The current paper aims to study the free vibration analysis of a sandwich plate in contact with quiescent fluid. The structure is made of an electro-rheological (ER) fluid core, and two laminated composite skins. The fluid is ideal, interacting partially with a plate, and fluid potential velocity is derived, satisfying continuity equation. Higher-order shear deformable theory is employed for the displacement field, and nonlinear Von-Karman strains are taken into account. After calculating the structural strain energy and kinetic energies of the fluid and plate, Galerkin approach and harmonic balance method are adopted to obtain natural frequencies of the system. Next, the accuracy and reliability of the developed model are confirmed, and then a detailed parametric study is conducted to examine the effects of different parameters such as geometrical dimensions of plate, fluid parameters and electric field strength on vibrational characteristics of the structure. The novelty of the presented model focuses on the nonlinear analysis of an ER sandwich panel coupled to ideal fluid, and the obtained results can guide the future design of composite ER panels.
