As the vibro-acoustic requirements of modern products become more stringent, the need for robust identification methods increases proportionally. Sometimes the identification of a component is greatly complicated by the presence of a supporting structure that cannot be removed during testing. This is where substructure decoupling finds its main applications. However, despite some recent advances in substructure decoupling, the number of successful applications has so far been limited. The main reason for this is the poor conditioning of the problem that tends to amplify noise and other measurement errors.

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Although wind turbine noise is mainly dominated by aero-acoustic noise, mechanical noise, coming from gearbox or generator, could—especially when it contains audible tonal components—result in nonconformity to local noise regulations. To reduce the mechanical noise from the gearbox, focus is put on first time right design. To achieve this, simulation models are being used earlier in the design process to predict possible issues. This paper starts with a short overview of the used model and gives additional insight in how forces from planetary gear stages should be introduced in the flexible housing. Main focus of this paper however is the approach that is being used to validate such a complex multibody model of a wind turbine gearbox. The validation approach consists of five levels: (1) individual components, (2) assembly of the empty gearbox housing, (3) the assembled gearbox, (4) the gearbox on the end-of-line (EOL) test rig, and (5) the gearbox in the wind turbine. This paper focuses on the experimental measurement results, the correlation approach for such complex models, and the results of this correlation for the first four levels showing the usability of these models to accurately predict the modal behavior.

In several cases, laboratory-based modelling approaches such as Experimental Modal Analysis and Transfer Path Analysis run into limitations with respect to technical and economical feasibility (accessibility of the structure, excitation feasibility, measurement time, accuracy, …) as well as model representativity. Therefore, approaches such as in-operation modal analysis (OMA) have been developed and are reaching a similar degree of acceptability as standard EMA, with all limitations regarding accuracy and observability of the structural dynamics. In the same line of reasoning fits the question of system characterization and identification using (or based on) other operation data types such as transmissibility functions and coherence functions and data analysis procedures such as principal component analysis. Using these testing and analysis paradigms instead of the classical load-FRF-response one, key analysis techniques such as transfer path and contribution analysis can be reconsidered.