Axisymmetric vibrations of a circular Chladni plate in air and fully submerged in water

In this study, experimental and numerical analyses were performed to determine the effects of water loading on the axisymmetric modes of vibration of a circular plate. The plate was harmonically excited at its centre through an extension bar and its outer edge was left free. The Chladni technique, which involves exciting the plate at a resonance and waiting for sand grains sprinkled on the plate to collect along the nodal circles, was used to identify and visualize the modes both in air and fully submerged in water. Surprisingly, inverse Chladni patterns were observed in water as particles were drawn towards the zero transversal velocity radii by the induced flow. A coupled acoustic-structural finite element model was built to simulate the same modes, which had been preliminarily validated against theoretical results of a completely free edged plate. A good agreement between experimental and numerical natural frequencies and mode shapes was found. The frequency reduction ratio due to the added mass effect was around 64 %. Moreover, measurable differences due to fluid-structure coupling were observed in the radii of the nodal circles between corresponding dry and wet modes.