| The urban water supply network system is the city's "lifeline" project.In order to ensure the normal and orderly operation,management and safety of the water supply network,the water supply network hydraulic model has become a necessary technical means.In addition,destructive water hammers in water supply networks occur from time to time.This not only results in the explosion of pipes,damages to facilities and waste of water resources,but also poses a serious threat to people's lives and property.Therefore,it is necessary to study the transient state(water hammer)of the pipe network system based on the hydraulic model.With the advancement of smart water services and the study of water supply leakage,the model of the water supply network also plays a decisive role.In view of the insufficient integration of the hydraulic model of the pipe network,the GIS system and the SCADA system,and the lack of research on the water hammer simulation of the water supply pipe network,it is proposed to use the GIS system and the SCADA system to complete the construction of the hydraulic model and the automatic distribution of the water demand.Then,on the basis of the steady state model,the numerical simulation study of the stop-pump water hammer and shut-off water hammer,which often occur in the water supply network and is a serious hazard,is carried out,and the corresponding protective measures are analyzed.The main work and achievements of this study are as follows:(1)The topic selected a district network in a mountainous city in Chongqing.Due to the special terrain,the pipe network system fluctuates,the elevation difference is large,and secondary pressure is common,which increases the difficulty of modeling the pipe network.Based on the high integration of the hydraulic model and GIS and SCADA systems,the constant-state hydraulic model and the extended period hydraulic model of the water supply network was established and checked,which greatly improved the modeling speed and accuracy.(2)The coarse-tuning and fine-tuning work completed the hydraulic model checking of the pipe network.In the fine tuning process,the pipe roughness coefficients were grouped according to the pipe and pipe diameters,and the water demand of the nodes was grouped according to the amount of water consumption,and the two model parameters of pipe roughness coefficient and node flow were checked.The calibration results are as follows: For the calibration of constant-state hydraulic model,100% calibration errors of the pressure monitoring points are within ±2m,50% are within ±1.5m,and flow deviations are within 10%.For the calibration of extended period hydraulic model,the percentage of the pressure monitoring point calibration error within ±3m is 98.61%,the percentage of the calibration error within ±2m is 72.22%,and the flow calibration deviations is within 10%.After the check,the hydraulic model basically meets the calibration standard.(3)A water hammer model was established based on the steady-state model,and a simulation study was conducted on the water hammer of the pump stop.The study shows: When stop-pump water hammer of the water supply network occurs,the maximum transient pressure value of many pipelines is greater than 1400 KPa,which exceeds the pressure capacity of the pipeline(1.4MPa).The minimum transient pressure of the pipeline is less than 0,and it is under negative pressure.Further analysis of the transient conditions of profile 1,profile 2 and profile 3,which are further away from the water hammer source,shows that the pipe network area closer to the pump is more affected.In the profile 1 closest to the pump,almost all the pipelines are under negative pressure,and a large number of steam holes appear.And the maximum hydraulic gradient of many pipelines is more than 50 meters above the steady state hydraulic gradient.The maximum value occurs near the rear of the pump.The maximum hydraulic gradient is 91.4 meters above the steady hydraulic gradient,and the pressure value reaches 1877 KPa.But all pipeline pressures at the profile 3 farthest from the pump don't fluctuate significantly.(4)The protective measures under the condition of stop-pump water hammer were studied.When the two-stage slow-closing valve was adopted(the first stage 10 s closes the valve by 60% and the second stage 50 s closes the remaining 40% of the valve),the transient condition of profile 1 was analyzed,it shows: After installing the slow-closing valve,the maximum hydraulic gradient line of the entire pipeline is significantly decreased;The difference between the maximum hydraulic gradient and steady state hydraulic gradient of most pipelines fall within 50 meters;The highest hydraulic gradient near the pump outlet also fall from 538.3 meters to 507.4 meters,pressure value from 1877 KPa down to 1568 KPa,it is still higher than the pipe anti-pressure capacity value;From the lowest hydraulic slope line,the entire pipeline is still under negative pressure.After using the slow-closing valve and the buffer exhaust valve,it find that: The difference between the maximum hydraulic slope and steady state hydraulic gradient of all pipelines fall below 20 meters,and the maximum hydraulic gradient near the pump outlet decrease from 507.4 meters to 461.4 meters,and the pressure values are all lower than the pipeline resistance capacity.In addition,negative pressure has also been eased to meet relevant regulations.Therefore,the water supply pipe network can use slow-closing valves and buffer exhaust valves in combination for protective measures.(5)The closing-valve water hammer simulation and protection measures for water supply network were studied.Simulation on the closing-valve water hammer in different positions of pipe network was studied,the results shows: When the valve is closed at the pipe network pump(upstream),the system generate a water hammer effect of high pressure and negative pressure;when the valve is closed midstream of the pipe network,there is almost only a high pressure effect in the upstream of the valve,and almost only a negative pressure effect in the downstream of the valve;when the valve is closed downstream of the pipe network,there is almost no water hammer effect.A comparative analysis of the 1s off valve,the 30 s off valve,and the 60 s off valve indicates that the slow closing of the valve can effectively protect the closing-valve water hammer and should therefore be the preferred measure.Study on protective measures for the 1s valve closing in the middle of the pipeline network shows that the most severe high pressure fluctuations occur at the upstream valve,and when no protective measures are taken,the maximum hydraulic gradient of most pipelines is more than 50 meters above the steady state hydraulic gradient.After the air valve and one-way pressure-regulating tower measures were taken upstream of the valve,the upstream high pressure was almost not weakened;After the air tank was taken upstream of the valve,the difference between the highest hydraulic gradient and the steady hydraulic gradient fell below 40 meters.Therefore,for the high pressure effect caused by closing-valve water hammer,it should consider the protective measures of the air tank or the two-way pressure regulating tower. |
PDF Full Text Request