STATIC AND DYNAMIC RELIABILITY ANALYSIS OF INTEGRAL SATELLITE IN VIEW OF LOW FAILURE PROBABILITY

摘要

In conventional safety-factor based design the un- certainty about structural and loading parameters is accounted for by means of safety factors which are applied in combination with the results of a deterministic analysis. In this case, however, the resulting degree of conservatism remains unquantified. This shortcoming is avoided in a probabilistic framework, where the uncertainties in material and geometric properties and in the loading are quantified in terms of probability distributions and propagated to the structural responses upon which the design is based (e.g. stresses). The application of probabilistic methods to structural design of large-scale structures remains a challenging task, because high levels of reliability imply the necessity to calculate very low failure probabilities. The associated difficulties increase in the presence of a high number of uncertain structural parameters, e.g. in the case of FE models of large-scale structures with many thousands DOF's, the performance of traditional methodologies for reliability analysis quickly deteriorates. Recently, a novel method for the estimation of low failure probabilities has been introduced. The method has been termed "Line Sampling" and hinges on the efficient, approximate estimation of the gradient in the space of uncertain parameters and the evaluation of samples along lines that are parallel to the approximate gradient. With this approach the estimation of sufficiently low failure probabilities (in the range of 10{sup}(-6)) is feasible at a tolerable computational cost. In the present paper, the application of this newly developed variance reduction technique is demonstrated in connection with ESA's INTEGRAL satellite. The FE model consists of roughly 120,000 DOF's and the number of uncertain structural parameters amounts to approximately 1300. Two load cases are considered in the present study: the first is a static load case, in which the critical response quantity is given by the force between the satellite and its solar panels; the second load case is dynamic and involves the frequency response of the satellite to harmonic excitation in the range between 5 and 100 Hz. The obtained results are very significant in that they show the feasibility of a full scale probabilistic reliability analysis, in a design context for aerospace structures.