The increasing number of international maritime regulations has significantly impacted the workload of ship surveyors. As compliance requirements grow, surveyors face higher levels of stress, which can lead to human errors and missed deficiencies during inspections. This study explores the potential quality improvement in the survey process by evaluating alternatives for the survey checklist. Using he CREAM (HRA) method, human error classifications and influencing factors were analyzed to identify critical points in the inspection process. Quantifying the human errors in the survey process is done by the use of a python simulation. Besides, four error reduction techniques are implemented to find the potential quality improvement in ship surveys.

In an era where global energy consumption has been rising steadily, the demand and supply of renewable energy sources have become increasingly important. Offshore wind is a promising renewable energy source, which has been actively developed in the last decades in the form of bottom-founded offshore wind, bound to shallow water. Floating Offshore Wind Turbines (FOWT) offer a solution for countries without shallow coastal waters with an abundance of wind potential. In a competitive market with different solutions, Bluewater Energy Services (Bluewater) has developed a tension leg platform (TLP) type substructure to support a 15MW turbine.

These FOWT installations are subject to the random nature of environmental loading which is highly stochastic in terms of amplitude, frequency and phase angle and is hence considered multiaxial non-proportional (random) variable amplitude loading. Multiaxial loading does not, however, guarantee a multiaxial stress response. One of the considerations for offshore structures subject to repetitive loading is fatigue lifetime estimation, which is predominantly done using uniaxial assessment methods. This is not an issue if the stress response is dominantly uniaxial, however, literature has demonstrated that evaluating a specimen subject mode-{I,III} multiaxial stress response using uniaxial (mode-{I}) assessment methods can lead to a significant overestimation of the fatigue lifetime.

To investigate the (multiaxial) stress response of fatigue-critical weld seams in TLP-type FOWT substructures, a new simulation methodology needed to be developed, which allowed for the structure's rigid body motions and elastic deformations to be captured. This methodology was built on an existing hybrid rigid-flexible modelling approach. It was improved upon by considering local (panel-based) hydrodynamic pressure and kinematic structural boundary conditions in order to conduct coupled (aerodynamic-hydrodynamic-mooring) analysis with integrated structural analysis. This approach allowed for the system motion and structural response to a dynamic metocean environment to be simulated using a range of commonly occurring seastates. The integrated coupled analysis was completely conducted within the Ansys environment.

Next, time-varying mode-{I,III} stress signals were reconstructed from the structural analysis model using a traction-based structural stress assessment method. In order to assess the extent to which fatigue-critical weld seams are subject to multiaxial stress response, a damage accumulation calculation should be conducted. However, given the added computational expense of such a calculation, a screening method was first considered in order to better understand the characteristics of stress response behaviour. The screening method considered was based on a Minimum-Circumscribed Ellipse method.

From this screening method, it was found that stress response behaviour is predictable and can be related to specific loading & response frequencies. Furthermore, it was found that parts of the considered structure were subject to significant levels of multiaxial non-proportional stress response and that applying uniaxial fatigue assessment criteria risks overestimating lifetime estimation and misplacing the governing fatigue hotspot. Finally, it was concluded that fatigue-critical weld seams in a FOWT TLP-type substructure are subject to multiaxial stress to the extent that multiaxial damage accumulation models should be considered. If this is not possible, a multiaxial stress response screening should be conducted to identify fatigue governing locations in the welds, as well as locations subject to multiaxial stress.

The offshore wind market has become a substantially growing industry to meet the worldwide increasing energy demands. This results in heavier crane operations on offshore jack-up vessels due to the increasing size of wind turbine components. To ensure the seabed can support the loads on the jack-up legs, a temporary foundation for the leg's footings is established before crane operations through a process known as preloading. Where the two diagonal opposing leg pairs are loaded alternatively by the weight of the vessel until a stable condition is reached. Traditionally, the capacity of those foundations is determined based on storm loads adopted from offshore oil and gas jack-up guidelines.

The main objective of this thesis is to develop a robust method for analysing the applied preload in past jack-up crane operations conducted by Jan de Nul's Vole au vent. This analysis aims to provide a better understanding of the effectiveness of traditional offshore jack-up guidelines within the rapidly growing offshore wind industry, where heavy crane operations are now performed on a daily basis. Such understanding is crucial, as these guidelines were not originally intended for the advanced state of the current offshore wind sector and are not specifically calibrated for its unique demands.

To accomplish this objective, a method is designed to assess the preload safety factors of past jacking operations and determine their optimal value for heavy lifting operations. This safety factor provides the ratio between operational leg reactions and applied preload. The developed models are then applied to a case study using measuring data from jacking operations of the Vole au vent to validate their effectiveness.

This method is based on reliability analyses which evaluate the probability of failure by assessing if a certain limit state is exceeded. Failure for jacking operations can occur when the leg reactions during crane operations become larger than the applied preload. From the acquired measuring data, certain probability distributions of the leg reactions can be obtained, which are used by a Monte Carlo Simulation to assess the probability of preload exceedance through the defined limit states. This probability of preload exceedance quantifies the reliability of the applied preload in different soil types at three offshore wind farm sites.

This research then defines optimal targets for the annual probability of preload exceedance based on the consequences of failure of operations in both low-risk and high-risk soil profiles. These targets provide a balance between operational efficiency and safety. From those targets, an optimal preload safety factor is obtained and compared to what was originally applied during the jack-up operations.

The findings of this thesis indicate the need to evaluate and improve the standards to better align with the industry's evolving requirements.

It is shown that the currently used preload safety factor from traditional offshore jack-up guidelines is not yet correctly calibrated for heavy crane operations on jack-up vessels. To achieve an optimal balance between operational efficiency and safety, the applied preload, with respect to the experienced loads from heavy crane operations, should be slightly lowered compared to what is currently applied.

In addition, this research observed that the measured conditions during jack-up operations are not correctly estimated, leading to operational and preload uncertainties.

The offshore wind market is rapidly growing, resulting in increasing wind turbine sizes, increasing distances to port, and a shift to deeper waters. A literature study in this thesis shows that existing wind turbine installation vessels, vessels under construction, and innovative concepts will not be able to install next-generation turbines or that they would have installation bottlenecks, making them cost-inefficient. This goes against the goal of decreasing the Levelized Cost of Energy (LCOE) of wind energy, to ensure that offshore wind stays competitive with other energy sources, enabling the energy transition. There is thus a gap between future demand of offshore wind installation vessels and current and near-term solutions. The research proposes a new floating monohull vessel concept, called Moonshot, to fill this gap. Moonshot will thus be different than traditional jack-up or semi-submersible installation vessel options.

In this research, various design strategies were analyzed. Based on the findings, a design strategy is developed to design and analyze Moonshot. A combination of Ulstein Design and Solution B.V.’s Controlled Innovation process and Blended Design were used and extended to develop this new concept. First, the important functions and design aspects of the design were established using Controlled Innovation. Blended Design was then used to create a design space of the design configurations and to explore multiple market scenarios to establish optimal ship parameters for further development. As part of the research, the existing design process and model were modularized and new features were developed to suit wind turbines, assess seakeeping behavior, and explore the design space of the future wind turbine installation vessel.

The results of this research aim to elucidate optimal design parameters across certain market scenarios. Results show how optimizing the design for financial performance, seakeeping behavior, or a combination of the two, influences the optimal design point. With the optimal design ranges, the initial design parameters for the next stage in the design of Moonshot are established. Finally, Blended Design is used to benchmark Moonshot against existing wind turbine installation solutions to assess its performance. A version of Moonshot is developed as a direct competitor for the largest jack-up design available, the NG-20000X. Benchmarking with the jack-up, an SSCV, and Huisman’s WIV concept showed that Moonshot would be a more efficient solution, capable of installing a larger number of turbines per year at a considerably lower cost per megawatt compared to the other solutions.

In summary, this research concludes Moonshot as an innovative concept to address the evolving challenges of offshore wind turbine installation. By combining innovative design strategies, extensive assessment, and optimization, Moonshot emerges as a promising contender in the quest for effective and cost-efficient installation solutions for offshore wind.

Catamarans are popular in the offshore sector as they combine good transverse stability and ample deck space with low wave resistance. However, their slender hull shape results in low restoring qualities in heave and pitch motions. The large motions in rough weather can often result in water impacting the underside of the deck connecting the two hulls, a phenomenon called cross-deck slamming. The impulse excitation from cross-deck slamming can then produce a transient hydroelastic response of the structure called whipping. Whipping excites mode shapes that would not normally be present in the response, as their natural frequencies are significantly higher than the wave encounter frequency. This results in detrimental contributions to fatigue life through high-amplitude cyclical bending moments. Both the calculation of slamming loads and the prediction of resulting structural responses have been a challenge for several decades. The highly nonlinear and three-dimensional character of the phenomenon, combined with the strongly coupled fluid-structure interaction means that it is unpredictable, and even the definition of slamming events has been a matter of disagreement among researchers.\\

Experiments are still a vital part of these investigations, for validating ever-improving numerical techniques. An essential issue with experiments is the extent to which mode shapes and natural frequencies can be emulated in model scale. Traditional hydroelastic models are segmented and use either a flexible backbone or flexible joints to introduce stiffness. This often results in an excellent description of the 2-node bending mode, but an increasing error for higher modes leads to stress inaccuracies. In this investigation, a fully elastic model of a catamaran is designed and produced for hydroelastic experiments. The advantages and limitations of the concept are identified, and the verification against structural models is presented.

The penetration of the renewable energy sources in the global market has been constantly growing over the last years. This trend is expected to accelerate even more in the future due to the improving technologies, the economies of scale, the competitive supply chains and the improving developer experience. The main challenge for a faster and wider implementation of these resources is their intermittent character and the limitations that this implies. A concept that successfully deals with this variable energy output is the Hybrid Power Plant (HPP). HPPs combine at least two different sources of energy with the goal of delivering stable power with reduced fluctuations throughout the year. In addition, HPPs present various other synergies such as in operational costs or in the developing processes, that could lead to a reduced Levelized Cost of Energy (LCOE). The goal of this thesis is to assess the potential synergy of a combined wind and solar park for the case of the Energy Storage Lake (ESL) of the project Delta21. The Delta21 project has a twofold character: firstly, the usage of the ESL as a large battery integrated with green energy production and secondly the protection of the inland against floods due to high sea level or superfluous river discharge. The main challenge for this specific case is the large water level fluctuations within the lake in a daily basis due to the operation of the lake. The feasibility of a hybrid wind and solar park can be examined by various different perspectives and disciplines. Among these relevant components, the most frequently studied ones are the optimization of the energy resources, the use of common electrical infrastructure and the effect of the intermittent wind turbine shadows on the solar panels. Due to the special conditions, with the large water level fluctuations met at the lake, two more components become critical. These are the type of foundation of the wind turbines and the mooring configuration for the floating solar units. This project is evaluating a new potential synergy that regards the use of the wind turbine towers as anchor- ing points for the floating solar units. Therefore, the research is focused on the estimation of the forces acting on a floating solar unit. These forces are a combination of wind loads acting on the solar panels and the freeboard of the floaters, and wave forces acting on the submerged part of the floaters. In particular, the technology of the floating solar boat as introduced by GroenLeven and the small-scale wind turbines as designed by Dutch Wind are adopted for this project. Analytical formulations are used for the calculation of the wind loads. As for the wave forces, the linear potential theory is used and the calculations of the hydrodynamic coefficients and wave exciting forces are performed through the Boundary Element Method (BEM) software NEMOH. After the computation of first order wave forces and the corresponding responses of the floaters, the far-field approach is used for the estimation of the Quadratic Transfer Function (QTF) of the drift force. The methodology developed in this project and the accuracy of the model are validated with the use of reference data that regard the interaction of connected floating units placed in a close proximity and the corresponding second order wave forces as predicted by the far-field approach.

With the climate goals of the Paris Agreement and the European Green Deal, countries need to reduce their carbon footprint and increase their renewable energy production. For countries with high population density, land-based photovoltaics (solar) takes up valuable space. Therefore, solar application at sea is considered.

One of the proposed designs is by the Joint Industry Project (JIP) Solar@Sea II. The JIP structure is flexible, inflatable, and considerably smaller than Very Large Floating Structures (VLFS). The goal is to mitigate the installation and transportation disadvantages associated with VLFS. Combining multiple of these singular structures in an array allows for the same operational solar footprint as would be the case for a single VLFS.

To keep the structure at the intended location, a mooring system needs to be designed. For the mooring line analysis, the motions of the attachment points of the mooring lines to the floating structure must be deter-mined. These motions are dependent on the interaction between the fluid, structure, and mooring line system. The development of a numerical method that is able to determine the flexible motions of the structure is required. This method should be suitable for the initial design stages of the structure and mooring system.

A numerical method for the deep-water regime in frequency domain was developed. The structural deformations are determined by means of the Finite Element Method (FEM) in ANSYS. The fluid interactions with the structure are determined by means of a lower order Boundary Element Method (BEM). The combined effect of both structural motions and fluid behavior is captured in an equation of motion. The motions of the flexible structure can then be determined by solving the equation of motion. The method is written in Python and the interaction with ANSYS is achieved by means of an ANSYS APDL interface.

The numerical method was successfully verified by comparison of results with analytical solutions. The nu-merical method is validated by comparing the numerical result with experimentally determined responses of a 1:1 scale JIP structure to incident regular deep-water waves as measured by MARIN. Suitable deep-water test cases were determined from the MARIN data. The undisturbed numerical wave was compared with the undisturbed deep wave measured by MARIN. Finally, three test cases were selected for the validation of the interaction of the structure and the wave. These consisted of a wave longer than the structure, a waveslightly shorter than the structure, and a significantly shorter wave than the structure.

The numerical method was able to accurately predict the structure motions for waves longer than the structure. For waves shorter than the structure, the error between the numerical method and the experimental data increased as the wavelength decreased. The errors found can likely be attributed to the nonlinear interaction of the ballast bags, which are not considered in the current numerical method. This cannot be confirmed based on the available experimental data.

The presented work is part of a larger intended method, which is not yet finished. Satisfactory results were found for the components considered in the verification. The validation provided points for improvement for the current numerical method. The response to waves longer than the structure can be determined accurately. The method is less accurate for waves shorter than the structure. The recommendation is therefore to research the effect of the ballast bags on the structure response in shorter waves. This could result in a better approximation for structural responses in shorter waves.

Structural health monitoring of maritime and offshore structures can contribute to the reduction of the amount of uncertainty in assessment of the operational loads and the structural integrity. Such a survey can also reduce the large safety margins during the design and optimize the conservative inspection and maintenance schedules. One of the emerging variants of structural health monitoring are the so-called digital twin systems that not only allow the monitoring of the structures, but can also simulate the past or the future state of the structural integrity. In the context of this thesis, the feasibility of a digital twin system for the structural health assessment of marine structures based on machine learning algorithms and utilization of big data is examined. The main research question is if the digital twin technology can be enhanced with machine learning to accurately monitor the structural health of marine structures in terms of loading and fatigue damage accumulation. In order to answer this question four modules have been developed and tested. The first module uses artificial neural networks trained on operational data to predict the fatigue damage accumulation and the frequency that corresponds to the maximum stress power density. The error of the developed networks turned out to be negligible in the investigated cases, with standard deviation of less than 4% in the predictions. The peak frequency of the stress power density is predicted using a random forest regression algorithm. The optimized version of the algorithm has led to an accuracy of 93% with standard deviation of less than 1% in the predictions.
The second module is used to recalibrate the design response amplitude operators of the structure using the predictions of the first module or the operational data, if available. The design response amplitude operators are scaled and shifted in order to minimize the deviation between the spectral fatigue calculations and the predicted (or measured) data.The third module is a static/quasi-static load-reconstruction module. Using on-board strain measurements it is able to calibrate the loading of the structure based on a reformulation of the conventional finite element problem for static and quasi-static loading. A sensitivity analysis of the algorithm effectiveness have been performed using multiple load cases in which the reconstruction error turned out negligible. The fourth and final module relates to structural reliability analysis. This module is based on the estimation of the Hansofer-Lind reliability index as a minimization problem. The employed optimization engine is a variation of the particle swarm optimization algorithm using chaotic system behaviour to iteratively calculate the user-defined parameters. The limit state equation is formulated in a way that it takes the uncertainties related to the fatigue damage accumulation prediction model and Miner's Rule into consideration. Uncertainties related to the material and the fabrication process are not taken into account. The developed modules have been tested on structural details of a vessel monitored in the scope of Monitas Joint Industry Project (JIP). About a year's worth of data has been used to train the machine learning algorithms.

A mathematical model has been developed to determine the timing of the tasks that can be performed on a variety of units to produce a variety of end states and to monitor the flow of the material through the network. The mathematical model is based on the work of Kondili et al. (1993) and is extended with the ability to monitor and restrict the shelf-life of a state, the ability to implement a mandatory storage action with shared storage and the ability to implement batch-size dependent processing times for batch-sizes that can only take a certain value.

During offshore construction with a Semi-Submersible Crane Vessel (SSCV) the vessel is station keeping by means of Dynamic Positioning (DP). DP enables a vessel to keep position and heading by utilizing its own propulsion, while being exposed to the environmental forces caused by waves, wind and current. In a comparison study between offshore measurements and time-domain simulations, an increased vessel/thruster response for the offshore measurement was observed. The results revealed, that in operational environmental conditions, the measured vessel response shows increased oscillations in Surge, Sway & Yaw, with periods of approx. 3-5 min. The goal of this thesis was to determine the causes for such an increased dynamic vessel response, which are not captured in time-domain simulations. At present, numerical methods and time-domain simulations that assess the DP performance of a vessel (e.g. aNySIM) assume a quasi-static current of which the variation is only caused by the tides. One thesis is, that time-varying currents on a scale of 1 to 5 minutes can cause an increased vessel response. Furthermore, the DP System as it is used onboard is not captured in aNySIM simulations. This means that the characteristics of the DP System onboard are but not represented in full detail in time-domain simulations. Vortex Induced Motion (VIM) has previously been observed to affect multi column floaters. However, the influence on a SSCV during DP-operations has not yet been studied. In this thesis it was investigated whether the unexpected increased motions originate from time-varying currents, VIM or the DP System itself. A significant challenge was posed to find current measurement data with a small enough time step to confirm the presence of such time-varying currents. One 45 min current measurement with a sampling rate of 1Hz became available. This measurement shows that time-varying currents on a scale of 1 to 5 minutes exist and cannot be assumed to be quasi-static. More research is required to confirm their presence. However, with this limited available data it was shown that time-varying currents can cause an unexpected motion response of a SSCV during DP-operations.In order to obtain the DP System characteristics, a DP Response Amplitude Operator (RAO) assessment was conducted wherein the spring and damping terms were derived as demanded by the controller and as experienced by the vessel. This assessment showed that between 20% to 67% of the demanded critical damping is lost over the control loop of the DP System. These damping losses cause the vessel to overshoot and the damped natural period to decrease. To determine the effects of VIM, current load tests carried out on the hull of an SSCV have been investigated. It was determined that strong currents on column type floaters can cause fluctuating forces and moments that originate from vortex shedding. Further, with real-time simulations it was demonstrated, that also VIM causes an increased, previously unknown, motion response of a SSCV. Lastly, a method was developed to extrapolate the current load test results to velocities below 2kn. Subsequently, in time-domain simulations it was shown that for current velocities above 0.5kn, the vessel experienced forces and moments that caused it to fluctuate around its setpoint.

A two-dimensional (2D) panel method is developed to find the first and second order wave forces acting on a semi-submerged cylinder in regular waves. The panel method is based on potential flow and the waves are modeled for both finite and infinite water depth. The motion is limited to heave, but allows for extensions to other modes as well. It uses boundary conditions for floating body dynamics with Neumann and mixed type boundaries on the surfaces. The waves are generated and the reflection of the waves is suppressed by generating absorbing boundary conditions (GABC) on the radiation surfaces. The model is used to investigate the hydrodynamics of an oscillating buoy wave energy converter (point energy converter). For this, an analytical solution of the optimal damping is used. The method uses panels along all boundaries to solve the boundary conditions. The model can be used for any time-harmonic free surface flow problem. A second order wave running through the domain is successfully modeled, without the interference of a body. Challenges of a second order model with body are explained. The boundary element method has innate challenges finding the correct solution to tangential flows on the panels and spatial derivatives of the velocity, which are required for the second order solutions.