【作者】 穆祥鹏；

【导师】 彭新民；

【作者基本信息】 天津大学 ， 水利水电工程， 2004， 硕士

【摘要】 由于流量调节或事故等原因长距离输水系统的恒定流条件被破坏,系统内发生非恒定流的现象称为输水系统的水力过渡过程。过渡过程发生时输水系统沿线的水力参数随时间发生急剧变化,往往超出恒定流的设计范围,从而对输水系统造成不利影响,故对输水系统过渡过程的研究对于输水工程的设计和运行是十分必要的。本文在前人研究、总结的理论基础上,对输水系统水力过渡过程中普遍涉及的几个问题进行了研究,提出了相应的结论。并结合实际工程对水力过渡过程进行了数值计算和理论分析,在寻求过渡过程的通用解法的同时,也为工程的设计和运行提供了科学的依据和建议。本文的研究主要包括以下几个方面:(1)对二相流的水击波速进行分析,把Pearsall提出的可变波速公式引入特征线法,针对水击波速变化的特点用线性插值的特征线法编制程序,对有压管道模型进行水击计算。通过计算本文研究了水中含有自由气泡的管路在水击时管道初始水头及管道特性等敏感因素对水击波速变化的影响,得出了上游水头降低、相对管壁厚增加、管材弹性模量增加都会引起水击波速变化加剧的结论,并对在水击计算时中采用固定波速值将引起较大偏差的情况进行了分析与总结。(2)针对输水系统在水力过渡过程发生时管道流态不断发生变化的特点,本文以流态为依据来计算系统的沿程摩阻系数,提高了过渡过程的计算精度。(3)针对调水工程水力过渡过程的处理中最为复杂的多段有压管道和多段明渠相结合的输水形式,应用Preissman虚拟缝理论对有压管道和明渠采用统一的插值特征线法进行求解,针对管道水击波速和明渠水面波速相差甚大的情况,对有压管道和明渠采用不同的分段长度,并提出了切实可行的时间步长取值方法。通过建立数学模型对实际工程的过渡过程进行计算分析,在验证了数学模型的可行性的同时,也为工程设计提供了依据和建议。更多还原

【Abstract】 In long distance water transfer system, the condition of steady flow is destroyedby the flow rate regulation and hydraulic accident, and then the unsteady flow occurs,which is called as hydraulic transient process. The hydraulic parameters in thetransient process will change quickly with time and usually overstep the design valueof steady flow, which will cause a negative effect on the system. So researches on thehydraulic transient process is necessary to design and operation of the water transfersystem. Based on the former theories, the thesis devotes effort to the studies on severaluniversal problems about hydraulic transients process and draw some conclusions.Then numerical computation is applied in a practical water diversion projects. Whileseeking for the uniform solution to hydraulic transients process, the thesis also bringsforward corresponding proofs and suggestions for project design. The researchesmade by this thesis include several aspects as below. 1. The water hammer wave speed of the two-phase flow is analyzed in this aspect.Pearsall’s alterable wave speed formula has been introduced in the characteristicsmethod. Then the transient flow in pipe systems is computed with the method ofinterpolation characteristics. The Influence of hypersensitive factors, such as headpressure、pipe characteristics, on the change of the water hammer wave speed in thetwo-phase flow is studied. On the basis of data analysis, the thesis draws theconclusion that the decline of head pressure and the increase of the relative thicknessof pipe and Young’s modulus of material all can enforce the change of the waterhammer wave speed. The bias arised in the process of computation is analysied in theend of this chapter.2. In view of the continuous change of flow pattern in pipe transient process,basing on analyzing the flow pattern, coefficient of friction resistance is computed.Thus the precision of computation can be improved.3. For the most complicated water transfer system, the Preissman’s method isapplied in the compuation process of the transient process of pressure pipe-openchannel system. Because of the great difference between the water hammer wavespeed and water surface wave speed, different dimensional step is applied to pressurepipe and open channel respectively and a applicable method about how to choose timestep is put forward. Founded on the analysis of the transient process model ofpractical project, the mathematic model is proved to be feasible and suggestions aremade out for the design and operation of pratical project.更多还原