Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resis...Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resistance strongly impact the overland flow process and watershed floods. In view of the universal existence of natural vegetation, such as Chlorophytum malayense(CM) or Ophiopogon bodinieri(OB), and the sand-gravel bed of the river channel, it is important to understand the role of different types of roughness elements in flow resistance. This study was performed to investigate and compare through flume experiments the behaviors of overland flow resistance by the reaction of multi-scale configuration of different roughness elements. The result showed that the resistance coefficient gradually reduced versus the increase of flow rate in unit width and tended to be a constant when q = 3.0 l/s.m, Fr = 1.0, and Re = 4000 for slopes of 6 to 10 degrees. The gap of the vegetated rough bed and the gravel rough bed is limited to the same as the gap of the two types of vegetation, CM and OB. It was noted that the vegetation contributed to the increase in form resistance negatively and may lead to the mean resistance on decrease. To classify the flow pattern, the laminar flows were described by DarcyWeisbach's equation. In the study the f-Re equation of vegetated bed was developed with f ?5000 Re.The friction coefficient for laminar flows can be regarded as the critical value for identifying the transformation point of the flow pattern.展开更多
Modeling for evaluation of effects of an indwelling hollow fiber oxygenator on the blood flow in human vena cava was carried out with involving an additional resistance term and variable vessel radius in the blood flo...Modeling for evaluation of effects of an indwelling hollow fiber oxygenator on the blood flow in human vena cava was carried out with involving an additional resistance term and variable vessel radius in the blood flow equation.The test of the stress-strain relationshiP of Pig′s vena cava was performed usingthe precise stress-strain instrument in our laboratory. The relationship between thecircumferential strain and stress of difrerent sections were introduced in determining the aditional resistance to the blood flow. An explicit difference method and iteration method were used to determine the additional pressure drop. The calculatedresults quantitatively reveal that the effect of the indwelling oxygenator on theblood flow is dependent upon the configuration of the oxygenator,the size of the vena cava vessel and its elasticity,and the blood flow,etc.. The low elastic modulus ofthe vena cava decreases the additional pressure drop significantly.展开更多
基金support from the authorities of the National Natural Science Foundation of China (Grant No. 41171016)Sichuan Province Science and technology support program (Grant No. 2014SZ0163)the Open Foundation of State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (Grant No. SKHL1309 and SKHL1418)
文摘Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resistance strongly impact the overland flow process and watershed floods. In view of the universal existence of natural vegetation, such as Chlorophytum malayense(CM) or Ophiopogon bodinieri(OB), and the sand-gravel bed of the river channel, it is important to understand the role of different types of roughness elements in flow resistance. This study was performed to investigate and compare through flume experiments the behaviors of overland flow resistance by the reaction of multi-scale configuration of different roughness elements. The result showed that the resistance coefficient gradually reduced versus the increase of flow rate in unit width and tended to be a constant when q = 3.0 l/s.m, Fr = 1.0, and Re = 4000 for slopes of 6 to 10 degrees. The gap of the vegetated rough bed and the gravel rough bed is limited to the same as the gap of the two types of vegetation, CM and OB. It was noted that the vegetation contributed to the increase in form resistance negatively and may lead to the mean resistance on decrease. To classify the flow pattern, the laminar flows were described by DarcyWeisbach's equation. In the study the f-Re equation of vegetated bed was developed with f ?5000 Re.The friction coefficient for laminar flows can be regarded as the critical value for identifying the transformation point of the flow pattern.
文摘Modeling for evaluation of effects of an indwelling hollow fiber oxygenator on the blood flow in human vena cava was carried out with involving an additional resistance term and variable vessel radius in the blood flow equation.The test of the stress-strain relationshiP of Pig′s vena cava was performed usingthe precise stress-strain instrument in our laboratory. The relationship between thecircumferential strain and stress of difrerent sections were introduced in determining the aditional resistance to the blood flow. An explicit difference method and iteration method were used to determine the additional pressure drop. The calculatedresults quantitatively reveal that the effect of the indwelling oxygenator on theblood flow is dependent upon the configuration of the oxygenator,the size of the vena cava vessel and its elasticity,and the blood flow,etc.. The low elastic modulus ofthe vena cava decreases the additional pressure drop significantly.
