Abstract: Measurement noise is a crucial factor in health monitoring on structure in situ. In this paper, the influence of measurement noise on global damage detection to offshore platform is studied. And a new concept as Damage Element Modal Influence Index (DEMI) is also proposed. A scaled physical experimental model of an offshore jacket platform is employed and a series of damage scenarios are simulated. By means of mode strain energy method based on local measurement, the relationship between damage detection result and Signal-Noise Ratio (SNR) of impulse response and DEMI are obtained. The experiment result indicates that when DEMI is larger than 5, the damage location and damage severity can be identified correctly even with small SNR signals; when DEMI is smaller than 0.5, the damage identification cannot be realized even with largest SNR signals; when DEMI is in the critical value of 0.9-1.5, SNR becomes the key factor of damage identification, that is when SNR is larger than 20, the damage location can be identified correctly, as SNR decreases to a certain value 10, both of damage location and damage severity evaluation cannot be realized.

摘要： 以海洋平台结构整体损伤检测中的测量噪声作为研究对象，提出损伤单元模态影响系数的概念。通过一系列冲击激励的物理模型试验，采用基于局部测量的模态应变能法，分析振动信号信噪比和损伤单元模态影响系数对损伤检测的影响规律。试验结果表明当模态影响系数较大(大于5)时，用很小的信噪比数据就可以准确识别出损伤单元位置和损伤程度；当系数较小(小于0.5)时，用最大的信噪比数据也无法准确识别；当系数为临界值(0.9～1.5)时，信噪比对结果影响较大，只有信噪比较大(大于20)时，才能准确识别损伤位置，当信噪比小到一定值(小于10)时，损伤定位和损伤程度评估均无法实现。

关键词: 声学, 海洋平台, 模态应变能法, 信噪比, 损伤单元模态影响系数, 试验分析