New coherence function with measurements of one sampling period

摘要

Errors in calculating FRFs of a mechanical system by applying the DFT to response and excitation series have been identified. A new coherence function and a fitting index based on the new coherence function are introduced to efficiently and physically evaluate qualities of a FRF. The new coherence function was applied to a calculated FRF of a two-degree-of-freedom mass-spring-damper system and measured FRFs of an aluminum cantilever beam and an outdoor rail. It has been shown that by use of the new coherence function meaningful and stable function values can be obtained using response and excitation series of only one sampling period and response advancement error in a DAS can be reflected, which can never be achieved by use of the conventional coherence function.