In the stable production stage CBM wells have the characteristics of high gas production and low water production. The use of continuous velocity tube technology for drainage can achieve better drainage results. Accurate and rapid prediction of the pressure drop of velocity pipe string production in a coalbed methane well has become the key to the operation and management of velocity pipe technology. This paper uses the nonlinear mapping and prediction capabilities of the BP neural network to build a three-layer BP neural network to construct a velocity pipe string production pressure drop prediction model. The model is based on gas production, water production, bottom hole pressure, pipe string diameter, and well depth. The five factors are input, and the pressure drop of the pipe string is the output, which can quickly and accurately realize the pressure drop analysis and calculation of the speed pipe drainage. The analysis shows that it is feasible to use the BP neural network to calculate and analyse the pressure drop of the velocity string of coalbed methane wells.
Cavitation is common in electrohydraulic servo valves and often adversely affects their performance. This study explores the influence of pre-stage cavitation on the performance of double-nozzle flapper pressure servo valves. The mechanism of cavitation is theoretically studied, a dynamic model of cavitation bubble motion is deduced, and the main factors affecting the development and variation of cavitation are determined. The software ADINA is used to establish a servo valve pre-stage fluid–structure interaction (FSI) model using the finite volume method. Cavitation is introduced to the model to conduct an FSI simulation of the influence of pre-stage cavitation on the performance of double-nozzle flapper pressure servo valves with nozzle diameters of 0.5, 0.55, 0.6, and 0.7 mm. An experiment on the servo valve is carried out to verify the simulation results. The simulation and experiment show that a nozzle diameter that is too small or large weakens the performance of a servo valve, and 0.6 mm is an ideal diameter; asymmetric double nozzles may reduce or improve the performance of a servo valve, and a combination of 0.6 and 0.55 mm nozzles is optimal; pre-stage cavitation influences the performance of a servo valve by changing the size and pressure gain of the dead zone; and excessive cavitation strength decreases or increases the dead zone and increases the pressure gain.
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