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由于功率谱的模态阶次是频响函数模态阶次的2倍,直接使用响应信号的功率谱进行模态参数识别容易导致识别过程中需要过高的系统阶次、运算量加大、数值算法不稳定等问题。因此使用功率谱的模态识别方法多为窄频带算法,难以适用于宽频带识别。针对该问题,在使用相关图法估计功率谱的过程中,仅对正时延相关函数进行傅里叶变换(FFT)可以实现功率谱降阶,并且降阶后的模态参数不发生变化。根据频响函数与降阶功率谱具有相似数学表达式的特点,将试验模态分析中的多参考点最小二乘复频域(p-LSCF)宽频带算法与降阶功率谱相结合,实现了环境激励条件下的模态参数识别。通过一个二层单跨框架结构仿真算例与一个建筑结构的实测算例进行了验证,结果表明:该方法能够较准确识别模态参数,具有耦合模态的识别能力;在模态选择中,除了借助于模态指示函数,高阶模态应利用稳定图加以判断。
Since the modal order of the power spectrum is 2 times of the modal order of the frequency response function, the direct use of the power spectrum of the response signal to identify the modal parameters easily leads to the system order that needs to be excessively high in the identification process, Numerical algorithm instability and other issues. Therefore, the use of power spectrum modal identification methods are mostly narrowband algorithm, it is difficult to apply to wideband identification. In order to solve the problem, in the process of estimating the power spectrum by using the correlation graph method, the power spectrum reduction can be achieved only by performing the Fourier transform (FFT) on the positive delay correlation function, and the mode parameters after the reduction do not change. According to the similar mathematical expressions of the frequency response function and the reduced order power spectrum, the multi-reference point least-squares complex frequency domain (p-LSCF) broadband algorithm in experimental modal analysis is combined with the reduced order power spectrum to achieve Modal parameter identification under environmental excitation conditions. A case study of a two-story single-span frame structure and a measured example of a building structure were carried out. The results show that the method can recognize the modal parameters more accurately and has the ability to recognize coupled modes. In the modal selection, In addition to using the modal indication function, the high-order mode should be judged by the stability map.