Development, Implementation, Validation and Applications of a Method for Simulation of Damaged and Intact Ships in Waves

Doktorsavhandling, 2014

The safety of ships at sea is a key aspect of shipping. Tragic passenger vessel accidents during the years motivates that large effort is spent on understanding the mechanisms of survivability of damaged ships. In the past few decades the development and use of numerical tools have resulted in a steady increase of the understanding and ability to assess these complex mechanisms. This thesis describes the mathematical model and numerical implementation of a tool for assessment of the behavior of damaged or intact ships in a seaway. It includes three validation studies, where the simulation results are compared to physical scale model tests. It also includes four applied studies. The mathematical model for ship motions is based on potential flow theory and a hybrid method often referred to as non-linear strip method. The hydrodynamic radiation and diffraction forces are based on linear theory. The forces are transferred from the frequency domain to the time domain by the Impulse Response Function concept. The forces from the incident waves are treated in a non-linear manner through body-exact pressure integration. A damage opening is defined through a grid of points and the flow of water through each grid point is determined through a formulation based on the Bernoulli equation. The behavior of flooded water is based on quasi-static assumptions where the floodwater surface is horizontal. The impact of viscosity on roll damping is treated through coefficients determined through experimental roll decay tests. The first validation study concerns capsize of a damaged Ro-Pax ship in waves, the second concerns progressive flooding of a barge with complex internal layout and the third study concerns parametric rolling of an intact container ship. The first two studies show a good agreement between simulations and experiments. The third study shows that the phenomenon of parametric roll is captured in the simulations but also that there are large discrepancies in roll amplitude for some of the tested cases. The first two conducted application studies are extensions of the validation studies for the damaged Ro-Pax and the containership sustaining parametric roll. The third presented application study refers to the modeling of the damage opening due to ship-to-ship collision by a FEM simulation procedure. Finally, the fourth conducted application study includes an accident investigation by use of the developed software tool. It is concluded that the tool can be used in many applications of practical interest in present stage of implementation. Opportunities for development of the tool to further increase the applicability and validity are also discussed.