This thesis investigates the erosion process of cohesive soil due to a submerged, moving, inclined water jet. This study provides a visualization and description of the failure mechanics of cohesive soil due to a submerged inclined water jet and develops a new equation for estimating the erosion process of cohesive soil while including the angle of the water jet as a parameter. Figures providing support to this new equation are also provided in Chapter 7. The primary variables tested are jetting angle, stand-off distance, forward velocity, and jetting velocity.

The study is guided by two primary research objectives. First, to visually and descriptively understand the failure mechanics of cohesive soil subjected to a submerged inclined water jet. Second, to develop a method of predicting the erosion process of cohesive soil, considering variable jet angles, stand-off distances, forward velocity, and jet velocity of a submerged inclined water jet.

Experimental testing was conducted in the "Dredging Lab" of Delft University of Technology. The experiment involved eroding cohesive soil blocks using half of a circular nozzle placed along the wall of a flume. This nozzle configuration allowed for the nozzle to be visible during testing. I designed several half nozzles that were tested in a flume provided by TU Delft. Nozzles with a variety of nozzle diameters were designed to have either a 25, 45, 65, 90, 115, 135, or 155 degree jetting angle. Seventy-two clay blocks with a known undrained shear strength were used as the cohesive test soil, allowing for immediate replacement after each test. Detailed experimental procedures are outlined in Section 5.3, offering insights into the design and execution of the tests.

The data analysis provides evidence that the jetting angle has a notable impact on the erosion process of cohesive soil. This includes a “deflecting jet” failure mode, the formation and prediction of the sediment plume, and the estimation of the erosion cavity depth. The failure mode of the soil can be seen in Section 5.5 and data analysis figures are provided in Chapter 6. Section 7.1.2 provides a new estimation for the erosion depth of cohesive soil using an inclined water jet (Equation 7.17). This study contributes to our understanding of cohesive soil erosion and methods of estimating erosion processes. The findings emphasize the crucial role of the jetting angle and provide a foundation for future research aimed at refining erosion prediction models and exploring additional parameters influencing the process. Practical applications may include improved design considerations for projects involving water jet erosion such as deep-sea mining, water injection dredging, trailing suction hopper dredgers, as well as other dredging processes involving water jetting.

An increased interest in the use of renewable energy, mainly accelerated by the growing awareness of the problem of global warming, has been observed over the last decades. For the installation of the popular monopile and other support structure types, high-energy pile driving is used in around 90% of the cases. The noise emitted by the pile driving forms a serious threat for marine mammals. To mitigate the underwater noise, air-bubble curtain systems are used in the offshore industry. A better understanding is required of the working principle of air-bubble curtain systems in practice to gain more insights into the air transport through the hose-nozzles (perforated pipes).
For this study a physical medium scale pneumatic model of the air-bubble curtain system was designed based on data available from the offshore industry. Tests were performed both in dry and wet conditions which approximate those that are seen in the industrial practice. The role of several geometrical and operational parameters of the pneumatic system, like the inlet pressure, inlet flow rate, internal hose diameter, nozzle diameter, nozzle spacing, static water pressure, on the operational conditions along the hose-nozzle is explored. The influence of the volumetric flow rate along the hose-nozzle on the pressure development along the hose-nozzle is examined. The examined correlation between air flow temperature and air flow rate at the inlet of the compressed air supply and the pressure development over the hose-nozzle forms valuable input for a future numerical model that includes the temperature of the inlet flow rate. The test setup with configurations of reduced lengths in dry conditions is used to experimentally determine the discharge coefficients of a range of different nozzles. Here, the limitations of the test setup are carefully considered and a comparison with numerical results provided by compressible flow theory is followed.

The increasing demand for rare minerals, such as lithium, cobalt, and copper, driven by the growth of the world population and the transition towards sustainable energy technologies, has become a pressing concern. These minerals are crucial for electrifying the transportation sector through electric vehicle production and are in high demand for the thriving high technology industry. However, their scarcity and high prices due to supply shortages necessitate alternative sources to meet these demands. In recent years, deep-sea mining has emerged as a promising solution to address the growing need for rare minerals. The vast potential reserves in the ocean floor offer an enticing opportunity for exploration and extraction. However, deep-sea mining comes with its engineering and environmental complexities that require thorough investigation and understanding. This research delves into the experimental study of a Coandă-Effect-Based Collector, aiming to understand its behaviour regarding water entrainment and cohesive sediment erosion. The focus is on understanding the collection mechanism to minimize clay pickup and maintain low clay concentration in the discharged mixture. This is vital in mitigating the impact of deep-sea mining activities on the marine environment. This research provides valuable insights into water entrainment and cohesive sediment erosion in the context of the Coandă-Effect-Based Collector. The findings emphasize the significance of operating parameters and shed light on the complexities of the collection mechanism. Future studies should explore additional data collection to understand the influence of the secondary jet duct better and employ reliable methods for measuring clay concentrations in the discharged water. Overall, these findings have important implications for optimizing collector design and mitigating the environmental impact of nodules mining activities.

Dredging is performed for various reasons, including port development, coastal defense and land reclamation. The economic and social importance of such projects is widely acknowledged, but there are growing concerns about the possible environmental impact of the dredge plumes that form as a temporary by-product of these activities. Suspended sediment blocks sunlight, and sediment that settles on the seabed buries coral and other organisms. These effects accumulate over the duration of a dredging project, and should be minimized.

An important step towards this goal is predicting plume formation and development. Here, we focus on an overflow plume from a trailer suction hopper dredger (TSHD). Although this subject has been studied for years, much is still unknown, due to the complex interaction of the processes involved. Because of this complexity, it is not uncommon in the industry to use rules of thumb, derived from empirical studies.

One such rule of thumb, based on an influential publication by Becker et al. (2015), relates to the fraction of the overflow plume that is still (or again) in suspension once the developing plume moves from the dynamic near-field to the passive far-field. This source term fraction (STF) is important, because the large-scale area models that model plume development in the far-field require information about the characteristics of the plume entering the far-field zone. Becker et al. (2015) presented a realistic range of 0-20% for the source term fraction. This range is based on a combination of measurements and expert opinions. Although Becker et al. (2015) recommend characterization monitoring at the start of a dredging project to determine whether the 0-20% range needs adjusting, this is not always done in practice, due to time pressure, costs, complexity or lack of necessity.

Building on the work by Becker et al., this thesis aims to support a more informed implementation of TSHD source terms on the computational grid of far-field models. In order to explore the behavior of SHD dredge plumes, numerical simulations were carried out using computational fluid dynamics model TUDflow3D. In these simulations, the values of three model input parameters – the water depth, the overflow density and the crossflow velocity – were varied to gain insight into the behavior of the plume under the conditions studied. For each of the three parameters, three representative values were chosen on the basis of expert advice, and all combinations were tested, leading to 27 numerical simulations.

The results of the numerical simulations show that the amount of sediment in the plume has reduced to less than 20% of the sediment in the overflow plume at 11-42 minutes of plume development, corresponding to a distance of 0-1895 m from the dredging location (500-3800 m from the moving vessel), depending on the specific conditions. It is important to note that (only) three conditions were varied
in this study. These conditions were all steady state (e.g. no tidal flows). In real-life situations, many more (combinations of) conditions and hence a wider range of results are possible. Conditions where the plume was found to travel relatively long and far into the far-field, are a high ambient current, a low water depth and low overflow densities. The effect of these factors corresponds with existing studies.

The contribution of this work lies in the broad characterization of the developing plume under these various conditions: not only the magnitude of the plume is investigated, but also its vertical and lateral
distribution. Specifically, the contribution of the bottom 6-13 % of the water column to the total plume flux is highlighted. This is particularly of interest, as this zone is typically not included in ADCP
measurements. This increases insight in the processes underlying plume development and supports the appropriate determination and implementation of the far-field source term, including a more informed
use of the 0-20% source term fraction range proposed by Becker et al. (2015).