Free surface and solid boundary effects on the free vibration of cantilevered composite plates

This paper investigates the effects of surrounding boundaries on the free vibration response of fully and partially submerged cantilevered composite plates and how these effects change due to material anisotropy. The results show that added mass significantly reduces the natural frequencies of cantilevered marine structures as a function of relative submergence depth, more so for composite plates than for steel plates because of the much lower ratio of effective structural mass to hydrodynamic added mass. Added mass effects are most dramatic for partially submerged plates as the plates move from being above to completely beneath the free surface. Free surface effects are shown to become negligible for a fully submerged plate parallel to the free surface when the depth of submergence exceeds 50% of the plate length. Solid boundaries are found to have limited effects for fully-submerged plates near a wall, where maximum decreases in resonance frequencies due to increases in added mass are only a few percent.