Fluid-structure Interaction Analysis Of Bending-torsion Coupling Vibration Of Thin-walled Ship Hull

The bending-torsion coupling vibration of ship hull attracts more attention in recent years. The vibrational analysis of ships involves the solution of a coupled fluid-structure interaction problem. The three-dimensional fluid-structure interaction analysis can precisely model both the ship structure and the fluid, but its cost is tremendous. This paper presents an alternative method which couples the thin-walled beam finite element method (FEM) and the two dimensional boundary element method (BEM) to solve the bending-torsion coupling vibration of ship hull in water.In this thesis the ship hull is modeled with a thin-walled beam element based on the Benscoter theory and Timoshenko beam theory. In the transverse section of ship, surface pressure is calculated with two-dimensional BEM and then the equivalent load of fluid is obtained. The relationship between the fluid loading and structural nodal velocity is established and the added mass matrix and added damping matrix caused by the fluid loading are derived. So the finite element model and the boundary element model are combined to form a coupled model with consideration of the effect of the sectorial shear stress and the free surface of the fluid. This model is applicable to open, closed and mixed section, for bending, torsion and bending-torsion coupling vibration analysis. Based on this model, a FORTRAN code is developed for modal analysis and response analysis in both full space and half space. Numerical analysis is performed for examples of thin-walled beams with simple section and mixed sections. Results from present method are compared with those from three-dimensional coupled analysis using ANSYS and the Lewis's added mass method.Through the modal analysis of ship models, natural frequency in both full space and half-space is discussed, and the effect of the fluid loading to different vibration modes (vertical bending, transverse bending, torsion and bending-torsion coupling) and different vibration orders is compared. Through the response analysis of ship models, the variety of response and the distribution of response in space are discussed. Numerical resultsshow that the present method is precise and feasible. Its superiority and practicability are also proved.