Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the ac...Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the acceleration or deceleration. Although the logarithmic linear profile can reduce the rate of deviation from this, only it is a lower-order approximate solution. In this paper, considering the unsteady and non-linear features of tidal motion, the double logarithmic profile near-bed layers in estuarine and coastal waters is established on the assumption that the turbulent shear stress along the water depth was parabolic distribution, and on the basis of Prandtl＇s mixing length theory and yon Karman＇s self-similar theory. Having been verified the data observed at the West Solent in the south of England, and comparison of the logarithmic linear profile, it found that the double logarithmic profile is more precious than the latter. At last, the discussed results showed that： （1） The parabolic distribution of the tidal shear stresses verified good by the field data and experimental data, can be better reflected the basic features of the tidal shear stress deviating from linear distribution that is downward when to accelerate, upward when to decelerate. （2） The traditional logarithmic velocity profile is the zero-order approximation solution of the double logarithmic profile, the logarithmic linear profile is the first order, and the logarithmic parabolic profile is the second order. （3） Ignoring the conditions of diffusion and convection in the tida movement, the double logarithmic profile can reflect the tidal properties of acceleration or deceleration, so that the calculation of the friction velocity and roughness length are more reasonable. When the acceleration or the deceleration is about zero, the double logarithmic profile becomes the logarithmic profile.展开更多
稻谷籽粒内部水分扩散的快慢决定了干燥速率。本文基于Logarithmic方程,建立稻谷水分传递动力学模型,并分析热风温度(40、50、60、70℃)和风速(0.3、0.4、0.5 m/s)对稻谷(湿基水分含量23.4%)有效水分扩散系数和扩散活化能的影响。结果表...稻谷籽粒内部水分扩散的快慢决定了干燥速率。本文基于Logarithmic方程,建立稻谷水分传递动力学模型,并分析热风温度(40、50、60、70℃)和风速(0.3、0.4、0.5 m/s)对稻谷(湿基水分含量23.4%)有效水分扩散系数和扩散活化能的影响。结果表明:随着干燥温度和风速的上升,稻谷干燥速率提高,同时对应的有效水分扩散系数越大,分别为5.123×10-12~2.141×10-11m^2/s;扩散活化能从32.94 k J/mol增加至36.30 k J/mol;对比常用的5种谷物干燥模型发现,Logarithmic模型对稻谷薄层干燥的拟合度较好,R2>0.997,RMSE<2.810×10^(-3),同时该模型模拟得出的有效水分扩散系数与实际差值均低于3.8×10^(-13)m^2/s,扩散活化能均低于2.53 k J/mol,与实际值基本吻合。展开更多
基金The National Natural Science Foundation of China under contract No.50339010the public welfare projects of Water Resources Ministry of China under contract No.200701026the Natural Science Foundation of the Jiangsu Higher Education institutions of China under contract No.09KJA170003
文摘Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the acceleration or deceleration. Although the logarithmic linear profile can reduce the rate of deviation from this, only it is a lower-order approximate solution. In this paper, considering the unsteady and non-linear features of tidal motion, the double logarithmic profile near-bed layers in estuarine and coastal waters is established on the assumption that the turbulent shear stress along the water depth was parabolic distribution, and on the basis of Prandtl＇s mixing length theory and yon Karman＇s self-similar theory. Having been verified the data observed at the West Solent in the south of England, and comparison of the logarithmic linear profile, it found that the double logarithmic profile is more precious than the latter. At last, the discussed results showed that： （1） The parabolic distribution of the tidal shear stresses verified good by the field data and experimental data, can be better reflected the basic features of the tidal shear stress deviating from linear distribution that is downward when to accelerate, upward when to decelerate. （2） The traditional logarithmic velocity profile is the zero-order approximation solution of the double logarithmic profile, the logarithmic linear profile is the first order, and the logarithmic parabolic profile is the second order. （3） Ignoring the conditions of diffusion and convection in the tida movement, the double logarithmic profile can reflect the tidal properties of acceleration or deceleration, so that the calculation of the friction velocity and roughness length are more reasonable. When the acceleration or the deceleration is about zero, the double logarithmic profile becomes the logarithmic profile.
文摘稻谷籽粒内部水分扩散的快慢决定了干燥速率。本文基于Logarithmic方程,建立稻谷水分传递动力学模型,并分析热风温度(40、50、60、70℃)和风速(0.3、0.4、0.5 m/s)对稻谷(湿基水分含量23.4%)有效水分扩散系数和扩散活化能的影响。结果表明:随着干燥温度和风速的上升,稻谷干燥速率提高,同时对应的有效水分扩散系数越大,分别为5.123×10-12~2.141×10-11m^2/s;扩散活化能从32.94 k J/mol增加至36.30 k J/mol;对比常用的5种谷物干燥模型发现,Logarithmic模型对稻谷薄层干燥的拟合度较好,R2>0.997,RMSE<2.810×10^(-3),同时该模型模拟得出的有效水分扩散系数与实际差值均低于3.8×10^(-13)m^2/s,扩散活化能均低于2.53 k J/mol,与实际值基本吻合。
