Transfer path analysis or TPA, as the name suggests, is the process of deconstructing the dynamic energy paths and to assess the severity of their contribution to the overall energy quantity being perceived at the target location.
The energy quantity could be noise, vibration or many other dynamic quantities in general. Both experimental and computational method exist as tools to perform classical transfer path analysis.
Need for TPA
Imagine a simple case of motorbike being driven on the road; the overall vibrations being perceived at the handle bar or on the seat is a net sum of at least 3 to 4 sources actively contributing to the output.
Even this simple model has varying forcing functions from the road-wheel interaction, inputs from engine and also possibly from the gearbox. There are multiple connection paths from the wheels, engine and gearbox to the end target location of handle bar or the seat where all the forces culminate and translate into vibrations.
Now to analyze and understand the overall severity of vibrations at the target location, each identified source & its transfer paths are to be systematically quantified; since the end output depicts the dynamic character of each of the source and their path, a methodology is to be devised and this approach is called Transfer Path Analysis.
This assessment helps in ranking of sources and paths that directly contribute in the mitigation process. The method and its application can be used in any of the complex configurations to understand and solve dynamic problems.
TPA Explained
The experimental TPA typically uses the source - path - receiver model using a series of cross powers, FRF's and energy density criteria between the identified source/s and the final assessment location. To bring some visualization to this concept, the following graphic is presented.
TPA visualisation schematic
A lot of detailing goes into actually conducting a reliable transfer path analysis task. Identifying the structural sub-systems as sources, paths and receivers play significant part of building a reliable TPA model. Good knowledge of the system being investigated play significant role in both conducting the tests, build the TPA model and to find solutions.
As a backdrop to conduct effective TPA, detailed testing expertise on natural frequency testing, structural testing using Modal, ODS and OMA would be of great significance. A lot of testing procedures, data outputs and their processing methods share similarities in TPA procedure as well.
Multi-source TPA and quantification
TPA can be both used at the prototype / development stage of a product and as well on a production model. The utility of this tool is immense and, in many cases, this approach is used in the iteration process for refinement of the product using both test and CAE based TPA tools.
Limited source, compact equipment TPA
NV Dynamics uses test based TPA in many of its consulting services, associating with client development teams. Some of the classical cases include tracing vibration transfer paths of a refrigeration compressor that has many piping connections in the circulation loop or in solving some of the whole body and hand arm vibration of earth moving machinery.
TPA has varied and innovative uses in solving complex dynamic issues, the tool itself is adaptable and can be configured to solve specific problems with good understanding of the problem and the product being tested.