Waves impacting on maritime structures can cause damage which endangers the environment around these structures. Due to high hydrodynamic loading, structures can enter the plastic regime, resulting possibly in structural failure. The understanding of the principles related to this structural failure due to waves is a key concept in this research. Due to a gap in existing literature, a simple approximation for the influence of plasticity on fluid-structure interaction is the first required step towards a better comprehension of structural failure of ship and offshore structures due to hydrodynamic loading. The choice is made to analyse a pendulum because of its ability to show clear and easy to interpret results, due to its few degrees of freedom. In an experiment, three different double pendulums are subjected to breaking waves created by dispersive focusing at three different locations in front of the pendulum. The top hinge of the pendulum is a normal hinge and the bottom hinge is a friction hinge that approximates plastic behaviour in a mechanical manner. The energy dissipated in the friction hinge, modelling plastic energy, and the energy transferred from the wave to the structure, called `total absorbed energy', decrease with increasing frictional torque. This means that when a structure allows for more plastic deformation, the energy that will be absorbed in total by the pendulum is larger. The energy transferred to the double pendulum shows more variability for the wave focused furthest away from the pendulum. A reduced-order model is constructed that can help explain the behaviour of the different pendulums. ... Read more

Natural gas accounts for just under a quarter of global energy demand. The gas is mainly delivered through pipelines, but is increasingly shipped overseas by liquefying it to LNG at -162 degrees Celcius. Fluids, containing free surfaces inside ships are likely to start sloshing, as ships move on waves. These fluids induce impact loading on the walls of the tanks. These impacts induce amplified motions in the tanks membranes in the order of millimeters to centimeters,resulting in permanent deformation that could exceed acceptable risk levels. In the industry one case of plastic deformation in the corrugated membranes of the LNG tanks was observed (Gavory and de Seze, 2009), but leakage was prevented. A growing desire for understanding sloshing behaviour raised and action was taken under the name of SLOHEL a JIP. Full scale experiments have been carried out. For investigating detailed structural response on the effect of Fluid-Structure Interaction on a prediction of the plastic deformation of a Mark III membrane, subjected to a local wave impact, a numerical application was carried out. In this thesis, the experiments became input for a numerical Fluid-Structure Interaction model, that is strong two-way coupled. The structural response of a local wave impact is analysed using LS Dyna. Two-way|coupled and one-way|uncoupled results are compared. The pressures of the fluid model have been validated after making simplifications and are within a range of ±10% compared to measured results of the SLOSHEL experiments for an wave impact velocity of 7 m/s. In the simulations three high pressure stages are identified on an impact between two corrugations. First, initial impact. Thereafter, lower corrugation impact ending with upper corrugation impact. At stage 3 large deformations were found in the foam layer behind the stainless steel membrane and for higher impact velocities also in the corrugated membrane. Uncoupled simulations, in which the structure is considered as rigid for the fluid solver, but is able to respond flexible in the structural solver, were performed. In coupled simulations, a full interactive model is considered in which pressures update as a result of structural displacements. This results in dry frequencies for uncoupled simulations and wet frequencies for coupled simulations. It was found that pressures in uncoupled simulations are in often higher. Displacements in the foam show for all cases higher displacements (10-25%) for uncoupled simulations. The plastic strains in the corrugated membrane are higher for high impact velocities (50-100%) for uncoupled simulations. The significance of accounting coupled Fluid-Structure Interaction increases when deformations become non-linear. For this specific case, when yield stress of the corrugations in the membrane is exceeded id est when plastic strain occurs, uncoupled simulations are not able to obtain accurate predictions in structural response. ... Read more

Correctly predicting the structural behavior of the Pioneering Spirit is vital for ensuring the structural integrity of the ship and the cargo. A detailed finite element model is used to predict the structural behavior of the Pioneering Spirit. The finite element method is based on fundamental principles in solid mechanics. However, when using finite element models considerable differences between the predicted and observed behavior of a structure can occur, even when best industry practices are used to create such models. Because of these
differences there is a need to validate the detailed finite element model of the Pioneering
Spirit.
Finite element model updating is a method that can validate finite element models. In this method the discrepancy between the measured behavior and the observed behavior is minimized by modifying model assumptions and parameters. Currently a number of sensors is installed on the Pioneering Spirit, which can be used to find the measured behavior. Whether or not the measured behavior is detailed enough to be used in the validation of the finite element model is the subject of this research. To investigate this a simplified finite element model of the Pioneering Spirit was created using beam elements, this model provides the predicted behavior. Then sensitivity-based finite element model updating was implemented and applied to the beam model.
Simulated
measurements were used to show that the beam model can be updated using the current sensor setup. When actual measurements were used to update the beam model it was found that the beam model does not correlate with the measured behavior, making it impossible to update the beam model in a meaningful way.
The detailed model does correlate with measured behavior. By assuming that the method will work similarly for the detailed model as it did for the beam model, it can be concluded that the detailed model can be validated using the current sensor setup for a static case. For a dynamic case this is not possible. ... Read more

In the past decades the understanding of fracture of ductile material has increased substantially. Research has shown that the onset of fracture highly depends on the full state of stress inside the material. Better understanding of fracture resulted in more advanced and complex fracture models being conceived, allowing researchers to predict fracture in ductile solids with improved accuracy.


Nonlinear finite element analysis is a powerful tool at the disposal of researchers to predict the response of ship and offshore structures. When it comes to simulating accidental loads, such as collisions, often basic criteria are applied to include fracture in a finite element model. However, accurate fracture prediction is of great importance to determine the ice resilience of vessels, or to obtain reliable estimates of the sustained damage due to maritime collision. This research focuses on the latter.


This thesis is concerned with bridging the gap between the recent developments in fracture prediction and the application of failure criteria in finite element analysis of ship collision. A selection of recently published fracture models has been made and experiments have been conducted on S235 structural steel for calibration and validation of these models. Four small scale experiments have been conducted. These experiments serve a dual purpose: first, to gather information on the material behaviour during deformation. Second, to obtain information on the effect of different stress conditions on fracture. An iterative method has been employed to accurately model the material behaviour. For the calibration of the fracture models a method has been conceived and applied that takes into account the full histories of stress and strain during the deformation process up to fracture.

Before application as failure criteria for finite elements, the calibrated fracture models require a correction based on the size of the elements: a modification to an already existing theoretical framework has been proposed and applied to obtain element-size dependent failure criteria.


A large scale drop tower experiment has been designed to simulate a so called raking damage scenario. This experiment has been conducted on the same material as the small scale experiments and serves as a validation for a finite element model that has been created using the information on the material behaviour obtained from the small scale experiments. The different failure criteria have been implemented into the commercial finite element package LS-DYNA and have been applied to the finite element model. The results have been compared to the results of the raking damage experiment.


It was concluded that the application of complex multi-parameter failure models in analysis of maritime collision does not necessarily provide an improvement over conventional fracture prediction methods. The inability of shell elements to accurately describe strain concentrations and the effect of the element size introduce uncertainties that overrule the benefits of stress-state dependent prediction of element failure. ... Read more