1885年英国皇家统计协会杂志发表了拉文斯坦(E.G.Ravenstein)的论文“迁移规律”(The Laws of Migration),标志着人口迁移结束了毫无任何理论的时代。这篇著名论文依据的是1881年英国人口普查资料。拉文斯坦又根据20多个国家的资料,于1...1885年英国皇家统计协会杂志发表了拉文斯坦(E.G.Ravenstein)的论文“迁移规律”(The Laws of Migration),标志着人口迁移结束了毫无任何理论的时代。这篇著名论文依据的是1881年英国人口普查资料。拉文斯坦又根据20多个国家的资料,于1889年发表了第二篇论文,题目仍称为“迁移规律”。论文发表后,虽然受到各种不同的评论,拉氐理论仍不愧认为是研究人口迁移理论的始点。拉氐“迁移规律”可点纳如下七则:展开更多
This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of ...This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions,showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.展开更多
Due to corner separation and other complex three-dimensional flows existing in the highly loaded stator, which influences the fan performance significantly, highly loaded stator blades of a transonic fan with a maximu...Due to corner separation and other complex three-dimensional flows existing in the highly loaded stator, which influences the fan performance significantly, highly loaded stator blades of a transonic fan with a maximum camber angle of 57° were studied in this paper and sector cascade experiment was adopted. In order to get the stator aerodynamic parameters as realistic as possible and conduct the experiment without the existence of rotor, an adjustable guide vane was designed to simulate the velocity magnitude and direction of the stator inlet flow. Results show that the adjustable guide vane can simulate the rotor outlet velocity direction and magnitude in most span range. The deviation angle is positive and the maximum value is nearly 21° because the severe separation is at 27% span. Corner separation exists on both pressure side and suction side and the location of separation initiation is determined. Finally, the stator blades were redesigned with some suction slots on the suction side. Experiment results show that the suction slots change the flow field structure, increase the capability of flow turning, and decrease the flow loss.展开更多
文摘1885年英国皇家统计协会杂志发表了拉文斯坦(E.G.Ravenstein)的论文“迁移规律”(The Laws of Migration),标志着人口迁移结束了毫无任何理论的时代。这篇著名论文依据的是1881年英国人口普查资料。拉文斯坦又根据20多个国家的资料,于1889年发表了第二篇论文,题目仍称为“迁移规律”。论文发表后,虽然受到各种不同的评论,拉氐理论仍不愧认为是研究人口迁移理论的始点。拉氐“迁移规律”可点纳如下七则:
基金supported by the National Key R & D program of China (Grant No. 2016YFC0800204)the National Key Basic Research Program of China (Grant No. 2015CB057801)Natural Science Foundation of China (Grant Nos. 51578499 & 51761130078)
文摘This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions,showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.
基金funded by the National Natural Science Foundation of China (51576024, 51436002)the Program for Liaoning innovative Research Team in University (LT2015004)
文摘Due to corner separation and other complex three-dimensional flows existing in the highly loaded stator, which influences the fan performance significantly, highly loaded stator blades of a transonic fan with a maximum camber angle of 57° were studied in this paper and sector cascade experiment was adopted. In order to get the stator aerodynamic parameters as realistic as possible and conduct the experiment without the existence of rotor, an adjustable guide vane was designed to simulate the velocity magnitude and direction of the stator inlet flow. Results show that the adjustable guide vane can simulate the rotor outlet velocity direction and magnitude in most span range. The deviation angle is positive and the maximum value is nearly 21° because the severe separation is at 27% span. Corner separation exists on both pressure side and suction side and the location of separation initiation is determined. Finally, the stator blades were redesigned with some suction slots on the suction side. Experiment results show that the suction slots change the flow field structure, increase the capability of flow turning, and decrease the flow loss.
