Identification of a vibration pattern from pressure measurements and radiation modes
LMA - CNRS
Monday 1 june, 2015, 17:20 - 17:40
0.6 Madrid (49)
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.
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