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Numerical simulation of non-isothermal transient gas flow is performed using implicit Steger-Warming finite difference method. Because of nonlinearity of the governing equations, they are linearized at each time step. The linearization either reduces computational effort or analyzes the flowfield more conveniently. In order to validate and evaluate the accuracy of current numerical method, Fanno and shock tube flows are investigated first. Then, transient flow in a gas pipeline that its inlet pressure changes with time is simulated. The results of present study show that Steger-Warming finite difference scheme can well captured the sudden changes in the flowfield. Moreover, the present method is able to analyze transient gas flows as nearly accurate as the nonlinear one with less computational effort.

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This note presents a theoretical analysis and numerical simulation of hydraulic transients in pressurized pipeline system made of a local polyethylene pipe-wall located at a steel pipeline system. The continuity and momentum equations are solved by the method of characteristic (MOC) taking into account the viscoelastic effect of the pipe-wall for polyethylene pipe. The polyethylene pipe length and location at the pipeline and the discharge flow rate are changed and their influence on transient flow is investigated. By comparing this pipeline system with one that is made of polyethylene pipe totally, the possibility of using local polyethylene pipe due to its effect on the pressure wave is investigated.

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Transient heat transfer from a storage fluid around a central tube is experimentally investigated in a wide range of Reynolds number, i.e. 700

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In this research the transient flow analysis in viscoelastic pipes considering Fluid Structure Interaction have been performed utilizing a newly developed formulation of Transfer Matrix Method in frequency domain. To obtain this extended form of TMM, mathematical processes was accomplished. Time domain governing equations have been transformed to frequency domain and then a suitable matrix form of them is used to study transient flow due to sudden valve closure. Obtaining a set of algebraic equations instead of integral equations and the ability to analyze this phenomenon without need to solve complex convolution integral, are some of the benefits of the frequency domain tools, which have been applied in this research. To verify the model, initially two cases of rigid and elastic pipe wall have been analyzed. Results showed good conformity comparing to experimental data and analytical solution available. Then having a set of reliable experimental data of transient flow in VE pipe, MatLab code was adopted to the model and fortunately here also results were in good compatibility with the experimental results. Also it has been showed that this model will be a suitable tool for parametric analysis and for determining the critical situations of the system. The results obtained from this research prove that using frequency domain tools will lead to an effective and precise model for simulating the transient flow characteristics in VE and also normal transmitting pipelines.

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Transient flows can also be analyzed in frequency domain in addition to time domain. The frequency domain needs no discretization in time and space and this is a one of the advantages of using this domain. Due to this reason, time of computations is reduced. For the frequency analysis of transient flows, the non-linear terms of governing equations and boundary conditions must be linearized. This causes errors in the output of the frequency domain over the exact model of the characteristics method (MOC). Understanding the effect of each non-linear terms separately in the error caused by the frequency domain leads to a greater insight into this domain and provides the basis for future activities to improve this domain. In this study, the individual effects of each non-linear terms of steady friction and valve in the generated error at the frequency domain output are shown by using a Reservoir-Pipe-Valve (RPV) system which has been excited oscillatory. This study has been shown that the effect of the friction term of steady flow on the generated error at the output of frequency domain is negligible, while the nonlinear term of the valve is the main cause of the error in the frequency domain.

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The Water Column Separation phenomenon is one of the transient flow regimes, which is created under conditions such as the sudden closing of the valve or the shutdown of the pump in the water supply network. Hard pressure fluctuations and damages caused by the mentioned phenomenon require identifying and providing a solution to prevent it. By this purpose, the present article investigates the possibility of Water Column Separation in a Loop Water Supply Network using Computational Fluid Dynamics method. Next, the Effect of the inlet velocity on the pressures created due to the Water Column Separation was investigated. For software validation, the Loop system provided by Wang et al. (2017) was selected. After ensuring the efficiency of the software to model the phenomenon of Water Column Separation, simulation was performed at different speeds. Checking the simulation results indicated the occurrence of Water Column Separation in the Intended Network. Also, the Results indicated that with the increase of the input Velocity, the maximum value of the Pressure in the Network increases and its minimum value decreases. In such a way that with a 12% increase in the input velocity, the maximum pressure value changes by 11.8% and the minimum value by 14.26%. In general, it can be said that by controlling the Velocity as an effective factor on the pressure fluctuations of the Water Column Separation, this phenomenon and the resulting damages are prevented.