Sinusoidal analysis of space shuttle main engine structures

Abstract

Turbopumps in the Space Shuttle main engine (SSME) generate sinusoidal vibrations due to imbalance of the rotating components. Since the true forcing functions necessary for sinusoidal analysis are difficult to formulate, a combined experimental/analytical technique is developed. The technique predicts the peak sinusoidal stresses in SSME structures using excitations prescribed at base points. This paper presents the technique and procedures implemented to perform the sinusoidal analysis for peak stresses in SSME components. Three analytical methods are considered for integration with a finite element model to perform the analysis. The limitations of each method are assessed and consideration is given to the factors guiding method selection. To reduce conservatism, a procedure has been established that combines the responses contributed by the excitations at different base points. Two methods are used to calculate the peak stresses at the stress component level; the first uses the response equation directly, while the second uses a conservative approximation. Simple systems are used to demonstrate the response sensitivity to the following items: the analytical method, the response combination routine, and the peak stress calculation procedure. The technique is finally applied to the analysis of SSME components. Results from one of the cases are compared with strain gage data with conservative but favorable agreement.