It is proved that air entrainment is one of the efficient measures dealing with cavi-tation control for the release works of hydropower projects. There are many factors to be considered in designing a chute aerator. O...It is proved that air entrainment is one of the efficient measures dealing with cavi-tation control for the release works of hydropower projects. There are many factors to be considered in designing a chute aerator. One of the most important factors concerns the cavity length below the aerator,which has outstanding effects on air entrainment against cavitation damage. It is crucial to determine reasonable emergence angle for the calculation of the cavity length. In the present paper the overall effects of structural and hydraulic parameters on the emergence angle of the flow from the aerator were analyzed. Four improved expressions of the emer-gence angle with weight coefficient were investigated through experimental data of 68 points observed from 12 aerators of 6 hydropower projects,of both model and prototype,on the basis of error theory. A method to calculate the cavity length be-low aerators was suggested,which considers overall effects of the above men-tioned parameters. Comparison between the method in this paper and the other five methods of calculating the cavity length showed that the present method is much more reliable than the existing methods while the mean error of the method is less than others.展开更多
Aerator is an important device for release works of hydraulic structures with high-speed flow in order to protect them from cavitation damage. This kind of protecting effect is related closely to cavity length below t...Aerator is an important device for release works of hydraulic structures with high-speed flow in order to protect them from cavitation damage. This kind of protecting effect is related closely to cavity length below the aerator, while the cavity length is dominated by the emergence angle over the aerator. Therefore it is crucial to determine this angle accurately. In the present paper the affecting intensities of flow depth and the fluctuating velocity on this angle were analyzed through two introduced parameters. Furthermore, the improved expressions of emergence angle estimation, for both ramp-type and step-type aerators, were presented by means of 68 sets of experimental data from 6 projects based on error theory. The results showed that the present method has higher accuracy than the previously reported methods.展开更多
The incidence of recurrent spontaneous abortion(RSA)in women of reproductive age is 1%-5%,which is a heavy physical and emotional blow to these women.Repeated curettage of uterine cavity will damage the endometrium,ca...The incidence of recurrent spontaneous abortion(RSA)in women of reproductive age is 1%-5%,which is a heavy physical and emotional blow to these women.Repeated curettage of uterine cavity will damage the endometrium,causing partial infection and leading to intrauterine adhesion(IUA).Repeated pregnancy loss causes a huge emotional trauma to both the patients and their families,including negative emotions,such as anxiety,stress,and frustrations.Therefore,patients with RSA are eager to seek medical help from their doctors before pregnancy again.However,the causes of RSA are complicated,with 50%of cases having unexplained etiologies.展开更多
Superplastic deformation mechanism of AZ31B magnesium alloy sheet was investigated. Maximum elongation of 216% and strain rate sensitivity of 0.36 were obtained at 723 K and a strain rate of 1×10?3s?1. It is foun...Superplastic deformation mechanism of AZ31B magnesium alloy sheet was investigated. Maximum elongation of 216% and strain rate sensitivity of 0.36 were obtained at 723 K and a strain rate of 1×10?3s?1. It is found that dynamic recrystallization occurs at the early deformation stage, and that grain boundary sliding is the dominant deformation mode of superplastic AZ31B sheet, whose fracture is due to the growth and interlinkage of cavities nucleated at grain boundary. A cavity growth model was established, and damage characteristic parameters as well as the critical value of damage variable were identified so as to provide a theoretical ground on which the plastic forming technology of magnesium alloy sheet can be optimized.展开更多
基金the National Natural Science Foundation of China (Grant No. 50539060)the Innovative Project of Graduate Student in Jiangsu Province (Grant No. 2005-60)
文摘It is proved that air entrainment is one of the efficient measures dealing with cavi-tation control for the release works of hydropower projects. There are many factors to be considered in designing a chute aerator. One of the most important factors concerns the cavity length below the aerator,which has outstanding effects on air entrainment against cavitation damage. It is crucial to determine reasonable emergence angle for the calculation of the cavity length. In the present paper the overall effects of structural and hydraulic parameters on the emergence angle of the flow from the aerator were analyzed. Four improved expressions of the emer-gence angle with weight coefficient were investigated through experimental data of 68 points observed from 12 aerators of 6 hydropower projects,of both model and prototype,on the basis of error theory. A method to calculate the cavity length be-low aerators was suggested,which considers overall effects of the above men-tioned parameters. Comparison between the method in this paper and the other five methods of calculating the cavity length showed that the present method is much more reliable than the existing methods while the mean error of the method is less than others.
基金supported by the National Natural Science Foundation of China (Grant No. 50539060)the Innovative Project of Graduate Student in Jiangsu Province (Grant No.2005-60).
文摘Aerator is an important device for release works of hydraulic structures with high-speed flow in order to protect them from cavitation damage. This kind of protecting effect is related closely to cavity length below the aerator, while the cavity length is dominated by the emergence angle over the aerator. Therefore it is crucial to determine this angle accurately. In the present paper the affecting intensities of flow depth and the fluctuating velocity on this angle were analyzed through two introduced parameters. Furthermore, the improved expressions of emergence angle estimation, for both ramp-type and step-type aerators, were presented by means of 68 sets of experimental data from 6 projects based on error theory. The results showed that the present method has higher accuracy than the previously reported methods.
文摘The incidence of recurrent spontaneous abortion(RSA)in women of reproductive age is 1%-5%,which is a heavy physical and emotional blow to these women.Repeated curettage of uterine cavity will damage the endometrium,causing partial infection and leading to intrauterine adhesion(IUA).Repeated pregnancy loss causes a huge emotional trauma to both the patients and their families,including negative emotions,such as anxiety,stress,and frustrations.Therefore,patients with RSA are eager to seek medical help from their doctors before pregnancy again.However,the causes of RSA are complicated,with 50%of cases having unexplained etiologies.
基金Project(2001AA331050-3) supported by the Hi-tech Research Program of China
文摘Superplastic deformation mechanism of AZ31B magnesium alloy sheet was investigated. Maximum elongation of 216% and strain rate sensitivity of 0.36 were obtained at 723 K and a strain rate of 1×10?3s?1. It is found that dynamic recrystallization occurs at the early deformation stage, and that grain boundary sliding is the dominant deformation mode of superplastic AZ31B sheet, whose fracture is due to the growth and interlinkage of cavities nucleated at grain boundary. A cavity growth model was established, and damage characteristic parameters as well as the critical value of damage variable were identified so as to provide a theoretical ground on which the plastic forming technology of magnesium alloy sheet can be optimized.
