General Framework for TPA
With the variety of TPA methods growing over the past years, the need for a clear classification of methods and their pros and cons became inevitable. In 2015, VIBES’ own Dr. Maarten van der Seijs and Dr. Dennis de Klerk, together with Prof. Dr. Daniel Rixen, proposed a general framework to structure the different TPA methods.
For the first time, similarities between well-known classical methods (such as mount-stiffness and matrix inversion) and the popular Operational TPA method have been made clear. More importantly, all recent approaches dealing with “Blocked Forces” were included and categorized into the component-based TPA family, in a way that helps the engineer choose the right approach, test bench design or source description for the case at hand. Research paper can be found here.
The three families of TPA as identified in the General Framework for Transfer Path Analysis* are listed below. The first two use some notion of force to split up in a source-transmission-receiver, while the transmissibility-based TPA is a response-only approach:
Classical TPA is intended to identify transfer path contributions in existing products. The source excitation is represented by interface forces, which are a property of the assembly they are measured in. Popular ways to obtain the interface forces are the matrix inverse method, the mount stiffness method or the direct force method, which uses force transducers mounted at the interfaces.
Component-based TPA is powerful to simulate component vibration levels in new products. The source excitation is characterized by a set of equivalent forces that are an intrinsic property of the active component itself. More popularly, these forces are known as blocked forces, as they are the would-be forces (and moments!) when measured against a rigid boundary. Blocked forces are the perfect means to characterize an active source on a test bench at a supplier and allow the OEM to make NVH predictions for new assemblies by ‘substructuring’ the components. The blocked forces are often obtained in-situ using a matrix inverse procedure, where the test environment may be either a component test bench or the actual vehicle itself.
- Transmissibility-based TPA
Transmissibility-based TPA is great for troubleshooting dominant sources and paths. Classical TPA and component-based-TPA can be tedious processes, as they require FRFs to be measured on several (sub-)assemblies. If one is merely interested in the path contributions of different uncorrelated sources through their interfaces, it is faster to use a transmissibility-based approach such as Operational TPA. As these methods use responses only, the insights gained from it are limited to ranking of sources and their dominant paths.
van der Seijs, de Klerk and Rixen, General framework for transfer path analysis: History, theory and classification of techniques, Mechanical Systems and Signal Processing (2016)
Please click here to read the full paper.