Improving the accuracy of SOD for modal parameters estimation of damped systems

The smooth orthogonal decomposition (SOD) method is one of the output only modal analysis methods, which is originally suggested for the undamped/lightly damped systems. In this paper, the error sources of the SOD method for damped vibrating systems have been investigated. Then, in order to improve the accuracy of SOD for modal analysis of damped systems, some modifications have been made on the traditional SOD algorithm, and instead of the forward two-point differential operator D, the central eight-point differential operator D (m) is used. In order to compare the accuracy of improved SOD and traditional SOD, the two methods are applied for vibration analysis of a discrete system subjected to the random white noise with the same excitation arrangement. The estimated results are compared with the exact solution obtained by the structural eigenvalue problem. The comparison reveals that the improved SOD is more accurate than the traditional SOD method. In addition, the effects of the excitation arrangement and the measurement noise on the estimated modal parameters are investigated.