Analysis of wave damping in pipeline having different pipe materials configuration under water hammer conditions

Hydraulic transient occurs whenever there is a sudden change in the flow velocity resulting in variation of pressure and flow in a water conductor system . Experiments have been conducted in a straight pipeline having material of Mild Steel (MS) and Glass Fibre Reinforced Plastic (GRP) pipelines and their combined configurations. From experiments, it has been observed that there is a smooth and strong damping of pressure waves in the pipeline system. Experimental results were compared with results obtained for classical water hammer equations solved in MATLAB and analyzed that there are several dissipative factors, other than fluid viscosity, responsible for strong damping of pressure wave amplitude. Further, an improvement in the governing equation of water hammer in a closed conduit was proposed by incorporating a different wave damping coefficient (a). The modified governing equations have been solved for each water hammer cycle using MATLAB. The numerical simulation results show that proposed approach gives better agreements between the experimental and computational results for all investigated cases.

Model Test Research on Pressure Wave in the Subway Tunnel

The pressure wave is of crucial importance for subway development since it greatly influences the comfort while taking. As the subway lines are rapidly developing in the cities, the pressure wave in different subway tunnel constructures is urgently needed to be studied and receded. In this paper, a subway tunnel pressure wave experimental system was designed, constructed, and tested. The influence of train model head shape, train model speed, shaft number in the tunnel, and bypass number in the tunnel on the pressure wave amplitude were experimented with and analyzed. The results show that the train model head shapes significantly impact the amplitude of the initial compression wave in the tunnel. The blunter train model head generates a greater amplitude of the initial compression wave. When the train passes through a single-track tunnel, the maximum positive pressure amplitude of the pressure wave in the tunnel is at the first compression wave at the tunnel entrance. The maximum negative pressure value in the tunnel is at the superposition of the initial compression wave reflected from the first time and the train's body, which is related to the length of the train's body, tunnel length, train's speed, and sound speed. The shaft set in the tunnel decreases the amplitude of the initial compression wave in the tunnel space behind, but it will increase the pressure wave's amplitude reflected in the tunnel when the train passes through the shaft. After the bypass tunnel is added, the initial compression wave propagation in the tunnel behind the bypass tunnel is receded. Still, it also increases the negative pressure amplitude when the train passes.

Study on the Dynamics of Local Pressure Boosting Pneumatic System

Local pressure boosting system is a complex and switched system, which is widely used in modern pneumatic systems, to optimize local pressure boosting system; firstly, the basic and the dimensionless mathematical models of the local pressure system were setup. Furthermore, the mathematical models were verified through the experimental study on the local pressure boosting system. Moreover, the influences of the tank’s three main parameters on the performance of local pressure boosting system were studied. It can be seen that the pressure wave amplitude is mainly affected by the dimensionless volume of the tank; its influence degree is 95.1%, and it increases when the later one decreases. The pressure loss of the tank is mainly affected by the dimensionless output pressure, and its influence degree is 68.7%, and it decreases rapidly with the increase of the dimensionless output pressure of the tank. Last, the optimization method of the local pressure boosting system was obtained.

Depressurization of Vertical Pipe with Temperature Gradient Modeled with WAHA Code

The subcooled decompression under temperature gradient experiment performed by Takeda and Toda in 1979 has been reproduced using the in-house code WAHA version 3. The sudden blowdown of a pressurized water pipe under temperature gradient generates a travelling pressure wave that changes from decompression to compression, and vice versa, every time it reaches the two-phase region near the orifice break. The pressure wave amplitude and frequency are obtained at different locations of the pipe's length. The value of the wave period during the first 20 ms of the experiment seems to be correct but the pressure amplitude is overpredicted. The main three parameters that contribute to the pressure wave behavior are: the break orifice (critical flow model), the ambient pressure at the outlet, and the number of volumes used for the calculation. Recent studies using RELAP5 code have reproduced the early pressure wave (transient) of the same experiment reducing the discharge coefficient and the bubble diameter. In the present paper, the long-term pipe pressure, that is, 2 seconds after rupture, is used to estimate the break orifice that originates the pressure wave. The numerical stability of the WAHA code is clearly proven with the results using different Courant numbers.

Assessment of water hammer effects on boiling water nuclear reactor core dynamics

Complex phenomena, as water hammer transients, occurring in nuclear power plants are still not very well investigated by the current best estimate computational tools. Within this frame work, a rapid positive reactivity addition into the core generated by a water hammer transient is considered. The numerical simulation of such phenomena was carried out using the coupled RELAP5/PARCS code. An over all data comparison shows good agreement between the calculated and measured core pressure wave trends. However, the predicted power response during the excursion phase did not correctly match the experimental tendency. Because of this, sensitivity studies have been carried out in order to identify the most influential parameters that govern the dynamics of the power excursion. After investigating the pressure wave amplitude and the void feed back responses, it was found that the disagreement between the calculated and measured data occurs mainly due to the RELAP5 low void condensation rate which seems to be questionable during rapid transients. .