Volynskyy D. Prediction of unsteady processes in large-scale complex gas transmission pipeline systems

This thesis is referred to research of unsteady gas dynamic processes in large-scale complex gas transmission pipeline systems with various operation modes based on mathematical modeling. It is proposed to use an explicit 5-point second-order-accurate total variation diminishing scheme for solving hyperbolic model of differential equations with partial derivatives describing unstable gas flow. It helps to eliminate frontal oscillations and smearing whilst treating various boundary condition in comparison with other methods. Basing on this scheme the algorithm and calculation method of operating modes of gas pipeline systems during emergencies were introduced and implemented in the software for modelling operation of the gas pipeline system, which is based on aggregation-simulation method. While simulating operation of theoretical gas pipeline the patterns of pressure wave propagation and consequences under conditions of emergency shutdown of pipeline were identified. In order to prove its efficiency the experimental research was carried out with the help of developed software basing on the field data of emergencies on two operating pipelines "Progress" and "Urengoy-Pomary-Uzhgorod". The results of modeling shown that the average relative deviation between the results obtained by mathematical model and experimental data is 2-2,5 %.