Flow resistance in fluvial open channels, especially in steep gravel-bed channels, still presents challenges to researchers and engineers. This article presents some new data from both the flume experiments and field ...Flow resistance in fluvial open channels, especially in steep gravel-bed channels, still presents challenges to researchers and engineers. This article presents some new data from both the flume experiments and field measurements. Data analysis using the divided hydraulic radius approach shows that the relative roughness plays a significant role in the bed form resistance. A new set of formulas that incorporate the relative roughness are proposed. As compared with several existing formulas, the proposed formulas can be used to better estimate the bed form resistance.展开更多
Sediment-laden flow measurement with Particle Tracking Velocimetry （PTV） introduces a series of finite-sized sampling bins along the vertical of the flow. Instantaneous velocities are collected at each bin and a sig...Sediment-laden flow measurement with Particle Tracking Velocimetry （PTV） introduces a series of finite-sized sampling bins along the vertical of the flow. Instantaneous velocities are collected at each bin and a significantly large sample is established to evaluate mean and root mean square （rms） velocities of the flow. Due to the presence of concentration gradient, the established sample for the solid phase involves more data from the lower part of the sampling bin than from the upper part. The concentration effect causes bias errors in the measured mean and rms velocities when velocity varies across the bin. These bias errors are analyti- cally quantified in this study based on simplified linear velocity and concentration distributions. Typical bulk flow characteristics from sediment-laden flow measurements are used to demonstrate rough estimation of the error magnitude. Results indicate that the mean velocity is underestimated while the rms velocity is overestimated in the ensemble-averaged measurement. The extent of devia- tion is commensurate with the bin size and the rate of concentration gradient. Procedures are proposed to assist determining an appro- priate sampling bin size in certain error limits.展开更多
The shading method is a simple but effective way of reducing image blooming in the measurement of open channel flows with the Particle Image Velocimetry （PIV）.The current paper proposes a simplified analytical model...The shading method is a simple but effective way of reducing image blooming in the measurement of open channel flows with the Particle Image Velocimetry （PIV）.The current paper proposes a simplified analytical model for light attenuation using this method.The model is verified against experimental data,and the influence of several parameters is illustrated numerically.The possible adverse effect due to the light attenuation is shown to be limited when the parameters in the shading method are in an adequate range,as shown by processing standard images of Case B in PIV Challenge 03.A simple criterion for setting the shade in experiment is given for controlling the errors caused by the shading technique within an acceptable range.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.50779082)the National Basic Research Program of China(973 Program,Grant No.2007CB407202)supported by the CSTC 2011
文摘Flow resistance in fluvial open channels, especially in steep gravel-bed channels, still presents challenges to researchers and engineers. This article presents some new data from both the flume experiments and field measurements. Data analysis using the divided hydraulic radius approach shows that the relative roughness plays a significant role in the bed form resistance. A new set of formulas that incorporate the relative roughness are proposed. As compared with several existing formulas, the proposed formulas can be used to better estimate the bed form resistance.
基金supported by the National Natural Science Foundation of China(Grant No.50779023)
文摘Sediment-laden flow measurement with Particle Tracking Velocimetry （PTV） introduces a series of finite-sized sampling bins along the vertical of the flow. Instantaneous velocities are collected at each bin and a significantly large sample is established to evaluate mean and root mean square （rms） velocities of the flow. Due to the presence of concentration gradient, the established sample for the solid phase involves more data from the lower part of the sampling bin than from the upper part. The concentration effect causes bias errors in the measured mean and rms velocities when velocity varies across the bin. These bias errors are analyti- cally quantified in this study based on simplified linear velocity and concentration distributions. Typical bulk flow characteristics from sediment-laden flow measurements are used to demonstrate rough estimation of the error magnitude. Results indicate that the mean velocity is underestimated while the rms velocity is overestimated in the ensemble-averaged measurement. The extent of devia- tion is commensurate with the bin size and the rate of concentration gradient. Procedures are proposed to assist determining an appro- priate sampling bin size in certain error limits.
基金Project supported by the National Natural Science Foundation of China (Grant No.50779023)
文摘The shading method is a simple but effective way of reducing image blooming in the measurement of open channel flows with the Particle Image Velocimetry （PIV）.The current paper proposes a simplified analytical model for light attenuation using this method.The model is verified against experimental data,and the influence of several parameters is illustrated numerically.The possible adverse effect due to the light attenuation is shown to be limited when the parameters in the shading method are in an adequate range,as shown by processing standard images of Case B in PIV Challenge 03.A simple criterion for setting the shade in experiment is given for controlling the errors caused by the shading technique within an acceptable range.
