On the basis of extensive survey to the Quaternary paleosols, soils and weathering layers in the vast northern China and the Loess Plateau, we found some unusually special phenomena of chemical components such as unsu...On the basis of extensive survey to the Quaternary paleosols, soils and weathering layers in the vast northern China and the Loess Plateau, we found some unusually special phenomena of chemical components such as unsuccessive illuvium, twin illuviums, unusually thick illuvium and multi-illuviums etc. According to the analysis on the content of CaCO 3 and the data of penetrating experiment, a new theory of illuvial depth or removal depth of CaCO 3 in weathering and leaching belt was constructed, which indicates that the time of CaCO 3 removing to the illuvial depth is very short, and the effect of time factor on illuvial depth can be ignored. The theory can be taken as a credible foundation for studying many geological and geographical problems in weathering and leaching belt. When the illuvial depth of CaCO 3 is bigger than the thickness of developing belt of soil or paleosol, it can be determined that the paleosol has turned into weathering crust. When the illuvial depth of CaCO 3 is bigger than the thickness of paleosol, paleosol is leaching moderately acid soil. When two, three layers or unusually thick CaCO 3 illuviums exist in the same weathering section or at the bottom of the same paleosol, there were two or more periods forming paleosol and corresponding climatic stages at that time. On the basis of the equation of relationship between mean annual rainfall (y) and illuvial depth of CaCO 3 (x) (y = 305.5x + 168.5) determined in the paper, mean annual precipitation during the development of paleosol can be calculated.展开更多
In the present paper, a new simulation method is developed for unsteady cavitating flow with air ventilation,which is very useful for alleviating the pressure oscillation in hydroturbine draft tube and reducing the dr...In the present paper, a new simulation method is developed for unsteady cavitating flow with air ventilation,which is very useful for alleviating the pressure oscillation in hydroturbine draft tube and reducing the drag force on an underwater vehicle. Because the fluid includes three components, i.e., the water, vapor, and air, the interactions between water–air and water–vapor are treated by applying the level set method, and the effect of surface tension is taken into account in governing equations. Further, the phase change between the water and the vapor is modeled by a homogeneous model,where the effect of air injection is considered by applying the air volume fraction in the mass transport equation. For calibration, the cavitating flows around a cylinder vehicle were simulated using the proposed method, and the numerical results were compared with the experimental data at three different ventilation conditions. The good agreement of cavitation evolutions between the simulation and the experiment indicated that the proposed method was acceptable for the simulation of ventilated cavitating flows with nature cavitation and would be usable for various engineering applications.Moreover, the vorticity analysis depicts that the vortex is closely related to cavitation evolution, and air injection much changes the vorticity production in cavitating flow. It was also revealed that vorticities only occurred in regions with high vapor/air volume fraction and the vortex stretching term created the most vorticities.展开更多
文摘On the basis of extensive survey to the Quaternary paleosols, soils and weathering layers in the vast northern China and the Loess Plateau, we found some unusually special phenomena of chemical components such as unsuccessive illuvium, twin illuviums, unusually thick illuvium and multi-illuviums etc. According to the analysis on the content of CaCO 3 and the data of penetrating experiment, a new theory of illuvial depth or removal depth of CaCO 3 in weathering and leaching belt was constructed, which indicates that the time of CaCO 3 removing to the illuvial depth is very short, and the effect of time factor on illuvial depth can be ignored. The theory can be taken as a credible foundation for studying many geological and geographical problems in weathering and leaching belt. When the illuvial depth of CaCO 3 is bigger than the thickness of developing belt of soil or paleosol, it can be determined that the paleosol has turned into weathering crust. When the illuvial depth of CaCO 3 is bigger than the thickness of paleosol, paleosol is leaching moderately acid soil. When two, three layers or unusually thick CaCO 3 illuviums exist in the same weathering section or at the bottom of the same paleosol, there were two or more periods forming paleosol and corresponding climatic stages at that time. On the basis of the equation of relationship between mean annual rainfall (y) and illuvial depth of CaCO 3 (x) (y = 305.5x + 168.5) determined in the paper, mean annual precipitation during the development of paleosol can be calculated.
基金supported by the National Natural Science Foundation of China(51179091,51306018,51206087and 51376100)the State Key Laboratory for Hydroscience and Engineering(2014-KY-05 and 2015-E-03)
文摘In the present paper, a new simulation method is developed for unsteady cavitating flow with air ventilation,which is very useful for alleviating the pressure oscillation in hydroturbine draft tube and reducing the drag force on an underwater vehicle. Because the fluid includes three components, i.e., the water, vapor, and air, the interactions between water–air and water–vapor are treated by applying the level set method, and the effect of surface tension is taken into account in governing equations. Further, the phase change between the water and the vapor is modeled by a homogeneous model,where the effect of air injection is considered by applying the air volume fraction in the mass transport equation. For calibration, the cavitating flows around a cylinder vehicle were simulated using the proposed method, and the numerical results were compared with the experimental data at three different ventilation conditions. The good agreement of cavitation evolutions between the simulation and the experiment indicated that the proposed method was acceptable for the simulation of ventilated cavitating flows with nature cavitation and would be usable for various engineering applications.Moreover, the vorticity analysis depicts that the vortex is closely related to cavitation evolution, and air injection much changes the vorticity production in cavitating flow. It was also revealed that vorticities only occurred in regions with high vapor/air volume fraction and the vortex stretching term created the most vorticities.
