Dynamic Responses of Composite Structures with Fluid-Structure Interaction

Abstract

As composite materials have been used for marine structures such as boats, ships, offshore structures, etc., the effect of FSI should be understood. In particular, FSI effect is expected to be significant for polymer composites because the water density is very comparable to the composites’ densities. For example, the density of a carbon composite is approximately 50% greater than the water density. Sandwich composites consisting of very low densities of core materials have lower densities than that of water. As a result, the hydrodynamic mass associated with FSI would be very critical to composite structures under water. The growing use of composites in ship masts, superstructures, deck grates, piping, ducting, rudders, propellers, stacks, and various submarine structures requires extensive modeling and testing to help designers, builders and operators better understand composite response [Mouritz, et al., 2001]. These materials are subjected to a wide spectrum of loads during manufacturing and service life. Dynamic loadings, in particular, impact type event, represent a serious design concern for use of composite. Composite structures are more susceptible to impact damage than similar metallic structures which are more ductile in nature and can absorb typically large amounts of energy without failure. Furthermore, the damage in composites from impact can go undetected even when the mechanical properties may be drastically reduced from an impact. For these reasons, numerous experimental and analytical studies have been conducted to study the dynamic response of composites subjected to impact loading [Abrate, 1994; Aslan, et al., 2003; Kwon & Wojcik, 1998]. According to the review of past works, most of the research effort has been focused on low velocity impact damage, specifically, the damage predictions, and the evaluation and prediction of residual properties of damaged laminates. All of the research completed thus far has focused on damage in composites under impact loading in dry environments to support development of composites in aircraft structures. As far as dynamic response of structures under water is concerned, a great deal amount of analytical and experimental studies have been conducted on the effect of fluid force on the natural frequencies, damping ratios and mode shapes of vibrating structures in contact with fluid. This is commonly known as the Fluid Structure Interaction (FSI) problem. FSI investigations have supported many problems in submarine signaling, offshore oil structure stability, and ship structure vibrations. Through these studies, many numerical and analytical methods have been developed in order to predict the added mass and the