Hydraulic response and accidental emergency dispatch of the long inverted siphon in north Hubei under accident conditions
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Abstract:
The Menglou-Qifang inverted siphon is a pressurized water delivery system with ultra-long pipelines and large diameters.Its safe operation is directly related to the normal and stable operation of the entire project.Under sudden accident conditions,complex changes such as water hammers and partial negative pressure may occur,and untimely emergency response or unreasonable scheduling measures may lead to serious accidental damage and water interruption.Therefore,it is of great significance to study the hydraulic response and emergency dispatch of long-distance water conveyance inverted siphon. Taking the Menglou-Qifang inverted siphon (72 km) in the North Hubei Water Resources Allocation Project as the research object,a onedimensional unsteady flow numerical calculation model for accidental conditions was established.The water delivery channel system simulation and control software (SCCS Version 1.0) was used to simulate the hydraulic response characteristics of the long inverted siphon under accidental conditions.The hydraulic response characteristics of different gate dispatching schemes were analyzed and compared,and gate dispatching strategies were proposed accordingly. The hydraulic response characteristics of the long inverted siphon are quite different under different dispatch gate modes.When the gate adopts the asynchronous same speed scheduling rule by keeping the closing time of each gate constant,increase the time interval at which the gate starts to close,and the pressure head of the inverted siphon will increase significantly.If the time interval increases to more than 15 minutes its peak value will exceed the limit.At the same time interval,different closing speeds have little effect on the hydraulic response process of the long inverted siphon,and the pressure range is only 0.49 m.When the gate adopts the synchronous all-speed dispatching rule,the closing time of the inverted siphon outlet has a significant impact on the water head along with the inverted siphon.The shorter the closing time,the more severe the hydraulic response and the easier it is to exceed the limit.When the closing time is less than 30 minutes,the pressure will exceed the limit.Extending the closing time of the inlet and upstream gates will cause more pressure water to enter the inverted siphon section,which is detrimental to the safety of the inverted siphon under accident conditions.When the closing time of the inlet and upstream gates exceeds 30 minutes,the pressure peak of the control section exceeds the design limit. Conclusions (1) In the emergency dispatch of the accident,the hydraulic response process of the inverted siphon is very rapid due to the large gap between the pressure wave velocity and the gravity wave velocity.It will climb to the peak pressure in a short time,and the pressure water will be discharged from the outlet gate in a short time so that the pressure along the entire inverted siphon will eventually stabilize at a safe level.(2) Compared with the synchronous all-speed and asynchronous samespeed scheduling methods,the synchronous all-speed scheduling method is more conducive to the safety of the inverted siphon.(3) Under the synchronous allometric scheduling rules,delaying the inverted siphon inlet and upstream gate closing time,extending the inlet and upstream gate closing time,or quickly closing the inverted siphon outlet and the downstream gate will inhibit the internal pressure water release process of the inverted siphon and make the pressure peaks rise rapidly,increasing the risk of pressure overruns.(4) Under the synchronous all-speed dispatching rules,for the water resources allocation project in northern Hubei,it is recommended that the inverted siphon inlet and upstream gates start to operate no later than 30 minutes after the exit and downstream gates start to close,and the inverted siphon outlet and downstream gates are closed for a long time,it should not be shorter than 30 min,and the closing time of the inverted siphon inlet and the upstream gate should not exceed 30 min.This is a reference set of emergency dispatch combinations for control gates.
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