Free Vibration analysis of a composite sandwich plate with a viscoelastic core in contact with water

composite sandwich plate widely used in manufacturing of the hull of advanced fast boat. sandwich plate of the boat hull that is contact with water in one side supply the Flexural stiffness and dissipate the vibrational energy cused by internal and external factors. In this paper, composite sandwich plate consider with two external laminate face consists of two type fiber Grphite and Glass in the epoxy resin with Polyisobutylene foam core. laminates of face have orthotropic elastic manner and core have isotropic viscoelastic manner that viscoelastic mechanical property of the core received from reference. In this paper for mechanical manner of the visoelastic core, relaxation Master Curve extract with used isothermal curves. Natural frequencies and mode shapes of the composite sandwich plate are determined with clamped boundary conditions in the finite element software. results of natural frequencies and mode shapes of the composite sandwich plate are compared in air and contact with water.