Local scour around pipelines crossing rivers or in marine environments is a significant concern.It can lead to failure of the pipelines resulting in environmental side effects and economic losses.This study developed ...Local scour around pipelines crossing rivers or in marine environments is a significant concern.It can lead to failure of the pipelines resulting in environmental side effects and economic losses.This study developed an experimental method to reduce local scour around pipelines with a steady flow of clear water by installing cylindrical and cubical sacrificial piles.Three sizes of sacrificial piles were examined in a linear arrangement.Sacrificial piles were installed on the upstream side of the pipeline at three distances.Maximum scour depth reduction rates below the pipeline were computed.The results showed that sacrificial piles could protect a pipeline from local scour.A portion of scoured sediment around the sacrificial piles was deposited beneath the pipeline.This sediment accumulation reduced the scour depth beneath the pipeline.Analysis of the experimental results demonstrated that the size of piles(d),the spacing between piles,and the distance between the pipe and piles(Xp)were the variables that reduced the maximum scour beneath the pipeline with a diameter of D.For the piles with d=0.40D and 0.64D,X_(p)=4OD was the optimal distance to install a group of piles,and cubical piles could mitigate scour more effectively than cylindrical piles under similar conditions.For the piles with d=D,the greatest reduction in scour depth was achieved at X_(p)=50D with any desired spacings between piles,and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.展开更多
Forest clear cutting alters the hydrological processes such as interception, evapotranspiration and infiltration of the forested watershed and consequently increases the amount of water and sediment leaving the waters...Forest clear cutting alters the hydrological processes such as interception, evapotranspiration and infiltration of the forested watershed and consequently increases the amount of water and sediment leaving the watershed. This study was conducted in the Upper Pearl River Watershed (UPRW) located in east-central Mississippito evaluate and compare the potential impacts of forest clear cutting on water and sediment yields using the Soil and Water Assessment Tool (SWAT) model. For this purpose, five hypothetical scenarios representing clear cutting at 10%, 20%, 30%, 55% and 75% of the total forest area of the watershed were generated. The SWAT model was first calibrated (1981-1995) and validated (1996-2008) for monthly stream flow, and later verified (February 2010 to December 2010) for monthly sediment load. Results show that the SWAT model was able to simulate stream flow and sediment load satisfactorily during the calibration/validation and verification periods, respectively. The potential changes caused in yields as a result of the changes in clearcut area were computed by comparing predicted yields from each clear cutting scenario and a base condition. Results from five scenarios demonstrate substantial increase in yields with an increase in the percentage of forest area clearcut. When compared with the base scenario, potential changes in water and sediment yields occur between 17% to 96% and 33% to 250%, respectively, with an increase in clearcut area from 10% to 75%. Results also indicate that, for all scenarios, percentage wise change is larger for sediment yield. Although predicted water and sediment yields generated from each scenario are subject to further verification with observed data, this study provides useful information about the potential amount of water and sediment yields that may be produced under each scenario, and that the potential changes that may happen on yields if similar magnitude of clear cutting occurs in the UPRW or in similar watershed.展开更多
A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The N...A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.展开更多
文摘Local scour around pipelines crossing rivers or in marine environments is a significant concern.It can lead to failure of the pipelines resulting in environmental side effects and economic losses.This study developed an experimental method to reduce local scour around pipelines with a steady flow of clear water by installing cylindrical and cubical sacrificial piles.Three sizes of sacrificial piles were examined in a linear arrangement.Sacrificial piles were installed on the upstream side of the pipeline at three distances.Maximum scour depth reduction rates below the pipeline were computed.The results showed that sacrificial piles could protect a pipeline from local scour.A portion of scoured sediment around the sacrificial piles was deposited beneath the pipeline.This sediment accumulation reduced the scour depth beneath the pipeline.Analysis of the experimental results demonstrated that the size of piles(d),the spacing between piles,and the distance between the pipe and piles(Xp)were the variables that reduced the maximum scour beneath the pipeline with a diameter of D.For the piles with d=0.40D and 0.64D,X_(p)=4OD was the optimal distance to install a group of piles,and cubical piles could mitigate scour more effectively than cylindrical piles under similar conditions.For the piles with d=D,the greatest reduction in scour depth was achieved at X_(p)=50D with any desired spacings between piles,and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.
文摘Forest clear cutting alters the hydrological processes such as interception, evapotranspiration and infiltration of the forested watershed and consequently increases the amount of water and sediment leaving the watershed. This study was conducted in the Upper Pearl River Watershed (UPRW) located in east-central Mississippito evaluate and compare the potential impacts of forest clear cutting on water and sediment yields using the Soil and Water Assessment Tool (SWAT) model. For this purpose, five hypothetical scenarios representing clear cutting at 10%, 20%, 30%, 55% and 75% of the total forest area of the watershed were generated. The SWAT model was first calibrated (1981-1995) and validated (1996-2008) for monthly stream flow, and later verified (February 2010 to December 2010) for monthly sediment load. Results show that the SWAT model was able to simulate stream flow and sediment load satisfactorily during the calibration/validation and verification periods, respectively. The potential changes caused in yields as a result of the changes in clearcut area were computed by comparing predicted yields from each clear cutting scenario and a base condition. Results from five scenarios demonstrate substantial increase in yields with an increase in the percentage of forest area clearcut. When compared with the base scenario, potential changes in water and sediment yields occur between 17% to 96% and 33% to 250%, respectively, with an increase in clearcut area from 10% to 75%. Results also indicate that, for all scenarios, percentage wise change is larger for sediment yield. Although predicted water and sediment yields generated from each scenario are subject to further verification with observed data, this study provides useful information about the potential amount of water and sediment yields that may be produced under each scenario, and that the potential changes that may happen on yields if similar magnitude of clear cutting occurs in the UPRW or in similar watershed.
基金supported by the National Natural Science Foundation of China (Grant No. 50679008)
文摘A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.
