One of the most important reasons to investigating fuel cells is the increased level of regulation regarding emissions in the maritime sector, while fuel cells offer the opportunity to reduce these emissions. It was not clear what the impact of these systems would be on a yacht, the aim of this project is therefore to gain more insight into these topics. The objective of this study was to investigate the impact on both the design and operation of a superyacht using fuel cells for energy supply on board. To reach this objective, first a review of different fuel cells and fuel technologies was executed. These conclusions are used to develop a decision making tool which will help in choosing between the different types of fuel and fuel cell techniques. Finally the tool is used to select the best possible fuel cell solution, for this option the impact on the design and operation of a fully fuel cell powered yacht is determined. The report is split up into two different parts, where in the first the technological review is carried out while the second part focused on the design study. In the first part a study was conducted into the status and characteristics of different fuel cell technologies and fuel storage solutions. Seven different types of fuel cells are investigated which can divided based on their operation temperatures (Low, Medium or High). Fourteen different types of fuels which are categorised as physical-, fuel- or material based hydrogen. The density of both separate systems were analysed and merged into a combined density for comparison reasons. Other factors which have been investigated are the: storage type, maturity, safety, and emissions. To be sure that a good choice can be made despite the many variables, these review subjects are used as decision criteria for the developed tool. In addition, the time influence on the density is taken into account by the adjustable time factor which is integrated in the tool. Specific preferences for a system can be given by changing the weighting factor for the different decision criteria. When changing the weight factors the order of all options will be rearranged by the tool, showing the ranking of the most promising solutions corresponding to the preferences of by the user. From this tool, it has become clear that a fuel cell solution should be specifically selected for any different type of application. A specific application could lead to the selection of a completely different type of technology, which is in contrast with a diesel combustion engine where only an appropriate size needs to be selected. The second part focuses on the design study of a fuel cell powered yacht, whereby an Oceanco yacht was used as reference. The most promising fuel cell solution for this yacht was selected based on the decision making tool and selected weighting criteria, a high temperature PEM fuel cell powered by methanol turned out to be the best solution. In order to determine the influence of the conversion to fuel cells additional research has been performed towards other factors which have an impact on the design. The following subjects were considered: regulations, fuel cell characteristics, energy storage, propulsion and electrical distribution. From these topics, several important conclusions have emerged. First of all the regulations have a substantial impact on the design of a yacht. Secondly, the fuel and fuel cells itself require more space compared to the original configuration, and the fuel cells require a larger battery system to be able to follow the fluctuating load of a yacht. Lastly, it became clear that the use of fuel cells makes it possible to have some volume and efficiency gains when switching to PODs and a DC energy distribution system. A detailed design study based on these findings made clear that the yacht needed to become longer to fit all the required systems while keeping the functional requirements for the owners the same. Additionally the system changes corresponding to the fuel cell conversion resulted in an increase in terms of weight. These changes in length and weight turned out to have negligible change on the resistance of the yacht. There are some factors which have an impact on the operation of the yacht. One of these is the fact that the lifespan of the used fuel cell technology is lower than that of a diesel combustion engine. A well designed hybrid system and by using shore power as much as possible, could be used to stretch the expected lifetime. Another operational issue could be the fact that this fuel cell technology is not fully developed which could influence the operability of the fuel cells. In addition, the methanol used as fuel is not as widely available as diesel. Positive influences are the fact that the overall efficiency increases while reducing all emissions with 100% except for the CO2 emissions which will be 14-20% lower compared to a diesel engine. When using green methanol, the overall emissions of the yacht will be completely reduced since it will be CO2 neutral. Additional advantages of fuel cells are the added comfort due to low noise and operation without any vibrations as well as an increased redundancy because of the modular design of the fuel cells.

For floating photovoltaic systems, an uncommon type of offshore structure is considered, which is very flexible and deforms with the motion of the waves. In this research, the bending characteristics of a drop-stitch floater is analysed, which is an inflatable panel. By inflating the drop-stitch floater to a low air pressure, it obtains a flattened shape and the ability to support the flexible solar panels, while still retaining flexibility to deform with the motion of the waves. The bending characteristics of a drop-stitch floater are more complex than common offshore structures due to different non-linearities: wrinkling, hyperelastic material behaviour and internal pressure-volume work. Getting a better understanding in the bending response is important to eventually determine the response and limit states in offshore conditions. A finite element and experimental analysis has been performed of the response in a three point bending load case. Also, an experimental uniaxial tensile test has been performed to evaluate the hyperelastic anisotropic material behaviour. Different yarns spacings, internal air pressures and face sheet thicknesses are evaluated. This showed that there are two types of failure modes with distinct behaviour for an uniaxial pure bending load case: a global wrinkling and folding failure mode.

Due to the growing quest for renewable energy, wind turbines grow in size. This means that higher demands are posed on the transporting structures, also called tower grillages, which brings its challenges for their design. The fact that the structures considered in this thesis are placed on a ship makes the design even more complicated. Therefore, a procedure is developed in this thesis that is able to optimize a tower grillage, while keeping the underlying ship intact. This tool is based on a combination of size and shape optimization. The optimization is performed with the dual annealing algorithm. The objective is mass reduction, with the stress in the grillage, and stress and buckling in the ship as constraints. These constraints are taken into account by a penalty function. The design variables are the angles at which the radial supports attach and the thicknesses of the radial supports and the other elements of the grillage. The main question that is answered in this thesis is how this optimization procedure can help in the design of a tower grillage, where the underlying ship structure is implemented as a boundary condition. First, a single layout is optimized with the ship modelled as a rigid boundary condition. Next, a model of a section of the ship is made and used as the boundary condition on the tower grillage. A comparison between these models showed that the main differences in stress between the two optimization results are seen in the largest parts of the grillage: the sides, the flanges and the can. The maximum stress in the latter two elements is larger, which also results in larger thicknesses in the optimization with the ship. This affects the average mass in the ship, which is increased with 5.7% when compared to the grillage on the rigid constraint. After that, a full grillage is optimized. A first attempt demonstrated that the stress in the ship could only be decreased a little with the initial settings of the optimization. That required a slightly different model, to make sure that the stress in the ship remains acceptable. With that model, a mass decrease of 32 tons could be obtained, which is a decrease of 9.1 % compared to the original design by Vuyk Engineering. From the different optimization steps became clear that the main factors influencing the optimal distribution of radial supports are the lengths of the supports, and the location of the outer brackets. The compliance of the ship changes the stresses in the grillage, and therefore the optimization result. The stress in the ship can be reduced only to some extent, so the effect of a stress violation in the initial design is that a new bracket design needs to be made. The results show that the stress is governing for the current optimization, and buckling is not. The conclusion is that the current procedure can help in the design by providing a global image of lighter layouts which avoid stress and buckling constraint violations in the ship. However, the limitation of the research is that the result is only a global image. It is therefore considered not worth the effort and time to apply the current method in an engineering environment. It does however show the potential of this method, so future enhancements can make the procedure suitable for engineering.

The current fatigue assessment methods for naval ships are intentionally conservative. This is in part due to uncertainties in the fatigue capacity (i.e. fatigue resistance) of the ship: the nominal and hot spot structural stress incorporate implicit conservatism due to the inherent data-scatter and the Linear Damage Accumulation Model (LDAM) by Palmgren and Miner is not sufficiently accurate to assess random variable amplitude loading histories. The safe-life engineering solution to this is to employ a safety factor. This typically reduces the critical damage from 1.0 to 0.5, or even 0.2, based on engineering judgement. The main flaw of the Linear Damage Accumulation Model is that it does not properly account for the effects of the loading history. To address this flaw the non-linear probabilistic fatigue damage accumulation model by Leonetti is researched and thoroughly validated with variable amplitude fatigue data from the literature. The combination between the effective notch stress and the model from Leonetti poses significant improvements in the quality of the fatigue life predictions. The effective notch stress is used to formulate a generalised fatigue resistance curve (reducing scatter due to different geometries, hot spot types and mean stress ratios), after which the non-linear probabilistic fatigue damage accumulation model is used to work towards a generalised damage accumulation model. For the considered variable amplitude fatigue databases from literature, the Effective Notch Stress Concept (ENSC) - Non-Linear Damage Accumulation Model (NLDAM) combination proves to reduce the lifetime ratio scatter index (1:1.13, instead of 1:1.28) the most in relation to the DNV method (Hot Spot Structural Stress concept with the LDAM), allowing to reduce the implicit conservatism in the fatigue-life model.

On board of High Speed marine Craft (HSC), the crew and the passengers are exposed to high levels of Whole Body Vibrations (WBV) and large magnitude Repeated mechanical Shocks (RS) caused by the motions of the craft. The HSCs are typically 10 meters long, capable of reaching a maximum speed up to 50 knots and widely used by various maritime organizations. However, the operators and crew suffer from fatigue and injuries, leading to a reduced effectiveness and operational capacity of the marine craft. In an attempt to reduce the physical loads, passive Shock Mitigating Seats (SMS) can be installed. Numerous research has shown that an improperly designed SMS may amplify the wave impacts forces through phenomena such as bottoming out and dynamic amplification. Therefore, it is necessary to ensure that a suspension design works properly by testing the performance during wave impact events, before the seat is manufactured and installed onboard the craft. The problem is that it is difficult to determine the performance of the seats in both the design and off-design conditions with either sea trials or laboratory tests. This research focuses on the prevention of injuries and adverse health effects due to repetitive wave impacts by incorporating an injury model in the analyses of various suspension principles in the design of SMS. In the current analyses of SMS either simplistic or specific models are used which restrict the application of these models to other suspension designs. Therefore, a computer program based on the finite element method is developed that allows realistic input accelerations in the surge, heave and pitch direction. The program incorporates highly non-linear elements, including the effect of bottoming. Additionally, the validity of the half-sine approximation for the wave impact excitation pulse was reviewed and concluded to be inappropriate for design purposes as it underestimates the probability of bottoming. Furthermore, the modified evaluation methods of ISO 2631 Part 5 using an optimized age-dependent coefficient based on gender in combination with a Weibull injury risk model were implemented to evaluate the resulting seat level accelerations. A case study was conducted on a Fast Raiding Interception and Special forces Craft (FRISC) of the Royal Netherlands Navy (RNLN). A design based on a parallelogram of pinned truss elements in combination with a coil spring element was altered by replacing the coil spring with a gas-spring element. The design was analysed with dynamic simulations of full-scale measurements of wave impacts on a lifeboat of the Royal Sea Rescue Institution (KNRM). For the most severe wave impact of the acceleration record, the seat level acceleration was reduced from 17.7 [g] to 2.8 [g]. An operator of the age of 24 years who is exposed to the accelerations for half an hour a day, 30 days a year for two consecutive years was assumed. The probability of spinal injury was reduced for a male operator from 99.5% to 16.3% and for a female operator from 100.0% to 42.0%. These results illustrate the high risk of injury to which the HSC operators are exposed. By incorporating highly non-linear elements and spinal injury models, the program and evaluation methods are capable of modelling various SMS suspension designs and analyse the performance. This can assist the seat designer, engineer or researcher with investigating suitable suspension designs before sea trials, experimental tests and prototype iterations. Therefore, the method offers the possibility to save time and reduce costs. Furthermore, the method can assist in defining new regulations in order to limit the exposure of the operators to physical loads and reduce the risk of spinal injury to an acceptable level.

The ongoing demand for bigger and more efficient ships pushes their designs towards the strength limits. Sometimes, ship structures are pushed beyond their limits with the possibility of significant negative economic and environmental impact or, in the worst case, impact on human life. This makes it explicitly clear why the development of accurate methods and models is still required to predict if a design can withstand the expected loads during its operations. In the past two decades, Machine Learning (ML) has been applied in the field of structural design. Still, the amount of research regarding the scalability and generalizability of ML within structural design is limited. This research aims to investigate the use, scalability, and generalizability of ML to predict the ultimate strength of stiffened panels. A large dataset of stiffened panels loaded under longitudinal uni-axial compression and lateral pressure is generated. This set is based on a representative geometrical parameter set in shipbuilding obtained by the optimization of an analytical buckling model for stiffened panels. This model incorporates several nonlinearities such as initial deflection, large deflection theory, and residual stress. Finite Element Analysis (FEA) is used to obtain the ultimate strength and stress distribution at the moment of failure for every stiffened panel. This data is used to train two Convolutional Neural Networks (CNN) to predict the ultimate strength and stress distribution at the moment of failure. Overall, the CNNs are an excellent tool for these predictions when sufficient data is available, the data shows substantial geometrical similarity to the training data, and when the data is within the scope of training. When predicting the ultimate strength of the stiffened panels in this research, it is required to have at least 4000 data samples to obtain a well-trained network. The scalability of the ultimate strength predictions produces acceptable results within the 5% margin of the training scope. Unstable prediction behavior is observed when predicting stress distributions. Both the ultimate strength and stress predicting models are also trained on stiffened panels curved in the transverse direction to test the generalizability of the CNNs. Poor predictive capabilities were observed when predicting the ultimate strength and stress distributions of the curved plates. The use of ML in structural engineering proves a useful concept and provides multiple opportunities for further research.

Offshore wind turbines are designed to persist harsh environmental conditions, including corrosion. Pitting corrosion is one of the most dangerous forms of corrosion. In combination with a fatigue loading, a corrosion pit could result into the failure of a structure, due to a minimal weight reduction. Of the corrosion fatigue process, the transition of a corrosion pit to a fatigue crack is one of the less understood topics. In this thesis, a combined analytical/numerical model is presented that implements mechanisms of both the fatigue, and the corrosion process to determine the moment in time and location in the corrosion pit of the pit-to-crack transition. The hypothesis used to build the model, is that the pit-to-crack transition occurs at the moment that a fatigue crack initiates. Assumptions are made to be able to predict the level of stress and strain at the surface and below the surface of a corrosion pit using a FEM model. Using the stress and strain levels, damage is accumulated until the failure criterion is reached, i.e. when a fatigue crack will initiate. In this research study, elliptical pit shapes are considered, with and without a certain roughness at the surface of the corrosion pit. From the results it is found that a more sharp shaped corrosion pit is a more favourable location for fatigue crack initiation, than a more blunt shaped corrosion pit. The number of cycles to fatigue crack initiation resulting from the developed model are higher, than the number of cycles to failure found by the DNV GL B1 SN-curve for free corrosion conditions. Also, the DNV GL SN-curve is more steep, than a fitted curve through the data points resulting from the developed model. Through a sensitivity study and by considering the number of assumptions and simplifications made in this research study, it is concluded that the spread and uncertainty of the outcome of the developed model is too large to be able to draw conclusions based on the comparison between the results and the DNV GL SN-curves. More research on the input parameters of the developed model will give more certainty and a better validity to the model. It is found that the effect of surface roughness to the fatigue crack initiation life is not substantial, because it affects the stress and strain levels only up to a relatively small depth. The location of fatigue crack initiation is in the pit bottom for blunt shaped corrosion pits, and in the pit wall for sharp shaped corrosion pits. For circular shaped corrosion pits, the difference between the fatigue crack initiation life at the pit wall and the pit bottom is negligible. It is concluded that the model gives a comprehensive basis for the prediction of the pit-to-crack transition, but more (experimental) research on the input parameters will be necessary to be able to give a substantiated estimate of structural life of offshore wind turbine foundations.

Highly-loaded low-speed roller bearings are frequently used in equipment offshore e.g. slew bearings in crane, sheave bearings and FPSO turret bearings. Reducing maintenance costs, increasing productivity, ensuring safety of people and structural integrity and longevity assurance of equipment can be achieved by the condition monitoring of highly-loaded low-speed roller bearings. Currently, very limited research is performed in the field of condition monitoring with acoustic emission (AE) monitoring for highly-loaded low-speed (<10 rpm) bearings with naturally developed damage. Acoustic emission monitoring has shown promising results in early stage and real time identification of defects according to literature. Furthermore, contamination of wear particles in lubricant shows an increase in AE activity according to literature. In this research, the applicability of AE monitoring for damage assessment of highly-loaded low-speed roller bearings is investigated in a full scale duration test. Furthermore, the influence of contaminated lubricant with steel particles is investigated in the contamination test to study the feasibility of real-time detection of contaminated lubricant during operations and as a supporting technique for wear debris analysis in lubricant. From the results, an increase in AE activity expressed in hit-rates is observed for a wide frequency band of 40 - 580 kHz during the duration test where the basic rating lifetime (L10) is consumed from 40% to 50%. Wear development in the bearing is observed during visual inspection and has been quantified with lubrication analysis. A safety limit and a limit if the bearing is at risk for the AE activity has been defined with the results of the baseline and duration test. This research suggests that AE monitoring can be applied on highly-loaded low-speed bearings to assess the damage for representative operational conditions. From the results of the lubricant contamination test, an increased AE activity with respect to higher lubricant contamination levels were observed. Furthermore, with a proper choice of the SNR-level, there is no masking effect of acoustic emission signals due to contaminated lubricant. The results of the contamination tests, indicates the possibility of detecting contaminated lubricant with AE monitoring.

With fossil fuels being phased out and growing global interest in a hydrogen economy, there is demand for re-purposing existing pipelines for transportation of hydrogen gas. However, hydrogen is known to have adverse affects on the properties of steels. Hydrogen will dissolve in the steel matrix and contribute to a reduction of mechanical properties, causing Hydrogen Embrittlement (HE). There is currently a knowledge gap about the behaviour of pipeline steels and their welds in a gaseous hydrogen environment that prevents re-purposing of pipelines for hydrogen transport. In this work, a combined approach of modelling and in-situ mechanical testing was used to assess the HE susceptibility of X60 pipeline steel and its girth welds. To this end, a novel tensile setup featuring in-situ charging with high pressure H2 gas and a sample geometry representing miniature pipelines was developed and validated. To our best knowledge, this setup design has not been reported elsewhere, making this a breakthrough design. An FEA modelling approach was used to estimate the pre-charging duration as well as to gain an insight into the stress states inside the notched samples. It was found that both the base and weld metals lose ductility when subjected to gaseous H2. The base metal showed 27% loss of ductility when subjected to 100 bar H2, which further increased to 40% in notched samples. A trend of increasing loss of ductility was found with increasing pressure for the weld metal, which showed up to 14% loss of ductility at 100 bar H2. The weld metal also retained more of its reduction in cross-sectional area after fracture in H2 as compared to N2 than the base metal. Other characteristics like yield strength and UTS were not affected by the hydrogen gas. The fracture mechanism in the both metals was found to change from microvoid coalescence (MVC) fracture to quasi-cleavage (QC) fracture. The base metal fracture mechanism changed to QC completely, while the weld metal only showed partial QC fracture. In the base metal, ductile fracture mechanisms like HELP and possibly AIDE were found to be dominant even in the QC fracture mode. It was concluded that the weld metal is less susceptible to HE than the base metal in a gaseous hydrogen environment. For both metals, HE effects were only observed at high amounts of plastic strain, which is outside of the operating conditions of a pipeline. However, before pipelines can be repurposed for hydrogen transport, fatigue testing should be performed to assess the influence of existing defects and cyclic loading conditions on the HE performance of both steels.

Topology Optimization is an optimization problem based on the distribution of material within a design domain under specific load states. The goal of this technology is minimizing a certain function, such as compliance, mass or frequency. This technology can improve the performance of components in different fields within the shipbuilding industry, depending on the function of the element and which type of ship they belong to. The three areas of application in which this technology was thought to have a big impact were weight reduction, aesthetics and comfort. It is a common thought that Topology Optimization could only help to the diminution of mass of bodies. Nonetheless, this reduction of weight does not benefit to all the ships. Cargo ships with a cargo limitation due to volume are less likely to take an advantage of its lightweight cutback than those with a cargo capacity limitation by weight. Moreover, vessels with a very low center of gravity would suffer stability disorders, such as cruise ships. The area of aesthetics was studied from a different point of view: now the construction industry was not perceived as only dedicated to maintain the integrity of structures, but an artistic point of view was explored with the target of resembling the ideas of consumers and transmitting feelings to customers. Vessels with a greater interest in the appearance are the ones dedicated to the transport of passengers, such as ferries and cruise ships and also those ships with a focus on the luxurious face of the marine construction sector, such as yachts. In the search of improvements regarding comfort, the focus was kept on the vibration phenomenon and the occurrence of noise. Vibrations are harmful for machinery, crew, passengers and the overall structure of the craft and therefore is an issue to be avoided as much as possible. With this target, Topology Optimization was applied on a mast under certain circumstances, taking into account the amount and allocation of navigation devices these elements must carry. This thesis aims to give an introduction to what can be achieved with the technology of Topology Optimization in the maritime sector. Although no decisive results were achieved for some of the previously presented elements, findings were attained and the potential of this application is positive. Nevertheless, more research is required in order to build solid confirmations about the profitability of the implementation of Topology Optimization. Moreover, manufacturing processes, and more specifically Additive Manufacturing is to be grown in order to fulfill the structural requirements of the optimal components. This refers not only to the fabrication process itself, but also to the implementation of this methodology in Regulations by Classification Societies.

At Damen’s Research and Development department, continuous improvements are made to existing design practices using recent technological developments and fatigue design is currently on the anvil. High speed craft operating around the globe are subject to millions of load cycles (resulting from ocean waves) and therefore suffer from metal fatigue. As per current practice, such vessels are designed for fatigue using inhouse software with a nominal stress approach supported by static sea-state scatter data and judgement based operational profiles. Recently, new data sources with real time sea-state data over the whole globe have come available, including GPS locations of ships. Together, this enables it to generate real time operational profiles for its ships. A total stress concept has been developed based on results from a JIP called VOMAS. This approach has shown to provide accurate fatigue lifetime estimates for arc-welded aluminium joints. Similar results are expected for steel joints as well. The main goal of this thesis was to explore possible improvements for the fatigue design methodology. A tool called Tanaav was developed for this purpose which makes use of both remote monitoring data and the total stress concept and provides an estimate of the yearly fatigue damage and fatigue lifetime. The tool has been used to predict the fatigue lifetime for three fatigue sensitive details in 46 FCS5009 vessels. Results have been compared to corresponding predictions using current and past fatigue analysis practices. It was observed that using both remote monitoring data as well as the total stress concept provides significant improvements in the predicted fatigue life time. Uncertainties in fatigue influence parameters affecting the predicted fatigue damage can be incorporated using probabilistic. This thesis proposes a method for this and presents two cases as a proof of concept. Work done in this thesis will be validated by Damen in future with the help of full-scale testing on an actual FCS5009 vessel during an offshore measurement campaign. After validation, this method will help in improving fatigue design practice, increasing design flexibility and in optimizing vessel weights in a responsible way.

In this 3D fracture-based topology optimization framework, the author extended the 2D framework on tailoring fracture resistance for brittle materials (Zhang et al., 2022) to 3D. In the optimization, the topology is described by radial basis functions interpolated level set function, and the problem is solved by the Interface-enriched Generalized Finite Element Method (IGFEM). Cracks are assumed to exist on enriched nodes that are added on the boundary of the geometry to increase the accuracy of approximation. The first part of the work assumes cracks to be semi-circular with the crack plane perpendicular to the boundary, and the crack opening direction to be either parallel to the 𝑋𝑍- or 𝑌𝑍-plane of the global coordinates. An extended framework that assumes crack opening direction perpendicular to the surface first principal stress is also developed at the end. The energy release rates (ERRs) of the cracks are evaluated with the topological derivative method, which requires only a stress field of the geometry and weight functions that relate the stress and stress intensity factors (SIFs). The weight functions are found by a finite element analysis on a cuboid with a crack. This approach is computationally efficient because it eliminates the need of actually modeling and meshing the crack planes in the geometry during optimization. Moreover, a 3D stress recovery technique (or stress improvement procedure, SIP) is used to recover the nodal stress non-locally to improve the accuracy. The objective function is then established with the 𝑝-mean aggregation of the ERRs. Finally, Numerical examples in 3D, including the famous L-bracket benchmark problem, are performed to prove the correctness and capacity of the framework. In conclusion, this extended framework shows more flexibility and provides more information to the optimized design than the 2D framework by considering an added dimension both in analyzed geometry and crack shape, i.e., the effect of the anisotropy of cracks can be captured.

Maintenance providers in commercial aviation are looking into new strategies to improve maintenance operations and aircraft availability in order to reduce cost and increase customer satisfaction. Aircraft availability and thus profitability highly relies on adequate maintenance because an aircraft is only profitable when flying. One of the strategies that can be used to achieve higher aircraft availability is Predictive Maintenance (PdM). The new generation of aircraft produces a flood of data enabling PdM, a maintenance strategy in which failure scan be predicted and maintenance takes place proactively instead of reactively. PdM is enabled by prognostics, which is an engineering discipline that aims to estimate the Remaining Useful Life (RUL) of(aircraft)components. However, using prognostic information effectively and determining the benefits and impact on processes in the supply chain of these maintenance providers still proves to be very difficult in practice. This is amplified by the fact that this prognostic information is imperfect, not only can prognostic models produce false alarms or fail to predict coming failures, the exact timing of these events is subject to uncertainties. On top of that, little research into the benefits of prognostic information in supply chains is available. Especially, research considering global supply chains with pool processes such as in commercial aviation, is very limited. Efficiency of supply chains in commercial aviation is important in order to increase aircraft availability, reduce delays and cancellations, and reduce supply chain operating costs. This study provides a novel approach to using imperfect prognostic information to optimize a global supply chain considering a pool process and answers there search question: ’How to optimize a supply chain in commercial aviation using imperfect prognostic information?’ A discrete simulation model has been selected and developed for the simulation of a global supply chain of spare components for Boeing 787 aircraft at KLM Engineering and Maintenance(E&M). This discrete simulation model provides insight in processes in this supply chain while simultaneously considering uncertainties and maintaining a superior computational time. Model verification shows thatthe model is programmed correctly and model validation shows the programmed model accurately represents the real supply chain in a case study at KLME&M. Simulation and optimization shows that enabling the supply chain at KLM E&M with prognostics can reduce the total cost by 20% per year. Results show that the prediction horizon, which is the amount of time failures can be predicted in advance, is the main contributor to this reduction in cost. Not only does this prediction horizon provide the supply chain department with enough time to ship components in a cheap manner, replacing components long before the failure massively reduces damage and thus repair cost. However, a sensitivity analysis shows there is a clear trade-off between minimizing cost and a reduction of the Mean Time Between Removals(MTBR). Cost can be minimized by predicting failures12 days in advance, which simultaneously results in an MTBR reduction of 2.1%.This effect can be mitigated when the accuracy of prognostic models is increased. Furthermore, there duction in cost heavily relies on the percentage of aircraft in the pool for which failures can be predicted.  This research shows the effects and potential benefits of using imperfect prognostic information in a supply chain in commercial aviation. Recommendations for further research are provided in order to use prognostics to optimize the entire logistics supply chain of aircraft maintenance, including the phase-out, reuse, and recycling of aircraft and their components. This could have a huge impact on the environmental impact and sustainability of the global industry that is commercial aviation.   

The state-of-the-art design approach of composite structures in Formula One (F1) rely on expensive full-scale crash tests and simple models that cannot describe the underlying physical phenomena during crushing. Although the models can describe the crush forces and resulting accelerations, their predictive capabilities are poor, and several iterations are usually required to arrive at a satisfactory design, causing the teams money and resources. Reductions in costs could be possible by reducing the number of full-scale experiments and increasing the amount of analysis. This thesis aims to evaluate the capabilities of a commercially available material model at two distinct modelling scales by conducting physical and virtual experiments on two different specimen geometries; tubular coupons and a new open-section channel specimen. Firstly, the new open-section specimen with a geometry representing the typical F1 crash structures was designed, manufactured and tested. The newly proposed specimen showed controlled failure modes, and displayed typical characteristics of composite structures under crushing loading. Secondly, the two specimen geometries were numerically analyzed on the macro-scale (laminate-level) and meso-scale (ply-level) using a commercially available material model implemented in the Abaqus finite element software. Mesh-dependency of the macro-scale approach was discussed and numerical aspects required to perform crush simulations on the meso-scale were identified and discussed. Lastly, calibration of the numerical models was performed to understand the effects of model inputs on the output responses, to evaluate the validity of the input parameters, and to assess two different calibration approaches; the first method is based on macro-scale modeling, while the second method is based on surrogate-based inverse parameter identification at the meso-scale. The numerical models could not reproduce the experimental crush responses of either geometry when using experimentally characterized material data. Following the second calibration approach, the qualitative and quantitative crush responses of the tubular specimen could be accurately described, but the channel specimen showed no improvements in their response. The macro-scale modelling approach with the current material model was judged to be impractical for large-scale analysis, and the meso-scale approach showed need for further developments.

The objective of this research is to evaluate what is required to make the operation of multiple robots feasible for large scale seafloor imaging campaigns. Three blocking issues were identified; high cost of subsea robots, limited handling efficiency and insufficiently performant localization technology. These are solved by applying, in order: novel engineering solutions, automation, and solutions from literature. A proof of concept system design and a model are developed to analyze how the physical parameters of the subsea robots relate to the performance of the subsea mapping system. A case study shows that for large areas, the proposed solution is 80 times faster and less costly than conventional approaches. In conclusion, there is a technically feasible approach that can be used photograph the seafloor in a more cost-effective manner on a large scale.

The increasing focus on reducing greenhouse gas emissions has led to the attractiveness of offshore hydrogen pipelines in achieving sustainable energy goals. Hydrogen, as a transport medium for energy, offers a viable alternative for transmitting large amounts of energy from offshore facilities to the shore. By storing hydrogen and subsequently converting it back into electricity during periods of peak demand, this approach aligns with the goal of establishing a green, net-zero economy by 2050. However, maritime activities in the proximity of offshore pipelines introduce a serious risk of damaging pipelines by accidental or emergency anchoring scenarios. Damage from dropped or dragged anchors can displace and harm pipelines, leading to environmental risks, safety hazards, and costly repair operations. Comparing hydrogen pipelines to existing oil and gas pipelines, there are significant differences. While oil leakage from anchor hooking poses risks to the environment and marine ecosystems, hydrogen imposes new risk factors which must be taken into account. Hydrogen negatively affects the structural integrity of pipelines, and anchor hooking leads to elevated stress levels within the pipeline material, accelerating fatigue crack growth, and reducing the operational lifespan of the pipeline. This leads to the following research question: ”What is the post-hooking lifetime of a hydrogen pipeline damaged by an anchor?” To address this research question, the methodology applied in this thesis consists of two main approaches: numerical simulations and a fatigue crack growth model. The simulations specifically consider an incident where an 8-inch pipeline was damaged by an AC-14 High Holding Power (HHP) anchor. The pipeline is internally pressurised at maximum gauge pressure, and simulations are conducted considering daily and yearly variations in loading cycles, specifically at 10% and 50% pressure reductions. Through these simulations, the stress distribution and variation within the pipeline material resulting from the anchor impact are investigated, providing insights into the behaviour of the pipeline under such conditions. The fatigue crack growth model used in this study is based on the Paris law, which describes the relationship between crack depth and the number of cycles required for crack propagation under cyclic loading conditions. The presence of hydrogen significantly accelerates the rate of fatigue crack growth. As a result, adjustments are made to the Paris law to account for this effect, particularly in determining the range in which the law remains applicable. The crack growth analysis focuses on determining a critical crack depth, which could possibly lead to pipeline failure. A Failure Assessment Diagram (FAD) is used to determine the maximum allowable crack size, ensuring the safety of the pipeline. The FAD, along with the wall thickness of the pipeline, serves as a critical criterion for assessing structural integrity. The remaining lifetime of the pipeline following an accident depends on which criterion, either the FAD or the wall thickness, indicates failure first. The crack growth analysis conducted in this research reveals that as the crack depth progresses under the influence of hydrogen, it eventually reaches a critical depth that introduces a potential risk of pipeline failure. Specifically, when considering yearly pressure variations, the crack reaches this critical depth in slightly over 8 years. Although the attained crack depth at this point is not yet through-thickness, the crack growth rate experiences a significant increase after 8 years, ultimately resulting in a through-thickness crack 9 years after the initial impact. The findings of this study have significant implications for the future development and maintenance of offshore hydrogen pipelines. By understanding the consequences of anchor hooking incidents and their impact on the operational lifespan of hydrogen pipelines, this research contributes to the development of robust and resilient infrastructure for a sustainable energy future.