Study On The Reliability Modeling Of System Like Pipeline And Wire Cable

In practical engineering, there are some very large structure objects in one dimension of size. Among these "continuous systems" are pipelines in airplane hydraulic pressure system, nuclear power plant, natural gas and oil transmission system, and wire cables in suspension bridge, etc. For reliability analysis and evaluation, if a large size continuous system is simply considered as one component, the reliability computation or experiment will be very difficult. However, if it is considered as a system, there are no evident "components". What's more, when the continuous system is taken as series system during reliability analysis, the dependent failure among segments should be taken into account so that the conventional series system reliability model is not applicable in case of independent failure.In addition, the failure probability problem of wire cable is similar to that of the continuous system like pipeline, besides the wire cable being considered as continuous system like pipeline, the cable is usually considered as a parallel-series system comprising of some wires, which exists load sharing and load transfer among wires. Therefore, the traditional dependent failure reliability model of parallel system is not applicable, and the new reliability model of parallel system like cable should be developed.With the reliability modeling of system such as pipeline and wire cable as the background, this paper emphasized on the method of their reliability modeling, and soloved the key problems such as dependent failure, load action for many times, segment-partition principle, the limit of reliability of continuous system, load sharing, cumulate damage. The detailed study achievements are shown as follows.(1) Firstly, the continuous system like pipeline was divided into series system composed of some virtual segments. Secondly, the reliability model (SC model in short)of dependent failure continuous system like pipeline was presented applying system-level stress-strength interference model in the condition of not assuming independent failure. The presented reliability model could reflect the dependent failure among segments and two factors concerning the strength dispersion of the object, i.e. material inhomogeneity factor and material quality instability factor. Finally, the SC model was verified by the Monte Carlo method, and was proved reasonable and exact.(2) On the basis of SC reliability model (static reliability model), the behavior of load action and that of strength degradation were described by stochastic process. Then, a time-dependent reliability model of dependent failure "continuous system" (dynamic reliability model) was developed taking into account dependent failure effect, stochastic load action and strength degradation processes from the systematic point of view. It shows that the failure rate curve of proposed reliability model has three typical characteristic of bathtub curve.(3) For one thing, the segment partition principle of continuous system is determined based on "parameter transition method" when the segment strength followed the Weibull distribution, which was that the specimen length could be taken as the equivalent segment length, and was proved by mathematicl deducion. Then, the relationship between reliability and the length of continuous system was simulated, and the reliability lower bound of continuous system was dicussed(4) First of all, the equivalent working time which was resulted from the load transfer for different life distribution was transformed based on damage equivalent principle. Then, the reliability of dependent failure parallel system like wire cable was computed by dividing several steps, and the fatigue life reliability model of dependent failure parallel system was presented applying the full probability formula. Finally, the proposed reliability model was analyzed in comparison with the fatigue life reliability model of dependent failure parallel system based on the equivalent probability transition.(5) The reliability model of fatigue cumulate damage was developed based on the Miner fatigue cumulate damage principle. Firstly, the reliability of parallel system like wire cable was computed by the Monte Carlo simulation when the component life followed as Weibull distribution. Secondly, the obvious formula expression of system reliability was deduced when the component life followed the Logarithm Normal distribution. Lastly, the reliability model of fatigue cumulative damage of load-sharing parallel system under stochastic load was proposed.