Processing the response signals by using the random decrement technique, a unique corresponding to each mode is obtained, which represents a free vibration response of the structure.
The decrement of higher modal response of the rotor system is lost when damper mass-factor exceeds a limiting range.
当质量参数超出某有效区间时，系统将失去对高阶模态响应的衰减作用。
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The theory of free response from random decrement technique and model parameter identification are researched; wheel sets of locomotive and vehicle are the research object of this paper.