When a ship reaches the shore, the water depth reduces and thus the under-keel clearance also reduces. The ship keel clearance influences the maneuverability of the sailing ship.

In this thesis project, the link between the fluid mud rheology and its density is first investigated. The exponential relation reformulated between the density and yield stress necessitates the direct measurement of rheology for navigability. It was confirmed true that the yield strength grows exponentially with the density of the fluid mud. However, at higher densities of mud, more thixotropy is observed in the flow curves. Besides, the Power-law relations were found for the relation with volumetric concentration, for yield stress in agreement with fractal dimension theory.

Second, quantification of the thixotropy effect of fluid mud is conducted to justify the importance of the time-dependency effect in the rheological modeling. We found that an unremolded fluid mud has high thixotropy even at high shear rates. However, diluted and remolded fluid mud at high shear rates found a negligible thixotropy effect. We also observed that Houska's modeling curve coincides perfectly with the flow curve of fluid mud at high shear rates, and also it integrates the thixotropy into the modeling.

Third, the total resistance of a plate moving through fluid mud is measured and compared to the frictional forces calculated using the available analytical formulas of a plate moving in Bingham fluids and Power-law fluids. The moving plate is an abstraction of a vessel's keel sailing through the fluid mud. We found that the total resistance of the plate moved in fluid mud at low velocity agrees with the frictional force of a plate moved in Bingham fluids. As the velocity increases, the stagnation pressure becomes significant, and the deviation of the total resistance of plate and frictional force of a plate increases. Thus, to estimate the total resistance of a plate moved in mud, normal forces (stagnation pressure) and vortices at edges should be investigated because these need to be subtracted.

The experimental data in this thesis are made resourceful to help researchers validate their Computational fluid dynamics(CFD) models in the application of sailing through the mud.

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.

Over recent years, there has been an increase in demands for rare and precious minerals worldwide. Mostly this is due to the rise of the world’s population and the drive towards a green energy transition and low carbon economy. Prices are rapidly increasing, and there is an identifiable risk of an increasing supply shortage of raw materials, including those identified as critical to Europe’s high technology sector. The development of surveying techniques and advances in new technologies in remotely operated vehicles (ROV) has allowed detecting that the most valuable and rare mineral resources are spread out in the sea-floor and international waters. Currently, the most significant setback towards exploitation licenses is not because of lack of technology but because of a lack of knowledge on deep-sea biodiversity and the impacts of mining on ecosystems. The ISA (International Seabed Authority) is responsible for the regulation, and the control of mineral-related activities in the international waters is currently working on drafting environmental regulations. This presents significant opportunities for research on the development of technologies that incurs in the least environmental impact possible. Currently, the main concerns are regarding the horizontal sediment-laden plume that is generated as a result of the mining process. Therefore, the industry is working towards the development of equipment that lessens the plumes spread. Work done in this research focuses on small scale sized laboratory experiments in which the sea-floor crawler’s outlet shape is varied, and its plume’s effects of the sediment waste and other effluents (SWOE) are measured. Besides gaining insight in the horizontal plume spreading under different conditions and geometries, the outcome of the research is to provide a set of measurement data that can be used for future numerical model validation towards determining an optimal outlet shape for the seabed crawler. For this purpose, a total of three diffusers were designed and tested based on a specific scaling factor and input parameters defined by IHC Mining. Experiments consisted of capturing visual imagery of the generated plume on both top and side views for further analysis and performing velocity and concentration profile measurements in different locations. The offset jet transition from jet to plume and the respective impingement point for all diffusers was compared. Velocity and concentration measurements were analyzed and compared to determine an ideal diffuser. Using diffusers reduces the plume’s initial momentum while maintaining the density differences and therefore reduces the transition from jet to plume, allowing for gentler deposition over the surface and resuspending less material. All experiments show similar behavior in which a free jet can be observed initially. Then, after substantial entrainment takes place, the jet impacts the bed due to the negative buoyancy. Once the discharge impinges the lower boundary, it forms a radially spreading layer along the boundary which transitions into a wall jet. Lowering the momentum of the jet by diffusing the outlet gave better results in terms of drawing the impingement point, and the deposition profiles nearer to the diffuser. Also, the measured velocity and concentration profiles considerably decreased, reducing the plumes spread.

Dams are an essential part of the Dutch flood defence works to protect the hinterland from flooding by the sea. Sand closures are the construction of closure dams with sand as the main building material. The rising and falling tide generates a current through the closure gap, which increases in strength as the gap becomes smaller. This current is quite strong and transports a significant amount of sand from the gap to areas where the current is weaker. The sand that is transported away from the closure gap is called the sand loss. The changing tide and constantly moving sand grains result in a dynamic environment. This makes it difficult to estimate the total amount of sand that is necessary to close the dam. It is important to be able to assess the amount of sand loss accurately, because it could make the difference between needing an extra dredging vessel or not. The costs of these dredging vessels are about 1 million euro's a week; therefore, having an unnecessary vessel present due to very conservative sand loss predictions is costly. Laboratory experiments and a numerical model were used to investigate the morphology during bedload transport under a lateral expansion. A streamwise bar formed behind the tip of the lateral expansion for both the laboratory experiments and the numerical simulations. However, it was not possible to replicate the bedforms that occurred during the laboratory experiments with the numerical model. These bedforms are deemed to be important for the morphology during bedload transport. The numerical model was used to expand the research to suspended sediment transport by decreasing the grain size of the sediment. In the obtained morphological patterns, four areas are distinguished where the morphology was found to depend on the flow velocity and the degree of turbulence in the flow. It is expected that a variation of these patterns can be found during a sand closure, although these findings should be validated with a laboratory experiment or in situ measurements. Therefore, it is recommended to set up a laboratory experiment to investigate the morphology under a mixing layer for suspended sediment transport. Based on the results of the laboratory experiments and the numerical model, it is advised to look into the possibility to use the sand deposited as a streamwise bar during a sand closure as an additional borrow pit to aid the closure process, since it would lead to less sailing time for the dredging vessels. For the first stage of a sand closure, it is advised to use a two-dimensional model that incorporates a bedload transport formula to model the sediment transport. It is important to use a parametrization of the bedforms that occur during bedload transport. For the final stage of a sand closure, which is the most critical phase due to high flow velocities, high degree of turbulence and time restriction, it is advised to use a three-dimensional model with a pick-up equation that takes the influence of turbulence on the grains into account, such as the pick-up formula of Okayasu et al.

The cable between Vlieland and Terschelling needs to be replaced. The thesis focusses on the replacement of this cable. Because of the sensitive environmental situation some additional hurdles will need to be taken in order to come up with a decent placement plan.