It was recently observed in a numerical study on a high order perturbation
method under heavy fluid loading that a loaded vibrating plate results, not
only in the classical frequency shift of the in vacuo single resonance (in both
the real part because of the fluid added mass and the imaginary part because of
energy lost by radiation), but also in an increase in the number of the
resonance. As a result of the loading, a single in vacuo resonance of the
structure is transformed into a multiple resonance. Here we show that this
phenomenon is a refinement of the Sanchez's classical result where it was
established, using asymptotic analysis, that in the case of a light loading
conditions " the scattering frequencies of a fluid loaded elastic structure (ie
the resonance frequencies) are nearly the real eigenfrequencies of the elastic
body alone and the complex scattering frequencies of the fluid with a rigid
solid ". A theoretical explanation of the multiple resonances is given using
classical results on theory of entire functions. It is established that every
single in vacuo resonance of a simply supported rectangular plate is
transformed into an infinite number of resonances under fluid-loading
condition.Comment: Proceedings of Noise and Vibration: Emerging Methods - NOVEM 200