Juha Plunt, Müller-BBM Scandinavia AB
Marieholmsgatan
9
SE-415
02 Göteborg
E-mail:
juha.plunt@muellerbbm.se
Transfer Path Analysis (TPA) is a
technique used when there is a need for quantitative ranking of the
contributions from different sources and transfer paths to a sound or vibration
response that has to be modified (reduced or enhanced). It is a common method
used during development of road vehicles.
The “classic” TPA relies on different
methods for estimating the interface forces (or volume velocities if airborne
sound sources) acting at different attachment points (radiating surfaces) of
the sources and “true” frequency response functions between these forces
(volume velocities) and the response of the transmitting system. These FRFs are
measured using artificial excitation (hammer, shaker or loudspeaker), in addition
to the operating sound and vibration measurements needed to derive operating
excitations. Also, the force estimation
methods rely on additional data; either extensive FRF measurements (inverse
matrix method) or special measurements of resilient element dynamic stiffness
(mount method).
A novel method, the Operating Transfer
Path Analysis (OTPA), is now available. It can separate source and path
contributions using only operational measurement data. The benefits are obvious
in terms of significantly reduced measurement time and effort. No modifications
to the measurement object are needed, like separating the source from the
supporting structure when measuring transfer path FRFs. All data is measured
simultaneously, and the method also allows accurate synthesis in the time
domain of the individual path contributions as well as the calculated total
response.
The large test effort has probably been
the main obstacle for using “classic” TPA for more detailed problem diagnosis
in structures such as buildings, off-shore platforms, ships or development of
other products like construction equipment, heavy machinery, appliances etc.
OTPA can be applied much more efficiently and without the need to turn off the
operating equipment, which makes it clearly attractive for analysis of noise
and vibration transmission in those applications.