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.

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.

This master thesis shows a study of the waves propagation phenomena inside a layered structure such as the MarkIII cargo containment system (CCS), widely used for the transport of the liquefied natural gas overseas. As a consequence of the wave impacts that take place inside the LNG tanks, strain waves start propagating, reflecting and transmitting at the interfaces which compose the layered structure. The aim of the thesis is to better understand how the propagation of strain waves inside a material resolves the discontinuity between liquid and structure at the moment of the impact, and how the theory of strain waves propagation can be applied to a theoretical model in order to define the deformation of the structure.

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.

When a grounding incident occurs, the officer of the watch is usually unable to assess the severity of the damage. Most ships do have damage response procedures in place. In case of military ships these are well developed, where a well-trained crew, in the form of damage parties, is available to respond adequately. For non-navy ships, this is hardly possible, mostly due to crew restrictions. But even for navy vessels, underwater damage is hard to assess because of accessibility issues of flooded compartments. This is undesirable because it needs to be known which compartments have flooded in order to assess the situation with respect to residual buoyancy and stability. Based on the outcome, the officer in charge can decide whether to evacuate or to stay on board and control the situation. For establishing which compartments will flood the extent of the raking damage must be known. It is proposed that the accelerations (or rather, decelerations) measured on board during a grounding incident can be used to make a prediction of the extent of raking damage. A three degree of freedom external dynamics calculation model for ship grounding has been made, which is used to predict the extent of bottom raking damage and the grounding force with associated decelerations of the ship in terms of surge, sway and yaw. When the ship decelerates, caused by a grounding event, these motions can be logged through continuous ship motion measurements. From these deceleration time traces it is possible to calculate the bottom damage path through a double integration with respect to time. Moreover, with these decelerations, the location of the raking damage along the ship’s bottom can be calculated as well. A straight forward method is proposed, which is validated against data on ship grounding external dynamics from earlier research and data from large-scale grounding experiments, both carried out in the nineties of the previous century.

The structures which HMC installs offshore are fabricated onshore and subsequently moved onto a barge or ship, seafastened and then transported to the offshore location. The process of moving a structure from the onshore quayside to the barge or ship is called the load-out. This load-out can be performed by lifting, skidding or using a trailer (SPMT). This thesis research focused only on a skidded load-out onto a barge. During the load-out the weight of the jacket or topside is gradually transferred from the quay to the barge. The barge gradually takes more of the load so ballast water needs to be continuously pumped or discharged depending on the location of the structure and the location of the ballast tank concerned. Improper ballasting during this process will cause the alignment between the quay and the barge to be disrupted which in turn causes peak loads in the topside or jacket and the barge. It is questioned if there are more suitable ballasting methods or a structural solution in order to lower these peak loads? It is also modeled what the effects are of quayside stiffness and the best method to model this stiffness. Therefore a 2-D representation of the entire load-out is made. This model will be made using the finite element method, via a numerical model, in MATLAB. A base case load-out of a topside will be applied to this model. Using this model, optimizing the ballast configuration will be researched. Several different criteria for the optimization were tested and its different effects on the forces during the load-out were researched and quantified. The structural solution of relocating the skidbeams to an area of lower deck stiffness was also tested and the results studied. The effects of the quayside stiffness and modelling methods were also quantified using the 2-D MATLAB model. The conclusion derived from the optimizations is that there are other ballast configurations which perform better in reducing the peak forces experienced during the load-out. The key to these optimizations is that they keep the barge-quay alignment as perfect as possible. If a critical element is present in the load-out the ballast configuration can be adjusted to lower the forces in this specific element. The results of the simulation in which the skidbeams were relocated show that this approach has no beneficial effects in reducing the forces during the load-out, mainly due to the presence of the transverse bulkheads in het barge. Furthermore for the modelling of the quayside it was proven that especially when using a low stiffness quayside, modelling the quayside without taking into account the foundation layer stiffness is inaccurate and can lead to lower forces in the model than which occur in reality.

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.