Seismic Reliability Analysis And Optimization Of Large-scale Network System Considering Corrosion

The seismic analysis of networks can be classified into two levels, elements and systems. Herein, the seismic analysis of elements means to evaluate the pipelines performance after the earthquake while the seismic analysis of systems is focused on whether the whole network can meet the consumers' requirements after the earthquake or not. Moreover, the goal of the seismic analysis of networks is to provide an optimization and design tool which is used to improve the network performance subject to seismic wave propagation. In this paper, an approach for calculating the stochastic seismic responses of buried pipeline with corrosions is presented. Several algorithms for seismic connectivity reliability analysis and optimization of networks is established. The content of this paper can be expressed as follows1. Homogeneous Markov chain with absorbing barrier, an effect mathematics tool for simulating the evolution of system with discrete states, is used to simulate the occurrence of corrosion on the pipeline. Combining with linear corrosion development model, the probability distribution of the pipeline corroded section area, which is assumed as a discrete stochastic variable, is derived. Furthermore, homogeneous Markov process is used to model the occurrence of corrosion on the pipeline and the probability density function of pipeline corroded section area, which is assumed as a continuous stochastic variable, is derived.2. On the basis of above two corrosion models of pipeline, elastic foundation beam method, a classical method for analyzing the seismic response of pipeline subject to seismic wave propagation, is used to express the seismic axial displacement and axial stress of pipeline as the function of the random variable, pipe segments section areas. Using random perturbation approach, the random seismic response of pipeline is simplified as the linear function of pipe segments section areas. Then the mean and covariance of the seismic response is derived. According to the third strength method, the limit state equation of the pipeline under earthquake is given and the seismic reliability of the pipeline is derived using first order method. 3. The concepts and three commonly used algorithms related to the network connectivity reliability analysis are introduced. Structural function recursive decomposition algorithm is presented to calculate the system reliability and several theorems are proved. On the basis of structural function recursive decomposition algorithm, the minimal path-based recursive decomposition algorithm(MPRDA) is explained from a new viewpoint. Furthermore, a modified minimal path-based recursive decomposition algorithm(MMPRDA) is derived. Also, MPRDA and MMPRDA are compared and the results indicate that MMPRDA owns higher efficiency than MPRDA.4. From the complementary viewpoint, complementary structural function recursive decomposition algorithm is also presented to calculate the system failure probability. On the basis of complementary structural function recursive decomposition algorithm, a minimal cut-based recursive decomposition algorithm(MCRDA) and a modified minimal cut-based decomposition algorithm(MMCRDA) are derived. These two algorithms have the advantage over MPRDA and MMPRDA on calculating the connectivity reliability of networks under strong earthquake which own low reliability edges. Also, the efficiency of MMPRDA and MMCRDA are compared and the reasons that MMPRDA is more suitable for the networks owning high reliability edges while MMCRDA is more suitable for the networks owning low reliability are analyzed.5. The goal of system connectivity reliability analysis is to guide network seismic optimization and design. In this paper, with network's cost and reliability as optimization object and restriction, a network topology optimization model is established. Combining with network elements investigation importance analysis, simulated annealing genetic algorithm are used to solve above optimization problem.6 Using above methods, the seismic reliability and optimal topology of gas network in Shenyang City are calculated with two cases being considered respectively, without corrosions and with corrosions.7 Using Microsoft Visual C+ +6.0 software, city gas system seismic reliability analysis and optimization software, is worked out. This soft-ware, owing friendly interface and convenient operation, can realize the modeling, analysis and displaying results of networks. The software provides powerful tool for the seismic research and design of gas network.