Problems in the Analysis of a Shock Sequence with Application to Gunfire Analysis and Simulation

Abstract

In the planning of a laboratory simulation based on a transient sequence, non-conventional techniques must be applied to the analysis of the sequence, due to the non-stationary character of the signals. This paper deals with the specific analysis problems of a transient sequence. The RMS and spectral content analysis of a single transient elucidates the distortion in the characterization of the sequence, when stationary time-series analysis methods are implemented. The way this distortion affects the simulation of the sequence is presented next. From this presentation, it can be concluded that the best method for the laboratory simulation of a transient sequence is the application of a measured time-history, while preserving the statistical features of the sequence. This conclusion has been implemented in the planning of the laboratory simulation of a gunfire-generated sequence of transients, produced by a gun installed on a helicopter. Statistics of the maximum values of each transient were calculated, for the sequences measured under changing firing conditions. Based on these statistics and on the knowledge of the total number of rounds, the number of transients of different maxima during the entire life cycle could be evaluated. Also a life-cycle representative sequence that could be simulated by a shaker was generated. A second method for the gun firing sequence simulation was also tested. In this case, the shot with maximal peak value was used and the number of equivalent shocks representing the entire lifecycle calculated, using a fatigue accumulation model. The weakness of the method is in the fatigue model.