A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed ma...A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed material, and variations in the dimension of bed forms. The model predicts the changes in the grain size distribution with the time and space during degradation process. The numerical model proposes that the armoring process in degrading channels does not depend only on hydraulic characteristics of the flow but also on variation in the grain size distribution of sediments on the bed. The model was applied and compared with the results obtained from experiments conducted in 24 m recirculating flume for two sizes of sand; a good agreement was found between observed and calculated values.展开更多
The rapid changes in flow pattern due to varying channel widths will make significantly impact on the hydraulic structures and evolutions of open channel. To better understand the impact of varying width, a flume expe...The rapid changes in flow pattern due to varying channel widths will make significantly impact on the hydraulic structures and evolutions of open channel. To better understand the impact of varying width, a flume experiment with adjustable width and a depth-averaged two-dimension numerical model were used to analyze the variations of flow parameters. Our experimental results showed that flow velocity gradually increased with decreasing water depth in converging region, and decreased with increasing water depth in diverging zones. It was also found that the turbulence intensity laws in three directions were not agreed with the theoretical relationships proposed by Nezu and Nakagawa in 1993 in straight open channel flows. The flow in the channel with varying width may change from the supercritical flow to the subcritical flow as a function of Froude number. Our numerical simulations with different flow rates showed that most of the hydraulic jumps in diverging region were submerged jump and the degree of submergence increased with increasing flow rate in gradual channel transition. When the flow rate increased, the range of supercritical flow rapidly decreased and the flow changed from the supercritieal condition to the subcritical condition in diverging sections.展开更多
The phenomenon of cyclic hardening is observed in fatigue tests of modified asphalt controlled by low strain/stress level and it is not clear how the phenomenon affects the fatigue properties of binders. The special t...The phenomenon of cyclic hardening is observed in fatigue tests of modified asphalt controlled by low strain/stress level and it is not clear how the phenomenon affects the fatigue properties of binders. The special time weep tests were performed to investigate the point. Tests results indicate that the cyclic hardening is caused by the rearrangement of molecules in binders, and it can make the inner structure of binders getting stable and increase the fatigue properties of asphalt binders. But fatigue damage occurs when fatigue tests start, no matter the phenomenon of cyclic hardening happens or not. If the controlled load is low, the effect of rearrangement of molecules on material is beyond the effect of fatigue damage so that the cyclic hardening can be observed. When the load conditions get worse, the effect of slight fatigue damages produced in hardening stage will show.展开更多
文摘A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed material, and variations in the dimension of bed forms. The model predicts the changes in the grain size distribution with the time and space during degradation process. The numerical model proposes that the armoring process in degrading channels does not depend only on hydraulic characteristics of the flow but also on variation in the grain size distribution of sediments on the bed. The model was applied and compared with the results obtained from experiments conducted in 24 m recirculating flume for two sizes of sand; a good agreement was found between observed and calculated values.
基金supported by the projects of Sichuan Province Science and technology support program (Grant No.2014SZ0163)National Natural Science Foundation of China (Grant No.41171016 and 51579163)the Open Foundation of State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University (SKHL1309)
文摘The rapid changes in flow pattern due to varying channel widths will make significantly impact on the hydraulic structures and evolutions of open channel. To better understand the impact of varying width, a flume experiment with adjustable width and a depth-averaged two-dimension numerical model were used to analyze the variations of flow parameters. Our experimental results showed that flow velocity gradually increased with decreasing water depth in converging region, and decreased with increasing water depth in diverging zones. It was also found that the turbulence intensity laws in three directions were not agreed with the theoretical relationships proposed by Nezu and Nakagawa in 1993 in straight open channel flows. The flow in the channel with varying width may change from the supercritical flow to the subcritical flow as a function of Froude number. Our numerical simulations with different flow rates showed that most of the hydraulic jumps in diverging region were submerged jump and the degree of submergence increased with increasing flow rate in gradual channel transition. When the flow rate increased, the range of supercritical flow rapidly decreased and the flow changed from the supercritieal condition to the subcritical condition in diverging sections.
文摘The phenomenon of cyclic hardening is observed in fatigue tests of modified asphalt controlled by low strain/stress level and it is not clear how the phenomenon affects the fatigue properties of binders. The special time weep tests were performed to investigate the point. Tests results indicate that the cyclic hardening is caused by the rearrangement of molecules in binders, and it can make the inner structure of binders getting stable and increase the fatigue properties of asphalt binders. But fatigue damage occurs when fatigue tests start, no matter the phenomenon of cyclic hardening happens or not. If the controlled load is low, the effect of rearrangement of molecules on material is beyond the effect of fatigue damage so that the cyclic hardening can be observed. When the load conditions get worse, the effect of slight fatigue damages produced in hardening stage will show.
