Studies of composite multihull ship structures using fluid structure interaction

Studies of composite multihull structure under wave loads, extreme loads, and blast loads have been conducted utilizing finite element and computational fluid dynamics (CFD) tools. A comprehensive finite element tool for structural analysis of composite multi-hull structures is developed. Two-way fluid structure interaction (FSI) is implemented by coupling finite element analysis (FEA) and CFD. FEA models have been developed using sandwich construction having composite face sheets and a foam core. Fluid domain was modeled using the CFD code, CFX and a wave motion was simulated based on Sea State 5. Stress analysis was performed and dynamic response of the hull was determined in time domain. The critical area with high stress gradient was identified and a sub model was developed. Force and displacement boundary conditions were transported to the sub model. Normal and interlaminar stress distributions through the thickness of the sandwich shell are estimated. Materials failure criteria for composites skin and foam core are applied on the sub model and structural integrity of each component is checked. An analysis without FSI is also performed on a reference model with identical load and boundary conditions and the result is compared with that of FSI.;In addition to hydrodynamic loads, the simulation of composite ship under extreme loads is performed. The wave slamming load is generated based on Sea state 6. Head sea, Quartering sea and Beam sea conditions are considered in the simulation. Stress and failure analyses of the hull were carried out using a global model while the local analysis for face/core debonding of the sandwich structure was accomplished through a sub modeling technique. Debonding region was specified in the sub model as an initial crack and strain energy release rate, G was calculated. The values of G were compared with Gc and a prediction was made as to the growth of delamination crack under extreme loading conditions. In the final analysis, an underwater explosion model was developed to study the composite hull resistance to blast load. The blast pressure function was defined at a high pressure source in the neighborhood of the hull and structural responses were obtained.