Identification of a vibration pattern from pressure measurements and radiation modes

Regular paper

LMA - CNRS

Monday 1 june, 2015, 17:20 - 17:40

0.6 Madrid (49)

Abstract:

The sound pressure radiated by a large transformer tank inside a power
substations may be
computed with a good accuracy from its vibration pattern, but this requires a
high density of
acceleration measurements, which are unconvenient and time-consuming. An
alternative could be to
use an holographic approach, using nearfield measurements to estimate the
vibration pattern with a
reasonable accuracy, or to compute the field propagated at larger distances
with a better accuracy.
This is however still difficult to perform on actual transformer tanks because
the tank shape is often
complex, and measurements very close to the tank raise security issues for an
online transformer.
The presented approach consists in using sparse pressure measurements
performed at uneven
locations (chosen to be compatible with practical constraints), and to
estimate the vibration pattern
as an expansion over a suitable set of functions defined over the tank
boundary. Several studies
suggest that the radiation modes of the tank are good candidates for this
expansion, allowing a
minimal number of terms for a targeted accuracy ; these modes are here
numerically computed using
a specific BEM code. A small inverse problem allows to estimate the expansion
coefficents from
sparse pressure measurements performed close enough to the vibrating surface.
The radiated field
may then be computed with good accuracy at locations further away. Simulations
based on actual
transformer vibration measurements allow to compare the pressure computed
using a classical BEM
approach, and its approximation using the above expansion.