The energy transition requires the maritime industry to shift to a different fuel. A long term solution is liquefied hydrogen, but there are many challenges to get there. On the short term liquefied natural gas (LNG) might be the most feasible option, because its use relies mostly on existing technologies. It is however not straightforward to take the design of an LNG tank used for cargo and implement it on a containership. The tank is not just a hold in the ship, but it is insulated with a specific cargo containment system (CCS). A CCS is typically made up of many layers, metal membranes to keep the LNG in, foam to provide insulation and plywood layers to provide enough strength. When the cargo tanks are scaled to meet the size requirements of a fuel tank, the fluid will behave differently and physics of load and response inside the tank scale as well. This means that with scaling the dominant loading mechanism on the tank walls changes. Simply scaling the CCS along with the hold dimensions is therefore not a safe choice. The current strength assessment of the tanks uses tuning factors that are based on experience with a specific size of LNG tanks. Most uncertainty in scaling is about the validity of the method considering variablity of the impact, phase transition and fluid-structure interaction (FSI). This thesis focusses on the fluid structure interaction of the CCS with the liquid within the cargo tank, both from a fundamental perspective and by looking at the wave impact on the tank walls…@en

Maritime structures operating out at sea experience large changes in wetted area because of free surface waves. Although these conditions are typical for maritime applications, a fundamental experiment that includes a structure in the air–water interface undergoing transitions from dry to wet and back does not appear to exist. This paper aims to fill that knowledge gap. We present an experiment in which a pendulum is suspended just above the still water level and then exposed to monochromatic free surface waves with different wave lengths. Additionally a reduced-order model is derived to compute the response of the pendulum and help interpret the experimental results. The motion response of the pendulum is demonstrated to depend highly on whether the wave period is much lower or higher than the dry natural period of the pendulum. Additionally, a sensitivity study with the wave amplitude in the model and a quantification of the variability in the experiment both indicate that the variability in the motion response of the pendulum is increased with respect to the variability of the incoming wave. We believe this experiment and the results make for an interesting benchmark of fluid–structure interaction in free surface waves. The properties of the pendulum and the experiment are available as open data at doi:10.4121/13187594 (Wellens and Bos, 2020).

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To study how an extreme wave load on a maritime structure causes structural deformation, an experiment is conducted to measure the response of a one degree-of-freedom pendulum in a focused, breaking wave. The tube that makes up the base of the pendulum covers almost the entire width of the tank so that three-dimensional effects can be considered small. The experiment varies the focus location with respect to the position of the pendulum as well as the vertical clearance between pendulum and mean free surface. Although the energy of the wave input was the same for all experiments, the response of the pendulum varied greatly with small variations of initial vertical clearance and wave focus location, with the wave breaking farthest away from the pendulum causing the largest response. A reduced-order model for the response of the pendulum shows the same behavior when initial clearance and focus location are varied. Even when initial clearance and focus location were kept the same between tests, large variability of the pendulum response was observed, meaning that the impulse exerted by the wave must have been different. This is different from the literature on breaking waves against rigid walls that found that local pressures show variability between experiments but that the impulse typically is the same. The experimental data and a description have been made available.

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Highly varying sloshing loads are a superposition of load components resulting from a sequence of different physical phenomena. However, not all features of spatial and temporal variations of sloshing loads and associated phenomena are equally important when failure of structure is considered. Therefore, the prediction of sloshing loads should be focused on those load components which lead to failure. These components can be found by employing a structural model, which should be fast computationally considering the huge number of possible sloshing loads. This paper presents a reduced order model based on the beam-foundation model which is derived for the Mark-III cargo containment system. The model is validated against a detailed finite element model and it conservatively predicts the stresses at failure locations. The calculation time using the model is approximately two orders smaller in comparison to a finite element model computation, which allows the model to be applied for finding governing load components and associated physical phenomena.

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The difference between 2D and 3D response is quantified using wide loads with different slopes and concentrated loads with different impact locations. For wide loads the slope is not important for the maximum indentation, but does effect the maximum stress. Similarly, when a concentrated load is small compared to the panel, the impact location is not important. There is however a large difference in response between the wide and concentrated loads. To conclude: the 2D response is only valid for wide loads with small slopes.@en

To predict loads on propellers in ice, model tests can be used. Using regular (refrigerated) cold model ice in ice basins is a valid option. However, these tests are expensive, difficult to reproduce and bound to time and location, due to the required cooling in ice model basins. An alternative would be to use warm model ice, a material with the properties of model ice at room temperature. This paper proposes one variety, using only materials available from DIY stores. Based on theoretical propeller-ice interaction models, it is assumed that the loads come from a crushing process. Hence, the compressive strength follows as dominant material property of ice. To match compressive strength of weak cold model ice, a large particle composite is proposed. Expanded Polystyrene (EPS) beads are used as particles, with paraffin as matrix to produce warm ice specimens. The compressive strength of these specimens were measured with a uniaxial compression test and matched with weak model ice. The specimens were designed for in-situ use in model scale propeller impact tests.@en

Ships sailing in ice require a propeller that is able to endure both extreme loads and fatigue loads and operate efficiently in ice and open water. Knowledge and descriptions of the physical processes of propeller-ice interaction are essential to model the interaction with its dominant parameters and finally predict the loads. The research described in this paper uses an experimental setup to determine if the crushing strength of ice, or in general a solid, is a dominant parameter in propeller-ice interaction as stated in empirical and theoretical models. Warm model ice, a paraffin based material to be used at room temperature, with ex-situ tested crushing strength, density and elasticity, is supplied to an in-situ model propeller at different rpms. One blade of the propeller is equipped with a six-component load sensor. Impacts are recorded in the time domain and synchronised with high speed footage. The data is analysed to understand and explain the impact behaviour by comparing it with rotational speed, load and footage. Scaling of the warm model ice properties is discussed as well due to density differences between warm model ice and sea ice.@en