vibration behavior of thick sandwich composite beam with flexible core resting on incompressible fluid foundation

In this research, free flexural vibration of a thick sandwich composite beam that is made up of two composite face sheets and a flexible foam-made core based on a fluid is investigated. governing equations for the sandwich beam were extracted using a higher-order theory. the face sheets were modeled using the first-order shear deformation theory (fsdt). in the analysis of the multilayer sandwich composite beam, the layers and the core in the middle were assumed to be well attached to one another, and continuous strain functions at the layer interfaces were assumed. moreover, displacements were assumed to be small, so that the analyses could be performed in linear elastic region with simply supported boundary condition for the beam. equations of motion of the beam were extracted using energy equations and hamilton’s principle. continuing with the research, effects of changing different parameters were evaluated; these included core thickness to total thickness ratio, beam length to total thickness ration, face sheet material, fluid density, and fluid height. the results showed that the presence of the liquid tend to lower the natural frequency of the structure. our investigations further indicated that the natural frequency follows an increasing trend with decreasing the fluid density.