Integrated hydro -static and -dynamic analysis and direct calculation of stress RAO for elastic floating structures

Abstract

This dissertation proposes an effective numerical method to integrate hydro-static and dynamic analysis of floating structures. In general, the waterline of floating structures is calculated through hydrostatic analysis and is used to construct wet-surface meshes for hydrodynamic analysis of floating structures. Those are time consuming and complicated tasks, in particular, when various loading conditions are considered. This study focuses on resolving the difficulties. A floating structure is modeled using the finite element method and the external fluid is modeled using the boundary element method. A single mesh is used for both hydro-static and dynamic analyses. Adopting a non-matching mesh treatment technique, the wet surface mesh of the floating structure does not need to match with free surface. Hydrodynamic analysis considering both rigid and flexible floating structures is possible without remeshing in various loading conditions. The effectiveness of the proposed method is demonstrated through several numerical examples.

In addition, we propose an efficient method for calculating the transfer function of stress in the frequency domain for hydroelastic analysis. After performing hydroelastic analysis in the frequency domain, stress values in the form of harmonic response with real and imaginary components are obtained. These stress values need to be combined to calculate representative stresses such as von-Mises stress and principal stress, which are non-harmonic responses, and require direct calculation of values over time to find the maximum value during one period. To overcome this challenge, this study proposes a method to efficiently obtain the transfer function of stress in the frequency domain for evaluating the strength of structures. This method is expected to be a valuable tool for implementing integrity analysis and real-time monitoring systems for structures, as well as evaluating the ultimate strength and fatigue strength of structures in reliability analysis.