Component transfer path analysis method with compensation for test bench dynamics

Abstract

In this article a component transfer path analysis (TPA) procedure is proposed. The method allows one to calculate the total system response resulting from a subcomponent's source excitation. It is based on the knowledge of the frequency response functions (FRFs) of the total system and on a measurement of the stand-alone subcomponent on a test bench. As the true source excitation, for example an engines combustion, is not measurable, equivalent forces at the subcomponent interface are found. The equivalent forces are multiplied with the total system FRFs from the subcomponent interface to response nodes of interest. The resulting responses at and in front of the subcomponent interface are shown to be physically exact for linear, time invariant and stationary operating systems. However, for the method to succeed, the source forces will have to be independent of the global dynamics. In addition, the test bench needs to be rigid in the frequency range of interest. This is typically hard to achieve for analysis in the mid frequency range (100–1000 Hz in vehicle acoustics). Therefore, a way to compensate for the test bench dynamics is also discussed. It is shown that one needs the receptance matrix of the free component at its interfaces and the operational motions of the interface on the test bench. Knowledge of the test bench dynamics is not needed. Measuring excitation and response at the source interface may not be feasible in practice due to space restrictions. In this case, the proposed TPA method can be extended with substitute nodes on the subsystem which are reachable on the test setup and the total system. With the knowledge of the free subcomponent FRFs, physically exact responses at and in front of the gearbox interface can also be calculated.