On the use of artificial excitation in operational transfer path analysis

• Estimation of transmissibility matrices using an external, artificial excitation.
• Artificial excitation estimates are of a better quality than operational estimates.
• The number of significant transmission paths can be determined using SVD.
• The methods are applied to a gear-box.

A new measurement procedure to obtain transmissibilities for application in a two-step transfer path analysis is presented. In the proposed method an external excitation, for instance by means of a non-instrumented hammer, is used to bring the structure into vibration. The resulting response is then used to estimate the transmissibilities. In most cases the transmissibilities thus determined are of a better quality as compared to the conventionally determined transmissibilities obtained during machine operation, i.e. in conventional operational transfer path analysis procedures. The reason of this is that when a structure is excited by hammer strokes, its responses are largely independent from each other, whilst vibrations induced by machine operation are in general not. The hammer stroke measurements can be performed relatively easy whilst the experimental effort is relatively low.Subsequently the transmissibilities are applied in a transfer path analysis (TPA) like approach. It was found that the transfer paths identification was of a better quality as compared to the identification of the transfer paths by means of a conventional operational transfer path analysis. The advantages of the method are illustrated by means of an experiment on a small gearbox.Additionally, a procedure to determine the number of significant transmission paths is proposed which is based upon a singular value decomposition of the response matrix. In the application discussed in the paper the number of significant structural transmission paths could be estimated by means of this procedure, as well as the order of magnitude of the strength of the acoustic path relative to that of the structural transmission paths.