Topology Reliability Of Long Distance Natural Gas Pipeline Network And Probability Distribution Of City Natural Gas Demand

With rapid development of China’s national economy, demand for natural gas continues to expand. Natural gas pipeline, which works as the connection between resources and market, will serve as a lifeline to make sure the sustainable development of the national economy. China has the world’s most complex and busiest natural gas pipeline system. Due to the difference of regional economic and technological development, the importance of the structure and the analysis of the vulnerability degree were not paid sufficiently attention. The connectivity reliability evaluation index of long distance natural gas pipeline network were not established. This paper paid attention to the topology structure of the long distance natural gas pipeline network, connectivity reliability of system and connectivity importance of tubulation.First of all, the structure of long distance natural gas pipeline network is analyzed. Then, based on the character of the long distance natural gas pipeline network, the graph theory and related theory is introduced into the long distance natural gas pipeline network system to make long distance natural gas pipeline network abstraction for network of point line, turning it into an abstract figure-topology.The connectivity reliability index of single gas source and more than one gas source were established for the topological structure of long distance natural gas pipeline network system based on the connectedness theory of network system-the minimal path, second terminal problem and the k tree, activeproblem, and the expression of the connectivity reliability was obtained base on the shortest path sets.In order to calculate the connectivity reliability, the logic expressions of connectivity reliability were converted into math problems-converting the shortest path sets into matrix, then conducted the special operations of vector and matrix. The calculation of long distance natural gas pipeline network system connectivity reliability was often related to the searching of the shortest path sets, the operations of the logical event, the algorithm of connectivity reliability. To avoid the exponential growth of reliability calculation, the simplification principle-the reasonable selection of the computing unit and the shortest path of topological structure system model were given. In addition, the connectedness importance degree ofpipe-probability connectedness importance degree and D connectedness importance degree were built to reflect the influence of each pipe on reliability of pipeline system. Thus, a fairly method to evaluate the spare structure based on the connectivity reliability.Due to the complexity of calculation, the reliability of connectivity evaluationis was realized by the MATLAB software. Finally, the effect of network topology on connectedness is analyzed by practical examples. Then the analysis of the reconstruction of one single gas source pipeline system reveals that the calculation of the long distance natural gas pipeline network system connectivity reliability is an effective method in guiding the design of pipeline system topological structure.In the process of operation, capacity of long distance natural gas pipeline network is changing. When the daily demand of city gas station is greater than the daily supply of gas resource; the users’ demand can not be met. Based on probability and statistics method, we can get the urban demand probability density function. Assuming the source gas probability distribution function, we can establish interference model of daily supply of gas resource-daily demand of city gas station. Then the expression of the gas supply reliability was established, and the gas supply reliability computational formula of different distribution were obtained. In order to avoid the influence of the type of distribution, the monte carlo simulation model was introduced to get the gas supply reliability. The result showed that the gas supply reliability calculated by the monte carlo simulation model was approximately equal to the gas supply reliability calculated by the computational formula, and the more the number of simulations are, the more accurate the result will be.The result will provide a hand for pipeline management personnel to prevent the intrusion and damage to pipeline network, also gives some suggestions about pipeline planning and construction, which has great practical significance.