuga,Scenedesmus quadricauda,Chroomonas acuta,Cryptomonas ovata,and Cryptomonas erosa.Redundancy analysis(RDA)showed that hydrodynamic factors(v,h)and water environmental factors(TN,COD_(Mn))were the main influencing factors of phytoplankton community structure.[Conclusion]The result show that the nutrient concentration,phytoplankton biomass,and density in Furong Creek in spring are significantly higher than in autumn.The GAM model,constructed by combining hydrodynamic and environmental factors,can effectively reflect the nonlinear relationship between phytoplankton diversity index and its driving factors.In spring,with an increase in nutrient concentration,the habitat conditions of low flow speed and high water depths formed by overflow weirs will lead to a decrease in the Shannon-Wiener index of phytoplankton and an intensified risk of eutrophication.However,a reasonable layout scheme of cascade weirs will improve the diversity of phytoplankton and reduce the risk of eutrophication in the river.The findings of this study can help deepen the understanding of the ecological and environmental effects of cascade weir construction in the river.展开更多
Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) w...Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.展开更多
In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fi...In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.展开更多
The broad-crested weir is convenient to construct and has a small amount of ex-cavation,widely used in practical engineering.Discharge computing has been the focus of research on this structure,thus developing general...The broad-crested weir is convenient to construct and has a small amount of ex-cavation,widely used in practical engineering.Discharge computing has been the focus of research on this structure,thus developing generalized regression neural network(GRNN),genetic programming(GP),and extreme learning machine(ELM)are used to predict the discharge coefficient(Cd)of the triangular broad-crested weir.The comprehensive analysis shows that the ELM model has high stability,predictive ability,and computational speed.The coefficient of determination(R^2)is 0.99982,the mean absolute percentage error(MAPE)is 0.000261,the Nash-Sutcliffe coefficient(NSE)is 0.99977,and the root means square error(RMSE)is 4.17E-05 in the testing phase.The apex angleθis the most critical parameter affecting the Cd,and the contribution to the Cd is 52.45%.A new computational formula is proposed and compared with the accuracy of empirical formulas,showing that the intelligent method has higher accuracy and efficiency.展开更多
文摘[Objective]The construction of weirs changes the hydraulic characteristics of rivers and affects the structure of phytoplankton communities and the health of aquatic ecosystems in the river.This study aims to explore the nonlinear response relationship between phytoplankton community structure and its driving factors in spring and autumn in Furong Creek under the construction of cascade weirs.[Methods]The structure of phytoplankton communities and related environmental factors were investigated in Furong Creek from 2023 to 2024.This study focused on the analysis of the changes of nutrient concentrations and biomass of phytoplankton in autumn and spring within the same dry season in Furong Creek.Redundancy analysis was used to identify the key factors influencing the structure of phytoplankton communities.The MIKE 11 model was employed to simulate the hydrodynamic changes in the river.Combined with total nitrogen and permanganate index,a GAM model of phytoplankton diversity index and hydrodynamic factors was developed,and the change of phytoplankton diversity after the optimized layout of the cascade weirs was fitted.[Results]The result showed that the annual average value of Shannon-Wiener diversity index of phytoplankton in Furong Creek was 2.79,which was in a state of mild pollution.A total of 239 species from 95 genera in 8 phyla were identified.Among the phytoplankton,Chlorophyta was the dominant group throughout the year in Furong Creek,followed by Bacillariophyta and Cyanophyta.The cell abundance of phytoplankton ranged from 3.11 to 20.64 mg/L and from 0.23 to 6.31 mg/L in spring and autumn,which indicated a clear seasonal succession of phytoplankton community structure.Compared with autumn,the relative abundance of Cyanophyta significantly decreased in spring across the whole river section,while Chrysophyta and Dinophyta showed significant increase at some monitoring sites,leading to water bloom phenomenon and a noticeable decline in the diversity of phytoplankton.The dominant species in the water bodies throughout the year were Cyclotella catenata,Chlorella vulgaris,Scenedesmus bijuga,Scenedesmus quadricauda,Chroomonas acuta,Cryptomonas ovata,and Cryptomonas erosa.Redundancy analysis(RDA)showed that hydrodynamic factors(v,h)and water environmental factors(TN,COD_(Mn))were the main influencing factors of phytoplankton community structure.[Conclusion]The result show that the nutrient concentration,phytoplankton biomass,and density in Furong Creek in spring are significantly higher than in autumn.The GAM model,constructed by combining hydrodynamic and environmental factors,can effectively reflect the nonlinear relationship between phytoplankton diversity index and its driving factors.In spring,with an increase in nutrient concentration,the habitat conditions of low flow speed and high water depths formed by overflow weirs will lead to a decrease in the Shannon-Wiener index of phytoplankton and an intensified risk of eutrophication.However,a reasonable layout scheme of cascade weirs will improve the diversity of phytoplankton and reduce the risk of eutrophication in the river.The findings of this study can help deepen the understanding of the ecological and environmental effects of cascade weir construction in the river.
基金supported by the Ministry of Public Works and Housing of Indonesia and Parahyangan Catholic University(Grant No.II/PD/2023-07/02-SJ).
文摘Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.
基金supported by the National Natural Science Foundation of China(Grant No.52069009).
文摘In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.
基金Xi'an University of Technology Excellent Master Seed Fund,Grant/Award Number:310/252082213。
文摘The broad-crested weir is convenient to construct and has a small amount of ex-cavation,widely used in practical engineering.Discharge computing has been the focus of research on this structure,thus developing generalized regression neural network(GRNN),genetic programming(GP),and extreme learning machine(ELM)are used to predict the discharge coefficient(Cd)of the triangular broad-crested weir.The comprehensive analysis shows that the ELM model has high stability,predictive ability,and computational speed.The coefficient of determination(R^2)is 0.99982,the mean absolute percentage error(MAPE)is 0.000261,the Nash-Sutcliffe coefficient(NSE)is 0.99977,and the root means square error(RMSE)is 4.17E-05 in the testing phase.The apex angleθis the most critical parameter affecting the Cd,and the contribution to the Cd is 52.45%.A new computational formula is proposed and compared with the accuracy of empirical formulas,showing that the intelligent method has higher accuracy and efficiency.
基金supported by NSFC(No.10871216 and No.11071267)Natural Science Foundation Project of CQ CSTC+1 种基金Science and Technology Research Project of Chongqing Municipal Education Commission(No.K J100419)the Excellent Young Teachers Program of Chongqing Jiaotong University,Chongqing,China
