Based on the results of the tidal flow Reynolds stresses of the field observations, indoor experiments, and numerical models, the parabolic distribution of the tidal flow Reynolds stress is proposed and its coefficien...Based on the results of the tidal flow Reynolds stresses of the field observations, indoor experiments, and numerical models, the parabolic distribution of the tidal flow Reynolds stress is proposed and its coefficients are determined theoretically in this paper. Having been well verified with the field data and experimental data, the proposed distribution of Reynolds stress is also compared with numerical model results, and a good agreement is obtained, showing that this distribution can well reflect the basic features of Reynolds stress deviating from the linear distribution that is downward when the tidal flow is of acceleration, upward when the tidal flow is of deceleration. Its dynamics cause is also discussed preliminarily and the influence of the water depth is pointed out from the definition of Reynolds stress, turbulent generation, transmission, and so on. The established expression for the vertical distribution of the tidal flow Reynolds stress is not only simple and explicit, but can also well reflect the features of the tidal flow acceleration and deceleration for further study on the velocity profile of tidal flow.展开更多
This paper presents the use of a high performance dual-plane electrical resistance tomography (ERT) system and a local dual-sensor conductance probe to measure the vertical upward oil-in-water pipe flows in which the ...This paper presents the use of a high performance dual-plane electrical resistance tomography (ERT) system and a local dual-sensor conductance probe to measure the vertical upward oil-in-water pipe flows in which the mean oil volume fraction is up to 23.1%. A sensitivity coefficient back-projection (SBP) algorithm was adopted to reconstruct the flow distributions and a cross correlation method was applied to obtain the oil velocity distributions. The oil volume fraction and velocity distributions obtained from both measurement techniques were compared and good agreement was found, which indicates that the ERT tech- nique can be used to measure the low fraction oil-water flows. Finally, the factors affecting measurement precision were discussed.展开更多
An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid...An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.展开更多
While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponen...While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponents such as 1/6 and 1/7 are generally applied. However, exponent of power law is an index representing bed resistance related with relative roughness and furthermore influences the shapes of vertical velocity distribution. The purpose of this study is to investigate characteristics of vertical velocity distribution of the natural rivers by testing and optimizing previous methods used for determination of power law exponent with vertical velocity distribution data collected with ADCPs during the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient has been calculated from the equation of Limerinos. And using theoretical and empirical formulae, and representing relationships between bed resistance and power law exponent, it has been evaluated whether the exponents suggested by these equations appropriately reproduce vertical velocity distribution of actual rivers. As a result, it has been confirmed that there is an increasing trend of power law exponent as bed resistance increases. Therefore, in order to correctly predict vertical velocity distribution in the natural rivers, it is necessary to use an exponent that reflects flow conditions at the field.展开更多
深入研究缺陷岩石的动力特性对保障深部煤矿巷道等地下硐室在掘进爆破、老顶来压等强扰动作用下的长效稳定具有重要意义。该研究基于天然裂纹长度的幂律分布假设,利用颗粒流软件建立了分离式霍普金森压杆试验系统以及含不同数量分布裂...深入研究缺陷岩石的动力特性对保障深部煤矿巷道等地下硐室在掘进爆破、老顶来压等强扰动作用下的长效稳定具有重要意义。该研究基于天然裂纹长度的幂律分布假设,利用颗粒流软件建立了分离式霍普金森压杆试验系统以及含不同数量分布裂纹的砂岩试件模型,研究了在冲击荷载作用下预制分布裂纹数量对砂岩试件强度、破坏等力学特性的影响。结果显示:(1)随预制裂纹数量(number of prefabricated cracks, NPC)的增加,砂岩试件强度近似呈线性减小趋势,而弹性模量降低规律更接近三次方程,并且随着NPC的增加,试件强度、弹性模量的离散性逐渐增大,试件峰后应力的降低过程也更为复杂;(2)随着NPC的增加,试件的AE事件曲线由单峰值、高极值向多峰值、低极值转变;(3)在冲击荷载作用下,试件中新生裂纹沿应力波传播方向渐进分布,由散斑形式逐渐连通扩展为片层状,并且随着NPC的增加,试件的破坏模式由四周破坏形式转变为自左至右的渐弱破坏形式;(4)试件主要沿应力波传播方向发生破裂,并且NPC越少,倾角沿应力波传播方向的新生裂纹占比越大。展开更多
The rapid development of nanotechnology has led to a need to further understand the physical char-acteristics of nanoparticles.In this paper,the flow characteristics of micro-nano alumina particles with different part...The rapid development of nanotechnology has led to a need to further understand the physical char-acteristics of nanoparticles.In this paper,the flow characteristics of micro-nano alumina particles with different particle sizes were characterized.The FT4 powder rheometer and the PT-X powder tester were used to measure the compression,friction,and dynamic properties of powders.Powder compressibility increased significantly as the particle size decreased from 27 μm to 30 nm.Pressure distribution in the silo was measured and predicted by Janssen's theory,with errors mostly less than 10%.The basic flow energy and the specific energy of the three powders were 4983,1734,and 244 mJ,and 6.80,11.70,and 6.70 mJ/g,respectively,indicating that there was no linear relationship between the change in flowability and particle size.The dynamic properties of the powders change from particle-dominated to agglomeration-dominated as the particle size decreases.The conclusion is supported by the results of field emission scanning electron microscopy.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50339010)the Public Fund Project of Ministry of Water Resource of China(Grant No.200701026)
文摘Based on the results of the tidal flow Reynolds stresses of the field observations, indoor experiments, and numerical models, the parabolic distribution of the tidal flow Reynolds stress is proposed and its coefficients are determined theoretically in this paper. Having been well verified with the field data and experimental data, the proposed distribution of Reynolds stress is also compared with numerical model results, and a good agreement is obtained, showing that this distribution can well reflect the basic features of Reynolds stress deviating from the linear distribution that is downward when the tidal flow is of acceleration, upward when the tidal flow is of deceleration. Its dynamics cause is also discussed preliminarily and the influence of the water depth is pointed out from the definition of Reynolds stress, turbulent generation, transmission, and so on. The established expression for the vertical distribution of the tidal flow Reynolds stress is not only simple and explicit, but can also well reflect the features of the tidal flow acceleration and deceleration for further study on the velocity profile of tidal flow.
基金Project (No. 15933) supported by the Royal Society-Chinese Acad-emy of Sciences Joint Project
文摘This paper presents the use of a high performance dual-plane electrical resistance tomography (ERT) system and a local dual-sensor conductance probe to measure the vertical upward oil-in-water pipe flows in which the mean oil volume fraction is up to 23.1%. A sensitivity coefficient back-projection (SBP) algorithm was adopted to reconstruct the flow distributions and a cross correlation method was applied to obtain the oil velocity distributions. The oil volume fraction and velocity distributions obtained from both measurement techniques were compared and good agreement was found, which indicates that the ERT tech- nique can be used to measure the low fraction oil-water flows. Finally, the factors affecting measurement precision were discussed.
基金supported by the National Science and Technology Major Project of China(No.2016ZX05028-004-003).
文摘An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.
文摘While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponents such as 1/6 and 1/7 are generally applied. However, exponent of power law is an index representing bed resistance related with relative roughness and furthermore influences the shapes of vertical velocity distribution. The purpose of this study is to investigate characteristics of vertical velocity distribution of the natural rivers by testing and optimizing previous methods used for determination of power law exponent with vertical velocity distribution data collected with ADCPs during the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient has been calculated from the equation of Limerinos. And using theoretical and empirical formulae, and representing relationships between bed resistance and power law exponent, it has been evaluated whether the exponents suggested by these equations appropriately reproduce vertical velocity distribution of actual rivers. As a result, it has been confirmed that there is an increasing trend of power law exponent as bed resistance increases. Therefore, in order to correctly predict vertical velocity distribution in the natural rivers, it is necessary to use an exponent that reflects flow conditions at the field.
文摘深入研究缺陷岩石的动力特性对保障深部煤矿巷道等地下硐室在掘进爆破、老顶来压等强扰动作用下的长效稳定具有重要意义。该研究基于天然裂纹长度的幂律分布假设,利用颗粒流软件建立了分离式霍普金森压杆试验系统以及含不同数量分布裂纹的砂岩试件模型,研究了在冲击荷载作用下预制分布裂纹数量对砂岩试件强度、破坏等力学特性的影响。结果显示:(1)随预制裂纹数量(number of prefabricated cracks, NPC)的增加,砂岩试件强度近似呈线性减小趋势,而弹性模量降低规律更接近三次方程,并且随着NPC的增加,试件强度、弹性模量的离散性逐渐增大,试件峰后应力的降低过程也更为复杂;(2)随着NPC的增加,试件的AE事件曲线由单峰值、高极值向多峰值、低极值转变;(3)在冲击荷载作用下,试件中新生裂纹沿应力波传播方向渐进分布,由散斑形式逐渐连通扩展为片层状,并且随着NPC的增加,试件的破坏模式由四周破坏形式转变为自左至右的渐弱破坏形式;(4)试件主要沿应力波传播方向发生破裂,并且NPC越少,倾角沿应力波传播方向的新生裂纹占比越大。
基金support from the National Natural Science Foundation of China(grant No.51876066)Shanghai Engineering Research Center of Coal Gasification(grant No.18DZ2283900).
文摘The rapid development of nanotechnology has led to a need to further understand the physical char-acteristics of nanoparticles.In this paper,the flow characteristics of micro-nano alumina particles with different particle sizes were characterized.The FT4 powder rheometer and the PT-X powder tester were used to measure the compression,friction,and dynamic properties of powders.Powder compressibility increased significantly as the particle size decreased from 27 μm to 30 nm.Pressure distribution in the silo was measured and predicted by Janssen's theory,with errors mostly less than 10%.The basic flow energy and the specific energy of the three powders were 4983,1734,and 244 mJ,and 6.80,11.70,and 6.70 mJ/g,respectively,indicating that there was no linear relationship between the change in flowability and particle size.The dynamic properties of the powders change from particle-dominated to agglomeration-dominated as the particle size decreases.The conclusion is supported by the results of field emission scanning electron microscopy.
