An underlying assumption of many operational modal analysis techniques is that the
excitation is evenly distributed over the system, i.e. the inputs are spatially white, and is constant
with frequency, i.e. frequentially white. This paper investigates the use of cyclostationarity, in
combination with the Frequency Domain Subspace identification technique, to relax these
constraints. Such a technique is suitable for application on systems which are excited by at least one
cyclostationary input with a unique cyclic frequency, such as an internal combustion engine in a car
or locomotive. The cyclostationary properties of this input are employed to reduce a multiple-inputmultiple-
output system to a single-input-multiple-output system by extracting the component of
each response measurement which is attributable to the cyclostationary input alone. The system
modal properties; the resonances, damping and mode shapes, are then identified using the frequency
domain subspace algorithm. The effectiveness of the technique is demonstrated through
experiments on a laboratory test rig and a passenger train, and compared with results obtained using
the knowledge of the inputs.
Operational Modal Analysis of a Spar-Type Floating Platform Using Frequency Domain Decomposition Method
