Polymax: a Revolution in Operational Modal Analysis

Recently the superior performance of the PolyMAX modal parameter estimation method using frequency response functions was demonstrated. The method can be implemented in a very similar way as the industry standard polyreference (time-domain) least-squares complex exponential method: in a first step a stabilisation diagram is constructed containing frequency, damping and participation information. Next, the mode shapes are found in a second least-squares step, based on the user selection of stable poles. One of the specific advantages of the technique lies in the very stable identification of the system poles and participation factors as a function of the specified system order, leading to easy-to-interpret stabilisation diagrams. This implies a potential for automating the method and to apply it to “difficult” estimation cases such as high-order and/or highly damped systems with large modal overlap. Furthermore, PolyMAX is computationally extremely efficient. In this paper the method will be extended to the operational case: only the structural response to some unknown inputs is available for system identification. Attention will be given to the pre-processing of the raw operational time data and the post-processing of the poles and operational reference factors to obtain the mode shapes. The paper also gives an overview of existing Operational Modal Analysis methods and discusses the positioning of PolyMAX herein.