Subsea pipelines are critical for oil and gas production and transport, more than 100.000kmof subsea pipelines have been laid. These pipelines are laid by specially designed ships which can lay these pipelines at great depth and a high speed. However, designing the supply chain to deliver joints (pipe pieces) to these pipe lay vessels can be very complex; there aremany possible supply vessel combinations andweather influences that can impact the supply chain. This makes trying to find a good solution a very difficult and time-consuming process currently with a lot of manual iterations. This is called the Allseas problem. To solve this supply chain problema mathematical model is developed, thismodel can solve the supply chain problem while taking into account the many constraints. The research question that is discussed in this thesis is: Can the optimal usage of supply vessels, required to solve the pipelay vessel supply problem, be determined using a scenario based mathematical optimisation model? This model can eliminate the need for the many manual iterations and deliver an optimal solution that the Logistics and chartering department can use. To supply joints to the pipelay vessels several different types of supply vessels can be used. These supply vessels have different characteristics such as; hold capacity, sailing speed, capital- and operational expenditure, and workability (ability to work in bad weather). The supply vessels must supply joints to the pipelay vessel which can have one or two pipe transfer cranes. The number of pipe transfer cranes that can be used significantly influences the speed at which the supply vessels can be unloaded. A final important influence on the supply chain problemis the weather; specifically the wave height and wind speed: they determine if a supply vessel can unload it joints, or if the pipelay vessel can lay pipe. The goal of the problem is to design a fleet of supply vessels that can deliver the cheapest possible set of routes that will supply all the required joints to the pipelay vessel on time. A scenario based mathematical optimisation model is developed to find the solution to the Allseas problem. Some important parameters for this model that are thoroughly researched are: the desired stock level of the pipelay vessel, i.e. how full should the holds be? The demand window, i.e. how close to the demanded number of joints should the model deliver. The final parameter of interest is the node duration, all joints must be delivered during a certain time window the parameter node duration changes the size of the time window. The influence of these parameters is also investigated when weather is simulated. The results of the developed program show that it is possible to make a mathematical model that determines the optimal pipe supply vessel usage. Some other interesting parameters settings have also been found by the model. Allseas always tries to keep the pipelay vessels stocked as full as possible, however, the mathematical model has shown that it ismore advantageous to try to keep the vessel at 80%capacity sine the supply vessels can unload faster that way ensuring shorter routes. Furthermore, the mathematical model has shown that it can deliver cheaper solutions than are currently designed. This has been proven by comparing the results of the mathematical model with a project that Allseas has completed. The mathematical model presented a solution that was ¼ 10% cheaper than the solution Allseas implemented.

Cutter suction dredgers (CSD) are highly vulnerable to large wave loading due to their stiff, spud-based mooring. Many mitigations targeted at reducing the resulting stresses on the spud and other critical operating components have been proposed in recent years, most notably by adding a level of flexibility to the connection between the pontoon and the spud for rotational motions. Investigating the merits of the implementation of a flexible spud keeper however are hindered by the lack of accurate, CSD-specific models that are able to simulate real waves in the working area, as well as the multibody system of a CSD and its complex interactions with the sea floor. In this thesis, an ANSYS AQWA model is developed to conduct an operability analysis of a CSD in operation in offshore, coastal conditions. Three modelling objectives were established to provide a complete analysis of the effect of increased flexibility in a spud keeper: adding non-linear wave effects, improvement of the soil boundary conditions, and building a dynamic multibody system of a CSD in ANSYS AQWA. A wave model is developed that expands upon standard Linear Wave Theory (LWT) through the use of Stokes 2nd Order Wave Theory (S2). S2 was found to be valid for a larger range of water depths and wave parameters than other wave theories, mainly in shallow, coastal conditions, which is the main operating area of a CSD. These non-linearities cannot be implemented into a frequency domain (FD) model, therefore a time domain (TD) model is required. A combination of S2 waves in a JONSWAP spectrum is used to simulate the motion and force response in TD, as well as second-order forces from the interaction of wave groups with the CSD. The model output is then used as a means of verification of these assumptions and to show the effect of the wave shapes on the spud bending stress. An altered spud model is proposed for shallow, wide spuds, using a rotational spring system instead of the commonly used clamped model. For the use-case of a CSD it shows a spud's tendency for rigid motion below the mudline, while also providing an upper operational limit for soil failure around the spud. The model output showed this upper limit to likely not be a important operational limit, but it can be used to investigate spud rotation below the mudline. Mooring effects from the cutter are absent in older models, but are added in the form of spring elements to better approach reality. Finally, a number of CSDs with different levels of flexibility are tested for four operational limits. The model shows a clear shift in motion resonance towards lower frequencies when the stiffness is decreased, while operability analysis in TD presents a significant increase in operability when a CSD is free to move in pitch. This completely flexible connection provides a major reduction in spud bending stress, but is governed by the acceleration limit of the pontoon. Other reduced stiffness designs are shown to only provide limited benefits to the operability.

Context: The shift to green energy offers a need for offshore wind farms. The transition from a relatively cheap energy production from carbohydrates, to a young offshore wind energy industry needs innovations to lower the cost. Increasing the efficiency of wind turbines and lowering the installation cost of a wind farm, will eventually make wind energy cheaper then energy produced by coal. A part of the installation process is the burial of the submerged power cables. The fragile power cables have to be buried a couple meters below the seabed, to be protected from anchors, fallen objects, and fishing activity. Problem definition: To submerge the power cable into the seabed, a trench have to be made. The soil of the seabed can consist of sand, silt, clay, rock or any combination of them. This research focuses on the trenching though clay. Clay has a very low permeability compared to sand, and clay has cohesive strength. For trenching in clay, a narrow plough is mostly used. These ploughs have a small frontal area and are build to cope with the high ploughing forces. A prediction of ploughing forces and velocities are made by models in preparation of cable burial projects. With accurate predictions, the best equipment can be chosen and a planning of the trenching operation can be made. The prediction models take into account the geometry of the plough and the soil characteristics. A reduction in pulling force results in an increase in ploughing velocity and therefore lowering the time and cost of cable installation. Approach: A large part of the pulling force in clay is caused by the adhesive force on the sides of the plough sliding through the clay. The adhesive force is therefore the main focus of this research. There are two main goals: the first goal is to investigate the adhesion force in relation to the strength of the clay; the second goal is to investigate ways to reduce the force caused by the adhesion. The adhesion factor is a parameter that is included in the prediction models. In literature of construction and agricultural engineering, predictions of adhesion factors and ways to reduce the adhesive force can be found. However, the circumstances during subsea ploughing are vastly different then in the other fields of engineering. Therefore, the approach of this study is to use small scale ploughing experiments with different strengths of clay to investigate the two goals under subsea ploughing conditions. For the experiments, a test setup is used. In this setup, a block of clay of a meter long can be hold into place in a water tank and be submerged. On top of the water tank, an electric motor can pull a cart over rails. A small scale plough can be bolted underneath the cart. During an experiment, the plough is pulled through the clay and the velocity and pulling forces are measured with sensors. Results and conclusions: The adhesion factors of three types of clay are found. The softest clay with a undrained shear strength of 25 kPa has a adhesion factor of 0.43. Literature shows that the adhesion force is about 1.0 at 25 kPa. This low adhesion factor could be the result of the frontal cutting that disrupt the clay. The residual shear strength is lower then the undisturbed clay. For the medium (80 kPa) and hard (131 kPa) clay the adhesion factor is respectively 0.68 and 0.53. These values are on the higher side of what literature reports. This could have to do with the relative high velocity during ploughing. The downward trend of adhesion factor with increasing clay strength does correspond to literature. To research the possibility of reducing the adhesion force, three small scale ploughs with modified adhesion surfaces are tested. The Alpha plough, which uses vertical gaps, reduced the adhesion force by 52 percent in both soft and hard clay. The Bravo plough, which uses convex shapes, reduced the adhesion force 39, 72 and 54 percent in respectively soft, medium and hard clay. The Charlie plough, which uses water nozzles at the adhesion surface, reduced the adhesion force by 70 percent in soft clay and 63 percent in hard clay. This experimental study obtained valuable knowledge of the adhesion factor and possibilities to reduce the adhesion force.

Maritime transport covers about 90%of world trade and is seen as one of the most cost-effective way of transporting goods. In order to safely accommodate vessels calling into ports, tugs are operated to assist various sized vessels with navigating, manoeuvring and berthing. Competition within the ship handling market has always been fierce. Boskalis Towage, through a network of joint ventures, offers harbour- and terminal towage services around the world, comprised of about 450 vessels. Operating a large fleet comes large Operating Expenses (OPEX). In order to deliver a more cost-effective service, Boskalis turns to business intelligence (BI) to help with the decision-making process. Maintenance is crucial for the operation of the vessels, but also a large part of the expenses. Large deviations in maintenance costs and operational performance exist between the joint ventures. However, the reasons behind these deviations are yet unclear due to the absence of continuous monitoring capabilities. The objective is therefore to increase the management capabilities of detailed performance monitoring of M&R expenses and performance of tugs, through which possible improvements can be determined. The M&R of tugs is influenced by various factors, such as utilisation, operational location and installed equipment. This research has evaluated the current Enterprise Performance Management (EPM) of Boskalis Towage and used literature on Maintenance Performance Management (MPM) in order to erect a multi-criteria hierarchical function-specific framework which is a framework for maintenance performance monitoring. The presented framework covers aspects of alignment with business objectives and plan, strategy and implementation. Moreover, the framework presents the maintenance function and its areas of performance measuring of equipment-, cost- and process performance across the organisational hierarchy. By performing a regression analysis of the maintenance data, this has also resulted in an increased understanding of the relationship between maintenance costs, operational data and vessel characteristics. As a result, an equation with acceptable statistical accuracy for running repairs has been found. The implementing of the MPM framework on the maintenance of tugs has resulted in the MPM model. This model focuses on the running repairs and dry docking direct costs and activities, incorporating basic maintenance types, i.e. Preventive Maintenance (PM) and Corrective Maintenance (CM). Running repairs have been evaluated in the time domain while the evaluation of dry dockings have been evaluated as events due to their relationship with regulatory surveys. The model incorporates operational-, maintenance- and financial data, tug specifications and operational conditions in order to evaluate maintenance performance. Maintenance Performance Indicators (MPIs) have been established to determine deviations and deficiencies among the different aspects of M&R. Challenges were faced on the aspects of data quality and data management, especially in the areas of maintenance process. The model has been validated through a detailed evaluation of five selected tugs. The underlying reasons for the underperformance of these tugs have been found and verified with knowledgable bodies and thus validating the model and its ability to determine underperformance and deviations. An alternative performance analysis method, Data Envelopment Analysis (DEA), has been researched and shows promise. The Slack-Based Measure (SBM) DEA model is a non-parametric frontier approach, based on Linear Programming (LP), to evaluate performance based on slacks (room for improvement) of Decision Making Units (DMUs). The method is capable of determining similarities in inefficiency in maintenance performance, comparing it to results from the MPM model. It, therefore, proves the method is capable of quick evaluation of maintenance performance and of determining new maintenance targets. However, the model is simplistic and requires further detailing and is unable to determine underlying reasons for underperformance. The regression equation and DEA have been used to formulate a so-called performance region which describes the lower- and upper bounds of the running repair costs for individual tugs. Unfortunately, data quality doesn’t allow for the determining of these bounds for all vessels nor for dry docking. New key benchmarking targets have been established through quartile values for respective Maintenance Performance Indicators (MPIs). With this newly obtained knowledge, future maintenance performance evaluation of tugs can now be performed with a higher detail through analysis conducted with the developed MPM model.

The clay adhesion phenomenon has been problematic in multiple engineering projects involving soft cohesive soils. In this dissertation, the adhesive characteristics of offshore high plasticity clay will be analyzed in support to deep sea mining applications. Adhesion of clays are particularly relevant in 2:1 swelling clays, where the magnitude of the force is highly dependant on the clay properties itself, working conditions and the soil engaging component surface material. The most prevalent force in offshore saturated conditions arises from the suction forces between micro-channels in the clay and the soil engaging component. Methods to reduce this adhesive force were assessed, ranging from solutions such as vibrations and electro-osmosis, to modifying the soil engaging surface to break continuous contacts between the clay and component. The natural adhesion of two typical offshore clays were experimentally determined by interface shear tests for the shear adhesion and pull-out tests for tensile adhesion. Interfacial shear strength was measured for typical materials found in the offshore industry, that being steel, aluminium, rubber and a polymer coating. Results from the tests showed that materials do have an impact on adhesive stresses. Similarly, pull-out tests showed this variation pattern. The influence of pull-out rates and contact time on adhesive tensile strength were also assessed and showed to increase with faster rates and longer contact times, respectively. In application to a typical rotational cutterwheel in deep sea mining, a scaled test-setup of a rack of cutter-teeth was dragged through the test clay to acquire horizontal cutting forces with the utilization of the experimentally found natural adhesion in the interface tests. The found adhesion value for the test clays were utilized to validate the cutting clay model from "The Delft Sand, Clay & Rock Cutting Model" (Miedema, 2019). Practical results from the scaled experiment seemed to coincide relatively well with the theoretical model. It is therefore recommended to further investigate the use of experimental means to determine adhesion of clays to develop an even more accurate empirical model.

The aim of this study is to conclude which parameters are influencing the most the hydrodynamic interaction between the two moored vessels in side-by-side configuration using frequency and time domain simulations. Furthermore to show what is the added value of the hydrodynamic input used in time domain investigations using 2 different integration schemes. Ultimately identify what is the impact on the mooring arrangements and what it needs to be done to ensure safe offloading operations. During the offloading process (18 to 24 hours), the transfer equipment needs to accommodate the relative motions between the two vessels. There are several parameters which might influence the operations, which are dependent on the location (i.e. environmental conditions) and on the mooring system (i.e. vessels size, draft, mooring arrangements, etc.). The side-by-side mooring system analyzed consists of a turret moored FLNG and various size of off-take carriers. A sensitivity analysis is done with respect to the physical parameters (i.e ship dimensions, loading conditions and separation distance) and modelling parameters (i.e parameters dependent on damping factor) in order to determine the effects on the first and second order quantities using frequency domain analysis. This represents the input for time domain numerical investigations in order to assess the relative motions and line tensions under certain environmental conditions. It is known that the diffraction-radiation tools overestimate the results in the gap region. This is an effect of using potential flow which do not count for viscous effects. To overcome this problem and to describe in a realistic mode, multiple methods or numerical techniques has been proposed. With this regard a detailed numerical investigation has been carried out to conclude what is the impact of varying the dissipation factor (i.e between 0 and 0.4) on first and second order quantities. Traditionally, the relative motions are determined using experimental tests which might be time-consuming. In particular for sensitivity analysis, numerical investigations are preferred in order to shape a main conclusion. Ultimately some of the results can be validated thorough experiments. The hydrodynamic interaction revealed important aspects, especially with respect to the off-take carrier. If the carrier is smaller the impact is higher due to the presence of the FLNG. Such that the carrier rolls significantly when there are head or following seas. Furthermore decrease in heave motion of the FLNG at the resonance frequency due to the roll of the carrier has been noticed. The same phenomena occur for heave of the carrier. Thus, this represents a strong coupling between heave-roll motion of the two vessels. Another important aspect revealed is with the respect to the shielding effects under beam conditions. In general FLNG is slightly influenced by the presence of the carrier. In particular, it can be noticed only when it is in ballast condition due to the fact that the draft and thus the displacement of the carrier is considerably higher. The sensitivity analysis points out that the modelling parameters (i.e dissipation factor) does hardly influence the response of the vessels even if it is considered or not. On the other hand drift forces are highly dependent on these parameters as a consequence of sharp changes of the wave elevations between the vessels. Such that if there is no dissipation factor to damp the wave elevation the resulted forces are extremely high compare to the cases where the dissipation factor is different than 0. This occurs only at the wave gap resonance and towards higher frequency region when diffraction effects are important. This is emphasized by the time domain analysis which prove that under the sea-states close to the gap resonance the lines and fenders tension reaches extreme magnitudes. Outside the gap resonance the relative motions and tensions are not influenced by the variation of the dissipation factor. The moored system (i.e FLNG-LNGC or FLNG-LPGC) is governed relatively by long crested waves. Thus it is expected to have higher line loads under these sea-states. The actual mooring design shows that under squall conditions (i.e Tp of 14s) the mooring lines exceeds the safe working limit for the FLNG-LNGC, while for FLNG-LPGC exceeds the minimum breaking load. In terms of relative motions for the same environmental conditions, the criteria is not satisfied. The proposed optimization of the mooring lines does bring reduction in the mooring line tensions, but not enough to drop below safe working limit for FLNG-LPGC configuration. On the other hand for FLNG-LNGC, the line tension is within the limits, but the relative motions still exceeds the criteria. Therefore choosing the optimum mooring configuration is a trade-off between line stiffness and location of the connection points of the mooring lines which sometimes may lead to unpractical solutions.

Contractors can be stimulated to offer sustainable product innovations through tenders in the GWW sector. But despite the sustainability ambitions of clients to achieve a 100% circular economy by 2050 and sustainably generated energy in the Netherlands, contractors are hindered from being able to offer sustainable product innovations by clients. To make recommendations to clients to optimize the preparation phase of public procurement. In order to contribute to this, it is made clear how contractors can be stimulated by investigating the influential (external) factors of the tender phase that can stimulate contractors to offer sustainable product innovations with a TRL level 7-9 during the tender phase.

This thesis report proposes a framework to implement Navigation, Guidance and Control (GNC) systems, that enable point-to-point autonomy for displacement vessels. A model-based control approach is chosen as the basis of the GNC systems. The resulting algorithms are implemented for verification in a 1:25 scale model of a Azimuth Stern Drive (ASD) 3111 Damen tug named "Damen Autonomous Ship", aka DASh. First, a compact maneuvering model that captures relevant dynamics of displacement vessel is formulated and identified using system identification. Secondly,the guidance system is automated such that it connects an initial state to a goal state with a collision free path that satisfies all input and differential constraints of the vessel model. To this end, the kinodynamic Rapidly-exploring Random Tree (RRT) algorithm is extended to use a maneuver automaton and optimal motion primitives in its steering function. A learned cost-to-go distance metric for the state space is formulatedto efficiently calculate distance between states, which is used to search for nearest neighbors in the kino- dynamic RRT algorithm. The performance of the planner using the learned cost-to-go distance metric is compared to a minimal curve length distance metric based on Dubins Curves and the commonly used straight-line Euclidean distance metric. It is shown that the learned cost-to-go and the minimal curve length distance metric result in paths of similar performance while the Euclidean metric performs severely worse. Lastly, the navigation and control systems are implemented on DASh. Due to disturbances present in real world environments, the paths must be tracked using feedback control. State estimation for navigation, based on position and heading measurements is performed by implementing an observer using a Extended Kalman Filter (EKF). Non-linear model predictive control (NMPC) in combination with thrust allocation is used to control the vessel during path execution. Due to real time requirements of DASh, the EKF, NMPC and the thrust allocation algorithm are directly implemented inefficient C ++, on the on-board computer of DASh. It is shown that NMPC converges to static reference positions faster and with less control inputs compared to traditional non-linear PD control. It is also shown that time-varying trajectories created by the kinodynamic RRT can be executed successfully. This shows that the identified model is suitable for use in model-based control and that the planned paths indeed satisfy the input and differential constraints of the vessel.

Offshore contractors use special cable laying vessels (CLV’s) in order to install subsea power cables, which transport offshore generated energy. Workability studies are performed to evaluate whether operations can be performed or not. These workability studies are subsequently a combination between operability assessments (performed in OrcaFlex months prior to operation) and forecasted weather windows. During the operability assessment, eventually limiting sea states are defined which are expressed in significant wave height (Hs), wave peak period (Tp) and incident wave angle relative to the vessel heading (a). If the forecasted weather windows exceed the predefined limiting sea states, operations cannot be executed. These current workability assessments are based on 1D JONSWAP spectra. This thesis contains an exploratory study of implementing a motion-based forecasting (MBF) method into workability studies, based on 2D wave spectra. This is done by focusing on the motions at the chute of the CLV, as this is where the subsea power cable leaves the CLV. Before MBF can be implemented, however, at first a specific limiting motion predictor needs to be identified that covers the cables integrity limits. Furthermore, this limiting motion needs to be quantified as well in order to compare this essentially composed new cable limit with MBF predicted chute motions. Subsequently, all cable integrity criteria need to be converted into this limiting motion to preserve the subsea power cables integrity. For normal cable lay operations, eventually all mechanical properties and cable limits are covered by three main cable integrity criteria. These are minimum bending radius (MBR), minimum bottom tension (BT) and maximum top tension (TT). By means of modelling a lot of various environmental loading conditions, the research described in this thesis shows that the chute z velocity is eventually indicated as a proper limiting motion predictor. Out of all investigated chute motions, chute z velocity (which represents the vertical velocity of the chute) shows the best correlations with the aforementioned cable integrity criteria. To determine workability by implementing motion based forecasting, this limiting chute z velocity needs to be quantified. The chute z velocity needs to account for all three main cable integrity limits, hence these limits are essentially converted into one single chute z velocity limit (which is essentially a new introduced cable limit). To quantify this limiting chute z velocity not the entire relation is of interest, but only the range close to breaching the cable integrity limits. Therefore, a percentile line method is introduced which is constructed on the 90th-percentile values per bin. Based on this research, it was found that binwidths must not exceed values of 0.5m/s to obtain robust results. However, no minimum amount of data points per bin was established as this varied for all assessed subsea power cables. Finally, workability studies of the current 1D JONSWAP (based on a single Hs −Tp sea state) method was compared to a 2D superimposed JONSWAP accounting for both swell and wind wave contributions. This comparison indicates that when determining workability based on more detailed 2D spectra, the workability study provides more smoothed results. This means, the higher chute z velocity peaks from the 1D total sea state are downscaled when simulating a 2D spectrum, whereas the lower chute z velocity peaks from the 1D total sea state are upscaled when implementing a 2D spectrum. The obtained motion-based chute z velocity forecasts indicate that optimization is possible by splitting the total sea states into both swell and sea waves contributions and accounting for wave spreading.

Numerous offshore wind farms have been constructed recently in the southern part of the North Sea. Their infield and export cables are buried for protection against dropped or dragged objects. In sandy soils, it is common to use tracked remotely operated vehicles, equipped with two water jetting swords. These swords fluidise the seabed and generate a backward flow of water-sediment mixture, allowing the cable to sink into the seabed. The southern part of the North Sea has a highly variable seabed topography characterised by sandwaves and megaripples. These seabed features have a significant influence on the trenching process. Existing models do not allow for an accurate estimation of the influence of seabed slopes on the trenching process and are often not based on fundamental physical processes. Two separate numerical models are developed; a jet trenching model describing the cable burial process and a traction model describing the seabed trafficability. The jet trenching model is divided into three parts; an erosion model describing the erosion of soil by the waterjets, a sedimentation model describing the re sedimentation process and resulting trench shape and a cable model describing the cable deflection. The erosion and sedimentation model combined describe the flow of water and sediment in the trench. The erosion model is based on a specific energy approach to determine the maximum allowable trencher velocity, limited by the eroding capacity of the jets. The sedimentation model describes the flow of water-sediment mixture through a rectangular channel, based on the shallow water equations. The channel width is able to evolve due to breaching and the bed elevation is controlled via erosion and sedimentation. The shallow water equations are solved on a staggered grid, following a one-dimensional finite volume scheme. A moving boundary is imposed on one side of the grid to simulate trencher movement. Seabed topography can be imported to model trencher performance on sand dunes. Tractive performance of the vehicle is modelled by considering its driving state. A constant velocity is assumed, hereby balancing thrust and resistance forces. Resistances due to static sinkage, slip sinkage, seabed slopes, current and internal running gear friction are included. The driving thrust force is found by integration of shear stress over track-seabed contact area, including effects of slippage and constant seabed slopes. A sensitivity study has been performed on the jet trenching model, where a strong influence on achieved depth of lowering was found to be caused by grain sizes and depth of the jetting sword below seabed. Influence of trencher velocity on depth of lowering was found to be associated with grain sizes. A higher trencher velocity has a positive effect on the achieved depth of lowering in coarse sand, whereas in fine sand the trencher velocity has a negligible influence on the depth of lowering. Validation of the model with field data shows reasonable agreement regarding average depth of lowering. When including sand dunes, results of the model show a similar depth of lowering trend as observed in field data. However, the amplitude of depth of lowering variation is underestimated by the model. The sensitivity study performed on the traction model showed that resulting slip ratio and power demand have a strong dependency on track-seabed contact area and corresponding normal pressure distribution. Work remains to include the effect of variable seabed slopes, since the current model is based on constant seabed slopes.

CSD spillage is defined as “any soil that is dislodged above the lowest cutter tip trajectory of a single swing, but is not sucked into the suction pipe”. In addition to higher energy consumption and material wear for delivering the targeted depth, spillage can lead to a variety of environmental issues. As of yet, no analytical model exists in literature that can estimate spillage rates for a given set of cutting parameters. This thesis presents the Sand-Rock Cutting Spillage Model (SRCSM), an engineering model that is particle size-agnostic and makes use of cutting parameters that are all available to the dredge operator. Prediction accuracy of 5 percentage point is achieved with a two-disc potential flow model complemented with empirical closing relationships. A triad of forces governs flow in the cutter head for typical cutting conditions: a centrifugal, suction and gravitational force are considered. For the centrifugal pump effect, and centrifugal pump effect only, the flow inside the cutter is considered steady, non-gravitational, inviscid and non-axial. This allows for the derivation of a pressure-discharge affinity law from the Navier-Stokes. The axial pump effect is governed by the mixture velocity at the suction mouth. It is hypothesized that the pressure difference over the discs drives an inflow at the disc closest to the nose. Centrifugal advection and rapid redeposition spillage are considered the two most significant spillage types out of the six classified. Centrifugal advection can be determined by identifying the onset of radial outflow at the disc near the cutter ring. The magnitude of rapid redeposition flow and its concentration depend on mixing effects that are proportional to the ratio particle settling velocity and the mixture velocity squared. The model is calibrated with three coefficients. User input parameters are the cutter geometry, cut-type factor fd,type (-1 for under-cut), bank slope angle ξ, cutter inclination angle λ, bank height h, step size lstep, rotational velocity ω, settling velocity vts, swing velocity vs, mixture velocity vm and material densities. Spillage=f(Dring,Dnose,Dpipe,b,fd,type,ξ,γ,h,lstep,ω,vts,vs,vm,ρq,ρb,ρw ) For calibration, an inverse flow number θ-1 is used that is proportional to the ratio of centrifugal flow over mixture flow. Spillage rates from SRCSM are in high agreement with reference data for sand (Miltenburg, 1983) and rock (Den Burger, 2003) in an under-cut swing. A sensitivity analysis suggests that most cutter head dynamics are adequately incorporated. The model is less reliable for (non-typical) inverse flow numbers of  θ-1= 6 [-] and higher due to a mixture velocity that drops below zero. In addition, the model is calibrated for a relatively high cutter inclination angle of 45 [deg] and bank angle of 45 [deg]. Caution should be observed with the results. It is also suggested that mixing effects related to the swing velocity are incorporated more explicitly in the model. For typical sand cutting conditions, the highest spillage reduction (-4.6%) is achieved by a 1 [%] smaller step size. For rock, the highest spillage reduction (-0.63%) is achieved for a 1 [%] decrease in swing velocity. Spillage appears to follow the theorem of Ellington (1934): it don’t mean a thing if it ain’t got that swing.

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.

On a global scale, the present-day demand of coastal protections, port expansions and construction of artificial islands, rises. To be able to accommodate for all these environmental changes, complex dredging operations have to be performed. Depending on the type of soil and in-situ conditions, a suitable excavation and transportation method has to be chosen. From an economic point of view it is desired to make this process as efficient as possible. The only way in doing this, is to understand the physics of the rock cutting process and be able to predict the behavior of the rock formation during cutting. This research focusses on the physics that come paired with the excavation of rock deposits under atmospheric conditions. The removal of rock results from the interaction between the cutting tool and intact rock, destructing the internal structure of the rock formation. A rock may either fail in a brittle tensile, brittle shear or ductile manner. Over the past decades various calculation models have been developed to predict the cutting forces in rock cutting. Most known prediction models assume one failure mechanism to be dominant, using a specific cutting tool geometry. For the sake of this research a sharp pickpoint is used. The elaborated, existing calculation models within this research using a sharp pickpoint as a cutting tool, all consider the rock cutting process to be a two-dimensional problem. To investigate if this hypothesis about the rock cutting process is correct, experimental research is conducted. A distinction is made between two different rock types, both varying in strength (e.g. sandstone and artificial rock). Experimental research revealed that the measured forces greatly underestimate the results of the existing prediction models. The author states that this inaccuracy partially arises from the fact that, in practice, the excavation of rock is actually a three-dimensional problem, since visual observations clearly showed that chips broke out sideways. Based on the experimental measurements, two new calculation models were set up, incorporating this three-dimensional effect. The first model implemented fracture mechanics theory, focussing on the required local crack tip stresses to initiate a tensile crack. Due to several unknown empirical parameters, the tensile-dominated fracture model gave unsatisfactory results, underestimating the measured cutting forces. The second model was set up by focussing on the actual physics that were observed during cutting. Based on visual observations and individual chip investigation, three different failure mechanisms can be substantiated that occur during cutting: crushing, major shear failure and tensile failure. By elaborating on the developed prediction model, it appears that the forces due to crushing dominate the total force spectrum. For a crushed zone to develop, penetration into the material is required. The author discovered that rock's resistance to obtain a certain penetration, needs to be accounted for when calculating the stresses within the crushed zone. By achieving the desired penetration, a large vertical force arises, indicating that frictional effects also need to be considered. This means that forces due to crushing are dependent on the hardness of the rock and frictional resistance between the cutting tool and rock's top interface. Based on production measurements and cutting groove analysis, the crushed zone dimensions were able to be determined, whereupon an expression for the pickpoint's indentation area was found. A surprising discovery was made during the analyzing phase of the force data. Regardless of the pre-set cutting configuration, a basic force level was observed during cutting, which is quite well-approximated by the crush force component, including frictional effects. Despite the formation of a crushed zone, chips failed in a cataclysmic manner. Individual chip investigation revealed that a certain fraction of shear and tensile failure is present along the failure plane. It appeared that the contribution due to tensile failure becomes more significant as the penetration depth of the pickpoint increases. This can be explained by the fact that a tensile crack has the ability to grow and propagate to the rock's top interface. The results of this research show that predictability of the forces increased significantly, compared to the existing two-dimensional calculation models.

The growth of the cruise industry throughout recent years and the changing public opinion on cruise ships has led to increasing concerns regarding the impact cruise vessels have on the world’s climate and environ- ment. Cruise passengers prefer not to be related with heavy polluting vessels. In fact, trends like responsible tourism and sustainable travel are increasing, especially among younger generations. In order to maintain a viable business model, cruise operators are compelled to consider exploring new energy sources and energy carriers to power their cruise vessels. Alternative carbon-neutral fuels are found to be a potential solution. As such, this research aims to evaluate the viability of possible alternative carbon-neutral fuels on board cruise ships.

Rock cutting is a challenging process. Heavy equipment, large cutting forces, high wear rates and large amounts of required energy are common challenges when cutting rock. Traditionally, rock cutting is based on a linear motion of the cutting tool. However, a significant improvement on the cutting performance is expected when using non-linear cutting techniques. Non-linear cutting can be achieved by using an actuator to create a vibrating or oscillating motion on top of the linear forward motion of the cutting tool. The focus in this paper is on the oscillating undercutting disc cutter. This disc attacks the rock like a chisel or pickpoint, aiming at a cutting process dominated by tensile failures. Although the discrete element method has been successfully used for various rock cutting processes, all these processes are based on linear rock cutting tools and most of these researches are based on 2D simulations. The use of a 3D approach is necessary to enable the simulation of oscillatory rock cutting tools. This paper utilizes discrete element method in 3D to investigate non-linear cutting processes, especially the effects of the design parameters such as frequency, velocity and eccentricity of the cutting tool. To resemble rock-like materials the particles are placed in a dense particle assembly and they are bonded together through perfect brittle elastic bonds. The bonds can fail in shear and in tension, allowing the dominant failure mechanisms, i.e. shear and tensile cracks, to occur. After failure of these bonds, particles can still interact through collisions. The simulation results show the effect of the tested design parameters and are compared with analytical models and actual experiments of oscillating undercutting discs.

Experience-based decision making by crew plays a key role in the safe and effective execution of maritime operations. For yachts and naval vessels, common operations can be identified as helicopter operations (take-off and landing), launch and recovery of small craft and (dis)embarkment to and from these small craft. All of these operations are limited by wave-induced ship motions. For these operations, experience-based decision making does however not always guarantee that the operations are carried out in the most safe and effective manner possible. Also, the level of comfort as experienced by a yacht-owner or guests can be directly affected by this type of decision making. With this in mind, Feadship aims to develop a Feadship Comfort System (FCS), which can contribute to the decision making process. One of the elements of this system is ought to be a waveradar. The aim of this thesis is to describe how the waveradar can be included effectively in the FCS, and how it can be used for the above mentioned operations. The waveradar is in basis a common navigation radar that can perform measurements of the surface elevation in the direct surrounding of a vessel. These measurements can be used to predict the ship's motions up to approximately two minutes ahead in time. With this, windows of opportunity can be distinguished when operations can be carried out best. These windows depend on the corresponding limiting criteria that are set on the ship's motions. A major issue is however that sea trials have shown that the roll prediction is inaccurate. Due to this problem, two methods are evaluated in this thesis to improve the accuracy of the roll prediction. These methods are set up such that they are practical in use and can be applied directly to the deterministic wave predictions from the waveradar. The first method is scaling the response based on the roll motion history, whereas the second method is based on scaling the roll damping. The latter is effectively linearising the viscous contribution to the roll damping. As no data from sea-trials is present to compare these methods, a benchmark calculation is carried out based on Cummins approach. In these time-domain calculations, a linear and non-linear roll damping coefficient are taken into account, which are based on a decay test that is available at De Voogt Naval Architects (DVNA). This follows from model tests performed by MARIN. Comparing both methods to this benchmark calculation showed that the method of scaled damping resulted in the best approximation, with a Pearson correlation coefficient of (only) 33 %. Also, in terms of the behaviour of the motion envelope, this method showed the closest approximation of the two methods. It is found that the way in which both methods influence the RAO of the roll motion has a great influence on the results found. More suitable methods that should provide a better approximation are suggested from this, such as a frequency dependent scaling of the roll damping. This is however not discussed further. With the method of scaled damping, the practical application of the waveradar within the FCS is evaluated. For the common operations of yachts and naval vessels, limiting criteria on ship motions are obtained from literature or stated by the author. The majority of these criteria are RMS values, for which a method is suggested to use them real-time. In this method, the most probable maxima are obtained from the RMS criteria, which are then applied as real-time criteria. This showed impractically large results, which showed that this method does not suffice. From this conclusion it follows that the analysis of the practical application of the waveradar is only carried out for the (dis)embarkment of small craft. From this, design considerations for the FCS are obtained, from which the main result is that heading suggestion is one of the most important tasks that the system needs to be capable of. Finally, a performance monitor has been evaluated for yachts at anchor. This performance monitor displays the predicted Comfort Rating (CR) real time, which can be used by the yachts crew to evaluate the current anchor location. This is a specific desire of Feadship and is developed next to the other operations. For this application, heading suggestion is also one of the most important tasks that the FCS needs to be capable of.

In dredging there are a lot of opportunities to improve the production processes and to make the production cycle more efficient, especially the excavation process of the draghead. The aim of this research is to determine the trailing forces and to estimate the production of the draghead. Besides that, the goal is to get more insight into how the draghead behaves, depending on the trailing velocities. The variations in the trailing velocities, soil characteristics, control settings and draghead and suction pipe geometries that can occur do not make it easy to determine the trailing forces on the draghead and suction pipe. Because of this complexity, it is also hard to define how to estimate the production. Therefore, the scope of this research is limited to just one sand type with specific soil characteristics. An analysis of the draghead and the suction pipe, with a freely suspended visor, showed the physical processes in and around the whole suction pipe system. Because the draghead is fixed to the suction pipe, the influence of suction pipe on the draghead is analysed first. After that, the draghead is divided into two parts, the visor and the visor house. With the use of force and moment balances the trailing forces are determined for every trailing velocity. In addition, the production and its production limits are defined. The calculations show that the increase of the trailing velocity results in higher trailing forces on the suction pipe and draghead. For a velocity of around 2 m/s the draghead, for a Damen SLK600 used in the case study, will lift of from the bed. It should be notified that, among other variables, the dredging depth has an effect on this ‘floating’ point. Moreover, the results showed that the drag forces at common trailing velocities of 1-2 m/s are relatively low compared to the soil excavation forces and therefore have a small share in the total trailing forces. When the suction pipe system is trailed against the current the dragforce becomes more significant. The interaction of the draghead with the bed causes several processes to take place. The resulting relevant trailing forces are mapped and determined. The settlement of the draghead causes a hump of sand to be pushed forwards which result in a sled force and a friction force. Besides that, the flow through the pipes will cause impulse forces in the bends and at the end of the jet pipe out of the nozzle. The jets fluidize the sand which results in the largest production contribution. Furthermore, it can be seen that the penetration depth and cavity width of the jets depend on the trailing velocity and determine the amount of sand that is loosened. The cavities can overlap at low trailing velocities, resulting in a jet production limit. The jets have a significant influence on the behaviour of the visor. The freely suspended visor will drop until a solid bed layer is reached. The cutting force and vacuum force are the dominant forces working on the visor. Application of the equilibrium-moment method showed that the visor is slowly moving upwards when the trailing velocity is increased. However, the cutting layer thickness remains almost constant for an increasing trailing velocity which results in a linear increase of the cutting production. The cutting production contributes, 20-25%, to the total situ production. The total jet and cutting production lead, together with the jet water inserted and ambient water flow, to the total production and mixture density. When the capacity of the dredging pump is insufficient, spillage will occur. This research shows the best possible estimate of the draghead production and corresponding trailing forces. It should be kept in mind that the calculations are based on a simplification of the suction pipe system and the geometries of the suction pipe system of Damen. Nevertheless, a lot of research can be performed into the processes that occur, to improve the results of the calculations. Suggestions for further research would be to determine the magnitude of the vacuum force, the erosion production which is not considered in this research or the on velocity depending cavity width. Validations of the results is another point of consideration. Thus, to determine trailing forces and production, the new approach used in this study contributes to a better understanding of the draghead.

For present-day drilling operations in deep and challenging well sections, a technology called casing while drilling can be used. It involves isolating and ‘casing’ a formation while drilling, where the casing itself is used as the drill pipe, which is cemented in after a certain depth is reached. By doing this, the need for separate casing runs will be eliminated and well stability is improved. The concept has become increasingly popular since the beginning of the 21st century, due to an increase in technical possibilities and use of this technique, which makes it more profitable. To enlarge a wellbore past its original drilled size, to enable lowering of the casing, an underreamer is used. Under reaming can be performed in a reaming while drilling (RWD) configuration. To perform these operations, the bottom-hole assembly (BHA) containing the underreamer is lowered in the casing string to a depth just below the casing shoe. Afterwards, drilling fluids are used to fill the casing and pumps will be engaged to drive a hydraulic piston in the underreamer assembly that opens the cutter blades. Hydraulic pressure is used to fold the blades outward and prohibits closure of the tool. The width of the reamed borehole is not only determined by the outer diameter of the casing couplings that have to fit thru, but there also has to be a clearance for the drilling mud. The annular space between the borehole and casing is relatively small which causes relatively high friction losses during current operation. Because of this, the dynamic pressure loss of the drilling fluid along the outside of the casing becomes too high. To lower the pressure, the borehole needs to be enlarged further than possible with underreamers currently available. There are also limitations on the length of the underreamer. From tests carried out by Huisman, it is found that an increase in length has adverse effects on the steering behaviour of the BHA. Therefore, the length of the reamer should be kept at a minimum. The DRILLSTAR Z600H design that is currently being used does not allow for a diameter enlargement. New concepts must be devised to enable this. A solution to this problem can provide Huisman Well Technology (HWT) with the opportunity to perform the drilling of more and deeper wells. A solution to the problem was found by splitting the piston and spring internally. This enabled the spring to be placed in the top part of the underreamer while the piston remains in the lower part. The blocks are located in the middle and fold out eccentrically to reach a hole diameter of 228.6 mm (9 inch). The angle under which the blocks fold out has been reduced from 60 degrees to 45 degrees to allow the underreamer to be shorter by 66 mm.

This paper examines a case study to determine the effects on system performance of the power plant and ship operational capabilities, this case is a ship designed by the company DEKC. It is a small general cargo vessel of 2999 GrT (Gross Tonnage) called the Future Trader. The ship design is finished and the ship will be equipped with a modular power plant and fuel storage on the aft of the ship. In total four different power plants will be compared. The first is the base line system, this consists of a single internal combustion engine fuelled by Marine Diesel Oil (MDO). The three other systems will be modular systems. They all use the concept of distributed generation. There is looked into a system with three internal combustion engines fuelled by MDO. Besides this there are two fuel cell systems. Each consists of two separated fuel cells and one uses hydrogen and the second ammonia as fuel. For those systems mathematical models are created to compare three modular power plants to each other and to a base line. With those models the effects on the Future Trader's range, fuel costs (operational capabilities) and emissions are researched. A modular power plant is installed on the aft of the ship, constructed of four power packs each in a Twenty foot Equivalent Unit (TEU). The four systems will be simulated on four voyages and the results will be normalised with respect to the first setup. It can be concluded that a modular system with the concept of Distributed Generation (DG) will reduce the ships overall performance in comparison to the single engine diesel electric system (base line). When reviewing the fuel cell systems with respect to the base line system it is found that the ammonia fuel cell system has zero emissions and it still offers a sufficient range. The increases in fuel costs are lower than that of the hydrogen fuel cell system. Hydrogen will also reduce harmful emissions to zero but the reduction in range is more severe. The increase in fuel costs is also significantly higher than for the base line. Overall ammonia seems the most promising of the non hydrocarbon fuels. The DG system is also useful as long as emission regulations remain unchanged. The MDO DG system can be loaded for large distance voyages and hydrogen can be loaded for short voyages if desired.

Since the ratification of and commitments made under the COP 21 summit, we have witnessed an increase towards implementing and utilizing renewable technologies in our energy mix. The global cumulative installed wind energy capacity in 2017 surpassed 540 GW, which is an increase of over 173% compared to 2010 levels. At the same time, Solar PV technology has also experienced a significant cost reduction, and the global installed capacity was 500 GW in 2018. Despite rapid development and growth, the overall contribution on the global energy scene is still limited. Fossil fuels still dominates the global energy supply, and are likely to do so in the coming years. This thesis explores the potential upside of considering synergies in the offshore domain, in order to further expand the diffusion of renewable technologies.