Computing Effective Mass Using the Modal Craig Bampton Framework

Abstract

Effective mass models are a powerful framework in mechanical design and qualification. They are a specialized modal model that use a base-acceleration input to yield the response of a base-mounted structure in single-axis dynamic environments. Applications include the computation of reaction forces of each mode of the base-mounted payload, the identification of the most “important” modes for loads analysis, and many others. Originally derived from a finite element model of the structure, many experimental techniques for computing effective mass models have also been developed. This work describes the derivation of a novel technique which utilizes the Craig-Bampton Modal framework to extract an effective mass model from a modal test and provides a much simpler formulation than previous methods while maintaining the accuracy of the computed effective mass model. Analytical and experimental demonstrations are provided along with practical recommendations for successful implementation.