The grid drop concept is introduced and used to develop a micromechanism-based methodology for calculating watershed flow concentration. The flow path and distance traveled by a grid drop to the outlet of the watershe...The grid drop concept is introduced and used to develop a micromechanism-based methodology for calculating watershed flow concentration. The flow path and distance traveled by a grid drop to the outlet of the watershed are obtained using a digital elevation model (DEM). Regarding the slope as an uneven carpet through which the grid drop passes, a formula for overland flow velocity differing from Manning's formula for stream flow as welt as Darcy's formula for pore flow is proposed. Compared with the commonly used unit hydrograph and isochronal methods, this new methodology has outstanding advantages in that it considers the influences of the slope velocity field and the heterogeneity of spatial distribution of rainfall on the flow concentration process, and includes only one parameter that needs to be calibrated. This method can also be effectively applied to the prediction of hydrologic processes in un-gauged basins.展开更多
To calculate the flow resistance of a main cable dehumidification system,this study considers the air flow in the main cable as the flow in a porous medium,and adopts the Hagen–Poiseuille equation by using average hy...To calculate the flow resistance of a main cable dehumidification system,this study considers the air flow in the main cable as the flow in a porous medium,and adopts the Hagen–Poiseuille equation by using average hydraulic radius and capillary bundle models.A mathematical derivation is combined with an experimental study to obtain a semi-empirical flow resistance formula.Additionally,Fluent software is used to simulate the flow resistance across the main cable relative to the experimental values.Based on the actual measured results for a Yangtze River bridge,this study verifies the semi-empirical formula,and indicates that it can be applied in actual engineering.展开更多
Velocity of debris flow is one of the most important characteristics for the protective construction design. Since debris flows are rare events, and observations are conducted only on stations in Russia, Ukraine, Ital...Velocity of debris flow is one of the most important characteristics for the protective construction design. Since debris flows are rare events, and observations are conducted only on stations in Russia, Ukraine, Italy, Switzerland, USA, China, Japan and New Zealand, the velocity is calculated rather than measured. Nowadays, a large number of videos with passing debris flows have appeared on the Internet. Scientists can use such video materials to obtain qualitative and quantitative characteristics of the debris flow. Therefore, the aim of our research is an attempt to measure the debris flow velocity using video materials and compare the obtained results with the calculated values using various methods. The debris flow that came down in Firgen, Austria on August 4, 2012 was chosen as the object of our study. The video was carried out from several angles, so it was possible to select a section of the channel, through which we could measure the debris flows waves velocity. In addition, we calculated the velocities of waves by formulas adopted in the regulatory documents and compared with the measured by video values. During the video analysis, debris flow velocities at different sites were observed: minimum—7.2 m/s and maximum—10 m/s. The calculated values varied from 4.5 m/s to 11.4 m/s. Moreover, we applied model of the transport-shear process of debris flow formation developed by Yu. B. Vinogradov. When we were comparing the obtained debris flow discharges with results from Austrian colleagues, we found out that the values were similar to each other. However, internal scatter in the model changed from 151 to 190 m3/s, while in the report of Austrian colleagues the discharges were from 80 to 250 m3/s.展开更多
On the basis of hypothesis of replacement and the vector formula of Newton’s law for a viscous fluid the way of a finding of resistance a slow flow by an incompressible fluid of bodies of the various form is represen...On the basis of hypothesis of replacement and the vector formula of Newton’s law for a viscous fluid the way of a finding of resistance a slow flow by an incompressible fluid of bodies of the various form is represented. Application of an offered way to calculation of a flow of various bodies is shown: a sphere, a cylinder, a oblong ellipsoid, a flat plate. Comparison with results of other authors is given.展开更多
Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria w...Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria were determined. Four flow patterns were identified: mixed, locally unstable, continuously stratified, and two-layer flow. Temperature distributions of the four types of flow patterns were analyzed and compared.The critical Froude numbers for unstable flow, FDcr1, and stable flow, FDcr2, were determined to be 6 and 1, respectively, and comparison of FDcr1 and FDcr2 to the peak Froude numbers, FD1 at the outer bank and FD2 at the inner bank along the anabranch, allowed the flow patterns to be assessed. Then, a discriminant based on initial Jeffreys-Keulegan stability parameters was established to distinguish the flow stages from twolayer flow to completely mixed flow. It is indicated that the three critical Jeffreys-Keulegan parameters increased with the diversion angle of braided rivers. Results also show that, compared to the stratified flow in straight and curved channels, it was more difficult for braided stratified flow to maintain as two-layer flow, and it more easily became mixed flow. Consequently, empirical expressions for stability criteria of the thermally stratified shear flow in braided rivers are presented.展开更多
为深入了解钢筋石笼在弯道渠首引水工程中的过流规律,选用流体体积(volume of fluid,VOF)法、多孔介质模型对钢筋石笼进行数值模拟,并对数值模型进行物理试验验证。研究得到不同孔隙率、水深、长度、高度等参数对钢筋石笼流速分布、过...为深入了解钢筋石笼在弯道渠首引水工程中的过流规律,选用流体体积(volume of fluid,VOF)法、多孔介质模型对钢筋石笼进行数值模拟,并对数值模型进行物理试验验证。研究得到不同孔隙率、水深、长度、高度等参数对钢筋石笼流速分布、过流规律的影响,并采用SPSS软件对所得数据拟合得到钢筋石笼流量公式、堰前水深公式。结果表明:钢筋石笼内部流量随着孔隙率、高度的增大而增大,但会受到水流回流的影响;钢筋石笼周围的绕流程度随着远端水深的增大而增大;钢筋石笼长度、远端水深及高度不宜过大;钢筋石笼综合流量系数与孔隙率n、钢筋石笼高度和钢筋石笼上游0.8 m处水头之比P/H0、钢筋石笼长度和钢筋石笼上游0.8 m处水头之比l/H0的关系较为显著,所得钢筋石笼流量计算公式的最大相对误差不超过5.0%,精度较高,可为引水总量的率定提供参考;得到的堰前水深公式精度较高,决定系数为0.966。研究可为钢筋石笼在引水工程上的应用提供参考和依据。展开更多
基金supported by the National Nature Science Foundation of China(Grant No.50609005)the Fok Ying-Tong Education Foundation for Young Teachers in the Higher Education Institutions of China(Grant No.101075)
文摘The grid drop concept is introduced and used to develop a micromechanism-based methodology for calculating watershed flow concentration. The flow path and distance traveled by a grid drop to the outlet of the watershed are obtained using a digital elevation model (DEM). Regarding the slope as an uneven carpet through which the grid drop passes, a formula for overland flow velocity differing from Manning's formula for stream flow as welt as Darcy's formula for pore flow is proposed. Compared with the commonly used unit hydrograph and isochronal methods, this new methodology has outstanding advantages in that it considers the influences of the slope velocity field and the heterogeneity of spatial distribution of rainfall on the flow concentration process, and includes only one parameter that needs to be calibrated. This method can also be effectively applied to the prediction of hydrologic processes in un-gauged basins.
基金Ministry of Communications and Provincial and Joint Research Project[2008-353-332-170].
文摘To calculate the flow resistance of a main cable dehumidification system,this study considers the air flow in the main cable as the flow in a porous medium,and adopts the Hagen–Poiseuille equation by using average hydraulic radius and capillary bundle models.A mathematical derivation is combined with an experimental study to obtain a semi-empirical flow resistance formula.Additionally,Fluent software is used to simulate the flow resistance across the main cable relative to the experimental values.Based on the actual measured results for a Yangtze River bridge,this study verifies the semi-empirical formula,and indicates that it can be applied in actual engineering.
文摘Velocity of debris flow is one of the most important characteristics for the protective construction design. Since debris flows are rare events, and observations are conducted only on stations in Russia, Ukraine, Italy, Switzerland, USA, China, Japan and New Zealand, the velocity is calculated rather than measured. Nowadays, a large number of videos with passing debris flows have appeared on the Internet. Scientists can use such video materials to obtain qualitative and quantitative characteristics of the debris flow. Therefore, the aim of our research is an attempt to measure the debris flow velocity using video materials and compare the obtained results with the calculated values using various methods. The debris flow that came down in Firgen, Austria on August 4, 2012 was chosen as the object of our study. The video was carried out from several angles, so it was possible to select a section of the channel, through which we could measure the debris flows waves velocity. In addition, we calculated the velocities of waves by formulas adopted in the regulatory documents and compared with the measured by video values. During the video analysis, debris flow velocities at different sites were observed: minimum—7.2 m/s and maximum—10 m/s. The calculated values varied from 4.5 m/s to 11.4 m/s. Moreover, we applied model of the transport-shear process of debris flow formation developed by Yu. B. Vinogradov. When we were comparing the obtained debris flow discharges with results from Austrian colleagues, we found out that the values were similar to each other. However, internal scatter in the model changed from 151 to 190 m3/s, while in the report of Austrian colleagues the discharges were from 80 to 250 m3/s.
文摘On the basis of hypothesis of replacement and the vector formula of Newton’s law for a viscous fluid the way of a finding of resistance a slow flow by an incompressible fluid of bodies of the various form is represented. Application of an offered way to calculation of a flow of various bodies is shown: a sphere, a cylinder, a oblong ellipsoid, a flat plate. Comparison with results of other authors is given.
基金supported by the National Natural Science Foundation of China(Grants No.51379058,51379060,and 51479064)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD Project)the Fundamental Research Funds for the Central Universities(Grants No.2016B06714 and 2014B07814)
文摘Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria were determined. Four flow patterns were identified: mixed, locally unstable, continuously stratified, and two-layer flow. Temperature distributions of the four types of flow patterns were analyzed and compared.The critical Froude numbers for unstable flow, FDcr1, and stable flow, FDcr2, were determined to be 6 and 1, respectively, and comparison of FDcr1 and FDcr2 to the peak Froude numbers, FD1 at the outer bank and FD2 at the inner bank along the anabranch, allowed the flow patterns to be assessed. Then, a discriminant based on initial Jeffreys-Keulegan stability parameters was established to distinguish the flow stages from twolayer flow to completely mixed flow. It is indicated that the three critical Jeffreys-Keulegan parameters increased with the diversion angle of braided rivers. Results also show that, compared to the stratified flow in straight and curved channels, it was more difficult for braided stratified flow to maintain as two-layer flow, and it more easily became mixed flow. Consequently, empirical expressions for stability criteria of the thermally stratified shear flow in braided rivers are presented.
文摘为深入了解钢筋石笼在弯道渠首引水工程中的过流规律,选用流体体积(volume of fluid,VOF)法、多孔介质模型对钢筋石笼进行数值模拟,并对数值模型进行物理试验验证。研究得到不同孔隙率、水深、长度、高度等参数对钢筋石笼流速分布、过流规律的影响,并采用SPSS软件对所得数据拟合得到钢筋石笼流量公式、堰前水深公式。结果表明:钢筋石笼内部流量随着孔隙率、高度的增大而增大,但会受到水流回流的影响;钢筋石笼周围的绕流程度随着远端水深的增大而增大;钢筋石笼长度、远端水深及高度不宜过大;钢筋石笼综合流量系数与孔隙率n、钢筋石笼高度和钢筋石笼上游0.8 m处水头之比P/H0、钢筋石笼长度和钢筋石笼上游0.8 m处水头之比l/H0的关系较为显著,所得钢筋石笼流量计算公式的最大相对误差不超过5.0%,精度较高,可为引水总量的率定提供参考;得到的堰前水深公式精度较高,决定系数为0.966。研究可为钢筋石笼在引水工程上的应用提供参考和依据。
