Prediction of global loads of intact, damaged and grounded ships using fluid-flexible structure interactions methods

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Insinööritieteiden korkeakoulu | Master's thesis
Marine Technology
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Master's Programme in Mechanical Engineering (MEC)
Ocean-going and restricted service vessels are operating in a threatening marine environment, with a probability of suffering collision and grounding events. These threats arise because of navigation in congested and shallow waters, extreme weather conditions, errors in cargo loading, etc. After accidents, the dynamic response of ship structures may change. This change is expected to be more prominent in flexible and slender ships with large deck openings. This thesis aims to determine the influence of deadweight, grounding, and damage on the hydroelastic response of ships. Two different methods were employed to solve the Fluid-Flexible Structure Interaction FFSI problem, namely Boundary Element Method BEM and the new Fully Coupled Acoustic Fluid Structural Interaction AFSI method. A nonlinear finite element analysis is carried out to obtain the prestressed condition of the hull girder following grounding. It is demonstrated that the deadweight widens the range of resonance frequencies and the highest modal internal elastic loads are associated with the fully-loaded condition. The change in elastic and rigid dynamic responses following grounding is observed to be dependent on the boundary conditions. However, the influence of prestressing on the linear dynamic response appears to be negligible. Hydroelasticity and acoustic analyses of three damage scenarios, namely global sagging deformation of the hull girder, side cracks, and a side collision, were carried out. The employed linear modal mechanical solver, BEM, and AFSI methods show no impact of damage on the dynamic response, resonance modes, and modal internal loads. The thesis confirms the limited capability of the available software. It is concluded that future studies should integrate non-linearity into modal and wet analyses. This can be achieved by carrying out modal experiments and developing new mathematical models to formulate the mechanics behind damage and prestresses in marine applications.
Hirdaris, Spyros
Thesis advisor
Tavakoli, Sasan
hydroelasticity, acoustic element method, grounding, ultimate strength, fluid-structure interactions, flexible structure
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