Optimal sensor placement for modal identification using system-realization methods

Abstract

The relationship between a previously published sensor placement technique, called Effective Independence, and system-realization methods of modal identification is presented. The sensor placement method maximizes spatial independence and signal strength of targeted mode shapes by maximizing the determinant of an associated Fisher information matrix. It is shown that the sensor placement method also enhances modal identification using system realization techniques by minimizing the size of the required test data matrix, maximizing the modal observability, enhancing the separation of target modes from computational or noise modes, and optimizing the estimation of the discrete system plant matrix. Three currently popular system-realization methods are considered in the analysis, including the Eigensystem Realization Algorithm, the Q-Markov COVER method, and the Polyreference method. A numerical example is also presented using the plyreference modal identification technique in conjunction with several sensor configurations selected using differing placement methods. The corresponding test data is from a modal survey performed on the Controls-Structures-Interaction Evolutionary Model testbed at the NASA LaRC Space Structures Research Laboratory. It is shown that the Effective Independence sensor configuration provides superior modal identification results as p~tedicted by the analytical work.