Investigation of Monte Carlo simulation in FAA program KRASH

Abstract

In 1971, the U.S. Army first supported the development of computer code KRASH to model the impact dynamics and mechanics of airframes. The Federal Aviation Administration continued this support in 1975. Many enhancements have been added to the initial code, and the current official release version is KRASH 85. The next step in the ongoing advancement of KRASH includes uncertainties in modeling capabilities, which is the contribution of this work. In particular, a Monte Carlo simulation framework has been utilized here to permit the input of parameter uncertainties, and thus allow the output variables to be bound with a degree of statistical confidence. An airframe model was selected and preliminary sensitivity tests were performed on four parameters, specifically the impact surface coefficient of dynamic friction, the internal beam damping constant, the external crushing spring damping ratio, and the material properties, including yield stresses. Results from these preliminary tests showed the model was sensitive to variation in the first three parameters, while it was insensitive to changes in the material properties. Accelerations and impulses were plotted for two of the masses in the model. The means and standard deviations at each time step were calculated and incorporated into the plots. Finally, verification whether the simulation yielded statistically significant results, and confidence bounds for results with large uncertainty are presented. The techniques outlined here are completely extendable to as general a KRASH model as desired.