In this paper we have analyzed precise gravity survey and gravity effects resulted from water loading, crustal deformation, ground water level change and precipitation before and after the water impoundment in the Thr...In this paper we have analyzed precise gravity survey and gravity effects resulted from water loading, crustal deformation, ground water level change and precipitation before and after the water impoundment in the Three Gorges Reservoir. We found that： ① In dam area of the reservoir, gravity effect resulted from water load increase is the most significant, maximum gravity change is 200×10^-8 m/s^2, but this effect is limited in amplitude and range. Gravity change can be observed about 5 km offshore. The gravity change caused by ground water level change is regional; and the impact of precipitation on it should not be neglected. ② At head area of the reservoir, the maximum gravity change is near Xiangxi. Monitoring the variation of gravity field and further study should continue in the future.展开更多
When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed,...When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed, on the assumption that the guide vane of thehydraulic turbine and the turbine discharge were all changed linearly. An exact maximum of thedraft-tube vacuum for the first-phase water-hammer and the last-phase water-hammer is obtained.Finally a much more reasonable formula of critical tailrace length is derived. The results of twocases show that the formula proposed can determine correctly and reasonably whether a tail-racesurge tank is needed or not, and are more suitable for project design than the formula suggested bythe specification.展开更多
基金Social Welfare Research Special Project of Ministry of Science and Technology (2004DIB3J131).
文摘In this paper we have analyzed precise gravity survey and gravity effects resulted from water loading, crustal deformation, ground water level change and precipitation before and after the water impoundment in the Three Gorges Reservoir. We found that： ① In dam area of the reservoir, gravity effect resulted from water load increase is the most significant, maximum gravity change is 200×10^-8 m/s^2, but this effect is limited in amplitude and range. Gravity change can be observed about 5 km offshore. The gravity change caused by ground water level change is regional; and the impact of precipitation on it should not be neglected. ② At head area of the reservoir, the maximum gravity change is near Xiangxi. Monitoring the variation of gravity field and further study should continue in the future.
文摘When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed, on the assumption that the guide vane of thehydraulic turbine and the turbine discharge were all changed linearly. An exact maximum of thedraft-tube vacuum for the first-phase water-hammer and the last-phase water-hammer is obtained.Finally a much more reasonable formula of critical tailrace length is derived. The results of twocases show that the formula proposed can determine correctly and reasonably whether a tail-racesurge tank is needed or not, and are more suitable for project design than the formula suggested bythe specification.
