Investigation of surface velocity pattern of power transformers tanks

It is common knowledge, that the surface velocity pattern of power transformers tanks and therefore the sound pressure level (SPL) are very sensitive to environmental influences, for example a temperature rise or a simple displacement, so a precalculation of the surface velocity and the SPL seem not to be feasible. By means of an experimental tank it is demonstrated, that the surface velocity pattern can be broken down into a linear combination of resonant modes near the excitation frequency. The magnitude and phase between the resonant modes are influenced by the environmental changes, but the shapes of the involved resonant modes are widely independent of the environmental influence. Therefore the resonant modes can be predicted with numerical simulation.