This thesis explores the measurement of low sediment concentrations in pipeline flows, a critical issue in deep-sea mining. The study aims to identify and validate a continuous measurement method capable of accurately detecting suspended sediment concentrations between 10-75 g/L. These measurements are essential for minimizing the environmental impact of sediment plumes generated by mining operations.

The research begins with an analysis of material properties and flow dynamics, emphasizing the role of sediment particle size, and density in influencing suspension and settling behaviours. Highlighting the differences between concentration measurement and density measurement and the additional error involved. A review of flow regimes, turbulence, and their effects on sediment distribution within pipelines sets the foundation for understanding the complexities of representative sampling.

The thesis evaluates a range of measurement methodologies against criteria such as accuracy, range, spatial and temporal resolution, safety, cost, and impact on the flow. Optical, acoustic, conductivity, and radioactive source sensors were unsuitable due to limited range, low accuracy, or safety concerns. Promising alternatives include the U-loop, Coriolis, and vibrating fork sensors. The U-loop offers good accuracy and range, but causes significant pressure drops. Coriolis sensors provide excellent accuracy and broad range, but require careful sampling to ensure reliability. The vibrating fork sensor is simple and has a good range, but suffers from low accuracy and limited spatial resolution.

A key aspect of this research is the experimental setup, which integrates multiple sensor technologies in a controlled flow loop environment. Detailed methodologies for sensor calibration, installation, and data collection ensured the testing conditions. Tests are conducted under varying sediment concentrations, sediment types, grain sizes, and flow velocities to validate the accuracy and reliability of each measurement method.

The results reveal significant differences in sensor performance across test conditions. Test variables such as sediment type, concentration, and flow velocity are shown to influence sensor performance.

In conclusion, suspended sediment concentrations from 10 - 75g/L can be measured accurately using a Coriolis sensor. This sensor directly measures density which can be converted into concentration with minimal calibration or correction, demonstrating superior accuracy and precision across diverse flow conditions. Although it reliably detects finer deep-sea sediment, minor challenges remain when measuring coarser materials, such as nodule fines. Overall, the findings contribute to the development of environmentally responsible deep-sea mining practices, by facilitating real-time and accurate sediment monitoring.

Offshore wind energy has become a crucial element of the global energy transition, with the North Sea being a major hub for offshore wind farms. As first-generation farms approach the end of their operational life, decommissioning offshore wind export cables has emerged as a significant technical challenge. This thesis focuses on the feasibility and limitations of using the cable pullout method for decommissioning offshore wind export cables, particularly examining the influence of burial depth and soil conditions.

This research is structured in two main phases. The first phase involves a comprehensive literature review to identify critical knowledge gaps and establish an overview and understanding of existing decommissioning practices. The second phase employs simulations using OrcaFlex software to model and analyze various cable pullout scenarios. These simulations focus on determining the limits and constraints imposed by burial depth and soil relative density for sandy soils commonly found in the North Sea.

Key findings from the literature study underscore the complexities of decommissioning, which encompass legal, environmental, economic, and technical considerations. One of the main conclusions is the importance of adopting a 'design for decommissioning' approach during the initial cable installation. This involves designing cables and selecting burial depths that facilitate easier future removal, thus promoting sustainability and cost-effectiveness. Additionally, this approach can help mitigate potential environmental impacts and regulatory challenges associated with cable removal.

Soil modelling plays a crucial role in understanding how burial depth and soil conditions influence resistance forces during cable pullout. Factors such as shear strength and burial depth are analyzed to determine the forces that oppose cable recovery. The model includes scenarios for fully drained, fully undrained, and partially drained uplift resistance, implemented in a Python script to simulate real-time resistance during pullout operations. To address buried cables, an external soil model is integrated into OrcaFlex, allowing dynamic simulations of soil resistance during cable pullout.

The simulation results with a 525 kV HVDC export cable reveal how soil resistance significantly increases with greater burial depth and higher soil density. These findings highlight the critical importance of burial and soil conditions in planning decommissioning operations and suggest that additional deburial techniques may be necessary when cable pullout is not feasible.

This thesis provides valuable insights and recommendations for future research and practical applications, aiming to support the offshore wind industry's evolving needs and enhance the sustainability of decommissioning processes. These findings are crucial as the industry anticipates a substantial increase in decommissioning activities, with offshore wind capacity expected to continue to grow.

This thesis investigates the physics of clay cutting, focusing on the challenges and complexities associated with mechanical excavation. The use of clay is inevitable as a sand replacement in the future. Clay is a fine grained soil with a dense structure that makes it relatively impermeable to water. It can act as a barrier which is beneficial in rivers. Clay can also obstruct constructions, so excavation is needed. By analyzing existing literature and
conducting extensive experiments, the study aims to shed light on the underlying mechanisms governing clay deformation and forces in linear cutting processes. Experiments are conducted using clay with a cohesion of 35 kPa and 60 kPa, while an adhesion ranging from 1.2 kPa to 12.5 kPa. For all parameters of the clay a test is conducted. Direct shear tests for cohesion, adhesion, internal and external friction angles. Tensile testing for the tensile strength of the clay. Cutting tests are conducted on clay with varying parameters, including cohesion, adhesion, cutting depth, blade length, blade angle, and cutting velocity.

The study identifies two primary cutting regimes: flow and curling. While other regimes are theoretically possible, they were not observed in the experiments. The other two regimes: shear and tear could be encounter when sand or silt is added to the clay. The main cutting force and the thrust force are made dimensionless in the analyse. The analysis revealed the relationship between the tested parameter and the cutting forces, highlighting its importance in the overall process. In the end a new model is presented for calculating the main cutting force and the thrust force. A key difference from existing literature is the use of the shear angle and the strengthening factor. The shear angle represents the inclination of the shear plane during clay deformation, while the strengthening factor quantifies the strain rate dependent increase in clay strength under faster deformation conditions. While the shear angle is generally overestimated, the strengthening factor is inaccurately applied. The main cutting force is primarily influenced by cohesion, shear angle, cutting depth and cutting velocity. In contrast, the thrust force is primarily affected by adhesion, external friction, cohesion, cutting depth, and blade angle.

Recommendations for further research include, exploring conditions that could lead to tear or shear failure in clay. The relationship between blade angle and cutting force for linear and non linear cutting. The non linear cutting is especially important in the field. While the experiments in this thesis involved linear cutting, field conditions involve circular blade movements with varying blade angles and cutting depths during the cutting process. This is attributable to the inherent characteristics of cutter suction dredgers. The strengthening factor should also be investigated for other types of clay.

The current supply of critical materials falls short of keeping up with the required pace to comply with the commitment governments worldwide made towards a decarbonised energy mix by 2050. To avoid dependency on large suppliers, lower the pressure on land mining expansion and still meet the metal demand of the rapidly growing green economy, more companies are turning their focus towards the deep-sea, where these critical metals are present in the form of nodules. However, sediment plumes from nodule collection can negatively impact marine ecosystems and hinder mining operations. This research investigates how slope angles and directions affect the near-field dispersion of turbidity currents discharged from a moving source during deep-sea mining (DSM). The study focuses on the Clarion-Clipperton Zone (CCZ), rich in the so-called polymetallic nodules.
Experiments were conducted at TU Delft's Offshore and Dredging Laboratory using a modular flume tank with an experimental setup scaled at 1:20. The configuration included a moving cart and diffuser system on a sloping seabed, with precise control over slope angles and velocity ratio. A homogeneous suspension of glass beads (used instead of CCZ sediment) with water was prepared in a mixing tank and discharged into the flume to simulate a turbidity current. Measurement techniques involved the acoustic Doppler velocimeter (ADV) and ultrasonic velocity profiler (UVP) sensors for mixture concentration and velocity data, complemented by multi-angle camera footage for visual analysis. Various slope angles (-5° to 5°) and velocity ratios (source velocity over discharge velocity, ζ = 1.00 and 1.25) were tested to observe their effects on the behaviour of a turbidity current, with device calibration and controlled experimental parameters ensuring accurate and comparable results.
A notable phenomenon was observed during the experiments, namely the formation of a bulge directed towards the diffuser. A higher velocity ratio and steeper slopes led to more significant bulges, with the bulge length and impingement angle increasing with slope steepness. Regarding velocity ratios, higher ratios resulted in larger dispersion angles and larger turbidity current heights in downhill driving experiments, while uphill conditions showed an inverse trend. The slope angles influence the dispersion by reducing the dispersion angle for steeper slopes in downhill driving experiments. Data analysis from the UVP, camera footage, and concentration measurements support these findings.
Future research should focus on influencing factors on bulge formation, assessing the influence of the concentration on the dispersion of a turbidity current, identifying parameter ranges for floating plumes, conducting experiments with reduced source velocities, scaling down experiments and using real CCZ sediment in saltwater.

This thesis scales methods for Gaussian process-based magnetic field mapping and localization
in five distinct ways.@en

To keep the global warming of the Earth to a minimum, the greenhouse gas emissions need to be reduced. Van Oord aims to be carbon neutral by 2050; therefore, Van Oord is exploring alternative fuels. Ammonia is a promising option to use as a fuel due to the forty times lower well-to-wake emissions than MGO when it is produced with green energy. There is no carbon content in ammonia. Furthermore, the expected cost of using ammonia as a fuel is lower than other competitive 'green' fuels, such as hydrogen or methanol, due to the lower storage or fuel fabrication cost of ammonia. The goal of this research is to determine if and when it is economically viable to use ammonia as a fuel to decarbonize a trailing suction hopper dredger (TSHD). This is expressed in cost per dredged material [€/m^3].
Ammonia needs to be handled, stored and consumed taking into account safety precautions to have a safe operable ship. Additionally, ammonia has poor combustion characteristics, and therefore a promoter such as hydrogen (7-11%) or MGO (40-60%) is necessary to initiate the combustion. Additionally, internal combustion engines (ICE) using ammonia as a fuel are expected to have a low transient load capability. Therefore, if there is no MGO present, the dynamic loading capability of the ICE with the load variation of the dredging process is a challenge. The same challenge applies for a Solid oxide fuel cell (SOFC), where the SOFC does hardly have transient load capabilities.
A TSHD currently has an ICE capable of dynamic loading, and the main reasons for this transient load is the change in propulsion power, which is dependent on the friction of the draghead and the sailing speed of the vessel. Furthermore, a sudden change in mixture density in the dredging tube during dredging will result in a sudden transient load. To cope with these transient loads, the energy supply on board of a TSHD must have transient load capabilities.
A fuel consumption model has been developed to compare five drive train configurations for the dredging project Kustlijnzorg with an operational profile of 30 days with respect to the original drivetrain. The total power demand [kW] and the transient load [kW/s] was included on a boolean way in this model. When the power demand or the transient load was too high then the model would stop. By means of this model, the main particulars of the engines, fuel cells and batteries regarding power and energy were determined. The output of this model was the amount of fuel consumed during 30 days. This fuel consumption model was validated with another project.
The Construction Industry Research and Information Association (CIRIA) has developed a method to valuate a TSHD. With this CIRIA methods, the value of a conventional TSHD is determined and compared with the value of the ammonia driven configurations. The value of a new vessel that operates on ammonia can be estimated with the help of a sustainability factor. It is found that the weekly cost of the vessel is mainly dependent on; the value of the vessel, which is dependent on the installed power and cost of technology, the fuel consumption, the cost of fuel and the carbon tax.
Currently, it is not economically feasible to use ammonia as a fuel to decarbonize a TSHD. So, not with an ICE or SOFC. However, when green ammonia is used in combination with a SOFC, then a TSHD can be fully decarbonized. In order to make ammonia an economically feasible option for a TSHD, the price of MGO and carbon has to increase, or the price of the SOFC and ammonia (grey and green) has to decrease significantly.
Currently it is unclear if the carbon tax in the future applies to tank-to-wake (TTW) or well-to-wake (WTW) emissions. If the WTW emissions are taxed, then grey ammonia is never a better choice than MGO in terms of cost. Which is also the case when considering the CO2 equivalent emissions.
To conclude, it is currently not economically feasible to decarbonize a TSHD using ammonia as a fuel based on the cost per dredged material [€/m^3]. The limited transient load capabilities of drive train configurations on ammonia, need a battery or MGO to cope with the transient load of a TSHD. Future progress in the technology or developments in the reduction of transient loads could make ammonia as a fuel for a TSHD a better option. Finally, future developments in the price of: carbon, ammonia and MGO can make it economically feasible to decarbonize a TSHD.

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 2^nd 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.

Over 5000 offshore wind turbine generators have been installed in the past decades. 80% of these wind turbines have a monopile foundation. Monopiles are hollow steel tubular piles with a diameter of up to 10m. The first phase of the monopile installation consists of the self-weight penetration into the seabed due to the mass of the monopile. Followed by the placement of the hammer, which installs the piles to the designated depth. A scour protection is deposited near the piles to avoid erosion (scour holes) around the monopiles. The scour protection consists of rock material with different size gradations and densities. Generally, the scour protection is installed in two campaigns. The first campaign consists of the installation of smaller rocks (filter layer), followed by the installation of bigger rocks (armour layer). Between these two campaigns, the monopile is installed through the filter layer. To achieve a more time-efficient installation sequence, in some projects a full scour protection (single layer) is deposited prior to the installation of the monopile. However, the technical feasibility of monopile installation through a scour protection has not been researched. Within practice, difficulties arise during the installation of monopiles through a single layer of scour protection. This leads to timely and costly delays.
This thesis contributes by use of simulations, to study the technical feasibility of monopile installation through scour protection. With a focus on the scour protection behavior in the first phase of the installation, where the monopile penetrates the seabed due to its mass, so-called self-weight penetration.
During monopile self-weight penetration, physical processes within the subsoil, scour protection, and monopile wall create penetration resistance. The most important physical processes during monopile self-weight penetration are identified using literature:
• The development of tip resistance due to the scour protection layer.
• The development of shaft resistance due to the scour protection layer.
• The self-weight penetration due to the weight and dimensions of the monopile.
• The interaction between the monopile wall and the scour protection rock and inter-rock interaction (interlocking, rotation, breaking, and protrusion of the subsoil).
The Discrete Element Method (DEM) is considered most suitable for the representation of the scour protection behavior and is an effective method for addressing engineering problems in granular materials. The most important reason for using DEM is due to the discontinuous behavior of the scour protection material.
The Discrete Element Method (DEM) is considered most suitable for the representation of the scour protection behavior. DEM is an effective method for addressing engineering problems in granular materials. The most important reason for using DEM is due to the discontinuous behavior the scour protection materials.
To set up the simulation, calibrated DEM input parameter sets are required to recreate reliable bulk behavior. These parameter input sets are found with the use of two Key Performance Indicators (KPIs) of the bulk material: the porosity and the angle of repose. These KPIs are included because they represent the inter particle frictional resistance to movement. With the calibrated input sets combined with data from a case study, the Full-Scale Monopile Simulation is set up. Consistent with the case study, the simulation is designed using a monopile with a tip diameter of 8m and a wall thickness of 0.08m. The seabed consists of a sandy subsoil and a scour protection on top.
To achieve a realistic stable simulation with a reasonable computational time, experiments are executed. Within an experimental design, a reference simulation is developed, followed by a parameter sensitivity analysis. The most important conclusions of the parameter sensitivity analysis are:
• When using an 8m diameter monopile, a minimum simulation domain of 12*12m2 is recommended. Resulting in a minimum of 2m space around the monopile.
• A subsoil is required for successful penetration through the scour protection layer.
• The subsoil input parameters are of significant influence on the penetration behavior of the monopile, due to the rock penetration into the subsoil.
• The scour protection thickness can be included as a variable parameter.
To verify whether the reference simulation properly represents practice, a qualitative validation is executed using the case study. Successful penetration is achieved within both the reference simulation and the case study. However, the current simulation does not present a comparable depth over time correlation. An underestimation of the penetration resistance is observed. Increasing the rolling resistance and therefore limiting the angular velocity of the particles results in higher penetration resistance. Restricting the angular velocity of the scour protection completely, results in an unsuccessful penetration.
Further research should focus on representative penetration resistance of the scour protection, combined with an alternative and more representative inclusion of the subsoil. Furthermore, the validation should be elaborated using adequate data from practice.

In recent decades, a significant amount of the research into deep sea polymetallic nodule mining has been conducted on the collecting vehicle and the riser system accommodating transport from the seabed to the mining support vessel.
The topside operation, however, is less commonly described in the literature. This part of the operation deserves attention because it significantly impacts project risk and cost.
After initial investigation the main research question was formed: What is the effect of moisture on the granular characteristics of polymetallic nodules in the context of bulk handling?
Royal IHC provided a container with around 50 kg of polymetallic nodules from the Clarion Clipperton Zone. These nodules have been used in earlier research, focused on the degradation of nodules in transport from the seabed to the sea surface. Resulting in broken and damaged nodules. Therefore these are a good representation of nodules coming from the vertical transport system.
The degraded nodules provide an unique opportunity to gain an understanding of the bulk behaviour of the nodules once they have arrived on the ship.
Four experimental setups were used to understand the granular characteristics of degraded polymetallic nodules in a non-destructive manner. In the first setup, particle properties such as density, porosity, and water content have been measured. The second setup identifies the shape of degraded nodules. The third setup measures the angle of repose for different nodule sizes and water content. The last setup measures the friction factor for different nodule sizes and water content, while changing the sliding surface between steel or rubber. Lastly, clay has been added to the sliding surface experiment.
Considering the angle of repose tests and the sliding and rolling friction angle, it is evident that the difference between dry and fully saturated nodules is minimal. For the friction angle: The maximum deviation between dry, saturated and CCZ clay is 8 % on steel and 9 % on rubber, corresponding to 2 degrees. For the angle of repose, the difference between dry and saturated is negligible.
It is concluded that the moisture content only contributes minimal level to bulk behaviour of nodules.

To fulfil the ever-increasing need for wind energy, European offshore wind farm sites are selected in deeper waters with seabed conditions which can consist of hard consolidated sediments or even rock. The deeper sites require the use of floating wind turbine foundations that are moored off to anchor piles in the seabed. For rock seabed sites, the anchor piles must be drilled. As the water depth of these sites increases, commercially available jack-up vessels are no longer able to operate. Therefore, the anchor pile drilling operation must be performed from the deck of a floating vessel. An extensive techno-economic analysis has led to the finding that a topside-operated drilling rig mounted on a large construction support vessel with heave compensation (HC) added is the most cost-effective configuration. The performed research focuses primarily on the determination of which HC method is most effective at changing water depths of 50 m up to 200 m. Leading to the understanding which site requires the use of active HC, limiting the resources required to construct future floating wind farms. The configurations are tested for relevant wave conditions, determined by assessing potential European floating wind farm sites.

Firstly, the research assesses the maximum allowable topside displacements before the drilling column reaches either the operational limits of plastic failure or bottom hole assembly lift-off. Secondly, the operational vessel motions are determined for the relevant environmental conditions. By comparing the results, the need for HC in the drilling configuration is determined. Third and finally, the passive and active HC methods are assessed for a 3-hourly time simulation under the before-mentioned environmental conditions. The assessment is performed using two performance criteria; weight on bit variation and the occurring drill-string stresses.

The performed analyses and simulations show that the vertical upward vessel motion is the limiting factor for the operation’s workability. Also, HC is required in every considered environmental condition. Further, the system operating with passive compensation shows a decreased stiffness with respect to the active system, most noticeable at 50 m water depth. This leads to higher frequency vibrations and stress variations being present in the drill-string of the active system. This effect is no longer noticeable for water depths larger than 50 m.

For locations with a water depth of 50 m, the active system shows favourable workability results. The active system shows a larger sensitivity to wave conditions with larger wave heights, as the stiffness is larger and more stress variations occur as a response. However, the results remain more favourable in comparison to the passive system as the lift-off percentage is significantly smaller. The passive and active systems show similar results when considering short waves in 50 m water depth, this is best witnessed in the weight on bit and lift-off percentages.

For locations with a water depth of 100 m and 200 m, the active and passive HC systems show comparable results for the performance criteria, for all considered wave conditions. The stresses remain within the ultimate limit state, the fatigue damage is negligible in comparison to the time required to perform the drilling operation, and the lift-off percentage for both configurations are in the same order. Therefore, as the workability of the two systems are so comparable for a water depth of 100 m and 200 m the availability, day-rate, and mobilisation complexity of the equipment will determine which HC system is most effective per project.

Due to urbanization, improved living standards and electrification, approximately five times more raw minerals are necessary in 2050 compared to 2018. In deep oceans, the seafloor contains these minerals in the form of polymetallic nodules. Nodules are about the size of golf balls that grow throughout the ocean at depths between 3500 m and 6000 m. They contain a wide variety of metals, such as manganese, copper, nickel, cobalt. Nowadays, for large-scale applications, hydraulic lifting is almost exclusively considered for vertical transportation through the water column. However, there is little research available about using other techniques instead. To tackle this knowledge gap, this thesis studies the feasibility of transporting the nodules using a concept of mechanical lifting. The concept used in this thesis consists of two alternating containers that are lowered and hoisted by lifting and guidance wires. Due to the conditions, such as the large depth, the environmental characteristics and the positioning and heading of the vehicles, there are technical uncertainties regarding mechanical lifting. Risks include the yaw rotation of the container, which might result in rope entanglement and wearing of the ropes. This thesis presents a study into the yawing stability of the concept of mechanical lifting for the vertical transportation of polymetallic nodules, which is a crucial factor to operate reliably.

The research question is answered by performing an experimental test and a CFD analysis. The experimental tests include the dynamics of the system while testing various configurations and is validated by an analytical integration in time and a CFD simulation at model scale. The CFD analysis takes away the uncertainties and unknowns: the drag force, the yawing moment and the fluctuation magnitudes and frequencies. The CFD analysis is performed using the open-source software OpenFOAM and simulates multiple configurations. The results of the simulations are compared to the restoring moment by the guidance wires, by transforming the excitation moments into static and dynamic responses of the system. The CFD model is validated by testing the model with a 2D cylinder and 3D sphere, and by performing a mesh convergence study. The CFD simulations are validated by literature. With the obtained drag forces, the energy consumption is calculated.

From the results, it can be concluded that the system can stably be transported at 2 m/s, as the static and dynamic responses are well within the safety limits. The largest response occurs in the middle of the water column, as the rotational stiffness is the smallest at that location. The dynamic response is smaller compared to the static response, as the high frequent fluctuations (f > 0.075 Hz) are damped. Rope entanglement will not occur during normal operation at 2 m/s. However, critical situations due to incidental events can arise, including a winch failure, friction or a sudden high current. This has not been evaluated in this research and therefore stability cannot be guaranteed. As lowering at 3 m/s with an inclined system and including the current results in a static maximum yawing rotation larger than the safety limit, the stability cannot be guaranteed for operating at 3 m/s.

Growing populations, high-technology applications and the energy transition raise the demand for rare earth elements. As a secure supply in the future is all but certain, opportunities arise for deep-sea mining. Polymetallic nodules
that are located on the vast, sediment-covered ocean floors, are one of the more promising deep-sea mineral occurrences. Large amounts of unwanted surrounding water and sediment are collected along with the nodules in the
harvesting process. Separating the sediment and excessive water from the nodules before transportation toward the surface could mitigate sediment plumes and be beneficial for energy consumption. In this research, the feasibility of a hydrocyclone inspired machine is investigated for this process. With model experimentation, the key performance parameters are studied using varying particle fractions, adjusting split ratio and conical angle. Timescale ratios are
used for particle scaling, and to describe their behaviour. The cyclones’ separation shows great potential. However, large particles can be problematic, and the energy consumption is too high for deep-sea operation. Therefore, topside utilisation is recommended.


Keywords: Polymetallic nodules, separation, hydrocylone, performance parameters, topside.

Due to the increased demand for materials like cobalt and nickel, there is an interest to mine polymetallic nodules from the deep-sea. These nodules are abundantly distributed along the abyssal plains, e.g., the Clarion Clipperton Zone (CCZ) in the North East Pacific. These nodules lay spread on top of a seabed consisting of very fine clayey sediment and will be collected by a seafloor mining tool (SMT). During the operation, the seabed will be disturbed, resulting in a suspended sediment plume discharged by the SMT. This plume can have a significant environmental impact through a blanketing effect on the abyssal fauna and create a disturbance in the water column affecting the entire food web structure. Hence, identifying the critical processes and quantification of sediment plume dispersion is essential to predict the potential environmental impact better and determine what technologies would enable a lower ecological impact. Spearman et al. (2020) investigated turbidity plumes generated by deep-sea mining experiments and discovered faster settling velocity than the theory described. They hypothesize that this is due to flocculation. The settling speed depends on the density, concentration, shape, and cohesive properties of the sediment. Flocculation in the deep-sea can occur in two ways, by salinity or by organic matter. Gillard et al. (2019) showed that the flocculation response of CCZ sediment strongly depends on the concentration and applied shear rate. To analyze to what extent aggregation could influence the plume dispersion, experiments are conducted in which the effect of aggregation can be adjusted selectively. Lock exchange experiments are used to analyze the impact of aggregation by comparing results with illite based on freshwater, saltwater, pre-existing bed, and added flocculant. Additional experiments with artificial CCZ sediment are done to ensure that the illite experiments are not too idealized. To prove that the settling velocity is increasing in saltwater, settling velocity tests have been performed. I performed experiments with illite suspensions in a settling column. An increase in settling velocity is observed due to the rise in salinity up to 75 g/L of illite. Lock exchange experiments are performed to mimic the particle-driven currents. The lock experiments involve a lock release of a fixed volume suspension of sediment from the mixing section into the outflow section. Similar observations were made by doing lock exchange experiments. A decrease in average head velocity is shown for all experiments up to 75 g/L of illite in saltwater. To further induce flocculation and mimic organic matter in the water column, experiments with flocculant were done. Mixing the flocculant, Zetag 4120 or Zetag 8125, in the mixing section will further decrease average head velocity compared to saltwater. Zetag 4120 even ensures very fast settling as the end of the tank will not be reached For low concentrations in saltwater, flocculation is shown as the tail decreases more rapidly than freshwater. Flocculation with higher mass concentrations of illite is shown when flocculant is added to the mixing section. Adding Zetag 4120 to saltwater makes the current even settle quicker. As the SMT will move over a pre-existing bed, experiments were done to see if a pre-existing clay bed has consequences for the behavior of the flow. A clay bed has been made by running a lock exchange experiment with a concentration of 100g/L. This test then had, depending on the next experiment, one day or two days settling time before it was used for the new experiment. One-day bed experiments overall encountered a decrease in average head velocity. Two-day bed experiments overall experienced an increase in average head velocity. To mimic the existing sediment in the CCZ and determine if illite experiments are not too idealized, experiments were done with artificial CCZ sediment. The currents behaved differently compared to illite, as they produced more coherent flows for low concentration. Also, it showed better effects on lowering the ecological impact when looked at mass concentrations of 100g/L of artificial CCZ sediment as gelling occurred. To minimize the environmental impact created by deep-sea mining, the SMT should produce a discharge between 50 and 100 g/L of artificial CCZ sediment. Gelling will occur, which has a positive effect on minimizing the plume dispersion.

Deep sea mining is an upcoming industry that comes with many unknowns. One of these uncertainties is the interaction between the deep sea mining collector and the seabed. Allseas collaborates with DeepGreen Metals to collect nodules in the Clarion Clipperton Zone (CCZ) in the Pacific Ocean. The CCZ seabed consists of a very soft cohesive soil. During a blackout, the collector sinks considerably into the soil. It must be retrieved as losing such an expensive asset is not desired. The umbilical is intended to lift the collector from the seabed. However, the umbilical has its limits due to its lifting capacity. Therefore, research is done to estimate the breakout force of the collector and to find possible load reduction options to stay within the umbilical’s boundaries. The breakout process is time-dependent and contains multiple soil resistance forces. These soil resistance factors are the suction, adhesion, side resistance and added soil mass. The soil suction is the dominant force, adding resisting during a breakout. Different load reduction options (e.g. eccentric lifting, perforations) are discussed, to reduce the breakout force of the object. However, in previous research the extracted objects are rigid, while the tracks of the collector are flexible to some extent. Experiments are conducted to investigate the effect of flexibility on the breakout force compared to rigid objects. Four experiments are executed in the laboratory, to test four different effects on the breakout, namely: the flexibility, grousers, eccentric lift and in situ time experiments. A test setup is designed to execute these experiments and five different test samples are selected, varying in size and material properties. During the experiments, the samples are extracted from an artificial CCZ soil. The experimental results are used to calibrate and validate the model. The model is developed to simulate the breakout process and to make an estimation of the required force to lift the collector from the seabed. The model consists of three main components: the lifting mechanism, soil and the object that should be lifted. A combination of the literature survey, experiments and the model provides sufficient information to estimate the lifting force of the collector. Load reduction options can be applied to reduce the breakout force during a quick lift. During a slow lift the collector can be retrieved from the seabed without additional load reduction options.

Recently, deep-sea mining has acquired renewed interest from commercial companies due to a rise in the demand of minerals and metals. Deep-sea mining is focussed on different minerals and rare earth elements found in the oceans that are increasingly used in the manufacturing of goods and products related to renewable energy. In order to collect these minerals, a mining operation at several kilometres depth has to be undertaken. Apart from the technical challenges that mining at several kilometres depth poses, also the environmental consequences receive a lot of attention and criticism from environmental agencies. Deep-sea mining operations are believed to cause damage to the environment by the sediment plume, as well as by producing light and noise which are absent under normal conditions at the deep ocean floor. The sediment plume is generated by the movement of the miner, but more importantly by the discharging of the picked up and unwanted sediment. This happens at the back of the miner using a set of diffusers. In order to acquire a better understanding of the effect that the initial concentration of the slurry has on the spatial spread of the sediment plume and turbidity current caused by the deep sea mining vehicle, experiments have been performed in which the initial concentration has been altered so that the characteristics of the ensuing current can be compared. The main objective of this research is to determine how changing the initial volumetric concentration of the discharge mixture influences the flow parameters after impingement and sediment flux inside the turbidity current for a constant sediment flux and discharge velocity.
One of the most important assumptions for investigating the influence of initial concentration of the slurries has to do with the different phases of the discharged flow. During the initial phase, the density difference between the slurry and ambient mixture is thought to be dominant for the settling process, as the mixture behaves as one coherent fluid. After impingement on the bottom, the mixture spreads downstream as a turbidity current. During this phase it is the weight of the solids inside the slurry that causes it to settle. Because there are a lot of solids present in these slurries this process of settling is controlled by both hindered settling and flocculation. Flocculation is the aggregation of cohesive particles, forming a larger, heavier particle. Clay, which is cohesive, is expected to be present at most mining sites, resulting in flocculation to be an important factor in the process.
The research has been performed by conducting a total of three different experiments. These experiments consist of pumping a pre-mixed slurry of water and spherical glass particles into a large modular tank, where is it discharged through a diffuser. For each experiment a mixture is prepared with a different concentration, which is discharged into the modular tank with three different flow rates in order to keep the sediment flux constant between each experiment. A total of three diffusers are used, one for each concentration. The diffusers differ in cross section in order to achieve a constant discharge velocity for all experiments. Experiments have been performed using both spherical glass particles and clay. The sediment flux is kept constant between different experiments as it is assumed that the sediment flux of real deep sea mining operations will be mainly determined by the width, cutting depth and velocity of the mainly vehicle. For performing measurements during the experiments, an ADV was used. This device is capable of measuring the velocity in three directions over a profile of 30 mm with 1 mm intervals. The ADV also measures the signal-to-noise ratio, which after performing a calibration can be used for calculating the concentration inside the turbidity current. Together this data can be used for determining the spatial spread of the turbidity current.
Based on the findings of this research, it is believed that a higher concentration than the 1% volumetric concentration that is currently being assumed by deep sea mining companies could prove to be beneficial in preventing the spatial spread of the sediment plume and subsequent turbidity current. It is believed that in general, increasing the initial concentration of the discharged slurry, and thereby decreasing the momentum/buoyancy ratio of the buoyant jet, directly leads to both the velocity and concentration of the turbidity current to decrease over a shorter distance after impingement, while the impingement distance itself is also decreased for a higher initial concentration. As such, the total reach of the turbidity current resulting from the slurry discharge from a deep sea mining vehicle can be decreased by using a higher initial concentration of said slurry. It is believed that mainly the higher density difference with the ambient water plays a vital role in decreasing the spatial spread of the sediment plumes produced by deep sea mining operations. The higher density achieved by a high concentration results in the plume to deflect towards to bottom over a shorter distance and a decrease in turbidity current height. This decrease in height is beneficial for the later stage of the turbidity current in which the dying out is dominated by the settling velocity of individual particles.

Turbidity currents are common in the waters around the world. They can be caused by earthquakes, collapsing slopes or other geological disturbances. However, turbidity currents can also be caused by deep sea mining activities. Deep sea mining is done with special mining vehicles. There are three main operations within this mining vehicle: collecting nodules, separating the nodules from the mixture and discharging the mixture of sediment and water towards the environment. After impingement of the discharged flow with the seabed, it is expected that the flow will take the form of a turbidity current. Turbidity currents belong to a larger class of flows called gravity currents. Furthermore, turbidity currents are typically defined as dilute flows in which particles are dominantly supported by fluid turbulence. These currents have an interstitial fluid that is a liquid, generally water. The objective of this research is to increase knowledge of the behavior of these currents and to obtain experimental results that can be used for validation of CFD models. In this research the influence of the initial concentration on the dispersion, deposition and entrainment of the current is investigated. In addition, the spread of particles within the current is researched. Furthermore, different types of sediment are used with various particle size ranges and particle properties. The experimental methodology can be divided in two parts. The first part are experiments that involve a full-depth lock release of a fixed volume suspension of a sediment with different particle size ranges and particle properties into water. The initial concentration is varied and the obtained current is recorded with a high-speed camera. The second part consists of multiple calibration procedures. During these procedures, different concentrations of sediment are mixed with water and the resulting solution is recorded. This data is used to create a calibration function that in turn can be used to quantify the concentrations of sediment in the previous recorded currents. The experimental methodology differs from previous work due to this calibration procedure. Afterwards, video processing is used to perform an analysis of the current. The resulting turbidity currents go through three phases as observed in the experiments and previous work. At the start, there is an initial phase where the front is formed and the current accelerates. During this phase a limited amount of particles settle out of the current. Afterwards, the current transitions into a second phase when the velocity of the front starts to decrease due to inertial forces and due to the start of particle settling at the rear of the current. The last phase is when the backflowing bore created by the ambient fluid at the release of the gate reaches the front and decelerates the current until viscous forces start to dominate until the current vanishes. The experiments shows that currents transporting fine particles reach higher velocities and may travel for longer distances in comparison to currents composed of larger particles. Furthermore, the combination of fine and large particles has a substantial effect on the currents dynamics. The currents composed of a mixture of these two sediment types travel longer distances than currents with only large particles. The performed experiments also focus on varying the initial concentration and sediment type. These show that larger particles tent to entrain more with the ambient fluid in comparison to smaller particles and thus they have a larger vertical dispersion. Furthermore, currents composed of sediment with only fine particles will have a more rapid transition into a dense front and a less dense middle and rear pat of the current. Currents composed of fine sediment and a combined sediment with small and large particles have a clear division between a dense basal layer and a less dense top layer within the current. At last, deposition patterns are different per sediment type. Sediment composed of larger particles will have a larger deposition rate than sediment composed of smaller particles. Furthermore combining both sediment types will increase the deposition rate at the beginning of the current.

The rising demand for minerals and metals and the depletion of land-based resources has created a renewed interest in the extraction of resources from the deep ocean, i.g., deep sea mining. This research focuses on the mining of manganese nodules, these are potato-shaped objects, 5-10cm in size, composed of metals half buried in the seafloor. A Seafloor Mining Tool (SMT) is used to mine the nodules, however, during mining besides the nodules, also the sediment around the nodules is collected. This sediment is separated in the SMT and discharged through a horizontal diffuser located at the rear of the SMT, thereby creating a sediment plume. The sediment plume needs to be reduced for environmental, economic and legal reasons. The sediment plume causes changes in the sediment characteristics, clogging of pores of suspension feeding organisms and burying of the benthic fauna. The plume will spread in all directions, thereby burying still to be collected nodules and reducing the pick-up efficiency, making the process inefficient from an economical perspective. Legal issues will arise when the discharged sediment plume spreads to other exploration areas owned by other parties or to environmentally protected areas. The aim of this research is to investigate the influence of the choice of diffuser height on the reduction of the sediment plume. To achieve this goal a Matlab model was made and small-scale experiments in the laboratory of Dredging Engineering were done. The Matlab model is based on the JETLAG model, described in 'Jets and Plumes' by Lee and Chu (2003), and is a Lagrangian model predicting the centerline trajectory of the plume. The small-scale experiments provide insight in the behaviour of the horizontal discharge plume at different diffuser heights and generate measurements to validate the model. A diffuser designed specifically for these experiments is produced and the height and flow velocity are differed. The experiments consist of visualization experiments, capturing top view and side view images of the buoyant jet, and experiments measuring the velocity and bottom concentration at different locations. The velocity profiles, sediment concentration, deposition pattern and impingement range are compared and analysed. The combined results from the model and the experiments show that the start of the impingement range increases with increasing diffuser height. Furthermore, a lower diffuser height increases the amount of bottom deposition near the diffuser outlet. The measured velocity profiles, near bottom concentration and impingement range are in agreement with this observation. The measured near bottom velocities at 15D from the diffuser outlet are approximately 0.1 and 0.2m/s, depending on the discharge velocity, both have the potential of resuspending settled sediment. This research suggests that the spreading of the plume can be reduced by the choice of diffuser height above the seafloor. Based on the diffuser heights tested in this research a diffuser height of 100mm is recommended. Since a higher diffuser decreases the amount of particles settling close to the source and a lower diffuser increases the potential for erosion. This research has shown that up to a distance of 15D from the diffuser, the near bottom velocities are large enough to cause erosion. Research into the near bottom velocity decay and magnitude further away from the source, inside the turbidity current, is necessary as well to understand the full spreading behaviour and the potential for erosion. Furthermore it is recommended to do research into spreading behaviour of finer particles, especially the behaviour of the actual deep sea sediment in combination with salt water causing flocculation. Moreover, research into the influence of the forward motion of the SMT is recommended since the SMT will create a wake that will influence the spreading behaviour of the plume. Research into the potential creation of a recirculation region caused by the limited entrainment at the rear of the SMT is recommended as well, this can be done by aligning the diffuser outlet with a screen.

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.