Several methods exist for reducing the mass and stiffness matrices of a finite element model to a test-analysis model whose degrees of freedom correspond to modal survey accelerometer locations. Four of these methods-static (Guyan) reduction, Improved Reduced System (IRS) method, Modal reduction, and Hybrid reduction-are compared for accuracy and robustness. Comparisons are made using two case studies: a simple finite element model of a generic spacecraft with simulated test data and a pretest finite element model of a large aerospace structure and corresponding modal survey results. The case studies suggest that the quality of the reduction process is problem dependent with none of the methods clearly superior to the others. However, the case studies show that the IRS method is an improvement over the Static reduction, and the Hybrid reduction is an improvement over the Modal reduction. This paper also reviews the theory behind each of the reduction methods.
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