Vibration Reliability Analysis Of Engine Piping Transport System

This paper comes from the fault caused by pipe leakage that is due to the vibration produced by an operative engine acting on the pipeline combined with it. It mainly discusses three issues: dynamic response of structures under stochastic process excitation, the calculation of dynamic reliability and structural dynamic optimum design.Random vibration theory is the basis of structural dynamic reliability theory. It is extremely difficult to establish and solve random vibration differential equations of structures due to the uncertainty of loads. Based on the basic theory of random vibration, a rule is taken into consideration in this article that the mean square solution of a linear stochastic ordinary differential equation has the same form as the definite solution of its corresponding certain differential equation. Pseudo loads can be constructed from known acceleration spectrum density based on the pseudo excitation method. The problem of stationary random vibration can be transformed into the solution of steady-state harmonic response, and then the calculation formulas for structural random response can be obtained in frequency domain. After that, Rice formula is used to deduce the level crossing rate of normal random response. On the assumption that the level crossing number of dynamic response obeys the Poisson distribution, the formula for structural dynamic reliability under Poisson hypothesis is given. On the assumption that the fatigue life of structural material obeys lognormal distribution, computing formulas for structural accumulative damage and fatigue lifetime can be obtained on the basis of Basquin equation. So theoretical calculation of structural dynamic reliability based on two kinds of criteria, namely the first passage failure criteria and the fatigue failure criteria, can be carried out. Then, reliability requirements can be introduced into constrained conditions based on the first-overstress mecha- nism under Poisson assumption and the mathematical model of optimization design on structural dimensions based on dynamical reliability can be obtained. So the structural dynamic optimization design can be carried into execution.The theoretical analysis made in this paper has certain practical significance. As a calculation example, a conveying pipeline combined with an engine is the subject in this paper. The acceleration generated from the vibration produced by the engine is regarded as a support excitation on the pipe and the random dynamic response of the structure is gained by using the pseudo-excitation method. Whereafter, the dynamic reliability can be figured out according to dynamic reliability theory and the dynamic optimization design can be operated on this basis. Thereupon, the reliability of the structure is improved. As a contrast, a finite element software is used to analysis the random response and the random fatigue of the pipe. From the result, it can be seen that the method proposed in this paper is simple, effective and conservative.