| The pipelines are complex and there are many structures in the long-distance water pipeline project.So,the water hammer protection has become an important problem to ensure the safe operation of water pipelines.Many diversion outlets are often reserved in long-distance water pipelines to meet the water demand of users along the route.Considering the water diversion outlets supplying water to the users in the future,the pressurized branch pipe will be formed,and its hydraulic transient process will inevitably have some impact on the water hammer protection of the trunk pipeline.Therefore,we must carry out detailed calculation and analysis of water hammer for this kind of branch pipe system in order to ensure the safe operation of the trunk pipeline.This paper analyzes the characteristics of the two-phase flow in the water pipeline and the hydraulic characteristics of the water delivery system with the branch pipes.In this paper,the basic differential equation of water hammer,the propagation and reflection of water hammer wave,and the basic principle of water hammer calculation of characteristic line method are discussed.And the boundary control equations for special position points such as pool,valve and branch point are further discussed.In this paper,the advantages and disadvantages of various types of water hammer protective equipment and their relevant boundary conditions are given.The flow diagram of water hammer calculation program in pipeline is given.The paper takes a water conservancy pipeline project with multiple reserved water outlets as an example,and uses the C++ programming to simulate the water hammer phenomenon of the pipelines under various working conditions.Combining with engineering cases,the influence of the branch pipes on the water hammer protection of the trunk pipeline is analyzed in detail when water is supplied to water distribution area by superimposed pressure,direct supply of trunk pipe pressure,or installation of pressure-stabilizing pool and new valve-opposed jet orifice high proportion pressure reducing and flow control valve at the intake of pressure stabilizing pool.Water hammer calculation is carried out in detail when the number of branch pipe and the ratio of branch diameter to trunk diameter are different under relevant water supply modes,and its influence on water hammer pressure rise and protection of the trunk pipeline is studied.According to the calculation result of the waterhammer,comparing with the water hammer pressure of trunk pipeline without branch pipes,the water hammer of trunk pipeline is greatly affected by the branch pipes when water is supplied to water distribution area by superimposed pressure and the ratio of branch diameter to trunk diameter exceeds 1/6.And the water hammer boosting is increased on the original basis.When the branch pipes adopt direct supply of trunk pipe pressure to directly supply water to water distribution area and the ratio of branch diameter to trunk diameter exceeds 1/6,the branch pipe has a greater influence on the water hammer of the trunk pipe.When the ratio is 1/6 to 1/4,the impact can be reduced by extending the valve closing time and the safe operation of the main pipe under the original water hammer protection measures is guaranteed.While the branch pipes are equipped with pressure-stabilizing pools and opposed jet orifice high proportion pressure reducing and flow control valves are installed at the intake to supply water to the diversion area,the influence of water hammer on the trunk pipe is small and it is independent of the number of branch and the diameter of the pipe.The influence of water hammer calculation and protection on the trunk pipe system can be neglected.The branch pipes adopt this way to supply water,which can guarantee the safe operation of the trunk pipeline under the original water hammer protection measures.Therefore,it is the safest way to deliver water.The results of this study provides a reference for water hammer protection in similar pipeline projects. |
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